GB2609419A

GB2609419A - Lateral flow test

Info

Publication number: GB2609419A
Application number: GB2110912.9A
Authority: GB
Inventors: Chong Cheah Boon; Volk Alexander; Cernusca Michael; Calaerts Geert
Original assignee: Ams International AG
Current assignee: Ams International AG
Priority date: 2021-07-29
Filing date: 2021-07-29
Publication date: 2023-02-08
Also published as: WO2023006615A1; GB202110912D0

Abstract

A time resolved fluorescence spectroscopy lateral flow test 100a comprising a lateral flow test strip 101 and an optical module 102. The lateral flow test strip comprises a quantum dot fluorescent label that emits fluorescence following illumination by a pulse of energy. The optical module comprises a pulsed energy source 103 for illuminating the test strip and a spectral sensor 104 for detecting fluorescence from the test strip in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip. The test strip may comprise a second quantum dot fluorescent label. The spectral sensor may perform plurality of time-gated measurements. The lateral flow test may be disposable, handheld, or provided in a housing. The spectral sensor and the pulsed energy source may be mounted on a PCB wherein the spectral sensor may comprise an ASIC.

Description

Lateral Flow Test

Field

The present disclosure relates to a lateral flow test and an optical module for use therewith.

Background

Time resolved fluorescence spectroscopy is a detection technique for quantifying molecules. In time resolved fluorescence spectroscopy, a sample is illuminated with energy corresponding to an excitation energy of a particle that exhibits fluorescent properties. When the energy source is switched off, the particle fluoresces for a time.

The wavelength and fluorescence lifetime or decay time (i.e. the time it takes to decay to fraction of the initial intensity, for example, to decay to 1/e or 36.79% of the original value) are characteristic of the particle and are used to quantify how much of a particle is present in the sample.

Conventional fluorescence spectroscopy is performed on microplate well based benchtop devices that typically have a xenon/halogen/deuterium broadband light source and/or double monochromator. Such devices measure absorbance, reflectance, fluorescence and/or luminescence of a sample being tested and require complex optomechanical setups that may include costly beam splitters, optical lenses and optical filters to guide the light inside the device. Microplate well based devices may also require pumps and other mechanical parts to control the flow of reagents, liquids and analytes in the wells inside the device. Given the cost and complexity of such devices, only a limited number of the devices may be available for use in a professional healthcare environment such as a hospital. If a large number of microplate tests need to be run, the benchtop device may be a bottleneck in how many tests can be provided in a given time.

Lateral flow tests are a type of assay that test for the presence of one or more target analytes in a fluid sample. The fluid sample is introduced onto a test strip where it flows by capillary action through one or more areas provided with a label whose properties are known, for example antibodies conjugated to gold nanoparticles. The target analyte binds with known conjugated proteins with label. The fluid sample including the target analyte now bound with a label then flows through one or more test and/or control areas where the target analyte with bound label becomes bound, for example to an antibody on the test and/or control area, and causes a detectable change, for example in colour, in the test and/or control area. The presence or absence of the analyte is then determined from the change in the test area. The control area indicates whether the test was successfully run. Lateral flow tests are typically designed for use in point-of-care environments such as in hospitals or at home where a quick, almost instant result is desired. Lateral flow tests are one-use only and are disposed of after use.

Lateral flow tests may be qualitative or quantitative tests. Qualitative tests present a colour change in visible light and a user may determine the result of the test (positive or negative) by sight alone. Qualitative tests do not allow the determination of how much of a target particle is present. In contrast, quantitative tests determine the strength or amount of a colour change in the sample and determine how much analyte is present from that change. Quantitative tests typically require complex reader optics and electronics to provide consistent and accurate readings, for example, those found in the above-described bench top sized fluorescence spectroscopy devices. Accordingly, as described above, even if a point-of-care environment has access to a large supply of lateral flow tests, they may not be able to read all of them quickly. This is particularly the case where only a small number of benchtop reader devices are available, resulting in a bottleneck in how many tests can be read in a given time period.

