GB2531724A

GB2531724A - SPR sensor

Info

Publication number: GB2531724A
Application number: GB1419076.3A
Authority: GB
Inventors: Roberts Matthew
Original assignee: Cambridge Display Technology Ltd
Current assignee: Cambridge Display Technology Ltd
Priority date: 2014-10-27
Filing date: 2014-10-27
Publication date: 2016-05-04
Also published as: GB201419076D0

Abstract

An SPR sensor for detecting a target analyte in a fluid comprises a light-transmissive substrate, a light-emitter (PLED) at a first location on a first surface of said substrate, a light-detector (OPV) at a second location on said first surface of said substrate, and a metal layer at a first location on a second surface of said substrate, wherein said second surface is opposite said first surface. The light-emitter is located at one or more points on a first ring (Fig 4a) having a first diameter and the light-detector is in a centre region of said first ring, or the emitter and detector positions may be swapped. The emitter and detector may be organic devices. Polarisation layers may be included on the sensor and the emitter may emit polarised light. The emitter and detector may be arranged as arrays with multiple emitters and detectors.

Description

SPR sensor

FIELD OF THE INVENTION

This invention generally relates to a surface plasmon resonance (SPR) sensor, in particular an SPR biosensor, and methods for detecting targets in a fluid using the SPR sensor.

BACKGROUND TO THE INVENTION

SPR has been used as a spectroscopy technique to determine the thickness of thin films in the nanometre range. Furthermore, SPR has been exploited to measure absorption of materials on the surface of a substrate.

Generally, in SPR, p-polarised light is used to excite surface plasmons at the surface of thin metal layers. Excitation of surface plasmons is based on total internal reflection when the light beam is reflected by the electrically conducting metal layer at the interface of a glass substrate with a sufficiently high refractive index and an external medium with a low refractive index. At a certain angle of incidence, surface plasmons are excited at resonance, resulting in a reduction of intensity of the reflected light.

Absorption of a material on the thin metal layer may result in a change of refractive index of the external medium at the interface between the external medium and the thin metal layer, and therefore a change in the SPR signal. Hence, the change in SPR signal generally allows for measuring the properties of the material absorbed on the interface. A membrane which may absorb, for example biological molecules may be prepared on top of the thin metal layer. Bonding of biological molecules to the membrane may result in a change in refractive index which may be detected using SPR.

(Organic) SPR sensors as well as organic light-emitting and light-detecting devices can be found in the prior art in, e.g. US 8,503,073 B2, US 2009/0256140 A1, US 2007/0229836 A1, US 7,221,456 B2, US 7,407,628 B2, US 7,998,413 B2 and http://www.es rf.eu/h ome/n ews/spotl ig h t/co ntent-n ews/spotl ight/spotl ig h t193. htm I. However, there is a need for further improvement of SPR sensors.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is therefore provided an SPR sensor comprising: a light-transmissive substrate; a light-emitter at a first location on a first surface of said substrate; a light-detector at a second location on said first surface of said substrate; and a metal layer at a first location on a second surface of said substrate, wherein said second surface is opposite said first surface; wherein said light-emitter is located at one or more points on a first ring having a first diameter; and wherein said light-detector is in a centre region of said first ring.

In a preferred embodiment of the SPR sensor, the light-emitter is located continuously over a circumference of the first ring.

The inventors have realised that the surface area of the light-emitter may be increased if the light-emitter is located at one or more points on a ring. Light-emitted by the light-emitter may be reflected by the metal layer before being detected by the light-detector. By using a configuration as outlined above, the signal-to-noise ratio may be advantageously improved compared to an SPR sensor known in the art.

Furthermore, the above configuration of a light-emitter located at one or more points on a ring and a light-detector located at a centre region of the ring may allow for performing SPR measurements which are independent of a horizontal direction of light emission from the light-emitter. Merely light emitted by the light-emitter generally into one direction may be detected by the light-detector after reflection of light at the metal layer.

The reference to the substrate being light-transmissive is to be understood as the substrate being transparent to at least a threshold transmittance of at least a wavelength or range of wavelengths at which the light-emitter emits light.

By using a single substrate onto which further components of the SPR sensor are prepared, further alignment optics may be omitted.

In order to further improve the signal-to-noise ratio, the SPR sensor may be configured such that light emitted by the light-emitter is detected by the light-detector only if an angle of incidence of light impinging on the metal layer essentially equals an angle of reflection of the light when it is reflected by the metal layer and directed towards the light-detector. Therefore, in a preferred embodiment, the metal layer is located continuously over a circumference of a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; and wherein a distance between said light-detector and said second ring is substantially the same for each point on said second ring.

In a further preferred embodiment of the SPR sensor, the metal layer is located at one or more points on a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-detector and said second ring is substantially the same for each point on said second ring; wherein each one of said one or more points on said first ring has a corresponding, respective point on said second ring such that light emitted by said light-emitter located at one of said one or more points on said first ring is reflected by said metal layer located at a said corresponding, respective point on said second ring, and wherein said reflected light is detected by said light-detector.

SPR occurs if the incident light wave vector equals the wave vector of the surface plasmon mode. The incident light wave vector depends on the angle of incidence of light impinging on the metal layer. It may therefore be preferable to vary the angle of incidence in order to ensure that the SPR condition is met. Hence, in a preferred embodiment of the SPR sensor, the first ring at which the light-emitter is located comprises a plurality of first rings each having a different said first diameter, and said light-emitter is located at one or more points on each one of said plurality of first rings.

In a further preferred embodiment of the SPR sensor, said metal layer is located at one or more points on a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-detector and said second ring is substantially the same for each point on said second ring; wherein said second ring comprises a plurality of second rings each having a different said second diameter, and said metal layer is located at one or more points on each one of said plurality of second rings; wherein each one of said one or more points on a said first ring has a corresponding, respective point on one said second ring of said plurality of second rings such that light emitted by said light-emitter located at one of said one or more points on a said first ring is reflected by said metal layer located at a said corresponding, respective point on one said second ring of said plurality of second rings, and wherein said reflected light is detected by said light-detector.

In another preferred embodiment of the SPR sensor in which the light-emitter is located continuously over a circumference of a said first ring, the first ring comprises a plurality of first rings each having a different said first diameter.

