GB2462332A - Microfluidic photobioreactor - Google Patents

Abstract

A method, system and apparatus are disclosed for the culture of photosynthetic organisms in a photobioreactor comprising a microfluidic channel. Preferably a single photobioreactor may be in the form of laminated waveguide sheets (figure 12) and several reactors may be connected in series (figure 14). The microfluidic channel or cavity may comprise a microstructured or holey optical fibre (16) and light to drive photosynthesis may be transmitted in that fibre.

Description

PHOTOBIOREACTORS

The present invention relates to systems and methods for cultivating photosynthetic organisms, and more particularly to such systems and methods which employ microfluidics. The present invention also extends to microfluidic bioreactors in their own right, and methods for using such microfluidic bioreactors.

It is increasingly desirable to be able to culture photosynthetic organisms, such as algae, on a commercial scale. Such organisms may be harvested and used as biomass. There is a growing need for biomass, for example for use as a biofuel feedstock, e.g. in the production of biodiesel or bioethanol. The use of photosynthetic organisms as a feedstock for the biofuel industry has been found to be particularly advantageous, allowing the generation of larger quantities of biomass more quickly than would be possible through other techniques, such as by growing trees or other larger crops.

Current techniques for cultivating photosynthetic organisms tend to involve the use of large scale systems, such as open pools or vats. Such systems have a number of drawbacks. For example, there are difficulties with controlling the climate in larger scale systems, particularly open systems. Yields may be weather dependent, varying according to levels of sunlight, and there is a greater likelihood of organisms falling prey, to viruses, grazers or predators. Another problem is the large amount of land which must be taken up to allow production on a mass scale.

The use of land for biomass production is increasingly controversial, and problematic, given the growing pressure on world food production.

The applicant has therefore realised that there remains a need for improved methods and systems for cultivating photosynthetic organisms which address the above and other problems of conventional systems and methods.

In accordance with a first aspect of the invention there is provided; a system for cultivating photosynthetic organisms comprising: at least one microfluidic photobioreactor unit, the microfluidic photobioreactor unit having; a fluid inlet, a fluid outlet, at least one microfluidic passageway connecting the fluid inlet and the fluid outlet, and means for transmitting light to the interior of said at least one passageway in use; the system further comprising a fluid including photosynthetic organisms.

The present invention therefore provides a system for cultivating photosynthetic organisms which uses one or more microfluidic photobioreactor units. Each microfluidic photobioreactor unit includes one or more microfluidic passageways connecting a fluid inlet and a fluid outlet thereof A fluid comprising photosynthetic organisms is preferably located within the microfluidic passageway or passageways. Means is provided for transmitting light to the interior of the microfluidic passageways, and thus to the fluid containing photosynthetic organisms located therein. In this way, when light is provided via the light transmitting means to the photosynthetic organisms located within the microfluidic passageway the necessary conditions to support growth of the organisms may be provided.

The present invention further extends to a method of cultivating photosynthetic organisms using the system of any of the aspects or embodiments of the invention. In accordance with a second aspect of the invention there is provided; a method of cultivating photosynthetic organisms, the method comprising: providing a microfluidic photobioreactor unit comprising; a fluid inlet, a fluid outlet, and at least one microfluidic passageway connecting the fluid inlet and the fluid outlet; the microfluidic photobioreactor further comprising means for transmitting light to the interior of the at least one microfluidic passageway; and wherein the method further comprises providing a fluid comprising photosynthetic organisms in said at least one microfluidic passageway, and using transmitting light to the fluid in the at least one microfluidic passageway using said light transmitting means.

In accordance with yet another aspect, the present invention extends to the use of a microfluidic photobioreactor to cultivate photosynthetic organisms.

It has been found that by using a microfluidic photobioreactor to cultivate the photosynthetic organisms, many of the problems associated with conventional techniques for cultivating such organisms may be overcome. The use of a microfluidic scale system may provide benefits in terms of ability to control the environment during cultivation of the organisms, and provide the optimum conditions for growth. For example, climate, e.g. temperature, may be controlled to a precise degree, and the content of the fluid controlled to provided growth media, or other nutrients as necessary to support growth of the organisms. The composition of the fluid may be readily changed by supplying other substances via the fluid inlet, and conditions may be adjusted by controlling a rate at which fluid is supplied to or collected from the device at the fluid inlet or outlet, Controlling the rate of movement of the fluid through the fluid passageways may flush through contaminants, or have the effect of diluting the content of the passageways as desired. As the content of the system may be closely controlled, problems of viruses and other contaminants may be reduced, and the closed nature of the system allows problems of grazers or other predators to be avoided. The invention also allows a monoculture, containing a single strain or organism to be more readily achieved if desired. The system may be set up in any location, regardless of the local environmental conditions, and might be used, for example, in an urban location, or even indoors.

Further benefits are provided in that the input and output of the system may be more readily measured, allowing optimum conditions for growth of the organisms to be determined empirically, and providing vital data for use in determining carbon credits etc. The organisms may be readily harvested by collecting fluid at the outlet of the microfluidic photobioreactor. This is a much simpler and less labour intensive operation than is required when attempting to harvest organisms cultivated in conventional large area systems e.g. ponds.

The use of a microfluidic photobioreactor system of this type provides a more space efficient system than conventional systems which occupy large areas of land, and therefore increase pressure on land for other uses, such as food production.

However, while remaining relatively small scale, the system of the present invention may be readily scaled up or down to a desired level of production. As discussed below, additional microfluidic photobioreactor units may be joined to the inlet and/or outlet of the first microfluidic photobioreactor unit to provide a modular system of any desired scale as described in more detail below. In contrast to conventional systems, even once scaled up, the present invention maintains the advantages, particularly in terms of control, provided by the use of a microfluidic system, as the conditions within each microfluidic photobioreactor unit may be precisely controlled. The system may be more reliable than conventional systems as it may not, and preferably does not, include moving parts.

Surprisingly, it has been found that the use of a microscale system to cultivate the photosynthetic organisms may allow relatively large volumes of the organisms to be generated over relatively short periods, and may rival or exceed production rates achievable using conventional larger scale systems. This is believed to be due to the greater efficiency which may be achieved due to the use of the microfluidic technology, and the ability to use a continuous flow processor. For example, it is believed that a doubling of a mass of photosynthetic organisms in the system may be achieved in periods of around 24 hours or less, and may be achievable in a period of 6 hours under certain conditions.

The term "microfluidic" used herein as applied to a passageway, system or bioreactor etc is intended to have its normal meaning in the art. Microfluidic structures constrain fluids over a small scale over which the behaviour of the fluid may differ from the macrofluidic behaviour of the fluid. Typically the structures constrain fluid over a sub-millimeter scale. Such technology has previously been used in the context of "lab on a chip" type devices.

In embodiments of the invention, the microfluidic passageways should therefore be of a dimension which results in a fluid located therein exhibiting microscopic rather than macroscopic behaviour. In embodiments, the passageway or passageways may have at least one dimension e.g. a height of less than I mm.

Each passageway may typically define a fluid holding volume in the order of nanoliters. In some embodiments the passageways may have a width in the range of from 30 microns to 200 microns.

In accordance with the invention the microfluidic passageway or passageways may be of any suitable form. It will be appreciated that the microfluidic photobioreactor unit may comprise one or more than one microfluidic passageway, and where the bioreactor comprises a plurality of such passageways, there may be any number of passageways present. If not explicitly stated, any of the features described below referring to "a passageway" or "the passageways" may be applied to a single passageway if only one passageway is present, or to or any or all of a plurality of passageways where present. Thus such references should be understood to refer to "the, each, or a" passageway.

Preferably the microfluidic passageway or passageways are (each) in the form of a tunnel.

The microfluidic passageway or passageways may be provided using any technique known in the art. The microfluidic passageway or passageways may be provided within the depth of a single layer of a substrate of the microfluidic photobioreactor unit. The passageways may be written or bored into the substrate.

This may be achieved using standard techniques in the field of microfluidics e.g. by an etching process, which may use a femtosecond pulse laser.

In other embodiments the microfluidic photobioreactor unit may comprise two separate layers which are joined to one another to provide the microfluidic passageway or passageways. In these embodiments the passageway or passageways may be provided by joining two separate layers of substrate material to one another in face to face relationship, the layers cooperating with one another such that when the layers are combined, at least one microfluidic passageway is defined within the multilayer structure. In these embodiments, one, or preferably both layers may comprise a channel or channels in their opposed surfaces. In this manner when the layers are joined to one another at least one tunnel is defined within the depth of the multilayer structure e.g. between the two layers, or at their interface.

The joining of layers or components to one another may be achieved in any desired maimer, e.g. using external bonding agents, or autogenous bonding techniques such as thermal or vacuum bonding. In embodiments using a bonding agent, the bonding agent may be chosen to be compatible with the material of the substrate(s) of the components. For example, to bond a fused silica substrate to another such substrate a fused silica bonding agent may be used. A femtosecond pulse laser may be used to fuse the glass sheets together. The same applies in any other context in which layers or components are joined to one another in accordance with the invention.

In some embodiments, a plurality of microfluidic passageways are provided between the inlet and the outlet in the form of a network of microfluidic passageways. The network of passageways may define any desired pattern. The network may comprise passageways which are arranged in parallel with one another.

This may be achieved using a single passageway associated with the inlet which branches into a plurality of sub-passageways downstream of the inlet. Some or all of the passageways may rejoin one another downstream, i.e. upstream of the outlet.

The passageways may repeatedly split and rejoin between the inlet and outlet. Thus there may be a plurality of groups of microfluidic passageways located between the inlet and outlet in which the passageways, which are in fluid communication with one another. In these embodiments, the passageways within the groups may be arranged in parallel with one another, The groups of microfluidic passageways may then be arranged in series with one anQther. It will be appreciated that numerous potential patterns of microfluidic passageways may be envisaged, and the skilled person may select the most appropriate arrangement of passageways depending upon the conditions to be obtained, the type of organism, size of reactor etc. In some preferred embodiments the unit includes only a single microfluidic passageway connecting the inlet and outlet. In these embodiments the passageway extends continuously between the inlet and outlet of the unit.

The passageway or passageways may be of any configuration. For example, the passageway or passageways may be may be linear, or arcuate or may comprise portions which are both linear and arcuate along their length. In some embodiments the photobioreactor unit comprises at least one serpentine microfluidic passageway.

In the preferred embodiments in which a single microfluidic passageway is provided, preferably the passageway is serpentine. Where a plurality of passageways is provided each may be of the same general shape, or the passageways may define different shapes. The most appropriate configuration may be chosen as desired for a given application or set of conditions. The use of microfluidic technology provides great flexibility in the configuration of the passageways.

In embodiments adjacent passageways may be spaced from one another by at least 1 mm, and, in embodiments, by less than 2 mm. In embodiments adjacent passageways are spaced from one another by around 0.5 mm. In embodiments in which a single passageway defines one or more turns, e.g. in a serpentine configuration, adjacent portions of the passageway may be spaced from one another by a distance in these ranges.

The microfluidic photoreactor unit comprises at least one inlet and outlet. In embodiments, there may be a plurality of inlets andlor outlets. There may be more than one inlet and a single outlet, or more than one outlet and a single inlet. In such embodiments the additional inletloutlet will be connected to the fluid passageway or passageways connecting the other inlet/outlet to the single inlet/outlet. There may be a plurality of sets of inlets and outlets, each set comprising an inlet and outlet connected by at least one microfluidic passageway. However, preferably the unit comprises only a single inlet and outlet.

The fluid inlet and outlet may be of any desired construction, and may be configured to cooperate with an upstream or downstream component to receive or supply fluid. For example, the inlet and outlet may be arranged to cooperate with a fluid conduit or the inlet or outlet of another unit. In some embodiments, the unit is in the form of a sheet, and the inlet and outlet are flush with the surface of the respective sheets. In these embodiments the inlet and outlet may be in the form of ports in the sheets. In some embodiments the inlet and outlet are provided on opposed major surfaces of the unit. In other embodiments the inlet and outlet may be provided on edges of the units. Preferably the inlet and outlet are interchangeable and may be identical in construction. This may facilitate connection between the units.

The microfluidic photobioreactor unit may be of any shape or size.

Preferably the unit is in the form of a sheet. The sheet may be of any dimensions.

The sheet may be square or rectangular. Preferably the sheet has a thickness of less than 2 mm, and preferably less than 1.5 mm. Preferably the sheet has a length of at least 50 cm, and preferably at least 100 cm. Preferably the sheet has a length of no more than 150 cm. In embodiments the length of the sheet is in the range of from 50 cm to 150 cm, or from 80 cm to 120 cm. The sheet may have a width in any of the above ranges given for length. Preferably the width is in the range of from 50 cm to cm. Preferably the length of the sheet is greater than the width of the sheet. In other embodiments the sheets may be of smaller dimensions. For example, the sheets may have a length andJor width in the range of from 100 mm to 200 mm. In these embodiments the sheets may be more readily combined with one another, or machined. The thickness of each sheet may be in the above ranges given for the larger sheet embodiments.

The unit may comprise one or more substrate layers. In embodiments in which the unit comprises a plurality of layers, preferably the layers are laminated to one another. As described above, the microfluidic passageways may be defined by one or two layers of the unit. There may then be additional layers present. As described below, in embodiments the light transmitting means may be located in the same or a different substrate layer to the layer or layers defining the microfluidic passageways. In some embodiments a plurality of sets of layers defining alternately microfluidic passageways and light transmitting means respectively may be built up.

Thus, in embodiments, the unit is in the form of a laminate structure defining at least two layers, or in embodiments, at least three layers. Multi-layer embodiments may facilitate manufacture allowing the different layers, and any necessary structure within the layers, to be fabricated separately.

