WO2008017819A1

WO2008017819A1 - Assay apparatus, assay reading apparatus and method

Info

Publication number: WO2008017819A1
Application number: PCT/GB2007/002974
Authority: WO
Inventors: Damian Bond; John Gilmour; Andrew Mitchell; Nasr-Eddine Djennati; Paul Couchman; Patricia Connolly
Original assignee: Ivmd (Uk) Limited
Priority date: 2006-08-08
Filing date: 2007-08-07
Publication date: 2008-02-14

Abstract

Assay apparatus comprising an assay device (2) arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample. The indication is detectable using electromagnetic radiation and the assay device comprises a device, such as a photovoltaic cell (4), for converting electromagnetic radiation which has been affected by the indication into electrical energy, thereby to quantify any indication produced. The output of the photovoltaic cell may be used to provide an output to a user, particularly a binary output.

Description

ASSAY APPARATUS. ASSAY READING APPARATUS AND METHOD

The present invention relates to assay apparatus, assay reading apparatus and to a method of reading an assay using such apparatus. The invention is particularly, although not exclusively, concerned with the reading of immunoassays, especially immunoassay strips.

Immunoassays are widely used in the medical field to detect the presence and/or concentration of substances of interest in body fluids. They are typically provided in the form of a test strip arranged to provide a visual indication of the results of the assay. One example is the so called lateral flow immunoassay in which a test result is indicated by the appearance of a coloured line on a test strip. Such strips are necessarily single use devices and so it is desirable that they can be manufactured at a reasonably low cost, and so that the environmental impact of their disposal is kept to a minimum.

Whilst immunoassays which provide a visual indication of a result are simple to use, the result of the assay is open to interpretation and thus subject to some unreliability, especially where the result is interpreted by a comparatively untrained person as opposed to, say, a medical professional. Various proposals have been made to overcome, this problem by the provision of assay reading devices, either incorporated into an assay strip or arranged to read an assay strip. Example devices suitable for reading the results of immunoassays which provide a visual result are disclosed in US 5,580,794, EP 0 653 625 and EP 0 833 145.

A common feature of these devices is the provision of a powered light source to illuminate the test strip or equivalent together and a powered light detector, typically a photodiode, and associated circuitry to read the strip. This necessitates the provision of a power supply for both the light source and detector, which increases the cost and complexity of the device, and can cause an environmental problem on disposal. It is perhaps for these reasons, as well as the general complexity of the device, that up to now a separate re-usable reader has typically been provided to read disposable single use assay strips. This leads to a further increased cost where a user may only wish to perform a single test, or limited number of tests, for example a pregnancy test. Also, provision of a separate reader brings its own technical problems, such as the need for accurate alignment of a test strip with the reader. Thus there is an increased risk of operator error as compared to a self contained single unit.

In is the object of the present invention to provide an improved, simplified, means for reading an assay, which enables cost effective production of self contained single use assay apparatus. Nevertheless the invention may also be implemented in a separate assay reader.

According to a first aspect of the present invention there is provided assay apparatus comprising an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, and comprising a device for converting electromagnetic radiation which has been affected by the indication into electrical energy, thereby to quantify any indication produced.

According to a second aspect of the present invention there is provided a reader for reading an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, the assay reader comprising a device for converting electromagnetic radiation which has been affected by the indication into electrical energy, thereby to quantify any indication produced.

According to a third aspect of the present invention there is provided a method of reading an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, the method comprising the steps of: directing electromagnetic radiation towards a region of the assay device at which the indication may be provided, collecting the electromagnetic radiation after transmission and/or reflection by the device and converting the collected electromagnetic radiation into electrical energy, thereby to quantify any indication produced by the assay device.

Converting electromagnetic radiation into electrical energy as a means of quantifying an indication produced by the assay device significantly reduces the power requirement of the apparatus or method compared to other sensing techniques.

The assay device may be an immunoassay device. The indication produced by the device is preferably detectable by electromagnetic radiation in the visible or near visible region of the electromagnetic spectrum.

