Fibre-optic probe cap

Abstract

A fibre-optic probe cap 210 for a fibre-optic probe 200 comprising at least one excitation fibre 220 for outputting illumination radiation and at least one collection fibre 230 for collecting radiatio

Description

Field of the Invention The present invention relates to fibre-optics and more specifically caps for fibre-optic probes. Background of the Invention Raman spectroscopy is a chemical analysis technique wherein an analyte is illuminated with a laser beam, and light scattered from the interaction of said laser beam with the analyte is captured and analyzed. Different types of molecules and / or bonds comprised in said analyte may absorb different frequencies of light. Thus, analysis of said scattered light may reveal structural and chemical properties of said analyte. One such application of Raman spectroscopy may be the analysis of biological materials. Such an application may comprise delivering laser light to a sample comprised in a bioreactor via a probe such as a fibre-optic probe, which may also be configured to collect scattered light. In such cases, there are existing probes that have been designed for use in bioreactors and bioprocessing in general, but these generally are complex optical systems involving large waveguides with interference filters at a tip of said probe, orfree-space assemblies comprising optical fibres only used in an umbilical cable (i.e., a cable comprising said optical fibres) that may have critical alignment. State of the art systems are generally expensive to manufacture and are highly sensitive to any shift in the alignment of their optical elements, meaning that they cannot be autoclaved too often without realignment, and also do not maintain their light collection efficiency. Additionally, state of the art probes may be sensitive to any signals generated by the laser light interacting with objects both in the near and the far field which may or may not be the target of the measurements (i.e., an analyte). Prior art probes are also typically sensitive to ambient light, which may lead to operators having to cover their bioreactors in light occluding materials to ensure correct operation. State of the art probes may not include in-built protection to prevent the exposure of said operator (i.e., human operator) to harmful laser radiation. Accordingly, there is a desire for improved Raman spectroscopy systems that address the above-mentioned state of the art shortcomings. Summary of the Invention In a first aspect there is provided a fibre-optic probe cap for a fibre-optic probe comprising at least one excitation fibre for outputting illumination radiation and at least one collection fibre for collecting radiation scattered or emitted from a sample, the cap comprising: a hollow body comprising a side wall and a base, said side wall defining a top opening for receiving the fibreoptic probe, wherein said hollow body is configured to support a fluid medium within an optical path of said illumination radiation outputted from said at least one excitation fibre of said fibreoptic probe; wherein said base comprises an optical absorbing surface for receiving said illumination radiation after having traversed the fluid medium; and wherein said optical absorbing surface is configured to substantially absorb incident light and reflect at least a portion of incident light away from the at least one collection fibre of the fibre-optic probe. When in use, the fire-optic probe cap according to the first aspect may prevent operator access to laser radiation while allowing the ingress of an analyte into the probe cap volume and may also prevent ambient light from reaching a probe, thus allowing use of said probe in a normal laboratory environment. The probe cap may dispose of residual excitation light after it has passed through an analyte of interest and may prevent the detection of weak signals from distant objects (i.e., optical interference), thus reducing an amount of background light detected by said probe allowing more repeatable measurement performance in optically noisy environments with respect to the prior art. The fibre-optic probe cap may further comprise at least one conduit disposed on the side wall of the hollow body and configured to allow passage of said fluid medium into the hollow body. The at least one conduit may be disposed non-radially through the side wall of the hollow body. In this way, interfering radiation (e.g., from a lab environment) entering said probe cap through the at least one conduit may not be directed to the at least one collection fibre without having first reflected off a surface (e.g., internal to the probe cap and / or conduit), thus reducing an intensity of said interfering radiation entering the collection fibre. The optical absorbing surface may be arranged to form an angle with respect to the incident light, said angle greater than an acceptance angle of said at least one collection fibre. In this way, any reflected radiation may not enter said at least one collection fibre, thus reducing interference. The optical absorbing surface of the base of the hollow body may comprise a polished surface configured to provide at least 90% specular reflection of illumination radiation not absorbed by said optical absorbing surface. By enabling specular reflection, it may be ensured that any reflected radiation is greater than an acceptance angle of said at least one collection fibre. The base of the hollow body may comprise a neutral density filter configured to