IMPROVEMENTS IN OR RELATING TO AN OPTICAL ELEMENT

Abstract

An assay cartridge for detecting a target component in a fluid is provided. The assay cartridge including an optical element comprising: a light pathway comprising an input surface, reflective surface and output surface configured to enable light to enter, reflect and create an evanescent field in the vicinity of the reflective surface and exit the element; a plurality of capture components deposited on the reflective surface in the vicinity of the evanescent field; and a transmission surface configured to enable emissions from the evanescent field to exit the element; wherein the assay cartridge is a single use cartridge.

Claims

1. An assay cartridge for detecting a target component in a fluid, the assay cartridge including an optical element comprising: a light pathway comprising an input surface, reflective surface and output surface configured to enable light to enter, reflect and create an evanescent field in the vicinity of the reflective surface and exit the element; a plurality of capture components deposited on the reflective surface in the vicinity of the evanescent field; and a transmission surface configured to enable emissions from the evanescent field to exit the element; wherein the assay cartridge is a single use cartridge.

2. The assay cartridge according to claim 1, wherein the single use nature of the cartridge is implemented through physical constraints.

3. The assay cartridge according to claim 2, further comprising a one way clip to ensure that the cartridge is single use.

4. The assay cartridge according to claim 1, wherein the single use nature of the cartridge is implemented through chemical constraints.

5. The assay cartridge according to claim 4, further comprising an irreversible spot to ensure that the cartridge is single use.

6. The assay cartridge according to claim 1, wherein the single use nature of the cartridge is implemented through data management.

7. The assay cartridge according to claim 6, further comprising an identity tag to ensure that the cartridge is single use.

8. The assay cartridge according to claim 7, wherein the identity tag is printed onto the cartridge.

9. The assay cartridge according to claim 7 or claim 8, wherein the identity tag is selected from a group including a barcode or a QR code.

10. The assay cartridge according to claim 7, wherein the identity tag is an RFID tag.

11. The assay cartridge according to any one of claims 1 to 10, wherein the emissions from the evanescent field are Mie, Raman or Rayleigh scattering.

12. The assay cartridge according to any one of claims 1 to 11, wherein at least one of the capture components is DNA or an antibody or a protein.

13. The assay cartridge according to any one of claims 1 to 12, wherein the fluid is saliva.

14. A method of fabricating an array of assay cartridges each cartridge being an assay cartridge according to any one of claims 1 to 13, the method comprising the steps of: fabricating a plurality of optical elements through the steps of: heating a preform to a temperature equal to or exceeding the glass transition temperature of the preform; drawing the preform into an elongate strand; and dividing the strand into a plurality of optical elements; mounting at least one optical element in each assay cartridge; and depositing at least one capture component on the reflective surface of each optical element.

15. The method according to claim 14, wherein the dividing of the strand into a plurality of optical elements involves cleaving the strand.

16. The method according to claim 14, wherein the dividing of the strand into a plurality of optical elements involves processing the strand with a laser.

17. The method according to claim 14, 15 or 16, wherein the dividing of the strand occurs perpendicular to the direction in which the preform is drawn.

18. The method according to claim 15, wherein the cleaving step takes place alternately from each side of the strand so that each optical element has a trapezoidal cross section.

19. The method according to any one of claims 14 to 18, wherein the assay cartridge includes a plurality of optical elements.

20. The method according to any one of claims 14 to 19, wherein the depositing of the capture component occurs by printing.

Description

[0074] The invention will now be further and more particularly described, by way of example only, and with reference to the accompanying drawings, in which:

[0075] FIG. 1 provides an optical element according to an aspect of the present invention;

[0076] FIG. 2 shows a cuboid optical element;

[0077] FIG. 3 shows a dove-prism optical element,

[0078] FIG. 4 shows diffraction grating at an input and/or output surface of the optical element according to FIG. 1;

[0079] FIG. 5 shows the diffraction grating at a transmission surface of the optical element according to FIG. 1;

[0080] FIG. 6 shows the optical element according to FIG. 1 with reflection grating;

[0081] FIG. 7 shows the optical element according to FIG. 1 with a Fresnel lens structure;

[0082] FIG. 8 provides an illustration of a waveguiding scenario using the optical element according to FIG. 1;

[0083] FIG. 9 shows the optical element according to FIG. 1 with a non-planar transmission surface;

[0084] FIG. 10 shows an apparatus set up according to an aspect of the invention;

[0085] FIG. 11 shows the apparatus according to FIG. 10 with a spatial filter;

