WO2002029387A1

WO2002029387A1 - Fluorescence probe and device for attachment thereto

Info

Publication number: WO2002029387A1
Application number: PCT/AU2001/001238
Authority: WO
Inventors: Robert John Francis
Original assignee: Varian Australia Pty Ltd
Priority date: 2000-10-03
Filing date: 2001-10-02
Publication date: 2002-04-11
Also published as: AUPR055000A0

Abstract

A device for attachment to a fluorescence of phosphorescence probe provides a beam stop and defines a reproducible measurement volume independent of the volume of a fluid into which the probe is inserted. The device (32) provides a member (36) having a black glossy surface (42) for absorbing any excess excitation light that is transmitted from the end (14) of a fibre optic probe that is not absorbed by intervening fluid. The member (36) is also tilted relative to probe end (14) such that its surface (42) will reflect any non-absorbed excitation light (44) (which is weakened due to adsorption by the member) away from entering the end (14) of the probe. This substantially prevents the input excitation light from mixing with the emission light which is collected at end (14).

Description

FLUORESCENCE PROBE AND DEVICE FOR ATTACHMENT THERETO

Technical Field The present invention relates to a probe for detecting fluorescence or like light emission such as phosphorescence in a fluid (hereinafter termed a fluorescence probe) and in particular to a device for attachment to a fluorescence probe which provides a stop for an excitation beam of light.

Background

A known fluorescence probe which is attachable to a fluorescence measuring instrument comprises a fibre optic bundle having a common end from which the fibres are bifurcated into two separated bundles (i.e. an excitation bundle and an emission bundle) each having an end. The common end is immersible into a fluid such as a liquid in a container whilst one bifurcated end is illuminated with excitation light for transmission of that light into the liquid from the common end. Fluorescence light emitted by the liquid enters the emission bundle fibres at the common end for detection by an emission detector at the other bifurcated end.

Problems with this arrangement are that the emission signal strength depends on the depth of the liquid between the common end and the container bottom, which can vary considerably. Also, excitation light reflected from the walls of the container may enter the emission fibres at the common end and thus increase the stray light level in the emission signal, which increases the limit of detection of the measurement.

An object of the present invention is to provide a device for attachment to a fluorescence probe for reducing the above problems.

The discussion of the background to the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge in Australia as at the priority date of the present application. Disclosure of the Invention

According to a first aspect of the present invention, there is provided a device for attachment to a probe, the probe being immersible in a fluid for transmission of excitation light into the fluid and for receiving fluorescence or phosphorescence light emitted by the fluid, the device including a structure for attaching the device to the probe and a member mounted on the structure so as to be spaced from the probe, which member provides a surface which generally faces the probe for receiving any excess excitation light from the probe that is not absorbed by intervening fluid, the surface being absorptive such that excess excitation light is substantially absorbed thereby.

Preferably the absorptive surface also has an orientation relative to the probe such that it reflects non-absorbed excess excitation light away from the probe.

The characteristics of the absorptive surface (for example its colour) are selected for it to be maximally absorptive for the wavelength or mix of wavelengths of the excitation light. Thus the member may provide, for example, a black glossy surface a fixed distance away from the probe to absorb the excess excitation light, the member preferably being tilted relative to the probe end to direct the reflected excitation light (which is weakened due to absorption by the member) away from the probe end such that the amount which mixes with the emission light collected by the emission fibres is reduced. The member, which is preferably a disc of a material for absorbing a maximum of excitation light falling upon it, for example polished black silica, or a material of another colour depending on the wavelength of the excitation light to be used, should have a size which covers the excitation beam of light emerging from the probe.

A member as described above in a device according to the invention acts as a beam stop and advantageously provides a defined and reproducible depth of measurement independent of the liquid container size. It also absorbs most of the excess excitation light and substantially reduces reflection back to the probe of the unabsorbed part of the excitation beam, thereby reducing the above described problems of the prior art.

The probe to which the device is attachable is preferably a bifurcated fibre optic bundle as described hereinabove, however the device is useable with other forms of probe. For example, the probe may utilise a single means for transmission of excitation light into a fluid and a single means for collection of the light emitted from the fluid, which means may each be an optical fibre, or a common single fibre.

