WO2009069009A1

WO2009069009A1 - Optical detection of particles in a magnetic biosensor using a waveguide

Info

Publication number: WO2009069009A1
Application number: PCT/IB2008/050412
Authority: WO
Inventors: Mark T. Johnson; Albert H. J. Immink; Dirk K. G. De Boer; Menno W. J. Prins; Jeroen H. Nieuwenhuis; Coen A. Verschuren
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-11-26
Filing date: 2008-02-05
Publication date: 2009-06-04

Abstract

The present invention provides a biosensor device comprising a sensor surface and an optical wave guide having an input, an output and first and second surfaces, said optical wave guide (5) being adapted to direct light entering the optical wave guide (5) through the input (20) to the output (21) via multiple reflections on said first and second surfaces (22, 23) including at least one reflection onsaid first surface (22) under an angle fulfilling the condition of total internal reflection, wherein the sensor surface is adjacent to the first surface of total internal reflection.

Description

OPTICAL DETECTION OF PARTICLES IN A MAGNETIC BIOSENSOR USING A WAVEGUIDE

FIELD OF THE INVENTION

The invention relates to the optical detection of particles in a biosensor based on magnetic particles.

BACKGROUND OF THE INVENTION

The use of magnetic beads as a component of a biosensor is a well established principle. Such a magnetic biosensor is, e.g., described in WO 2006/079998. A typical magnetic biosensor configuration is shown in Fig. 1. It comprises a silicon chip with electronics 201, a current wire 202 to provide a magnetic field 207 and a giant magneto resistance (GMR) strip 203 to detect magnetic fields. The biosensor further comprises a sensor surface 204 with a bio-active layer 205, to which super-paramagnetic particles 206, which are appropriately coated, may bind. The magnetic field 207 induces a dipole in the super-paramagnetic particle, whose magnetic field 208 may be detected by the GMR sensor 203.

Alternatively to this magnetic detection method an optical approach has recently been proposed. Instead of a silicon substrate containing sensitive magnetic sensors a simple injection moulded substrate is used. The required surface sensitivity is achieved via the principle of frustrated total internal reflection (FTIR). Figs. 2a and 2b schematically show the functional principle of FTIR with a parallel and a focused light beam, respectively: A cuvette or cartridge 100 with diameter D and a hemispherical bottom with radius of curvature R has a sample volume or well 101 with a sensor surface 102. A light source 103 illuminates the sensor surface 102 along light path 105. The light 106, which is reflected at the sensor surface 102, is detected at a sensor 104. The incoming light beam 105 fulfils the condition of total internal reflection, i.e., the angle between light path 105 and the perpendicular to the sensor surface 102 is larger than the critical angle. If particles are close to the sensor surface 102, the scatter a portion of the evanescent field, thus leading to an attenuation of the reflected light intensity measured at the sensor 104. Nevertheless, it is still advantageous to provide a means for generating a magnetic field in order to actuate the magnetic particles towards the sensor surface for accelerated binding and to further remove particles, which have bound to the bio-active layer, by 'magnetic washing'.

A combination of an optical read-out with magnetic labels for actuation provides several advantages: The cartridge is cheap, since it does not contain a GMR chip and can consist of a relatively simple, injection-moulded piece of polymer material that also contains the fluidic channels for filling the cartridge.

The combination further allows for large multiplexing possibilities for multi-analyte testing: The binding or sensor surface in a disposable cartridge can be optically scanned over a large area. Alternatively, large-area imaging is possible allowing a large detection array. Such an array (located on an optical transparent surface) can be made by e.g. ink-jet printing of different binding molecules on the optical surface.

The method also enables high-throughput testing by using multiple beams and multiple detectors and multiple actuation magnets (either mechanically moved or electro -magnetically actuated).

Actuation and sensing are orthogonal: Magnetic actuation of the magnetic particles (by large magnetic fields and magnetic field gradients) does not influence the optical sensing part. This is in contrast to the GMR based read-out method where the large actuation fields require a subsequent 'resetting' of the sensor before an accurate read- signal can be obtained. The optical method allows a continuous monitoring of the signal during actuation. This provides a lot of insight into the assay process and it allows easy kinetic detection methods based on signal slopes.

