The present invention relates to a luminescence-based sensor assembly of the type comprising a superstrate; a substrate mounting an emitting spot, array of spots or a layer transmitting luminescence into the substrate; an excitation source; and a detector for measuring some of the light emitted into and transmitted out of the substrate.
Conventionally, for luminescence-based sensing, luminescence molecules forming a spot, an array of spots, or a layer, are placed on a substrate and a detector is used to detect the luminescence.
A vast number of assays carried out in biotechnology and the pharmaceutical industry use surface-bound molecules such as antibodies, which can specifically bind molecules such as antigens, from a fluid, typically a liquid flowing above. If the captured molecules contain a luminescent (which may be a fluorescent) moiety or can be labelled with one, either directly or via another molecule, they can be excited by light and subsequently the luminescence emerging from these captured molecules can provide a means for detecting the specific surface captured molecules. Within the present specification the molecules that have been captured are considered as forming a first layer, whereas other molecules which have not been bound or captured may be considered as forming a second layer. The space that extends from the surface including the luminescence label defines the first layer. It is normally the molecules forming the first layer that are of interest for detection purposes.
In many of these applications, the luminescence is excited by a so-called evanescent wave, which has the advantage of exciting the luminescence at or near the substrate interface, i.e. the first layer, rather than in the bulk superstrate above the substrate, the second layer. Essentially, it is the molecules bound, or adjacent, to the surface of the substrate which are excited and the luminescent molecules that are further away from the surface are not excited and therefore, their luminescence is not transmitted to the substrate. The evanescent wave may be used to control the distance from the surface at which the materials are excited. Essentially, this is achieved due to the localisation of the electromagnetic field of the evanescent wave in close vicinity to the interface between the superstrate and the substrate. The use of such a waveform ensures that the detected light is restricted in origin to a source close to the substrate interface, which is the preferred region of interest. As the illuminating light does not impinge on other molecules above this region there can be no excitation of those molecules and hence they will not contribute to the detected luminescence.
While evanescent wave excitation is extremely useful and effective, in certain circumstances it is not practical or convenient. Excitation by the evanescent field, which is confined to a small region above the waveguide surface and used to excite fluorescently-labelled surface attached molecules, is not particularly efficient, as only a small fraction of energy of the source of the excitation light is used for the actual excitation. This is predominantly due to the following reasons:
Indeed, it would be preferable to use another, more efficient method of providing the excitation. In particular, if excitation is provided by direct illumination from within the superstrate or from below the substrate, most of the optical energy provided by the source can be used for excitation. Although this configuration improves the efficiency of excitation, it also holds some disadvantages. Namely, if a source of direct illumination is used, there may be luminescence generated in the superstrate by molecules other than those captured on the surface of the substrate, namely, by molecules in the superstrate further away from the interface of the substrate and superstrate. The latter luminescence would also be delivered to the detector causing difficulties in distinguishing between the luminescence generated at or close to the interface between the substrate and the superstrate, i.e. that emitting from the first layer and the luminescence generated further away from the interface in the superstrate itself, that originating in the second layer.
U.S. Pat. No. 4,810,658 describes a method of optical analysis of a test sample which utilises direct illumination to excite the sample. The resultant luminescence is coupled into a waveguide where it propagates along the waveguide until it exits at a side surface thereof. It is described how by selectively positioning the detector at angles about the optical axis of the waveguide that it is possible to attribute that detected light as being due to molecules bound to the surface of the waveguide. As this arrangement relies on the detection of light which has propagated within the waveguide, the emerging signal is an integration of luminescence captured along the waveguide and is therefore not suitable for discriminating between individual sources provided on the waveguide.
A further disadvantage is that the propagation of light within a waveguide requires multiple reflections on the side walls of the waveguide which leads to inevitable losses in intensity of the signal that is eventually detected. Such losses can reduce the sensitivity of the overall apparatus.