A further problem of using fluorescence spectroscopy, in particular bench top devices, to read lateral flow tests is that the material (for example nitrocellulose) of the test strip itself may exhibit auto-fluorescence i.e. fluorescence from a non-label or target material that results in noise in the signal. Non-target biological materials found in the sample when it is collected may also exhibit auto-fluorescence. This can reduce the signal to noise ratio and make it difficult to read the result. Typically, bench top devices also require multiple excitation sources or a monochromator to select wavelength, each emitting a single wavelength matched to the excitation wavelength of the specific fluorophore they are attempting to excite. The use of multiple excitation sources adds to the monetary cost of such devices.

Finally, conventional organic dyes that are typically used for fluorescence spectroscopy suffer from photo bleaching. This is where exposure to environmental light causes the fluorescent label to lose its fluorescent capabilities over time. This significantly reduces the shelf life of any lateral flow tests that would use such dyes as labels. Additionally, organic dyes are only able to produce fluorescence for a limited number of illumination cycles before they lose their fluorescence activity. Other problems of conventional organic dyes for fluorescence spectroscopy include: a relatively small stoke shift, stability and reproducibility issues, low sensitivity, and limited colour choices.

Summary

The inventors have appreciated that the above problems of bench top fluorescence spectroscopy devices in the field of lateral flow tests may be solved by combining the three concepts of: (i) time resolved fluorescence spectroscopy, (ii) quantum dot fluorescence labels, and (iii) an integrated optical module with a disposable or semi-disposable lateral flow test. The optical module has an integrated spectral sensor and pulsed energy source that take the place of the complex optics and electronics of known benchtop devices. The spectral sensor makes time gated measurements synchronised with pulse times of the pulsed energy source. Synergistically, the replacement of the high sensitivity benchtop optics and electronics with a miniaturised, integrated spectral sensor and pulsed energy source is made possible by using quantum dots as the fluorescent label. This is because the signal-to-noise ratio of fluorescence signals from quantum dot labels is better than conventional organic dyes.

Specifically, with reference to the above-described problems, quantum dots are highly fluorescent (for example having a quantum efficiency of almost 1), are resistant to photo bleaching, and have higher stability thereby ensuring reproducibility between tests and increasing the shelf life of the tests. Further, they can be produced in colloidal suspensions with narrow emission spectra, making them amenable to both spatial and spectral multiplexing. They also have fluorescent lifetimes in the range of 100-500ns to comfortably avoid unwanted, background fluorescence from the sample and/or test strip and they have a large stoke shift so their signal is easily distinguishable over the optical module's excitation energy source to avoid unwanted background from the excitation. The above factors thus provide an order of magnitude improvement of signal to noise ratio, allowing a cheap, simpler spectral sensor ASIC and pulsed energy source to be used in the optical module instead of the expensive and complex optics and electronics typically used by conventional bench top devices. In particular, as quantum dot labels emit strong fluorescence in narrow bands they synergise very well with spectral sensors, which synergistically are configured to detect signals in specific, narrow wavelength bands Thus, the advantages of fluorescence spectroscopy may be provided in a cheap, miniaturised, disposable way without the need for an expensive, bulky benchtop device.

Further and synergistically, as the spectral sensor ASIC and pulsed energy source do not rely on complex optics and electronics compared to benchtop devices, and have only a single illumination and detection optical path, multiplexed spatial, spectral and lifetime or temporal measurements may all be made in the same optical path using the same optical module. In addition, quantum dots can be made so that they fluoresce with different fluorescence wavelengths despite having the same excitation wavelength (for example a peak around 340nm to 360nm). This accordingly does not require multiple excitation wavelengths and is thus advantageous over a bench top reader with multiple sources. In benchtop readers, multiplexing is typically done by using moving optomechanical parts and mirrors and changing the optical path inside the device, which is inconvenient and not possible in a miniaturised device.

Thus, according to a first aspect, there is provided a lateral flow test comprising: a test strip and an optical module, wherein the optical module comprises: a pulsed energy source for illuminating the test strip; and a spectral sensor for detecting fluorescence from the test strip in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip, and wherein the test strip comprises: a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse.

In some implementations, the test strip may comprise a second quantum dot fluorescent label for binding to a second target on the test strip, the second quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse.

Advantageously, this allows multiple analytes to be detected using the same test.

In some implementations, the present disclosure allows spatial, spectral and lifetime or temporal measurement modes to be multiplexed in an integrated, miniaturised, disposable way as is described below. Advantageously, this provides a greater degree of flexibility to test for many different types of analytes that may have different sensitivities to different measurement modes.

