WO2024033027A1

WO2024033027A1 - Reader system for a lateral flow test and according method

Info

Publication number: WO2024033027A1
Application number: PCT/EP2023/069860
Authority: WO
Inventors: Boon Chong CHEAH; Axel Schubert; Alec Reader; Giuliano Manzi; Sandesh CHITTOORI
Original assignee: Ams Osram AG
Current assignee: Ams Osram AG
Priority date: 2022-08-11
Filing date: 2023-07-18
Publication date: 2024-02-15
Anticipated expiration: 2025-02-11

Abstract

The invention relates to a reader system (30) for reading out a test line (16) or a control line (18) of a strip assay (4) of a lateral flow test (2). The reader system (30) shall work with a large variety of simple light sources and simple spectral sensors and shall provide readouts with a high signal-to-noise ratio. According to the invention, the reader system (30) comprises a support (32) on which the strip assay (4) rests in a nominal position during readout, a light source (36) for illuminating the strip assay (4) in a region comprising the test line (16) and/or the control line (18), a spectral sensor (42) located above the strip assay (4) when the strip assay is in the nominal position, for sensing light emerging from the test line (16) or the control line (18), wherein the light source (36) is located to a side of the strip assay (4) when the strip assay (4) is in the nominal position, such that light emitted by the light source (36) predominantly impinges on a side edge (40) of the strip assay (4) and couples preferably co-planarly into the strip assay (4).

Description

READER SYSTEM FOR A LATERAL FLOW TEST AND ACCORDING METHOD

DESCRIPTION

TECHNICAL FIELD

The invention relates to a reader system for reading out a test line or a control line of a strip assay of a lateral flow test . The invention also relates to a corresponding method .

BACKGROUND

In a lateral flow test ( LET ) a fluid sample , called analyte , is applied to a sample pad of an elongate strip assay . Driven by capillary forces , the sample spreads laterally towards an absorbent pad, thereby crossing several biologically or chemically active regions . The underlying chemical reactions can be used to detect the presence of a target substance ( e . g . , an antigen) in the analyte , which is usually indicated by colouring of a test line embedded into the strip assay . Similarly, colouring of a control line indicates validity of the test .

Today, LFTs are predominantly in-vitro bio-diagnostics devices with applications in medical , veterinary, environmental or food safety . Prominent uses relate , for example , to the detection of C0VID19 , HIV, or glucose (diabetes ) .

The test line or control line of a LET may be inspected visually . However, in large-scale tests or screenings an automated, obj ective , and quantitative assessment or readout is required .

In the field of lateral flow tests , there are multiple detection platforms or techniques to read out the test line from the strip . Two of the most commonly known optical readout methods are based on colorimetry or fluorescence . Colorimetry is based on the reflection or transmission of light from the strip, where the intensity of the light corresponds to the concentration of the target substance of interest . Fluorescence is based on the excitation of fluorescent light by means of source light impacting onto a fluorescent dye that emits at a di f ferent wavelength with varying intensity, which corresponds to the concentration of the target substance of interest .

In both instances , the light source is as source of a dominant background noise which decreases the signal to noise ratio ( SNR) . In order to circumvent this , there are a lot of ef forts to work on time gated fluorescence . In this technique , the fluorescent dyes are excited by a light source for a short pulse , and the decay of the emission light from the dyes is immediately measured back by the sensor . However, most of the fluorescent dyes have a short li fetime , around 1 ns to 100 ns . Only a few fluorescent dyes , such as lanthanides have li fetimes within ps to ms .

This makes the light and sensor system designs very di f ficult and complicated and therefore expensive . Timing constraints limit the system to usage of only a few dyes that have comparatively long li fetimes . This severely limits possible areas of application for the LFT .

SUMMARY

An obj ective underlying the present invention is to provide a reader system for reading out a test line or a control line of a strip assay of a lateral flow test . The reader system shall work with a large variety of simple light sources and simple spectral sensors and shall provide readouts with a high signal-to-noise ratio . Furthermore , a corresponding method shall be provided .

