WO2009060350A1

WO2009060350A1 - Microelectronic sensor device

Info

Publication number: WO2009060350A1
Application number: PCT/IB2008/054493
Authority: WO
Inventors: Maarten M.J.W. Van Herpen; Dirk L.J Vossen; Murray F. Gillies; Derk J.W. Klunder; Mark T. Johnson; Marc W.G. Ponjee
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-11-09
Filing date: 2008-10-29
Publication date: 2009-05-14

Abstract

The invention concerns a microelectronic sensor device (100) for the detection of target components (19) near a binding surface (12). The sensor (100) comprises an aperture defining structure (20), at least one aperture (4) having a smallest in plane aperture dimension (W1) smaller than a diffraction limit defined by the radiation wavelength and a medium for containing the target components (10). A source (21) is provided for emitting a beam of radiation (101) having a wavelength incident at the aperture defining structure (20), for providing evanescent radiation, in response to the radiation (101) incident at the structure (20), in a detection volume (13) formed in the aperture (14). In addition a detector (31) is provided for determining radiation (102) from the target component (10) present in the detection volume (13), in response to the emitted incident radiation (101) from the source (21). An electrode (112) is provided near the aperture defining structure (20), so as to transport the target components (10) in between the apertures (4) by applying an electric field; and a charging circuit (113) for charging the electrode (112).

Description

MICROELECTRONIC SENSOR DEVICE

FIELD OF THE INVENTION

The invention relates to a microelectronic sensor device for the detection of target components.

BACKGROUND OF THE INVENTION

In an inhomogeneous assay, the concentration of a targeted bio- molecule can be determined by measuring the surface concentration of the targeted bio-molecule or beads (that are representative for the targeted bio molecule) bound at the sensor surface. As an example, one can think of a competitive assay where the binding surface (substrate) is covered with target molecules. The beads may be covered with antibodies that are specific to the target molecule and are dispersed in a fluid that contains the target molecules. The free target molecule in the sample competes with the immobilized target molecule on the sensor surface for binding to the antibody-coated bead. In case of a low concentration, the chance that an antibody binds with a target molecule at the sensor surface is higher than the chance that an antibody binds with a target molecule in the solution. By measuring the surface concentration of beads that are bound at the substrate, one can determine the concentration of the target molecule. Accurate measurement of the concentration however requires a highly surface-specific detection scheme that is sufficiently insensitive for beads in the solution. Furthermore, the detected signal should be independent from the sample matrix, which can be whole blood, whole-saliva, urine or any other biological fluid.

For optical detection schemes, high surface specificity can be achieved by reducing the measurement volume. One-way to achieve this is by confocal imaging where the measurement volume is reduced to typically a few wavelengths (e.g., 1 micron). WO2006/136991 discloses a luminescence sensor using sub-wavelength apertures or slits. One aspect of this publication is that only particles, in particular, luminophores, that are present in between the slits are detectable. This offers a benefit of very surface specific detection of particles, for example, detection of specific bio molecules by analyzing particles involved in a hybridization reaction with the biomolecule. However, the transport process of particles into the slits is relatively slow and may impede hybridization reaction speed of biomolecules to be analyzed.

For alternative detection techniques, background radiation from a bulk medium may impede detectability of the particles of choice or may involve complex fluid channel arrangements. US6790671 discloses a fluid channel wherein an evanescent field is produced by "nano-slits", provided in a metal film layer, which can be electrically charged to position a polymer in front of the slit. Propagating radiation that leaves the nano-slit is used to illuminate in a fluid channel a fluorophore for visual detection. The fluid channel is used to physically confine a particle to be detected. This device and method are less suited for sensor multiplexing (i.e. the parallel electrical manipulation of different sensors and sensor surfaces), label multiplexing (i.e. the parallel electrical manipulation of different types of labels) and chamber multiplexing (i.e. the parallel electrical manipulation of different reaction chambers).

SUMMARY OF THE INVENTION

A desire exists to provide a microelectronic sensor device for the detection of target components wherein transport of target components within the apertures can be accelerated. The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

According to an aspect, an optical device provides evanescent radiation, in response to incident radiation, in a detection volume for containing a target component in a medium, the detection volume having at least one in-plane dimension (Wl) smaller than a diffraction limit defined by the radiation wavelength and the medium. The target components are transported in the detection volume by applying an electric field.

