US20090180927A1 - Assay test strips and reading same - Google Patents

Abstract

An assay test strip includes a flow path, a sample receiving zone, a label, a detection zone that includes a region of interest, and at least one position marker. The at least one position marker is aligned with respect to the region of interest such that location of the at least one position marker indicates a position of the region of interest. A diagnostic test system includes a reader that obtains light intensity measurement from exposed regions of the test strip, and a data analyzer that performs at least one of (a) identifying ones of the light intensity measurements obtained from the test region based on at least one measurement obtained from the at least one reference feature, and (b) generating a control signal modifying at least one operational parameter of the reader based on at least one measurement obtained from the at least one reference feature.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• Under 35 U.S.C. § 120, this application claims the benefit of U.S. patent application Ser. No. 11/112,807, filed Apr. 22, 2005, by Patrick T. Petruno et al. and entitled “LATERAL FLOW ASSAY SYSTEMS AND METHODS,” which is incorporated herein by reference.
BACKGROUND
• Assay test kits are currently available for testing for a wide variety of medical and environmental conditions or compounds, such as a hormone, a metabolite, a toxin, or a pathogen-derived antigen.FIG. 1 shows a typical lateralflow test strip10 that includes asample receiving zone12, alabeling zone14, adetection zone15, and anabsorbent zone20 on acommon substrate22. These zones12-20 typically are made of a material (e.g., chemically-treated nitrocellulose) that allows fluid to flow from thesample receiving zone12 to theabsorbent zone22 by capillary action. Thedetection zone15 includes atest region16 for detecting the presence of a target analyte in a fluid sample and acontrol region18 for indicating the completion of an assay test.
• FIGS. 2A and 2B show an assay performed by an exemplary implementation of thetest strip10. A fluid sample24 (e.g., blood, urine, or saliva) is applied to thesample receiving zone12. In the example shown inFIGS. 2A and 2B, thefluid sample24 includes a target analyte26 (i.e., a molecule or compound that can be assayed by the test strip10). Capillary action draws theliquid sample24 downstream into thelabeling zone14, which contains asubstance28 for indirect labeling of thetarget analyte26. In the illustrated example, the labelingsubstance28 consists of an immunoglobulin30 with a detectable particle32 (e.g., a reflective colloidal gold or silver particle). The immunoglobulin30 specifically binds thetarget analyte26 to form a labeled target analyte complex. In some other implementations, the labelingsubstance28 is a non-immunoglobulin labeled compound that specifically binds thetarget analyte26 to form a labeled target analyte complex.
• The labeled target analyte complexes, along with excess quantities of the labeling substance, are carried along the lateral flow path into thetest region16, which containsimmobilized compounds34 that are capable of specifically binding thetarget analyte26. In the illustrated example, theimmobilized compounds34 are immunoglobulins that specifically bind the labeled target analyte complexes and thereby retain the labeled target analyte complexes in thetest region16. The presence of the labeled analyte in the sample typically is evidenced by a visually detectable coloring of thetest region16 that appears as a result of the accumulation of the labeling substance in thetest region16.
• Thecontrol region18 typically is designed to indicate that an assay has been performed to completion.Compounds35 in thecontrol region18 bind and retain the labelingsubstance28. The labelingsubstance28 typically becomes visible in thecontrol region18 after a sufficient quantity of the labelingsubstance28 has accumulated. When thetarget analyte26 is not present in the sample, thetest region16 will not be colored, whereas thecontrol region18 will be colored to indicate that assay has been performed. Theabsorbent zone20 captures excess quantities of thefluid sample24.
• In the non-competitive-type of lateral flow assay test strip designs shown inFIGS. 2A and 2B, an increase in the concentration of the analyte in the sample results in an increase in the concentration of labels in the test region. Conversely, in competitive-type of lateral flow assay test strip designs, an increase in the concentration of the analyte in the fluid sample results in a decrease in the concentration of labels in the test region.
• Although visual inspection of lateral flow assay devices of the type described above are able to provide qualitative assay results, such a method of reading these types of devices is unable to provide quantitative assay measurements and therefore is prone to interpretation errors. Automated and semi-automated lateral flow assay readers have been developed in an effort to overcome this deficiency.
• In one approach, a portable lateral flow assay reader performs assays on bodily fluids to detect the presence of certain hormones, glucose, or other bodily fluids of interest. Membrane test strips containing a fluid sample are inserted directly into a receiving port of a reader. The receiving port is shielded to improve sensitivity and reduce the entry of stray or ambient light into the reader. The reader includes a light source and one or more sensors that detect the intensity of light reflected from the detection zones of the test strips that are inserted into the receiving port.