To make a spatial mode measurement, the first and second quantum dot fluorescent labels are provided on spatially separated areas of the test strip, and the spatially separated areas may be measured separately (for example by moving the test strip over the sensor so that each line may be measured separately). The spectral sensor is thus configured to distinguish between fluorescence from the first and second quantum dots by spatial position on the test strip. The test strip may accordingly be provided with spatially separated dots, lines and/or other shapes having different or the same fluorescent labels thereon, each testing for a different analyte.

To make a spectral mode measurement, the first and second quantum dot fluorescent labels are provided on spatially overlapping areas of the test strip. Instead of distinguishing between fluorescence signals spatially, the first and second labels fluoresce in respective first and second wavelengths of the plurality of wavelengths. The spectral sensor comprises a plurality of detection channels, each detection channel configured to detect one of the plurality of wavelengths to distinguish between fluorescence from the first and second quantum dots by wavelength i.e. spectrally. Thus, the signal strengths in the different detection channels correspond to how much of each of each analyte is present.

To make a lifetime or temporal mode measurement, the first and second quantum dot fluorescent labels are provided on spatially overlapping areas of the test strip and fluoresce for respective first and second fluorescence lifetimes, which do not overlap with each other and which can accordingly be distinguished from each other. The spectral sensor is configured first to separate the fluorescence signals by wavelength as above for the spectral mode measurement and then additionally to calculate the fluorescence lifetime for each detected wavelength. The calculated lifetimes may then be used to distinguish between fluorescence from the first and second quantum dots by fluorescence lifetime.

In some implementations, the pulsed energy source is configured to illuminate the test strip in a plurality of wavelengths corresponding to respective excitation wavelengths of the first and second quantum dot fluorescent labels.

Advantageously, this means there is no need to provide multiple separate energy sources in the way that benchtop devices do thereby reducing the complexity and cost of the system.

In some implementations, the lateral flow test is a disposable, handheld lateral flow test, wherein the optical module and test strip are provided in a housing configured to be held by a user.

Advantageously, this allows the lateral flow tests to be easily stored and handled without the test strip part being separate from the optical reading part.

In some implementations, the lateral flow test comprises a printed circuit board (PCB) positioned in the housing, the spectral sensor and the pulsed energy source being mounted on the PCB. In some implementations, the spectral sensor comprises an application specific integrated circuit (ASIC) mounted on the PCB in the housing.

Advantageously, integrating the spectral sensor, for example an ASIC, and the pulsed energy source on the same PCB in the housing, reduces circuit parasitics. This is particularly important for fluorescence spectroscopy measurements where measurement sensitivity is highly dependent on accurate pulse timings and widths, and accurate measurement windows of the time-gated measurements. Thus, sensitivity may be greatly improved in a mass producible way compared to any system where excitation source and sensor are separate.

In some implementations, the pulsed energy source is configured to emit a plurality of pulses and the spectral sensor is configured to detect fluorescence from the test strip at a plurality of the predetermined times after the start of each of said pulses to calculate an average fluorescence signal value.

Advantageously, this averaging reduces any noise caused by unwanted variations and/or jitter in the pulsing of the energy source and/or variations in the fluorescence label quality thereby improve the signal to noise ratio. In particular, as the excitation pulse is often in the region of a few nanoseconds or picoseconds, it is difficult to consistently produce the exact same pulse length, resulting in pulse jitter that introduces noise in the timing of the fluorescence measurements. This can be overcome by repeating the measurement a plurality of times and taking the average. However, if organic dyes were to be used, they lose their ability to fluoresce after a small number of cycles, preventing the ability to reduce noise by averaging. Thus, the use of quantum dots provides a synergistic advantage when measurements are made over many illumination cycles as quantum dots do not lose their ability to fluoresce in the same way that organic dyes do.

In some implementations, the lateral flow test is configured to perform multiplexed spatial mode, spectral mode, and temporal mode measurements of the test strip with the spectral sensor.

Advantageously, this provides multi-analyte detection with different modes in a single lateral flow test using a single optical path in a miniaturised, disposable way.

In some implementations, the spectral sensor comprises a detection channel configured to measure an intensity of the excitation pulse and to correct for any detected excitation pulse in the measured fluorescence signal, for example by subtracting it from the measured fluorescence signal. For example, the spectral sensor may be configured to additionally switch on (i.e. time-gated) at the same time the initial illumination occurs and before fluorescence is expected to occur to allow the excitation pulse to be measured.