In another aspect there is provided a method of transporting a target component in an detection volume formed in an aperture, the method comprising: providing an aperture defining structure; at least one aperture having a smallest in plane aperture dimension (Wl) smaller than a diffraction limit defined by the radiation wavelength and a medium for containing the target components; emitting a beam of radiation having a wavelength incident at the aperture defining structure, for providing evanescent radiation, in response to the radiation incident at the structure, in a detection volume formed in the aperture; and detecting radiation from the target component present in the detection volume, in response to the emitted incident radiation from the source transporting the target components in between the apertures by applying an electric field. 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 a general setup of a microelectronic sensor device according to an aspect of the present invention;

Fig. 2 shows an illustrative schematic detail of the embodiment of Fig. 1;

Figs. 3A and 3B schematically show an alternative embodiment; Figs. 4A and 4B schematically show an alternative embodiment; Fig. 5 schematically shows an alternative embodiment;

Fig. 6 schematically shows an alternative embodiment; Fig. 7 schematically shows an alternative embodiment; Fig. 8 schematically shows an alternative embodiment in a sample chamber; Fig. 9 shows a schematic circuit arrangement for charging the microelectronic sensor device.

DETAILED DESCRIPTION OF EMBODIMENTS

The microelectronic sensor device according to the present invention may serve for the qualitative or quantitative detection of target components, wherein the target components may for example be biological substances like biomolecules, complexes, cell fractions or cells. The term "label and/or particle" shall denote a particle (atom, molecule, complex, nanoparticle, microparticle etc.) that has some property (e.g. optical density, magnetic susceptibility, electrical charge.) which can be detected, thus indirectly revealing the presence of the associated target component. A "target component" and a "label particle" may be identical. In addition, the microelectronic sensor device, according to an aspect of the invention may comprise the following components: a) The sensor is provided with a plurality of aperture defining structures having a first smallest in plane aperture dimension (Wl) smaller than a diffraction limit, the diffraction limit (Wmin) being defined by a medium for containing the target components:

Wmin=λ /(2*nmedium) (1)

with λ the wavelength in vacuum and n_medium the refractive index of the medium in front of the wire grid. In a preferred embodiment, the aperture defining structure defines a first and a second in-plane vector that are parallel to a slab of material that is not transparent (examples are metals such as gold (Au), silver (Ag), chromium (Cr), aluminium (Al)). The first (smallest) in-plane aperture dimension is parallel to the first in-plane vector and the second (largest) in-plane aperture dimension is parallel to the second in-plane vector.

Accordingly two types of apertures can be distinguished.

1. Apertures of the first-type with a first in-plane dimension Wl below the diffraction limit and a second in-plane dimension W2 above the diffraction limit there is a transmission plane that is composed of the first in-plane vector and a third vector that is normal to the first and second in-plane vectors. R-polarized incident light, that is light having an electric field orthogonal to the plane of transmission, is substantially reflected by the aperture defining structure and generates an evanescent field inside the aperture. T-polarized light incident on an aperture defining structure composed of apertures of the first type, that is light having an electric field parallel to the planes of transmission of the one or more apertures, is substantially transmitted by the aperture defining structure and generates a propagating field inside the aperture.

2. For apertures of the second-type with both in-plane dimensions below the diffraction limit we cannot define a plane of transmission. Incident light of any polarization (such as linearly, circularly, elliptically, randomly polarized) is substantially reflected by the aperture defining structure and generates an evanescent field inside the aperture.