The microfluidic photobioreactor unit may be formed from any suitable material. The material is preferably environmentally inert. In embodiments the photobioreactor is formed from a glass substrate. The glass may be a borosilicate glass, fused silica, fused quartz or any other glass substrate. In other embodiments the microfluidic photobioreactor device is formed of a polymeric material. In some embodiments the microfluidic passageways may comprise a coating to facilitate flow of the fluid and/or organisms therethrough. The coating may inhibit sticking of the organisms to the walls of the passageways, and may, for example, be a hydrophobic coating.

In some preferred embodiments the microfluidic photobioreactor unit is formed from only one material. In these embodiments all components, including the light transmitting means are integrally formed with the unit.

In accordance with the invention, the microfluidic photobioreactor unit further comprises means for transmitting light to fluid within the passageways in use. In this way, light is provided to the photosynthetic organisms located within the passageways. The light transmitting means forms part of the self contained structure of the unit, and is permanently attached thereto. The light transmitting means may be integrally formed with the unit, or may be a separate component or components joined thereto.

Preferably the means for transmitting light comprises an input and means for distributing light to the interior of the passageway or passageways from the input.

The light transmitting means may further comprise an output. In preferred embodiments the light transmitting means comprises a light input and a light output.

This may facilitate joining of the unit with one or more other units to create a larger scale photobioreactor as discussed below.

Preferably the light transmitting means is arranged so as to distribute light from an input to a plurality of regions within a given microfluidic passageway or passageways of the unit. Preferably the light transmitting means is arranged to distribute light from the input to a plurality of different regions within a given microfluidic passageway of the unit. The regions are preferably different regions along the length of the or each passageway or passageways. In some embodiments the regions are a plurality of discrete regions along the length of the or each passageway or passageways. The light transmitting means may provide light to a discrete point or points, or the regions may be elongate. In embodiments the points are located at regular intervals along the length of the passageways, for example in the order of every 0.5 mm. In other embodiments the regions may be a continuous region along a part or the entire length of the passageway.

It will be appreciated that any configuration of the light transmitting means may be envisaged, and the most appropriate form may be chosen with respect to the type of organisms to be cultured, the configuration and size of the unit etc. The light transmitting means may comprise one or more light distribution paths associated with the unit. The light distribution paths may be arranged in series or parallel with one another. For example, the light transmitting means may comprise a network or grid of light distribution paths defining a network. The light transmitting means may comprise at least one main path and a plurality of side branches for distributing light. The light transmitting means may be arranged to transmit light to a plurality of discrete points along the length of each side branch, andlor main path. This may be achieved by providing a plurality of terminations extending from each side branch and/or main path. Preferably at least one side branch is provided with terminations. Preferably the light transmitting means defines a single input, and preferably a single output. As described with respect to the microfluidic passageways, it is envisaged that the unit may comprise one or more sets of light transmitting means having an input, and preferably output, and associated light distributing means.

Preferably the means for transmitting light comprises an optical waveguide.

The optical waveguide may then provide the means for distributing light. The optical waveguide is preferably at-ranged to provide light to a plurality of regions within the or each microfluidic passageway as discussed above. Preferably the optical waveguide comprises one or more light outlets along its length for this purpose. There may be a plurality of outlets spaced from one another along the length of the waveguide. The outlets may be elongate. In some embodiments an outlet may extend continuously along at least a portion of the length of the waveguide. In other embodiments the outlets may be in the form of a plurality of discrete points. The outlets may be provided by openings in a wall (or cladding) of a waveguide, as described below. The outlets may be provided between an input and an output of the light transmitting means.

The waveguide may define a light guiding manifold for distributing light to the passageway or passageways. The manifold may define any light guiding pattern.

The manifold may be in the form of a grid. Preferably the manifold comprises one or more main paths and a plurality of side branches for transmitting light. In some embodiments the manifold defines a plurality of terminations which provide light to a plurality of points along the length of a passageway or passageways. In embodiments having a main path and side branches, the side branches may define said terminations.

In embodiments in which the light transmitting means defines a main path and side branches, whether it is in the form of an optical waveguide or not, preferably the main path is located in a peripheral region of the unit. Preferably the main path is arranged to extend along an edge of the unit, preferably along the length of the unit. Thus the main path may extend along a longer edge of the unit.

The side branches may extend substantially perpendicular to the main path. These arrangements are particularly suitable when the unit is in the form of a sheet.

Preferably the inlet, and outlet, where provided, of the light transmitting means is located at an edge of the unit.

In some embodiments in which the unit comprises a serpentine microfluidic passageway, the light transmitting means may comprise a main light transmitting path and a plurality of side branches associated with each ioop of the serpentine passageway for transmitting light to different regions along the length of the passageway. In embodiments each side branch may extend along the centre of each loop.or between adjacent loops with terminations extending outwardly therefrom at intervals along its length. The terminations may extend on either side of the branch.

In other embodiments the light transmitting means may comprise a serpentine light distributing path. In some embodiments in which the unit comprises a serpentine microfluidic passageway, the serpentine light distributing path may be oriented at 90 degrees to the serpentine microfluidic passageway.

In embodiments the means for transmitting light may be arranged to provide light directly to the interior of the passageways or to a region close to the interior of the passageway from which light may propagate to the interior of the passageway in use. Any configuration may be used which allows light to reach the interior of the passageways so that it may be used by photosynthetic organisms located therein.

Thus in embodiments, the terminations may extend to points within or adjacent the passageways.

The light transmitting means may be arranged in the same plane or a different plane to the microfluidic passageways within the depth of the unit. In embodiments the light transmitting means is arranged to overlie or underlie the microfluidic passageways. In some embodiments the light transmitting means may form a part of the wall of the microfluidic passageway. In embodiments the light transmitting means may intersect the microfluidic pasageway or passageways.

-12 -The means for transmitting light may be provided by a separate component or components joined to the substrate having the microfluidic passageways, or may be formed integrally with the substrate. The means for transmitting light may therefore be formed of the same or a different material to that defining the substrate in which the microfluidic passageways are defined.

In some embodiments the light transmitting means may be provided by selectively altering the light transmitting properties of the substrate of the microfluidic photobioreactor. The material of the substrate may be treated to create regions which more readily propagate light, the treated regions defining the light transmitting means. It will be appreciated that these regions will transmit light more readily than untreated regions. Techniques are known in the art which may provide regions which more readily propagate light than surrounding areas. In these embodiments the light transmitting means preferably comprises an optical waveguide which has been written into the substrate of the microfluidic photobioreactor unit. A suitable pattern of such areas may be written into the substrate e.g. using a laser etching technique as known in the art. Such arrangements are advantageous in reducing the number of materials and components to be used, and may allow the microfluidic photobioreactor unit to be made of a single material. Light outlets to enable light from the waveguide to reach the interior of the microfluidic passageways may be provided by means of one or more openings in the wall of the waveguide in these embodiments. The pattern of waveguide written into the substrate may be arranged to include discontinuities for this purpose.

In other embodiments, the light transmitting means may be formed by one or more additional components joined to the photobioreactor unit. The component or components may be embedded into the substrate of the unit. In a simple embodiment the light transmitting means may comprise an optical waveguide in the form of an optical fiber. The an optical fiber may comprise a plurality of branches, or terminations associated with different points along the length of a fluid passageway or passageways of the unit. Preferably the light transmitting means does not comprise an optical waveguide in the form of a film. In embodiments in which the light transmitting means comprises an optical fiber, the optical fiber -13-preferably comprises core and a cladding, there being openings in the cladding to allow light to reach the microfluidic passageways. In some embodiments the cladding may comprise a plurality of discrete openings along its length for transmitting light to the interior of the microfluidic passageway or passageways at a plurality of discrete points. In other embodiments there may be one or more slits in the cladding for transmitting light to the microfluidic passageway e.g. along a length of the passageway. The cladding may comprise a continuous slit along its length for this purpose.

The microfluidic passageway or passageways may be arranged to intersect with the light transmitting means e.g. an optical fiber or cladding thereof, or a waveguide written into the substrate to create an opening in the waveguide. The microfluidic passageway or passageways may intersect and form a notch in the light transmitting means at one or more points to allow light to be transmitted to the interior of the passageway. For example, the passageway may form a notch in the cladding of an optical fiber of the light transmitting means. In some embodiments the microfluidic passageways may be formed in a substrate already containing the light transmitting means. These embodiments may allow the microfluidic and light transmitting features to be formed in the same substrate layer.

The light transmitting means may be provided in the same substrate layer or layers as the or a substrate layer or layers in which mircofludic passageways are provided. In these embodiments the light transmitting means may be located in a different region of the same layer e.g. adjacent or above or below the fluid passageways provided that light may reach the interior of the passageways. In other embodiments the means for transmitting light is provided in a separate layer attached to the substrate layer or layers defining the microfluidic passageways. The means for transmitting light may be provided on one side of the layer having the microfluidic passageways. In preferred each layer is in the form of a sheet. In these embodiments the microfluidic photobioreactor may define a laminate structure comprising one or more layers which define the microfluidic passageways and a different layer or layers providing the light transmitting means. The light transmitting means may be integrally formed with, or written into the layer, or joined thereto as discussed above. In embodiments in which the light transmitting -14 -means is provided in a separate layer to the microfluidic passageways, the inlet or outlet of the microfluidic passageways should extend through the light transmitting means layer if necessary to permit interconnection with an adjacent unit. This may not be necessary if the inlet/outlet is provided in an edge of a unit.

There may be more than one set of light transmitting means. In some embodiments the microfluidic passageway or passageways are sandwiched between first and second sets of light transmitting means. The light transmitting means may each be of the same or different construction. Additional light transmitting means may be provided in the same manner as the first. For example a further light transmitting means may be written into the substrate defining the microfluidic passageways on the side remote from the first light transmitting means. In multilayer structures a further set of light transmitting means may be provided in an additional separately formed and attached layer located on the other side of the layer comprising the microfluidic passageways. Each light transmitting means may share the same light input or may be associated with one or more separate inputs associated with the given light transmitting means.

In other embodiments the light transmitting means may be sandwiched between first and second sets of microfluidic passageways. It is envisaged that in such laminate structures additional layers of microfluidic passageways or light transmitting means may be built up in an alternating fashion. Intervening layers without either type of formation may be provided so long as they do not interfere with transmission of light to the passageways. The unit may therefore be in the form of a laminate structure, the first microfluidic passageway or passageways being located in a first layer or set of adjacent layers, the unit further comprising one or more additional microfluidic passageway or passageways located in a further layer or set of adjacent layers, the additional microfluidic passageway or passageways being separated from the first microfluidic passageway or passageways by the light transmitting means. The light transmitting means may be provided in a different layer to either set of microfluidic passageways, andlor may be provided in a part of the same layer or layers.. In some embodiments the light transmitting means is provided in a third separately formed layer located between the first and second layers. -15-

The light transmitting means preferably comprises an input to allow connection directly or indirectly to a light source. There may be an output for connection to another unit or a light connector, although this is not essential. If the unit is to be connected other units in use, preferably an input and an outliut is provided. This may allow one unit to be connected to another unit such that the light output of one is connected to the light input of another to allow light to pass from one unit to the next. The input and output are preferably interchangeable. This may allow the units to be connected in any orientation with one another.

Similar arrangements may be produced without using a laminate structure by building alternating layers of light transmitting means and passageways within a unitary structure. Where not otherwise stated, any or all of the features described with respect to the light transmitting means may be provided in conjunction with any or all of the light transmitting means where a plurality of such means is provided.

It will be appreciated that the light transmitting means need not include a source of light, provided that it is arranged to distribute light provided to the input thereof when connected.

The light may be any light which may be useful in photosynthesis. The term "light" herein is intended to refer to electromagnetic radiation comprising or consisting of wavelengths which may be used in photosynthesis. The light may be light from a light source; a lamp, such as an LED lamp. In embodiments the LED may be arranged to emit only red and/or blue light in order to reduce energy consumption. In other embodiments, the light may be light from a source from a luminaire or a laser. In yet other embodiments, the light arranged may be natural light e.g. sunlight.

A light source or source may be indirectly or directly connected to the input.

In embodiments the light transmitting means may be arranged to receive light from a remote light source. The input may then be connected to a connector for providing light to the light transmitting means. In some embodiments light is input to the unit via at least one other unit in accordance with the invention in any of its aspects or embodiments. In these embodiments the input of the light transmitting means is connected to the output of the light transmitting means of an adjacent unit.

In embodiments the light is natural light, and the system further comprises means for providing light from a remote light source or sources to the light transmitting means. Such means may comprise one or more connectors associated with an input of the light transmitting means. Suitable connectors might be in the form of a fiber optic cable or cables. In embodiments the light transmitting means may be arranged to transmit natural light to the input. For example, sunlight might be collected and passed along connectors such as fiber optic cables to the light transmitting means, or may be directly incident on an input of the light transmitting means. Light from the light source may therefore travel over any distance to the unit, and may travel over tens, or hundreds of meters.

In embodiments the system may comprise means for collecting natural light and providing the light to an input of the light transmitting means. The receiving means may be arranged to collect natural light, and may be in the form of a solar panel, for example. These embodiments may be particularly advantageous in environmental terms. In embodiments in which the system comprises means for providing light from a remote source to the light transmitting means, it is not necessary for the light transmitting means to be located in the vicinity of natural light. The light may be collected and provided to the light transmitting means from a remote source. Thus the microfluidic photobioreactor need not be located in natural light, and could be located indoors, or even underground with an appropriate arrangement used to collect and provide natural light to the light transmitting means e.g. from an outside area, e.g. a solar panel etc. In embodiments the system further comprises at least one light source arranged to provide light to the light transmitting means. In embodiments one or more light sources may be connected to an input of the light transmitting means, and the method may comprise the step of attaching a light source to an input of the light transmitting means.

