GB2402474A - Analyte assay reading device having unequal numbers of photodetectors and test-strip zones - Google Patents

Analyte assay reading device having unequal numbers of photodetectors and test-strip zones Download PDF

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Publication number
GB2402474A
GB2402474A GB0312802A GB0312802A GB2402474A GB 2402474 A GB2402474 A GB 2402474A GB 0312802 A GB0312802 A GB 0312802A GB 0312802 A GB0312802 A GB 0312802A GB 2402474 A GB2402474 A GB 2402474A
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Prior art keywords
zone
light
test strip
test
reading device
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GB0312802A
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GB0312802D0 (en
Inventor
Andrew Peter Phelan
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Alere Switzerland GmbH
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Inverness Medical Switzerland GmbH
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Application filed by Inverness Medical Switzerland GmbH filed Critical Inverness Medical Switzerland GmbH
Priority to GB0312802A priority Critical patent/GB2402474A/en
Publication of GB0312802D0 publication Critical patent/GB0312802D0/en
Priority to US10/741,416 priority patent/US7239394B2/en
Priority to US10/816,216 priority patent/US7315378B2/en
Priority to ES04253078T priority patent/ES2323311T3/en
Priority to DE602004019315T priority patent/DE602004019315D1/en
Priority to DK04253078T priority patent/DK1484601T3/en
Priority to EP20100184102 priority patent/EP2385363A3/en
Priority to EP04253078A priority patent/EP1484601B1/en
Priority to AT04253078T priority patent/ATE422241T1/en
Priority to EP09151850A priority patent/EP2128604A1/en
Priority to DE102004027131.3A priority patent/DE102004027131B4/en
Priority to DE202004008809U priority patent/DE202004008809U1/en
Priority to CN200410063910.0A priority patent/CN1573316B/en
Priority to JP2004166895A priority patent/JP4630003B2/en
Priority to CN2011100408017A priority patent/CN102162789A/en
Priority to CN200910126685.3A priority patent/CN101650298B/en
Priority to FR0406066A priority patent/FR2855876B1/en
Priority to CN201110040811.0A priority patent/CN102162790A/en
Publication of GB2402474A publication Critical patent/GB2402474A/en
Priority to HK05103243.4A priority patent/HK1070692A1/en
Priority to US11/773,325 priority patent/US7616315B2/en
Priority to US12/615,723 priority patent/US20100172802A1/en
Priority to AU2010200451A priority patent/AU2010200451B2/en
Priority to US12/967,780 priority patent/US20110178723A1/en
Priority to US13/537,987 priority patent/US20130149776A1/en
Priority to US14/319,344 priority patent/US9933362B2/en
Priority to US15/906,489 priority patent/US10309899B2/en
Priority to US16/399,036 priority patent/US10830699B2/en
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/27—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using photo-electric detection ; circuits for computing concentration
    • G01N21/274—Calibration, base line adjustment, drift correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/4738—Diffuse reflection, e.g. also for testing fluids, fibrous materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/8483—Investigating reagent band
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/8483—Investigating reagent band
    • G01N2021/8488—Investigating reagent band the band presenting reference patches
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/8483—Investigating reagent band
    • G01N2021/8494—Measuring or storing parameters of the band
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/061—Sources
    • G01N2201/06106—Plural sources used for calibration
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2201/00—Features of devices classified in G01N21/00
    • G01N2201/06—Illumination; Optics
    • G01N2201/062—LED's
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
    • G01N31/22—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using chemical indicators

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Engineering & Computer Science (AREA)
  • Molecular Biology (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Plasma & Fusion (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Investigating Or Analysing Materials By The Use Of Chemical Reactions (AREA)

Abstract

An assay result reading device has at least one light source 10, at least one test strip zone and at least one photodetector 12 detecting zone emanated light, where the number of zones present on the test-strip differs from the number of detectors provided. When the number of detectors is greater than the number of zones each detector detects light from more than one zone, and when the number of zones is greater than the number of detectors each detector detect light from more than one zone. It is preferable to have one light source per strip zone and less photodetectors than light sources so that a single zone is "commonly read" by more than one detector. The embodiment shows a device having three LED light sources 10a, 10b, 10c, two photodiodes 12 and three test-strip regions, each of the photodiodes detecting light from two zones. The specific arrangement of light sources and detectors may obviate the need for careful alignment of the assay strip and the reader device.