In some embodiments, the sensor comprises a carrier with a binding surface at which target components can collect. The term "binding surface" is chosen here primarily as a unique reference to a particular part of the surface of the carrier, and though the target components will in many applications actually bind to said surface, this does not necessarily need to be the case. All that is required is that the target components can reach the binding surface to collect there (typically in concentrations determined by parameters associated to the target components, to their interaction with the binding surface, to their mobility and the like). For transmissive arrangement, the carrier preferably has a high transparency for light of a given spectral range, particularly light emitted by the light source that will be defined below. The carrier may for example be produced from glass or some transparent plastic. The carrier may be permeable; it provides a carrying function for aperture defining structures provided on the carrier having a smallest in plane aperture dimension (Wl) smaller than a diffraction limit. b) A source for emitting a beam of radiation, called "incident light beam" in the following, into the aforementioned carrier such that it is at least partly reflected, at least in an investigation region at the binding surface of the carrier. The light source may for example be a laser or a light emitting diode (LED), optionally provided with some optics for shaping and directing the incident light beam. The "investigation region" may be a sub-region of the binding surface or comprise the complete binding surface; it will typically have the shape of a substantially circular spot that is illuminated by the incident light beam. The aperture defining structure causing at least R polarized light to be reflected. In response to the radiation incident at the structure evanescent radiation is generated in a detection volume formed in the aperture. c) A detector for determining radiation from the target component present in the detection volume, in response to the emitted incident radiation from the source. The detector may comprise any suitable sensor or plurality of sensors by which light of a given spectrum can be detected, for example a photodiode, a photo resistor, a photocell, or a photo multiplier tube. Where in this specification the term light or radiation is used, it is meant to encompass all types of electromagnetic radiation, in particular, depending on context, as well visible as non visible electromagnetic radiation.

The microelectronic sensor device may be used for a qualitative detection of target components, yielding for example a simple binary response with respect to a particular target molecule ("present" or "not-present"). Preferably the sensor device comprises however an evaluation module for quantitatively determining the amount of target components in the investigation region from the detected reflected light. This can for example be based on the fact that the amount of light in an evanescent light wave, that is absorbed or scattered by target components, is proportional to the concentration of these target components in the investigation region. The amount of target components in the investigation region may in turn be indicative of the concentration of these components in a sample fluid that is in communication with the aperture according to the kinetics of the related binding processes. Turning to Fig. 1 a general setup is shown of a microelectronic sensor device 100 according to an aspect of the present invention. A central component of this device is the carrier 11 that may for example be made from glass or transparent plastic like polystyrene. The carrier 11 is located next to a sample chamber 2 in which a sample fluid with target components to be detected (e.g. drugs, antibodies, DNA, etc.) can be provided. Chamber 2 may in addition be defined by upstanding walls 111 that, in a preferred embodiment, are repeated continuously to form a plurality of adjacent walls 111, forming a well-plate for example, for microbiological assays. The sample further comprises particles 10, for example electrically charged or fluorescent particles, wherein these particles 10 are usually functionalized with binding sites (e.g., antibodies) for specific binding of aforementioned target components (for simplicity only the particles 10 are shown in the Fig.). Other label particles, for example superparamagnetic beads, could be used as well.

In this embodiment, the interface between the carrier 11 and the sample chamber 2 is formed by a surface called "binding surface" 12. This binding surface 12 may optionally be coated with capture elements, e.g. antibodies, ligands, which can specifically bind the target components.

The sensor device 100 further comprises a light source 21, for example a laser or a LED, which generates an incident light beam 101 that is transmitted into the carrier 11. The incident light beam 101 arrives at the binding surface 12. Radiation from the target component 102 leaves the carrier 11 and is detected by a light detector 31, e.g. a photodiode. Alternatively, the light detector 31 may determine the power/energy of the reflected light beam 102 (e.g. expressed by the light intensity of this light beam in the whole spectrum or a certain part of the spectrum). The measurement results are evaluated and optionally monitored over an observation period by an evaluation and recording module 32 that is coupled to the detector 31. On the carrier surface 12, a slab of material that is not transparent, preferably metal (for example gold (Au), silver (Ag), chromium (Cr), aluminium (Al)) is provided in the form of strips 20, defining a wire grid having a smallest in plane aperture dimension (Wl) smaller than a diffraction limit, the diffraction limit defined by the ratio between wavelength and twice the refractive index of the medium 2 containing the target components 10. The angle of incidence θ can in principle vary from 0° to 90°. Due to the diffraction limited nature of the aperture, in investigation area 13 an evanescent field is created that may be selectively disturbed due to the presence of particles that are bound by carrier surface 12 or at least within reach of the evanescent field generated by the aperture defining structures 20. An electrode 112 is provided near the aperture defining structure 20, so as to transport the target components 10 in or out the detection volume formed between the apertures 4 by applying an electric field. A charging circuit 113 is provided for charging said electrode. In this embodiment, the base electrode 112 is of a transparent nature such as ITO and is arranged in carrier 4. A dielectric layer 114, for instance of SiO2 is provided for electrically isolating the aperture defining structure 20 from the base electrode 112.