The system is very surface-sensitive due to the exponential decreasing evanescent field in the FTIR approach and allows for low-noise read-out (compare the 1/f-noise problems in GMR type of sensors that requires complicated signal processing for modulation and demodulation). Finally, no electrical connection between the cartridge and the reader and/or a controller is needed. An optical window is the only requirement to probe the cartridge. Thus, a contact-less read-out can be performed. In addition, it has been proposed to use active matrix large area electronics (LAE) as a platform for future generation products requiring lab-on-a-chip functionalities. At present the various modalities of a lab-on-a-chip are assembled from loose components. In the case of a typical platform, these modalities include sample preparation, sample amplification, sample concentration and sample sensing. It is envisaged that rather than constructing the platform from individual passive modules that it would be preferable to integrate the modalities onto a substrate using active components (for instance using an active matrix approach). This would allow lower volumes of sample to be used for analysis whilst many parallel assays could be run. In addition, as the substrate is transparent this approach is compatible with the optical detection approach described above.

In the LAE approach, it is particularly attractive to incorporate magnetic manipulation devices onto the glass substrate in order to move the magnetic particles towards and away from the array of capture sites (in vertical and/or lateral direction) without requiring bulky external magnetic actuators. These devices will normally take the form of a current carrying wire, optionally in association with a soft magnetic layer (such as NiFe alloys - to act as a magnetic flux conductor). A major advantage of such an approach is that many different localized magnetic fields can be realized by sending defined currents through different wires on the substrate.

One issue of such devices is that the current carrying wires and the associated switching devices (such as diodes, thin film transistors, MIM diodes etc.), magnetic flux conductors etc. are not transparent. If the magnetic beads become focused above the devices (as will in general be the function of the devices), it will no longer be possible to detect them using the optical approach defined above. This is schematically indicated in Figs. 3a and 3b showing a setup similar to the one depicted in Fig. 2a. However, here an additional coil 110 with a ferrite core 109 is provided for generating a magnetic field. As indicated by dashed lines in Fig. 3b, the area accessible by illumination is restricted due to the assembly of the magnet.

Generally, an optical structure as schematically shown in Fig. 3a or 3b should be designed such that a magnet having a core diameter of 3mm can be positioned at a distance of lmm from the sensor surface, while maintaining a sufficiently wide optical path having a width of around 0.8mm. In a typical design, the windings of the electromagnet have an outer diameter of 5mm. Such a configuration provides a sufficiently uniform magnetic field over the detection area on the sensor surface. A smaller core or winding diameter would lead to unacceptable non-uniformities. Furthermore, a larger distance of the magnet from the sensor surface would significantly reduce the actuation force on the magnetic beads, leading to longer measurement times or unacceptable large currents through the electromagnet.

In the above described configuration, the outside diameter of the windings of the electromagnet conflicts with the requirements for the optical cartridge in that the area accessible for illumination is restricted, as indicated above with reference to Fig. 3b. The problem may be reduced by decreasing the angle between the optical beam and the sensor surface to around 20°, which is significantly away from the critical angle for total internal reflection, namely by about 10° instead of 5° for a typical configuration.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to overcome the above- mentioned problem. It is, in particular, an object to provide a possibility of optically detecting magnetic particles behind non-transparent devices. This object is achieved with the features of the claims. The present invention is based on the idea to incorporate a wave guiding structure or other optical feature into the biosensor, whereby the illumination used for FTIR can reach the magnetic beads and the presence of the beads at the sensor surface can be detected by the optical detection system via an in-direct or multiply-scattered light path. Accordingly, the present invention provides a biosensor device comprising a sensor surface and an optical wave guide having an input, an output and first and second surfaces. The optical wave guide is adapted to direct light entering the optical wave guide through the input to the output via multiple reflections on said first and second surfaces including at least one reflection on said first surface under an angle fulfilling the condition of total internal reflection. Also, the first and second surfaces may both be surfaces of total internal reflection. The sensor surface is adjacent to the first surface. The device may further comprise a magnetic field element, which is preferably adjacent to the second surface of total internal reflection. Thus, the optical wave guide is adapted for guiding light between the magnetic field element and the sensor surface.

Accordingly, the sensor surface is not illuminated on a direct path, but rather via an optical wave guide or similar structure. Therefore, the illumination does not interfere with the magnetic field element or any further non-transparent structure situated below or adjacent the sensor surface.