Description

Title: Improvements in or Relating to Systems for Optical Detection or
Measurement
Field of invention
This invention relates to assay devices for the measurement of analyses. In particular it relates to electronic readers for use with assay teststrips which use optical methods of measurement.
Background of the Invention
Disposable analytical devices suitable for home testing of analyses are now widely commercially available. A lateral flow immunoassay device suitable for this purpose for the measurement of the pregnancy hormone human chorionic gonadotropin (hCG) is sold by Unipath under the brandname ClearBlue _and is disclosed in EP291194.
EP291194 discloses an immunoassay device comprising a porous carrier containing a particulate labelled specific binding reagent for an analyte, which reagent is freely mobile when in the moist state, and an unlabelled specific binding reagent for the same analyte, which reagent is immobilised in a detection zone or test zone downstream from the unlabelled specific binding reagent. Liquid sample suspected of containing analyte is applied to the porous carrier whereupon it interacts with the particulate labelled binding reagent to form an analyte-binding partner complex. The particulate label is coloured and is typically gold or a dyed polymer, for example latex or polyurethane. The complex thereafter migrates into a detection zone whereupon it forms a further complex with the immobilised unlabelled specific binding reagent enabling the extent of analyte present to be observed.
However such commercially available devices as disclosed above require the result to be interpreted by the user. This introduces a degree of subjectivity, which is undesirable.
Electronic readers for use in combination with assay test-strips for determining the concentration and/or amount of analyte in a fluid sample are known. EP653625 discloses such a device which uses an optical method in order to determine the result. An assay test strip such as that disclosed in EP291194 is inserted into a reader such that the strip is aligned with optics present within the reader. Light from a light source, such as a light emitting diode (LED), is shone onto the test strip and either reflected or transmitted light is detected by a photodetector. Typically, the reader will have more than one LED, and a corresponding photodetector is provided for each of the plurality of LEDs.
US5580794 discloses a fully disposable integrated assay reader and lateral flow assay test strip whereby optics present in the reader enable the result to be determined optically using reflectance measurements.
An important consideration in assay reading devices of this type is the requirement that the assay reader and the test strip are carefully aligned. This is because the visible signal formed in the detection zone (and the control zone, if present) is fairly narrow (about lmm wide), so a small displacement of the detection or control zone relative to the respective photodetector may significantly affect the reading made by the photodetector. In addition, it is generally important that the photodetector is as close as possible to the test strip, since the amount of light which is 'captured' by the photodiode is fairly small, and the signal intensity normally obeys the inverse square law, so that it diminishes rapidly as the separation between the test strip and the photodetector increases. Thus there is a requirement for the user to carefully align the test stick with the assay result reader which, especially for devices intended to be used in the home, can be problematic.
One solution to this problem is provided by US 5580794, wherein the assay strip is provided as an integral component of the result reader, thereby avoiding the need for the user to insert the test strip into the reader. An alternative solution is taught by EP 0833145, which discloses a test strip and assay result reader combination, wherein the assay result reading device can be successfully triggered to make a reading only when there is a precise three-dimensional fit between the test strip and the reader, thereby ensuring the correct alignment has been obtained.
Summary of the Invention
It is an object of the invention to provide an inexpensive, typically disposable, assay reader either for use with, or in integral combination with, an assay test strip such as disclosed by EP291 194.
It is a further object of the invention to provide an assay reader whereby the optics are provided within the reader in a compact arrangement.
It is yet a further object of the invention to provide an assay reader whereby the optics are arranged within the reader so as to provide an optimal or near optimal path length between the light source and photodetector thus ensuring a strong signal.
In a first aspect the invention provides an assay result reading device for reading the result of an assay performed using a test strip, the device comprising: a light source or sources, said light source/s emitting light incident upon at least two, spatially separated zones of the test strip; and a photodetector which detects light emanating from each of the two said zones. A photodetector which is used to detect light emanating from two distinct zones of the test strip, may be referred to as a "shared" photodetector.
In a second aspect the invention provides an assay result reading device for reading the result of an assay performed using a test strip, the device comprising: at least one light source incident upon a zone of the test strip; and at least two photodetectors both of which are able to detect some of the light emanating from the zone of the test strip illuminated by the light source. Such a zone, "read" by two or more photodetectors, may be referred to as a "commonly read zone".
In a third aspect, the invention provides a method of reading the result of an assay performed using a test strip, the method comprising the use of an assay result reading device in accordance with the first and/or second aspects defined above.
An advantage associated with the arrangement defined in relation to the first aspect of the invention is that of simplicity and economy. The manufacturing cost of the device is an especially important consideration if the reader is intended to be disposable: the photodetectors themselves, being relatively expensive components, form a significant part of the overall cost.