For the preferred probe, the common end and the ends of the bifurcated bundles are usually each held in assembly by a ferrule. With this construction, the structure for attaching the device of the invention to the probe preferably includes a screw thread for engaging a complementary screw thread on the ferrule at the common end. However other alternative attaching arrangements are possible, for example the structure of the device may incorporate a clamping arrangement or may be adhesively attachable to the probe.

The structure which carries the light absorbing and reflective member spaced from the light transmitting and receiving end of the probe provides, in effect, a frame which allows the fluid under measurement to flow relatively freely between the probe and the member. This structure may be made from stainless steel or other suitable inert material.

The light absorbing and reflective member may be adhesively or otherwise attached to the structure and should comprise an inert material which does not fluoresce. Other possible materials for the member may be carbon, plastic, ceramic or opaque glass of an appropriate colour.

An advantage of the invention is that the sloped member substantially prevents direct entry of ambient or room light into the emission collection fibres.

According to a second aspect, the present invention provides a fluorescence or phosphorescence probe including at least one optical fibre having an end for transmission of excitation light into a fluid and for receiving fluorescence or phosphorescence light emitted by the fluid, a member mounted on the optical fibre and spaced from the end of the optical fibre such that a fluid under measurement can intervene between the end of the optical fibre and the member, wherein the member provides a surface which generally forces the optical fibre end for receiving any excess excitation light that is not absorbed by the intervening fluid, the surface being absorptive such that excess excitation light is substantially absorbed thereby, the surface also preferably being orientated relative to the end of the optical fibre such that it reflects non- absorbed excess excitation light in a direction away from entering the end of the optical fibre.

For a better understanding of the present invention and to show how it may be carried into effect, an embodiment of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings.

Brief Description of Drawings

Fig.1 shows in cross-section a preferred probe to which a device according to the invention is attachable.

Fig. 2 is a cross-sectional front view of an embodiment of a device according to the invention attached to the common end of the probe of Fig. 1.

Fig. 3 is a cross-sectional side view of the Fig. 2 arrangement, and

Fig. 4 is a diagrammatic sketch to explain the functioning of the device of Figs. 2 and 3.

Description of Preferred Embodiment

A fluorescence or phosphorescence measurement probe 10 (Fig. 1 ) with which the invention is useable comprises a bifurcated bundle of optical fibres 12 having a common end 14 held in assembly by a ferrule 16. An end 18 of one of the bifurcated bundle of fibres 17 is held in assembly by a ferrule 20 and the end 22 of the other bundle of fibres 21 is held in assembly by a ferrule 24. The bundle of fibres 17 is an excitation bundle of fibres and transmits an input beam of excitation light 26 from end 18 to common end 14 for transmission into a fluid into which the common end 14-16 may be immersed.

The bundle of fibres 21 is an emission bundle of fibres which transmits i emitted fluorescence light 28 from the fluid, which is collected by the emission fibres at the common end 14, to the end 22 and to an emission detector (not shown). The common end 14 can consist of randomly mixed fibres, or concentric rings of alternately excitation fibres 17 and emission collection fibres 21.

Ferrule 16, at common end 14 has a reduced diameter portion 30 which is externally screw threaded.

A device 32 according to an embodiment of the invention (see Figs. 2 and 3) includes a structure 34 for attaching the device to the ferrule 16 of probe 10 and a member 36 mounted on the structure. The structure 34 includes an annular portion 38 which is internally screw-threaded such that it can be screwed on to the threaded portion 30 of ferrule 16. Two narrow legs 40 depend from annular portion 38 and the member 36 is attached to the ends of the legs 40. Structure 34 may be manufactured from stainless steel.

Member 36 is a disc of a material which absorbs a maximum of excitation light falling upon it, preferably polished black silica. It provides a surface 42 which generally faces the common end 14 of probe 10 for receiving excess excitation light 26 that is not absorbed by the intervening fluid. Thus a high proportion of such excess excitation light is absorbed by the member 36. The member 36 is orientated at a set angle φ (see Fig. 4) to the probe end 14 such that non-absorbed excitation light is reflected away from the probe end 14. The diameter of member 36 needs to be large enough for the area of surface 42 to cover the excitation beam 44 which emerges from common end 14.