It is preferred, that the optical wave guide comprises a dielectric layer.

The refractive index of said dielectric layer should be higher than that of the sample in contact with the sensor surface. For instance, if the sample liquid is optically similar to water with an index of refraction of about 1.3, a suitable material for the dielectric layer would be Siθ2 with an index of refraction of about 1.5.

In order to improve the optical properties of the optical wave guide, the magnetic field element may be coated with a reflectivity-enhancing layer. Said layer may comprise a first layer with low refractive index and a second layer with high refractive index. For example, the first layer could be made of AI2O3 or SiO₂ and the second layer could comprise TiO₂.

The skilled person will understand that it is preferred that the thickness of the first and/or second layer is about one quarter of the wavelength of the light within the layer. It is furthermore advantageous, if the thickness of the dielectric layer is at least one half of the wavelength of the light in order to provide effective coupling. Generally, the light propagation within the light guide will improve with increasing thickness of the dielectric layer up to roughly 10 times the wavelength.

According to an embodiment of the invention, the optical wave guide may be arranged in an optical substrate that is part of a biosensor cartridge. Reflective layers are provided on the second surface and on a portion of the first surface in order to provide for the multiple reflections in the wave guide. The area of the first surface where the total internal reflection should occur should not be coated with a reflective material. Preferably, the reflective surfaces comprise reflective metallic layers such as silver or aluminium which preferably are non-magnetic in order not to influence the externally applied magnetic field.

Instead of providing reflective layers on the first and second surfaces, the reflective index of material which forms the optical substrate may be chosen such that total internal reflections occur on the first and second surfaces of the optical wave guide. In this case, it has to be assured that the reflective index of medium on the outside of the optical cartridge is sufficiently low to cause total internal reflection. In a preferred embodiment, the optical substrate is surrounded by air except for the area adjacent to the first surface where the sample fluid is arranged.

Since multiple reflections of the light within the light guide causes increased attenuation of the light, the optical wave guide is preferably dimensioned such that the light is reflected less than 20 times.

It will be clear to the skilled person that all the components usually used within a (magnetic) biosensor may be provided as well. For example, the sensor surface may comprise a bio-active layer.

Furthermore, the magnetic field element may comprise an array of magnetic sub-elements, e.g., an active matrix device. Alternatively, an array or matrix of biosensors as described above may be provided. Thus, an array of sensor surfaces with a corresponding array of respective optical wave guides forms a biosensor matrix or array. Preferably the magnetic field element or focussing device for actuation of the magnetic particles is implemented in a large area electronics technology, i.e, active electronics on a transparent substrate.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the functional principle of a common magnetic biosensor. Fig. 2a schematically shows the functional principle of FTIR with a parallel light beam.

Fig. 2b schematically shows the functional principle of FTIR with a focused light beam. Figs. 3a and 3b schematically illustrate a combination of optical detection with magnetic actuation.

Fig. 4 schematically shows a first embodiment of a magnetic biosensor device according to the present invention.

Fig. 5 schematically illustrates problems of an ill-conceived design of a magnetic biosensor device.

Fig. 6 schematically illustrates an alternative embodiment of a magnetic biosensor device according to the present invention.

Fig. 7 schematically illustrates yet another embodiment of a magnetic biosensor device according to the present invention. Fig. 8 shows a schematic diagram of an active matrix magnetic field array.

Fig. 9 shows a schematic diagram of an active matrix magnetic field element system with single driver and de-multiplex circuit.

Fig. 10 shows a schematic diagram of a local driver for an active matrix magnetic field element system. Fig. 11 shows a schematic diagram of a local current driver for an active matrix magnetic field element system with a memory element.

DETAILED DESCRIPTION OF EMBODIMENTS A first embodiment of a magnetic biosensor device according to the present invention is shown in Fig. 4. The device comprises an optical input window 1 and an optical exit window 2 for coupling light into and out off the device. A sample volume (channel, well or the like) 10 may be filled with a sample liquid to be analyzed. Said sample volume 10 further comprises super-paramagnetic particles 9, which are optionally coated with capture molecules and/or a bio-active layer.