Advantageously, this is made possible by the use of a spectral sensor that allows not only fluorescence wavelengths to be detected and distinguished from each other, but also the wavelength of the excitation pulse. Accordingly, if any of the excitation pulse is remaining in the fluorescence signal, in conjunction with the large stoke shift of quantum dots and high optical density (cut-off) of the spectral filters, this may be removed to further increase signal to noise ratio.

According to a second aspect of the present disclosure, there is provided an optical module for use in the lateral flow test described above, the lateral flow test comprising a test strip, the test strip comprising a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by an excitation pulse, wherein the optical module comprises: a pulsed energy source for illuminating a test strip of the lateral flow test with an excitation pulse; and a spectral sensor for detecting fluorescence from the test strip in a plurality of wavelengths at one or more predetermined times after the start of the pulse of the pulsed energy source illuminates the test strip.

According to a third aspect of the present disclosure, there is provided a method for reading a lateral flow test, the method comprising: illuminating a test strip of the lateral flow test with a pulsed energy source of an optical module of the lateral flow test, wherein the test strip comprises: a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse; and detecting fluorescence from the test strip with a spectral sensor of the optical module in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip.

Advantageously, this method provides the advantages described above in connection with the lateral flow test and optical module described herein.

Brief Description of the Drawings

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figures la and lb schematically show respectively show lateral flow tests respectively with reflective mode and transmission mode measurements.

Figure 2 shows a lateral flow test housing according to the present disclosure.

Figure 3 illustratively shows a layout of a spectral sensor according to the present disclosure.

Figure 4 illustratively shows a functional block diagram of a spectral sensor and electrical signal processor circuitry according to the present disclosure.

Figure 5 shows an illustrative plot of fluorescence intensity in arbitrary units against time in nanoseconds comparing an organic dye and a quantum dot label.

Figure 6 illustrates a time-gated measurement process of a spectral sensor according to

the present disclosure.

Figure 7 illustrates a test strip of a lateral flow test according to the present disclosure.

Figure 8 illustrates a plot of photoluminescence or fluorescence against wavelength of different quantum dots labels.

Figure 9a illustrates a plot of fluorescence lifetimes for different quantum dot labels.

Figure 9b illustrates a plot of intensity On arbitrary units) against fluorescence time (in ns) for three different quantum dot labels.

Figure 10 is a flowchart of a method according to the present disclosure.

Like elements are indicated by like reference numerals.

Detailed Description of the Drawinqs

Figures la and lb schematically show respectively show lateral flow tests 100a, 100b illustrating reflection mode and transmission mode operation. The lateral flow tests 100a, 100b comprise a test strip 101 and an optical module 102. The optical module comprises a pulsed energy source 103 for illuminating the test strip 101 and a spectral sensor 104, for example an application specific integrated circuit (ASIC), for detecting fluorescence from the test strip. The components of the lateral flow test may be provided in a housing (not shown in Figures la and 1b) with openings therein to deposit a sample on the test strip 103 to run the test. The test strip 101 comprises one or more test or control areas 105 where fluorescence from quantum dot fluorescent labels are detectable during a reading of the test. In the reflection mode of operation (Figure la), the pulsed energy source 103 and spectral sensor 104 are arranged facing the same side of the test strip 101 whereby the excitation pulse illuminates the same side of the test strip 101 as that from which fluorescence is being detected. In the transmission mode of operation (Figure 1b), the pulsed energy source 103 and spectral sensor 104 are arranged on opposite sides of the test strip 101 whereby the excitation pulse illuminates the opposite side of the test strip 101 from which fluorescence is being detected. An advantage of transmission mode operation is that the illumination is perpendicular to the sample, providing equal illumination and reducing wavelength-spreading effects that can occur in reflective mode setups where the illumination is at a non-perpendicular angle relative to the sample.

It is envisaged that the pulse from the pulsed energy source may have a width of under 1% of the fluorescence lifetime of the target fluorescent quantum dot being measured. For example if the fluorescence lifetime is 100ns, the pulse of the pulsed energy source will have a width of ins consistently for each emitted pulse.