The method of the invention may extend to the step of providing light to the light transmitting means in any of the above described manners.

Light may be provided to any further sets of light transmitting means in any of the above manners. Where a plurality of sets of light transmitting means are provided, they may be associated with the same or different light sources.

-17 -Preferably the system further comprises means for supplying the fluid to the microfluidic photobioreactor unit, and the method comprises supplying the fluid to the inlet of the unit. This may comprise connecting a fluid source to the input of the unit. The system may further comprise a source of the fluid, e.g. connected to the inlet of the unit. The fluid source may be connected directly or indirectly to the inlet. In some embodiments the fluid may be supplied to the inlet using one or more fluid conduits such as a pipe. Fluid may be provided to the inlet of the microfluidic photobioreactor unit directly from a fluid source e.g. a reservoir of source fluid, and/or from the outlet of another microfluidic photobioreactor unit as described below, or the outlet of another device. Fluid supply means may also be used to supply different fluids, or different concentrations of fluids to the system as desired, e.g. to control rates of growth or photosynthesis of organisms. Thus the system may be arranged such that fluid may be supplied from more than one source to the inlet of the unit. Valve means may be provided to determine the source from which fluid is received at any given time.

Preferably the system further comprises means for receiving fluid after the fluid has passed through the unit. Such means may be connected directly or indirectly to the outlet. For example, a fluid conduit such as a pipe may be connected to the fluid outlet to transmit fluid to the fluid receiving means. The means for receiving fluid may be a fluid container, or may be the inlet of another microfluidic photobioreactor unit. Thus the fluid may be subjected to further processing before being collected. In some embodiments the system may be arranged such that fluid may follow one or more of a plurality of paths on leaving the outlet of the unit. Thus the fluid may follow a path which results in it entering the inlet of another unit and/or may follow a path which does not results in it entering the inlet of another unit. Other paths may lead to another system, collection means etc. There may be valves arranged to direct fluid along a given one or ones of the plurality of paths.

In embodiments of the invention the fluid flows through the unit from the inlet to the outlet and the system is arranged to cause fluid to flow in this manner.

The present invention in any of its aspects and embodiments provides an improved system, apparatus or method for culturing photosynthetic organisms which allows -18-the use of a continuous flow process. This may provide the ability to obtain greater yields than is possible using conventional processes using open systems such as pools, vats etc. In preferred embodiments, the method comprises causing the fluid to flow continuously through the or each microfluidic photobioreactor unit.

Preferably the system comprises means for providing a continuous flow of the fluid through the or each microflUidic photobioreactor unit. Such means may comprise a pump or similar associated with a fluid source. Preferably the system comprises means for controlling a rate of flow of fluid through the unit. The unit may comprise such means, or a control valve or similar may be associated with a fluid source.

The system may comprise means for controlling the flow of fluid through the system, and the method may comprise such a step. Controlling the rate of fluid flow may be used to control the rate of photosynthesis and hence growth rates of organisms. Such means may be arranged to control fluid flow through the system in any manner. The control means may control flow of fluid to the unit, or through the unit. For example, control means may be located upstream of an inlet of the unit, or between the inlet and outlet of the unit, or both. In embodiments in which a plurality of units are provided the control means may be provided between adjacent units. Preferably the system comprises means for controlling fluid flow through a given part or parts of the unit. For example, in embodiments in which a single microfluidic pathway is provided, the means may control a rate of flow of fluid along the pathway. In embodiments in which a plurality of passageways are provided the control means may be arranged to control flow through one or more passageways or sections of a network of passageways between the inlet and outlet.

Flow rates may be varied by altering the number of microfluidic passageways through which fluid may pass between the inlet and outlet, and the system may comprise means for controlling fluid flow in this manner. The control means may comprise one or more valves. Valves may therefore be provided at the inlet, outlet and/or at any point in the fluid path between the inlet and outlet. In embodiments in which more than one unit is provided control means may be located between the unit in addition to or alternatively to any of the above locations with respect to a given unit. -19-

The system may comprise further features useful in the culturing of organisms. For example, the system may comprise means for controlling conditions within the unit, e.g. the temperature of the fluid in the unit, andlor means for controlling the composition of the fluid comprising the organisms, and the method may comprise carrying out such steps. In embodiments in which a plurality of units are interconnected with one another, preferably means is provided for controlling conditions within each individual unit, and the method comprises such a step.

Preferably the method comprises means for controlling the conditions within a selected part or parts of a given unit, and the method comprises such a step.

Features for controlling conditions may be located anywhere in the system comprising the unit which allows them to perform their stated function i.e. anywhere within a fluid flow path. The features may be provided in any of the locations described above in relation to controlling fluid flow. Thus such features may be located upstream or downstream of each unit e.g. between a fluid supply and the inlet, between adjacent units, between the outlet and a fluid collector, or the unit may comprise such features e.g. between the inlet and outlet, or combinations thereof. The system may comprise one or more of a heat exchange device, gas exchange device, valve, pump e.g. a microfluidic or peristaltic pump etc. and may comprise any number of any of these or similar features. Gas exchange devices or pumps may be used to control the rate of photosynthesis and/or growth of organisms. The method may comprise locating one or more such features in the fluid flow path e.g. at any of the above locations. In embodiments comprising a plurality of units, such any of the above features may be associated with each unit, and/or located in the fluid path between the units.

In embodiments the system may comprise a fluid path to enable fluid to bypass the unit, i.e. such that it does not have to flow through the unit from the input to the output. The system may therefore comprise means operable to cause fluid to bypass the unit. Such means may comprise an alternative fluid passageway and an associated valve etc. This may allow fluid to be readily redirected to isolate a unit if defective, or for other reasons. In embodiments comprising a plurality of units this may allow a given one of the units to be easily taken out of operation but without interfering flow of the fluid through adjacent units. Thus in embodiments -20 -comprising a plurality of the units, the system comprises means operable to cause fluid to bypass any given one of the units. In some embodiments bypass means is provided associated with a pump upstream of the unit. Thus the bypass means may comprise a bypass tube and valves. Preferably the unit is connected to at least one further like unit.

It will be appreciated that a plurality of the microfluidic photobioreactor units of any of the embodiments of the invention may be interconnected with one another in the system to produce a larger composite microfluidic photobioreactor.

The units may be of the same or different construction to one another. While fluid may be input separately to each unit, the units are preferably arranged such that fluid may flow between the units. Preferably the system therefore comprises a plurality of microfluidic photobioreactor units connected to one another to permit flow of fluid between the units. The units may be connected to one another in any manner which permits fluid communication between the respective inlets and outlets thereof. Preferably the unit is arranged such that the inlet and outlet thereof may each be connected to a like unit in a manner which permits fluid flow between the units. Preferably the inlet arranged to be connectable to either an inlet or an outlet of another like unit, and the outlet is arranged to be connectable to either the inlet or the outlet of a like unit. Preferably the inlet and outlet are interchangeable. This may allow the units to be interchangeably connected to one another. Thus the inlet and outlet may be identical or indistinguishable.

In these preferred embodiments including a plurality of units, each unit acts as a building block, and the units may be combined at will with any number of like units to create a composite microfluidic photobioreactor of greater dimensions, and fluid handling volume. The system is a modular system, providing the advantages of scalability.

In embodiments only a first of the units is connected to a fluid source, and preferably light source. In embodiment all units downstream of a first unit receive light and fluid only from a preceding unit.

It is believed that a composite microfluidic photobioreactor system of this type is advantageous in its own right.

In accordance with a further aspect of the invention there is provided a modular assembly for a microfluidic photobioreactor system; the assembly comprising: a plurality of microfluidic photobioreactor units; each unit comprising; a fluid inlet, a fluid outlet, one or more microfluidic passageways connecting the fluid inlet and the fluid outlet, and means for transmitting light to fluid within the passageways in use, the units being such that the fluid inlet of one unit may be connected to the fluid outlet of another of the units, and the fluid outlet of the unit may be connected to the fluid inlet of another one of the units to provide a composite microfluidic photobioreactor comprising a plurality of the units.

Preferably the light transmitting means of each unit comprise an input and an output which may be connected in a similar manner. The present invention extends to a method of assembling a composite modular microfluidic photobioreactor using a plurality of the units of the modular assembly, the method comprising joining a unit to at least one other unit such that the outlet of one unit is connected to the inlet of the other unit, and preferably such that an input of a light transmitting means of one unit is connected to an output of the light transmitting means of another unit.

In accordance with the invention in any of its aspects and embodiments in which a plurality of units are connected to one another, the inlet of the microfluidic photobioreactor unit may be connected to an outlet of a like unit and/or the outlet of the unit connected to the inlet of a like unit. It will be appreciated that any number of units may be connected to one another in any manner. The units may be connected in series and/or parallel. Preferably the units are arranged such that fluid flows sequentially through the units between an inlet and an outlet of the system. In these embodiments the inlet of a first one of the units may be connected to a fluid source and the outlet of a final one of the units connected to means for collecting fluid after it has passed through each of the intervening units.

In any aspect or embodiment of the invention comprising a plurality of microfluidic photobioreactor units, the inlets and outlets of the units maybe directly or indirectly joined to one another. For example one unit may be connected to an -22 -adjacent unit or units such that an inlet and outlet of the adjacent units contact one another to allow fluid to flow between the units. In other embodiments a fluid conduit or conduits may extend between the respective inlet and outlet of the different units to connect the inlet and outlet. In embodiments the units are spaced from one another by a fluid connector or connectors, and adjacent units may not contact one another. The conduit or conduits may be flexible connectors, such as hose. In some embodiments, tubing such as Tygon tubing is used.

Whether the units are connected directly or indirectly, a plurality of the units may be connected to one another in edge to edge or face to face relationship. The most appropriate arrangement may depend whether the inlet and outlet of each unit is located in an edge or edges of the unit or in a major surface or surfaces of the unit. The light input and output where present should be located appropriately especially if direct connection is to be used.

In embodiments the units may be arranged such that fluid may additionally enter the inlet from sources other than the outlet of another unit andlor may leave the outlet by a path other than the path leading to the inlet of an adjacent unit. This may allow fluid to be introduced from or removed from the system at any point between units e.g. to control the composition of the fluid etc. In embodiments a plurality of different fluid paths may be provided between the inlet and outlet of adjacent units.

The paths may be in parallel with one another. In addition to a fluid path along which fluid may flow to reach the inlet of the adjacent unit, there may be one or more additional paths. Preferably at least one of the fluid paths is arranged such that fluid flowing along the path does not enter the inlet of an adjacent unit. For example, there may be a bypass path along which fluid may be directed to avoid entering the adjacent unit. There may be a path which along which fluid may flow to be collected. Thus, some or all of the fluid may be tapped off before entering the adjacent unit. It will be appreciated that one or more valves may be associated with a fluid conduit or conduits connecting first and second units. Other devices such as pumps, heat or gas exchange devices etc may be inserted between adjacent units. In other embodiments the units may be connected directly to one another.

It will be appreciated that light will need to be provided to the light transmitting means of each unit in aspects and embodiments including multiple -23 -units. While light may be provided separately to an input of the light transmitting means of each unit, in other embodiments the light transmitting means of the units may be interconnected with one another. Thus, the output of the light transmitting means of one unit may be connected to the input of the light transmitting means of the adjacent unit. In the same manner as the fluid inputs arid outputs, the light inputs and outputs of the units are preferably interchangeable with one another.

The light inputs and outputs may be connected to one another using separate light conductors, such as optical fibers, or may be joined directly to one another. In some embodiments the light inputs and outputs may be bonded to one another.

While in some embodiments the units are indirectly connected to one another by connectors e.g. fluid conduits, and, in some cases, light conductors, in other embodiments the units are directly joined to one another in a manner which permits fluid to flow between the units. Thus the units may be joined to one another in a manner which directly connects the fluid inlet andlor outlet and preferably the light input/output of the adjacent units. Preferably this is achieved by bonding the units to one another. This may be achieved by bonding only in the region of the fluid connection i.e. the inlet/outlet, or the units may be bonded to one another over an entire contacting area. In some embodiments the unit is bonded over an entire interface with an adjacent unit. The units may be arranged to have planar contacting faces to facilitate bonding. Bonding may be achieved in any suitable manner e.g. by a bonding agent or agents, e.g. adhesives, or a fused silica bonding agent, or a thermal or vacuum bonding process etc. In some embodiments in which the inlet and outlet are in the form of ports in the respective surfade of the unit the ports may be placed in fluid communication with one another by joining the surrounding surfaces to one another. In these embodiments the units are preferably permanently attached to one another.

In these embodiments the units combine to provide a composite microfluidic photobioreactor unit. In these embodiments, the units form sub-units of the composite self supporting photobioreactor unit. The units may not be detached from one another, but it may be seen that the composite photobioreactor comprises a plurality of subunits which have been joined to one another to provide the composite unit. The composite photobioreactor may be of any form, and is preferably in the -24-form of a block. The block may be in the shape of a cube or cuboid. In embodiments in which a composite microfluidic photobioreactor unit is provided, a plurality of the composite units may be connected to one another in series or parallel.

In preferred embodiments the units are each in the form of sheets as described above. In these embodiments a plurality of the sheets may be directly or indirectly joined to one another in edge to edge or face to face relationship. In some preferred embodiments the sheets are laminated to one another to provide a composite photobioreactor unit, which may be of a cuboid shape. The fluid inlets and outlets or light inputs and outputs may be directly and/or indirectly joined to one another in any manner which results in a respective inlet and outlet of the units being located in fluid communication with one another as described above, and light being transmitted to organisms within the structure. The sheets may themselves be multilayer sheets comprising separate layers which have been joined to one another.