[0086] FIG. 12A provides an illustration of the spatial filter arrangement;

[0087] FIG. 12B provides an alternative illustration of the spatial filter;

[0088] FIG. 13 provides a graph showing the signal to background ratio of the optical element according to FIG. 1; and

[0089] FIG. 14 provides a graph showing a comparison between two test cartridges; and

[0090] FIG. 15 shows a cross sectional view of a cartridge incorporating to optical element of FIG. 1; and

[0091] FIG. 16 shows, schematically the steps in the method of fabricating a plurality of optical elements according to the present invention;

[0092] FIG. 17A shows, schematically, a preform prior to the drawing process that forms part of the method illustrated in FIG. 16;

[0093] FIG. 17B shows, schematically, an elongate strand following the drawing process that forms part of the method illustrated in FIG. 16;

[0094] FIGS. 18A and 18B provide, respectively, side and top views of a single optical element fabricated in the method illustrated in FIG. 16;

[0095] FIGS. 19A and 19B show, respectively top and side views of a chip containing the optical element illustrated in FIGS. 18A and 18B;

[0096] FIG. 20A shows a top view of the chip with multiple optical elements; and

[0097] FIG. 20B shows a front view of the chip according to FIG. 20A.

[0098] Referring to FIGS. 1 to 7, there is provided an optical element 10 comprising a light pathway 12 comprising an input surface 14, a reflective surface 16 and an output surface 18. The input surface 14 enables light 12, such as an incident light beam, to enter into the optical element 10. The input surface 14 and/or the output surface 18 can be a refractive or a diffractive or a transmissive surface. In some instances, the incident light beam is refracted at the input surface 14 upon entry into the optical element 10. The light is directed towards the reflective surface 16 where one or more capture components 22 such as antibodies are deposited onto the reflective surface 16. The capture components are directly printed onto the reflective surface 16 of the optical element 10, as shown in FIG. 1.

[0099] Referring to FIGS. 1 to 7, the reflective surface 16 is able to reflect the light 12 by total internal reflection. As the light reaches the reflective surface 16, the light can be configured to excite the capture components 22. This may cause the capture components 22 to emit light at a specific wavelength. The light may undergo a single reflection or it may undergo multiple reflections at the reflective surface 16. As shown in FIGS. 1 to 7, there is provided a transmission surface 20 which is configured to enable emissions from the capture components 22 to exit the element 10. The transmission surface 20 can be a diffractive, or a refractive or a non-planar surface. The emissions from the capture components may be luminescence for example, fluorescence or phosphorescence. The reflected light 12 can exit the optical element 10 through the output surface 18.

[0100] Referring to FIGS. 1 to 3, the optical element 10 may be in a prism form, or a dove prism or a cuboid or any other suitable configuration to enable light to enter, reflect and exit. The optical element can be made from plastic, polymer or glass or any other suitable materials.

[0101] As shown in FIGS. 1 and 2, the prism- or cuboid-optical element 10 introduces an incident light beam 12 for a single reflection at the reflective surface 16, where the target components 22 are deposited, through an angular change resulting from refraction. Alternatively, the prism-optical element 10 may introduce an incident light beam 12 for a single reflection at the reflective surface 16 without an angular change resulting from refraction, as shown in FIG. 3.

[0102] Referring to FIG. 4, there is provided at least one diffraction grating 28 at the input surface 14 or at the output surface 18 or both. Depending on the location and required path of the light, the diffraction grating 28 may work in transmission or reflection. The diffraction grating 28 may be configured to diffract the light into several beams travelling in different directions. As an example, the diffraction grating 28 located at the input surface 14 may diffract the incident light beam as it enters into the optical element 10. In some embodiments, the diffraction grating can be used to diffract the incident light beam onto the reflected surface 16. In another example, the diffraction grating 28 can diffract the reflected light at the output surface 18. As shown in FIG. 4, the optical element 10, which may be a cuboid optical element, introduces an incident light beam 12 for a single reflection at the reflective surface 16 through an angular change resulting from a diffraction grating 28 working in transmission. Referring to FIG. 5, there is provided at least one diffraction grating 28 located at the transmission surface 20.

[0103] Referring to FIG. 6, there is shown an optical element 10 which introduces an incident light beam for a single reflection at the reflective surface 16 through an angular change resulting from at least one diffraction grating 28 working in reflection. The diffraction grating 28 is provided in order to reflect the light within the optical element 10. In some embodiments, the diffraction grating may be configured to provide total internal reflection of the light. The diffraction grating 28 can be positioned at the output surface 18 as shown in FIG. 6. Additionally or alternatively, the diffraction grating may be provided at the input surface and/or at the transmission surface of the optical element.

