WO2011144652A2

WO2011144652A2 - Method for depositing sensor material on a substrate

Info

Publication number: WO2011144652A2
Application number: PCT/EP2011/058031
Authority: WO
Inventors: Jan Harries Hansen; Hans Ole Nielsen; Anders Kristensen; Morten Bo Lindholm Mikkelsen; Rodolphe Charly Willy Marie
Original assignee: Delta Dansk Elektronik, Lys & Akustik; Danmarks Tekniske Universitet
Priority date: 2010-05-18
Filing date: 2011-05-18
Publication date: 2011-11-24
Also published as: EP2572185A2; WO2011144652A3

Abstract

A method for manufacturing a sensor, the method comprising: providing at least a sensor deposition area of a surface of a substrate with a predetermined microstructure; depositing a layer of sensor material on the microstructured sensor deposition area. The layer is generally deposited in liquid form and then immobilized by evaporation. Additional microstructures may provide optical functions. A layered product is obtained by this method.

Description

Method for depositing sensor material on a substrate TECHNICAL FIELD

Disclosed herein are a method for depositing of a material, such as a sensor material, on a surface of a substrate, and a substrate having a material deposited on its surface.

BACKGROUND

Sensor material, e.g. optical sensors and/or monitors based on absorption and/or fluoresce nee detection, are used in a wide variety of applications.

Optical sensors in the form of adhesive patches or labels that can be adhered to a surface are known in the art. US 2009/0028756 discloses a process for manufacturing of an oxygen sensitive patch to hold or

encapsulate sensing molecules. However, such adhesive patches are cumbersome to secure to a surface, in particular when the surface is the inside surface of a container such as a bottle. It is thus desirable to provide a more efficient method of applying a material such as a sensor material to a surface in a reproducible and cost effective manner.

It is further desirable to devise a method for producing a sensor spot of a sensor material that is suitable even for sensor materials of low viscosity. For such materials having a low viscosity known methods, such as screen printing or tampon printing, have been found to provide unsatisfactory results.

It is further desirable to provide a method that is suitable for high volume production of sensor spots on objects.

SUMMARY

According to one aspect, disclosed herein are a method for depositing sensor material on a surface, and a corresponding sensor. Embodiments of the method disclosed herein comprise:

- providing at least a deposition area on the surface of a substrate with a predetermined microstructure;

- depositing a sensor material on the microstructured deposition area to provide a sensor area.

According to another aspect, disclosed herein are a method for depositing a material on a surface, and a corresponding product.

Embodiments of the method disclosed herein comprise:

- depositing a liquid on the microstructured deposition area;

- immobilising/fixating at least a part of the deposited liquid.

In embodiments of the method described herein, a microstructure is thus provided on the surface of the substrate that is adapted to create conditions for hemiwicking of the liquid to be deposited. Hemiwicking is used for reproducibly creating on a given area a liquid film of a well-defined thickness that is thinner or thicker than the thickness (defined by the area and the contact angle) otherwise obtained by depositing the liquid on a flat surface over an equivalent area by any other mean. For the purpose of the present description, the term liquid is intended to refer to any material that, at least during the deposition process (i.e. under conditions such as temperature, pressure, etc at which the deposition process is performed) flows and takes the shape of a container. In some embodiments the liquid has a viscosity of less than 1 Pa s, e.g. between 0.1 mPa s and 1 Pa s. A layer of material, e.g. a sensor material, may thus be deposited with a high degree of homogeneity by depositing a material on a microstructured surface. The superwetting properties of such a surface result in the formation of a very homogeneous film of material. Embodiments of the method described herein thus allow the deposition of materials even of very low viscosity, e.g. sol-gel, on a spot with homogeneous thickness and within a limited area. Embodiments of the method described herein allow the deposition of a material layer on a substrate such that the material layer is thinner than the layers normally obtainable by conventional methods such as needle printing, tampon printing, screen printing, due to the surface tension of the deposited material. Furthermore, the size, shape and thickness of a spot of deposited material layer may accurately and reproducibly be controlled. Embodiments of the method disclosed herein thus employs hemiwicking on a microstructured surface so as to evenly distribute, on a length scale larger than the period of the surface microstructures, a material, which is to be immobilized on the surface. The material may be deposited on the microstructured deposition area by placing a volume of said material of a predetermined size on the microstructured area. Guided by the microstructures, the material spreads homogeneously across the microstructured area until it reaches a thickness, which is determined by the microstructure geometry, and properties of the deposited material and the substrate material.

The layer thickness of the deposited material is independent of the deposited volume, provided that the volume of the deposited material is less than what is required to completely fill the microstructured sensor area, i.e., if the deposited material does not reach the edges of the microstructured area. When the microstructured area is provided sufficiently large, and in particular larger than the lateral extent of the layer of deposited material resulting from a droplet of the predetermined size, a layer with homogeneous thickness may be provided despite inevitable variations in droplet volume.

The thickness and/or the shape of the generated spot of deposited materia! may accurately be controlled by the choice of the microstructure. For example, the microstructure may be formed as a plurality of protrusions arranged in a predetermined pattern, e.g. a regular grid; for example the microstructure may be provided in the form of pillars arranged in a square or hexagonal grid. The pillars may have a circular or other cross section, e.g. square, hexagonal, etc. The form and size of the protrusions, as well as the geometry of the pattern may be chosen so as to obtain the desired shape of the resulting spot of deposited material and/or so as to obtain the desired thickness of the material layer across the entire microstructured area. In particular, the resulting thickness of the layer of deposited material may be controlled to be smaller than the thickness determined by the contact angle. In particular, the height of the microstructures and the contact angle of the deposited material govern the deposited material thickness. When the deposited material is immobilised by evaporation of a solvent, the shrinkage of the material due to solvent evaporation also influences the deposited material thickness.

For the purpose of the present description, the term microstructure refers to a surface structure in which micrometer-scale features - e.g. having

dimensions between Ο.ΐμηι and 500 μιη - are arranged in a pattern, e.g. a regular pattern, e.g. in the form of pillars in a square or hexagonal grid. The micrometer-scale features may be depressions and/or protrusions of a predetermined cross-sectional geometry, e.g. cylindrical or conical pillars. The micrometer-scale features may have a shape having an extent in at least one dimension, e.g. in two or even all three dimensions, between 0.1 μιη and 500 μιη, e.g. between 0.1 and 100 μηη. The final shape of the deposited 'drop¹ may be controlled by the geometry of the grid of pillars, e.g. as described in L. Courbin et al., Imbibition by polygonal spreading on

microdecorated surfaces, Nature Materials 6, 661 - 664 (2007). However, a random pattern of pillars may be used as well. The conditions for the occurrence of hemiwicking may be controlled, for a given contact angle between the substrate material and the material to be deposited, by choosing a suitable ratio between the height of the protrusions and the nearest neighbour distance between protrusions. In some embodiments, the protrusions may have the form of pillars having a height of between 1 pm og 1 mm, and cross-sectional diameters of between 0.1 pm and 100 μιη; the pitch distance between pillars may be between 1 pm and 500 pm. In some embodiments, the microstructure of the deposition area defines a photonic crystal, e.g. a two-dimensional photonic crystal comprising a two- dimensional pattern of features, e.g. protrusions and/or depressions. The term photonic crystal refers to periodic optical microstructures operable to affect the motion of photons. A photonic crystal may be composed of periodic dielectric or metallo-dielectric micro-structures that affect the propagation of electromagnetic waves (EM) by defining regularly repeating internal regions of high and low dielectric constant.