For example, the light transmitting means may be provided in a different layer to the microfluidic passageways, which may themselves be formed from a plurality of sheets.

In accordance with a further aspect of the present invention there is provided a method of assembling a microfluidic photobioreactor, the method comprising; providing a plurality of microfluidic photobioreactor sheets each comprising; a fluid inlet, a fluid outlet, one or more microfluidic passageways connecting the fluid inlet and the fluid outlet, and means for transmitting light to fluid within the passageways in use, the method comprising bonding the sheets to one another such that the outlet of one sheet is connected to the inlet of another of the sheets to enable fluid to flow sequentially through the sheets.

In accordance with the invention in any of its aspects and embodiments, a composite laminar microfluidic photobioreactor unit may be built up by combining alternately fluid conducting and light transmitting sheets. In some embodiments the present invention may provide a method of assembling a microfluidic photobioreactor, the method comprising providing a first group of fluid conducting sheets, each having an inlet, an outlet and one or more microfluidic passageways -25 -connecting the inlet and the outlet, providing a second group of light transmitting sheets, each comprising light transmitting means having an input arid an output and a light distributing path or paths therebetween, and laminating sheets from the first and second groups of sheets to one another in an alternating maimer to provide a microfluidic photobioreactor having alternating fluid conducting and light transmitting sheets, the photobioreactor comprising at least two fluid conducting sheets and at least two light transmitting sheets; the method comprising arranging the sheets such that the outlet of one fluid conducting sheet is connected to the inlet of the next fluid conducting sheet, and arranging the light transmitting sheets so as to provide light to the interior of the microfluidic passageways in at least one adjacent fluid conducting sheet.

In accordance with yet another aspect of the invention there is provided; a microfluidic photobioreactor comprising; a plurality of fluid conducting sheets, each having a fluid inlet, a fluid outlet and one or more microfluidic passageways connecting the inlet and the outlet, and a plurality of light transmitting sheets, each comprising light transmitting means having an input and an output and a light distributing path or paths therebetween, the fluid conducting sheets and light transmitting sheets being laminated to one another in an alternating manner such that each light transmitting sheet is interposed between adjacent fluid conducting sheets, wherein the outlet of one fluid conducting sheet is connected to the input of the next fluid conducting sheet, and the output of one light transmitting sheet is connected to the input of the next light transmitting sheet, such that in use, fluid may flow sequentially through the fluidS conducting sheets of the photobioreactor, and the light transmitting sheets are arranged to transmit light to the interior of the microfluidic passageways of the or each adjacent fluid conducting sheet.

The present invention in accordance with these further aspects of the invention may include any or all of the features described in respect of the other aspects and embodiments of the invention.

In preferred embodiments in which the system comprises a plurality of units connected to one another to permit fluid to flow between the units, at least one of a -26 -pump, gas exchange device or heat exchange device is preferably located in a fluid path between the units. In a system comprising more than two units, such devices may be located between all adjacent units, or at certain intervals, e.g. after every second unit etc. In any of the embodiments in which a plurality of units are combined to provide a composite unit, the composite unit may be have a size in the ranges described in relation to an individual unit, or the individual units may be of smaller dimension.

The location of the inlet and outlet and configuration of each unit will dictate the shape and size of the composite units obtainable. For example, in embodiments in which each unit is in the form of a sheet, the inlet and outlet may be provided on the respective major surfaces of the sheet. The sheets may then be joined in face to face relationship with one another with the inlet and outlet of adjacent sheets cooperating with one another. This may provide a composite unit of greater thickness, and depending upon the number of sheets involved may define a cuboid or other three dimensional structure. In other embodiments the inlet and outlet may be provided in the edge of the sheets, and the units may be combined with one another to provide a composite unit in the form of a sheet of greater area.

The Applicant has realised that one particularly simple way to provide a microfluidic photobioreactor in accordance with the invention e.g. for cultivating photosynthetic organisms, is to use a microstructured optical fiber. Optical fibers are known which include microstructure in the form of one or more microcavities.

These may provide air holes in the fiber. The applicant has realised that these microcavities may advantageously be used as microfluidic passageways such that the optical fiber may provide a microfluidic photobioreactor when fluid is appropriately passed therethrough. The optical fiber may, by virtue of its inherent characteristics, transmit light to the interior of the microcavities, and hence to organisms in a fluid therein. In preferred embodiments, the microcavity may then provide a microfluidic passageway along which a fluid comprising photosynthetic organisms may flow in use while the optical fiber provides light to organisms in the fluid. Thus, in accordance with yet another embodiment, the microfluidic photobioreactor unit may comprise a microstructured optical fiber.

-27 -Microstructured optical fibers suitable for use in accordance with these embodiments of the invention are known for use in other contexts. Examples of suitable fibers are described in the paper entitled "Microstructured-core optical fiber for evanescent sensing applications" to Cordeiro Ct al, published on 25 December 2006, Vol. 14, No 26 Optics Express 13056. US 7110646 describes a microfluidic optical fiber device.

In accordance with a further aspect of the invention there is provided; a system for cultivating photosynthetic organisms, the system comprising a microfluidic photobioreactor; the microfluidic photobioreactor comprising a microstructured optical fiber defining at least one internal microcavity which may act as a microfluidic passageway in use, wherein the microcavity contains a fluid comprising photosynthetic organisms.

In accordance with yet another aspect of the invention there is provided a method of cultivating photosynthetic organisms comprising; providing a microstructured optical fiber comprising at least one internal microcavity which may act as a microfluidic passageway in use; providing a fluid comprising photosynthetic organisms in the microcavity; and providing light to the organisms in said microcavity using the optical fiber.

In accordance with a further aspect the present invention extends to the use of a microstructured optical fiber comprising at least one internal microcavity as a microfluidic photobioreactor, and more particularly to the use of a microstructured optical fiber comprising at least one internal microcavity as a microfluidic photobioreactor for cultivating photosynthetic organisms.

In these further aspects and embodiments of the invention which use a microstructured optical fiber, the at least one microcavity is any microcavity which is capable of providing a microfluidic passageway when a fluid is located therein in use. The microcavity is preferably an axially extending microcavity. The microcavity then extends between the ends of the optical fiber. Preferably the microcavity extends the entire length of the optical fiber. Preferably the microcavity extends parallel to the axis of the fiber. Preferably the microcavity defines a tunnel extending through the optical fiber.

The microcavity may be of any dimension suitable to allow it to act as a microfluidic passageway in use. Preferably the microcavity is of a sub-millimeter scale, e.g. has a diameter of less than 1 mm. The microcavity may be of any shape in cross section. Preferably the microcavity is circular in cross section.

The optical fiber may comprise only one microcavity provided that it has dimensions suitable to act as a microfluidic passageway. For example, the optical fiber may be a hollow fiber. In preferred embodiments the optical fiber comprises a plurality of microcavities, such that the optical fiber may define a plurality of microfluidic passageways when fluid is located in the microcavities in use. In some embodiments the plurality of microcavities comprise a plurality of axially extending microcavities extending parallel to the axis of the optical fiber. The microcavities may be uniformly or non uniformly dispersed throughout the cross section of the fiber. Optical fibers comprising a plurality of internal cavities are known for use in other contexts. A standard optical fiber of this type may be used, with fluid being supplied to any or all of the internal cavities.

Where a plurality of microcavities are provided, they may be of the same or different construction. For example, they may be of the same or different cross sectional area or shape. In embodiments in which the optical fiber comprises a pluralityof internal microcavities, any or all of the microcavities may comprise a fluid containing the organisms. Some microcavities may not contain the fluid, and may be left empty. Thus in embodiments, the optical fiber comprises a plurality of microcavities, wherein at least one of the microcavities contains the fluid comprising photosynthetic organisms, and at least one of the microcavities does not contain any fluid.

The optical fiber may comprise microcavities in the core andlor cladding of the optical fiber. The microcavities which contain the fluid comprising photosynthetic organisms in accordance with these further aspects of the invention may be microcavities of the core or cladding or both. For example, only microcavities in the core or only microcavities in the cladding may contain the fluid if microcavities are present in the cladding and core, or both microcavities in the -29 -core and cladding may comprise fluid. In some embodiments the microcavities define holes in a solid core of the optical fiber.

As described in relation to the other aspects and embodiments of the invention above, preferably the fluid flows through the microcavity or microcavities, and the system comprises means for causing the fluid to flow through the microcavity or microcavities. Preferably the fluid flows continuously through the microcavity or microcavities and the system comprises means for causing the fluid to flow continuously through the microcavity or microcavities.

It is believed that causing fluid to move through a microstructured optical fiber is new and advantageous in its own right.

In accordance with a further aspect of the invention there is provided a method of using a microstructured optical fiber, the optical fiber comprising at least internal microcavity, the method comprising causing a fluid to move through the microcavity. Preferably the fluid is a liquid. As discussed above, preferably the fluid is caused to flow continuously through the microcavity. Preferably the microcavity is axially extending, and preferably extends the entire length of the optical fiber. Preferably the method therefore comprises causing a fluid to move through the microcavity from one end of the optical fiber to the other. Preferably the method further comprises causing fluid to enter the microcavity at one end of the optical fiber and to leave the optical fiber through the other end of the microcavity.

The method may involve providing a fluid supply and connecting the fluid supply to an end of the fiber to provide fluid to the microcavity and/or collecting fluid from the other end of the microcavity. Fluid may be passed along any number of a plurality of microcavities of the optical fiber in this manner in embodiments in which the optical fiber has a plurality of microcavities. These aspects of the invention are advantageous in that the microstructured optical fiber may provide a new and simple form of microfluidic device.

in accordance with the invention in any of the aspects and embodiments using a microstructured optical fiber, preferably the optical fiber has a length of at least 1 m, and preferably in the range of from 8 m to I 2m. It will be appreciated that the length of the optical fiber may be selected as desired, and the most appropriate -30 -length will depend upon the conditions, number of optical fibers present in the system, space constraints etc. Preferably the optical fiber is formed of silicon. For example, the fiber may be of a fused silica substrate. However, the optical fiber may comprise any suitable material or materials used in this context, and may be e.g. of a polymeric material.

Preferably the system comprises a fluid port through which fluid may enter the microcavity or microcavities. Preferably the system comprises a fluid port through which fluid may leave the microcavity or microcavities. Preferably a fluid port is provided at each of the respective ends of the optical fiber: The ports may be arranged at one or both ends of the optical fiber. In some embodiments the ports are provided such that fluid may enter and/or leave the microcavities via the end faces of the optical fiber, e.g. via open ends of the microcavities. However, it is envisaged that one or more fluid ports could be arranged to allow fluid to be provided to or leave a microcavity at a point between the ends of the fiber. A suitable passageway may then need to be bored into the fiber to connect with the microcavity therein.

The fluid port may be arranged in any manner which provides fluid access tO the interior of the microcavity, e.g. from the exterior of the fiber. The optical fiber may comprise one or more additional fluid port. The additional fluid port may then be located between the ends of the fiber. The fluid ports may, if desired be connected to one another by a suitable arrangement of connectors. It will be appreciated that a fluid port may provide a fluid inlet or outlet in use. Thus, the system may comprise a respective fluid inlet and outlet at the ends of the optical fiber. The inlet and outlet may be interchangeable in use depending upon the direction of fluid flow in the optical fiber, and hence are referred to as fluid ports.

In preferred embodiments at least one adaptor is attached to the optical fiber and arranged such that fluid may enter or leave at least one microcavity of the optical fiber via the adaptor. Preferably the adaptor comprises a fluid port which provides the fluid inlet or outlet to the optical fiber in use. Preferably an adaptor is provided at one or both ends of the optical fiber. Where multiple adaptors are provided, the adaptors are preferably of like construction.

Preferably the adaptor is arranged such that fluid may enter or leave the or a microcavity of the optical fiber via an end face of the optical fiber in use.

Preferably the adaptor comprises at least one internal passageway thr6ugh which fluid may pass between a fluid port of the adaptor and the interior of the optical fiber in use. The fluid passageway therefore comprises an optical fiber end and an end remote from the optical fiber. The fluid port is provided at the end remote from the optical fiber. Preferably the at least one passageway of the adaptor is a microfluidic passageway.

The fluid port is preferably in an exterior surface of the adaptor. The fluid port may be arranged to enable it to be located in fluid communication with a fluid connector for supplying or removing fluid from the optical fiber in use. The connector may be any suitable connector e.g. of the type described in relation to the other embodiments above. For example, the connector may be a flexible connector, e.g. tubing, such as Tygon tubing. A connector may be connected to the fluid port using a luer connector.

The fluid passageway of the adaptor preferably has an outlet which is registrable with a microcavity of the optical fiber in use to allow fluid to flow between the microcavity and the fluid passageway. In some embodiments the adaptor comprises means for locating an end of an optical fiber such that a microcavity of the optical fiber is in fluid communication with a fluid passageway of the adaptor to enable fluid to flow to or from the microcavity via the passageway.

For example, the adaptor may comprise a channel or bore configured to snugly fit around an end portion of the optical fiber and maintain the micro cavity in fluid communication with the fluid passageway of the adaptor. The adaptor may be arranged to receive an end of the fiber. The adaptor may comprise guide means to aid locating of the fiber in the appropriate orientation with respect to the adaptor to result in the microcavity or cavities being registered with the outlet or outlets of the fluid passageway(s) of the adaptor.