The magnetic biosensor device further comprises a magnetic field element 3. Said element may simply be a wire for conducting an electric current. But more sophisticated elements are conceivable as well, as will be discussed below. However, the majority of electrically conducting materials and magnetic flux conducting materials are metallic in character, and are thus highly reflective. During an assay, the magnetic field element 3 is used to attract the superparamagnetic particles 9 or target beads to a capture site situated on a sensor surface 4 directly above the magnetic element 3. After the target beads 9 have been captured, a further magnetic field (not shown) can be used to remove the beads, which are not bound to the sensor surface 4. In order to detect the presence of the beads 9, the magnetic element 3 or wire is coated by a dielectric layer 5 a which works as a wave guide 5.

The dielectric layer should have a refractive index which exceeds that of the sample fluid within the sample volume 10. E.g., if the fluid is similar to water with n=1.3, the dielectric layer could be SiC>2 with n=1.5. Light from a light source 7 can now reach the beads by channelling along the wave guide 5, wherein the light is reflected from the top of the (metallic) magnetic element 3 or wire and at the interface of the dielectric layer 5a and the sample fluid. The presence of the beads 9 at the sensor surface 4 is then detected by an attenuation of the reflected light by the beads 9, which scatter a portion of the evanescent light field. A further advantage of the dielectric layer 5 a is that the optical wave-guiding material can also serve as insulating material to avoid electrical shorting between the magnetic element 3 and the sample fluid.

One issue of such an approach is the low signal at the detector 8. This may result from either attenuation of light along the wave guide 5. After multiple reflections light losses will occur due to non-perfect reflection at the dielectric/metal interface. One possibility to reduce this effect is to choose a metal with the highest possible reflectivity, such as silver, which has a reflectivity of about 95%. However, the metal of choice in most large area electronics (LAE) devices is aluminum, which has a lower reflectivity of around 90%.

The optical properties of the device may be optimized, though, by providing a thin double layer coating 6 comprising a first layer 6a with a relatively low refractive index (such as AI2O3 or Siθ2 with n=1.5) and a second layer 6b with a relatively high refractive index (such as Tiθ2 with n=2.1). The thickness of the layers should be around one quarter of a wavelength of the light in the layer (accounting for the refractive index of the layer). Such an arrangement increases the reflectivity of the combined structure (aluminum and double layer) significantly compared with simply a layer of aluminum.

A further reason for a low signal at the detector 8, may be poor in- coupling of light into the dielectric layer 5a. In general, the dielectric layer 5a should have a thickness of at least one half of the wavelength of the light to exhibit effective in- coupling. The reason for this being that in thinner layers not all modes of the light will propagate through the wave guide. The light propagation/in-coupling will generally improve as the layer thickness increases, whilst little further improvement will occur once the layer thickness exceeds 10 times the wavelength of the light.

Both of the above-mentioned effects become more pronounced as the length of the wave guide 5 (the dimension of the light guide 5 in the direction from light source 7 to detector 8) increases. In a preferred embodiment, it is advantageous to restrict the length of the non-transparent layer and the wave guide to less than a certain number of reflections of the light through the wave guide, preferably to less than 20 reflections.

The skilled person will understand that further geometrical considerations have to be taken into account. For instance, one has to avoid any unwanted signal arriving at the detector 8. For this reason, it is preferred that the dielectric layer 5 a is given substantially the same or similar lateral dimensions as those of the magnetic element 3. If the dielectric layer 5 a is wider than the magnetic element 3 as indicated in Fig. 5, this may result in unwanted reflections falling into the detector. Whilst the preferred embodiment described above can be implemented to reduce the light signal loss through the wave guide, there may still be a considerable signal reduction in practical implementations. More importantly, the absolute magnitude of the signal may vary from one detection point on the sensor surface to another resulting from small variations in the properties of the wave guide (e.g., thickness of layers, details of surface roughness, geometrical factors etc.).

For this reason, it will be highly preferred to make use of a magnetic biosensor device according to the present invention in an assay, wherein only the change in the measured signal level (and not the absolute magnitude) is considered. For example, one may perform a measurement of the light intensity detected at all measurement points of the sensor surface while the sample contains a reference fluid such as water only in order to provide a reference or background result. Then this reference may be compared with the light intensity distribution of the sample of interest. In a more preferred assay, the light intensity is continuously monitored during the assay. This allows for interpretation of measurements made according to changes of the measured intensity distribution across the device, such as how the kinetics of the binding process depends on the target concentration in the sample.