A further advantage is that the arrangement can provide greater accuracy and reduce the need for accurate positioning of the test strip relative to the reader. Suppose, for example, a test strip were provided with two separate, but closely spaced, control zones and a photodetector were positioned in the reader so as to be between the two control zones. If the test strip were slightly mix-aligned, laterally, relative to the assay reader device, the signal from one of the control zones would be less intense as the zone in question would be further from the photodetector. However, the other control zone would necessarily be closer to the photodetector by a corresponding amount, and would therefore provide a stronger signal to compensate for the weaker signal from the other zone. Furthermore it has been observed that the amount of bound material present at a particular zone will vary along the length of the zone in the direction of liquid flow. Preferential binding of the analyte takes place at the leading boundary edge and diminishes along the length of the zone in the direction of liquid flow. Thus any mis- aligurnent may result in a greater error than might have been expected if the analyte were captured in a uniform fashion. US 5968839 discloses an electronic assay reader for use with a test strip, wherein it is attempted to compensate for this non-uniform binding by the provision in the relevant binding zone of a plurality of deposits of immobilised capture reagent, the density of which deposits increases from the leading boundary to the trailing edge of the zone.
Similarly, the arrangement defined in relation to the second aspect of the invention also reduces the requirement for precise relative positioning of the test strip and the assay result s reading device: there is an in-built signal compensation for any misalignment between the test strip and the assay result reader for any zone which is commonly read by the two or more photodetectors, since relative movement of the commonly read zone away from one of the photodetectors will necessarily (within certain limits) involve movement by a corresponding amount towards the other photodetector/s.
The light emanating from the zone or zones, as appropriate, may be light which is reflected from the test strip or, in the case of a test strip which is transparent or translucent (especially when wet e.g. following the application of a liquid sample), light which is transmitted through the test strip. For the purposes of the present specification, light incident upon a particular zone of a test strip from a light source, and reflected by the strip or transmitted therethrough, may be regarded as "emanating" from the strip, although of course the light actually originates from the light source.
The preferred light sources are light emitting diodes (LEDs), and the preferred photodetector is a photodiode.
Reflected light and/or transmitted light may be measured by the photodetector. For the purposes of this invention, reflected light is taken to mean that light from the light source is reflected from the test strip onto the photodetector. In this situation, the detector is typically provided on the same side of the test strip as the light source. Transmitted light refers to light that passes through the test strip and typically the detector is provided on the opposite side of the test strip to the light source. For the purposes of a reflectance measurement, the test strip may be provided with a backing such as a white reflective MylarRTM plastic layer. Thus light from the light source will fall upon the test strip, some will be reflected from its surface and some will penetrate into the test strip and be reflected at any depth up to and including the depth at which the reflective layer is provided. Thus, a reflectance type of measurement may actually involve transmission of light through at least some of the thickness of the test strip. Generally, measurement of reflected light is preferred.
It is especially preferred that the reading device of the second aspect comprises a plurality of light sources, each light source being incident upon a respective zone of the test strip.
In principle, an assay result reading device in accordance with the invention may comprise any number of light sources and any number of photodetectors. For example, one embodiment in accordance with the first aspect of the invention which is expressly envisaged is the use of three light sources, each illuminating a respective zone of a test strip, and a single photodetector which is shared by all three zones. In practice it is difficult to arrange for more than three zones to share a single photodetector, since the photodetector will have trouble in detecting a sufficiently strong signal from those zones which are furthest away.
Preferably an assay result reader will be in accordance with both the first and second aspects of the invention. Desirably the reader will comprise a plurality of light sources and a smaller plurality of photodetectors. In particular, where the reader comprises X light sources for illuminating the test strip, it will comprise X-1 photodetectors. By sharing of the photodetectors between the respective light sources, the number of detectors required might be reduced still further, e.g. using three photodetectors to detect light emanating from an assay test strip that has been illuminated by five light sources.
More specifically, a preferred embodiment of the invention comprises a first, second and third light source, each light source illuminating respective first, second or third zones of a test strip. Conveniently the first light source illuminates a test zone or detection zone; the second light source illuminates a reference zone; and the third light source illuminates a control zone. The test or detection zone is a zone of the test strip in which an optical signal is formed (e.g. accumulation or deposition of a label, such as a particulate coloured binding reagent) in the presence or absence, as appropriate, of the analyte of interest. (By way of explanation some assay formats, such as displacement assays, may lead to the formation of signal in the absence of the analyte of interest) . The control zone is a zone of the test strip in which an optical signal is formed irrespective of the presence or absence of the analyte of interest to show that the test has been correctly performed and/or that the binding reagents are functional. The reference zone is a zone wherein, typically, only "background" signal is formed which can be used, for example, to calibrate the assay result reading device and/or to provide a background signal against which the test signal may be referenced.
This particular preferred embodiment also comprises two photodetectors. The first photodetector is substantially adjacent to or primarily associated with the first light source and is intended to detect light emanating the zone of the test strip illuminated by the respective light source. However the photodetector is so positioned as to be also capable of detecting some of the light emanating from the second zone of the test strip, illuminated by the second light source.
The second photodetector is substantially adjacent to or primarily associated with the third light source and is intended to detect light emanating from the zone of the test strip illuminated by the respective light source. However the photodetector is so positioned as to be also capable of detecting some of the light emanating from the second zone of the test strip, illuminated by the second light source.