Preferably an outlet of the internal passageway of the adaptor is located in a surface of the adaptor which abuts the optical fiber in use, preferably the end face of the optical fiber. The outlet may be located in an end face of the locating means of the adaptor e.g. the blind end of a bore or channel which receives an end of the optical fiber in use. In preferred embodiments the adaptor comprises a plurality of fluid passageways which may respectively be located in fluid communication with -32 -each of a plurality of microcavities of the optical fiber in use. The fluid passageways may be distinct from one another over their entire length, and may be associated with different fluid ports at the end remote from the optical fiber.

However, it is envisaged that the passageways might merge with one another away from the optical fiber end.

The adaptor may extend around the entire circumference of the optical fiber, or only a portion thereof. Any arrangement may be used which may provide a suitably fluid tight connection to an or a microcavity of the optical fiber in use.

Preferably the adaptor is arranged to fit around the entire circumference of the fiber, and comprises a bore for receiving the fiber.

The adaptor is preferably permanently attached to the optical fiber. This may be achieved using any suitable technique. In some embodiments the fiber is bonded to the adaptor, preferably using an index matching gel.

The adaptor may be a single piece or multi piece adaptor. In some embodiments the adaptor comprises first and second sections which are fitted together to locate an optical fiber therebetween. The first and second sections may define respective channels which cooperate to provide a bore for receiving the fiber when the first and second sections are fitted together. Preferably each channel is V shaped in cross section. In some embodiments in which the adaptor comprises fluid passageways to be associated with different ones of a plurality of microcavities of the optical fiber, the fluid passageways may be located in different sections of the adaptor when it is a multipiece adaptor. For example, the adaptor may comprise matching first and second sections e.g. which are mirror images of one another. The adaptor may comprise upper and lower sections, each having at least one fluid passageway to be associated with a respective upper or lower microcavity of the fiber in use. The upper and lower sections refer to sections which may be located as upper and lower sections when the adaptor and optical fibers are appropriately oriented in use.

In embodiments, the adaptor may be connected to a fluid source, or means for collecting fluid. The adaptor may be directly connected to such other components, or via other connectors, e.g. tubing as described above in relation to the -33 -other embodiments. The connector may supply fluid to a conditioning circuit as described above, e.g. prior to being returned to another optical fiber of the system.

It will be appreciated that, as described in respect of the other aspects and embodiments of the invention above, the invention in these further aspects may provide a flexible and scalable system. Thus, if desired, the microstructured optical fiber may be connected to one or more like optical fibers so as to permit fluid to flow between the first and second optical fibers. The optical fibers may be of the same or different lengths. This may allow the path of the photosynthetic organisms to be increased or decreased as desired to obtain a desired yield. Each optical fiber may then provide a modular unit of a larger photobioreactor system. These embodiments are advantageous, as by providing a plurality of relatively shorter sections of optical fiber with appropriate connections therebetween, any sections which develop a problem may be more easily isolated, and the system provides a greater ability to control the conditions within the system and adjust them as appropriate, as well as being able to supply or remove fluid at more frequent intervals.

The microstructured optical fibers may be connected to one another as desired. The optical fibers may be connected in series or parallel with one another.

In some embodiments, the microstructured optical fiber comprises an adaptor as described above (where not explicitly stated, references to the "optical fiber" herein in relation to these aspects and embodiments of the invention should be understood to refer to the microstructured optical fiber unless the context demands otherwise). In preferred embodiments the optical fiber is connected to one or more other optical fibers using the adaptor. Preferably the adaptor locates the optical fiber in fluid communication with another like optical fiber. The adaptor may locate the optical fibers in fluid conin-iunication with one another in any manner, and may do so directly or indirectly. Preferably the adaptor is arranged such that the microcavities of the optical fibers do not directly contact one another. For example, an internal passageway of the adaptor may place the microcavity of a first optical fiber in fluid communication with a microcavity of a second optical fiber directly, or via external connectors, or a combination thereof.

In accordance with yet another aspect of the invention there is provided a modular assembly for a microfluidic photobioreactor system, the assembly comprising: a plurality of microstructured optical fibers; each optical fiber comprising one or more axially extending microcavity through which may provide a microfluidic passageway through which fluid may pass in use; and at least one adaptor, the adaptor being arranged to enable the microcavity of one of the microstructured optical fibers to be connected to a microcavity of another of the optical fibers in use to provide a composite microfluidic photobioreactor comprising a plurality of the optical fibers.

The present invention extends to a method of assembling a microfluidic photobioreactor using the assembly, the method comprising placing first and second microstructured optical fibers of the assembly in fluid communication with one another using the adaptor.

It will be appreciated that in accordance with any aspects or embodiments of the invention in which a plurality of optical fibers are connected to one another to permit fluid flow therebetween via an adaptor, the adaptor may place the first and second optical fibers in fluid communication with one another without the use of additional components, or one or more additional connectors may be used. In preferred embodiments the adaptor is arranged such that fluid passing between the optical fibers via the adaptor passes through at least one internal passageway of the adaptor.

In some preferred embodiments the adaptor therefore is arranged to receive first and second optical fibers. The adaptor may be arranged to locate the optical fibers in end to end or side by side relationship, or any other arrangement which permits fluid flow between them, with or without the use of external connectors.

Preferably the adaptor is arranged to maintain the optical fibers spaced from one another. Preferably the adaptor is arranged maintain the first and second optical fibers in an end to end configuration with respect to one another. Preferably the adaptor comprises opposed ends, each being arranged to receive a respective optical -35 -fiber. Of course, it may be envisaged that an adaptor might be arranged to connect more than two optical fibers.

In some embodiments, the adaptor is comprises first and second locating means for locating the ends of first and second optical fibers such that at least one microcavity of each optical fiber is in fluid communication with an internal passageway of the adaptor. The fibers may be located in fluid communication with the same, or preferably different fluid passageways. Preferably each fluid passageway is associated with a respective fluid port at its end remote from the optical fiber. Preferably the fluid ports of the respective passageways are connected to one another by one or more additional connectors. This may provide a more flexible system providing the ability to bypass adjacent optical fibers if desired, or to cause fluid to flow along a path which includes one or more devices arranged to control conditions in the fluid e.g. a pump, gas exchanger, heat exchanger etc. Preferably at least one valve is provided in the fluid path between the first and second optical fibers. Preferably a path is provided which enables fluid to bypass one of the optica1 fibers.

It will be appreciated that rather using external connectors and components, such as pumps, heat or gas exchangers etc., all circuitry and connections may be provided on the adaptor.

The connection between the optical fibers in these embodiments in which the microfluidic photobioreäctor in the form of an optical fiber may incorporate any of the features described in relation to the other aspects of the invention to the extent they are not inconsistent therewith. This applies equally to the system, which may include any of the features previously described, e.g. in relation to the nature of the fluid, organism, connection configurations where multiple units are involved etc. In accordance with the invention in any of the further embodiments comprising an adaptor, preferably the adaptor is in the form of a chip. Thus, the adaptor is preferably substantially planar. The adaptor may be rectangular in cross section. In embodiments in which the adaptors may be used to connect a plurality of optical fibers to one another the adaptors may be located at regular or irregular intervals along the length of the system. Preferably the adaptor is a rigid adaptor. -.36-

It will be appreciated that in preferred embodiments, the adaptor is itself a microfluidic device. The adaptor may comprise any configuration of microfluidic passageways.

In accordance with the invention, light may be provided to the fluid within the microcavity or microcavities of the or each optical fiber in any suitable manner.

The system should be arranged that at least some light will be absorbed by a fluid passing through the microcavity of the or each fiber of the system when light is passed along the fiber i.e. in the usual manner. The optical fiber is arranged such that light transmitted by the optical fiber may be absorbed by photosynthetic organisms located within the or each microcavity. Thus, the optical fiber is arranged such that light transmitted along the optical fiber may reach the interior of the microcavity. The method extends to the step of passing light along the or each optical fiber. The light may then be used by the organisms to carry out photosynthesis. The system may further comprise means for providing light to the optical fiber for transmission along the fiber. The system may comprise any suitable light source for this purpose.

In embodiments including a plurality of the optical fibers, the system may further comprise means for transmitting light between the first and second optical fibers. This maybe desirable if there is a gap between the ends of the fibers. Any suitable arrangement may be used. In preferred embodiments the means for transmitting light between fibers comprises a lens. This may be in the form of any suitable micro lens, and may be a ball lens. In some embodiments the light transmitting means may be mounted to the adaptor. The adaptor may comprise locating means for locating the light transmitting means e.g. a lens between the first and second optical fibers. In other embodiments any other form of light source may be used to provide or top up the light supplied to any or all of the optical fibers of the system. It will be appreciated that a light transmitting means may be unnecessary if sufficient light may pass between the fibers, e.g. if they are in close proximity to one another, or, for example, if a separate light source is associated with each.

It will be appreciated that in use, fluid may be arranged to flow in either direction along the or each optical fiber, and the system may allow the fluid direction to be reversed as desired.

While the aspects of the invention using microstructured optical fibers have been described with particular reference to the context of cultivating photosynthetic organisms, it is believed that the use of a microstructured optical fiber as a microfluidic photobioreactor is advantageous in its own right, and the present invention extends to the use of a microstructured optical fiber as a microfluidic photobioreactor. The present invention also extends to a microfluidic photobioreactor system comprising a microfluidic photobioreactor comprising a microstructured optical fiber having at least one internal microcavity which provides a microfluidic passageway in use. In these embodiments, the system may provide a microfluidic system which may be used in the context of any bioreaction, and may include any or all of the features previously described in relation to the context of cultivating photosynthetic organisms. The system may include any number of microstructured optical fibers.

The present invention extends to a system for culturing photosynthetic organisms comprising a microfluidic photobioreactor in accordance with any of the aspects and embodiments of the invention comprising a fluid containing photosynthetic organisms in said microfluidic passageway or passageways thereof, and to a method of culturing photosynthetic organisms using a microfluidic photobioreactor in accordance with any of the aspects or embodiments of the invention. In these aspects, the microfluidic photobioreactor may be of any of the forms discussed, e.g. a sheet, optical fiber etc. In accordance with the invention in any of its aspects or embodiments, the photosynthetic organism may be any desired type of organism or organisms. The fluid may comprise a single strain of organism or multiple strains. The organisms are microorganisms, and may algae andlor phytoplankton. The fluid comprising the organism may be any suitable medium. In embodiments the fluid is an aqueous suspension. The fluid may comprise a growth medium. The fluid may comprise additives such as nutrients, and other substances useful in promoting the growth of -38 -the organisms. In some embodiments the fluid may be provided by desalinated seawater. Minerals may be added to the fluid.

The fluid may be collected and processed as desired to recover the organisms and render them suitable for use in a further process. The method may further comprise extracting organisms from the fluid. In embodiments the method may comprise using organisms from the collected fluid as biomass. The method may comprise using the collected organisms as a feedstock for the biofuel industry. Such a step may comprise refining or otherwise treating the organisms and/or fluid to render it suitable for the intended use. The method may therefore comprise processing organisms collected to render them suitable for use a feedstock for the biofuel industry.

It is envisaged that units in accordance with different aspects of the invention might be combined with one another, although preferably each unit in a composite system is of the same construction.

The present invention in accordance with the further aspects of the invention may include any or all of the features described in respect of the other aspects and embodiments of the invention.

In accordance with the invention in any of its aspects or embodiments the fluid is preferably a liquid, most preferably an aqueous liquid.

Some preferred embodiments of the present invention will now be described by way of example and with reference to the accompanying drawings of which:-Figure 1 illustrates a microfluidic photobioreactor unit in the form of a sheet formed from separate light transmitting and fluid conducting sheets which have been joined to one another in accordance with a first embodiment of the invention.

Figure 2 illustrates the fluid conducting sheet of the photobioreactor unit of Figure 1; Figure 3 illustrates the light transmitting sheet of the photobioreactor unit of the embodiments of Figure 1; Figure 4 is a schematic view illustrating the way in which the light transmitting and fluid conducting sheets interact with one another in the photobioreactor of the embodiment of Figure 1; -39 -Figure 5 illustrates a microfluidic photobioreactor unit in accordance with a further embodiment of the invention in which the microfluidic passageways and the light transmitting means are provided in the same sheet; Figure 6 illustrates the way in which the light transmitting means provides light to the interior of the microfluidic passageway in the embodiment of Figure 5 in which the waveguide and microfluidic passageway are written into the same sheet; Figure 7 is a cross sectional view along the line 7-7 in Figure 6; Figure 8 illustrates the way in which the light transmitting sheet provides light to the microfluidic passageways provided in a separate sheet in the embodiment of Figures 1 to 4; Figure 9 illustrates one way in which two microfluidic photobioreactor units in accordance with the invention may be joined to one another in series in edge to edge relationship; Figure 10 is a corresponding view illustrating how the units may be connected in series but in face to face relationship; Figures 11 and 12 illustrate two ways in which a plurality of light transmitting and fluid conducting sheets may be combined to form a composite microfluidic photobioreactor unit in the form of a block; Figures 13 A and 1 3B illustrate schematically the light transmitting sheet and fluid conducting sheets of the embodiment of Figure 12 in more detail; Figure 14 illustrates the combination of a plurality of composite microfluidic photobioreactor units in accordance with the embodiment of Figure 12 in series; and Figure 15 illustrates an arrangement similar to that of Figure 14 but including additional bypass and conditioning circuits; Figure 16 illustrates a further embodiment of the present invention in which the microfluidic photobioreactor is in the form of a microstructured optical fiber; Figure 17 illustrates the way in which two optical fibers in accordance with the embodiment of Figure 16 may be connected to one another via an adaptor in the form of a micro fluidic chip; Figure 18 schematically illustrates the way in which a plurality of microfluidic photobioreactors in accordance with the embodiment of Figure 17 may -40 -be connected to one another using adaptors as shown in Figure 17 to provide a composite system including bypass and conditioning circuits.