The signal-to-noise ratio may be improved even further by preventing light from being directed towards the light-detector if the angle of incidence of light falling onto the metal layer does not equal (or does not substantially equal) an angle of reflection of the light when reflected by the metal layer. Therefore, in a preferred embodiment, said metal layer is located continuously over a circumference of a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-detector and said second ring is substantially the same for each point on said second ring; wherein said second ring comprises a plurality of second rings each having a different said second diameter; wherein each one of said plurality of first rings has a corresponding, respective second ring of said plurality of second rings such that light emitted by a said light-emitter located continuously over a circumference of one of said plurality of first rings is reflected by said metal layer located continuously over a circumference of a said corresponding, respective second ring, and wherein said reflected light is detected by said light-detector.

In a preferred embodiment, the SPR sensor further comprises an absorbing layer at a second location on said second surface for absorbing light emitted by said light-emitter; and wherein said absorbing layer is configured such that light emitted by said light-emitter is directed towards said light-detector only if an angle of incidence of said light falling onto said metal layer is equal (or substantially equal) to an angle of reflection of said light when reflected by said metal layer. Preferably, the absorbing layer is located at one or more points on a third ring having a third diameter. In embodiments, the third diameter is different from the second diameter (when the metal layer is located at one or more points on a second ring), so that the absorbing layer and the metal layer do not overlap. The third ring may have a third centre region, wherein said third centre region substantially coincides with said first centre region. In some embodiments, the third ring comprises a plurality of third rings each having a different said third diameter.

The SPR sensor as described above may be modified insofar that the light-emitter(s) and the light-detector are exchanged.

Therefore, in a related aspect of the invention, there is provided an SPR sensor comprising: a light-transmissive substrate; a light-detector at a first location on a first surface of said substrate; a light-emitter at a second location on said first surface of said substrate; and a metal layer at a first location on a second surface of said substrate, wherein said second surface is opposite said first surface; wherein said light-detector is located at one or more points on a first ring having a first diameter; and wherein said light-emitter is in a centre region of said first ring.

In a preferred embodiment of the SPR sensor, the light-detector is located continuously over a circumference of said first ring.

Such a configuration, in which the light-detector is located at one or more points on a ring, allows for increasing the surface area of the light-detector. Therefore, the light-detector sensitivity may be advantageously increased. Hence, the signal-to-noise ratio may be improved compared to an SPR sensor known in the art.

In line with the above-described preferred embodiments, the signal-to-noise ratio may further be improved by providing an SPR sensor, wherein said metal layer is located continuously over a circumference of a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; and wherein a distance between said light-emitter and said second ring is substantially the same for each point on said second ring.

In a further preferred embodiment, the metal layer is located at one or more points on a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-emitter and said second ring is substantially the same for each point on said second ring; wherein each one of said one or more points on said first ring has a corresponding, respective point on said second ring such that light emitted by said light-emitter is detected by said light-detector located at one of said one or more points on said first ring when said light is reflected by said metal layer located at a said corresponding, respective point on said second ring.

In another preferred embodiment of the SPR sensor, the first ring comprises a plurality of first rings each having a different said first diameter, and said light-detector is located at one or more points on each one of said plurality of first rings. Such a configuration allows for, in particular, varying the angle of incidence of light to be reflected by the metal layer. This may ensure that an SPR condition is met.

In a further preferred embodiment of the SPR sensor, the first ring comprises a plurality of first rings each having a different said first diameter, and said light-detector is located at one or more points on each one of said plurality of first rings.

In line with the above, the metal layer may be located at one or more points on each of a plurality of rings. Therefore, in a preferred embodiment, the metal layer is located at one or more points on a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-emitter and said second ring is substantially the same for each point on said second ring; wherein said second ring comprises a plurality of second rings each having a different said second diameter, and wherein said metal layer is located at one or more points on each one of said plurality of second rings; wherein each one of said one or more points on a said first ring has a corresponding, respective point on one said second ring of said plurality of second rings such that light emitted by said light-emitter is detected by said light-detector located at one of said one or more points on a said first ring when said light is reflected by said metal layer located at a said corresponding, respective point on one said second ring of said plurality of second rings.

In an embodiment in which the light-detector is located continuously over a circumference of a said first ring, the first ring may comprises a plurality of first rings each having a different said first diameter.

The signal-to-noise ratio may be improved even further by preventing light being directed towards the light-detector if the angle of incidence of light falling onto the metal layer does not equal (or does not substantially equal) an angle of reflection of the light when reflected by the metal layer. Therefore, in a preferred embodiment of the SPR sensor, said metal layer is located continuously over a circumference of a second ring having a second diameter, wherein said second diameter is essentially half said first diameter; wherein a distance between said light-emitter and said second ring is substantially the same for each point on said second ring; wherein said second ring comprises a plurality of second rings each having a different said second diameter; and wherein each one of said plurality of first rings has a corresponding, respective second ring of said plurality of second rings such that light emitted by said light-emitter is detected by said light-detector located continuously over a circumference of one of said plurality of first rings when said light is reflected by said metal layer located continuously over a circumference of a said corresponding, respective second ring.

As outlined above, in a preferred embodiment, the SPR sensor further comprises an absorbing layer at a second location on said second surface for absorbing light emitted by said light-emitter; and wherein said absorbing layer is configured such that light emitted by said light-emitter is directed towards said light-detector only if an angle of incidence of said light falling onto said metal layer is equal (or substantially equal) to an angle of reflection of said light when reflected by said metal layer. Preferably, the absorbing layer is located at one or more points on a third ring having a third diameter.

In embodiments, the third diameter is different from the second diameter (when the metal layer is located at one or more points on a second ring), so that the absorbing layer and the metal layer do not overlap. The third ring may have a third centre region, wherein said third centre region substantially coincides with said first centre region. In some embodiments, the third ring comprises a plurality of third rings each having a different said third diameter.

In an alternative configuration of the SPR sensor, the light-emitter or light-detector, respectively, located at a centre region of a ring as described above, may be replaced with a respective light-emitter or light-detector located at one or more points on a ring.

Therefore, in a related aspect of the invention, there is provided an SPR sensor comprising: a light-transmissive substrate; a light-emitter located at one or more points on a first ring on a first surface of said substrate, wherein said first ring has a first diameter; a light-detector located at one or more points on a second ring on said first surface of said substrate, wherein said second ring has a second diameter; a metal layer at a first location on a second surface of said substrate, wherein said second surface is opposite said first surface; wherein said first diameter is different from said second diameter; wherein said first ring has a first centre region, said second ring has a second centre region, and wherein said first centre region substantially coincides with said second centre region.