Accordingly, this embodiment is in accordance with the first aspect of the invention since it comprises a plurality of light sources and a photodetector which detects light emanating from at least two spatially separated zones of the test strip. In addition, this embodiment described above is in accordance with the second aspect of the invention, since it; comprises two photodetectors, both of which are able to detect some of the light emanating from a zone of the test strip (in this instance, two photodetectors are able to detect light emanating from the second zone of the test strip).
It is preferred that, when the assay strip is correctly inserted into a reader device in accordance with the second aspect of the invention, the commonly read zone will be at a position intermediate between the two photodetectors, such that (within certain limits) a lateral movement away from one of the photodetectors will inevitably involve a t corresponding lateral movement towards the other photodetectors, so as to allow for the desired signal compensation effect. Typically, but not essentially, the commonly read zone will be approximately equidistant from the two photodetectors when the test strip is correctly positioned within the reader.
It is also preferred that, where an assay result reading device in accordance with the invention comprises a plurality of light sources, these are advantageously arranged such that a particular zone is illuminated only by a single one of the plurality of light sources.
For example, optical baffles may be provided between or around the light sources so as to limit the portion of the test strip illuminated by each light source.
For the avoidance of doubt, it is expressly stated that any of the features of the invention described as "preferred", "desirable", "convenient", "advantageous" or the like may be adopted in an embodiment of the invention in combination with any other feature or features sodescribed, or may be adopted in isolation, unless the context dictates otherwise.
The invention will now be further described by way of illustrative example and with reference to the accompanying drawings, in which: Figure 1 is a perspective view of an assay result reader in accordance with the preferred features of the first and second aspects of the invention; Figure 2 is a block diagram illustrating schematically some of the internal components of the reading device embodiment depicted in Figure 1; and Figures 3-5 are schematic representations of an embodiment incorporating a preferred light source/photodetector arrangement.
Example 1
An embodiment of an assay result reading device in accordance with the first and second aspects of the invention is illustrated in Figure 1.
The reading device is about 12cm long and about 2cm wide and is generally finger or cigar-shaped. However, any convenient shape may be employed, such as a credit card -shaped reader. The device comprises a housing 2 formed from a light- impermeable synthetic plastics material (e. g. polycarbonate, ABS, polystyrene, high density polyethylene, or polypropylene or polystyrol containing an appropriate light-blocking pigment, such as carbon). At one end of the reading device is a narrow slot or aperture 4 by which a test strip (not shown) can be inserted into the reader.
On its upper face the reader comprises two oval-shaped apertures. One aperture accommodates the screen of a liquid crystal display 6 which displays information to a user e.g. the results of an assay, in qualitative or quantitative terms. The other aperture accommodates an eject mechanism actuator 8 (in the form of a despressible button), which when actuated, forcibly ejects an inserted assay device from the assay reading device.
The test strip for use with the reading device is a generally conventional lateral flow test stick e.g. of the sort disclosed in US 6, 156,271, US 5,504,013, EP 728309, or EP 782707. The test strip and a surface or surfaces of the slot in the reader, into which the test strip is inserted, are so shaped and dimensioned that the test strip can only be successfully inserted into the reader in the appropriate orientation.
When a test strip is correctly inserted into the reader, a switch is closed which activates the reader from a "dormant" mode, which is the normal state adopted by the reader, thereby reducing energy consumption.
Enclosed within the housing of the reader (and therefore not visible in Figure 1) are a number of further components, illustrated schematically in Figure 2.
Referring to Figure 2, the reader comprises three LEDs 10a, b, and c. When a test strip is inserted into the reader, each LED10 is aligned with a respective zone of the test strip.
LED 10a is aligned with the test zone, LED 10b is aligned with the reference zone and LED 10c is aligned with the control zone. Two photodiodes 12 detect light reflected from the various zones and generate a current, the magnitude of which is proportional to the amount of light incident upon the photodiodes 12. The current is converted into a voltage, buffered by buffer 14 and fed into an analogue to digital converter (ADC, 16). The resulting digital signal is read by microcontroller 18.
One photodiode detects light reflected from the test zone and some of the light reflected from the reference zone. The other photodiode 12 detects some of the light reflected from the reference zone and the light reflected from the control zone. The microcontroller 18 switches on the LEDs l 0 one at a time, so that only one of the three zones is illuminated at any given time - in this way the signals generated by light reflected from the respective zones can be discriminated on a temporal basis.
Figure 2 further shows, schematically, the switch 20 which is closed by insertion of an assay device into the reader, and which activates the microcontroller 18. Although not shown in Figure 2, the device further comprises a power source (typically a button cell), and an LCD device responsive to output from the microcontroller 18.
In use, a dry test strip (i.e. prior to contacting the sample) is inserted into the reader, this closes the switch 20 activating the reader device, which then performs an initial calibration. The intensity of light output from different LEDs 10 is rarely identical.
Similarly, the photodetectors 12 are unlikely to have identical sensitivities. Since such variation could affect the assay reading an initial calibration is effected, in which the microcontroller adjusts the length of time that each of the three LEDs is illuminated, so that the measured signal from each of the three zones (test, reference and control) is approximately equal and at a suitable operating position in a linear region of the response profile of the system (such that a change in intensity of light reflected from the various zones each zone whilst the test strip is dry - subsequent measurements ("test values") are I normalised by reference to the calibration value for the respective zones (i.e. normalised value = test value/calibration value).