The features of the microstructured deposition area may have a shape having an extent in at least one dimension, e.g. in two or even all three dimensions, between 0.1 and 2 μιη, e.g. between 0.1 pm and 1.5 pm such as between 0.1 pm and 1 pm e.g. between 0.4 pm and 0.9 pm. The features of the microstructured deposition area may be arranged in a two-dimensional pattern (e.g. a periodic pattern periodic in one or two dimensions) across the deposition area where the spacing (e.g. the centre-to-centre distance, in the following also referred to as pitch distance) between neighbouring features in at least one dimension, e.g. in two or even all three dimensions, is between 0.1 and 2 μηη, e.g. between 0.1 pm and 1.5 pm such as between 0.1 pm and 1 pm e.g. between 0.4 pm and 0.9 pm.

The surface of the microstructured deposition area may thus have two functions. Firstly, it may facilitate deposition of a second, functionalized material by droplet dispensing/ink-jet and hemiwicking as described herein. Secondly, it may define a periodic modulation of the refractive index to form a Bragg grating or photonic crystal (PhC). Alternatively or additionally, it may define a periodic modulation of another optical parameter. The microstructures of the deposition area, e.g. a periodic surface corrugation, which defines the PhC, may be formed by nanoimprinting into the surface of a polymer planar/slab waveguide or on a polymer fiber, or any other suitable method for creating microstructures as described herein and known as such in the art.

The distance/height ratio determines how fast a droplet of the deposited material spreads across the micro structured deposition area. Hence, the immobilisation may be initiated after complete spreading of the drop, or be performed at a speed much slower than the spreading of the drop. For example, in embodiments where the immobilisation is performed by evaporation of a solvent, the distance/height ratio may be selected such that the spreading of the droplet occurs significantly faster (i.e. sufficiently fast to only allow a small part of the solvent to evaporate during the time it takes for the spreading to occur) than the evaporation of solvent so as to assure an even deposition thickness, and to avoid ring-shaped deposits (see e.g. Deegan et al., Capillary flow as the cause of ring stains from dried liquid drops, Nature, Vol. 389, 23 October 1997.). This puts a limit on how far a droplet can be spread. However, it will be appreciated that temperature and pressure can control the evaporation rate. Furthermore, due to the evaporation of the solvent, the volume of the deposited materia! is reduced during immobilisation; the remaining immobilised material may thus cover the surface of the microstructure as a thin layer conformal to the structured surface. In such embodiments, the pattern in which the pillars are arranged determines the resulting material density due to the conformal coverage.

As mentioned above, the features, e.g. periodically arranged pillars, of the microstructure may have dimensions (period and/or height and/or structure width) in the sub-micrometer range, e.g. between 100 nm and 1 pm. When scaling down the dimensions of the surface structures, compared to the results reported by Laurent Courbin et al. (ibid.), the propagation velocity of the spreading liquid, i.e. the material to be deposited, will scale linearly with the geometry, so that the liquid will spread over a distance that is scaling linearly with the structure size. For example, when linearly scaling down the dimensions of the surface structures by a factor of approximately 100, e.g. from 10 pm to 100 nm, the surface-to-volume ratio of the liquid between the pillars is equally increased by a factor of 100. This has two important implications for the spreading of liquid: the evaporation time will decrease by a factor of 100 and the hydraulic resistance increases by a factor of 100³ = 10⁶. The interfacial free energy gained per unit length for a liquid spread on a patterned hydrophilic surface is given by (see e.g. Jose Bico, Uwe Thiele, David Quere, Wetting of textured surfaces, Colloids and Surfaces A 206, 41- 46 (2002)): dF = (JSL - Ysv) r - <t>s)dx + γ_ιν{1 - <p_s)dx where γ denotes the surface energy, indices SL, SV and LV refer to the solid- liquid, solid-vapor, and liquid-vapor interfaces, respectively, r denotes the roughness, i.e. the ratio of the real surface area to the horizontal projection of the surface area, and ¾ denotes the pillar-coverage. However, for a linear scaling of the dimensions of the surface structures, this energy is unchanged since the geometrical factors (roughness r and piilar- coverage e¾) remain constant during the scaling. The energy per volume, i.e., the pressure, is thus increased by a factor of 100² = 10⁴. The flow rate is equally decreased by a factor of 10⁴, and with the before mentioned factor 10⁶ increase of the hydraulic resistance, the velocity will scale linearly with the dimensions of the surface structures. During a given time, the liquid will thus propagate a distance which is 100 shorter on the down-scaled structures than on the full-scale structures, and during this time, the same fraction of liquid will evaporate. The down-scaling is thus not expected to change the time scale dramatically. Use of hemiwicking to spread liquid on a surface can thus be extended into the sub-micrometer regime. Besides coating of photonic crystals, hemiwicking by microstructures enable sub- micrometer liquid films to be deposited. For the purpose of the present description, the term immobilising is intended to refer to any process for causing deposited layer to remain fixed as an integral layer covering and attached to at least a portion of the deposition area. The immobilising/fixation of the deposited liquid may be performed by a variety of techniques, e.g. by curing, hardening the deposited liquid, by evaporation of a solvent, by a sedimentation process, by covering the deposited liquid by a sealing layer, e.g. a foil, membrane etc. and/or a combination of the above. For example, the deposited material may be immobilized on the surface by solvent evaporation, by cross-linking due light exposure, exposure by other forms of electromagnetic radiation, and/or by thermal treatment, and/or by any other suitable curing process. Materials which remain liquid after deposition on the microstructures are also a possibility; such materials may be immobilized by depositing a cover layer, e.g. a membrane, on top of the deposited liquid. Hence, the process results in a composite layered product in which a substrate layer and a layer of deposited material are efficiently bonded to each other. In some embodiments, e.g. due to the removal of the liquid, e.g. by solvent evaporation, the immobilising process may cause a volume reduction of the immobilised material compared to the initially deposited volume. This may result in the immobilised material having a local thickness, measured in the spaces between protrusions of the microstructure, smaller than the height of the microstructure. This may also result in a convex upper surface of the immobilised deposited sensor material. In that case the optical path through the film on vertical side walls is much larger than the thickness of the film that an analyte has to diffuse through, and a larger surface is achieved, thus reducing the response time of the sensor

Examples of materials and particles that can be deposited using hemiwicking include so!-gels, polymers, glue, organic molecules, dyes, biomolecules, quantum dots, nanocrystals, catalyst particles, metal particles, mikroorgansims, ionic liquids.