In a preferred embodiment of the SPR sensor, the light-emitter is located continuously over a circumference of said first ring, and said light-detector is located continuously over a circumference of said second ring.

In order to cover a broader range of angles of incidence of light impinging on the metal layer, a plurality of light-emitters and a plurality of light-detectors located at one or more points on respective rings may be used. Therefore, in a preferred embodiment, said first ring comprises a plurality of first rings each having a different said first diameter; and said second ring comprises a plurality of second rings each having a different said second diameter.

In order to improve the signal-to-noise ratio further, in a preferred embodiment, the metal layer is located continuously over a circumference of a third ring having a third diameter, wherein said third diameter is essentially half of a sum of said first and second diameters; wherein said third ring has a third centre region; and wherein said third centre region substantially coincides with said first and second centre regions.

If a plurality of light-emitters and a plurality of light-detectors located on different rings with different diameters are exploited, the metal layer may preferably be located at one or more points on each of a plurality of rings. Therefore, in a preferred embodiment, said third ring comprises a plurality of third rings, wherein each of said third rings has a different said third diameter; and wherein each one of said plurality of first rings has a corresponding, respective third ring of said plurality of third rings and a corresponding, respective second ring of said plurality of second rings, wherein said third rings are configured such that light emitted by each one of said plurality of light-emitters located continuously over a circumference of one said first ring of said plurality of first rings is directed towards said light-detector located continuously over a circumference of one said corresponding, respective second ring of said plurality of second rings when said light is reflected by said metal layer located continuously over a circumference of a said corresponding, respective third ring of said plurality of third rings. This may allow for improving the signal-to-noise ratio further as light emitted by a light-emitter is detected by a corresponding light-detector if an angle of incidence of light impinging on the corresponding metal layer essentially equals an angle of reflection of light when it is reflected by the metal layer and directed towards the light-detector.

In order to further improve the signal-to-noise ratio, one or more absorbing layers may be exploited to reduce the possibility of light being directed towards a light-detector if the angle of incidence of light falling onto the metal layer (or a metal ring) does not equal (or does not substantially equal) an angle of reflection of light when reflected by the metal layer. Therefore, in a preferred embodiment, the SPR sensor further comprises an absorbing layer at a second location on said second surface for absorbing light emitted by said light-emitter; and wherein said absorbing layer is configured such that light emitted by said light-emitter is directed towards said light-detector only if an angle of incidence of said light falling onto said metal layer is equal to (or substantially equal to) an angle of reflection of said light when reflected by said metal layer. Preferably, said absorbing layer is located at one or more points on a fourth ring having a fourth diameter, wherein said fourth ring has a fourth centre region, and wherein said fourth centre region substantially coincides with said first centre region. Where the metal layer is located at one or more points on a third ring, the fourth diameter is different from the third diameter. In a preferred embodiment, said fourth ring comprises a plurality of fourth rings each having a different said fourth diameter.

In a preferred embodiment of the SPR sensor, the light-emitter emits light at a first range of wavelengths and the light-detector detects light at a second range of wavelengths, wherein the first range of wavelengths and the second range of wavelengths overlap at least partially. This allows for exploiting SPR as described herein in embodiments. Often, the absorption and emission spectra of a single material do not overlap at all, or overlap only partially. Therefore, it may be preferably to use different materials or material compositions for the light-emitter and light-detector, respectively. Hence, in a preferred embodiment of the SPR sensor, a material or material composition of the light-emitter is different from a material or material composition of the light-detector. The materials or material compositions of light-emitter and light-detector may be chosen such that the overlap between the emission spectrum of the light-emitter and the absorption spectrum of the light-detector exceeds a threshold range of wavelengths.

In a further preferred embodiment of the SPR sensor, the light-emitter comprises an organic light-emitter. Additionally or alternatively, in a preferred embodiment, the light-detector comprises an organic light-detector. It may be particularly preferable to exploit different materials or material compositions for light-emitter and light-detector, respectively, as outlined above, because generally, the emission and absorption spectra of a single organic material overlap only partially.

It may be preferable to prepare embodiments of the SPR sensor described herein at low cost. Therefore, in a preferred embodiment, the substrate of the SPR sensor comprises an organic substrate.

The skilled person will appreciate that a high refractive index substrate is required in order to observe SPR when a thin metal layer prepared on top of the substrate is excited by p-polarised light. High refractive index organic substrates may be prepared as outlined in, e.g. Y. Wang et al., Proceedings of SPIE, vol. 5724, 42, 2005, and T. Flaim et al., (Brewer Science Inc.), "High Refractive Index Polymer Coatings for Optoelectronics Applications", SPIE Proceedings of Optical Systems Design 2003.

In embodiments, the refractive index of the substrate adjacent the metal layer is at least n 1.0, more preferably n 1.5, more preferably n 1.7, or even more preferably n 1.9.

In order to increase the refractive index of the substrate, metal-oxide nanoparticles may be incorporated into the substrate. These metal-oxide nanoparticles include, but are not limited to, tin oxide, titanium oxide, cadmium oxide, zirconium oxide, tantalum oxide, hafnium oxide, silicon oxide, aluminium oxide, or the like.

In a further aspect of the invention, there is provided an organic SPR sensor comprising: a light-transmissive substrate; a light-emitter at a first location on a first surface of said substrate; a light-detector at a second location on said first surface of said substrate; and a metal layer on a second surface of said substrate, wherein said second surface is opposite said first surface; wherein said light-emitter comprises an organic light-emitter; and said light-detector comprises an organic light-detector.

As outlined above, in a preferred embodiment of the organic SPR sensor, the substrate further comprises metal-oxide nanoparticles. By incorporating metal-oxide nanoparticles into the substrate, the refractive index may be increased.

It may be preferable to provide a light emission source with a narrow bandwidth (and/or similarly a light-detector with a narrow bandwidth response). Therefore, in a preferred embodiment of the organic SPR sensor, the organic light-emitter comprises a micro-cavity organic light-emitting diode or a micro-cavity polymer light-emitting diode. Additionally or alternatively, an organic-based micro-cavity may be used for the light-detector. Additionally or alternatively, the micro-cavity may be strengthened using a thicker metal layer. This may reduce the control reflectance down to a relatively small baseline signal close to zero, and may therefore improve the signal-to-noise ratio.

In a preferred embodiment, the organic SPR sensor comprises an organic substrate.