Figure 2 illustrates a lateral flow test housing 200 in which the components shown in Figures la and lb may be housed. The housing 200 is provided with an opening 201 into which a sample may be deposited. It is envisaged that the lateral flow test is a disposable, handheld lateral flow test and the housing is thus configured to be held by a user in contrast to a much larger sized benchtop sized device.

Figure 3 illustratively shows a layout of an exemplary spectral sensor 300 according to the present disclosure that may be used in connection with any of Figures 1-2. The spectral sensor 300 comprises an array 301 of photodiodes each having a corresponding colour filter Fl, F2, F3, F4, F5, F6, F7, F8, C, NIR provided in front thereof thereby controlling what wavelength of light is received by each photodiode. One or more photodiodes may also be provided with a clear filter C or no filter at all to allow all wavelengths to reach the corresponding photodiode. One or more of the photodiodes may also be provided with a near infrared (NIR) filter. The example array 301 in Figure 3 comprises a 4x4 array of photodiodes and filters arranged in pairs so that at least two photodiodes are provided in each colour channel to provide redundancy in case one of the two photodiodes fails. Two photodiodes immediately adjacent the 4x4 array 301 (but still forming part of the spectral sensor) are provided with a clear filter, for example to provide a reference signal against which the colour changes detected by the other photodiodes may be calibrated or compared. One or more photodiodes are also provided with the NIR filter for detecting any infrared colour changes on the test strip. In the example spectral sensor 301 of Figure 3, ten detection channels are provided corresponding to the following approximate spectral bands: Fl (350-440nm), F2 (415-475nm), F3 (445-515nm), F4 (475-555nm), F5 (515-595nm), F6 (550-630nm), F7(580-680nm), F8 (630-730nm), C (390-1000nm), NIR (850-1000nm). At least some of the bands may overlap with each other and it is envisaged that any suitable arrangement of photodiodes and colour filters may be used to control the spectral sensitivity of the sensor to different wavelengths depending on the fluorescence wavelength being measured from the test strip of the lateral flow test assay. It is envisaged that the pairwise arrangement of Figure 3 that provides at least two photodiodes per colour may be omitted such that only a single photodiode per colour is provided although such an arrangement is less robust as there is no redundancy.

A particular advantage of providing not only colour filters but also one or more clear filters C or filterless optical paths is that the spectral sensor does not require a separate reference signal from a separate optical detector positioned elsewhere in or near the spectral sensor. This reduces the complexity and bulky size of the device and thus manufacturing cost. Further, as the photodiodes of the clear channel may be formed in the same substrate as part of the same die in the same process, all the photodiodes are likely to have the same temperature and other operating condition variations (e.g. any drift caused by changes in temperature is likely to be identical for all of the photodiodes so can be compensated for more easily). In contrast, compared to when a reference signal is obtained from a separate reference sample using a separate optical detector such as in benchtop fluorescence spectroscopy devices, operating condition variations will not be the same as that of the spectral sensor so it is more difficult to compensate for any such variations. Such reference samples also typically require a separate optical pathway in addition to the optical pathway in which the test sample is being read, which increases the size and bulk of the benchtop readers.

Finally, at least one of the detection channels of the spectral sensor may be configured to detect the wavelength corresponding to the excitation pulse of the pulsed energy source. Thus, to the extent any of this pulse remains detectable during a measurement window, the signal from the detection channel used to measure the pulse may be used to remove it from the fluorescence measurement thereby further improving signal to noise ratio.

The spectral sensor of the present disclosure may be integrated or mounted into or onto a printed circuit board (PCB) positioned in the housing of the lateral flow test and may be integrated with or provided with an electrical signal processor such as a microprocessor thereby providing an application specific integrated circuit (ASIC) spectral sensor as shown in Figure 4.

Figure 4 illustratively shows a functional block diagram of spectral sensor ASIC circuitry 400 that may be used with any of Figures 1-3. The circuitry 400 may include a one or more of the following pins: positive supply terminal (VDD), ground (PGND and GND), serial interface clock signal line (SCL), serial interface data signal line (SDA), interrupt (INT), general purpose input/output (GP10), and/or LED current sink input (LDR) to provide an interface between the photodiodes of the spectral sensor 401 and the other components of the ASIC such as, for example, a microcontroller unit (MCU). Signal processing may be provided through an 12C serial communication bus as will be appreciated by the skilled person. As will also be appreciated by the skilled person, a power supply and/or any additional resistors, capacitors and or other electronic components may also be provided. The ASIC may further comprise one or more multiplexers and analogue to digital converters to optionally multiplex and subsequently convert analogue signals output by the photodiodes of the spectral sensor to a digital signal in corresponding data channels that may be output, for example through the serial interface data signal line (SDA) for further processing and ultimately reading of the intensity of a colour change and/or making a fluorescence measurement of the assay test region.