To conduct an assay, a sample receiving portion of the test strip is contacted with the liquid sample. In this case of a urine sample for instance, the sample receiving portion may be held in a urine stream, or a urine sample collected in a receptacle and the sample receiving portion briefly (about 5-10 seconds) immersed in the sample. Sampling may be performed whilst the test strip is inserted in the reader or, less preferably, the strip can be briefly removed from the reader for sampling and then reintroduced into the reader.
Measurements of reflected light intensity from one or more (preferably all three) of the zones are then commenced, typically after a specific timed interval following insertion of the test strip into the reader. Desirably the measurements are taken at regular intervals (e.g. at between 1-10 second intervals, preferably at between 1-5 second intervals). The measurements are made as a sequence of many readings over short (10 milliseconds or less) periods of time, interleaved zone by zone, thereby minimising any effects due to variation of ambient light intensity which may penetrate into the interior of the reader housing.
Example 2
This example described in greater detail the features of the preferred arrangement of LEDs and photodiodes outlined in Example 1.
Figure 3 is a schematic representation of the layout of the 3 LED/2 Photodiode optical system described in Example 1. Figure 4 is a schematic representation of a side elevation of one LED/Photodiode, and illustrating their position relative to a nitrocellulose test strip.
Figure 5 is a schematic plan view of the LED/Photodiode arrangement, again illustrating their position relative to a test strip.
Referring to Figure 3, an optics block component for accommodation within an assay result reading device in accordance with the invention comprises three LEDs (LED 1, 2 and 3) and two photodetectors (PDT and PD2). Light from LED 1 illuminates a test zone of a test strip (not shown) inserted into the reader. Light reflected from the test zone is detected by PDI. Light from LED3 illuminates a conko1 zone of the test skip and light reflected therefrom is detected by PD2. Light from LED2 illuminates a reference zone of the test strip.
Each LED is optically isolated by light-impermeable baffles 14, which ensure that each LED is capable of illuminating only its respective zone of the test strip. However the surfaces of the bakes facing LED2 are angled so as to allow LED2 to illuminate a slightly wider portion of the test strip than LED1 or 3, and this in turn allows light reflected from the reference zone to be detected by both PD1 and PD2.
The relative positioning of the test strip, LEDs and photodiodes may be better understood by reference to Figures 4 and 5.
Referring to Figure 4, a test strip 20 is inserted into the reading device above the plane of the LEDs and photodiodes. The test strip 20 is of laminate construction comprising an uppermost backing layer 22 of reflective opaque white MylarRTM, a synthetic plastics material, and a lowermost front layer 24 of clear MylarRTM. Sandwiched between the MylarRTM layers 22, 24 is a layer of porous material 26 (typically nitrocellulose). The purpose of the MylarRTM layers is to protect the delicate nikocellulose and provide mechanical strength and rigidity. In addition, the opaque backing layer 22 is relatively highly reflective, and this serves to improve contrast: relatively little light is absorbed by the layers 24, 26 and much of the light incident upon the various zones would therefore tend to pass straight through the test strip, but the reflective MylarRTM backing layer 22 ensures that this light is reflected. In addition, since the particulate label accumulating in the nitrocellulose layer 26 absorbs only a portion of the light as it passes through in a generally upwards direction, the label has in effect a second chance to absorb light as it passes back through the test skip 20 in a generally downwards direction, having been reflected by the opaque MylarRTM backing layer 22. This significantly improves the signal: noise ratio.
As--can be seen from Figure 4 and 5, the photodiodes PD1 and PD2 are aligned with their respective LEDs, LED1 and 3, but are offset, in that the LEDs lie towards one side of the test strip whilst the photodiodes lie towards the other side. Having the photodiodes offset in this way avoids, or at least reduces, the amount of specular reflection from the clear MylarRTM layer 24 detected by the photodiodes (i.e. light which is reflected directly from the initial MylarR M layer 24 without ever penetrating into the nitocellulose layer detection of such reflections would decrease the signal: noise ratio).
Referring to Figure 4 the relationship between signal intensity (I) and the angle (a) of the reflected light relative to the photodiode is I Oc cos 84.
Furthermore, the relationship between signal intensity (I) and the distance (x) of the photodiode from the reflecting object is I a: /X2 (i. e. the inverse square law).
It is apparent that, in view of the inverse square law, it would generally be preferred to position the photodiodes as close as possible to the test strip (i.e. decrease x), so as to increase the signal intensity I. However, merely decreasing the vertical separation y between the photodiode and the test strip would increase angle 3, decreasing the value of cos and therefore tend to reduce the signal intensity.
An alternative approach to improve signal intensity would be to reposition the photodiode nearer the centre of the system (indicated by the dotted lines in Figure 4) which would simultaneously decrease X and O. However, this is found to be undesirable as it increases the likelihood of detecting specular reflections. Accordingly an aligned but offset position for the photodiodes provides an optimal compromise of all these considerations.
It will be noted from Figure 5 that photodiode 1 is aligned with the test zone and photodiode 2 is aligned with the control zone. This alignment ensures that any variation of the relative positioning of the test strip and assay reader has minimal effect on the angle (3.
Whilst PD1 and PD2 are not aligned with the reference zone, and are therefore subject to a relatively large (and therefore undesirable) angle of 0, this problem is not significant because (i) the use of two detectors to read the reference zone allows for compensation of any positional variation, since relative movement of the test strip so as to increase for one photodetector will decrease for the other photodetector; and (ii) the reference zone is used to give a background reading for calibration purposes - the photodiodes are not required to measure the signal intensity from a narrow line (as with the test or control zones), and so the measurement of the reference zone signal is inherently less sensitive to variation from mix-positioning.