In embodiments of the SPR sensor described in this specification, the SPR sensor may further comprise a filter on said first surface of said substrate, wherein said filter is between said substrate and said light-emitter and/or between said substrate and said light-detector. Alternatively, the filter may be incorporated on the second surface of the substrate, wherein the filter is placed between the substrate and the metal layer. Such a filter may be an interference filter or band-pass filter. Hence, such a filter may allow for changing the bandwidth of light emitted by the light-emitter and/or detected by the light-detector. The interference filter may be a high-pass, low-pass, band-pass or band-rejection filter.

In a further preferred embodiment, the SPR sensor further comprises: a first filter on said first surface of said substrate, wherein said filter is between said substrate and said light-emitter and/or between said substrate and said light-detector; and a second filter on said second surface of said substrate, wherein said filter is between said substrate and said metal layer. Again, the first and second filters may be interference and/or band-pass filters, allowing for modification of the bandwidth of light emitted and detected by the light-emitter and the light-detector, respectively.

It may be preferable to exploit not only a single filter, but rather a plurality of filters. Therefore, in a preferred embodiment of the SPR sensor, the filter comprises a plurality of filters. Each of the plurality of filters may filter a different wavelength or range of wavelengths. This may be particularly preferable if different light-emitters with different emission spectra/wavelengths are used.

Generally, polarised light with its electric field component parallel to the plane of incidence is called p-polarised, while light with its electric field component perpendicular to the plane of incidence is denoted s-polarised. The plane of incidence is hereby defined by the plane of the metal layer. The skilled person will appreciate that only p-polarised light may give rise to SPR. In contrast, s-polarised light results in undesirable background noise. In order to increase the fraction of p-polarised light of the light beam impinging on the metal layer, a polarisation layer may be used such that light emitted by the light-emitter is predominantly p-polarised before it strikes the metal layer. Therefore, in a preferred embodiment, the SPR sensor further comprises a polarisation layer on said first surface of said substrate, wherein said polarisation layer is between said substrate and said light-emitter, and said polarisation layer is configured such that light emitted by said light-emitter comprises p-polarised light. It will be understood that the higher the p-polarised component of the light, the lower the undesirable background signal due to s-polarised light. In embodiments, the light is p-polarised preferably to at least 10%, more preferably 20%, more preferably 30%, more preferably 40%, more preferably 50%, more preferably 60%, more preferably 70%, more preferably 80%, more preferably 90%, or even more preferably to 100%.

It will be appreciated that the polarisation layer may comprise a plurality of polarisation layers. Furthermore, the polarisation layer may additionally or alternatively be incorporated on the second surface of the substrate between the substrate and the metal layer.

In a related aspect of the invention, there is provided an SPR sensor comprising: a light-transmissive substrate; a light-emitter at a first location on a first surface of said substrate; a light-detector at a second location on said first surface of said substrate; and a metal layer on a second surface of said substrate, wherein said second surface is opposite said first surface; and a polarisation layer on said first surface of said substrate, wherein said polarisation layer is between said substrate and said light-emitter, and said polarisation layer is configured such that light emitted by said light-emitter comprises p-polarised light. In embodiments, the light is p-polarised preferably to at least 10%, more preferably 20%, more preferably 30%, more preferably 40%, more preferably 50%, more preferably 60%, more preferably 70%, more preferably 80%, more preferably 90%, or even more preferably to 100%. It will be understood that additionally or alternatively, the polarisation layer, which may comprise a plurality of polarisation layers, may be incorporated into the SPR sensor on the second surface between the substrate and the metal layer.

It may be preferable to prepare an SPR sensor based on an organic light-emitter in which light emitted by the organic light-emitter comprises p-polarised light. Therefore, in a related aspect of the invention, there is provided an organic SPR sensor comprising: a light-transmissive substrate; a light-emitter at a first location on a first surface of said substrate; a light-detector at a second location on said first surface of said substrate; and a metal layer on a second surface of said substrate, wherein said second surface is opposite said first surface; wherein said light-emitter comprises an organic light-emitter configured to emit light, wherein said light comprises p-polarised light. In embodiments, light emitted by the light-emitter is p-polarised preferably to at least 10%, more preferably 20%, more preferably 30%, more preferably 40%, more preferably 50%, more preferably 60%, more preferably 70%, more preferably 80%, more preferably 90%, or even more preferably to 100%.

In a preferred embodiment, the light-emitter comprises a preferred alignment direction along which said light-emitter preferably aligns; said light-emitter further comprising an emission dipole moment, said emission dipole moment comprising a first component and a second component, wherein said first and second components are perpendicular to each other; and wherein said first component is parallel to said preferred alignment direction; and wherein said second component is larger than said first component. In some embodiments, the preferred alignment direction is parallel to a backbone of said light-emitter. The backbone may be substantially parallel to said first surface.

An organic light-emitter emitting predominantly p-polarised light may be prepared using a molecule or polymer with a dipole moment aligned essentially perpendicular to the long axis of the molecule or polymer backbone.

The skilled person will appreciate that the refractive index changes upon absorption of a material on top of the metal layer. A target material in a fluid may be detected by bringing the fluid into contact with the metal layer. Changes in the SPR signal may allow for determining properties, such as, but not limited to binding properties of the target material to the metal layer.

Therefore, in a preferred embodiment, the SPR sensor comprises a channel adjacent the metal layer, wherein the channel is in direct contact with the metal layer. In preferred embodiments, the channel may be shaped substantially as a ring.

In a further preferred embodiment of the SPR sensor, the channel comprises: an inlet at a first channel region, an outlet at a second channel region; and a barrier in each of the first and second channel regions configured to prevent a fluid from flowing in opposite directions at any location of the channel. The skilled person will appreciate that other means may be provided in order to ensure that the fluid comprising the target material may flow in a single direction at any location in the channel.

The light-emitter and light-detector may degrade if they are exposed to, for example air/oxygen or moisture. Therefore, in a preferred embodiment, the SPR sensor may further comprise an encapsulation layer on the first surface of the substrate to encapsulate the light-emitter and/or the light-detector. This may be particularly preferable when using organic light-emitter and/or light-detector since organic materials are known to degrade when exposed to oxygen or moisture. However, in some embodiments, an encapsulation layer may be superfluous if light-emitter and light-detector do not degrade in the surrounding environment, in particular since light-emitter and light-detector are separated from the channel region and may not get in contact with the analyte.