• In another approach, a reader detects an intensity of a detection signal arising in one or more measurement zones in a detection zone of a lateral flow assay test strip as a result of the presence of an immobilized labeled target analyte complex. The reader generates a baseline of signal intensity from the measurement zones by interpolating between values of the detection signal outside of the measurement zones and inside of the detection zone. The reader quantifies a value of signal intensity representative of the immobilized labeled target analyte complex with respect to the baseline. In this process, the reader locates a beginning boundary and an ending boundary for the one or more measurement zones on the test strip, allowing an automatic or semi-automatic analytical instrument, or a human reader, to determine certain results of the lateral flow assay. The signals from the measurement zones are quantified or compared with respect to the baseline. Quantified values corresponding to the respective concentration of compounds in different measurement zones may then be compared with one another to detect the presence of antigens in the sample.
• The measurements that are made by the above-described lateral flow assay readers are based on signals from regions of the test strips that typically are significantly larger than the regions of interest. As a result, these measurements tend to have high noise levels and, consequently, these measurements may yield inaccurate or incorrect results when low concentrations of analytes are involved.
SUMMARY
• In one aspect, the invention features an assay test strip that includes a flow path for a fluid sample, a sample receiving zone, a label, a detection zone, and at least one position marker. The sample receiving zone is coupled to the flow path. The label specifically binds a target analyte. The detection zone is coupled to the flow path and includes a region of interest and an immobilized test reagent that specifically binds the target analyte. The at least one position marker is aligned with respect to the region of interest such that location of the at least one position marker indicates a position of the region of interest.
• In one aspect, the invention features an assay test strip that includes a flow path for a fluid sample, a sample receiving zone, a label, a detection zone, and at least one reference feature. The sample receiving zone is coupled to the flow path. The label specifically binds a target analyte. The detection zone is coupled to the flow path and includes an immobilized test reagent that specifically binds the target analyte. The at least one reference feature is exposed for optical inspection and has a calibrated amount of the label.
• In another aspect, the invention features a diagnostic test system that includes a housing, a reader, and a data analyzer. The housing includes a port constructed and arranged to receive a test strip. The test strip includes a flow path for a fluid sample, a sample receiving zone coupled to the flow path, a label that specifically binds a target analyte, a detection zone, and at least one reference feature. The detection zone is coupled to the flow path and includes a test region. The test region is exposed for optical inspection and has an immobilized test reagent that specifically binds the target analyte. The reader is operable to obtain light intensity measurements from exposed regions of the test strip when the test strip is loaded in the port. The data analyzer is operable to perform operations including at least one of (a) identifying ones of the light intensity measurements obtained from the test region based on at least one measurement obtained from the at least one reference feature, and (b) generating a control signal modifying at least one operational parameter of the reader based on at least one measurement obtained from the at least one reference feature.
• The invention also features a diagnostic test method in accordance with which a test strip is received. The test strip includes a flow path for a fluid sample, a sample receiving zone coupled to the flow path, a label that specifically binds a target analyte, a detection zone, and at least one reference feature. The detection zone is coupled to the flow path and includes a test region. The test region is exposed for optical inspection and has an immobilized test reagent that specifically binds the target analyte. Light intensity measurements are obtained from exposed regions of the test strip. At least one of the following is performed: (a) identifying ones of the light intensity measurements obtained from the test region based on at least one measurement obtained from the at least one reference feature, and (b) generating a control signal modifying the obtaining of light intensity measurements from exposed regions of the test strip based on at least one measurement obtained from the at least one reference feature.
• Other features and advantages of the invention will become apparent from the following description, including the drawings and the claims.
DESCRIPTION OF DRAWINGS
• FIG. 1 is a diagrammatic view of a prior art implementation of an assay test strip.
• FIG. 2A is a diagrammatic view of a fluid sample being applied to an application zone of the assay test strip shown inFIG. 1.
• FIG. 2B is a diagrammatic view of the assay test strip shown inFIG. 2A after the fluid sample has flowed across the test strip to an absorption zone.
• FIG. 3 is a block diagram of an embodiment of a test strip that is loaded into an embodiment of a diagnostic test system.
• FIG. 4 is a flow diagram of an embodiment of a diagnostic test method.
• FIG. 5A is a diagrammatic side view of an implementation of the diagnostic test system shown inFIG. 3 that includes a two-dimensional light detector array obtaining light intensity measurements from regions of a test strip.