A charging voltage may be in the order of several volts, for instance, depending on the dielectric layer thickness ranging between 1 and 100 V.

In Fig. 2 an illustrative schematic view is shown of the binding surface 12 depicted in Fig. 1. It shows that the surface is provided with a plurality of aperture defining structures 20. In particular, in the shown embodiment, these structures can be provided by metal wires or strips 20, defining apertures Wlof the above-mentioned first-type. Typically, these strips are formed as a periodic structure of elongated parallel wires 20. Such a structure is typically referenced as a wire grid. Although the invention can be applied in a periodic structure (grating structure), this is not necessary, indeed the structure may also be aperiodic or quasi periodic. The aperture dimension Wl of the smallest dimension, or, if applicable, a grating period Λ, is typically smaller than the diffraction limit, the diffraction limit defined by a principal wavelength or band of wavelengths of the incident light beam and a medium for containing the target components. Preferably, the incident light beam is exclusively comprised of radiation having wavelengths above the diffraction limited wavelength, which is defined as twice the smallest aperture dimension (Wl) times the refractive index of the medium 2 containing the target components 10. A nice property of aperture defining structures with apertures of the first-type such as the wire-grid technology is that the light inside the aperture can be switched from an evanescent mode (as depicted in Fig. 2) to a propagating mode quite easily by switching the polarization of the input light, which enables both surface specific and bulk measurements.

Typical sizes of the beads 10 are in the order of 10-1000 nm. Typical parameters for a wire grid made of Aluminium used for red excitation light (e.g., HeNe laser having a wavelength of 632.8 nm) are a period of 140 nm (50 % of the diffraction limit in water for this wavelength); duty cycle of 50 % and a height of 160 nm. For these parameters, the (1/e) intensity decay length in an aperture filled with water is only 17 nm. The maximum bead size (i.e., beads that 'just' fit in the space between the wires) is limited to somewhat smaller than 70 nm for these parameters. As an example consider the case of beads with a diameter of 200 nm.

For this diameter, a period of 580 nm and a duty cycle of 2/3 is a reasonable choice; opening between the wires of 387 nm. In order to avoid propagating diffraction orders for the transmitted light, the grating period should be below the diffraction limit in water (index of refraction of 1.33): for a period of 580 nm, this implies that the wavelength of the incident light is at least 1540 nm. For a wavelength of 1600 nm and a thickness of 600 nm, this results in an (1/e) intensity decay length of 109 nm and a background suppression (for the bulk on top of the wire grid) of 250.

As an alternative the wire grids 20 may be replaced by an array of 2D sub-diffraction limited apertures, also referenced as a pin-hole structure. In this case the aperture defining structures is composed of apertures of the second-type mentioned here above. Accordingly these arrays have a high reflection (and evanescent fields inside the apertures) for any polarization.

In the embodiment of Fig. 2 the wire grid acts as a counter electrode having an opposite polarity to a base electrode 114 located elsewhere in the sample chamber 2. Although not necessary, in the shown embodiment the wiregrid is provided as a periodic structure of period Lambda (Λ). The wiregrid has a thickness T in the order of a few decay lengths of the evanescent field to ensure that the wave is not propagated into the sample chamber 2. Incident radiation 101 is schematically shown as reflected. Radiation 102 is an optical response of the particle 10 which is within the evanescent field; the response may non-limitatively include reflection, scattering or luminescence.