[0104] In an alternative embodiment, not shown in the accompanying drawings, the light beam takes a similar path to that illustrated in FIG. 6, but the reflection comes not from a grating, but from a reflective surface provided by a reflective material being applied to the surface of the optical element. In some examples, this is a silvered surface.

[0105] The input surface 14 may have a number of different functionalities as illustrated in FIG. 6. In some instances, the input surface 14 may be configured to allow an incident light beam to enter 24 into the optical element 10 as well as enabling the incident light beam to exit 26 from it. Additionally or alternatively, the output surface 18 may be configured to allow an incident light beam to exit the optical element as well as enabling the incident light beam to enter the optical element. In some embodiments, not illustrated in the accompanying drawings, wherein the optical element is triangular in cross section, the transmission surface 20 may act as an input surface and/or an output surface of the optical element. For example, the transmission surface 20 may be configured to enable light to enter and/or exit the optical element.

[0106] Referring to FIG. 7, there is provided an optical element 10 which introduces an incident light beam for a single reflection at the reflective surface 16 through an angular change resulting from an optical lens structure i.e. a Fresnel lens structure 32 located at the transmission surface 20. The incident light beam enters 24 at the transmission surface 20 and through the Fresnel lens structure 32, where the light is directed towards the reflective surface 16. The light then undergoes total internal reflection at the reflective surface 16. The incident light beam is able to exit 26 at the transmission surface 20 through the Fresnel lens structure 32. Moreover, the Fresnel structure 32 could be fabricated more readily with an optical element made from a polymer than with an optical element made from glass.

[0107] Referring to FIG. 8, there is provided an optical element 10 to enable light to enter 24 and exit 26. The optical element 10 comprises a reflective surface 16 where the target components 22 are deposited. FIG. 8 shows a waveguiding scenario.

[0108] As shown in FIG. 9, there is shown an optical element 10 with a non-planar transmission surface 20. The non-planar surface 20 can be utilised to aid with light collection or imaging applications. This may be particularly useful for optical elements constructed from polymer, since complex volumes can be fabricated with much greater ease and lower cost compared with optical elements made from glass.

[0109] The optical element as shown in FIGS. 1 to 9 can form part of an assay cartridge for detecting a target component in a biological fluid such as a saliva or urine or whole blood, plasma or serum sample. The capture component deposited on the reflective surface of the optical element may be selected to capture the target component to be detected. Additionally, the optical element may be disposable that is intended to be used once or a few times.

[0110] In some embodiments, the reflective surface of the optical element may be configured to form a portion of a microfluidic flow channel. The target component, which may be in a liquid form, can be deposited directly via printing directly onto the reflective surface of the optical element. In some embodiments, the capture components can be premixed with detection reagents prior to being directly deposited onto the reflective surface. In some embodiments, the receptor molecules may be deposited onto the reflective surface. Additionally or alternatively, the reagents and receptor molecules can be deposited onto the reflective surface, or the detection reagents and the receptor molecules can be deposited onto the reflective surface within diffusion distance.

[0111] In addition, the reflective surface of the optical element may further comprise one or more solid layers e.g. polymer film or glass plate, ports, wells, channels, chambers, valves, pumps, heaters or electrodes. Such structures may be integrated into the reflective surface of the optical element and/or in one or more material layers on the reflective surface of the optical element.

[0112] The optical element and/or the solid layers can be fabricated using moulding e.g. injection moulding, soft lithography or replica moulding, hot embossing, or nanoimprint lithography, 3D printing e.g. stereolithography, photocuring of inkjet-printed droplets, fused deposition modelling, or two-photon polymerisation, micro- or nanofabrication e.g. photolithography or electron beam lithography, anodic aluminium oxidation, laser-cutting, laser ablation, and/or machining.

[0113] Any of the solid layers on top of the reflective surface of the optical element may be assembled or laminated using one or any combination of contact pressure, heat, adhesive, and/or surface activation (ultra violet (UV)/ozone/plasma). Materials through which the laser beam passes are preferably of similar refractive index.