In some embodiments, the material comprises a sensor material as described herein. To this end, the deposited material may comprise a reagent dye, such as, e.g., Ru(ll)-tris(4,7-diphenyl-1 ,10-phenanthroline) or 8- hydroxypyrene-1,3,6-trisulfonic acid trisodium salt, thus making the deposited material sensitive to analytes, such as, e.g., oxygen or pH. In some embodiments, the substrate layer and the immobilised deposited layer differ in at least one optical parameter, such as refractive index, absorbtion spectrum, and/or opto-thermal behavior. In some embodiments the deposited material comprises an optically functionalised material, e.g. comprising a controllable optical component having at least one controllable optical parameter that may be electrically, optically or otherwise controlled, e.g. by irradiation of electromagnetic radiation such as light. The term controllable optical component is intended to refer to any component having an optica] property that may be actuated, altered, amplified, and/or otherwise controlled by an optical, electrical or other control input to the controllable optical component.

The deposited material may comprise a base material. The base material may further be doped with an optically functional dopant. Hence the deposited material may comprise the base material as matrix and an optically functional material included in the matrix. The base material may comprise an organic or hybrid material, which in liquid form can be coated on the microstructured deposition area, making use of hemiwicking to spread the material and produce a liquid film of well-defined thickness, as defined herein. This base material may consist of or comprise a polymer (such as, for example, SU-8, P MA, TOPAS®) in at least one solvent, or a hybrid material (such as, for example, ORMOCER®, soi-ge! material, hydrogel) in at least one solvent.

The base material may itself be optically functional, e.g., by having an inherent absorption at a given wave-length or range of wave-lengths. Alternatively or additionally, dopants may be added to the base material to obtain predetermined optica! properties of the material. Examples of such optical properties may include a specific optical absorption/transmission spectrum, a specific fluorescence spectrum, a specific refractive index, and/or a specific thermal or opto-thermal behaviour, and/or other properties.

Examples of dopants operable to provide an optical function include dye molecules (fluorescent or non-fluorescent), nanocrystals, carbon black, carbon nanotubes, metal particles, organo-metallic molecules, etc. Laser dyes, such as, e.g., rhodamine, can also be added to the base material as a dopant to obtain optical gain. As mentioned above, reagent dyes may also be added so as to make the functionalized material sensitive to analytes.

The functionalized material (base material and, where the material comprises one or more dopants, the dopant(s)) or part of it is immobilized, e.g., by evaporation of solvents or curing (e.g., condensation or cross-linking by heating or UV-exposure) or cooling below the glass transition temperature.

Generally, the substrate may comprise any suitable material such as a polymer, a plastic, glass, etc. Examples of suitable substrate materials include inorganic materials, such as silicon, silicon oxides, silicon nitrides, III- V materials, such as, e.g., GaAs, AiAs, etc. Further examples of suitable substrate materials include organic materials, such as, but not limited to, SU- 8, polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS),TOPAS® (cyclic olefin copolymer), organically modified ceramics (ORMOCER®). The substrate material may be optically transparent or reflective at the used wavelengths of light or other electromagnetic radiation. The substrate material may be doped or undoped in order to tune optical properties, such as bandgap, absorption, transmition and reflection spectra. In some embodiments the method further comprises provision of a buffer area adapted to receive excess material from the microstructured deposition area during deposition of the material and/or to feed deposited materia! towards the microstructured deposition area during deposition of the material. Consequently, detrimental effects of variations in volume/droplet size on the homogeneity of the resulting layer of deposited material are reduced or even eliminated. The buffer area may be an annular area surrounding the microstructured deposition area, or otherwise surround the microstructured deposition area. Alternatively, the buffer area may be arranged adjacent to the microstructured deposition area. Hence the buffer area may abut the microstructured area, e.g. along a radially outer periphery of the microstructured deposition area and/or along another periphery of the microstructured deposition area.

The buffer area may also be provided with a predetermined microstructure, e.g. by a plurality of protrusions arranged in a predetermined pattern, where the geometry and/or size of the protrusions and/or the pattern in which they are arranged may differ from the corresponding microstructure of the microstructured deposition area. For example, the buffer area may comprise pillars of a different height and/or cross-sectional size than corresponding pillars of the microstructured area, and/or arranged with a different inter-pillar spacing.

When the microstructure comprises a plurality of conical or truncated-conical pillars the microstructure may also be applied to a curved surface, e.g. using injection moulding and/or hot embossing. Furthermore, irrespective of whether the surface is curved or not, the shape of the features forming the microstructure that allows hemiwicking of the fluid may be designed such that the microstructure also improves or even optimizes the extraction of the light from a deposited sensor material during use as an optical sensor. For example, when the microstructure is an array of pillars that have a truncated- conical shape, the light emitted from a deposited sensor material may be directed to the optical sensing element through reflections on the inner surfaces of the pillar.

In embodiments where the deposited material is a sensor material, the sensor may be an invasive or a non-invasive sensor. The sensor may be an optical sensor, e.g. a non-invasive optica! sensor. Hence, the sensor result may be detectable by detecting light or other electromagnetic radiation emitted by the sensor material, e.g. fluorescence and/or phosphorescence, and/or the like. Suitable sensor materials include a sol-gel including an active sensor material dissolved in a solution deposited on the surface by a sol-gel process. Examples of of suitable sensor materials are disclosed in Higgins et al, Analyst 2008, vol. 133, p. 241.

Generally, a sol-gel process, also known as chemical solution deposition, is a wet-chemical technique suitable for the fabrication of materials, e.g. a metal oxide, or glass, starting from a chemical solution acting as a precursor for an integrated network, or gel, of discrete particles or network polymers. The process typically includes the removal of liquid after deposition of the precursor on the surface, e.g. by sedimentation and removal of the remaining solvent, by drying, and/or the like. Afterwards, a thermal treatment, or firing process, may be employed.