As outlined above, the refractive index of the substrate should be sufficiently high so that SPR may be excited in a thin metal layer prepared on top of the substrate. It may be sufficient if the refractive index of the substrate is high enough adjacent to the metal layer which is in contact with the fluid comprising the target material to be detected. Therefore, the substrate may consist of two or more layers, whereby the layer onto which the metal layer is prepared has a relatively high refractive index. In embodiments, the refractive index of the substrate adjacent the metal layer is at least n 1.0, more preferably n 1.5, more preferably n 1.7, or even more preferably n 1.9.

Therefore, in a preferred embodiment of the SPR sensor, the substrate comprises at least a first substrate layer and a second substrate layer. The first substrate layer may comprise a first substrate material or first substrate material composition, and the second substrate layer may comprise a second substrate material or second substrate material composition. The refractive indices of the first and second substrate layers may be different. Preferably, the metal layer may be prepared on top of the substrate layer which has a higher refractive index than the other substrate layer.

In a preferred embodiment of the SPR sensor, the substrate comprises a third substrate layer, the third substrate layer comprising a third substrate material or third substrate material composition. The third substrate material or the third substrate material composition may be essentially identical to the first substrate material or the first substrate material composition, and the second substrate layer may be sandwiched between the first and third substrate layers. Such a configuration may allow that the angle of incidence of light impinging on the metal layer is the same as the angle at which light emitted by the light-emitter enters the substrate.

It will be understood that the thicknesses of the various substrate layers relative to each other may vary depending on various factors, such as, but not limited to, the cost of each of the materials used for the different substrate layers.

In embodiments, a grating may be provided on the surface of the substrate onto which the metal layer is prepared. This may allow for light being reflected by the metal layer at one or more preferable angles. Furthermore, if the surface of the substrate is roughened, the diffraction efficiency may be improved. This may result in enhanced SPR properties (extended range of refractive indices, sharper resonances, etc.).

In a further aspect of the invention, there is provided a system comprising: the SPR sensor as outlined in any one of the embodiments described herein; a read-out unit coupled to the light-detector, said read-out unit to provide read-out data of light detected by the light-detector; and a processor configured to process said read-out data.

In a preferred embodiment, the system further comprises a memory, wherein the processor is further configured to store the processed read-out data in the memory.

The optical read-out unit of the system may be an optical read-out unit or an electrical read-out unit. A combination of optical and electrical read-out units may be exploited, in particular when a plurality of light-detectors is used.

In a related aspect of the invention, there is provided a method for detecting a target in a fluid, the method comprising: determining an intensity of light detected by the light-detector of the SPR sensor of any one of the embodiments described herein, wherein the light is emitted by the light-emitter of the SPR sensor and reflected by the metal layer of the SPR sensor before said light is detected by said light-detector; bringing the fluid into contact with the metal layer; and determining a change in the intensity when the fluid is in contact with the metal layer to detect the target in the fluid.

In a preferred embodiment of the method, the determination of the intensity and the change in said intensity comprise determining the intensity and the change in said intensity at different angles of incidence of the light impinging on the metal layer. This embodiment may be particularly preferable if a plurality of light-emitters and a plurality of light-detectors are used. Exploiting different angles of incidence may allow for investigating the target(s) in the fluid at different resonance conditions.

The SPR sensor described herein may, in embodiments, comprise a first array of light-emitters and a second array of light-detectors. When light is detected by one of the light-detectors, it may be preferable to determine which one of the light-emitters has emitted the light which is being detected by the light-detector. This information may be used in order to determine the properties of a target material in a fluid.

Therefore, in a further related aspect of the invention, there is provided a method for detecting a target in a fluid, the method comprising: providing a light-transmissive substrate, said substrate comprising (i) a first array of light-emitters on a first surface of said substrate and a second array of light-detectors on said first surface of said substrate; and (ii) a metal layer on a second surface of said substrate, wherein said second surface is opposite said first surface; the method further comprising determining an intensity of light detected by a first light-detector of said second array of light-detectors, wherein said light is emitted by a first light-emitter of said first array of light-emitters and reflected by said metal layer before said light is detected by said first light-detector; determining said first light-emitter of said first array of light-emitters by applying an orthogonal binary vector model; bringing said fluid into contact with said metal layer; determining a change in said intensity when said fluid is in contact with said metal layer to detect said target in said fluid if said light detected by said first light-detector is determined to still be emitted by said first light-emitter.

This method allows for preventing 'false' signals which may arise if light detected by one of the light-detectors may be emitted by two different light-emitters before and after bringing the fluid into contact with the metal layer.

In an alternative approach, light-emission by the array of light-emitters may be sequenced, such that a determination as to which of the light-emitters has emitted light being detected by a light-detector may easily be made.

Therefore, in a related aspect of the invention, there is provided a method for detecting a target in a fluid, the method comprising: providing a light-transmissive substrate, said substrate comprising (i) a first array of light-emitters on a first surface of said substrate and a second array of light-detectors on said first surface of said substrate; and (H) a metal layer on a second surface of said substrate, wherein said second surface is opposite said first surface; the method further comprising sequencing a light-emission by said light-emitters of said first array; determining an intensity of light detected by said second array of light-detectors, wherein said emitted light is reflected by said metal layer before said light is detected by said second array of light-detectors; bringing said fluid into contact with said metal layer; determining a change in said intensity when said fluid is in contact with said metal layer to detect said target in said fluid.

In a preferred embodiment of the method, said determining of the change is based on said light being emitted and detected by a single pair of light-emitter and light-detector before and after said fluid is brought into contact with the metal layer.

In a related aspect of the invention, embodiments of the SPR sensor as described herein may be incorporated into a microfluidic chip.