Claims (10)

1. An assay result reading device for reading the result of an assay performed using a test - strip, the device comprising: a light source or sources, said light source/s emitting light incident upon at least two, spatially separated zones of the test skip; and a photodetector which detects light emanating from each of the two said zones.
2. An assay result reading device for reading the result of an assay performed using a test strip, the device comprising: at least one light source incident upon a zone of the test strip; and at least two photodetectors both of which are able to detect some of the light emanating from the zone of the test strip illuminated by the light source.
3. A reading device in accordance with claim 1 and in accordance with claim 2.
4. A reading device in accordance with any one of the preceding claims, comprising a plurality of light sources.
5. A reading device in accordance with any one of the preceding claims, wherein the light source or sources comprises LEDs.
6. A reading device in accordance with any one of the preceding claims, wherein the photodetector is a photodiode.
7. A reading device in accordance with claim 1 or any claim dependent thereon, wherein the photodetector is positioned between the spatially separated zones.
8. A reading device in accordance with claim 2 or any claim dependent thereon, wherein the zone is positioned between the two photodetectors.
9. A method of reading the result of an assay performed using a test strip, the method comprising use of an assay result reading device in accordance with any one of the preceding claims.
10. An assay result reading device substantially as hereinbefore described and with reference to the accompanying drawings.
GB0312802A 2003-06-04 2003-06-04 Analyte assay reading device having unequal numbers of photodetectors and test-strip zones Withdrawn GB2402474A (en)