• FIG. 5B is a diagrammatic view of the two-dimensional light detector array shown inFIG. 5A in which ones of the light detectors that are positioned to obtain light intensity measurements from the test region and the control region are highlighted.
• FIG. 6 is an exemplary graph of light intensity plotted as a function of position in the two-dimensional light detector array shown inFIGS. 5A and 5B.
• FIG. 7 is a flow diagram of an embodiment of a method of reading a test strip having at least one position marker.
• FIG. 8 is a flow diagram of an embodiment of a method of identifying light intensity measurements that are obtained from a region of interest based on light intensity measurements that are obtained from at least one optical position marker.
• FIG. 9 is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 10 is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 11 is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 12A is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 12B is a graph of light intensity plotted as a function of position along the test strip shown inFIG. 12A.
• FIG. 13A is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 13B is a diagrammatic view of a detection system on a portion of the test strip shown inFIG. 13A.
• FIG. 13C is a diagrammatic view of the detection system on a different portion of the test strip shown inFIG. 13B.
• FIG. 14A is a diagrammatic view of an implementation of the test strip shown inFIG. 3.
• FIG. 14B is a diagrammatic view of a detection system on a portion of the test strip shown inFIG. 14A.
• FIG. 14C is a diagrammatic view of the detection system on a different portion of the test strip shown inFIG. 14B.
• FIG. 15 is a flow diagram of an embodiment of a method of calibrating light intensity measurements that are obtained from a region of interest.
• FIG. 16 is a diagrammatic view of an implementation of the diagnostic test system shown inFIG. 3.
• FIG. 17 is a flow diagram of an embodiment of a method of calibrating an illumination source of a diagnostic test system.
DETAILED DESCRIPTION
• In the following description, like reference numbers are used to identify like elements. Furthermore, the drawings are intended to illustrate major features of exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale.
I. Introduction
• The embodiments that are described in detail below provide lateral flow assay test strips that have one or more reference features. These embodiments also provide diagnostic test systems that are configured to read such test strips in ways that improve the accuracy and precision with which analytes in a fluid sample may be assayed.
• In some embodiments, the reference features are position markers that are aligned with respect to regions of interest in the test strip. These embodiments enable the levels of noise (e.g., noise caused by reflection of light or intrinsic fluorescence from materials in the test strip) in assay measurements to be reduced by restricting the measurements to the regions of interest on the test strip based on measurements obtained from the reference features. In this way, these embodiments increase the signal-to-noise levels of these measurements and, thereby, increase measurement sensitivity and reduce the incidence of erroneous results for low concentrations of analytes.
• In some embodiments, the reference features are calibration regions that provide a reference optical response that may be used by embodiments of the diagnostic test system to calibrate one or more components of a diagnostic test system and the assay measurements obtained by such a system and, thereby, increase the accuracy of the lateral flow assay results.
• The terms “assay test strip” and “lateral flow assay test strip” encompass both competitive and non-competitive types of lateral flow assay test strips. A lateral flow assay test strip generally includes a sample receiving zone and a detection zone, and may or may not have a labeling zone. In some implementations, a lateral flow assay test strip includes a sample receiving zone that is located vertically above a labeling zone, and additionally includes a detection zone that is located laterally downstream of the labeling zone.
• The term “analyte” refers to a substance that can be assayed by the test strip. Examples of different types of analytes include organic compounds (e.g., proteins and amino acids), hormones, metabolites, antibodies, pathogen-derived antigens, drugs, toxins, and microorganisms (e.g., bacteria and viruses).
• As used herein the term “label” refers to a substance that has specific binding affinity for an analyte and that has a detectable characteristic feature that can be distinguished from other elements of the test strip. The label may include a combination of a labeling substance (e.g., a fluorescent particle, such as a quantum dot) that provides the detectable characteristic feature and a probe substance (e.g., an immunoglobulin) that provides the specific binding affinity for the analyte. In some implementations, the labels have distinctive optical properties, such as luminescence (e.g., fluorescence) or reflective properties, which allow regions of the test strip containing different labels to be distinguished from one another.
• The term “reagent” refers to a substance that reacts chemically or biologically with a target substance, such as a label or an analyte.
• The term “capture region” refers to a region on a test strip that includes one or more immobilized reagents.
• The term “test region” refers to a capture region containing an immobilized reagent with a specific binding affinity for an analyte.
• The term “control region” refers to a capture region containing an immobilized reagent with a specific binding affinity for a label.
