GB2377492A

GB2377492A - Detecting analytes

Info

Publication number: GB2377492A
Application number: GB0216339A
Authority: GB
Inventors: Brian Philip Allen
Original assignee: e2v Technologies UK Ltd; Marconi Applied Technologies Ltd
Current assignee: Teledyne UK Ltd
Priority date: 2001-07-14
Filing date: 2002-07-15
Publication date: 2003-01-15
Also published as: WO2003008946A1; GB0117230D0; GB0216339D0

Abstract

A sensor to detect an analyte suitable for applications such as medical diagnostics, fermentation or fire detection, comprises an optical waveguide 5, which includes a number of branches 6-10. A region 11-15 of each waveguide is associated with a material which reacts selectively with the analyte. The material may coat the waveguides or be incorporated into pores in the waveguide. When the material interacts with the analyte, which may be introduced via a channel 2, a change in the refractive index occurs in the region of the waveguide. This change is detected by guiding a beam of light into the waveguides and detecting a change in a characteristic of the emerging light, e.g. light intensity. The sensor device may be fabricated within or on a substrate, employing materials such as silicon, Gallium Arsenide or glass.

Description

This invention relates to a method of, and a sensor for, detecting analytes.

There are a number of analyte detectors on the market in the form of chemical sensors and biosensors. These sensors typically incorporate surface acoustic wave (SAW) devices, bulk acoustic wave (BAW) devices and the like, which are arranged to react selectively with an analyte, or a number of particular analytes, of interest to the user. In recent years, there has been a drive towards sensors that occupy small volumes.

The invention provides a sensor arranged to detect an analyte, the sensor comprising an optical waveguide, a region of which is associated with a material arranged to react

selectively with an analyte, a change in the effective refractive index of the region being z : l indicative of the presence of the analyte.

The provision of an optical waveguide permits the device to be manufactured to a very small scale.

The invention lends itself to incorporation in a miniature chemical sensor or biosensor.

The term"miniature"is intended to encompass all devices on a small scale, including nano-scale and micro-scale devices, so-called miniaturised total analysis systems (u- TAS), lab-on-a-chip technologies and the like.

Preferably, the sensor is arranged to detect a plurality of analytes. This may be achieved by having a plurality of waveguides, a region of each waveguide being associated with a material arranged to react selectively with at least one analyte.

The invention further provides a method of detecting an analyte comprising the steps of passing light through a waveguide, a region of which is associated with a material arranged to react selectively with an analyte, and detecting a characteristic of the emerging light, a change in which characteristic is indicative of the presence of the analyte.

The invention will now be described, by way of example, with reference to the accompanying drawing, which is a plan view, partly in section, of a sensor constructed according to the invention.

With reference to the drawing, an analyte sensor constructed according to the invention is shown, but not to scale, and indicated generally by the reference numeral 1. In this embodiment, the sensor 1 is generally rectangular and has a channel 2 running through it, from one side 3 of the sensor to the opposite side 4. A fluid to be analysed may be caused to flow along this channel 2, either by a user sampling the fluid and introducing it into the channel, or else by locating the sensor in situ.

In accordance with the invention, the sensor I further comprises an optical waveguide 5.

In this embodiment, the waveguide 5 branches into a number of sub-guides 6 to 10 inclusive, each of which traverses the channel 2. The waveguides 5 to 10 and the

channel 2 comprise a single planar array. Each waveguide branch 6 to 10 includes a coating material I to 15 respectively. Each coating 11-15 has been applied to the respective waveguide 6-10 in the region where the guide crosses the channel 2 so that, in use, the coating material is exposed to the fluid in the channel.

Each of the coatings 11 to 15 is arranged to react selectively with an analyte of interest, which analyte may be present in the sample fluid in the channel 2. A number of arrangements are possible which may be implemented by the skilled person. For example, each of the coatings may react with the same analyte, but in a different manner, such as with different speeds of absorption, different strengths of reaction, etc.

This arrangement permits a positive identification of the particular analyte and/or allows detailed information to be gathered about the analyte. Alternatively, the coatings may together react with more than one analyte. As a further alternative, the coating materials may react with different respective analytes. This latter arrangement may permit the detection of many substances.

Another factor that may influence the choice of coating materials employed is the degree of reusability required of the sensor. If a reusable sensor is needed then coating materials having weak, reversible reactions with the analytes of interest may be employed, so that purging the sensor of the sample fluid causes analytes to be desorbed and the sensor to return to its original condition. If a one-off or disposable sensor is required, the choice of coatings may be different, so that coatings having strong, irreversible reactions with the analytes of interest may be employed.

Each coating 11-15 may be applied to the outer surface of each waveguide, or may be incorporated in pores in the waveguide itself. A combination of these coating arrangements may be possible.