provide the optical absorbing surface. The neutral density filter may comprise a polished glass having an optical density of at least 3. The optical absorbing surface of the base of the hollow body may comprise an interference filter and an absorptive filter disposed between said interference filter and the base. Said interference filter may be configured to transmit illumination radiation and block generated and / or reflected radiation from the absorptive filter. The hollow body may comprise one or more materials that are non-transparent to ambient light. The fibre-optic probe cap may be configured to receive a fibre-optic probe coaxially such that a probe tip of the fibre-optic probe is disposed at least 2mm beyond an upper edge of the at least one conduit in an axial direction of the fibre-optic probe and probe cap towards the base. In this way, any bubbles that may become trapped in an analyte disposed within the probe cap may remain outside a visible field of the at least one collection fibre and / or the at least one excitation fibre. In a second aspect, there is provided a fibre-optic probe comprising: at least one excitation fibre for outputting illumination radiation: at least one collection fibre for collecting radiation scattered or emitted from a sample; and the fibre-optic probe cap of the first aspect. Said at least one excitation fibre may comprise one or more multimode optical fibres. The fibre-optic probe may be a Raman spectroscopy probe. In a third aspect, there is provided a Raman spectroscopy system comprising: the fibre-optic probe of the second aspect; a spectrometer configured to receive scattered radiation from a sample; and a light source configured to provide illumination radiation to the at least one excitation fibre of the fibre-optic probe. Brief Description of the Drawings Figure 1 depicts a typical spectrometry system; Figure 2 depicts a fibre-optic probe and probe cap in accordance with aspects of the present disclosure; and Figure 3 depicts a fibre-optic probe cap in accordance with aspects of the present disclosure. Detailed Description Figure 1 describes graphically a simplified typical spectroscopy measurement system. Said system may comprise a base station 100, for example a spectrometer, and a radiation source 110. Base station 110 may be a Raman spectrometer and radiation source 110 may be a laser source. Fibre-optic probe 140 may be operably connected to base station 100 via umbilical cable 150, and at least partially submerged in analyte 130 within bioreactor 120. Fibre-optic probe 140 maybe be configured to deliver radiation to analyte 130, collect radiation scattered from said analyte 130 and transmit collected radiation to base station 100. As described previously, fibre-optic probe 140 may be sensitive to any signals generated by radiation interacting with objects both in the near and the far field which may or may not be the target of the measurements (i.e., analyte 130). The bioreactor 120 of such a system as shown in Figure 1 may be required to be covered with an opaque blackout material to prevent radiation ingress into probe 140. Some systems try to address these issues e.g., in lensed probe designs by focusing light through a small conduit. This may remove radiation that has not passed through a focal point of the lensed system, in effect providing an angular spatial filter. While this may partially reduce background signals, distant signals may still result in a scattered signal. These systems may still require that bioreactors are wrapped in a light-tight material, such as aluminium foil to block the remaining background. To address the shortcomings of the prior art, the inventors have devised a fibre-optic probe cap and fibre-optic probe comprising said probe cap. The proposed probe may be more resistant to sterilization by autoclaving owing to the elimination of alignment-sensitive optical elements. The probe cap may prevent operator access to laser radiation while allowing the ingress of an analyte into the probe cap volume and may also prevent ambient light from reaching the probe, thus allowing use of said probe in a normal laboratory environment. The probe cap may dispose of residual excitation light after it has passed through the analyte of interest and may prevent the detection of weak signals from distant objects (i.e., optical interference), thus reducing an amount of background light detected by said probe allowing more repeatable measurement performance in optically noisy environments with respect to the prior art. Said fibre-optic probe may comprise at least one excitation optical fibre housed in a probe body. In some examples, said probe may comprise a bundle of said excitation fibres. Said excitation fibre may be connected to an illumination source and configured to output illumination radiation into a sample, or analyte, (e.g., a volume of liquid, typically a cell culture media, typically with a high water content). Said probe may further comprise at least one collection fibre for collecting radiation scattered or emitted from said analyte. Said collection fibre may be operably connected to a spectrometer and may transmit captured reflected light to said spectrometer to be analyzed. Said probe cap may be disposed at an end of the probe and may comprise a neutral density (ND) filter angled such that any light incident on said ND filter may be absorbed by said ND filter or reflected in such a way that it cannot enter the collection fibre. In this way, only light scattered by said analyte