Yet a further disadvantage is the requirement for the detection system to be placed perpendicular to an end or side surface of the waveguide which increases the overall dimensions of the test configuration, thereby making it unsuitable for certain applications.
There is therefore a need for a system and method that can be used for the detection of surface-generated luminescence which employs the excitation of the luminescent molecules by direct illumination, i.e., using the full power of the source of the excitation light, and yet can be used to selectively discriminate between the source of the luminescence.
In this specification, the term “critical angle” is used in its conventional sense as being Arcsin N2/N1 or Sin−1 N2/N1 where N1 is the refractive index of the optically denser material called the substrate and N2 is the refractive index of the less dense material, usually called the superstrate. Generally, the superstrate is the environment in which the surface binding or luminescent material is present, typically water or air. The condition N2<N1 must be satisfied.
The present invention is directed towards providing a means and apparatus for detecting that luminescence emitted into a substrate, which is emitted from molecules close to the superstrate/substrate interface but excited by direct illumination.
According to the present invention, there is provided a luminescence-based sensor assembly comprising a superstrate; a substrate mounting an emitting layer capable of transmitting luminescence into the substrate; an excitation source; and a detector for measuring some of the emitted light in the substrate which is subsequently transmitted out of the substrate, characterised in that the excitation source provides direct illumination and the detected luminescence originates from a close vicinity of the superstrate/substrate interface.
Desirably, the excitation source is in the superstrate remote from the substrate. Typically the excitation source is provided above the substrate, although it will be appreciated that direct illumination may equally be effected by the provision of a source below the substrate.
The invention utilises the concept that the angular emission pattern from luminescent, typically fluorescent moieties depends strongly on proximity to the superstrate/substrate interface. Based on this, the invention applies angle-selective detection principles to discriminate between the luminescence from the surface-bound moieties and those located in the bulk of the fluid, that is to say, in the superstrate above the superstrate/substrate interface. Essentially, this is arranged by ensuring that only light transmitted into the substrate and propagating in a particular angular range above the critical angle of the superstrate/substrate interface is detected. Within the present invention the term “first layer” will be used to describe those moieties which are bound or adjacent to the substrate and whose luminescence is of interest, and the term “second layer” to all those other moieties.
Putting it in another way, a key feature of the present invention is that no light emerging from a sufficiently large distance above the substrate/superstrate interface, which emanates from inside the superstrate, can be propagated within the higher refractive index substrate at angles greater than the critical angle. However, when the source of the luminescence is close to the surface of the two materials, the radiation can be coupled into the waves propagating in the higher refractive index medium at angles greater than the critical angle. Consequently, detection of the luminescence in a particular range of angles greater than the critical angle provides the means of detecting the light originating from molecules located at or close to the surface.
One way of achieving this is by providing a light barrier in or on the substrate, which light barrier is arranged to block any light, which has been transmitted into the substrate at an angle below the critical angle.
Alternatively, the barrier can be mounted on the detector so that any light transmitted through the substrate from the emitting molecules at an angle below the critical angle, will be blocked from detection.
Another way of achieving the detection of the light radiated in the substrate at angles greater than the critical angle is to configure the substrate internally or externally so that only the light propagating at angles greater than the critical angle is redirected towards the detector.
Accordingly the invention provides a luminescent sensor configuration for use in a medium having a first refractive index, the sensor configuration comprising a source of direct illumination, a substrate having an upper and lower surface and being of a second refractive index, a material capable of luminescence, a detector arrangement provided below the lower surface of the substrate and adapted to detect light emitted through that lower surface, and wherein, in use, the medium and the substrate meet along the upper surface of the substrate which defines the boundary between the first and second refractive indices, the material capable of luminescence is excited by the source of direct illumination, thereby luminescing and the detector arrangement is adapted to discriminate between luminescent light emitted from a region within a predetermined distance of the upper surface and light emitted from any other regions, the discrimination being effected by selective detection of light emitted from the luminescent material at angles greater than the critical angle of the medium/substrate interface.