[0114] For a typical bioassay, the capture components may need to be deposited onto the reflective surface in an evanescent region, on an interface that is part of the optical element or part of a solid layer above the optical element; reagents may be disposed on a wall or porous medium in a fluid path upstream of the receptors. Methods for depositing or dispensing capture components, and/or receptors may include, but is not limiting to, noncontact deposition e.g. inkjet and/or contact deposition e.g. using dip-pen lithography, capillary tubes, spilt pins or ink stamps. Additionally or alternatively, capture components may be deposited or dispensed or printed directly onto untreated surfaces of the optical element. In some embodiments, it may be beneficial or required to prepare surfaces of the optical element through functionalisation such as using silanisation and/or activation e.g. using UV/ozone.

[0115] Additionally or alternatively, functionalisation may be used to immobilise capture components or to passivate the surfaces e.g. reflective surface of the optical element using bovine serum albumin and/or polyethylene glycol, in order to prevent non-specific binding.

[0116] Referring to FIG. 10, there is provided an apparatus 40 for detecting the presence and/or the amount of a target component 22 in a biological fluid. The apparatus 40 comprising an assay cartridge including an optical element 10 and a detector 42 for detecting the presence and/or the amount of the emitted light to provide an indication of the presence and/or the amount of the target component 22 within the sample. In addition, there is provided an imaging lens 44, which may be located between the optical element 10 and the detector 42. In some instances, one or more imaging lens may be provided. The imaging lens 44 can be used to focus the emitted light from the target components onto the detector 42, as shown in FIG. 10.

[0117] FIG. 11 shows the apparatus 40 with the optical element. Emissions such as fluorescence emissions from the target components 22 exits through the transmission surface of the optical element. A first imaging lens 44 is provided and may be configured to focus the emitted light onto an aperture 46 i.e. a spatial filter. The inclusion of a spatial filter could be utilised to eliminate out-of-plane signals e.g.

[0118] out-of-plane fluorescence signals. A second imaging lens 48 is provided which may be configured to focus the remaining emission signal i.e. in-plane fluorescence signal onto the detector 42 e.g. a CCD to form an image of the sample.

[0119] FIGS. 12A and 12B demonstrate how the spatial filter 46 can significantly reduce or eliminate out-of-plane fluorescence signals. FIG. 12A shows that the fluorescence signal derived from the target component can be directed by an imaging lens 44 onto the spatial filter (aperture) 46. The light directed towards the spatial filter as shown in FIG. 12A can be referred to as in-plane fluorescence. In this example as illustrated in FIG. 12A, all the fluorescence from the target component is able to pass through the spatial filter 46 to be detected by the detector 42 to provide data of the target component.

[0120] As shown in FIG. 12B, the fluorescence signals coming from the optical element 10 are out-of-plane. As a result, the out-of-plane fluorescence contributes to the background and/or noise level and therefore reduces the signal-to-background and/or signal-to-noise ratio. Therefore, the spatial filter 46 as shown in FIG. 12B is configured to eliminate out-of-plane fluorescence and consequently only a fraction passes through the spatial filter (aperture) 46. Eliminating the out-of-plane fluorescence may result in an improved signal-to-background and/or signal-to-noise ratios.

EXAMPLE 1

Prism-Based Optical Element

[0121] FIG. 13 shows the measured signal-to-background ratio measured for four cartridges on both an exemplary end-launched (non-prismatic optical element) and a prism-based optical element system. As shown in FIG. 13, a prism-based optical element system resulted in a higher signal-to-background ratio, leading to a more sensitive configuration.

[0122] This data compares a specific end-launched configuration that deployed a cost efficient substrate that was readily available. It is not possible to generalise the conclusions from this data set to all end-launched configurations. In this specific experiment, the signal-to-background ratio is higher in the prism-based configuration by a factor of between 20 and 40. Without being bound to a specific theory, it is believed that the prism configuration performs better because when the incident light beam undergoes total internal reflection at a boundary between two different optical media, an evanescent field is generated in the lower refractive index medium, exciting fluorophores in close-proximity i.e. within a few hundred nanometres of the surface. However, a fraction of light is also scattered at the reflective surface, therefore contaminating the pure evanescent field, penetrating through the sample solution resulting in background luminescence from luminophores in solution.