An alternative embodiment of a biosensor device according to the present invention is shown in Fig. 6. According to this embodiment, the optical wave guide is arranged in an optical substrate 25. The optical substrate 25 may be an injection- moulded piece of plastic that is part of a biosensor cartridge which is used in combination with a magnet comprising a core 109 and a core 110, similar to the device shown in Fig. 3a and 3b.

Light enters the optical substrate 25 through an input window 20 and, after multiple reflections inside the optical substrate 25, the light leaves the optical substrate 25 through an output window 21. The liquid to be tested including the magnetic beads is arranged in sample volume 10. The refractive index of the material forming the optical substrate 25 should thus be considerably larger than that of water, so that the light undergoes a total internal reflection on the surface of the optical substrate 25 adjacent to sample volume 10.

The wave guide in the optical substrate 25 according to the embodiment shown in Fig. 6 includes reflective surfaces 22a and 23a which ensure that the incoming light beam is reflected several times inside the wave guide before leaving the optical substrate 25. Accordingly, reflective metallic layers may be arranged on the optical substrate 25 which may be made from silver or aluminium, that is, materials which are non-magnetic and thus do not influence the externally applied magnetic fields. The reflective surfaces 22a and 23a may be produced by sputter deposition of metallic layers with a thickness in a range between 20 and lOOnm. For increased robustness, the metallic layers may be coated with a protective thin layer of silicon nitrate, having a thickness of for example 5 to 20nm, or other dielectric material. In the embodiment shown in Fig. 6, regions 27 outside the optical substrate 25 adjacent to the reflective surfaces 22a and 23a comprise an underfill material. Alternatively, in order to avoid the need for providing reflective surfaces as shown in Fig. 6, it may be made use of the fact that the light beam entering the optical substrate generally has an angle with respect to the surfaces of the optical substrate which is below the critical angle for total internal reflection, provided that the optical substrate has a refractive index that is sufficiently high compared with the refractive index of the medium surrounding the optical substrate. This is schematically illustrated in Fig. 7. In order to provide for an efficient total internal reflection, the surfaces of the optical substrate 25 ' are preferably optically polished. In a preferred configuration, air with a refractive index of n=l is provided in the area 26 outside of the optical substrate 25', except for the area adjacent to the sample volume 10 and certain regions 27 filled with an underfill material. In a further preferred configuration, the second surface 23 facing the magnet may be protected by a layer of low refractive index material having a refractive index of n=1.4 or lower, such as calcium fluoride or similar materials. Such materials are commonly used in the fabrication of, for example, anti-reflection coatings or optical filter multi-layer structures. The configurations shown in Fig. 6 and 7 allow a reduction of the distance between the magnet and the sensor surface, that is, the thickness of the optical substrate 25, 25'. Further, the configurations allow for wider magnet designs, so that lower currents can be used for the same actuation forces.

The thickness of the optical substrate 25, 25' in the region where the multiple reflections occur should be large compared to the ratio of the wavelength of the light and the refractive index of the material forming the optical substrate 25, 25'. For example, for a wavelength of 650nm and n=1.6, the thickness of the optical substrate should be larger than 406nm. The reason is that for an optical substrate having a thickness close to or below this value, the substrate will act as a planar wave guide. The presence of absorbing layers or interface roughness will lead to significant and unwanted light attenuation and/or scattering. A further embodiment of the present invention relates to large area electronic (LAE) implementations. The magnetic biosensor device as described above may comprise a magnetic field element which is fabricated from one of the well known large area electronics technologies, such as a-Si, LTPS or organic transistor technologies. The magnetic field element may be fabricated on various substrates such as glass or plastic. Alternatively, the so-called EPLAR process can be used to manufacture the magnetic field element on a flexible or conformal substrate. Alternatively, the magnetic field element could be manufactured on a rigid substrate (e.g. glass) and transferred to a flexible substrate. The active matrix allows for independently controlling a large number of components, namely the magnetic field elements or magnetic sub-elements on the device with a small number of control terminals. Addressing of the magnetic element or array is generally one-line at a time (as will be explained below) - in contrast to the usual random access approach of addressing a CMOS based device. The use of an active matrix makes it feasible to drive a voltage or current signal to a large number of devices (order 10-1000000) in a controlled manner. This is not feasible if every electrode were to be individually connected to an electrical connection and controlled by a dedicated control device, as the costs and space required to incorporate such a control system would be prohibitive. In this case, a preferred embodiment is to realise the array of magnetic field generating elements in the form of a matrix device, and preferably an active matrix device (or alternatively being driven in a multiplexed manner). In an active matrix or a multiplexed device, it is possible to re-direct a driving signal from one driver to a multiplicity of magnetic field generating elements, without requiring that each magnetic field generating element is connected to the outside world by 2 contact terminals.