The angles greater than the critical angle are desirably angles within a specific range which are predetermined for optimum performance of the system.
Desirably, the predefined distance is within the range of upto about 4 λ, desirably about 0.5 λ to about 3 λ, and more preferably within the range of about 1 to about 2 λ, wherein λ is the wavelength of the luminescence light.
As detailed above, the luminescent molecules contained within the predefined distance may be considered as forming a first layer whereas those molecules or materials outside that distance may be considered as forming a second layer.
The angle at which the luminescence is emitted into the substrate and subsequently selectively detected is preferably further greater than a threshold angle, the threshold angle being an angle which satisfies the equation:
Is(θtr)/Ib(θtr)=Ftr,
where Is(θtr) is the intensity of light emitted from the first layer at the threshold angle, Ib(θtr) is the intensity of light emitted by the second layer at the threshold angle and Ftr is a confidence or performance factor which is selected by the user. Ib(θtr) typically corresponds to a background level within the configuration system such that the equation reduces to providing a threshold angle which satisfies the equation that the signal-to-background ratio of the measurement of the luminescence originating from the first layer is greater than some specified value Ftr.
The background level may in certain circumstances be considered a noise level for the system, although it will be appreciated that there are many different contributions within a system that may affect the overall background level.
In a first embodiment the first and second layers have the same refractive index. In an alternative embodiment, the first and second layers have a different refractive index.
In one embodiment, the light may be emitted into the substrate from more than one source and the detector arrangement is adapted to spatially discriminate between the origins or sources of the detected light.
Typically, the configuration includes at least one portion of capture material adapted to capture a specific target species, the at least one portion of capture material being coupled to the substrate and adapted, in use, to capture any of a predefined target substance within the medium, the capture or tagging effecting the formation of a captured species, which either directly or indirectly is adapted to luminescence upon excitation, such luminescence being detectable by the detector.
The captured species or material may be directly capable of luminescence or may require a subsequent combination with a further material to effect the formation of a luminescent source, thereby forming an indirect source of luminescence.
In certain embodiments at least two distinct portions of capture material are provided, each portion being coupled to the substrate and wherein the substrate is configured to redirect light emitted by each portion towards the detector such that the light received at the detector from a first portion is spatially independent from the light received at the detector from a second portion.
The light detected by the detector may be detected without undergoing total internal reflection within the substrate prior to detection.
Desirably, the detector arrangement includes at least one optical redirection element at either an upper or lower surfaces of the substrate, the optical redirection element adapted to redirect light emitted by the luminescent material into the substrate at an angle greater than the critical angle out of the substrate and towards a detector.
This at least one optical redirection element may be adapted to redirect the light using total internal reflection.
A plurality of optical redirection elements may be provided, each element comprising a frusto-conical structure raised above the upper surface of the substrate, each frusto-conical structure having side walls and an upper surface, luminescent material being carried on the upper surface of the structure, and wherein light emitted by the material into the structure is internally reflected by the side walls of the structure and directed towards a detector positioned beneath the substrate.
Alternatively, a plurality of optical redirection elements, each element in the form of a ridge raised above the upper surface of the substrate and extending along the upper surface of the substrate may be provided, the ridge having side walls and an upper surface, luminescent material being carried on the upper surface of the ridge, and wherein light emitted by the material into the ridge is internally reflected by the side walls of the ridge and directed towards a detector positioned beneath the substrate.
The at least one optical redirection element may be adapted to redirect the light using refraction. Such an element may be in the form of one or more prisms optically coupled, or integral, to a lower surface of the substrate, the prism being adapted to receive light incident on the lower surface of the substrate and redirect that light sidewardly towards a detector.
In another embodiment the at least one optical redirection element is adapted to redirect the light using diffraction, which may be provided by a diffractive optical element provided at the lower surface of the substrate.