It will be understood that any combination of embodiments of the SPR sensor described herein may be exploited. For example, the use of filters, absorbing layers, organic materials, micro-cavities, different materials for light-detector and light-emitter, metal-oxide nanoparticles, polarisation layers, channels, encapsulation layers, two or more substrate layers, etc., may be incorporated into any of the embodiments of the SPR sensor described in this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described by way of example only, with reference to the accompanying figures in which: Figure 1 shows a schematic side-view of an SPR sensor according to embodiments of the present invention; Figure 2 shows a simulation of reflectance and electroluminescence as a function of wavelength; Figure 3 shows a simulation of reflectance and electroluminescence as a function of wavelength; Figures 4a -f show schematic top-views of SPR sensors according to embodiments of the present invention; Figure 5 shows a schematic top view of an SPR sensor according to an embodiment of the present invention; Figure 6 shows a schematic side-view of a substrate according to an embodiment of the present invention; Figure 7 shows a schematic side-view of an SPR sensor according to embodiments of the present invention; Figure 8 shows a schematic side-view of substrate and metal layer according to embodiments of the present invention; Figure 9 shows a schematic side-view of metal and membrane layers according to an embodiment of the present invention; Figures 10a and b show schematic illustrations of organic light-emitters; Figure 11 shows a schematic side-view of an SPR sensor according to embodiments of the present invention; Figures 12a -c show simulations of reflectance and electroluminescence as a function of wavelength for different reflective indices; and Figure 13 shows a system according to an embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a schematic illustration of an example SPR sensor (not to scale). The substrate in this example is a glass with a high refractive index of n1 = 1.9. In this example, a dense lanthanum flint glass, H-ZLaF75, with a thickness of approximately 1 mm is used.

On a first surface of the glass substrate, a polymer LED (PLED) micro-cavity is provided. In this example, the PLED micro-cavity has a width of approximately 200 pm. An organic photovoltaic (OPV) device is provided on the same, first surface of the glass substrate. The OPV device is separated from the PLED micro-cavity by a distance of, in this example, approximately 3.4 mm.

On a second surface of the glass substrate, opposite the first surface, a 50 nm thin metal layer of Ag or Au is provided. The metal layer has the same distance to the PLED micro-cavity and the OPV device. Furthermore, in this example, two absorbing layers ("black absorber") are prepared on the second surface of the substrate. The absorbing layers absorb light emitted by the PLED micro-cavity, and ensure that light emitted by the PLED micro-cavity is detected by the OPV device only if the angle of incidence of the light beam impinging on the metal layer (substantially) equals the angle of reflection. A channel may be provided above the metal layer.

SPR occurs when the incident light wave vector equals the wave vector of the plasmon mode. The incident light wave vector is dependent on the angle of incidence of light impinging on the metal layer. In this example illustration, the angle of incidence is 60 deg to the normal. The SPR condition is dependent on the refractive index of the substrate, n1, as well as the refractive index of the external medium, n2, which is in contact with the metal layer. The refractive index of the external material is, in this example, approximately n2 = 1.5. Typically, n2 is in the range of 1.35 to 1.6. If a material binds to the metal layer, the refractive index of the external medium at the interface between the metal layer and the external medium changes slightly. Therefore, properties of the target materials in the fluid may be analysed by comparing the SPR signal with and without the fluid being in contact with the metal layer.

The emission of the PLED micro-cavity, the geometries of the SPR sensor (including, for example, the angle of incidence), refractive index of the substrate, wavelength of the light-emitter, and other parameters known to the person skilled in the art, may be tuned so that SPR occurs without the fluid comprising the target being in contact with the metal layer. At the SPR condition, the reflectance, detected by the OPV device, is at its minimum.

As outlined above, the presence of a target material binding to the metal layer will result in small changes in the refractive index n2. Therefore, at the previously obtained SPR condition, the fluid comprising the target to be detected is flown over the substrate such that the fluid is in contact with the thin metal layer. This will result in an increase in reflectance, as detected by the OPV device.

It will be understood that the materials and dimensions of the various layers shown in Figure 1 are merely exemplary to outline the operating principle of embodiments of the SPR sensor described herein. The skilled person will appreciate that a variety of other materials and material combinations may be used to prepare the SPR sensor.

Figure 2 shows a simulation of reflectance and electroluminescence as a function of wavelength for the device shown in Figure 1. In this example, the refractive index n1 = 1.9, the Ag layer has a thickness of 50 nm and light emitted by the PLED micro-cavity is p-polarised. In this simulation, the Ag layer is coated with a material of refractive index, n2, which is varied between n2 = 1.5 and n2 = 1.6.

As shown in the electroluminescence spectrum in Figure 2, the PLED micro-cavity in this example has a maximum electroluminescence at approximately A = 570 nm. Such a PLED micro-cavity spectrum may be representative of achievable emission from a bottom emitting micro-cavity device at 60 deg.

The simulation of the reflectance as detected by the OPV device shows that, in this example, no SPR occurs if the refractive index of the external medium is n2 = 1.6. For n2 = 1.5, SPR occurs, whereby the reflectance spectrum has a minimum at A r-570 nm.

As shown in Figure 2, when the refractive index of the external medium, n2, changes only slightly, the reflectance spectrum changes significantly. For example, for n2 = 1.505, the reflectance increases, in this simulation, to approximately 0.3 at A = 570 nm, and the minimum of the reflectance shifts to approximately A = 580 nm. If the refractive index n2 increases further, in this example simulation to n2 = 1.51, the reflectance at A 7-i-570 nm increases to approximately 0.6 and the reflectance minimum is found at A 590 nm.

In order to obtain an estimate for the total light intensity detected by the OPV device, the PLED micro-cavity spectrum is multiplied by the modelled reflectance spectrum. As shown in the table of Figure 2, a small refractive index change from n2 = 1.5 to n2 = 1.505, i.e. An2 = 0.005, may result in a significant, measurable change in light intensity at the OPV device by a factor of 1.3 for p-polarised light. In this simulation, a refractive index change of tn2 = 0.01 (An2 = 0.1) from n2 = 1.5 results in an intensity change at the OPV device by a factor of 1.9 (3.7).

Therefore, the SPR sensor with this geometry has a sufficient sensitivity for changes of the refractive index of the external medium as small as An2 = 0.005.

The sensitivity and range of refractive index changes that can be detected may be increased further by introducing, for example, a filter (for example a band-pass filter) between the OPV and the substrate, or by extending the device architecture to multiple angles of light impinging on the metal layer. There is further scope for tuning the SPR condition by adjusting, for example, but not limited to, dimensions of the SPR sensor, angles of light-emission of the light-emitter and/or wavelengths exploited. Furthermore, as outlined above, an array of light-emitters and light-detectors may be provided.

The skilled person will appreciate that embodiments of the SPR sensor described herein may be used in a microfluidic device, for example for temporal dynamics, or for a single measurement.

Figure 3 shows a simulation of reflectance and electroluminescence as a function of wavelength. The same device parameters are used for this simulation as in Figure 3, except that the light-emitter has a narrower bandwidth. Alternatively or additionally, the light-detector response may be narrowed. For example, a micro-cavity OLED may be exploited, and/or line/interference filters may be provided between the glass substrate and the OLED and/or OPV device, respectively.