A microfluidic photobioreactor unit 1 in accordance with a first embodiment of the invention will be described with respect to Figures 1 to 4.

The unit is in the form of a multilayer sheet. The sheet is of borosilicate glass, fused silica, fused quartz or another glass substrate. Rather than being formed from glass, it will be appreciated that the units may be formed of a polymeric material. The pumps and heat exchangers and other devices may be formed within the system as microfluidic features as described in EP 1922364. The sheet may conveniently have dimensions of 1150 x 850 x 1.1 mm. This is the size of a standard borofloat glass sheet manufactured by Schott. In the embodiment of Figure 1, the microfluidic photobioreactor unit is rectangular in shape. The microfluidic passageways may be coated to prevent organisms from sticking to their interior walls. This may be achieved using a hydrophobic coating, for example.

The microfluidic photobioreactor I includes a first fluid conducting sheet 10 (shown in Fig. 2) and a second light transmitting sheet 20 (shown in Fig. 3) which are bonded to one another in face to face relationship. The photobioreactor is therefore of a laminate structure. The individual sheets are not shown in Figure 1, but are illustrated in Figures 2 and 3 respectively.

The fluid conducting sheet 10 defines a single continuous serpentine microfluidic passageway in the form of a tunnel 3 extending between an inlet 5 and an outlet 7 in opposite corners of the sheet. The inlet and outlet are in the form of fluid ports in the edges of the sheet. Only the fluid inlet and outlet are schematically illustrated in Figure 1 and the path of the microfluidie passageway is not shown.

The microfluidic tunnel 3 has a diameter of 100 microns, and is written into the sheet by an etching process as known in the art. Adjacent portions of the channel are separated by distance d as shown in Figure 2 of 0.5 mm. It will be appreciated that the dimensions i.e. width or height of the microfluidic tunnel may be of any type suitable in relation to the organism to be used. Typical dimensions may be in the range of from 30 to 200 microns, although larger featured microfluidic passageways may be used provided that they still allow a given fluid located therein to exhibit appropriate microfluidic behaviour. It will also be appreciated that the -41 -microfluidic tunnel may, rather than being written into the depth of the substrate layer of the unit, be provided by bonding two separate sheets having appropriate channels in their surface together to define a tunnel within the multi-layer sheet obtained.

The microfluidic photobioreactor sheet includes a second sheet 20 having the light transmitting means. This sheet is shown in Figure 3. Again, only the input 11 and output 13 of the light transmitting means is shown in Figure 1, and not the light distributing path therebetween. The light transmitting means 9 is in the form of an optical waveguide, and comprises a light distributing path 15 in the form of an optical waveguide having first and second main light transmitting paths 17 and 19 extending along the major edges of the sheet. A plurality of side light transmitting branches 21 connect the main paths 17,19. Each side branch 21 includes a plurality of terminations at intervals 23 along their length. In this way when the light transmitting sheet 20 is laminated to the fluid conducting sheet 10 shown in Figure 2, the terminations 21 may transmit light to discrete points along the length of the microfluidic passageway 3 as shown in Figure 4 when the light transmitting means 9 is connected to a light source. The light transmitting means may comprise an optical fiber, or may instead be written into the substrate of the sheet. Figure 4 shows schematically the relationship between the light transmitting means and the fluid conducting passageways in the region A of the sheet in Figure 1. In embodiments the terminals provide a light point termination located at intervals of every 0.5 mm along the length of the microfluidic tunnel.

Rather than being provided with a plurality of terminations, the light transmitting means may comprise an optical fiber having a cladding with openings to provide light to the microfluidic tunnel. The cladding may comprise a plurality of discrete openings along its length or may comprise a continuous slit along its length to provide light at discrete points or along a continuous length of the microfluidic passageway.

In the embodiment illustrated the light transmitting means comprises an optical waveguide which is separately formed and attached to the light transmitting sheet. Instead, the light transmitting means may comprise an optical waveguide which is integrally formed with e.g. written into the sheet. The waveguide may be -42 -produced using any micro optical technique, and may be provided by writing the waveguide into the substrate above or below the microfluidic tunnel. Methods of providing such an optical waveguide are described in US 7,294,454, US 6768850 and "Manufacturing by laser direct-write of three-dimensional devices containing optical and microfluidic networks" -Said et al., Translume, presented at the SPIE Photonics West meeting held in San Jose, CA -January 24-29, 2004. The waveguide written into the sheet may be designed to include a plurality of openings in its walls to allow light to reach the microfluidic passageway in a similar manner to embodiments in which the waveguide is provided by an optical fiber having openings in its cladding.

The light input 11 is attached to a connector in the form of a fiber optical cable 22, and thus to a light source in the form of a lamp 24. In other embodiments the light source may be in the form of a luminaire, laser, LED etc. The light source may be directly connected to the input rather than using a connector 22. The light may be natural light in which means for collecting natural light, e.g. a solar panel may instead be connected to the input of the light transmitting means. Any light source may be used. It is not necessary that the light source necessarily transmits white light. For example, an LED emitting light only in the red or blue part of the spectrum may be used to reduce the amount of electricity consumption.

The light source may be a remote light source. For example, an appropriate system of light fiber optic cables or other light transmitting means may be located between the inlet and a light source. This may enable natural light to be collected using a solar panel and transmitted to a microfluidic photobioreactor device which is located some distance away, usually in a basement, or other more convenient locations. This means that it is not necessary for the microfluidic photobioreactor unit of the present invention to be located in daylight.

The glass sheets 10 and 20 may be bonded to one another with a bonding agent selected appropriately with respect to the substrate of the glass sheet, such as a fused silica binding agent for fused silica substrate, or by thermal bonding of vacuum fusion bonding. Suitable processes are described in U5 6,289,695. In other embodiments a femtosecond pulse laser may also be used to fuse the sheets together.

-43 -It will be appreciated that a plurality of sheets may be built up in the manner described with respect to Figures 1 to 4 to provide a microfluidic photobioreactor unit having any number of alternating sheets of waveguides and microfluidic channels if desired, and it is not necessary that the unit comprises only two such sheets.

Rather than locating the microfluidic tunnel and the light transmitting means in separate sheets which are bonded together, both of these features may be provided in the same substrate layer of the microfluidic photobioreactor unit. A single layer microfluidic photobioreactor unit in accordance with another embodiment of the invention is illustrated in Figure 5. The microfluidic photobioreactor sheet 30 is in the form of a sheet similar to that of the first embodiment described in relation to Figures 1 to 4. The microfluidic tunnel 32 is written into the sheet in the same way as described above, and defines an inlet 34 and an outlet 36. The light transmitting means 38 is in the form of a waveguide and defines an input 40 and an output 42 connected by a serpentine passageway 44 oriented at 90 degrees to the microfluidic tunnel 32. The microfluidic tunnel 32 might alternatively be provided by joining two different sheets to one another. The light transmitting means may then be provided in either of the sheets defining the microfluidic tunnel.

In the embodiment of Figure 5, the light transmitting means 38 is provided by an optical waveguide written into the sheet 30. The light transmitting means intersects the microfluidic tunnel 32 at a plurality of points, 46, 48 etc. In these regions the microfluidic tunnel forms a notch in the wall of the optical waveguide to allow light to enter the microfluidic tunnel. This may be achieved by writing the light transmitting means into the sheet and then cutting the microfluidic tunnel into the sheet to create notches in the light transmitting means. The region of the intersection 46 is shown in more detail in Figure 6. Figure 7 illustrates a vertical cross section through the light transmitting means and the microfluidic tunnel in the region of the intersection 46. In other embodiments, the light transmitting means may be located above the microfluidic tunnel, and the wall of the waveguide may define a continuous slit along its length for transmitting light to the interior of the tunnel, or a plurality of openings, or terminations as described in more detail with reference to Figure 3. The arrangement in which the light transmitting means is located in a different plane to the microfluidic tunnel is illustrated in Figure 8.

Rather than being written into the substrate, the optical waveguide may be provided by a separate optical fiber located within the sheet, and openings may be provided in a cladding of the fiber to allow light to reach the interior of the microfluidic passageway.

In the embodiments of Figures 1 to 8 the light input and output and fluid inlet and outlet may be used interchangeably. Thus depending upon the way the unit is connected in the system the inlet e.g. 5 may act as the outlet 7 and the outlet 7 as the inlet 5 etc. This provides greater flexibility in combining units. The symmetric construction of the units facilitates this.

In the embodiments shown in Figures 1 to 8, it will be appreciated that the fluid inlet and outlets and light inputs and outputs are located in the edges of the sheets. However, inputs, outputs, inlets and outlets may equally be located in the major surface of the sheets or in both locations. The most appropriate location would depend upon whether the sheets are to be joined to other sheets, and the way in which it is desired to join them, as described in more detail below.

In accordance with the invention, a fluid comprising a photosynthetic organism and a suitable growth culture is caused to flow through the microfluidic tunnel from the inlet to the outlet of the unit in a continuous manner. A suitable type of organism and culture is described in the paper "Culturing the marine cyanobactenum Prochiorococcus" , Moore et al, Limnology and Oceanography: Methods 2007, 353 to 362.

For example, in accordance with the embodiment of Figures 1 to 4, the inlet is connected to a source of fluid containing photosynthetic organisms in use. The source may be the outlet of an adjacent similar unit, or a fluid container, etc. The connection may be a direct connection or via one or more fluid conduits. Light is input to the light transmitting means via light input 11 in any of the manners described above, e.g. by connecting the input to a lamp, or a collector of natural light such as a solar panel. In this way, the photosynthetic organisms may grow as the fluid moves through the unit towards the outlet 7. Fluid leaving the outlet 7 of the system may be used as the input to an adjacent similar unit, andlor may be directed to a collecting system. The collected fluid may undergo refinement and other processes to extract the desired organisms, and render them for an intended final use, such as providing biomass, or a feedstock for the biofuel industry. A pump e.g. a peristaltic pump, gas exchanger, heat exchanger or any other devices may be provided in the fluid path within the unit, or upstream or downstream thereof to provide the conditions required to promote growth of organisms.

Figure 9 shows the way in which two microfluidic photobioreactor units in accordance any of the embodiments previously described may be connected to one another using fluid conduits. Fluid flows along a conduit 429 to the inlet 450 of the unit 400. The fluid may be from a fluid source or the outlet of another unit (not shown), or elsewhere. The fluid flows through the microfluidic passageway of the unit 400 to reach the outlet 470. Here it flows along fluid conduit 430 to a valve 450. The valve may be used to then direct fluid along a conduit 451 through pump 440, a gas exchanger 442 and a heat exchanger 444 to valve 438, and/or directly through conduit 432 to the valve. Causing fluid to flow through the conduit 451 may allow conditions in the fluid having the photosynthetic organisms to be more closely controlled in order to ensure optimum conditions for growth of the organisms. The valve 438 may then direct fluid through conduit 434 to the inlet 437 of the next unit 420, or along conduit 436 such that it does not flow through the unit.

The path 436 therefore allows the unit 420 to be bypassed. Valve 428 and conduit 431 may similarly allow the first unit 400 to be bypassed e.g. if the unit is found to be defective. Light is provided to the light inputs of the units by separate sources, or to one unit with appropriate connection between the light output and input of the units 400 420 (not shown). A suitable fluid conduit may be Tygon tubing.

In the embodiment of Figure 9, the adjacent units are located such that they are side-by-side. In the embodiment of Figure 10, the units are located one in front of the other. The units 500, 510 and 520 are connected by fluid conduits 530 and 540 to allow fluid to flow between them. The fluid conduits connect the respective fluid outlet and inlet of the adjacent units. As the inlets and outlets are identical the orientation of the sheets is not critical, as inlets and outlets may be used interchangeably. As described with respect to Figure 9, any combination of pumps, heat exchanger or gas exchangers may be located between the sheets, or between certain sheets i.e. not each adjacent sheet but every third sheet etc. It will be -46 -understood that any number of sheets may be added to the composite photobioreactors of the embodiments of Figures 9 or 10 to provide a larger scale system if desired.

Rather than connecting the units together with separate connectors as shown in Figures 9 and 10, the units may be bonded directly to one another to provide a connection between the fluid inlets and outlets, and the light inputs and outputs of different units. The units may also be directly bonded to one another in embodiments in which separate connectors are used if the inletloutlet and outputlinput of each unit is on an edge.

In the embodiment of Figure 11 two fluid conducting sheets 600 of the type shown in Figure 2 are bonded to one another with a light transmitting sheet 610 as shown in Figure 3 sandwiched therebetween. The first fluid conducting sheet 600 includes a fluid inlet 611. Fluid flows through the microfluidic tunnel in the sheet to the fluid outlet 614. A port 612 is provided in the relevant part of the light transmitting sheet 610 to allow fluid to pass from a fluid outlet 614 to the fluid inlet 616 of the fluid conducting sheet on the other side of the light transmitting sheet 610. Fluid then flows through the second fluid conducting sheet to the fluid outlet 618. In this way fluid flows between the sheets. Light is provided to the input of the sheet 612 and is then transmitted by the sheet to the interior of the microfluidic tunnels of one or both of the adjacent fluid conducting sheets. Any number of sheets may be combined in this way, alternating fluid conducting and light transmitting sheets toprovide a composite microfluidic photobioreactor, e.g. in the form of a block such as the cube 650. The corresponding light inputs and outputs of the light transmitting sheets may be connected in a similar manner to the fluid inlets and outlets of the fluid conducting sheets if additional light transmitting sheets are used.