The lower surface of the substrate may be structurally configured to both reflect and refract light radiated into the substrate, the reflection and refraction of the light effecting a redirection of light towards a detector, the light redirected being that light having propagating within the substrate at an angle greater than the critical angle of the substrate/medium interface.
The selective detection of light may be effected by providing the substrate with non-parallel upper and lower surfaces, the angle of the upper and lower surfaces being such that the light emitted by the luminescence material is incident on the surfaces at angles greater than the critical angle of the substrate/medium interface, thereby effecting a propagation of light along an axis of the substrate towards a detector.
The sensor configuration may be further modified so as to detect light radiated into the substrate by the luminescent material at angles which are not less than the critical angle of the luminescent material/substrate interface and greater than the critical angle of the medium/substrate interface.
The detector is desirably a CMOS, a CCD or a photodiode type detector, which can be located at a specific location below the substrate.
The sensor may be provided initially with a bio-recognition element, the bio-recognition element being sensitive to and adapted to couple with a compatible biological sample of preselected variety in the medium with which the sensor is used. In such element types, a combination of the bio-recognition element with the preselected sample variety effects the formation of a material capable of luminescence. In other element types, a sandwich assay is formed by a further coupling of the coupled biological sample/bio-recognition element with a luminescent tag or label to effect the formation of the luminescent material.
The invention arises out of our analysis of the radiation of dipoles placed above a higher refractive index substrate which reveals that the luminescence exhibits strong spatial anisotropy, with significantly greater amounts of luminescence radiated within a certain interval of angles. It has been appreciated by the present inventors that a significant amount of luminescence is radiated into the higher refractive index substrate at angles greater than the critical angle of the substrate/superstrate interface. Thus, in most substrates, a significant amount of the luminescence is radiated into the substrate and is trapped there. Accordingly, the idea is to provide a range of configurations which exploit these findings and ensures that the luminescence, instead of being trapped permanently within the substrate, is transmitted out of it for subsequent detection and measurement.
Our analysis of the radiation of dipoles placed above a higher refractive index substrate also reveals that the luminescence originating from molecules which are located further away from the substrate/superstrate interface than some specific distance, denoted by ts, cannot propagate within the substrate at angles greater than some specific angle, denoted by θs. However, the luminescence originating from molecules which are located within the distance ts above the substrate/superstrate interface can emit light which is propagating in the substrate at angles greater than θs.
In one embodiment of the invention, the luminescence-based sensor is so arranged that the light is directed through the exit surface substantially normally-thereto.
In another embodiment of the invention, at least either the upper surface mounting the emitter or the lower surface of the substrate is not planar. If planar, the surfaces are not parallel.
In one embodiment of the invention, the interfaces of the substrate are so configured that the internal reflection at the interface on which the light impinges is substantially prevented and allows the light to be transmitted through the substrate.
In another embodiment of the invention, the interfaces of the substrate are so configured that the light is reflected from at least one interface before being directed out of the substrate to the detector.
The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which:—
FIGS. 2(A) and (b) are side views showing the effect of light generated at different distances from the surface of a substrate.
a and 3b are side views of luminescence-based sensor assemblies according to the invention.
a to 15d show modified structures for detecting luminescence according to embodiments of the present invention.
The thickness t1 of the layer forming the spot is assumed to be uniform and typically in the range of hundreds of nanometres. Typically, the dimensions of such a spot are determined by the application and will be defined by the user. Furthermore, for simplicity, the size of the spot is assumed to be small compared to the size of the area of the detection system, which is used to detect the luminescence produced by the spot. The latter restriction is assumed only to ensure that the luminescent spot “appears” to the detector as a spot rather than as an area over which the radiated intensity would have to be integrated. Consequently, the lateral (x-y) dimensions do not have to be considered and only the angular dependence of the radiated intensity needs to be taken into account in the following analysis. The luminescent spot is assumed to be covered by the environment, which is either air (na=1.0) or water (nw=1.33). The slide is surrounded by air from below.