When the deposited material comprises a carrying solvent and an active material, the microstructure permitting hemiwicking enables to maximize the optical thickness of the film while keeping the physical thickness of the film low in order to optimize the signal level versus response time of the active material. For example, if the solvent fraction is high, the resulting film of material after evaporation of the solvent would be a thin layer conformal to the microstructure. In that case, the optical path through the fiim deposited on vertical side walls of the microstructure is much larger than the thickness of the film that an analyte has to diffuse through. Generally the deposited material after evaporation of the solvent has an increased surface-area-to- volume ratio, thus facilitating an increased diffusion of analytes into the sensor material for a given size of the sensor area, thus resulting in a stronger optical signal, it will be appreciated that the term layer thickness refers to an average layer thickness, e.g. averaged over an area comprising at least 100 protrusions. The microstructure may comprise a plurality of protrusions arranged in a pattern across the deposition area; and the method may comprise determining at least one parameter to control a thickness of the layer of deposited material; wherein the at least one parameter may be chosen from a height of the protrusions, a pitch distance between neighbouring protrusions, and a cross-sectional size of the protrusions. In particular, in some embodiments, the thickness of the layer of deposited material is controlled by the height of the microstructure, the nearest neighbor distance between protrusions of the microstructure, by the contact angle between the deposited material and the substrate, and by the material shrinkage during the immobilizing step, e.g. by evaporation of a solvent. When the at least one parameter varies across at least a part of the deposition area so as to cause the thickness of the layer of deposited material to vary across at least the part of the deposition area, the volume of deposited material may be caused to vary across the deposition area. When the deposited material is a sensor material, different response times within a single sensor spot may thus be achieved. Varying the at least one parameter, may also be used for locally modifying the hydraulic resistance when filling a non-radially symmetric structure, e.g. a structure with a buffer area adjacent to a sensor area. Similarly, a plurality of separate deposition areas, e.g. a plurality of sensors on respective sensor areas, may be provided, in particular the plurality of sensors may include at least two sensors having different thickness of the respective layer of sensor material. Hence, sensors of different properties, e.g. sensitivity, may be provided. Again, the different material thickness and/or distribution may be obtained by providing variations in profile height/spacing of the microstructure.

Embodiments of the method described herein are particularly suitable for providing sensor spots on an inside surface of a container, e.g. a container for accommodating a fluid, e.g. a bottle, a tube, a flask, a bag, a microtitre plate, and/or the like. The surface may be planar or have a curvature in one or more directions.

The deposited sensor material may thus be used to sense e.g. analytes or other properties of a medium (e.g. a fluid) in contact with the surface, e.g. a medium inside a container. In particular, the sensor may be read by detecting light emitted from the sensor responsive to the detected property. The light emission may be detected through the wall of a container by a detector placed outside the container.

In some embodiments, the method comprises providing one or more optical elements e.g. as a separate layer of the layered sensor structure, e.g. sandwiched between the substrate and the sensor material and/or formed on a surface of the substrate opposite the surface on which the microstructured deposition area is provided. Alternatively or additionally and optical element may be integrated into the substrate, e.g. by providing a structure, e.g. a micro- and/or nanostructure on the surface of the substrate opposite the surface on which the microstructured deposition area is provided, or at the interface between the sensor material and the substrate.

In some embodiments, the microstructure deposited in the deposition area may comprise micro-features at different length scales superimposed each other, e.g. by simultaneous structuring on two different length scales. Microstructures on one length scale may e.g. function to spread the liquid, while micro- or even nanostructures on the other length scale may be operable to improve some optical properties, such as, control of light directionality, smoothing refractive index contrast at an interface etc.

For the purpose of the present description, the term nanostructure refers to a surface structure in which nanometer-scale features are arranged in a pattern, e.g. a regular or irregular pattern. The nanometer-scale features may be depressions and/or protrusions of a predetermined cross-sectional geometry, e.g. cylindrical or conical pillars. The nanometer-scale features may have a shape having an extent in at least one dimension, e.g. in two or even all three dimensions, between 1 nm and 1 μιη. Nanostructures can be applied in the same process as the microstructures, e.g., hot-embossing stamps with nanostructures on top of microstructures can be produced.

The present invention relates to different aspects including the method described above and in the following, corresponding apparatus and products, each yielding one or more of the benefits and advantages described in connection with the above-mentioned method, and each having one or more embodiments corresponding to the embodiments described in connection with the above-mentioned method, and/or disclosed in the dependent claims.

In particular, disclosed herein are embodiments of a layered product comprising:

- a substrate layer having a surface, wherein at least a deposition area of the surface is provided with a microstructure;

- a layer of immobilised deposited material covering at least a portion of the deposition area.

Further disclosed herein are embodiments of an optical element, e.g. an optically controllable optica! element such as an optothermally actuated, reconfigurable optical element, an optically pumped photonic crystal dye laser, or the like. Embodiments of the optical element may comprise a layered product as described herein, wherein the microstructure comprises micro-features, e.g. in the form of protrusions, such as pillars, and/or depressions, forming a photonic crystal. The micro-features may be arranged in a two-dimensional pattern (e.g. a periodic pattern periodic in one or two dimensions) across the deposition area where the spacing (e.g. the pitch distance) between neighbouring features in at least one dimension, e.g. in two or even all three dimensions, is between 0.1 and 2 μιΐη, e.g. between 0.1 pm and 1.5 pm such as between 0.1 pm and 1 pm e.g. between 0.4 pm and 0.9 pm. The substrate layer and the immobilised deposited layer differ in at least one optical parameter. BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects will be apparent and elucidated from the embodiments described with reference to the drawing in which:

Fig. 1 illustrates an embodiment of a process of depositing a sensor material on a substrate.

Fig. 2 illustrates an embodiment of a sensor where the microstructured sensor area has a superimposed structure of a length scale smaller than the microstrucure, e.g. another microstructure or a nanostructure.

Fig. 3 illustrates an embodiment of a sensor where the sensor area is surrounded by a microstructured buffer area.

Fig. 4 illustrates an embodiment of a sensor where the sensor area is provided on a curved surface.

Fig. 5 shows an enlarged cross sectional view of a portion of a sensor area. Fig. 6 illustrates the conformal material deposition on length scales of the order of the microstructure period. Fig. 6a) shows an example of a sensor material in liquid form after partial evaporation of the solvent, while Fig. 6b) shows the sensor material after complete evaporation of the solvents.

Fig. 7 shows a SE micrograph of microstructures imprinted in polycarbonate foil with sol-gel sensor material deposited between the pillars. The table in b shows the positions on the test imprints of the different geometries. SQ refers to square lattice, TRI refers to hexagonal lattice, first number is the pillar radius, and second number is the center-to-center distance of the pillars. The test structures were made with structure heights ranging between 10 μιη and 50 pm.

Fig. 8 schematically illustrates operation of an optothermal!y actuated, reconfigurable optical element (polymer photonic crystals).

Fig. 9 illustrates the change in the PhC device's dispersion relation.