In the case of DNA (negatively charged) the presence of electrodes 114, 20 results in an actuation of the molecules 10 towards the space 4 between the wires 20 of the wire grid, where e.g., the target molecules can bind with the target molecules (hybridization), for a positively charged wire grid and a negatively charged base electrode. Unbound background molecules can be removed by reversing the polarities of the wire grid 20 and the base electrode 114 (see also Fig. 3B). Accordingly, a second electrode 114 is provided at a distance from the wire grid 20, to surround the detection volume 4 by electrodes. This may result in reduction of the contribution of biological background molecules to the detected luminescent signal and in actuation of bio molecules towards or away from the space 4 between the wires 10 of the wire grid over distances larger than 1 micron. A proper polarity of the counter and base electrodes may result in a drift of the biomolecules 10 towards the space between the wires. The targeted biomolecules may bind selectively (hybridization) with binding surface 12. The background molecules that are not (or only weakly) bound to the binding surface 12 can be removed from the space 4 between the wires 20 by reversing the polarity of the electrodes 114, while the target molecules 10 remain bound to the binding surface 12. As a result the biological background between the wires 20 of the wire grid may be reduced.

Using evanescent excitation (i.e., illumination of the wire grid from the bottom with properly polarized excitation light) only the luminophores bound to the hybridized target molecules 10 are excited and we can do a virtually background free measurement.

In the shown embodiment a current supply 115 is connected to the aperture defining structure 20, and a temperature controller 116 for controlling the current supply. Accordingly, the wire grid 20 can be used also as heater for temperature control. This can be achieved by- in addition to the voltage difference between the wire grid 20 and the base electrode 114- feeding a current through the wires of the wire grid by current supply 115. The dissipated power is converted into heat and results in a temperature increase of the environment/fluid on top of the wire grid. The current fed through the wires 20 may result in an in-plane potential difference between the ends of the wires and as a result in a non-uniform potential difference between the base electrode 114 and the wire grid 20. Potentially this can lead to non-uniform actuation forces. In order to compensate for this non-uniformity the same current can be fed through the second electrode 114 as well, which may result in a more uniform voltage difference between the electrodes 20, 114.

Alternatively, the current can be provided in the form of an AC signal with a low duty cycle (but with a higher peak intensity). In that case, the delivered power can be controlled either using Pulse Width Modulation and/or Pulse height Modulation. It has been observed (at least in electrophoretic display systems and probably also for DNA) that charged particles move less far when driven with a short, but higher intensity pulse. In this case, the AC frequency can be substantially lower than 1 kHz. Figs. 3 A and 3B show a variation of the embodiment of Fig. 2. In this embodiment, transparent electrode 311 is arranged as carrier. The aperture defining structures 20 are arranged on the carrier 311 and an isolator 114 is provided for electrically isolating the aperture defining structure from the base electrode 311. Fig. 3A shows actuation of bio molecules 10, 312 towards / through the space 4 between wires 20. Wires 20 are positioned on top of insulating layer 114. A transparent electrode 5, such as ITO is used as electrode near the aperture 4 defining wires 20. Insulating layer 114 may be planar or may be edged back as shown in Figs. 3A and 3B. In the first situation binding surface 12 is formed by insulating layer 114; in second case binding surface 12 is formed by transparent electrode 5. In the shown figure schematically shown bio molecules 313 are attached to binding surface 12. By applying a positive voltage of for instance 0.5-5 Volt molecules 10 are moved towards / through the space of the wires by increase of electric field in the space 4 in between the wires 20 of the wire grids.

Fig. 3B shows actuation of nonhybridized biomolecules away from the wires. These biomolecules may be excessive biomolecules 312 not bound to target molecules 313 or may be molecules of a wrong type so that a binding between target molecule 313 and bio molecule 10 is not formed. Thus by applying a negative voltage to transparent electrode 311, the electric field 351 is reversed into electric field 352 and nonhybridized molecules 312 are actuated away from the wires 20 in a direction of distanced electrode 114, that is positively charged with respect to the transparent electrode 311.