The predicted angular distribution of the luminescence emerging from the small luminescent spot deposited on the glass substrate is shown in
The situation is similar when the detector is placed below the glass substrate. Due to reflections taking place at the bottom glass/air interface, the light impinging at this interface is transmitted to air only if the incident angle lies within the angular range θε−θcas,θcas, where θcas=arcsin(na/ns)≈413° is the critical angle of the substrate (glass)/air interface. This light is schematically depicted by the dashed arrows 330. Due to the refraction, the light propagating inside the substrate at angles θε−θcas,θcas is partially transmitted into the air under the substrate at angles θε−90°,90°. The solid 300 and dashed 310 lines within the angular range θε−θcas,θxas demonstrate that the amount of luminescence transmitted to air below the glass substrate is also relatively small.
The light propagating inside the substrate at angles greater than the critical angle θcas is totally internally reflected t the lower substrate/air interface. If the environment covering the slide is air, as shown in
The above analysis of the radiation properties of light propagating indicates that the propagation of the light within the substrate is independent of the way the radiation was excited. It will be understood therefore that any type of excitation, which would provide the same spatial distribution of the radiating molecules, would result in the same characteristics of the radiated luminescence.
Referring to
Referring now to
Referring to
If one assumes the luminescent source to behave as a radiating dipole such as what is described in Polerecky et al (Applied Optics 39 (22): 3968-3977 Aug. 1, 2000), it can be shown that the angular distribution of the intensity of the light radiated below the critical angle does not appreciably change with the distance of the dipole from the substrate.
As can be seen from the graphs in
Furthermore, a peak starts emerging at θ≈110° for greater values of td. Although the present invention is not intended to be limited to any one specific theory it is thought that this is due to interference of the luminescence radiated directly into the environment and that reflected from the environment/substrate interface. The number of these peaks, which form a fringe-like pattern in the angular distribution of the intensity, would increase with increasing distance td (not shown in the Figure).
The most significant changes in the intensity profile are observed within the angular range θεθces,90°, where θces is either θcas=41.3°or θcws=61.3°, depending on whether the environment is air or water, respectively. In particular, the intensity fall-off above the critical angle is more abrupt for greater distances td. Furthermore, for a distance as low as td=0.5λ, there is almost no luminescence radiated above the critical angle θces, as shown by the dash-dotted line. These important features can be explained as follows. The electromagnetic field, which propagates in the glass substrate at angles θεθces,90° is exponentially decreasing in the environment. A characteristic penetration depth of this so-called evanescent field is approximately λ and it decreases with the increasing propagation angle θ. Because the luminescence at these angles is provided by coupling of the dipole's near-field with the evanescent field, it is understandable that its intensity is decreasing for increasing θ. Moreover, for a sufficiently large distance of the dipole from the surface, the evanescent field does not reach the dipole's position. This implies that there is very little luminescence radiated above the critical angle for such large distances due to a weak coupling of the evanescent field and the dipole's near-field, as concluded above.
The above description was with reference to a single radiating dipole provided at various distances above a substrate.
Notable changes are observed at angles θεθces,θcis; where θxis=arcsin(n1/ns)≈70.7° is the critical angle of the layer/substrate interface. Within this angular range, the angular distribution of intensity exhibits a distinct peak. This peak is more pronounced and shifted towards θcis for greater values of the thickness of the dipole layer. Furthermore, at these greater thickness', the sharp peak is accompanied by several less significant peaks, which “emerge” from the angular position determined by θces. This is demonstrated by the dash-dotted line in
The behaviour of the radiated intensity described above can be qualitatively understood by considering the following arguments. The electromagnetic field, which corresponds to the modes propagating in the glass substrate at angles θεθces,θcis is propagating within the dipole layer. Due to interference effects caused by the reflections at the substrate/layer and layer/environment interfaces, the magnitude of the field can be considerably enhanced for a certain value of the angle θ. The coupling efficiency between the near-field of the dipoles inside the layer and the far-field propagating in the glass is proportional to the magnitude of the field inside the dipole layer. Therefore, the enhancement of the radiated intensity at a particular angle θ is a consequence of the enhancement of the field corresponding to the modes propagating at this angle.