DETAILED DESCRIPTION

Fig. 1 schematically shows an embodiment of the process for printing a sol- gel on a substrate, e.g. on the inside surface of a container.

Fig. 1a illustrates the initial step of the process where a substrate 101 is positioned sandwiched between a stamp tool 102 and a counter piate 106. Generally, the substrate may have any suitable material such as a polymer, a plastic, glass, in the context of sensors to be read out through the substrate layer, the material should transmit electromagnetic radiation in the wavelength range used for activating and/or reading the sensor. In some embodiments, the microstructure may comprise nanoporous pillars or other nanoporous protrusions. The substrate 101 may be the material of the wall of a container such as a bottle, or the substrate may be a material that has been deposited on the inner surface of a bottle. When the sensor Is an optical sensor for optical read-out by visible or invisible electromagnetic radiation of a predetermined wavelength or range of wavelength, and when the substrate is transparent for radiation of said wavelength or range of wavelengths, the sensor may be read out from the side of the substrate that is not in contact with the sample to be analysed.

The stamp tool 102 has a microstructured stamp surface 103 for imprinting a corresponding microstructure onto the surface 104 of the substrate facing the stamp tool 102. The counter plate 106 also has a structured stamp surface 107 for imprinting a corresponding structure on the surface 105 of the substrate that faces the counter plate. The structure of the counter plate may also be a microstructure or have any other suitable dimension. For example, the structure 107 may be a micro- and/or nanostructure configured to function as a lens and/or filtering for the radiation used for excitation of the sensor and/or for the radiation emitted by the sensor. For example the structure may provide a focussing and/or coilimating lens, a d iff user, an aperture, and/or the like. For example, an aperture may be used to obscure those parts of the sensor area, or of a buffer area, that are not used for optical read-out.

The stamp tool 102 may be arranged on an elongated support (not shown in fig. 1 ) allowing the stamp tool to be inserted through an opening of a container such as a bottle, and allowing stamping on the inside surface of such container.

Fig. 1b) illustrates the printing step in which the stamp tool 102 and/or the counter plate 106 are moved towards and pressed against the substrate 101 , so as to cause the microstructure 103 and the structure 107 to be imprinted into the respective opposing surfaces 104 and 105 of the substrate 101. This imprinting may be performed by any suitable process for imprinting micro- structures into a substrate, e.g. by hot embossing. Alternatively the microstructure 104 and/or the structure 107 may be created by an alternative method, e.g. injection moulding, machining (e.g. by laser, micromachining and/or the like), etching such as chemical etching, structured layer (photoresist SU-8), etc., or combinations thereof.

Fig. 1c) schematically shows a cross sectional view of the substrate with the imprinted microstructure 103 and a structure 109 imprinted on the surface opposite the microstructure 103. Fig. 1d) shows a top view of the substrate illustrating a pattern of pillars arranged in a regular grid. In the example of fig. 1d), the pillars have a square cross section and are arranged in a quadratic grid. It will be appreciated, however, that the pillars may have a different cross sectional geometry, e.g. round, circular, elliptic, polygonal, etc. and/or may be arranged in a different type of grid, e.g. a rectangular grid, a hexagonal grid, a polygonal grid, etc. It will be appreciated that the micro-structure may be uniform across the sensor area. Alternatively the microstructure may vary across the sensor area.

Fig. 1e) illustrates the subsequent step of depositing a functional material, e.g. a sol gel 10 on the microstructured portion 08 of the surface 104. Even though the present embodiment of a deposition process will be described with reference to a sol-gel, it will be appreciated that the process may also be applied to other functional materials as described herein. For example, a predetermined volume of sol gel, e.g. one or more drops of a predetermined droplet size, may be deposited on the microstructured surface area 108. The sol-gel, will spread across the microstructured surface area by hemiwicking. The resulting sol-gel patch covers an area of a defined size, and has a defined thickness. The thickness is controlled by the microstructure 108 which is adapted to create conditions for hemiwicking of the deposited functional material onto the structured surface. Hemiwicking is the process by which the liquid material fills the microstructure defined on the surface up to the upper edge of the structure. The conditions for hemiwicking are met when the geometry of the structure matches the contact angle of the liquid on the substrate material. The process of and conditions for hemiwicking are e.g. described in the article "Wetting and Roughness" by David Quere, Annu. Rev. Mater. Res. 2008.38:71-99. The deposition process may further include a drying and/or other additional steps. For example, the deposition of the materials can be done by various methods like needle deposition, jet printing, micropipettes etc. An example of a thermal treatment of the material is described in: Higgins et al, Analyst 2008,vol 133,p241

Fig. 1f) shows the substrate with the resulting sol gel patch 08. As described above, the surface 105 of the substrate 101 opposite the printed patch of so! gel can be microstructured too by using a microstructured counter plate while embossing. The counter plate then works as a stamp for imprinting/embossing too. The microstructured surface can be used for controlling the optical properties of the substrate/air interface. For example, a Fresnel lens type of structure can be embossed in order to focus the excitation light (alternatively collimate the emission light) from/to the instrument for measuring optical properties of the sol gel material (e.g. fluorescence, anti-reflection, etc.). it will be appreciated, however, that in alternative embodiments, the surface opposite the sensor may be provided without an imprinted structure.

Fig. 1g) illustrates the use of the resulting sensor patch. In use, a substance 113, e.g. a liquid or gas, to be analysed is brought into contact with the sensor patch 108. For example, when the sensor patch is provided on the inside surface of a container, and when the container is filled with a substance, the substance may be analysed by the sensor patch. To this end, excitation light 112 may be radiated onto the sensor patch from the opposite side of the substrate, e.g. from the outside of the container. The excitation light may be generated by any suitable light source, e.g. light emitting diodes ( LED's.) For example, the excitation light may be directed onto the structure 109 on the outside surface of the substrate as a co!limated excitation light beam. The structure 109 may then focus the collimated light beam onto the sensor patch 108, i.e. the excitation light beam penetrates the substrates and impinges on the sensor patch 108. Responsive to the interaction of the sensor material deposited on the sensor patch with the substance 113, the sensor material emits light, e.g. by way of fluorescence or by another mechanism resulting in the emission of light from the sensor material responsive to a property of the substance 113, e.g. as disclosed in Lackowics, J.R.: Principles of Fluoresence Spectroscopy, 1999, Sec. 19.4 , Sensing by Collisional Quenching,

At least a part of the emitted light penetrates the substrate 101 and the structure 107 on the opposite surface of the substrate. The structure 107 may then collimate the emitted light resulting in a collimated light beam 111 which may then be detected by a suitable detector, e.g. a one or more photodiodes such as a Hamamatsu Silicon Photodiode type S1336, and analysed so as to determine a property of the substance, e.g. so as to determine dissolved oxygen, pH, and/or the like. It will be appreciated, that alternative embodiments of sensor patches may be excited and/or read out from other directions, e.g. from the same side of the substrate on which the sensor spot is deposited. Yet alternatively, in some embodiments, the sensor may be excited and/or read-out by other means than light or other radiation, e.g. complex impedance, capacitance, resistance, magnetic properties, and/or the like.