The light transmitting sheets may only transmit light to one adjacent fluid conducting sheet in embodiments in which there are equal numbers of each type of sheet. In embodiments, a composite microfluidic photobioreactor having equal numbers of each type of sheet may be provided by appropriately bonding microfluidic photobioreactor units of the type shown in Figure 1 to each other, with each unit including a light conducting sheet and a fluid conducting sheet, or similarly single sheet units e.g. of the type shown in Figure 5 may be bonded to one -47 -another. The fluid conducting and light transmitting sheets need not be separate from one another when joined to make the composite photobioreactor unit. The sheets may be bonded to one another using a femtosecond pulse laser, or in any of the manners described above.

Figure 12 illustrates the way in which four fluid conducting sheets 700 may be bonded together with light transmitting sheets 710 interspersed between them to provide a composite microfluidic photobioreactor unit. Figures 13 A and 13 B illustrate respectively the positions of the inputs/outputs and inlets/outlets on the light transmitting sheet 710 and the fluid conducting sheet 700 in more detail. The light transmitting sheet 710 has light input 720 and light output 730 and ports 740 which cooperate with the inlet and outlet respectively of the adjacent fluid conducting sheets to allow fluid to move from one fluid conducting sheet to the next. The fluid conducting sheet has an inlet/outlet point 750 in each corner. This allows the sheet to be used in any orientation. When bonded to an adjacent light transmitting sheet only the pair of points 750 adjacent ports in the light transmitting sheet will act as the inlet and outlet of the sheet with the other inlet/outlets being sealed by the light transmitting sheet. In embodiments the inlet/outlet 750 of the respective fluid conducting sheets may cooperate to allow light to pass from a source 780 from the light input 720 of one light transmitting sheet to the correspondingly positioned light input of the next sheet.

It will be appreciated that the illustrated arrangement of fluid inlets and outlets and light inputs and outputs and their arrangement to permit light and fluid to move through the composite microfluidic photobioreactor unit are merely exemplary, and any suitable arrangement may be used, including using some external connectors.

Composite microfluidic photobioreactor units in accordance with the embodiments of Figures 11 to 13 may be connected to one another in series or parallel. Figure 14 illustrates an arrangement in which composite photobioreactor units 800, 810 and 820 are connected in series with one another. This Figure illustrates schematically the fluid path between the units.

Figure 15 illustrates an arrangement in which the composite units 900, 910, 920 and 930 are connected in series with one another as in Figure 14. However, -48 -here additional fluid paths are provided to allow fluid to bypass any or all of the units, or to pass through a conditioning circuit 970 including a heat exchanger, pump and gas exchanger 940, 950 and 960. This may allow the conditions in the fluid to be controlled. The different fluid paths are connected via valves. For example, fluid leaving the unit 910 can flow via path 990 to enter unit 920 or can flow via bypass path 992 to another valve, where the fluid may follow path 993 toward the inlet of.

unit 930 or may bypass unit 930 via path 994.

Figure 16 illustrates a microfluidic photobioreactor in accordance with yet another embodiment of the invention. In this embodiment the microfluidic photobioreactor unit is in the form of a microstructured optical fiber 1000. The optical fiber includes a plurality of microcavities 1002 arranged in its core and cladding regions, and extending parallel to the axis of the optical fiber from one end to the other, extending the entire length of the optical fiber. These microcavities define air holes in the form of tunnels in the optical fiber.

Optical fibers of this microstructured construction are known. Examples of suitable optical fibers may be found, for example in US 7110646, and also described for example in the paper "Microstructured-core optical fiber for evanescent sensing applications" -Christiano Cordeiro et al, Optical Society of America, published 25 December 2006, Vol. 14, No. 26 Optics Express 13056.

It will be appreciated that the pattern of microcavities need not be as shown in Figure 16, and the optical cavities may be located only in the core or cladding regions or both. In accordance with the invention it is necessary only that there is at least one microcavity which is suitable for use as a microfluidic channel.

In accordance with the invention, two of the microcavities in the microstructured optical fiber 1000, microcavities 1004 and 1006, are used as microfluidic channels, with the fluid comprising photosynthetic organisms being passed through these cavities. When a suitable fluid comprising photosynthetic organisms of the type described in respect of the earlier embodiments of the invention is passed through these cavities, and light passed along the microstructured optical fiber in the normal manner, a certain amount of light will be absorbed by the fluid flowing through the microfluidic channels 1004, 1006 enabling photosynthesis to take place.

-49 -In one embodiment, the microstructured optical fiber 1000 may have a diameter of 500 microns, and the air holes e.g. 1004, 1006 used as the microfluidic channels have a diameter of 40 microns. -Fluid may be caused to continuously flow along the microfluidic passageways 1004, 1006 in the microstructured optical fiber 1000 in any suitable maimer. One preferred embodiment illustrating the way in which the microstructured optical fiber may be connected into an overall microfluidic system, and enabling the microstructured optical fiber to be placed in fluid communication with another microstructured optical fiber to provide a larger composite microfluidic photobioreactor will now be described with respect to Figures 17 and 18.

In accordance with the invention in this preferred embodiment, an end 1008 of the microstructured optical fiber 1000 is connected to an adaptor 1010. The adaptor 1010 is in the form of a chip. Figure 17 only illustrates the lower half of the chip. In use, a matching upper half is located over the top of the microstructured optical fiber 1000 to cover the microstructured optical fiber 1000 and enclose it within the chip.

The adaptor 1010 includes a V-shaped groove 1012 at one end 1014. The V-shaped groove 1012 is configured to provide a locating means for locating the end 1008 of the microstructured optical fiber in a manner such that the end of the microfluidic channel 1004 in the end face of the microstructured optical fiber is registered respectively with the microfluidic channel 1016 in the chip.

Figure 17 shows the lower half of an adaptor. In use, the microstructured optical fiber 1000 is located in the locating groove 1012, and a matching half of the adaptor located over the top of the microstructured optical fiber to surround the microstructured optical fiber and maintain it in place.

The microfluidic passageway 1016 has one outlet to a fluid port 1018 at the exterior of the chip. A luer connector 1020 is attached to the fluid port 1018. The other end of the microfluidic channel 1016 terminates in an outlet 1022 at the blind end of the locating groove 1012.

In use, the end 1008 of the microstructured optical fiber 1000 is located in the locating groove 1012. The end face of the microstructured optical fiber abuts the blind end of the groove 1012 in a manner such that the microfluidic channel 1004 of -50 -the microstructured optical fiber 1000 is registered with the outlet 1022 of microfluidic channel 1016. The microfluidic channel 1016 has a diameter corresponding to the diameter of the microfluidic channel 1004 to which it is to be connected in the microstruetured optical fiber 1000. Thus in the embodiment illustrated, the microfluidic passageway 1016 has a diameter of 40 microns.

An index matching gel may be used to seal between the microstructured optical fiber and the chip 1010 to ensure that the air holes in the fiber remain clear.

Any suitable technique may, however, be used to bond the face of the microstructured optical fiber to the chip in a manner that the microfluidic passageway 1004 is aligned with the outlet 1022 of microfluidic channel 1016.

The microstructured optical fiber and the chip may both be made from silica, although it is envisaged that in other embodiments the chip may be made from silicon, or other glass or polymeric substances.

Once the microstructured optical fiber has been located in place with the lower microfluidic passageway 1004 connected to the outlet 1022, the matching upper half of the chip may be located over the top of the microstructured optical fiber, and the upper microfluidic passageway 1006 of the microstructured optical fiber 1000 connected to an outlet of a microfluidic passageway in the upper half of the chip, and thus to a fluid port for connecting to external connectors in the same manner as described in relation to the lower microfluidic cavity 1004.

The luer connector 1020 may be connected to fluid connectors such as Tygon tubing in the same manner as described in respect of the other embodiments above. This may allow the chip to be connected into a fluid network e.g. to a fluid source or fluid collecting receptacle, or to other microstructured optical fibers if it is desired to provide a composite microfluidic photobioreactor including more than one microstructured optical fiber.

As will be seen, the chip in the embodiments of Figure 17 is configured to receive the end of a second microstructured optical fiber 2000. Connection of the end 2002 of the microstructured optical fiber 2000 to the chip 1010 may be achieved in the same manner as described with respect to the first microstructured optical fiber 1000. The second V-shaped groove 2012 at the other end 1015 of the chip is configured for receiving the end 2002 of the fiber 2000. At the blind end of the groove 2012 a microfluidic passageway 2016 terminates, providing a fluid outlet 2022 which may be connected in the same manner as described in relation to the first microstructured optical fiber to a microfluidic tunnel defined in the microstructured optical fiber 2000. The top half of the chip, not shown in Figure 17, may similarly comprise a microfluidic passageway associated with the upper half of the blind ended groove for fitting over the top half of the microstructured optical fiber and cooperating with a microfluidic channel in the upper half of the fiber.

The microfluidic passageway 2016 is connected to a fluid port (not shown) and for example via luer connector to Tygon tubing in the same manner as described with respect to microfluidic passageway 1016. Thus, in use, the fluid ports 1020 and the corresponding fluid port associated with microfluidic passageway 2016 may be connected to one another to allow fluid to be transmitted between one microstructured optical fiber 1000 and the second microstructured optical fiber 2000 or vice versa via the external connector and the internal passageways 1022 and 2022.

As shown in Figure 17, the chip 1010 includes a recess 1011 which may be used to retain a ball lens 2018. The ball lens may be used to help transmit light between the end of the microstructured optical fibers 1000, 2000 in use.

Operation of the embodiment shown in Figure 17 will now be described. In use a fluid is passed through the microfluidic passageways 1004, 1006 in the microstructured optical fiber 1000 towards the end face 1008. On reaching the end, the fluid in the passageway 1004 enters the microfluidic channel 1016 in the chip with which it is registered and flows to the fluid port 1018 and thus through the luer connector 1020 to a connector associated therewith, such as a length of Tygon tubing. The connector is directly or indirectly connected to a corresponding luer connector associated with an exterior fluid port at the end of the microfluidic channel 2016 remote from the end which is connected to the microstructured optical fiber 2000 on the other side of the chip 1010. In this way, the fluid enters the microfluidic channel 2016 and flows through the port 2022 into a microcavity of the microstructured optical fiber 2000 which is registered with the outlet 2022. The fluid may then continue to flow along the second microstructured optical fiber 2000 towards its other end. The end of that fiber may similarly be connected to another -52 -length of microstructured optical fiber, or to another fluid connector for transmitting the fluid to a different part of the system. Similarly, fluid passing along the upper passageway 1006 flows into a corresponding microfluidic passageway located on the upper half of the chip, which is connected to a microfluidic passageway in the other side of the chip which is connected to a microcavity in the upper half of the microstructured optical fiber 2000.

Light is passed along the microstructured optical fiber 1000, and is absorbed by the fluid flowing through the microfluidic cavity 1004 in the microstructured optical fiber. On reaching the end of the microstructured optical fiber 1000, the light is transmitted via the ball lens to the microstructured optical fiber 2000 so that it may then be passed along the microstructured optical fiber 2000 and to the fluid flowing therethrough to enable photosynthesis to occur.

Although a ball lens is illustrated, any type of microlens which may focus light tightly as it crosses the gap between the ends of the microstructured optical fibers 1000, 2000 may be used. In some embodiments it not be necessary to provide any lens if a sufficient amount of light is able to pass the gap, e.g. if the gap is smaller. Alternatively, each microstructured optical fiber may have its own light source.

In the embodiment illustrated, external fluid connectors are used to connect the microfluidic channels 1016, 2016. However, it is envisaged that the microfluidic channels might be connected to one another within the body of the chip.

Furthermore, the chip may comprise internal features such as pumps, heat exchangers, gas exchangers and valves, etc., to allow conditioning and controlling of conditions in the fluid as it passes between the microstructured optical fibers, and to allow fluid to be directed either between the microstructured optical fibers or to an outlet if desired, and/or to provide further fluids to the microstructured optical fibers.

Any number of microcavities of the respective microstructured optical fibers may be connected to one another in a similar manner to that described above.

Figure 18 shows one way in which a chip of the type shown in Figure 1 may be connected into a microfluidic system in a similar manner to the embodiments illustrated previously. In the embodiment illustrated in Figure 18 the chip 1010 is connected to two further chips 1030, 1040 by a suitable network of fluid connectors.

-53 -The external fluid port 1018 is connected to an external connector 3000. An additional fluid port 1019, not shown in Figure 17, is located in the opposite corner of the chip and is likewise connected to a connector 3002. The fluid ports 2018, 2019 at the other end of the chip 1010, 2019 are likewise connected to lengths of connector 3004, 3006.

In use, fluid passing along the connectors 3000, 3002 after leaving microstructured optical fiber 1000 reaches valves 3008, 3010 respectively. Fluid passing along connector 3000 or 3002 passes a conditioning section comprising a heat pump 3016, a gas exchanger 3018 and a pump 3020 before reaching the valves 3008, 3010. At this point the valves may be used to either cause the fluid to continue along connectors 3004, 3006 to enter the second microstructured optical fiber 2000 and move towards chip 1030, or to continue along connectors 3012, 3014 in order to bypass the chip 1030, or components of the fluid may move along both paths.

Similarly, fluid which has passed through the chip 1030 may enter the chip 1040 or bypass the chip using the appropriate set of valves and connectors shown in Figure 18.

A top-up light source 3022 is provided to provide additional light to the microstructured optical fiber after chip 1040. The top-up light source 3022 may provide light to the chip 1040 and hence microstructured optical fiber 3024 via a conventional optical fiber 3023, for example.

The connectors 3014, 3012 etc., may be flexible Tygon tubing or any similar form of connector.