The angular dependence of intensity of the luminescence radiated into the glass substrate is shown in
In particular, the field corresponding to the intensity observed at these angles is evanescent in the buffer layer. When the thickness of the buffer layer is sufficiently large, the field barely reaches the luminescent layer, which decreases the coupling efficiency between the near-field of the radiating dipoles and the radiated field. Consequently, the amount of luminescence propagating in the glass substrate at angles θ>θcis is very small for greater values of tb.
Firstly, it is considered that the sol-gel layer does not and the bulk layer does contain luminescent molecules, as shown in
On the other hand, the contribution of the bulk layer to the luminescence observed within the angular range θεθcws,θcis is small and does not significantly change when the bulk layer thickness exceeds the value of approximately 4λ, as demonstrated by the dash and dash-dotted lines in
If one considers the opposite case, i.e. where the sol layer does and the bulk layer does not contain luminescent molecules, which is shown in the example of
In the scenario where both the sol gel layer and the bulk layer contain luminescent material and assuming that both the layers have equal densities of molecules, as is shown in
It will thus be appreciated that the graph demonstrates that it is possible to distinguish between the contributions originating from the doped sol-gel layer and the luminescent bulk layer. This is due to the fact that these two contributions are observed within different angular regions. In particular, the main contribution originating from the bulk layer is radiated at angles below the critical angle θcws, while the main contribution originating from the thin sol-gel layer is observed at angles above the critical angle θcws. Although the distinction between the two contributions is not sharp around the critical angle θcws, there is a definite angle, denoted by θtr, above which the contribution originating from the bulk layer is negligible in comparison to the contribution originating from the sol-gel layer. The value of this angle can be determined by combining this analysis and the background signal characteristics of the particular detection system. It will therefore be appreciated that by applying the technique of the present invention that it is possible to discriminate in the light detected at a detector where that light originated, i.e. whether it is due to luminescence of luminescent molecules in a region close to the substrate interface or whether it is due to the luminescence of the molecules outside that region.
To explain this behaviour, the contributions originating from the surface and bulk layers are plotted separately.
This is shown in
Using the technique of the present invention it is possible to distinguish between surface bound and bulk molecules which are luminescently labelled, which is of particular interest to biosensors. This has specific application in such biosensors in order to discriminate between surface-bound and bulk molecules which are luminescently labelled.
Using such an ability to distinguish the origin of the luminescence enables the present inventors to provide a method and technique which is adapted to enable detection of the luminescence originating from a region adjacent to the substrate interface and excited by a direct illumination. The thickness of the region of interest, which is in the order of the luminescence wavelength λ, can be tailored according to the needs of a particular application.
In the following analysis, the substrate is considered to be made of glass (ns=1.515) and the environment containing the luminescent species is water (nw=1.33). Similar conclusions can be, however, drawn for any other set of parameters, as will be apparent to those skilled in the art. As was detailed above the detection of the luminescence originating from a thin layer adjacent to the (glass) substrate, i.e., the surface layer, can be achieved by measuring a specific fraction of the luminescence, in particular that propagating in the (glass) substrate above the threshold angle θtr. This conclusion is demonstrated in
Is(θtr)/Ib(θtr)>Ftr
Accordingly θtr can be defined as that angle which provides for the left-hand and right-hand sides of the above equation to be equal and the configurations developed in this application use the detection of light above this angle.