The indication may therefore be a visible one. It could, however, only be detectable by use of near infra red or ultraviolet radiation, and thus be invisible, or substantially so. An advantage of this latter arrangement is that a user would be unable to choose to read the assay device themselves.

The indication may result in a change in the way in which incident electromagnetic radiation is absorbed, reflected or refracted by the device, for example a colour change. In one arrangement the device transmits visible electromagnetic radiation and the indication comprises a reduction of the amount of radiation transmitted by a given region of the device.

Example suitable assay devices include lateral flow immunoassay devices and devices where it is desired to measure the presence of a fluid, or a wave front or meniscus in a fluid. The assay device may be an immunoassay strip.

The device for converting electromagnetic radiation into electrical energy is preferably a photovoltaic cell. The assay device preferably comprises an at least partially transparent to light material and is arranged to produce a visible indication on a surface of and/or within the material. The photovoltaic cell is preferably mounted relative to the assay device such that light transmitted through the device in the region where the indication may be produced enters the photovoltaic cell. Thus, when a visible indication is produced the proportion of light incident on the device which enters the photovoltaic cell after travelling through the device is altered. This, in turn, affects the output of electrical energy from the photovoltaic cell.

The apparatus may be operated using ambient light. Alternatively, a light source may be provided.

Preferably means are provided for measuring the output of the photovoltaic cell, and outputting a measurement result to a user.

In one arrangement the apparatus is arranged to provide a binary output, for example yes or no. In this case means are provided for determining if the output of the photovoltaic cell is above or below a chosen threshold, and outputting an appropriate result to a user.

In another arrangement a second photovoltaic cell is provided at a location where it will not be affected by the indication and the output is compared with the output of the first photovoltaic cell to determine the presence or otherwise of the indication. The second photovoltaic cell serves to provide a reference signal indicative of the ambient light level. The apparatus may include means for determining if the difference between the output of two photovoltaic cells reaches a predetermined value.

Any suitable output means can be employed, for example a lamp such as an

LED which is illuminated or not illuminated to indicate a yes or no result, or a display screen such as a liquid crystal display (LCD) arranged to display the word YES or NO or some other word or indicia as appropriate. Where a result with greater quantisation is required multiple lamps could be employed to indicate different values, or a result could be displayed on a screen using alphanumeric characters. Any output device can be used as desired.

A timing device may be provided to measure a predetermined period of time between introduction of a sample to be tested to the assay device and reading of the device. A sensing means may be provided to determine when a sample is introduced. The sensing means may comprise a pair of electrodes.

The assay device may produce more than one indication, and a respective photovoltaic cell may be provided to quantify each indication. In particular the assay device may be arranged to produce a reference indication, to confirm that it is functioning correctly, at least in some respects.

In one embodiment the device comprises an elongate strip of material, forming a base, on which an immunoassay strip is mounted. One, two, or three photovoltaic cells are mounted in apertures or transparent regions of the base beneath a chosen region or regions of the immunoassay strip, and arranged to receive light transmitted through the immunoassay strip. One or two photovoltaic cells may be mounted beneath areas of the immunoassay strip where indications may be formed. The indication may comprise a reduction in the light transmitting properties of the strip, or a change in its colour, and may be caused by the build up of a substance in an area of the strip. An additional photovoltaic cell may be mounted beneath an area of the strip where no indication can be formed, in order to provide a reference signal.

In order that the invention may be more clearly understood an embodiment thereof will now be described by way of example with reference to the accompany drawings of which: Figure 1 is a schematic plan view of an immunoassay apparatus according to the invention;

Figure 2 is a side view of the apparatus of figure 1 ;

Figure 3 is a plan view of the base of the apparatus of figure 1 ;

Figure 4 is a plan view of the base of figure 4 with the photovoltaic cells removed; and

Figure 5 is a schematic block circuit diagram of the test strip of figure

1.

In the figures like reference numerals are used to identify like components throughout. Broken lines are used in figures 1 and 2 to show hidden detail. In what follows the terms top, bottom, side and the like are used for convenience only and refer to the apparatus as illustrated, and should not be taken to be otherwise limiting.