may enter the collection fibre. Said fibre-optic probe and probe cap may protect operators and bystanders from harmful radiation by absorbing and / or redirecting said radiation in such a way that exposure is minimized. Referring to Figure 2, fibre-optic probe 200 may comprise at least one excitation fibre 220, also known as a laser delivery fibre configured to output, or transmit, illumination radiation from probe tip 240. Fibre-optic probe 200 may further comprise at least one collection fibre 230 configured to collect radiation scattered or emitted from a sample or analyte (not shown). In some examples the scattered radiation may comprise Raman scattering. Said at least one excitation fibre 220 and at least one collection fibre 230 may be disposed adjacently and in proximity with one another within probe tip 240. In some examples, said at least one excitation fibre 220 and at least one collection fibre 230 are disposed less than 1mm apart, less than 500pm apart, less than 50 pm apart, less than 1pm apart, or less than 500nm apart. A number of excitation fibres and / or collection fibres may be in in the range of 1 to 25. In some examples, a number of excitation fibres and / or collection fibres may be determined based on an optimal packing of said fibres. In a specific example, a number of collection fibres may be a hexagonal centered number for optimal packing of collection fibres. Said at least one excitation fibre 220 and / or at least one collection fibre 230 may comprise a multi- or single-mode optical fibre such as plastic fibres, plastic clad fibres, silica fibres, polarization maintaining fibres, or photonic crystal fibres. Said at least one excitation fibre 220 and at least one collection fibre 230 may be secured (e.g., with an adhesive) in a narrow opening comprised in probe tip 240 that may hold said at least one excitation fibre 220 and at least one collection fibre 230 in place. Said fibre-optic-probe 200 may be comprised of a metal such as stainless steel or any other suitable material such as a biocompatible plastic e.g., polycarbonate, polyethylene terephthalate (PET) and / or the like. Said fibre-optic probe 200 may be connected to a base station, for example a Raman spectrometer, and a radiation source, for example a 785nm wavelength laser. Probe cap 210 may comprise a hollow body 270 comprising a side wall 272 and a base 274, said side wall defining a top opening for receiving the fibre-optic probe. Said hollow body may be configured to support a sample or analyte, e.g., a fluid medium. Said fibre-optic probe 200 and probe cap 210 may comprise a fastening means 260 for securing said probe cap 210 to fibre-optic probe 200. In the example shown in Figure 2, said fastening comprises threads disposed on said probe cap 210 and fibre-optic probe 200. In other examples not shown, said fastening means may comprise any of a bayonet fit, compression fit, magnetic fit, snap fit and / or any other suitable type of fit. Said probe cap 200 may be comprised of a metal such as stainless steel or any other suitable material such as a biocompatible plastic. Said probe cap 200 may be comprised of one or more materials that are non-transparent to ambient light. In some examples, probe cap 200 may comprise at least one conduit 250 disposed on the side wall 272 of the hollow body 270. Said conduit may be configured to allow passage of a fluid medium (e.g., a sample or analyte) into (and out from) said hollow body 270 and into an optical path 290 of said illumination radiation outputted from said at least one excitation fibre 220 of said fibre-optic probe 200. Said at least one conduit 250 may be rectangular in shape. In some examples said at least one conduit may comprise a rectangle having first and second side lengths in a range of 1mm to 10mm. In a specific example said dimensions may be in the range of 1 to 3mm for a first side length corresponding to a radial direction of the probe cap 210, and 7 to 9mm for a second side length corresponding to an axial direction of the probe cap 210. Such dimensions may be determined to prevent trapped air within said fluid medium, i.e., bubbles, whilst limiting an amount of ambient or environmental radiation that may enter said probe cap 210. Thus, radiation e.g., from ambient lighting, or radiation scattering and / or fluorescence from outside the analyte of interest may be reduced, thus reducing an amount of background light comprised in radiation entering the at least one collection fibre 230. When a measurement environment changes (e.g., lab lighting), a variable background radiation may be introduced into measurements, the removal of which may be non-trivial. Said cap comprising conduits may 250 may help to alleviate this issue by blocking background radiation. When a fibre-optic probe (e.g., fibre-optic probe 200) is inserted into probe cap 210, the relative locations of probe tip 240 and the at least one conduit 250 are such that said probe tip extends at least 2mm beyond an upper edge 295 of the at least one conduit 250 towards a base 274 of the probe cap 200, wherein an upper edge of the at least one conduit corresponds to an edge closest to the fastening means 260. That is, in operation said fibreoptic probe 200 and probe cap 210 may be disposed coaxially, and probe tip 240 may be disposed at least 2mm beyond an upper edge 295 of the at least one conduit in an axial direction of the fibre-optic probe 200 and probe cap 210 towards the base 274. This dimension corresponds to Figure reference X in Figure 