As shown in the table of Figure 3, by narrowing the bandwidth, the sensitivity may be significantly increased. A small refractive index change from n2 = 1.5 to n2 = 1.505, i.e. An2 = 0.005, may result in a significant, measurable change of intensity at the OPV device by a factor of 18. In this simulation, a refractive index change of An2 = 0.01 (An2 = 0.1) from n2 = 1.5 results in an intensity change of a factor of 40 (70).

As outlined in the summary section of this specification, the sensitivity of the SPR sensor may be increased even further by increasing the surface area of light-emitter and/or light-detector.

Figures 4a -f show top-views of schematic illustrations according to embodiments of the SPR sensor (not to scale).

In Figure 4a, a PLED light source is prepared on a first surface of the substrate. An OPV ring detector is prepared on the first surface of the substrate. The PLED light source is in the centre of the OPV ring. The metal layer and flow channel, in this example embodiment, are prepared over the entire second surface of the substrate. It will be understood that in some embodiments the PLED light source may be replaced with an OPV detector, and the OPV ring may be replaced with a PLED ring.

In Figure 4b, the metal layer comprises a ring on the second surface of the substrate.

Light-emitted by the PLED light source is reflected by the metal layer and detected by the OPV ring. The flow channel may be prepared on top of the metal layer, in this example, shaped substantially as a ring. The diameter of the metal ring is substantially half the diameter of the OPV ring. This ensures that light emitted by the PLED light source is detected by the OPV ring only if an angle of incidence of light impinging on the metal layer equals an angle of reflection of the light when it is reflected by the metal layer and directed towards the OPV ring.

Figure 4c shows a further example embodiment of the SPR sensor with, in this case, two OPV rings on the first surface of the substrate. In this example, the metal layer is prepared over the entire second surface of the substrate. Such a configuration of the SPR sensor may allow for varying the angle of incidence of light falling onto the metal layer.

Figure 4d shows another embodiment of the SPR sensor with, in this example, two OPV rings and two metal layer rings. The PLED light source is prepared in a centre region of the OPV rings. Such a configuration allows for increasing the sensitivity of the SPR sensor even further by reducing background-noise.

In Figure 4e, the PLED light source comprises a ring. As shown, the diameter of the metal ring is preferably half of the sum of the diameters of the OPV ring and the PLED ring, respectively. This ensures that light emitted by the PLED light source is (predominantly) detected by the OPV ring only if an angle of incidence of light impinging on the metal layer equals an angle of reflection of the light when it is reflected by the metal layer and directed towards the OPV ring.

In Figure 4f, the OPV ring is located at different points on a ring and the PLED light source is in a centre region of the ring. It will be understood that other example embodiments may additionally or alternatively comprise a PLED light source located at different points on a ring. Furthermore, it will be appreciated that any of the PLED light sources or OPV detectors shown in Figures 4a -e may be configured at one or more points on a ring. The PLED light source and the OPV detector may be configured at one or more locations on one or more rings in a regular or irregular pattern.

As mentioned above in relation to Figure 4a, in some embodiments of the SPR sensor shown in Figures 4b -f, the PLED light source may be replaced with an OPV detector and the OPV detector may be replaced with a PLED light source. Further configurations and combinations of PLED light sources, metal layers and OPV detectors of the SPR sensor will be immediately apparent to those skilled in the art.

Figure 5 shows a top view of a schematic illustration according to an embodiment of the SPR sensor (not to scale). The flow channel comprises an inlet and an outlet. This allows for bringing a fluid comprising a target material to be detected and/or analysed into contact with the metal layer. In order to prevent a fluid from flowing in opposite directions at any location of the channel, barriers may be provided at the inlet and outlet regions of the flow channel.

Figure 6 shows a side-view of a schematic illustration of a substrate according to an embodiment of the SPR sensor described herein (not to scale). The substrate may comprise, in this example, three substrate layers. As outlined above, the metal layer may preferably be prepared on a substrate with a high refractive index. However, a transparent substrate with a high refractive index may increase the cost of preparing the SPR sensor significantly. Therefore, the substrate may comprise a plurality of layers. The different layers may comprise different materials or material compositions with different refractive indices. The substrate layer onto which the metal layer is prepared may preferably have a higher refractive index than the other substrate layers. This may allow for, in particular, decreasing preparation costs as a low-cost substrate layer with a (potentially) low refractive index may be combined with a different higher refractive index substrate layer made of a different material. In a preferred embodiment, the substrate comprises three (or more) substrate layers. The substrate layer onto which the metal layer is prepared may hereby be made of the same material as the substrate layer onto which light-emitter and light-detector are prepared. This may ensure that the angle at which light emitted by the light-emitter into the substrate is the same as the angle of incidence of the light when it impinges on the metal layer.

Furthermore, the angle of reflectance may therefore be the same as the angle at which the light beam exits the substrate before being detected by the light-detector.

Figure 7 shows a side-view of a schematic illustration of an SPR sensor according to embodiments described herein (not to scale). As shown, filters may be incorporated into the SPR sensor between the substrate and one or more of light-emitter, light-detector and metal layer. The filters may be, for example interference filters or band-pass filters. It will be understood that (a) particular type(s) of filters may be exploited depending on specific requirements needed during measurements. As described above, these filters may be used to increase the sensitivity of the SPR sensor, in particular by providing a narrow bandwidth light beam.

Furthermore, as shown in Figure 7, a polarisation layer may be used such that light emitted by the light-emitter is predominantly p-polarised before it strikes the metal layer. Background noise arising from s-polarised light may be reduced using a polarisation layer.

It will be understood that the filters and polarisation layer(s) may be prepared in a variety of configurations. For example, the filters and/or polarisation layers may be incorporated into the substrate, rather than prepared on top of a surface of the substrate. Furthermore, the filters may be prepared over an entire surface (or both surfaces) of the substrate, potentially avoiding patterning processes. The skilled person will immediately understand that different configurations may be exploited depending on specific requirements needed during measurements.

Figure 8 shows a schematic illustration of a metal layer, in this example Ag (not to scale). As outlined above, if a target is absorbed on the metal layer, the refractive index of the external medium, n2, at the interface between the metal layer and the external medium changes slightly. As a high refractive index of the substrate is needed, the refractive index n1 may be increased by incorporating nanoparticles, in particular metal-oxide nanoparticles into the substrate in the vicinity of the metal layer. Additionally or alternatively, the surface of the substrate may be roughened (for example by providing surface-relief gratings) in order to improve diffraction efficiencies. The device shown in Figure 8 may therefore result in enhanced SPR properties (extended range of refractive indices, sharper resonances, etc.).