Figure 5 shows an illustrative plot 500 of fluorescence intensity in arbitrary units against time in nanoseconds demonstrating a comparison of a typical organic fluorophore dye label 501 with a quantum dot label 502 after illumination with an excitation pulse 503 at time t = 0. The example organic fluorophore dye fluorescence decays to a 1/e fraction of excitation pulse intensity after only 5ns so has a fluorescence lifetime I(dye) 5ns whereas the example quantum dot takes 200ns to a 1/e fraction so has a fluorescence lifetime r(Qo) of 200ns. Accordingly, when quantum dots are used as labels in accordance with the present disclosure, it is envisaged that a time-gated measurement window is selected at one or more predetermined times after the start of the excitation pulse around the known fluorescence lifetime of the quantum dot used in the lateral flow test. In the example of Figure 1, this measurement window 504 is around 200ns after the excitation pulse (for example between 100-300ns. These timings are exemplary only and are not intended to be limiting. Other time measurement windows are also envisaged depending on the fluorescence time of the quantum dot used.

Figure 6 illustrates a time-gated measurement process 600 of a spectral sensor according to the present disclosure. A pulsed energy source emits an excitation pulse at a first time 601 to illuminate the test strip, exciting the quantum dot that begins to fluoresce. After a predetermined time 602, for example 2Ons, the measurement window 603 of the spectral sensor begins. The delay allows any unwanted fluorescence and noise from non-target analytes to decay so that such that these do not adversely affect the signal to noise ratio. Optionally, the spectral sensor auto zeroes a first portion 604 of the data collected in the measurement window before the start of integration time. This ensures any variations as the collected signal ramps up do not introduce noise into the measurement and further reduces the risk that faster decaying fluorescence from a non-target analyte is collected during the measurement.

At a predetermined time after the excitation pulse, integration 605 of the detected signal begins and this may continue for a predetermined number of internal clock cycles provided by an internal clock or sync signal 606. The example of Figure 6, integration time is five clock cycles, although other numbers of cycles may be used. This time-gated integration time acts as a boxcar averager or low pass filter to remove noise from the signal. For example, if integration time lasts for multiple pulses of 500ns, this may integrate to a few milliseconds of measured data. When the integration time 605 ends, the collected data is read to a data register, for example communicated from to or from a data buffer using a known I2C protocol. The system is then returned to an idle state 607 waiting for the next excitation pulse to begin the next measurement window. An interrupt signal based may also be used to start or stop the integration time 605.

Figures 7-9 illustrate different measurement modes that may be multiplexed in the same lateral flow test to provide multi-analyte detection. In particular, when it is desired to test for more than one analyte on a single test strip, the lateral flow test is configured so that different fluorescent quantum dot labels bind to each of the target analytes. Each fluorescent quantum dot label exhibits different fluorescent properties. These differences allow the different detection signals to be distinguished.

For example, the detection signals may be distinguished spatially, spectrally and/or temporally (i.e. by fluorescence lifetime).

For spatial mode measurements, the presence or lack thereof of signals at expected positions allows different signals to be separated by position.

For spectral mode measurements, the different quantum dot labels may all be provided on the same or overlapping areas of the test strip but emit fluorescence at different wavelength or wavelength bands that are detected only in the detection channel in the spectral sensor configured to detect that specific wavelength or wavelength band. The intensity in each channel corresponds to the intensity of a corresponding fluorescence from one of the quantum dots labels.

For temporal mode measurements, the different quantum dot labels may again all be provided on the same or overlapping areas of the test strip but each have a known, different fluorescence lifetime. By measuring signal intensity over time (after spectral separation), the lifetime may be determined for each of the signals and used to quantify the amount of analyte present in the sample.