Fig. 4A shows an alternative embodiment, wherein a distanced wire is not present but may be additionally present (not shown). In this embodiment a wire grid 20 forms in plane arranged electrodes that are alternatingly charged (see Fig. 4B). In particular, on substrate 11 isolating dams 114 are provided (e.g. glass wires, SU-8 walls, acrylate, resist). Fig. 4A shows a situation where metal wires 20 are without electrical charge. Preferably, a capture molecule is used that only binds with the substrate material 11 or the barrier material 20 and the target DNA is deposited over the substrate. When excitation light is directed onto the wires 20 from the substrate side 11, fluorescence may be detected from within the space 4 between dams 114 and wires 20. The figure shows bound molecules 406, an unbound background molecule 407 within the detection space and an unbound background molecule 408 (just outside the evanescent field). Fig. 4A accordingly shows that detection volume 4 is extended from between wires 20 into carrier 11 by means of upstanding walls 114. Wires 20 formed by conducting material can be used as electrodes by attaching them to charging circuit 113 (See Fig. 1).

Fig. 4B shows what happens if the electrical wires 20 are charged (in this example individual adjacent wires 20 are charged with alternating polarities, but the process may be done with different polarities on groups of wires 20). Since the fluorophores 408, 407 have an electrical charge (for example DNA has a negative charge), they will be drawn towards or away from the wires 20, depending on the polarity. Fig. 4B shows that (unbound) background molecules 407 and 408 are now drawn to the positive electrode, pulling them both out of the detection areas 4. The bound molecules 406 are unaffected, because the bond strength is strong enough to keep them attached to the substrate.

Fig. 5 shows an alternative embodiment the substrate may comprise a conducting top layer 510 (for example ITO), top layer may be patterned. In this embodiment, a voltage can be applied between the layer 510 and the wires 20. By applying a positive voltage to the wires 20, background particles will be drawn out of the detection volume 4. Conversely, by applying a negative voltage to the wires 20 and a positive voltage through the conducting top layer 510, bioparticles will be drawn into the detection volume 4 to (selectively) bind with binding surface 12.

Fig. 6. shows a further embodiment wherein a stacked wire grid structure is used. The stacked structure now comprises a bottom wire grid layer 20a, an insulating layer 611 and a top wire grid 20b. The R-polarized excitation light (which is incident on the bottom side, through the substrate), is blocked by the wire grids 20a, creating an evanescent excitation volume 4. The aim is to remove background particles 407, 408 from this volume 4. By applying a negative voltage to wires 20a and a positive voltage to wires 20b, negatively charged bioparticles such as DNA are attached to positively charged upper wires 20b, so that they are drawn out of a detection volume 4.

Accordingly, positive and negative potentials are applied to the wires of the wire grid in order to use electrokinetics to manipulate the molecules 406, 407, 408 into and out of the detection volume 4. In this way, the wires 20a, b of the wire grid provide evanescent excitation and function as electrodes to manipulate the molecules to be detected. In one embodiment the wire grid 20a, 20b can be controlled based on active matrix principles (i.e. line at a time addressing) or based on CMOS (i.e. DRAM addressing).

Thus, in this embodiment the aperture defining structures comprise stacked sets of elongated metal strips 20a, 20b. Through electrode pads (not shown), a charging circuit arranged for charging each set alternating charges can be applied to the electrodes.

In the embodiment of Fig. 6 the stacks are electrically isolated from each other by an electric insulating layer 611. Alternatively, the stacks can be freely suspended. In such an embodiment the stacks can form a light guide wherein the volume between the stacks can be provided as detection volume. In such an embodiment it may be advantageous for having small gap distance between the stacks wire grids 20a, 20b of a typical gap distance varying from 0-200 nanometer. For such a small distance the electric field is strongly inhomogeneous, which gives rise to a dielectrophoretic and resulting in a translational motion of neutral matter caused by polarization effects in a nonuniform electric field. The dielectric force is proportional to the gradient of the squared absolute value of the electric field and a pre-factor that depends on the dielectric constant of the particles on which the force is being exerted and the dielectric constant of the medium containing the particles. The dielectric constants of the particle and the surrounding medium depend on the frequency of the electric field, and as a consequence the sign of said pre-factor depends on the frequency. This enables to control the sign of the dielectrophoretic force by controlling the frequency. By applying a voltage of a proper frequency (as explained above) to upper and lower grids 20a, 20b dielectrophoresis, can be used to concentrate molecules 406 in a relevant detection volume between the wire grids 20a, 20b.