Figure 9 shows a side-view of a schematic illustration of metal and membrane layers according to embodiments described herein (not to scale). In this example, a membrane layer is prepared on top of the metal layer. The surface of the membrane may comprise one or more receptors so that specific targets in the fluid may be detected. It will be understood that only a single type of receptor may be used, or different types of receptors such that different target materials may be investigated.

As outlined above, SPR may only be excited by p-polarised light, whereas s-polarised light results in undesirable background noise. Hence, the sensitivity of the SPR sensor may be increased by increasing the p-polarised component of light impinging on the metal layer. As described above, a polarisation layer may be provided such that light impinging on the metal layer is predominantly p-polarised. Additionally or alternatively, a light-emitter which emits light that is p-polarised to at least a certain threshold may be exploited in the SPR sensor described herein.

Figures 10a and b show schematic illustrations of organic light-emitters. The backbone and the light-emitting part of the organic material are indicated. Figure 10a shows a schematic of a common organic material with a dipole moment generally aligned with the backbone. Light emitted by the organic material is predominantly s-polarised, and therefore undesirable for use in an SPR sensor. Figure 10b shows a schematic illustration of an organic light-emitter according to embodiments of the SPR sensor described herein. It can be seen that the material is prepared such that the dipole moment of the light-emitting part of the organic is aligned generally perpendicular to the backbone. Light emitted by the organic light-emitter of Figure 10b is therefore p-polarised to a higher level compared to light emitted by the light-emitter shown in Figure 10a.

Figure 11 shows a schematic side-view of an SPR sensor according to embodiments described herein. In this example, glass substrate, metal layer and absorbing layers are identical to those shown in Figure 1.

The SPR sensor in Figure 11 comprises three PLEDs and three corresponding OPV devices. Light emitted by the three PLEDs impinges on the metal layer at three different angles, in this example 50 deg, 60 deg and 70 deg. In addition to the different angles of incidence of light emitted by the various PLEDs, the PLEDs may emit light at different wavelengths or ranges of wavelengths.

Expanding the device to include an array of light-emitters and light-detectors may be used to tune for a range of buffer refractive indices.

Figures 12a -c show simulations of reflectance and electroluminescence as a function of wavelength for the device shown in Figure 11. In this example, the refractive index n1 = 1.9, the Ag layer has a thickness of 50 nm, light emitted by the PLEDs is p-polarised, and the refractive index of the external medium, n2, is varied dependent on the angle if incidence of light impinging on the metal layer.

As shown in the electroluminescence spectra in Figures 12a -c, the PLEDs in this example have a maximum electroluminescence at approximately A = 570 nm.

As shown in the simulation of Figure 12a, the reflectance of light emitted by PLED 1 (angle of incidence 50 deg) and detected by OPV 1, in this example, is close to 1 for n2 = 1.45. In other words, no SPR occurs if the refractive index of the external medium is n2 = 1.45. For n2 = 1.35, SPR occurs, whereby the reflectance spectrum has a minimum at A = 570 nm.

A small change in the refractive index of the external medium, n2, may therefore result in a significant change of the reflectance spectrum, and therefore the intensity detected at the OPV device. For example, for n2 = 1.355, the reflectance increases, in this simulation, to approximately 0.4 at A = 570 nm, and the minimum of the reflectance shifts to approximately A = 580 nm. If the refractive index n2 increases further, in this example simulation to n2 = 1.36, the reflectance at A = 570 nm increases to approximately 0.7 and the reflectance minimum is found at A = 595 nm.

As shown in the simulation of Figure 12b, the reflectance of light emitted by PLED 2 (angle of incidence 60 deg) and detected by OPV 2, in this example, is close to 1 for n2 = 1.6. In other words, no SPR occurs if the refractive index of the external medium is n2 = 1.6. For n2 = 1.5, SPR occurs, whereby the reflectance spectrum has a minimum at A = 570 nm.

For n2 = 1.505, the reflectance increases, in this simulation, to approximately 0.3 at A =-570 nm, and the minimum of the reflectance shifts to approximately A = 575 nm. If the refractive index n2 increases further, in this example simulation ton2 = 1.51, the reflectance at A = 570 nm increases to approximately 0.6 and the reflectance minimum is found at A = 590 nm.

As shown in the simulation of Figure 12c, the reflectance of light emitted by PLED 3 (angle of incidence 70 deg) and detected by OPV 3, in this example, is close to 1 for n2 = 1.7. In other words, no SPR occurs if the refractive index of the external medium is n2 = 1.7. For n2 = 1.6, SPR occurs, whereby the reflectance spectrum has a minimum at A = 565 nm.

For n2 = 1.605, the reflectance increases, in this simulation, to approximately 0.2 at A =-565 nm, and the minimum of the reflectance shifts to approximately A = 570 nm. If the refractive index n2 increases further, in this example simulation to n2 = 1.61, the reflectance at A = 565 nm increases to approximately 0.55 and the reflectance minimum is found at A = 580 nm.

It can be seen that, in this example, if the emission spectrum is kept constant, and the PLED/sample/OPV angle is varied from 50 deg to 70 deg, then each pair of PLED/OPV may be tuned for a different refractive index, for example of different buffers/fluids comprising the target.

Furthermore, the simulations of Figures 12a -c show that the light-emitter spectrum may be changed to provide for further control over accessible ranges of the refractive index n2.

The sensitivity of the SPR sensor may be further improved via combinations of responses from various light-emitters/detectors at different angles.

These example simulations show that changes of n2 of the order 5 x 10-3 may be detected with embodiments of the SPR sensor described herein. It will be understood that ultimate detection limits depend, in particular, on the specifications of light-emitter and light-detector and may be improved by a few orders of magnitude.

Figure 13 shows a system incorporating an SPR sensor as described herein. The SPR sensor may be coupled to a read-out unit which may be an optical or electrical read-out unit. It will be understood that both optical and electrical read-out units may be exploited concurrently, in particular where a plurality of light-detectors is used. The read-out unit is in communication with a processor which is configured to process output data produced by the read-out unit. The data may then be stored in a memory.

The processor may further be used to control measurements performed with the SPR sensor. It will be understood that a different processor may be exploited to control the SPR sensor.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art and lying within the spirit and scope of the claims appended hereto.