According to claim 1 the device-related obj ective is met by a reader system for reading out a test line or a control line of a strip assay of a lateral flow test , comprising • a support on which the strip assay rests in a nominal position during readout ,

• a light source for illuminating the strip assay in a region comprising the test line and/or the control line ,

• a spectral sensor located above the strip assay when the strip assay is in the nominal position, for sensing light emerging from the test line or the control line , wherein the light source is located to a side of the strip assay when the strip assay is in the nominal position, such that light emitted by the light source predominantly impinges or impacts on a side edge of the strip assay and couples essentially co-planarly into the strip assay .

Utili zing the materials of the strip assay, in particular the backing card on which the chemically active regions of the LFT are usually fixed or applied, the light enters the strip assay from the side . This prevents light from the light source from reaching the sensor directly, since the gradient of the light emission is oriented perpendicular to the surface normal of the sensor . This configuration will therefore yield high signal-to-noise ratios .

In a preferred mode of operation, called fluorescence mode , the spectral sensor is configured to sense fluorescent light emerging from a dye in the test line or the control light after excitation by the light of the light source . With that , the light source will not need to be pulsed since the signal- to-noise ratio is optimi zed, and time-gated measurement is not required .

Preferably, the light source is placed such that only a small fraction of the light from the light source (preferably < 10% ) can reach the sensor . More preferably, the light source is placed such that light from the light source does not directly reach the spectral sensor . Furthermore , the light source is preferably placed such that only a small portion of the light from the light source (preferably < 10% ) can reach the spectral sensor by a single reflection at an outer surface of the strip assay . More preferably, the light source is placed such that no light from the light source does reach the spectral sensor by a single reflection at an outer surface of the strip assay .

The light source preferably is a directed light source and preferably arranged such that the light of the light source is directed parallel to the test line or the control line .

In a particularly simple and cost-ef ficient embodiment , the light source is a LED or an OLED .

Spectral multiplexing may be applied for a preferred embodiment , wherein a plurality of spectral sensors , preferably with di f ferent spectral ranges , is assigned to the test line or the control line . In this case said plurality of spectral sensors preferably senses light ef fected by a single light source . This also allows for LFTs designed for multianalyte tests . Di f ferent segments or areas of a test or control line or area may then be read out simultaneously .

In terms of method, the present invention provides a method for reading out a test line or a control line of a strip assay of a lateral flow test , wherein light from a light source is directed onto a side edge of the strip assay and coupled co-planarly into the strip assay in a region comprising the test line or the control line , and wherein light emerging from or passing through the test line or the control line is sensed by a spectral sensor above the strip assay .

What has been said with respect to the device may analogously be applied to the method, and therefore need not be further repeated here . Device embodiments and details have a counterpart in the method . Again, no explication is required here in view of the above description .

In summary, the present invention allows for a low-cost reader system for a strip assay of a LET with low demands on the light source and the sensor . There is no demand for a pulsed light source . Rather, simple DC light sources may be suf ficient . Consequently, there is no need for time gated sensors with complicated timing speci fications . In fluorescent mode all fluorescent dyes can be used, there is no restriction to long fluorescence li fetimes . Hence , a large variety of di f ferent LFTs can be sensed . Spectral multiplexing and multi-analyte configurations may be reali zed in a simple manner . The whole reader system can be built with a small form factor .

BRIEF DESCRIPTION OF DRAWINGS

Further below, exemplary embodiments of the invention are discussed with reference to the accompanying drawings .

Fig . 1 shows a partially cut perspective view of a lateral flow test with a strip assay .

Fig . 2 shows in a purely schematic manner a cross section through a reader system for reading out a test line or a control line of such a strip assay, wherein the section plane runs through the according test line or control line .

Fig . 3 shows a partially cut perspective view of said reader system .

DETAILED DESCRIPTION

Fig . 1 shows in a schematic manner a perspective view of a partially cut lateral flow test ( LFT ) 2 . A LFT 2 comprises an assay also known as a lateral flow device , lateral flow immunochromatographic assay, or rapid test , which is a simple device intended to detect the presence of a target substance in a liquid sample without the need for speciali zed and costly equipment . LFTs 2 are widely used in medical diagnostics in the home , at the point of care , and in the laboratory . The LFT 2 comprises an elongated strip assay 4 which in a view from above may have a generally rectangular shape with a longitudinal direction x and a transverse direction y . The height of the strip assay 4 in direction z is relatively small in comparison to the lateral dimensions , i . e . , to the dimensions in longitudinal direction and transverse direction . The strip assay 4 typically comprises a sample pad 10 , a conj ugate pad 12 , a membrane or reaction matrix 14 with a test line 16 and a control line 18 , and an absorbent pad 20 , arranged in this order along longitudinal direction x . As shown in the Fig . 1 , the individual components or regions may overlap each other and are applied to a common backing card 22 for fixation . In Fig . 1 the backing card 22 forms a lower side of the strip assay 4 , while the other components mentioned above form an upper side .