Fig. 7 shows what happens if an electrical voltage of proper frequency is applied. In this case the background molecule 407 and the signal molecule 406 are drawn into the detection volume 4. Subsequently, the signal molecule 406 will bind to the surface, but the background molecule 407 will not bind, when not captured on the substrate 11. Again, the same steps could be taken as in embodiment 1 to collect molecules from the larger sample volume depicted in Fig. 8.

Specifically, Fig. 8 shows a sample chamber 2 wherein a medium can be provided containing bio molecules of interest. The chamber 2 comprises a wire grid 20 arranged on isolator stacks 114. Accordingly detection volume 4 is provided between the apertures of wire grid 20 and extending below the wire grid via stacks 114 into the carrier 11.

Next, a few things can be done. First, the polarities can be reversed, thus changing the electrical charge on the wires from + to - for all wires. This makes the molecules move around more. Another possibility is to periodically turn the field on and off, in order to make the molecules move away (via diffusion or self-repulsion) and towards the electrodes. Yet another possibility is to vary the driving frequency of the electric field to manipulate the molecules towards and away form the electrodes by using a dielectrophoretic force. This is advantageous, because if the molecules cannot bind specifically to a specific hybridisation location, the fluid should be mixed such that the molecules have a chance to bond to the other hybridisation spots. This increases the chance that the molecules will bind to the substrate l.One may also combine this, for example by applying a certain + and - charge, then turning the field off, and then applying the opposite charge.

If desired, one may also add a wash step, in order to wash away all unbound background molecules 7, before detection is done. Here, di-electrophoresis is used to concentrate signal molecules within the space between the two wire grids. This is advantageous, because the space between the wire grids has the highest excitation intensity and detection efficiency. Accordingly, the signal molecules are concentrated within space 4, such that they may bind more quickly to binding sites present on the wires 20 and substrate 11. This is achieved using a dielectric force 702, pulling the signal molecules 408 between the wires, in order to concentrate the signal molecules within space 4, thus decreasing the hybridization time. This force 702 is induced by driving the electrodes of the wire grid with an AC voltage, where neighbouring electrodes have opposite voltages. A reference on dielectrophoresis can be found in D.J. Bakewell, H. Morgan,

"Dielectrophoresis of DNA: Time- and Frequency-Dependent Collections on Microelectrodes", IEEE Transactions on Nanobio science 5 (1), 1-8 (March 2006). For a wire grid having aperture spacing of about 100 nm, an AC charge of about 0.2 - 1 V may be applied to alternating wires. Preferably, this invention is integrated into a matrix comprising electronic switches (e.g. transistors, diodes). Even more preferably, the invention is integrated in a Large Area Electronics (e.g. a-Si, LTPS) biosensor. Fig. 9 shows how the electrical scheme for this invention may look like for previous embodiments. Connecting electrode pads 92a, 92 are formed by side strips oppositely arranged seen in the length direction of the largest aperture W2. Thus, adjacent metal strips 20 are alternatively connected to strips 92a or 92b to form a nested comb structure. One of the pads 92a, 92b may be grounded while the other may be connected to voltage driver 113. Alternatively, pads 92a may be arranged as partly overlapping (viewed in a direction perpendicular to the plane), especially for the stacked strip arrangement of Fig. 6. Voltage driver 113 may be arranged for reversing the polarities of the electrodes.

Thus in this embodiment, the aperture defining structures comprise sets of elongated metal strips 20 alternatingly in plane positioned to define the apertures between the strips, each set connected via connecting electrode pads 92a, 92b, the charging circuit arranged for charging the electrodes with opposite polarities.

The device and method can be used as rapid, robust, and easy to use point-of-care biosensors for small sample volumes. The reaction chamber can be a disposable item to be used with a compact reader, containing the one or more field generating means and one or more detection means. Also, the device, methods and systems of the present invention can be used in automated high-throughput testing. In this case, the reaction chamber is e.g. a well-plate or cuvette, fitting into an automated instrument. Other variations to the disclosed embodiments within the scope of the following claims 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. The term "comprising" does not exclude other elements or steps, that "a" or "an" does not exclude a plurality, and that a single processor or other unit may fulfill the functions of several means. Moreover, reference signs in the claims shall not be construed as limiting the scope of the claims.