It will be appreciated that in most practical applications, the intensity of luminescence is always characterised by some non-zero background signal. These background signals may have contributions from electronic and other sources of noise, and represent a threshold value above which it is possible to detect a signal. Therefore, the value of θtr can be chosen in such a way that Ib(θtr) within the above equation corresponds to this background level. Consequently, the definition above is simply a formal expression of the requirement that the signal-to-background ratio of the measurement of the luminescence originating from the surface layer be greater than some specified value Ftr. This also justifies the definition of θtr given by the equation. It can be seen from
It will be appreciated that the choice of threshold angle is dependent on the configuration parameters but also on the confidence factor that is required by the user. This choice of threshold angle is provided by an analysis of the values of the threshold angles required to ensure that only the luminescence from within the surface layer is detected. As was detailed above this is provided by an examination of the values provided by the graphical output of
It will be appreciated that this initial definition of the optical properties of the system configuration enables one to perform a calculation of the angular distribution of the radiated luminescence. Once this distribution is calculated, the value of the thickness t1 is chosen, according to the requirements of the application, the performance factor is chosen and then the threshold angle can immediately found.
As follows from the curves in
It is important to emphasise that the excitation of luminescence was not mentioned in the above analysis at all. This is because the angular properties of the emitted luminescence, which are exploited in this technique, are independent of the way how the luminescent molecules are excited. Therefore, it is possible to use direct illumination for efficient excitation of the molecules while detecting the luminescence originating specifically from a close vicinity of the surface. This is what makes this technique very attractive.
It will be appreciated that application of the technique of the present invention enables one to extract information from areas where the luminescence of interest is that generated specifically by the molecules located in close vicinity to the surface. In particular, the present invention provides a method for the detection of such luminescence. In contrast to the conventional method that employs evanescent-wave excitation, this method enables one to use direct illumination to excite the luminescent molecules. The distinction between the luminescence radiated by molecules located in the bulk and near the surface is achieved by the measurement and appropriate treatment of the angular profile of luminescence intensity. In particular, by measuring the emitted luminescence above a certain threshold angle θtr, only the luminescence originating from molecules located closer to the surface than some corresponding distance ts is detected. Taking into account that the excitation by direct illumination is much more efficient than that provided by the evanescent-wave excitation technique, for reasons including that more of the emitted light from the light source can be used for exciting the luminescence material, the method of the present application can be particularly attractive in immunosensing applications.
It will be appreciated that the above description identifies that, using the method of the present invention, it is possible to differentiate between the source of luminescence, i.e. that it is possible to discriminate between light originating directly or indirectly from a captured material or that originating from some spurious signal within a bulk layer, based on an angular orientation of the detector relative to the tagged material. The present invention however also provides for a modification of the substrate to which the tagged material is optically coupled so as to enable the specific out-coupling of light radiated into the substrate at angles greater than the threshold angle to a suitably positioned detector.
a to 15d illustrate exemplary embodiments of the present invention and show how a sensor configuration can be arranged so as to specifically outcouple the light of interest.
In the embodiment of
The embodiment of
Referring now to
Accordingly it will be appreciated that the present invention provides a technique for the collection of surface generated luminescence excited by direct illumination. The ability to discriminate by origin of the luminescence enables the use of such direct illumination, which is advantageous in that the sensitivity of sensor arrays utilising such techniques can be increased due to higher levels of illumination than hereintobefore possible.
In the specification the terms “comprise, comprises, comprised and comprising” or any variation thereof and the terms “include, includes, included and including” or any variation thereof are considered to be totally interchangeable and they should all be afforded the widest possible interpretation.
It will be further appreciated that the invention is not limited to the embodiments hereinbefore described but may be varied in both construction and detail. Furthermore, although certain embodiments may have been described with reference to specific integers or components it will be appreciated that individual components from different embodiments may be interchangeable depending on the desire of the user without departing from the scope of the present invention. It will ne further appreciated that although the present invention has been described with reference to specific substrate or medium (fluid) types, that it is not intended to limit the present invention to these specific exemplary embodiments of the invention.
Number | Date | Country | Kind |
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S2001/0825 | Sep 2001 | IE | national |
S2002/0041 | Jan 2002 | IE | national |
S2002/0553 | Jul 2002 | IE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IE02/00133 | 9/11/2002 | WO |