The microstructured surface 108 may further be provided with a superimposed structure of a smaller length scale, e.g. another microstructure or even a nanostructure, e.g. as illustrated in fig. 2. Fig. 2a shows a substrate 101 having a microstructured sensor area 108 on which a sensor material is deposited by a sol gel process, e.g. as described in connection with fig. 1. Fig. 2b shows an enlarged view of a part of the surface, in particular the surface 8 between two protrusions 138 forming the microstructure. Hence, the superimposed structure is provided at the interface between the sol gel 148 and the substrate 101. By adding a superimposed structure of the surface 118 where the sol gel is deposited, the light transmission from the sol gel to the substrate can be optimized. The superimposed structure may be a photonic crystal structure that improves or even optimizes the refractive index at the sol-gel/substrate interface so as to avoid reflections of the light to be extracted from the so! gel. The selectivity of the optical properties of the sol- gel/substrate interface can be tuned by modifying the geometrical parameters of the superimposed structure, e.g. the pitch of the periodic structure forming the photonic crystal.

Fig. 3 shows an embodiment of a sensor where a microstructured sensor area 108 covered by a sol gel patch is surrounded by a buffer area 128. In the example of fig. 3, the buffer area is provided with a microstructure different from the microstructure of the sensor area 108, e.g. a structure where the pillars have a height and/or are arranged in a pattern (e.g. having a different pitch distance) different from the pillars of the sensor area. The different micostrucres 108 and 128 may thus be adapted such that the buffer area functions as a sink for excess sensor material, e.g. when the deposited volume of soi gel is larger than required to cover the sensor area with the 108 with a uniform thickness. Hence, the formation of a central part of the sensor area having a larger thickness than the peripheral portions of the sensor area 108 may be avoided.

Alternatively or additionally, the microstructure of the buffer area 128 may be adapted so as to function as a feeder area. During the deposition process, the sensor material is deposited on the feeder area from which it spreads across the sensor area 108 facilitated by the hemiwicking. However, any excess fluid may remain on the feeder area, thus resulting in a sensor area covered by a layer of sensor material of uniform and well-controllable thickness, while the feeder area may be covered by a thicker layer. It will be appreciated that the buffer area 128 may be provided adjacent to the sensor area 108 in different ways, e.g. directly abutting the sensor area as shown in fig. 3c or distant from but connected to the sensor area by a microstructured channel 150 as shown in fig. 3d. Hence, a central sensor area 108 with uniform thickness may be achieved, even when the volume of deposited sol gel cannot be controlled with great accuracy.

It will be appreciated that the sensor area may comprise at least two domains of microstructured surface facilitating hemiwicking, such that the different domains have different depths and/or different geometries in order to create, from one single fluid deposition event/placement, several patches (domains) of the sensor material of different thicknesses. This can be used for example for creating measurements area of various characteristic response time. Similarly, a single feeder area may be connected to more than one sensor areas, e.g. having different microstructures. When printing a patch of sol gel inside a container, such as a bottle, sample holder, test tube, etc. so as to form a sensor layer inside the container, difficulties may arise when the surface on which the sensor material is to be deposited is not planar.

Fig, 4 illustrates an embodiment of a sensor patch 108 deposited on a curved surface, in this example the inside surface of a bottle 400. Fig. 1 a shows a cross sectional view of the bottle having a sensor patch 108 on its inside surface at the bottom of the bottle. Fig. 4b shows an enlarged view of the sensor patch provided by imprinting a microstructure onto the -substrate 101 (e.g. the material of the wall of the bottle or a material deposited on the wall), and depositing a sensor material on the microstructured surface by a sol gel process as described in connection with fig. 1. In this embodiment, the pillars 108a forming the microstructure have a conical shape, i.e. a lateral dimension that decreases with increasing distance from the base surface. Such a conical shape facilitates imprinting the structure onto the curved surface of the substrate 101. Furthermore, pillars that have a truncated-conical shape cause the light emitted from the sensor material to be directed to the optical sensing element through reflections on the inner surfaces of the pillar.

Fig. 5 shows an enlarged cross sectional view of a portion of a sensor area. In particular, fig. 5 shows two pillars 108a and the deposited sensor material 148 filling out the space between the pillars 108a. Due to the removal of the liquid, e.g. by solvent evaporation, during the deposition process, the sensor material shrinks resulting in a convex upper surface. In that case the optical path through the film on vertical side walls is much larger than the thickness of the film that an anaiyte has to diffuse through, and a larger surface is achieved, thus reducing the response time of the sensor. In some embodiments a plurality of successive layers may be deposited, thus filling the depressions resulting from the evaporation process. Such a successive deposition of multiple layers may be controlled to result in a step-like surface structure.

Hence, as described herein, on a microstructured surface, hemiwicking can be used to evenly distribute, on a length scale larger than the period of the surface microstructures, a material, which is to be immobilized on the surface. Material redistribution caused by solvent evaporation, i.e. the so- called "coffee ring effect" (see e.g. Robert D. Deegan, Oigica Bakajin, Todd F. Dupont, Greb Huber, Sidney R. Nagel and Thomas A. Witten, Capillary flow as the cause of ring stains from dried liquid drops, Nature 389, 827-829 (1997), doi: 0.1038/39827), can be avoided because differential evaporation rates, on the before mentioned length scale, are avoided.

This is due to the surface to volume ratio being constant all over the surface of the liquid spread by hemiwicking, when considering length scales larger than the microstructure period.