[0123] Another source of background is autofluorescence from the optical element that the incident light travels through. It is useful to consider the fraction of light intensity that contributes to the desired evanescent field compared to the fraction of light intensity which generates unwanted autofluorescence. This is defined as the evanescence-autofluorescence ratio. The prism optical element is capable of generating an evanescent field with little or no scattered light contamination, owing to the fact that only a single reflection is undergone at a high-quality reflective surface, compared to waveguiding where in effect multiple reflections occur, with each one generating a scattered component. Additionally, during waveguiding a fraction of the light energy can scatter to higher angles such that they are no longer guided by waveguide and are outside the critical angle. This unguided light will travel straight through the sample solution and will thus contribute to the background. Furthermore, due the optical confinement of the waveguiding configuration, the prism optical element configuration has an inherently higher evanescence-autofluorescence ratio. The data presented in FIG. 13 are based on a prism interfaced with a microscope slide using index-matching material.

EXAMPLE 2

Single Use Optical Element

[0124] FIG. 14 shows a comparison between two testing cartridges based on microscope slides prepared in the same manner. One cartridge can be removed and replaced between each measurement, whilst the other can be kept directly on the reflective surface of the prism optical element for all measurements. It is reasonably expected that the fluorescence signal would decay with increasing numbers of measurement due to photobleaching of the fluorophores. It is shown in FIG. 14 that the signal from the cartridge that was kept on the prism decayed in a smooth fashion, whilst the signal from the cartridge that was removed and replaced between each measurement decayed in a less consistent manner.

[0125] A possible route to alleviate this issue can be to develop a deformable polymer layer on the prism to provide index-matching. The microscope slide component of the cartridge could be pressed into the polymer, which would deform to provide optical contact. However, developing such a polymer with all the required properties i.e. refractive index, optical quality, elastic properties and low autofluorescence, is a considerable task and still suffers from some of the issues that plague index-matching fluids, i.e. cleanliness, contaminants and would additionally come with a lifetime which may prove to be problematic. An alternative route is to provide the prism optical element (or similar optical element) as the consumable single-use optical element. This would negate the issues with index-matching materials since they would no longer be required.

[0126] Referring to FIG. 15, there is provided a cartridge 10 comprising a sample management module 11 for collecting a fluid sample. The sample is a liquid sample such as a saliva sample.

[0127] The sample management module 11 further comprises a lid 22. The lid is provided with a clip 23. The clip 23 is opening resistant such that, under normal conditions, the user is not easily able to re-open the lid once it has been closed. The lid 22 can be closed via action by the user or by any other means.

[0128] Referring to FIG. 16, there is provided a preform 100 within a heating chamber 102. The preform 100 can be drawn, typically in a downward direction 104 into an elongate strand 116. The drawing of the preform 10 in a downward direction 114 can be influenced by gravity, or by the use of an actuator. In some instances, pressure may also be applied to draw the preform in a downward direction. The elongate strand 116 can be divided into a plurality of optical elements 118. As shown in FIG. 16, dividing the elongate strand 116 may involve cleaving the strand using a cleaving apparatus or it may involve processing which can be carried out by a laser 120, which may be a CO.sub.2 laser.

[0129] The preform 100 may be made from any material such as glass or polymer. In some instances, fused silica is a desirable material for the preform since it exhibits low auto-fluorescence properties.

[0130] The preform 100 can be held in the heating chamber 112 such as a furnace on a drawing tower, which is typically several meters tall. The preform 110 is heated by the furnace to a temperature equal to or exceeding the transition temperature of the preform. For example, silica has a transition temperature around 2000° C., whereas some polymers have transition temperatures around 300° C. The preform can be heated to a temperature at or slightly above the transition temperature, but below the crystallisation temperature, as this will facilitate the drawing of the preform 110 into an elongate strand 116.

[0131] The elongate strand 116 may then be attached to a rotating drum or caning machine at the bottom of the tower (not shown in the drawings), which can be set to pull the elongate strand down at a controlled and specified rate. Control of the pulling and feeding rates may give accurate control over the dimensions of the elongate strand. The elongate strand can then be spooled onto the drum and transferred to a bobbing for storage. Alternatively, the elongate strand be cut at appropriate lengths and stored in a long glass capillary tube.

[0132] Referring to FIGS. 17A and 17B, there is provided a preform 100 and an elongate strand 116. As shown in FIG. 17A, the preform may have a larger side length than the elongate strand. Referring to FIG. 17A, the preform has a square cross section and the side length of the preform may be between 50 mm to 100 mm, or it may be more than 10, 20, 30, 40, 50, 60, 70, 80 or 90 mm. In some embodiments, the side length of the preform may be less than 100, 90, 80, 70, 60, 50, 40, 30 or 20 mm. For example, the depth and/or width of the preform may be 50 mm. A rectangular cross section preform may also be utilised with each side falling within the ranges exemplified above for a square cross section preform.