Referring to the drawings, an immunoassay apparatus comprises a base 1 formed from an elongate substantially rectangular strip of plastics material, for example polystyrene. An elongate immunoassay strip 2 of partially transparent porous material, such as nitrocellulose, is mounted on the base 1, and overhangs one end of the base. The strip 2 stops short of the other end of the base 1, and an LCD display 3 and photovoltaic cell 4 are mounted over an electronic circuit 5 on the remainder of the base 1, to which each are electrically connected.

Three, spaced apart, elongate, substantially parallel apertures 6, 7 and 8 are formed in the base 1. A respective matched photovoltaic cell 9, 10, 11 is mounted in each aperture, such that the light receiving part of the photovoltaic cell is directed towards the immunoassay strip 2. Each photovoltaic cell 9, 10, 11 is electrically connected to the circuit 5.

The overhanging end of the immunoassay strip 2 is provided with two spaced apart electrodes 12 spaced from the free end of the strip 2 and electrically connected to the electronic circuit 5.

The electronic circuit comprises three amplifiers and three low pass filters 13, the output of each photovoltaic cell 9, 10, 11 mounted in the apertures 6, 7, 8 in the base 1 is connected to a respective amplifier and filter. The filters remove any effects of noise pick up, to provide a substantially DC output. The output of each amplifier and filter combination is connected to a logic control circuit 14. The logic control circuit 14 is in turn connected to a timer 15 and to an LCD display driver 16 which drives the LCD display 3. The timer is connected to the electrodes 12 on the immunoassay strip 2. The outputs of the central photovoltaic cell 10 are also connected to a threshold circuit which is, in turn, connected to the logic control circuit 14.

The immunoassay strip 2 comprises a first area 18, the sample deposit area, extending from the electrical contacts to the free end of the strip 2. To the other side of the electrical contacts 12 is a central area 19 which extends up to the region of the strip which extends over the aperture 8 in the base 1 nearest the free end of the immunoassay strip 1. The remainder of the immunoassay strip 2 forms a test results area 20.

In this example the apparatus is arranged to determine the presence of hCG

(human chorionic gonadotropin) in a urine sample. If the level of hCG in a particular sample exceeds a certain level this is indicative of a pregnancy in the donor. Of course it will be appreciated that the apparatus could be arranged to test for another substance of interest. The sample deposit area 18 is intended to receive a fluid sample for analysis. In use, a urine sample is applied to the free end of the strip 10 and then flows by capillary action towards the test area 20, via the central area 19. The central area 19 of the strip is provided with pre-deposited hCG 21, or an analogue thereof, labelled with colloidal gold tag particles 22 which contain a specific probe for the hCG molecule. During flow of a sample along the strip the tag particles become bound, by kinetics or preferential binding, to free hCG 21 in the sample to produce complexes 23 which are released into solution.

The test result area 20 is provided with a line of capture reagent 24, the test line, extending over the aperture 8 nearest the free end of the immunoassay strip 2, and hence its associated photovoltaic cell 11. The capture reagent 24 specifically binds to and captures hCG. In use tagged hCG complexes which migrate to the test results area will become captured on the test line 24, resulting in a build up of colloidal gold on the test line 24 producing a visible line of colloidal gold on the strip 2, over the photovoltaic cell 11. Formation of the visible line reduces the amount of light which may be transmitted through the strip 2 onto the photovoltaic cell 11.

Beyond the test line 24 of capture reagent 24 is a thicker line 25, the reference line, of another reagent chosen to capture the colloidal gold particles attached to the hCG specific probe, which will be present in any test solution migrating along the test strip. Thus colloidal gold will build up on this line of reagent during use, whether or not hGC is present in a test sample. Appearance of this line thus signifies correct operation of the test strip (at least in some respects), and is a common feature of such strips. The line of reagent 25 is positioned over the aperture 5 in the base 1 closest to the circuit 5 end of the base 1, and its associated photovoltaic cell 9.