During usage , the strip assay 4 may be at least partially enclosed by a housing 24 which provides protection for the strip assay 4 against physical damage and environmental influences . Access to certain regions on the upper side of the strip assay 4 is provided by means of openings or windows in the housing 24 . In particular, there is a sample port 26 providing physical access to the sample pad 10 , and a there is a readout port 28 facilitating at least visual or optical access to the test line 16 and the control line 18 . The housing 24 typically comprises a lower part and an upper part , being engaged with a snap lock or the like . Both parts can be separated from each other to remove or exchange the strip assay 4 .

As is well-known in the art , a sample fluid called analyte is applied through the sample port 26 on the sample pad 10 . The sample pad 10 acts as a sponge and holds an excess of sample fluid . Once soaked, the analyte flows along longitudinal x- direction to the absorbent pad 20 , thereby passing the other regions of the upper side of the strip assay 4 . Once the analyte passes the conj ugate pad 12 , there occurs a reaction between the analyte and some reactive constituents embedded into the conj ugate pad 12 . The thus-modi fied analyte then migrates to the reaction matrix 14, usually leading to further reactions in the test line 16 and/or the control line 18. This may result in a change of properties of the test line 16 and/or the control line 18 which may be visually or optically inspected. The test line 16 and the control line 18 are typically aligned along transverse direction (in y- direction) and extend over some portion of the width of the strip assay 4. Finally, the analyte reaches the absorbent pad 20 or wicking pad which wicks the liquid from the reaction matrix 14, thereby ensuring flow from the sample pad 10 through the conjugate pad 12 and the membrane or reaction matrix 14.

As mentioned, the LFT 2 is intended to detect the presence of a target substance in a liquid sample. Because the target substance is often a biological antigen, many lateral flow tests 2 are known as rapid antigen tests. For example, the conjugate pad 12 may be a pad in which the manufacturer has stored freeze dried bio-active particles called conjugates in a salt-sugar matrix. The conjugate pad 12 contains all the reagents required for an optimized chemical reaction between the target molecule (e.g., an antigen) and its chemical partner (e.g., antibody) that has been immobilized on the particle's surface. This marks target particles as they pass through the pad and continue across to the test and control lines 16, 18. The test line 16 shows a signal, often a (change of) colour. The control line 18 contains affinity ligands which show whether the sample has flowed through and the biomolecules in the conjugate pad 12 are active. After passing these reaction zones, the fluid enters the final porous material, the wick or absorbent pad 20, that acts as a waste container.

Hence, the test line 16 and/or the control line 18 may change their colour (e.g., hue and/or saturation) , depending on the outcome of the underlying chemical direction. For a quantitative detection or readout of this colour change an optical measuring process known as colorimetry may be used. This may involve illuminating the test line 16 and/or the control line 18 from above with a dedicated light source and measuring spectral properties of the reflected light with a spectral sensor or detector arranged above the respective portion of the reaction matrix 14 .

In another embodiment the test line 16 and/or the control line 18 may comprise a fluorescent dye which is to be activated or altered by the underlying chemical reaction . For a quantitative detection or readout of such an ef fect a measurement of fluorescent light emitted by the dye upon excitation is employed . This may involve illuminating the test line 16 and/or the control line 18 from above with a dedicated light source and measuring spectral properties of the emitted fluorescent light with a spectral sensor or detector arranged above the respective portion of the reaction matrix 14 . Typically, the fluorescent light has a di f ferent wavelength than the incident stimulating or exciting light , which has to be considered for the measurement . Furthermore , the measurement has to adapt to the comparatively short li fe span of the fluorescent light centres in the dye and therefore the pulsed nature of the fluorescent light .