Figure 7 illustrates a test strip 700 of a lateral flow test according to the present disclosure where different quantum dot fluorescent labels are provided on spatially separated areas 701, 702, 703, 704, 705. Whilst Figure 7 uses spatially separated lines, other shapes are envisaged such as dots, circles, squares crosses and others arranged in grids and/or other patterns. The test strip 700 of Figure allows for spatial mode measurements to be made and the measured signals to be spatially distinguished.

Figure 8 illustrates a plot 800 of photoluminescence or fluorescence against wavelength of different quantum dots labels demonstrating how they signals from these quantum dot labels may be distinguished spectrally, for example using a spectral sensor of the present invention. Figure 8 illustratively shows six different types of quantum dot labels having fluorescence wavelength bands with peaks of around 1.0 normalised photoluminescence 801, 802, 803, 804, 805, 806 respectively around 508nm, 530nm, 554nm, 571m, 583nm, and 608nm. The plot 800 also shows a normalised absorbance 807 of a typical quantum dot indicating what wavelengths may be used for the excitation pulse (for example, it is envisaged the excitation pulse may be an ultraviolet pulse with a wavelength around 300nm where normalised absorbance is close to 1.0). It is envisaged that other quantum dot labels may be used as will be appreciated by the skilled person. These wavelength bands may each uniquely be detected in only one of the detection channels of the spectral sensor configured to detect signals of a corresponding wavelength, thereby allowing the measured signals to be spectrally distinguished.

Figure 9a illustrates a plot 900a of fluorescence lifetimes for different quantum dot labels 901, 902, 903 (DAPI, Red CdSe, Red ZAIS) calculated from, for example, the intensity of the signals in Figure 9b. The Fluorescence lifetime of DAPI is around 2.72 ns, of Red CdSe is around 20.1 ns, and of Red ZAIS is around 148ns.

Figure 9b illustrates a plot 900b of intensity (in arbitrary units) against fluorescence time On ns) for three different quantum dot labels 904, 905, 906. The calculation of a signal intensity reduction to a known fraction at an expected time, for example t1, t2 or t3 for each of the three quantum dot labels may be used to determine the fluorescence lifetimes shown in, for example, Figure 9a.

Figure 10 is a flow chart of a method 1000 according to the present disclosure. The method comprises corresponds to a method of using the above described lateral flow test and optical module and comprises illuminating 1001 a test strip of the lateral flow test with a pulsed energy source of an optical module of the lateral flow test. As described above, the test strip comprises: a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse. The method further comprises detecting 1002 fluorescence from the test strip with a spectral sensor of the optical module in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip. The detected fluorescence intensity and/or lifetime may be used to quantitatively determine the strength of a colour change and thus determine the quantity of analyte present in a sample. The advantages highlighted above in connection with the lateral flow test and optical module described herein are equally applicable to the present method.

Other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the scope of the claims appended hereto.

For example, it is envisaged that the present disclosure may be used in the biodiagnostics field such as in medical, veterinary, environmental and food safety fields where lateral flow tests may be used. The term semi-disposable used herein may refer to reusing a reader a small number of times before it is disposed of, for example by providing a small number of test strips in each device, for example between, 2, 3, 4, 5, 10 and/or 20 strips in the device.

List of reference signs: 100a lateral flow test 100b lateral flow test 101 test strip 102 optical module 103 pulsed energy source 104 spectral sensor test or control areas lateral flow test housing 201 opening 300 spectral sensor 301 array of photodiodes 400 circuitry 401 spectral sensor 500 plot of fluorescence intensity against time 501 organic fluorophore dye label 502 quantum dot label 503 excitation pulse 504 measurement window 600 time-gated measurement process 601 first time 602 predetermined time 603 measurement window 604 zeroed first portion of collected data 605 integration 606 clock signal 607 idle state 700 test strip 701 spatially separated area 702 spatially separated area 703 spatially separated area 704 spatially separated area 705 spatially separated area 800 plot of photoluminescence or fluorescence against wavelength 801 508nm peak 802 530nm peak 803 554nm peak 804 571m peak 805 583nm peak 806 608nm peak 807 normalised absorbance 900a plot of fluorescence lifetimes for different quantum dots 900b plot of intensity against fluorescence time for different quantum dots 901 DAPI quantum dot label 902 Red CdSe quantum dot label 903 Red ZAIS quantum dot label 904 first quantum dot label fluorescence intensity 905 second quantum dot label fluorescence intensity 906 third quantum dot label fluorescence intensity 1000 method for reading a lateral flow test 1001 illuminating 1002 detecting