2. In this way, any bubbles that may become trapped in an analyte disposed within the probe cap 250 may remain outside a visible field of the at least one collection fibre 230 and / or the at least one excitation fibre 220. The number of conduits 250 may be selected in accordance with the requirements of any particular use case. In some examples, the number of conduits 250 may be based on a viscosity and / or volume of a sample to pass through said conduits. Conduits 250 may be spaced radially at even intervals on the side wall 272 of probe cap 200. Referring to Figure 3, said conduits 250 may be disposed in the side wall 272 of probe cap 200 in a non-radial manner. In this way, any radiation 395 entering the probe cap 200 through said conduits 250 may not enter the at least one collection fibre 230 without having first reflected from an internal surface of the probe cap 200. This is because the non-radial conduits are disposed such that they do not provide a direct line of sight from an exterior of the probe cap 200 to the at least one collection fibre 230. In this way, an intensity of radiation (e.g., environmental radiation from lab lighting) penetrating the probe cap 200 and entering the at least one collection fibre 230 may be reduced, thus reducing interference. Probe cap 200 may further comprise a base 274, wherein said base may comprise an optical absorbing surface 280. In operation, said optical absorbing surface is configured to substantially absorb incident light (e.g., light transmitted from said at least one excitation fibre 220 and / or background radiation) and reflect at least a portion of incident light away from the at least one collection fibre 230. In this way, light that is not scattered or reflected by said analyte may be disposed of without entering said at least one collection fibre 230. Said optical absorbing surface 280 may be configured to maximally absorb laser radiation and not re-emit fluorescence in the Raman band. Said optical absorbing surface may be configured to absorb up to 99.9% of incident light. In some examples, said optical absorbing surface 280 is arranged to form an angle with respect to the incident light 290, wherein said angle is suitable such that scattered or reflected radiation is directed from said optical absorbing surface 280 at an angle greater than an acceptance angle of said at least one collection fibre 230. That is, said collection fibre 230 may comprise an acceptance angle which may define a maximum angle at which radiation incident on said collection fibre 230 will be transmitted (or in the case of excitation fibre 220, the maximum angle at which light will be transmitted). By angling said optical absorbing surface 280, it may be possible to selectively redirect radiation not absorbed by said optical absorbing surface 280 such that the radiation may not enter said at least one collection fibre 230. Thus, un-scattered radiation (e.g., radiation that has not been scattered by said sample or analyte) may be disposed of without entering said at least one collection fibre 230. In some examples, said angle is in the range of 20 - 24 degrees. In a more specific example, said angle is 22 degrees. In some examples, said angle may based on an acceptance angle of the at least one collection fibre 230. In some examples, said optical absorbing surface 280 is polished to enable specular reflection. Said optical absorbing surface may be configured to enable at least 90% specular reflection of radiation reflected by said optical absorbing surface. At least 90% specular reflection may ensure that reflected radiation is directed from said optical absorbing surface 280 at an angle greater than an acceptance angle of said at least one collection fibre 230 to provide a reduction in background radiation entering said at least one collection fibre 230. In some examples said polished surface may comply with scratch / dig standard MIL-PRF-13830B 60 / 40. In some examples, said optical absorbing surface 280 may comprise a neutral density filter. Said neutral density filter may comprise polished glass and / or may have an optical density of 3. An example of a suitable commercially available optical density filter is Shotts NG3 glass. In some examples said optical absorbing surface may comprise a wavelength variable filter, for example infrared transmitting filter glass. In an example not shown, said optical absorbing surface may comprise an interference filter and an absorptive filter disposed between said interference filter and the base 274. In this example, the interference filter may be configured to transmit illumination radiation (e.g., laser light from excitation fibre 220) and block any unwanted radiation (e.g., infrared) generated and / or reflected in the absorptive filter. In some examples the interference filter may be a short pass interference filter. Accordingly, said optical absorbing surface 280 may prevent any ambient light that enters said probe cap 210 from entering said at least one collection fibre 230. Said fibre-optic probe 200 and probe cap 210 may deliver and collect radiation from a vessel filled with a fluid (e.g., a sample or analyte) with minimal interference from external radiation sources or unintended measurements. Said fibre-optic probe 200 may be operatively connected to a base station, e.g., a spectrometer or and Raman spectrometer. Said fibre-optic probe 200 may have no alignment-sensitive optical elements in the probe tip, thus, said fibreoptic probe 200 may be autoclaved more times than