Claims

CLAIMS:

1. An optical device for providing evanescent radiation, in response to incident radiation (101), in a detection volume (4) for containing a target component in a medium, the detection volume having at least one in-plane dimension (Wl) smaller than a diffraction limit defined by the radiation wavelength and the medium, wherein the optical device is arranged to transport the target components in the detection volume by applying an electric field (351).

2. The optical device according to claim 1, wherein the evanescent radiation is provided by an aperture defining structures having a smallest in plane aperture dimension (Wl) smaller than the diffraction limit, and wherein the detection volume (4) is provided between said aperture defining structures.

3. The optical device according to claim 1, wherein the optical device comprises aperture defining structures (20) that define a largest in plane aperture dimension (W2) that is larger than the diffraction limit.

4. The optical device according to claim 1, wherein the aperture defining structures (20) comprise metal material, and wherein the electric field is applied by an electrode (112) that is formed by the aperture defining structures.

5. The optical device according to claim 2, further comprising a carrier

(11), and the detection volume is provided between the aperture defining structures and extends into the carrier.

6. The optical device according to claim 1, further comprising a base electrode (112) arranged in a carrier, the aperture defining structures arranged on the carrier and an isolator (114) for electrically isolating the aperture defining structure from the base electrode.

7. The optical device according to claim 6, wherein the base electrode is transparent.

8. The optical device according to claim 1, wherein the electric field is applied by a first electrode (311), and a second electrode (114) is provided at a distance from the aperture defining structures to surround the detection volume by electrodes.

9. The optical device according to claim 1, wherein the aperture defining structures comprise sets of elongated metal strips (20a, 20b) alternatingly in plane positioned to define the apertures between the strips, each set connected via connecting electrode pads, the charging circuit arranged for charging the electrodes with mutually opposite polarities.

10. The optical device according to claim 1, wherein the aperture defining structures comprise stacked sets of elongated metal strips (20a, 20b), the sets comprising electrode pads, and a charging circuit (113) is arranged for charging each set via said electrode pads with mutually opposite polarities.

11. The optical device according to claim 10, wherein the stacked sets are electrically isolated from each other by an electric insulating layer (114) or by spacing the stacks.

12. The optical device according to claim 9 or 10, wherein the connecting electrode pads are formed by side strips oppositely arranged and/or by partly overlapping strips arranged transversely relative to the metal strips.

13. The optical device according to claim 1, wherein the electric field is applied by electrodes charged by a charging circuit that is arranged for reversing the polarities of the electrodes.

14. The optical device according to claim 1, further comprising a current supply (115) to the aperture defining structure, and a temperature controller (116) for controlling the current supply.

15. A microelectronic sensor comprising: an optical device according to claim 1 ; a source (21) for emitting a beam of radiation having a wavelength incident at the optical device, for providing evanescent radiation in the detection volume, in response to the radiation incident at the optical device; and a detector ( 31) for detecting radiation from the target component present in the detection volume, in response to the emitted incident radiation from the source.

16. A method of transporting a target component in a detection volume (4) formed in an aperture, the method comprising: providing an aperture defining structure (20), at least one aperture having a smallest in plane aperture dimension (Wl) smaller than a diffraction limit defined by the radiation wavelength and a medium for containing the target components; emitting a beam of radiation (101) having a wavelength incident at the aperture defining structure, for providing evanescent radiation, in response to the radiation incident at the structure, in the detection volume formed in the aperture; and detecting radiation (102) from the target component present in the detection volume, in response to the emitted incident radiation from the source; and transporting the target components in between the apertures by applying an electric field (351).

17. A method according to claim 16, further comprising: applying a positive charge near the aperture defining structures, so as to attract the targets components into the apertures; binding the target components onto a binding surface (12), provided in the apertures; and applying a negative charge near the aperture defining structures, so as to repel unbound components away from the apertures.

18. A method according to claim 16, wherein said target component is arranged to bind with a biomolecule.

19. A method according to claim 16, wherein an AC charge is applied to the aperture defining structures, so as to attract and/or to repel the bio molecules into the apertures by dielectrophoresis by varying an AC driving frequency.