With reference to Fig. 4, L is the distance between common end 14 of probe 10 and the centre of surface 42 of member 36, and φ is the angle of member 36 relative to common end 14. The lines 46i, 48i and 50i, 52i represent extreme rays of light emerging from a bundle of optical fibres for example of numerical aperture (NA) 0.22. The angle of emergence is defined by the equation NA=sine (a/2) where a is the full cone angle of the emergent rays. The lines 46r, 48r and 50r, 52r represent the above excitation rays, respectively, after attenuation and reflection from the absorbing surface 42. Ray 46r, although it intersects the fibre bundle common end 14, is outside the cone of acceptance of the emission fibres 21. For a bundle of silica optical fibres with NA of 0.22 and L=10mm, a suitable diameter for member 36 is 10 mm, with φ=20°.

The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the scope of the following claims.

Claims

1. A device for attachment to a probe, the probe being immersible in a fluid for transmission of excitation light into the fluid and for receiving fluorescence or phosphorescence light emitted by the fluid, the device including a structure for attaching the device to the probe and a member mounted on the structure so as to be spaced from the probe, which member provides a surface which generally faces the probe for receiving any excess excitation light from the probe that is not absorbed by intervening fluid, the surface being absorptive such that excess excitation light is substantially absorbed thereby.

2. A device according to claim 1 wherein said absorptive surface has an orientation relative to the probe such that it reflects non-absorbed excess excitation light away from the probe.

3. A device according to claim 1 or claim 2 wherein said member provides a black surface for absorbing excess excitation light.

4. A device according to claim 1 , 2 or 3 wherein said member is a disc that is mounted on said structure such that in use it is tilted relative an end of a probe to which the device is attached.

5. A device according to any one of claims 1 to 4 wherein said member is made of an inert material that does not fluoresce, being a material selected from the group: polished black silica, carbon, plastic, ceramic and opaque glass.

6. A device according to any one of claims 1 to 5 wherein said structure is frame-like such that in use of the device fluid under measurement can flow relatively freely between a probe end to which the device is attached and said member.

7. A device according to claim 6 wherein said structure includes an end portion for attachment to a probe and at least one leg which depends from the end portion, said member being mounted on said leg spaced from said end portion.

8. A device according to claim 7 wherein said end portion of said structure is annular and is adapted for attachment to a ferrule of a probe made of a bundle of optical fibres, the ferrule holding the optical fibres in assembly at an end thereof.

9. A device according to claim 8 wherein said annular end portion is internally screw threaded for engaging a complementary external screw thread on a said ferrule.

10. A fluorescence or phosphorescence probe including at least one optical fibre having an end for transmission of excitation light into a fluid and for receiving fluorescence or phosphorescence light emitted by the fluid, a member mounted on the optical fibre and spaced from the end of the optical fibre, such that a fluid under measurement can intervene between the end of the optical fibre and the member, wherein the member provides a surface which generally faces the optical fibre end for receiving any excess excitation light that is not absorbed by the intervening fluid, the surface being absorptive such that excess excitation light is substantially absorbed thereby.

1 1. A probe according to claim 10 wherein said surface is oriented relative to the end of the optical fibre such that it reflects non-absorbed excess excitation light in a direction away from entering the end of the optical fibre.

12. A device according to claim 11 wherein there are a plurality of optical fibres for transmission of excitation light into a fluid and for receiving fluorescence or phosphorescence light emitted by the fluid.

13. A device according to claim 12 wherein the plurality of fibres are bundled together to provide a common end for immersion in a fluid, wherein the plurality of fibres extending from the common end are bifurcated into two separated bundles each having an end, whereby one bundle is for transmission of the excitation light and the other bundle is for receiving the emission light.

14. A device according to claim 13 wherein the fibres are bundled together by a ferrule to provide the common end, and wherein said member that provides the absorptive surface is mounted via a structure that is attached to the ferrule and which allows a fluid under measurement to intervene between the common end and the absorptive surface of the member.

15. A device , according to claim 14 wherein the structure is removably attached to. the ferrule.

16. A device according to claim 15 wherein the structure is removably attached to the ferrule via complementary screw threads on the structure and the ferrule.

17. A device according to any one of claims 10 to 16 wherein said member that provides the absorptive surface is a disc that is mounted such that it is tilted relative to the end of the at least one optical fibre.

18. A device according to claim 17 wherein the absorptive surface of the member is black and glossy.