On length scales of the order of the microstructure period, surface tension will govern the shape of the liquid-air interface, and the liquid will climb up the pillars to keep a fixed contact angle with the sidewalls, as illustrated in fig. 6. This may cause uneven evaporation and hence material redistribution on length scales of the order of the microstructure period. Fig. 6a shows a cross- section of micropillar structures filled with liquid 610 after partial evaporation of the solvent. Initially, i.e. during deposition prior to evaporation, the iiquid-air interface may be fiat (i.e. defining an angle of about 90° relative to the vertical side walls of the pillars), in particular in embodiments where the spacing between pillars is small. During evaporation, the liquid crawls up the sidewalls to keep the contact angle fixed. Fig. 6b shows the same pillars after complete solvent evaporation, the solid content of the liquid is deposited on the surface as a thin film of immobilised materials 620 which conforms to the surface structure, i.e. extends at least partially along the vertical side surfaces of the pillars. Example: deposition of sensor material

Initially, the contact angle of a drop of sensor material deposited on the PC foil was measured using a Kruss DSA 100 drop-shape analysis system. The contact angle was measured to between 10° - 15°. The fast solvent evaporation made it difficult to estimate the angle more accurately than being in the above interval.The sensor material was an oxygen sensor material as described in Higgins et al, Analyst 2008, vol. 133, p. 241. Silicon stamps for imprinting a plurality of different deposition areas were prepared using standard silicon microfabrication techniques: UV-lithography and reactive-ion etching (RIE). Each area comprised a plurality of cylindrical pillars arranged in regular grids, as illustrated in fig. 7. In particular, fig. 7a shows a perspective view of a plurality of resulting pillars on a substrate covered by a thin layer of deposited material, while fig. 7b illustrates a plurality of areas with different grids. Each grid being identified by a letter code identifying the lattice structure (SQ for square lattice and TRI for triangular lattice), followed by two numbers identifying the pillar radius and the lattice period, respectively, in micrometers.

Grids of different pillar heights h (i.e. structure depths) were created. In particular structures having structure depths of 10 pm, 15 pm, 20 pm, 30 pm, and 50 pm were prepared. The pillar radius R ranged from 2.5 pm to 50 pm, The pillar I period (i.e. the pitch distance between neighbouring pillars) ranged from 5 pm to 200 pm. Square and triangular lattices of 7 mm diameter were prepared. Mesas ranged from 10 pm to 30 pm.

The stamps were used to imprint deposition areas on PC foil. The imprinting was performed using an EVG 520 hot embosser at 15 bar pressure, a temperature of 170°C. The imprint time was 10 min. The T_g of the PC was 150°C. Demolding occurred at 120°C. Droplets of the sol-gel senor material were deposited on the resulting respective imprinted deposition areas with a needle tip. Depending on the pillar geometry the droplets spread fast {i.e. hemiwiching occurred), spread slowly, or stayed where deposited.

The Ethanol used as solvent in the sensor material evaporated within 10s.

For some structures, solvent evaporation can drive material towards the edge of the droplet and cause a ring-shaped deposit. Generally hemiwicking was observed for pillar height to pillar period ratios (h/l) of above 0.2. For these ratios a homogenous film was produced. Thin films of material were left after evaporation resulting in a thin conformal layer. In a fast spreading regime (h/l > 2) very homogeneous films of desirable thickness were achieved.

Example: selection of microstructurs

In the above example, in order to find preferred microstructures for fabricating sensor spots by uniform spreading of an example of sol-gel sensor material, the ETEOS-based sol-gel oxygen sensor material, which is described in Clare Higgins, Dorota Wencel, Conor S. Burke, Brian D. MacCraith, and Colette McDonagh, Novel hybrid optical sensor materials for in-breath 02 analysis, Analyst 133, 241-247 (2008), DOI: 10.1039/b716197b, the material was deposited on a series of 7mm diameter arrays of pillars of different patterns, dimensions, heights, and periods (as described in connection with Fig. 7b), which were fabricated by hot embossing in polycarbonate foil. It was found that homogeneous films were produced for microstructures with a ratio between pillar height h and inter-pillar distance l larger than 2 (h/l>2).

The evaporation time depends on the volatility of the solvents and the thickness of the liquid film (which again depends on the height of the microstructures), and the spreading time depends on the advancing contact angle on the substrate material and the viscosity of the deposited liquid material. This result is therefore valid for this specific combination of materials and conditions. For volatile solvents, fast spreading, and hence high aspect ratio structures, are preferred. The preferred structure also depends on the desired spreading distance.

On a hexagonal lattice with h=23pm, Γ=9.5μηι, d=30pm, 1=11μιη, and h/l=2.1 , a 5pm final layer thickness of the deposited sensor material was measured. This structure was chosen as a preferred one, and the performance of 38 oxygen sensors, which were fabricated by depositing oxygen sensor material on this structure, was found to be very close to the results published by Higgins et al. (ibid.)

Fig. 8 schematically illustrates operation of an optothermally actuated, reconfigurable optical element (polymer photonic crystals). Photonic crystals (PhCs) are strong candidates for compact optical devices for manipulation of light, micro-lasers, sensors, and for optical switches. Embodiments of layered structures as described herein may be used to produce opto-thermally actuated, adaptive polymer photonic crystal devices.

Fig. 8a schematically illustrates a two-layer PhC device. The PhC device comprise a substrate layer 821 and a layer of immobilised deposited material 822.

The substrate layer 821 may be a polymer, such as SU-8, polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS), a cyclic olefin copolymer (e.g. TOPAS®), or another suitable organic or inorganic material. The substrate material may be optically transparent or reflective at the used wavelengths of light. The substrate material can be doped or undoped in order to tune optical properties, such as bandgap, absorption, transmition and reflection spectra. The substrate layer 821 comprises a microstructured deposition area 823. The deposition area may comprise periodically arranged pillars or other micrometer scale features defining a photonic crystal. The microstruture may be formed by nanoimprinting into the surface of a polymer planar/slab waveguide or on a polymer fiber, or on another suitable substrate layer 821. The micro structured surface 823 has two functions, namely to facilitate deposition of the second material 822, and to define a periodic modulation of the refractive index to form a Bragg grating or photonic crystal (PhC). The periodic pillars of the deposition area 823 may have dimensions (period and/or height and/or structure width) in the range 100 nm to 1 pm. In particular the dimension may be selected so as to correspond to the wavelength λ₂ of the light to be manipulated by the optical element.

The deposited material 822 may be an optically functionalised polymer or other suitable optically functionalised material, e.g. a material having a refractive index that may be altered by irradiation of light or other electromagnetic radiation of a predetermined wavelength λ-ι. To this end the polymer may be doped by nanocrystals, an infrared absorber dye, or another suitable dopant causing a change in the PhC device's dispersion relation and thereby changing the throughput emission angle. The functionalized polymer material 822 may be deposited on the deposition area 823 by droplet dispensing/ink-jet and hemiwicking as described herein, and immobilised e.g., by evaporation of a solvent, by curing (e.g. condensation or cross- linking by heating or UV-exposure).

As illustrated in fig. 8a, when incident light 820 of suitable wavelength λι impinges on the grating formed by deposition area 823, the light may be redirected under a given angle dependent on the difference in refractive index ni and n₂ of the deposited layer 822 and the substrate layer 821 , respectively, in the example of fig. 8a, the light is emitted orthogonally compared to the incident light 820, as illustrated by arrow 824. When a gate signal 825, e.g. in the form of light at suitable wavelength λι, is coupled to the system it locally changes the temperature and thereby the refractive index of the deposited layer containing nanocrystals or an infrared absorber dye, causing a change in the PhC device's dispersion relation and thereby changing the throughput emission angle, as illustrated by arrow 826.