Both the test 24 and reference 25 lines are narrower than their associated photovoltaic cells 9, 11 allowing for some tolerance is aligning the lines with the photovoltaic cells when manufacturing the apparatus.

It will be appreciated that the immunoassay strip is, save for provision of the electrodes 12, of conventional construction. The purpose of the remainder of the apparatus is to automatically read a test result form the immunoassay strip.

Power for the electronic circuit 5 is provided by photovoltaic cell 4. Jn an alternative embodiment the photovoltaic cell could be replaced with a conventional chemical cell or battery, or indeed any other suitable electrical power supply.

In use, when a urine sample is introduced onto the sample deposit area 18 of the immunoassay strip 2 this changes the electrical resistance between the two electrodes 12. This change in resistance is monitored by the electronic circuit 5 and causes the timer 15 to start to measure a predetermined period, in the present example three minutes. This is the period which must elapse between introduction of a sample to the test area 18 and reading of the result of the test.

The apparatus must be exposed to light, either natural or artificial. Light penetrates the immunoassay strip and in the region of the apertures 9, 10, 11 in the base 1 enters the photovoltaic cells, causing them to generate an electrical signal.

After the predetermined time has elapsed, the logic circuit compares the output of the three photovoltaic cells 9, 10, 11 (amplified and filtered as appropriate) mounted on the base 1 in order to read the results of the test.

Starting from the free end of the immunoassay strip, the output of the first photovoltaic cell 11 will be affected by any build up of colloidal gold on the test line of reagent 24. The output of the second photovoltaic cell 10 will depend only on the level of incident light. The output of the third photovoltaic cell 9 will be affected by the build up of colloidal gold on the reference line of reagent 25. The output signal of the second 10 and third 9 photovoltaic cells are first compared by the logic circuit to determine if there is a build up of colloidal gold along the reference line 25, indicating that the immunoassay strip has functioned correctly. If the difference in outputs reaches a predetermined value, then the output of the first 11 and second 10 photovoltaic cells are compared to determine if there is a build up of colloidal gold along the test line 24. If the difference reaches a certain value the outcome of the test is positive, if not the outcome is negative, and the logical circuit causes the word YES or NO to be displayed on the LCD screen as appropriate. Alternatively, if the difference in output signals between the second 10 and third 9 photovoltaic cells does not reach the predetermined value the logic circuit causes the word VOID to be displayed on the LCD screen.

The apparatus provides a convenient and economic way to perform and automatically read the result of an immunoassay. Use of photovoltaic cells to measure changes in the level of light transmitted by the immunoassay strip results in a lower power consumption than other approaches, enabling power requirements of the electronic circuit 5 to be met by way of a fourth photovoltaic cell if desired. This allows for reduced cost of manufacture, and lower environmental impact on disposal than for comparable apparatus.

The above embodiment is described by way of example only. Many variations are possible without departing from the invention.

Claims

1. Assay apparatus comprising an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, and comprising a device for converting electromagnetic radiation which has been affected by the indication into electrical energy, thereby to quantify any indication produced.

2. A reader for reading an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, the assay reader comprising a device for converting electromagnetic radiation which has been affected by the indication into electrical energy, thereby to quantify any indication produced.

3. Apparatus as claimed in claim 1 wherein the assay device is an immunoassay device.

4. Apparatus as claimed in either claim 1 or 3 wherein the indication produced by the assay device is detectable by electromagnetic radiation in the visible or near visible region of the electromagnetic spectrum.

5. Apparatus as claimed in either claim 1 or 3 wherein the indication produced by the assay device is only detectable by use of near infra red or ultraviolet radiation.

6. Apparatus as claimed in any of claims 1 and 3 to 5 wherein the indication produced by the assay device results in a change in the way in which incident electromagnetic radiation is absorbed, reflected or refracted by the assay device.

7. Apparatus as claimed in claim 6 wherein the indication comprises a colour change.

8. Apparatus as claimed in claim 6 wherein the indication comprises a reduction of the amount of radiation transmitted by a given region of the assay device.