other available probes that are alignment sensitive. Furthermore, said probe cap 210 may be capable of disposing of emitted optical radiation after it has passed through a sample or analyte without directing said radiation into a collection fibre. As such, said probe and probe cap may offer improved background radiation rejection and reduced sensitivity to ambient radiation interference. Said fibre-optic probe cap 210 may be used with or without conduits 250. That is, in the case where there are no conduits 250, a sample or analyte may be pre-loaded into the hollow body 270 of the probe cap 210 before being secured to a fibre-optic probe 200. In the case where the probe cap 200 comprises at least one conduit 250, the probe cap 210 may first be secured to a fibre-optic probe 200. Subsequently, the fibre-optic probe 200 and probe cap 210 may be submerged in a fluid medium (e.g., a sample or analyte disposed in a bioreactor such as described with reference to Figure 1). Said at least one conduit 250 may allow passage of said fluid medium into (and out from) said hollow body 270. There is further provided a Raman spectroscopy system comprising fibre-optic probe 200 and probe cap 210. Said Raman spectroscopy system may comprise a spectrometer configured to receive scattered radiation from a sample; and a light source configured to provide illumination radiation to the at least one excitation fibre of the fibre-optic probe. Said fibre-optic probe 200 and probe cap 210 may prevent optical stimulation of other components of a spectrometry system following excitation of an analyte thus preventing unwanted background radiation signal from other objects and media from both Raman and other effects (such as fluorescence). Aspects of the present disclosure may provide for reduced construction complexity with respect to currently available probes as the presently disclosed probe does not require critical alignment e.g., of lenses. Additionally, this may provide for a single use probe. The description provided herein may be directed to specific implementations. It should be understood that the discussion provided herein is provided for the purpose of enabling a person with ordinary skill in the art to make and use any subject matter defined herein by the subject matter of the claims. It should be intended that the subject matter of the claims not be limited to the implementations and illustrations provided herein, but include modified forms of those implementations including portions of implementations and combinations of elements of different implementations in accordance with the claims. It should be appreciated that in the development of any such implementation, as in any engineering or design project, numerous implementation-specific decisions should be made to achieve a developers’ specific goals, such as compliance with system-related and business related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort may be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having benefit of this disclosure. Reference has been made in detail to various implementations, examples of which are illustrated in the accompanying drawings and figures. In the detailed description, numerous specific details are set forth to provide a thorough understanding of the disclosure provided herein. However, the disclosure provided herein may be practiced without these specific details. In some other instances, well-known methods, procedures, components, circuits, and networks have not been described in detail so as not to unnecessarily obscure details of the embodiments. It should also be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element. The first element and the second element are both elements, respectively, but they are not to be considered the same element The terminology used in the description of the disclosure provided herein is for the purpose of describing particular implementations and is not intended to limit the disclosure provided herein. As used in the description of the disclosure provided herein and appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “and / or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The terms “includes,” “including,” “comprises,” and / or “comprising,” when used in this specification, specify a presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. While the foregoing is directed to implementations of various techniques described herein, other and further implementations may be devised in accordance with the disclosure herein, which may be determined by the claims that follow. Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A fibre-optic probe cap for a fibre-optic probe comprising at least one excitation fibre for outputting illumination radiation and at least one collection fibre for collecting radiation scattered or emitted from a sample, the cap comprising:a hollow body comprising a side wall and a base, said side wall defining a top opening for receiving the fibre-optic probe, wherein said hollow body is configured to support a fluid medium within an optical path of said illumination radiation outputted from said at least one excitation fibre of said fibre-optic probe;wherein said base comprises an optical absorbing surface for receiving said illumination radiation after having traversed the fluid medium; andwherein said optical absorbing surface is configured to substantially absorb incident light and reflect at least a portion of incident light away from the at least one collection fibre of the fibre-optic probe.