Priority Applications (27)

Application Number Priority Date Filing Date Title
GB0312802A GB2402474A (en) 2003-06-04 2003-06-04 Analyte assay reading device having unequal numbers of photodetectors and test-strip zones
US10/741,416 US7239394B2 (en) 2003-06-04 2003-12-19 Early determination of assay results
US10/816,216 US7315378B2 (en) 2003-06-04 2004-04-01 Optical arrangement for assay reading device
EP09151850A EP2128604A1 (en) 2003-06-04 2004-05-25 Optical arrangement for assay reading device
DE602004019315T DE602004019315D1 (en) 2003-06-04 2004-05-25 Optical arrangement for an assay reader
ES04253078T ES2323311T3 (en) 2003-06-04 2004-05-25 OPTICAL PROVISION FOR ANALYSIS READING DEVICE.
DK04253078T DK1484601T3 (en) 2003-06-04 2004-05-25 Optical device for an assay reading device
EP20100184102 EP2385363A3 (en) 2003-06-04 2004-05-25 Optical arrangement for assay reading device
EP04253078A EP1484601B1 (en) 2003-06-04 2004-05-25 Optical arrangement for assay reading device
AT04253078T ATE422241T1 (en) 2003-06-04 2004-05-25 OPTICAL ARRANGEMENT FOR AN ASSAY READER
DE102004027131.3A DE102004027131B4 (en) 2003-06-04 2004-06-03 Optical arrangement for assay reading device
DE202004008809U DE202004008809U1 (en) 2003-06-04 2004-06-03 Optical arrangement for assay reader
JP2004166895A JP4630003B2 (en) 2003-06-04 2004-06-04 Analysis result reading device and method for executing analysis
CN200410063910.0A CN1573316B (en) 2003-06-04 2004-06-04 Optical arrangement for assay reading device
CN201110040811.0A CN102162790A (en) 2003-06-04 2004-06-04 Optical arrangement for assay reading device
CN2011100408017A CN102162789A (en) 2003-06-04 2004-06-04 Optical arrangement for assay reading device
CN200910126685.3A CN101650298B (en) 2003-06-04 2004-06-04 Optical arrangement for assay reading device
FR0406066A FR2855876B1 (en) 2003-06-04 2004-06-04 OPTICAL ARRANGEMENT FOR A TEST READING DEVICE
HK05103243.4A HK1070692A1 (en) 2003-06-04 2005-04-15 Optical arrangement for assay reading device
US11/773,325 US7616315B2 (en) 2003-06-04 2007-07-03 Assay devices and methods
US12/615,723 US20100172802A1 (en) 2003-06-04 2009-11-10 Assay devices and methods
AU2010200451A AU2010200451B2 (en) 2003-06-04 2010-02-09 Optical arrangement for assay reading device
US12/967,780 US20110178723A1 (en) 2003-06-04 2010-12-14 Assay Devices and Methods
US13/537,987 US20130149776A1 (en) 2003-06-04 2012-06-29 Assay Devices and Methods
US14/319,344 US9933362B2 (en) 2003-06-04 2014-06-30 Assay devices and methods
US15/906,489 US10309899B2 (en) 2003-06-04 2018-02-27 Assay devices and methods
US16/399,036 US10830699B2 (en) 2003-06-04 2019-04-30 Assay devices and methods

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0312802A GB2402474A (en) 2003-06-04 2003-06-04 Analyte assay reading device having unequal numbers of photodetectors and test-strip zones

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GB0312802D0 GB0312802D0 (en) 2003-07-09
GB2402474A true GB2402474A (en) 2004-12-08

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EP1674853A1 (en) * 2004-12-23 2006-06-28 Agilent Technologies, Inc. A method of reading an assay using low resolution detection
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