It will be appreciated that any arrangement of microstructured optical fibers may be used when combining microstructured optical fibers into a composite system, and the fibers may be arranged in series or parallel with one another. Rather than being connected as shown in the embodiments, the fibers may be connected directly to one another and with or without the aid of additional connectors.

In some embodiments the adaptor chips 1010 etc., may be located at distances of around of every 10 meters. Thus the lengths of microstructured optical fiber between the chips may be 10 meter lengths.

-54 -In one embodiment as shown in Figure 17, the chip may be formed from a fused silica substrate. The microstructured optical fibers may also be formed from a fused silica material.

The microfluidic photobioreactor in accordance with any of the aspects and embodiments of the present invention provides the advantage that it may allow relatively high yields of photosynthetic microorganisms such as algae or phytoplanctum to be produced. The use of microfluidic system allows conditions within the microfluidic passageways to be closely controlled, allowing optimum conditions for growth to be maintained. Close control may be provided over variables such as the concentration of the fluid, the growth medium, nutrient levels, temperature, light levels etc., and the risk of organisms being exposed to predators or grazers may be reduced. Similarly, it is easier to maintain a single strain i.e. monoculture of the organisms in the system, and to avoid contamination by other organisms or viruses etc. Due to their small scale, the microfluidic photobioreactors of the present invention may be readily located anywhere, even in urban areas, and are more space efficient than conventional methods of generating photosynthetic organisms for use as biomass, or a feedstock for the biofuel industry. The present invention also provides a more quantifiable system, in which output levels of organisms may be more readily determined. Harvesting is also made easier, as it is only necessary to collect fluid at an appropriate point when it has flowed through a unit or units, and to extract the organisms therefrom.

As the process is a continuous flow process, the units may provide greater yields than may be obtained using conventional methods for culturing photosynthetic organisms.

Claims (60)

1. -55 -Claims 1. A system for cultivating photosynthetic organisms comprising: at least one microfluidic photobioreactor unit, the microfluidic photobioreactor unit having; a fluid inlet, a fluid outlet, and at least one microfluidic passageway connecting the fluid inlet and the fluid outlet, and means for transmitting light to the interior of said at least one passageway in use; the system further comprising a fluid including photosynthetic organisms in said at least one microfluidic passageway.
2. 2. A system of claim 1, wherein the at least one microfluidic passageway is written into the substrate of the microfluidic photobioreactor unit.
3. 3. The system of claim 1, wherein the unit comprises two separate layers joined to one another to provide the at least one microfluidic passageway.
4. 4. The system of any preceding claim, wherein the unit comprises a single microfluidic passageway, the passageway being a serpentine passageway.
5. 5. The system of any preceding claim, wherein the means for transmitting light comprises an input and means for distributing light from the input, wherein the means for distributing light is in the form of an optical waveguide.
6. 6. The system of claim 5, wherein the optical waveguide comprises an optical fiber or fibers.
7. 7. The system of any of claims 1 to 5, wherein the light transmitting means is written into a substrate layer of the unit.

   -56 -
8. 8. The system of any of claims 5 to 7, wherein the light transmitting means comprises one or more openings for transmitting light to the interior of the at least one microfluidic passageway.
9. 9. The system of any preceding claim, wherein the light transmitting means is provided in a separate layer laminated to the layer or layers of the unit which define the microfluidic passageway or passageways.
10. 10. The system of any of preceding claim, wherein the light transmitting means intersects the microfluidic passageway or passageways to provide light thereto.
11. 11. The system of any preceding claim, wherein an input of the light transmitting means is connected to a light source in the form of one or more of a lamp, a luminaire, LED, or laser.
12. 12. The system of any preceding claim, wherein the light is natural light and the system comprises means for providing natural light to an input of the light transmitting means.
13. 13. The system of any preceding claim, further comprising means for causing fluid to continuously flow through the unit.
14. 14. The system of any preceding claim, further comprising one or more of a gas exchanger, valve, pump and/or heat exchange device.
15. 15. The system of any preceding claim, wherein the microfluidic photobioreactor unit is in the form of a sheet.
16. 16. The system of any preceding claim, further comprising one or more additional microfluidic photobioreactor units of the same construction joined to said microfluidic photobioreactor unit in a manner which permits flow of fluid between the units.

    -57 -
17. 17. The system of any preceding claim, wherein the outlet of said unit is connected to the fluid inlet of a like unit andlor the inlet of the unit is connected to the fluid outlet of a like unit.
18. 18. The system of any of claims 16 or 17, wherein the units are joined to one another by means of fluid conduits.
19. 19. The system of claim 16 or 17, wherein the units are bonded to one another such that the respective fluid inlets and outlets of the units are directly joined to one another.
20. 20. The system of any of claims 16 to 19, wherein the respective inputs and outputs of the light transmitting means of adjacent units are connected to one another.
21. 21. The system of any of claims 16, 17, 19 or 20, wherein the units are laminated to one another to provide a composite microfluidic photobioreactor unit.
22. 22. The system of claim 21, wherein the composite microfluidic photobioreactor unit is in the form of a block; preferably a cube.
23. 23. A method of cultivating photosynthetic organisms, the method comprising providing a microfluidic photobioreactor unit comprising: a fluid inlet, a fluid outlet, and at least one microfluidic passageway connecting the fluid inlet and the fluid outlet; the microfluidic photobioreactor further comprising means for transmitting light to the interior of the at least one microfluidic passageway; and wherein the method further comprises providing a fluid comprising photosynthetic organisms in said at least one microfluidic passageway, and using said light transmitting means to transmit light to the fluid in the at least one microfluidic passageway.

    -58 -
24. 24. The method of claim 23, comprising causing the fluid to flow continuously through said unit.
25. 25. The method of claim 23 or 24, further comprising connecting a fluid source to said input.
26. 26. The method of any of claims 23 to 25, further comprising providing natural light to an input of the light transmitting means.
27. 27. The method of any of claims 23 to 26, further comprising collecting fluid which has passed through the unit.
28. 28. The methoä of any of claims 23 to 27, further comprising using photosynthetic organisms extracted from fluid collected from the system as biomass, or as a feedstock for the biofuel industry.
29. 29. The method of any of claims 23 to 28, further comprising connecting one or more like units to said unit in a manner which permits fluid to flow between the units.
30. 30. A modular assembly for a microfluidic photobioreactor system, the assembly comprising: a plurality of microfluidic photobioreactor units; each unit comprising a fluid inlet, a fluid outlet, one or more microuluidic passageways connecting the fluid inlet and the fluid outlet, and means for transmitting light to fluid within the passageways in use; the units being such that the fluid inlet of one unit may be connected to the fluid outlet of another of the units, and a fluid outlet of the unit may be connected to the fluid inlet of another one of the units to provide a composite microfluidic photobioreactor comprising a plurality of the units.

    -59 -
31. 31. A method of assembling a composite modular microfluidic photobioreactor using the modular assembly of claim 30, the method comprising joining a unit to at least one other unit such that the fluid outlet of one unit is connected to the fluid inlet of the other unit, and preferably such that an input of a light transmitting means of one unit is connected to an output of the light transmitting means of another unit.
32. 32. A method of assembling a microfluidic photobioreactor, the method comprising: providing a plurality of microfluidic photobioreactor sheets each comprising a fluid inlet, a fluid outlet, one or more microfluidic passageways connecting the fluid inlet and the fluid outlet, and means for transmitting light to fluid within the passageways in use; the method comprising bonding the sheets to one another such that the outlet of one sheet is connected to the inlet of another of the sheets to enable fluid to flow between the sheets.
33. 33. A method of assembling a composite microfluidic photobioreactor unit, the method comprising: providing a first group of fluid conducting sheets, each having an inlet, an outlet and one or more microfluidic passageways connecting the inlet and the outlet; providing a second group of light transmitting sheets, each comprising light transmitting means having and input and an output and a light distributing path or paths therebetween; alternately laminating sheets from the first and second group of sheets to one another to provide a microfluidic photobioreactor having alternating fluid conducting and light transmitting sheets; wherein the photobioreactor comprises at least two fluid conducting sheets and at least two light transmitting sheets, the sheet being arranged such that the outlet of one fluid conducting sheet is connected to the inlet of the next fluid conducting sheet, and the intervening light transmitting sheet being arranged to provide light to the interior of the microfluidic passageways in at least one adjacent fluid conducting sheet.

    -60 -
34. 34. A microfluidic photobioreactor comprising: a plurality of fluid conducting sheets, each having a fluid inlet, a fluid outlet and one or more microfluidic passageways connecting the inlet and the outlet; and a plurality of light transmitting sheets, each comprising light transmitting means having an input and an output and a light distributing path or paths therebetween; the fluid conducting sheets and light transmitting sheets being laminated to one another in an alternating manner such that each light transmitting sheet is interposed between two fluid conducting sheets, wherein the outlet of one fluid conducting sheet is connected to the input of the next fluid conducting sheet, and the output of one light transmitting sheet is connected to the input of the next light transmitting sheet, such that in use, fluid may flow sequentially through the fluid conducting sheets of the photobioreactor, and the light transmitting sheets are arranged to transmit light to the interior of the microfluidic passageways of an or each adjacent fluid conducting sheet.
35. 35. The use of a microfluidic photobioreactor in accordance with, or obtained in accordance with any of claims 30 to 34 to cultivate photosynthetic organisms.
36. 36. A microfluidic photobioreactor in accordance with, or obtained in accordance with any of claims 30 to 35 comprising a fluid containing photosynthetic organisms.
37. 37. A system for cultivating photosynthetic organisms, the system comprising: a microfluidic photobioreactor comprising a microstructured optical fiber having at least one internal microcavity which provides a microfluidic passageway; wherein the microcavity contains a fluid comprising synthetic organisms.
38. 38. The system of claim 37, wherein at least one end of the microstructured optical fiber is connected to an adaptor arranged to allow fluid to enter and/or leave the optical fiber via the adaptor in use. 6l-
39. 39. The system of claim 38, wherein the adaptor comprises at least one internal microfluidic passageway registered with an end of the microcavity of the optical fiber, whereby fluid may enter or leave the microcavity of the optical fiber via said microfluidic passageway of the adaptor.
40. 40. The system of claim 38 or 39, wherein the adaptor comprises means for locating the end of the microstructured optical fiber such that a microcavity of the optical fiber is in fluid communication with a respective microfluidic passageway of the adaptor.
41. 41. The system of any of claims 38 to 40, wherein the adaptor is attached to a further microstructured optical fiber of like construction, the adaptor placing the microcavity of the first optical fiber in fluid communication with a microcavity of the second optical fiber thereby enabling fluid to pass between the microstructured optical fibers.
42. 42. The system of any of claims 38 to 41, wherein the optical fiber comprises a second adaptorat its other end, the second adaptor being of like construction to the first adaptor.
43. 43. The system of any of claims 38 to 42, wherein the adaptor is in the form of a microfluidic chip.
44. 44. The system of any of claims 37 to 40, wherein the microstructured optical fiber is connected to a second optical fiber of like construction, the microcavity of the first optical fiber being in fluid communication with a microcavity of the second optical fiber.
45. 45. The system of claim 41 or 44, further comprising a lens for transmitting light between the ends of the microstructured optical fibers.

    -62 -
46. 46. The system of any of claims 37 to 45, comprising means for causing fluid to flow continuously through the microcavity.
47. 47. A method of cultivating photosynthetic organisms comprising: providing a microstructured optical fiber comprising at least one internal microcavity which may act as a microfluidic passageway in use; providing a fluid comprising photosynthetic organisms in the microcavity; and passing light along the optical fiber to provide light to the organisms in said microcavity.
48. 48. The method of claim 47, comprising causing fluid to flow continually through the microcavity of said optical fiber.
49. 49. The method of claim 47 or 48, further comprising connecting an adaptor to at least one end of the optical fiber, the adaptor being arranged to allow fluid to enter and/or leave the optical fiber via the adaptor.
50. 50. The method of any of claims 47 to 49, further comprising connecting the microstructured optical fiber to a second optical fiber of like construction, and placing the microcavity of the first optical fiber in fluid communication with a microcavity of the second optical fiber.
51. 51. A modular assembly for a microfluidic photobioreactor system, the assembly comprising: a plurality of microstructured optical fibers; each optical fiber comprising one or more axially extending microcavity providing a microfluidic passageway through which a fluid may pass in use; and at least one adaptor, the adaptor being arranged to enable the microcavity of one optical fiber to be connected to a microcavity passageway of another of the optical fibers in use to allow fluid to flow between the optical fibers and thereby to provide a composite microfluidic photobioreactor comprising a plurality of the optical fibers.

    -63 -
52. 52. A method of assembling a microfluidic photobioreactor using the assembly of claim 51, the method comprising placing first and second optical fibers of the assembly in fluid communication with one another using the adaptor.
53. 53. The system, method or assembly of any of claims 37 to 52, wherein the or each microcavity extends axially along the entire length of the or each optical fiber.
54. 54. The use of a microstructured optical fiber comprising at least one internal microcavity as a microfluidic photobioreactor.
55. 55. A method of using a microstructured optical fiber, the optical fiber comprising at least internal microcavity, the method comprising causing a fluid to move through the microcavity.
56. 56. The method of claim 55 comprising causing said fluid to move continuously through the microcavity.
57. 57. A microfluidic photobioreactor comprising a microstructured optical fiber having at least one internal microcavity which provides a microfluidic passageway in use.
58. 58. The system or method of claim I or 23, wherein said microfluidic photobioreactor unit comprises a microstructured optical fiber having at least one internal microcavity providing said microfluidic passageway.
59. 59. The use of a microfluidic photobioreactor to cultivate photosynthetic organisms.
60. 60. A system, method, modular assembly or microfluidic photobioreactor substantially as herein described and/or with reference to any one of the accompanying drawings.