II. Diagnostic Test System Architecture
• A. Overview
• FIG. 3 shows an embodiment of adiagnostic test system40 that includes ahousing42, areader44, adata analyzer46, and amemory47. Thehousing42 includes aport48 for receiving atest strip50. When thetest strip50 is loaded in theport48, thereader44 obtains light intensity measurements from thetest strip50. In general, the light intensity measurements may be unfiltered or they may be filtered in terms of at least one of wavelength and polarization. The data analyzer46 computes at least one parameter from one or more of the light intensity measurements. Aresults indicator52 provides an indication of one or more of the results of an assay of thetest strip50. In some implementations, thediagnostic test system40 is fabricated from relatively inexpensive components enabling it to be used for disposable or single-use applications.
• Thehousing42 may be made of any one of a wide variety of materials, including plastic and metal. Thehousing42 forms a protective enclosure for thereader44, thedata analyzer46, thepower supply54, and other components of thediagnostic test system40. Thehousing42 also defines a receptacle that mechanically registers thetest strip50 with respect to thereader44. The receptacle may be designed to receive any one of a wide variety of different types oftest strips50, including test strips of the type shown inFIG. 1.
• In the illustrated embodiments, each of thetest strips50 is a non-competitive type of assay test strip that supports lateral flow of a fluid sample along alateral flow direction51 and includes a labeling zone containing a labeling substance that binds a label to a target analyte and a detection zone that includes at least one test region containing an immobilized substance that binds the target analyte. One or more areas of the detection zone, including at least a portion of the test region, are exposed for optical inspection by thereader44. The exposed areas of the detection zone may or may not be covered by an optically transparent window.
• In other embodiments, the test strips are competitive type of lateral flow assay test strips in which the concentrations of the label in the test region decreases with increasing concentration of the target analyte in the fluid sample. Some of these embodiments include a labeling zone, whereas others of these implementations do not include a labeling zone.
• Some of these competitive lateral flow assay test strip embodiments include a labeling zone that contains a label that specifically binds target analytes in the fluid sample, and a test region that contains immobilized target analytes as opposed to immobilized test reagents (e.g., antibodies) that specifically bind any non-bound labels in the fluid sample. In operation, the test region will be labeled when there is no analyte present in the fluid sample. However, if target analytes are present in the fluid sample, the fluid sample analytes saturate the label's binding sites in the labeling zone, well before the label flows to the test region. Consequently, when the label flows through the test region, there are no binding sites remaining on the label, so the label passes by and the test region remains unlabeled.
• In other competitive lateral flow assay test strip embodiments, the labeling zone contains only pre-labeled analytes (e.g., gold adhered to analyte) and the test region contains immobilized test reagents with an affinity for the analyte. In these embodiments, if the fluid sample contains unlabeled analyte in a concentration that is large compared to the concentration of the pre-labeled analyte in the labeling zone, then label concentration in the test region will appear proportionately reduced.
• Thereader44 includes one or more optoelectronic components for optically inspecting the exposed areas of the detection zone of thetest strip50. In some implementations, thereader44 includes at least one light source and at least one light detector. In some implementations, the light source may include a semiconductor light-emitting diode and the light detector may include a semiconductor photodiode. Depending on the nature of the label that is used by thetest strip50, the light source may be designed to emit light within a particular wavelength range or light with a particular polarization. For example, if the label is a fluorescent label, such as a quantum dot, the light source may be designed to illuminate the exposed areas of the detection zone of thetest strip50 with light in a wavelength range that induces fluorescent emission from the label. Similarly, the light detector may be designed to selectively capture light from the exposed areas of the detection zone. For example, if the label is a fluorescent label, the light detector may be designed to selectively capture light within the wavelength range of the fluorescent light emitted by the label or with light of a particular polarization. On the other hand, if the label is a reflective-type label, the light detector may be designed to selectively capture light within the wavelength range of the light emitted by the light source. To these ends, the light detector may include one or more optical filters that define the wavelength ranges or polarizations axes of the captured light.
• The data analyzer46 processes the light intensity measurements that are obtained by thereader44. In general, thedata analyzer46 may be implemented in any computing or processing environment, including in digital electronic circuitry or in computer hardware, firmware, or software. In some embodiments, thedata analyzer46 includes a processor (e.g., a microcontroller, a microprocessor, or ASIC) and an analog-to-digital converter. In the illustrated embodiment, thedata analyzer46 is incorporated within thehousing42 of thediagnostic test system40. In other embodiments, thedata analyzer46 is located in a separate device, such as a computer, that may communicate with thediagnostic test system40 over a wired or wireless connection.