The change in dispersion relation and the resulting change in throughput angle is further illustrated in Figs 9a and b illustrating the dispersion relation without and the altered dispersion relation with presence of the gate signal 825, respectively. It will be appreciated that alternatively or additionally to the deposited layer being optically functionalised, the substrate layer may be optically functionalised.

The device layout described with reference to fig. 8 may also be used to fabricate other optical elements such as an optically pumped photonic crystal dye lasers. Such a laser may be manufactured by functionalizing the substrate 821 and/or the deposited layer 822 with a laser dye. In this embodiment, the photonic crystal 823 may be configured to have a photonic band-edge in the gain window of the laser dye, whereby the photonic crystal forms the laser resonator, with laser emission in-plane or normal to the substrate plane (vertically emitting lasers). The lasers can be realized with laser emission covering the vacuum wavelength range from e.g. 400 nm to 900 nm or even 1500 nm, defined by the availability of laser dyes. The structure dimensions, i.e., pitch and/or height and/or width of the periodic (1 D or 2D) structures of the deposition area 823 for such a laser device correspondingly are in the range from 100 nm to 2 μιτι. Although some embodiments have been described and shown in detail, the invention is not restricted to them, but may also be embodied in other ways within the scope of the subject matter defined in the following claims.

Embodiments of the method and the sensor described herein may be used in a variety of fields, e.g. for various applications within analytics, e.g. the detection or quantification of analytes in fluids. Embodiments of the method and sensor described herein may also be used in biocultures, biofermentors, microtitre plates, and/or the like. The mere fact that certain measures are recited in mutually different dependent claims or described in different embodiments does not indicate that a combination of these measures cannot be used to advantage.

Even though embodiments of the invention have mainly been described in the context of optical sensors, it will be appreciated that the deposition an immobilising of a materia! on a surface as described herein may also be applied to other depositable materials. Embodiments of the method described herein provide an efficient way of providing composite layered structures where very thin layers of a depositable material is deposited and immobilised on a predetermined area of a surface. Embodiments of the method described herein may advantageously be used when only a small part of the surface is to be coated with a material. Furthermore, embodiments of the method described herein may advantageously be used for depositing materials of low viscosity where screen- or stamp-printing may not work.

Furthermore, even though embodiments of the invention have mainly been described in the context of imprinting microstructures, it will be appreciated that other techniques for providing a microstructure on a surface may equally be used, e.g. injection moulding, machining (e.g. by laser, micromachining and/or the like), etching such as chemical etching, structured layer (photoresist SU-8), etc., or combinations thereof.

It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claims

CLAIMS:

1. A method for manufacturing a sensor, the method comprising:

- providing at least a deposition area of a surface of a substrate with a predetermined microstructure;

- depositing a layer of sensor material on the microstructured deposition area so as to provide a sensor area;

2. A method according to claim 1 , wherein the sensor material is a liquid sensor material, and the method further comprises immobilising at least a part of the deposited liquid material resulting in an immobilised layer of sensor material bonded to the surface of the substrate.

3. A method according to claim 2, wherein immobilising comprises reducing the volume of the deposited sensor material.

4. A method according to claim 2 or 3, wherein the immobilised layer of sensor material has a thickness smaller than a height of the microstructure. 5. A method according to any one of claims 2 through 4, wherein the immobilised layer of sensor material has a convex shape between protrusions of the microstructure.

6. A method according to any one of claims 1 through 5, comprising providing a plurality of sensors on respective sensor areas of a surface.

7. A method according to claim 6, wherein the plurality of sensors includes at least two sensors having different thickness of the respective layer of sensor material.

8. A method for depositing a material on a surface, the method comprising: - providing at least a deposition area on the surface of a substrate with a predetermined microstructure;

- depositing a liquid material on the microstructured deposition area;

- immobilising at least a part of the deposited liquid material,

9. A method according to claim 8, wherein the predetermined microstructure comprises micro-features arranged in a two-dimensional pattern across the deposition area, having a spacing between neighbouring micro-features between 0.1 and 2 μητι.

10. A method according to any one of the preceding claims, wherein the surface is an inner surface of a container or conduit for transporting a fluid.

11. A method according to claim 10, wherein the surface is an inner surface of a disposable container for transporting a fluid.

12. A method according to any one of the preceding claims, wherein the microstructure comprises a plurality of protrusions arranged in a pattern across the deposition area; wherein the method comprises determining at least one parameter to control a thickness of the layer of deposited material; wherein the at least one parameter is chosen from a height of the protrusions, a pitch distance between neighbouring protrusions, and a cross- sectional size of the protrusions. 13. A method according to claim 12, wherein the at least one parameter varies across at least a part of the depostion area so as to cause the thickness of the layer of deposited material to vary across at least the part of the deposition area. 14. A method according to any one of the preceding claims, wherein the microstructure comprises a plurality of conical or truncated-conical pillars.

15. A method according to any one of the preceding claims comprising providing the microstructure by a process chosen from injection molding, hot embossing, and laser microstructuring, micromachining, chemical etching, photoresist layer structuring.

16. A method according to any one of the preceding claims, further comprising providing an additional layer operating as an optical element. 7. A method according to claim 16, wherein the optical element is chosen from a lens, a diffuser, and an optica! filter.

18. A method according to any one of the preceding claims,, comprising providing a structure on a surface of the substrate opposite from the surface including the deposition area.

19. A method according to any one of the preceding claims, further comprising providing a buffer area adjacent to the deposition area and adapted to receive access deposited material from the deposition area during deposition of the material and/or to feed deposited material towards the deposition area during deposition of the material.

20. A method according to any one of the preceding claims, wherein the microstructure comprises micro-features having a size, in at least one dimension, of between 0.1 μιτι and 500μιη₍

21. A sensor comprising:

- a substrate having a surface including a microstructured sensor area; and

- a layer of sensor material deposited on the microstructured sensor area.

22. A sensor according to claim 21 , wherein the layer of sensor material is an immobilised layer of sensor material bonded to the surface of the substrate.

23. Use of a sensor as defined in claim 21 or 22 for monitoring of a bioculture.

24. A layered product comprising:

25. An optical element comprising a layered product according to claim 24, wherein the microstructure comprises a photonic crystal.

26. An optical element according to claim 25, wherein the substrate layer and the immobilised deposited layer differ in at least one optical parameter.

27. An optical element according to claim 25 or 26, wherein the immobilised deposited material comprises a controllable optical component.

28. An optical element according to claim 27, wherein the controllable optical component comprises a laser dye. 29. An optical element according to claim 27, wherein the controllable optical component comprises an optothermally actuatable component having a temperature-dependent refractive index.