Fig. 8 schematically shows a diagram of an active matrix magnetic field element according to a preferred embodiment of the present invention. Said active matrix element comprises a number of magnetic sub-elements 11 and respective transistor switches 12. The matrix acts as a distribution network to route the electrical signals required for the magnetic (field generating) sub-elements 11 from a central driver to the magnetic sub-elements 11. It is preferred that the biosensor device according to the present invention provides a corresponding matrix of optical wave guides, each of them having its own input and output and a surface of total internal reflection adjacent to a magnetic sub- element 11. In other words: The segment 11a indicated by the dashed rectangle in Fig. 8 corresponds to a biosensor device depicted in Fig. 4. Thus, a whole array or matrix of these single devices may be provided. In order to perform a measurement at each of these sub-devices 11a, the array or matrix of devices may be (automatically) moved with respect to the light source and detector. Alternatively, a scanning optics may be used to couple light into each optical wave guide and to detect the respective signals. In this embodiment, the magnetic (field generating) sub-elements 11 are provided as a regular array of (identical) units, whereby the magnetic sub-elements are connected to the driver via the transistors 12 of the active matrix. The gates of the transistors are connected to a select driver 14 (preferably a standard shift register gate driver as used for an AMLCD), whilst the source is connected to the magnetic field generating element driver or gate driver 13, for example a set of voltage or current drivers.

The active matrix is operated as follows: To activate a given magnetic (field generating) sub-element 11, the transistors 12 in the entire line of compartments incorporating the required magnetic sub-element 11 are switched into the conducting state (by, e.g., applying a positive voltage to the gates from the select driver 14). The signal (voltage or current) in the column where the magnetic field sub-element is situated is set to its desired value. This signal is passed through the conducting TFT to the magnetic sub-element 11, resulting in a local magnetic field at the desired position. The driving signal in all other columns is held at a voltage or current, which will not cause a magnetic field (this will typically be OV or OA). After the magnetic field has been generated, the transistors in the line are again set to the nonconducting state, preventing further activation of the magnetic (field generating) sub- element.

It is also possible to activate more than one magnetic field generating sub- element in a given line simultaneously by applying a signal to more than one column in the array. It is possible to sequentially activate magnetic sub-elements in different lines by activating another line (using the gate driver 13) and applying a signal to one or more columns in the array.

Fig. 9 schematically shows a diagram of an active matrix magnetic field element according to a modification of the second embodiment of the present invention. Whilst in the embodiment shown in Fig. 8 a driver, which is capable of providing (if required) signals to all columns of the array simultaneously, was considered, it would also be feasible to provide a more simple driver with a function of a de-multiplexer. In the modified embodiment depicted in Fig. 9 only a single output driver 15 is required to generate the magnetic field signal (e.g. a voltage or a current). The function of the de-multiplex circuit 16 with switches 17 is simply to route the magnetic field generating element signal to one of the columns, whereby only the magnetic field generating sub-element 11 is activated in the selected line in that column.

A problem with the simple approach of individually driving each magnetic field sub-element through two contact terminals is that an external driver is required to provide the electrical signals for each magnetic field sub-element (i.e. a current source for a wire-based magnetic sub-element). As a consequence, each driver can only activate a single magnetic sub-element at a time, which means that magnetic field sub-elements attached to the same driver must be activated sequentially. This makes it difficult to maintain steady state magnetic profiles. Furthermore, if a driving current is required, it is not always possible to bring the current from the driver to the magnetic sub-element without a loss of current, due to leakage effects.