In both scenarios , colorimetry and fluorescence measurement , the described reflective mode of the measurement has drawbacks in that the light used for illuminating the test line 16 and/or the control line 18 is reflected back into the spectral sensor . Hence , the illuminating light source causes a dominant background noise which increases the signal-to- noise ratio ( SNR) . This is particularly annoying for the fluorescence measurement scenario in which the fluorescent dye has a low luminosity anyway . As explained in the introduction, time-gated fluorescence may to some extent solve this problem but usually leads to complex illumination and sensor designs and also imposes constraints on possible light sources and fluorescent dyes to be used in the strip assay 4 . In order to circumvent these problems , the invention provides a di f ferent kind of solution which is schematically illustrated in Fig . 2 and Fig . 3 .

A LFT readout device or reader system 30 according to the invention comprises a support 32 or seat onto which a strip assay 4 of the kind described above is to be placed during measurement . To this end, the strip assay 4 is preferably removed and isolated from the housing 24 . Preferably, the support 32 comprises a flat bearing area on which the backing card 22 of the strip assay 4 lies flat such that the functional elements of the strip assay 4 like the sample pad 10 , the conj ugate pad 12 , the reaction matrix 14 , and the absorbent pad 20 point upwards . Lateral and/or longitudinal stops may ensure that the strip assay 4 rests in a predetermined position during measurement . Additionally, or alternatively, there may be movable or clampable fixing means to temporarily fix the strip assay 4 in the intended position . After the measurement , the strip assay 4 may be removed or disposed from the reader system 30 , giving way for the next strip assay 4 to be assessed or read out .

A light source 36 , preferably a directed light source , is placed lateral ( sideways ) to the support 32 of the strip assay 4 and thus lateral to the strip assay 4 when it rests in its intended measurement position . The arrangement is such that light emitted by the light source 36 couples essentially co-planarly ( from the side , parallel to the plane of the strip assay 4 ) into the backing card 22 and/or reaction matrix 14 of the strip assay 4 to illuminate either the test line 16 or the control line 18 ( or both) . Therefore , the light source 36 is placed preferably at the same x-position as the test line 16 or the control line 18 and at roughly the same height z as the strip assay 4 . The light source 36 has a light emission area 38 facing the adj acent side area or side edge 40 of the strip assay 4 . Thus , the light source 36 emits a light beam or light cone predominantly in y-direction towards and into the strip assay 4 via its side edge 40 . Utili zing the materials of the backing card 22 and/or the reaction matrix 14 , the light can enter them and travels through the material .

In the fluorescence case this leads to fluorescence excitation of the dyes within the test line 16 or control line 18 and thus fluorescent light , some part of which is emitted upwards . This fluorescent light is sensed by an optical sensor, in particular a spectral senor 42 , placed above the strip assay 4 , preferably at the same x-position as the light source 36 and at a suitable y-position corresponding to a fluorescent light emitting region of the reaction matrix 14 . Therefore , essentially only or mainly fluorescent light enters the spectral sensor 42 . Excitatory light from the light source 36 reaches the spectral sensor 42 only by way of scattering or internal reflection inside the strip assay 4 , but neither directly nor by direct surface reflection on the outer (upper ) surface of the reaction matrix 14 . Hence , the disturbing influence of the source light is largely eliminated, and excellent signal-to-noise ratios can be achieved even with conventional spectral sensors 42 .

Therefore , there is at least less need for complicated and expensive time-gated fluorescence measurements with fast electronics . Rather, the light source 36 and the sensor system have less stringent requirements , especially with respect to timing speci fications .

This will also allow the use of a variety of di f ferent light sources 36 . In particular, the light source 36 can be almost any light-emitting diode ( LED) or other light source 36 with a suitable frequency range .

The spectral sensor 42 may in principle be any optical sensor which is sensitive to incident light of a certain frequency range which is compatible with the measurement principle . This may be light in the visual range , but neighbouring ranges like infrared ( IR) and ultraviolet (UV) may be included as well . In a simple case the spectral sensor 42 may be a photodiode. Optional upstream colour filters may be present for adjusting the sensed frequency range.

The associated measurement and evaluation routines or algorithms may be implemented in hardware, in software, or in a combination of both. There may be a common control unit for both the light source (s) 36 and the spectral sensor (s) 42. The readout or control electronics may be integrated into a single sensor device or may be placed off-site, with suitable cable-based or wireless line connections to the actual sensor probe .