In use, a light beam is coupled into the waveguide 5 by, for example, a diffraction grating (not shown). The light beam may be produced by, for instance, a helium-neon laser, a cw or pulse laser or a light emitting diode (LED). The light beam then divides into part beams and propagates in the waveguides 6 to 10, as guided light waves. When one of the materials, say, coating 15 associated with the waveguide 10 reacts with one or more analytes, a change in refractive index occurs in the coating, and hence in the waveguide 10 itself. Thus, a change in refractive index indicates to the user the presence of an analyte in the sample.

The respective outputs 16 to 20 of the waveguides 6 to 10 may be in communication with one or more detectors (not shown). The detectors are arranged to detect changes in the refractive indexes of the respective waveguides should the sample in the channel 2 contain an analyte or analytes that react with the coatings on the waveguides.

A possible method of detecting the change in refractive index is to measure the change in light intensity of each guided mode. Alternative methods will be apparent to the person skilled in the art.

One of the waveguides, say waveguide 6, may be left uncoated and used to provide a control or reference beam. In a further variation, this reference beam may be arranged

to interfere with one or more output light beams from the other waveguides 7-10. The phase difference of the part beams is dependent on the length of the optical paths, and hence on the difference in effective refractive index.

The sensor device may be fabricated in a solid state planar technology employing materials such as silicon, Gallium Arsenide (Ga As) or glass, for example. The waveguides may be fabricated within or on a substrate to form waveguide channels, such as ridged waveguides. The waveguides may be formed by doping regions of material with, for example, rare earth metals, in order to change the refractive index. In an alternative technique, locally applied external electric fields are employed in order to locally modify the material and create a waveguide as determined from Maxwell's equations. Further techniques will be apparent to the skilled person.

The dimensions of the sensor shown in Figure I may be of the order of a few centimetres, or even smaller. Conveniently, sensors may be produced of credit card size.

Since the sensor comprises mostly passive components, a large number of sensors may be manufactured at low cost. The sensor is suitable for many applications such as medical diagnostics, fermentation, fire detection, etc.

A more basic version of the sensor of Figure I may be produced having a single waveguide. However, this embodiment may not be limited to having just one coating.

For example, in fire detection, a number of different fuel vapours may be present in a

sample and the presence of any one of those vapours needs to be detected. If one waveguide is used, this could be coated at different regions with coatings arranged to interact with one or more fuel vapours. Thus, the presence of one or more of these vapours would cause a detectable change in the effective refractive index of the waveguide. In this embodiment, the waveguide may be arranged to cross the channel a plurality of times, each crossing region being associated with a different coating material. Alternatively, the channel 2 may be co-axial with the waveguide so that all of the coating materials are exposed to the sample fluid.

Claims

CLAIMS 1. A sensor arranged to detect an analyte, the sensor comprising an optical waveguide, a region of which is associated with a material arranged to react selectively with an analyte, a change in refractive index of the region being indicative of the presence of the analyte.
2. A sensor arranged to detect a plurality of analytes, the sensor comprising a plurality of optical waveguides, a region of each waveguide being associated with a material arranged to react selectively with at least one analyte, a change in refractive index of a region being indicative of the presence of at least one analyte.
3. A sensor as claimed in claim 2, in which the waveguides are coated with materials arranged to react with different respective analytes.
4. A sensor as claimed in claim 1, 2 or 3, further comprising means arranged to produce a light beam and to guide the beam into the or each optical waveguide.
5. A sensor as claimed in claim 4, in which the light producing means includes a laser.
6. A sensor as claimed in claim 4, in which the light producing means includes a light emitting diode.

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7. A sensor as claimed in any previous claim, further comprising a detector arranged to detect a characteristic of light emerging from the or each waveguide, a change of which characteristic is indicative of a change in refractive index of the region.
8. A sensor as claimed in claim 7, in which the detector is arranged to detect the intensity of light emerging from the or each waveguide.
9. A sensor as claimed in any previous claim, further comprising a channel arranged, in use, to accommodate a sample for analysis, the channel also being arranged so that the or each material is exposed to the sample.
10. A sensor as claimed in any preceding claim, in which the or each waveguide is coated with the material.
11. A sensor as claimed in any preceding claim, in which the or each optical waveguide is porous, and the material is arranged to occupy pores of the waveguide.
12. A sensor as claimed in any preceding claim in which the or each waveguide is located within a substrate.
13. A sensor as claimed in any preceding claim in which the or each waveguide is located on a substrate.
14. A sensor, substantially as hereinbefore described with reference to, or as illustrated in, the accompanying drawing.

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15. A miniature chemical sensor incorporating a sensor as claimed in any preceding claim.
16. A miniature biosensor incorporating a sensor as claimed in any one of claims I to 12.
17. A method of detecting an analyte, comprising the steps of passing light through a waveguide, a region of which is associated with a material arranged to interact selectively with an analyte, and detecting a characteristic of the emerging light, a change of which characteristic is indicative of the presence of the analyte.
18. A method of detecting an analyte, substantially as hereinbefore described, with reference to the accompanying drawing.