[0133] In some embodiments, the height of the preform can be 100 to 1000 mm, or it may be more than 100, 200, 300, 400, 500, 600, 700, 800 or 900 mm. In some embodiments, the height of the preform may be less than 1000, 900, 800, 700, 600, 500, 400, 300 or 200 mm. For example, the height of the preform is 500 mm.

[0134] The preform can be of any shape such as a square, circle or rectangle. The cross section dimension of the preform may be in any suitable dimension that can then be drawn into an elongate strand. As an example, the dimensions of the preform may be 50 mm×50 mm×500 mm.

[0135] Referring to FIG. 17B, the cross sectional dimension of the elongate strand may be in any suitable dimension. As an example, the cross sectional dimension of the elongate strand may be 1 mm×1 mm×1.25 km. In another example, the cross section of the elongate strand may be more than 1 mm×1 mm, 2 mm×2 mm, 4 mm×4 mm, 6 mm×6 mm or 8 mm×8 mm. In some embodiments, the cross section dimension of the strand may be less than 10 mm×10 mm, 8 mm×8 mm, 6 mm×6 mm, 4 mm×4 mm or 2 mm×2 mm.

[0136] The elongate strand can then be processed into individual optical elements. This can be achieved by utilising a mechanical cleaver, which is essentially controlled breaking of the elongate strand to produce an optical surface. For example, commercially available mechanical cleavers can be used to cleave the elongate strand at an angle of up to 15° to create an optical element e.g. a prism optical element such as a micro-dove prism. In some embodiments, the optical element (not shown in the accompanied drawings) may be a cuboid, rectangular or a triangular optical element. Moreover, the elongate strand can be cleaved by the mechanical cleaver at any angle to create a plurality of optical element.

[0137] Additionally or alternatively, CO.sub.2 or other laser processing can be used to process the elongate strand into a plurality of optical elements. Using a laser to divide the elongate strand can produce excellent surface finish which may not require further polishing when used in the context of a component of an assay cartridge.

[0138] The fabrication process may also include the step of polishing and/or cleaning the surfaces of the preform, elongate strand and/or the optical element.

[0139] Although the illustrated embodiment shows a rectilinear preform and corresponding elongate strand, other geometries are possible without departing from the methodology described. For example, a triangular or octagonal preform can be drawn and then cut orthogonally to create an optical element that is triangular or octagonal in cross section.

[0140] As shown in FIGS. 18A and 18B, there is provided, respectively, a side view and top view of an optical element 118. The optical element 118 can receive an incident light beam 122 and the incident light beam can be reflected via total internal reflection at the evanescent region 124. The length of the optical element may be between 1 mm to 30 mm, or it may be more than 1, 5, 10, 15, 20 or 25 mm. In some embodiments, the length of the optical element may be less than 30, 25, 20, 15, 10 or 5 mm. In some embodiments, the length of the optical element is between 10 and 20 mm. In some embodiments, the length of the optical element is approximately 13 mm.

[0141] The beam width that enters or exits the optical element may be between 0.1 to 2 mm, or it may be more than 0.1, 0.5, 1 or 1.5 mm. In some embodiments, the beam width may be less than 2, 1.5, 1 or 0.5 mm. For example, the beam width is less than or equal to 0.5 mm.

[0142] Depending on the shape of the preform and the angle of the cleaving, the optical element may have an evanescent region, adjacent to a reflection surface that is either a cleaved surface, in the case of a triangular or octagonal cross section preform; or a drawn surface, in the case of a rectilinear cross section preform.

[0143] Referring to FIGS. 19A and 19B, there is shown a top view (FIG. 19A) and a front view (FIG. 19B) of an optical element 118 being interfaced with a test cartridge/chip 126. An input light beam 128 can enter the optical element on the chip interface. The chip interface can be fabricated from injection moulded polymer.

[0144] Referring to FIGS. 20A and 20B, there is provided a top view (FIG. 20A) and a front view (FIG. 20B) of the chip interface 126. As shown in FIGS. 20A and 20B, a plurality of optical elements 118 can be interfaced in a single chip 126, therefore maximising the interrogation area. The number of optical elements 118 that can interface in a chip 126 can vary substantially. An aperture or a mask 130 can also be used to spatially shape the input collimated laser beam in order to illuminate the desired target regions.

[0145] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure.

[0146] “and/or” where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example “A and/or B” is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0147] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments which are described.

[0148] It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments. It is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.