Further, all kinds of fluorescent dyes, in particular single or multiple dyes, in the reaction matrix 14 can be used. The choice it not limited to such dyes with long fluorescence lifetimes, leading to great freedom of design in different application areas of LFTs, such as testing for C0VID19, HIV, glucose, or pregnancy.

If both the test line 16 and the control line 18 are to be sensed within a singer reader system 30, then there expediently is a first light source 36 with an associated spectral sensor 42 at the x-position of the test line 16, and there is a second light source 36' with an associated spectral sensor 42' at the x-position of the control line 18. Of course, this can be generalized to further test or control or similar lines.

The light source 36 preferably is arranged in a small lateral distance or gap (in y-direction) to the strip assay 4 in the range of millimetres or less. It may even be in contact with the strip assay 4 when the latter is in the intended measurement position. Hence, a direct coupling of the source light into the strip assay 4 without noteworthy attenuation and without much stray light reaching the spectral sensor 42 directly is achieved. Optionally, there may be a focussing optical element like a lens arranged between the light source 36 and the strip assay 4 to ef fectively direct the light into the strip assay 4 .

Similarly, the spectral sensor 42 is preferably arranged in a small distance ( in z-direction) or with a small gap above the strip assay 4 in the range of millimetres or less , such that incoming light from the reaction matrix 14 is attenuated as little as possible while ambient light or direct light from the light source 36 does not reach the spectral sensor 42 .

In a particularly advantageous application, there may be several spectral sensors 42 associated with and illuminated by a single light source 36 . In particular, there may be two or more spectral sensors 42 placed above the strip assay 4 in a transversally aligned row, i . e . , one placed after the other (with or without some distance in between) along y-direction, at the same x-position . The spectral sensors 42 of such a row may be designed to operate in di f ferent spectral ranges , therefore allowing for multispectral analysis and/or spectral multiplexing . Such an arrangement is also advantageous for multi-analyte strip assays 4 , wherein several analytes might be applied laterally separated ( in y-direction) , side-by- side , on the sample pad 10 to form parallel lanes or capillary flow traces in longitudinal direction ( in x- direction) . In this case , each test or control " line" can be divided into line segments , the segments possibly being designed to support di f ferent chemical reactions .

The system described above with all its variations can also be used for the colorimetry case . In this case also light from the light source 36 is coupled into the strip assay 4 from the side , leading to an " internal illumination" of the test line 16 or the control line 18 . The light is at least partially internally deflected or scattered in upward direction to reach the spectral sensor 42 placed above the strip assay 4 . Again, direct impact of the source light or of outer-surface reflected source light onto the spectral sensor 42 is avoided . This will again yield high signal-to-noise ratios .

While the foregoing description was related to a "naked" strip assay 4 being placed in the reader system 30 , the measurement will in principle also work for a strip assay 4 enclosed by a housing 10 , provided that the housing 10 comprises a suitable opening or window at the side edge 40 facing the light source 36 to allow for coupling of incident source light .

The light source 36 and the spectral sensor 42 may be fixed to suitable elements or supports of a housing or a frame of the reader system 30 .

The skilled person will understand that in the preceding description and appended claims positional terms such as ' above ' , ' along ' , ' side ' , etc . are made with reference to conceptual illustrations , such as those shown in the appended drawings . These terms are used for ease of reference but are not intended to be of limiting nature . These terms are therefore to be understood as referring to an obj ect when in an orientation as shown in the accompanying drawings .

For example , while a standard configuration of the reader system 30 has been described, wherein the strip assay 4 lies flat in hori zontal alignment on the support 32 , the whole system might in principle be aligned or rotated in arbitrary manner in space , provided that the strip assay 4 is suitably fixed or kept in the intended position during measurement .

Furthermore , while the test line 16 and the control line 18 preferably have indeed a " line" shape , the terminology used here is intended to also cover the slightly more general case of a test area or a control area of any suitable shape . That is , the terms "test line" or "control line" are generally to be understood in a broad sense . It will be appreciated that aspects of the present invention can be implemented in any convenient way including by way of suitable hardware and/or software . For example , a device arranged to implement the invention may be created using appropriate hardware components . Alternatively, a programmable device may be programmed to implement at least some of the algorithms or method steps of some of the embodiments of the disclosure . The invention therefore also provides suitable computer programs for implementing aspects of the invention . Such computer programs can be carried on suitable carrier media including tangible carrier media ( e . g . , hard disks , CD ROMs and so on) and intangible carrier media such as communications signals .