9. Apparatus as claimed in any of claims 1 and 3 to 8 wherein the assay device comprises an at least partially transparent to light material and is arranged to produce the indication on a surface of and/or within the material.

10. Apparatus as claimed in claim 9 wherein the device for converting electromagnetic radiation which has been affected by the indication into electrical energy is mounted relative to the assay device such that light transmitted through the assay device in the region where the indication may be produced enters the device for converting electromagnetic radiation which has been affected by the indication into electrical energy.

11. Apparatus as claimed in and of claims 1 and 3 to 9 or the reader claimed in claim 2 wherein the device for converting electromagnetic radiation into electrical energy is a photovoltaic cell.

12. Apparatus as claimed in any of claims 1 and 3 to 11 or a reader as claimed in either of claims 3 or 11 comprising a light source.

13. Apparatus or a reader as claimed in either claim 11 or 12 wherein means are provided for measuring the output of the photovoltaic cell, and outputting a measurement result to a user.

14. Apparatus or a reader as claimed in claim 13 arranged to provide a binary output to a user.

15. Apparatus as claimed in any of claims 1 and 3 to 14, or a reader as claimed in any of claims 2 and 11 to 14 wherein a second device for converting electromagnetic radiation into electrical energy is provided at a location where it will not be affected by the indication and its output is compared with the output of the device for converting electromagnetic radiation which has been affected by the indication into electrical energy to determine the presence or otherwise of the indication.

16. Apparatus or a reader as claimed in claim 15 comprising means for determining the difference between the output of the two devices for converting electromagnetic radiation into electrical energy.

17. Apparatus or a reader as claimed in claim 13 or any of claims 14 to 16 when dependent, directly or indirectly, on claim 13 wherein the means for outputting a measurement result to a user is one or more of a lamp, an LED, a display screen and a liquid crystal display (LCD).

18. Apparatus as claimed in any of claims 1 and 3 to 17, or a reader as claimed in any of claims 2 and 11 to 17 comprising a timing device to measure a predetermined period of time between introduction of a sample to be tested to the assay device and reading of the device.

19. Apparatus as claimed in any of claims 1 and 3 to 18, or a reader as claimed in any of claims 2 and 11 to 18 comprising a sensing means to determine when a sample is introduced.

20. Apparatus as claimed in any of claims 1 and 3 to 19, or a reader as claimed in any of claims 2 and 11 to 18 wherein the assay device is arrange to produce more than one indication.

21. Apparatus as claimed in claim 1 or any of claims 3 to 20 when dependent directly or indirectly on claim 1 wherein the assay device comprises an elongate strip of material, forming a base, on which an immunoassay strip is mounted.

22. Apparatus as claimed in claim 21 wherein one, two, or three photovoltaic cells are mounted in apertures or transparent regions of the base beneath a chosen region or regions of the immunoassay strip, and arranged to receive light transmitted through the immunoassay strip.

23. A method of reading an assay device arranged to provide an indication of the presence and/or concentration of a substance of interest in a sample, the indication being detectable using electromagnetic radiation, the method comprising the steps of: directing electromagnetic radiation towards a region of the assay device at which the indication may be provided, collecting the electromagnetic radiation after transmission and/or reflection by the device and converting the collected electromagnetic radiation into electrical energy, thereby to quantify any indication produced by the assay device.

24. A method as claimed in claim 23 wherein the electromagnetic radiation is in the visible or near visible region of the electromagnetic spectrum.

25. A method as claimed in claim 23 wherein the electromagnetic radiation is near infra red or ultraviolet radiation.

26. A method as claimed in any of claims 23 to 25 wherein the indication produced by the device results in a change in the way in which incident electromagnetic radiation is absorbed, reflected or refracted by the assay device.

27. A method as claimed in any of claims 23 to 26 wherein the electromagnetic energy radiation is collected by a photovoltaic cell.

28. A method as claimed in any of claims 23 to 27 wherein the indication produced by the assay device is quantified to provide a binary output.

29. A method as claimed in any of claims 23 to 28 comprising the steps of introducing a sample onto the assay device and waiting a predetermined time period before quantifying the indication produced by the device.