Claims

CLAIMS: 1. A lateral flow test comprising: a test strip and an optical module, wherein the optical module comprises.a pulsed energy source for illuminating the test strip; and a spectral sensor for detecting fluorescence from the test strip in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip, and wherein the test strip comprises: a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse.
2. The lateral flow test of claim 1, wherein the test strip comprises a second quantum dot fluorescent label for binding to a second target on the test strip, the second quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse.
3. The lateral flow test of claim 2, wherein the first and second quantum dot fluorescent labels are provided on spatially separated areas of the test strip, and the spectral sensor is configured to distinguish between fluorescence from the first and second quantum dots by spatial position.
4. The lateral flow test of claim 2, wherein the first and second quantum dot fluorescent labels are provided on spatially overlapping areas of the test strip and fluoresce in respective first and second wavelengths of the plurality of wavelengths.
5. The lateral flow test of claim 4, wherein the spectral sensor comprises a plurality of detection channels, each detection channel configured to detect one of the plurality of wavelengths to distinguish between fluorescence from the first and second quantum dots by wavelength.
6. The lateral flow test of claim 2, wherein the first and second quantum dot fluorescent labels are provided on spatially overlapping areas of the test strip and fluoresce for respective first and second fluorescence lifetimes.
7. The lateral flow test of claim 6, wherein the spectral sensor is configured to perform a plurality of time-gated measurements at said one or more predetermined times to distinguish between fluorescence from the first and second quantum dots by fluorescence lifetime.
8. The lateral flow test of claims 2-7, wherein the pulsed energy source is configured to illuminate the test strip in a plurality of wavelengths corresponding to respective excitation wavelengths of the first and second quantum dot fluorescent labels.
9. The lateral flow test of any preceding claim, wherein the lateral flow test is a disposable, handheld lateral flow test, the optical module and test strip being provided in a housing configured to be held by a user.
10. The lateral flow test of claim 9 comprising a printed circuit board (PCB) positioned in the housing, the spectral sensor and the pulsed energy source being mounted on the PCB.
11. The lateral flow test of claim 10, wherein the spectral sensor comprises an application specific integrated circuit (ASIC) mounted on the PCB in the housing.
12. The lateral flow test of any preceding claim, wherein the pulsed energy source is configured to emit a plurality of pulses and the spectral sensor is configured to detect fluorescence from the test strip at a plurality of the predetermined times after the start of each of said pulses to calculate an average fluorescence signal value.
13. The lateral flow test of any preceding claim, wherein the spectral sensor and pulsed energy source are arranged facing the same side of the test strip and are configured to perform a reflective mode measurement.
14. The lateral flow test of any of claims 1-12, wherein the spectral sensor and pulsed energy source are arranged on opposite sides of the test strip and are configured to perform a transmission mode measurement.
15. The lateral flow test of any preceding claim configured to perform multiplexed spatial mode, spectral mode, and temporal mode measurements of the test strip with the spectral sensor.
16. The lateral flow test of any preceding claim, wherein the spectral sensor comprises a detection channel configured to measure an intensity of the excitation pulse and to correct for any detected pulse in the measured fluorescence signal.
17. An optical module for use in a lateral flow test, the lateral flow test comprising a test strip, the test strip comprising a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by an excitation pulse, wherein the optical module comprises: a pulsed energy source for illuminating a test strip of the lateral flow test with an excitation pulse; and a spectral sensor for detecting fluorescence from the test strip in a plurality of wavelengths at one or more predetermined times after the start of the pulse of the pulsed energy source illuminates the test strip.
18. A method for reading a lateral flow test, the method comprising: illuminating a test strip of the lateral flow test with a pulsed energy source of an optical module of the lateral flow test, wherein the test strip comprises: a first quantum dot fluorescent label for binding to a first target on the test strip, the first quantum dot fluorescent label being configured to emit fluorescence following illumination by the pulse; and detecting fluorescence from the test strip with a spectral sensor of the optical module in a plurality of wavelengths at one or more predetermined times after the start of a pulse of the pulsed energy source illuminates the test strip.