For this reason, it may be preferred to use the active matrix technology to create an integrated magnetic field generating element driver per magnetic field element. Figure 10 illustrates such a local driver, where now every magnetic (field generating) sub-element 11 comprises not only a select transistor 12, but also a local current source. Whilst there are many methods to realise such a local current source, the most simple embodiment requires the addition of just a second transistor 18, the current flowing through this transistor being defined by the voltage at the gate 19 (i.e. the trans- conductance of the transistor I = const x (Vpower -Vgate -Vt)², wherein Vt is the threshold voltage of the transistor 12). Now, the programming of the magnetic field signal may be achieved by simply providing a specified voltage from the voltage driver via the select transistor 12 to the gate 19 of the current source transistor 18.

In still a further embodiment, the local driver can be provided with a local memory function, whereby it becomes possible to extend the drive signal beyond the time that the compartment is addressed. In many cases, the memory element could be a simple capacitor. For example, in the case of a current signal as shown in Fig. 11, the extra capacitor 20 is situated to store the voltage on the gate of the current source transistor 18 and maintain the magnetic (field generating) sub-element current I whilst, e.g., another line of magnetic sub-elements 11 is being addressed. Adding the memory allows the magnetic field signal to be applied for a longer period of time, whereby the magnetic field profile can be better controlled.

The magnetic biosensor device according to the present invention can be used in different assays such as sandwich assays, competition or inhibition assays and agglutination assays. The device may also be used for cell analysis by binding magnetic labels to cells (e.g. via antigen-antibody binding, whereby the antigen is part of the cell membrane) and moving the magnetic particles and thus the cells over the magnetic field generating matrices as described above. The magnetic biosensor device may further be used for PCR or real-time PCR using magnetic labels for actuation and/or detection. The above-described active matrices for generating local magnetic fields can be used in a similar way for local heat generation. In this way the different steps involved in PCR that need different temperatures can be carried out at different places on the substrate. A simultaneous optical read-out is possible for each of the different places on the substrate.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. Biosensor device comprising a sensor surface (4) and an optical wave guide (5) having an input (20), an output (21) and first and second surfaces (22, 23), said optical wave guide (5) being adapted to direct light entering the optical wave guide (5) through the input (20) to the output (21) via multiple reflections on said first and second surfaces (22, 23) including at least one reflection on said first surface (22) under an angle fulfilling the condition of total internal reflection, wherein the sensor surface (4) is adjacent to the first surface (22).

2. Device according to claim 1, wherein the first and second surfaces (22, 23) are surfaces of total internal reflection.

3. Device according to claim 1, further comprising a magnetic field element (3).

4. Device according to claim 3, wherein the magnetic field element (3) is adjacent to the second surface (23).

5. Device according to claim 1, wherein the optical wave guide (5) comprises a dielectric layer (5 a).

6. Device according to claim 5, wherein the dielectric layer (5 a) comprises SiC>2

7. Device according to claim 3, wherein the magnetic field element (3) is coated with a reflectivity-enhancing layer (6).

8. Device according to claim 7, wherein the reflectivity-enhancing layer (6) comprises a first layer (6a) with low refractive index and a second layer (6b) with high refractive index.

9. Device according to claim 8, wherein the first layer (6a) comprises AI2O3 or SiC>2.

10. Device according to claim 8, wherein the second layer (6b) comprises Tiθ2.

11. Device according to claim 8, wherein the thickness of the first and/or second layer is about one quarter of the wavelength of the light.

12. Device according to claim 5, wherein the thickness of the dielectric layer (5a) is at least one half of the wavelength of the light.

13. Device according to claim 1, wherein the optical wave guide further comprises reflective layers (22a, 23a) provided on the second surface (23) and part of the first surface (22).

14. Device according to claim 1, wherein the optical wave guide is arranged in an optical substrate (25, 25').

15. Device according to claim 14, wherein the optical substrate (25') has a refractive index that is larger than the refractive index of the medium surrounding the optical substrate (25') so that total internal reflections occur on the first and second surfaces (22, 23).

16. Device according to claim 15, wherein a layer of low refractive index material is provided on the second surface (23).

17. Device according to claim 1, wherein the optical wave guide (5) is dimensioned such that the light is reflected less than 20 times.

18. Device according to claim 1, wherein the sensor surface (4) comprises a bio-active layer (205).

19. Device according to claim 3, wherein the magnetic field element (3) comprises an array of magnetic sub-elements (11).

20. Device according to claim 19, wherein the array of magnetic sub-elements (11) is an active matrix device.

21. Biosensor matrix device, comprising an array or matrix of sensors according to any one of claims 1 to 18.