Although the disclosure has been described in terms of preferred embodiments as set forth above , it should be understood that these embodiments are illustrative only and that the claims are not limited to those embodiments . Those skilled in the art will be able to make modi fications and alternatives in view of the disclosure which are contemplated as falling within the scope of the appended claims . Each feature disclosed or illustrated in the present speci fication may be incorporated in any embodiments , whether alone or in any appropriate combination with any other feature disclosed or illustrated herein .

LIST OF REFERENCE SIGNS lateral flow test (LFT) 2 strip assay 4 sample pad 10 conjugate pad 12 reaction matrix 14 test line 16 control line 18 absorbent pad 20 backing card 22 housing 24 sample port 26 readout port 28 reader system 30 support 32 light source 36, 36' light emission area 38 side edge 40 spectral sensor 42, 42'

Claims

1. A reader system (30) for reading out a test line (16) or a control line (18) of a strip assay (4) of a lateral flow test (2) , comprising

• a support (32) on which the strip assay (4) rests in a nominal position during readout,

• a light source (36) for illuminating the strip assay (4) in a region comprising the test line (16) and/or the control line (18) ,

• a spectral sensor (42) located above the strip assay (4) when the strip assay is in the nominal position, for sensing light emerging from the test line (16) or the control line (18) , wherein the light source (36) is located to a side of the strip assay (4) when the strip assay (4) is in the nominal position, such that light emitted by the light source (36) predominantly impinges on a side edge (40) of the strip assay (4) and couples preferably co-planarly into the strip assay (4) .

2. The reader system (30) according to claim 1, wherein the spectral sensor (42) is configured to sense fluorescent light emerging from a dye in the test line (16) or the control line (18) after excitation by the light of the light source (36) .

3. The reader system (30) according to claim 1, wherein the spectral sensor (42) is configured to sense light emerging from the strip assay (4) which results from the light of the light source (36) after entering the strip assay (4) via the side edge (40) , internal deflection in the strip assay (4) , and transmission through the test line (16) or the control line (18) .

4. The reader system (30) according to any one of the preceding claims, wherein the light source (36) is placed such that light from the light source (36) does not directly reach the spectral sensor (42) . 5. The reader system (30) according to any one of the preceding claims, wherein the light source (36) is placed such that light from the light source (36) does not reach the spectral sensor (42) by a single reflection at an outer surface of the strip assay (4) .

6. The reader system (30) according to any one of the preceding claims, wherein the light source (36) is a directed light source.

7. The reader system (30) according to claim 6, wherein the light of the light source (36) is directed parallel to the test line (16) or the control line (18) .

8. The reader system (30) according to any one of the preceding claims, wherein the light source (36) is a LED or an OLED.

9. The reader system (30) according to any one of the preceding claims, wherein a plurality of spectral sensors

(42) , preferably with different spectral ranges, is assigned to the test line (16) or the control line (18) .

10. The reader system (30) according to claim 9, wherein said plurality of spectral sensors (42) senses light effected by a single light source (36) .

11. A method for reading out a test line (16) or a control line (18) of a strip assay (4) of a lateral flow test (2) , wherein light from a light source (36) is directed onto a side edge (40) of the strip assay (4) and coupled co-planarly into the strip assay (4) in a region comprising the test line (16) or the control line (18) , and wherein light emerging from or passing through the test line (16) or the control line (18) is sensed by a spectral sensor (42) above the strip assay ( 4 ) . 12. The method according to claim 11, wherein the spectral sensor (42) senses fluorescent light emitted by a dye in the test line (16) or the control line (18) after excitation by light from the light source (36) .

13. The method according to claim 11, wherein the spectral sensor (42) senses light emerging from the strip assay (4) which results from the light of the light source (36) after entering the strip assay via the side edge (40) , internal deflection in the strip assay (4) , and transmission through the test line (16) or the control line (18) .

14. The method according to any one of claims 11 to 13, wherein the strip assay (4) comprises a backing card (22) into which the light from the light source (36) is coupled co-planarly and guided therein like in a waveguide.