2. The fibre-opticprobe cap of claim 1 further comprising at last one conduit disposed on the side wall of the hollow body and configured to allow passage of said fluid medium into the hollow body.

3. The fibre-opticprobe cap of claim 2, wherein the at least one conduit is disposed non-radially through the side wall of the hollow body.

4. The fibre-optic probe cap of any of claim 1, claim 2 or claim 3, wherein the optical absorbing surface is arranged to form an angle with respect to the incident light, said angle greater than an acceptance angle of said at least one collection fibre.

5. The fibre-optic probe cap of any previous claim, wherein the optical absorbing surface of the base of the hollow body comprises a polished surface configured to provide at least 90% specular reflection of illumination radiation not absorbed by said optical absorbing surface.

6. The fibre-optic probe cap of any of claims 1 to 5, wherein the base of the hollow body comprises a neutral density filter configured to provide the optical absorbing surface.

7. The fibre-optic probe cap of claim 6, wherein the neutral density filter comprises a polished glass having an optical density of at least 3.

8. The fibre-optic probe cap of any of claims 1 to 5, wherein the optical absorbing surface comprises an interference filter and an absorptive filter disposed between said interference filter and the base, said interference filter configured to transmit illumination radiation and block generated and / or reflected radiation from the absorptive filter.

9. The fibre-optic probe cap of any previous claim, wherein the hollow body comprises one or more materials that are non-transparent to ambient light.

10. The fibre-optic probe cap of any of claims 2 to 9 configured to receive a fibre-optic probe coaxially such that a probe tip of the fibre-optic probe is disposed at least 2mm beyond an upper edge of the at least one conduit in an axial direction of the fibre-optic probe and probe cap towards the base.

11. A fibre-optic probe comprising:at least one excitation fibre for outputting illumination radiation:at least one collection fibre for collecting radiation scattered or emitted from a sample; andthe fibre-optic probe cap of any of claims 1 to 10.

12. The fibre-optic probe of claim 11, wherein said at least one excitation fibre comprises one or more multimode optical fibres.

13. The fibre-optic probe of claim 11 or 12, wherein said at least one collection fibre comprises one or more multimode optical fibres.

14. The fibre-optic probe of any of claims 11 to 13, being a Raman spectroscopy probe.

515. A Raman spectroscopy system comprising:the fibre-optic probe of any of claims 11 to 14;a spectrometer configured to receive scattered radiation from a sample; anda light source configured to provide illumination radiation to the at least one excitation fibre of 10 the fibre-optic probe.14

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