• In general, theresults indicator52 may include any one of a wide variety of different mechanisms for indicating one or more results of an assay test. In some implementations, theresults indicator52 includes one or more lights (e.g., light-emitting diodes) that are activated to indicate, for example, a positive test result and the completion of the assay test (i.e., when sufficient quantity oflabeling substance28 has accumulated in the control region). In other implementations, theresults indicator52 includes an alphanumeric display (e.g., a two or three character light-emitting diode array) for presenting assay test results.
• Apower supply54 supplies power to the active components of thediagnostic test system40, including thereader44, thedata analyzer46, and theresults indicator52. Thepower supply54 may be implemented by, for example, a replaceable battery or a rechargeable battery. In other embodiments, the diagnostic test system may be powered by an external host device (e.g., a computer connected by a USB cable).
• FIG. 4 shows an embodiment of a diagnostic test method that is executable by the implementations of thediagnostic test system40 described below. In accordance with this method, thereader44 obtains separable localized light intensity measurements from regions of the exposed area of the detection zone of thetest strip50 when thetest strip50 is loaded in theport48 of the diagnostic test system40 (FIG. 4, block60). As used herein, the term “separable localized light intensity measurements” refers to the ability of thereader44 to transmit or record the light intensity measurements from respective localized regions of the test strip in a way that allows thedata analyzer46 to individually analyze each of the light intensity measurements.
• In some embodiments in accordance with the invention, each of the separable localized regions from which the light intensity measurements are obtained by thereader44 is characterized by at least one surface dimension that is smaller than the dimension of the exposed area of the detection zone that is transverse to thelateral flow direction51. In some implementations, each of these localized regions has a surface dimension that is approximately the same size or smaller than the narrowest dimension of a region of interest in the detection zone15 (e.g., the test region, the control region, or a region of an immobilized labeled or unlabeled complex).
• After thereader44 has obtained light intensity measurements from such localized regions of interest in the detection zone15 (FIG. 4, block60), thedata analyzer46 identifies ones of the light intensity measurements obtained from the regions of interest (FIG. 4, block62). In this process, thedata analyzer46 isolates the measurements corresponding to regions of interest from the measurements corresponding to other regions of thetest strip50. The isolated measurements have higher signal-to-noise ratios than aggregated measurements that include measurements from regions outside of the regions of interest.
• The data analyzer46 then computes at least one parameter from ones of the identified light intensity measurements (FIG. 4, block64). Exemplary parameters include peak intensity and aggregate intensity values. Since the measurements that are used to compute these parameters have higher signal-to-noise ratios, they characterize the region of interest with greater accuracy and, thereby, improve the results of the lateral flow assay.
• B. An Exemplary Implementation of the Diagnostic Test System
• FIG. 5A shows an exemplary implementation of thediagnostic test system40 that includes alight source66, a two-dimensional array68 oflight detectors70, and alens72. InFIG. 5A, the gross structural features of thetest strip50 are substantially the same as the corresponding features thetest strip10, which is shown inFIG. 1. In particular, thetest strip50 includes thesample receiving zone12, thelabeling zone14, thedetection zone15, and theabsorbent zone20 on thecommon substrate22. In the illustrated implementation, a substantial portion of thedetection zone15 is exposed for optical inspection.
• In operation, thelight source66 illuminates with light76 the exposed portion of thedetection zone15, including thetest region16 and thecontrol region18 of thetest strip50. The illuminatinglight76 may be broadband or narrowband and may be polarized or non-polarized. Thelight detector array68 obtains separable localized light intensity measurements from the illuminated regions of thedetection zone15. In general, the light intensity measurements may be unfiltered or they may be filtered in terms of at least one of wavelength and polarization. Thelight detector array68 may be synchronized with thelight source66. In general, thelight detector array68 may measure light intensity while thedetection zone15 is being illuminated or after thelight source66 has illuminated thedetection zone15. Light reflected or fluorescing from thedetection zone15 is focused by thelens72 onto the individuallight detectors70 of thelight detector array68. Each of thelight detectors70 receives light from a respective localized region of thedetection zone15. That is, eachlight detector70 is able to resolve or separably image a respective localized region of thedetection zone15. In this implementation, the localized regions are characterized by a surface dimension that is at most as large as the narrowest dimension of the test andcontrol regions16,18 (i.e., the dimensions ofregions16,18 that are along the lateral flow direction). In the illustrated implementations, the localized regions are characterized by square dimensions that are approximately equal to one-third of the size of the test andcontrol regions16,18 along the lateral flow direction. Thelight detectors70 produce signals representative of the amount of light received from the respective localized regions. These signals may be stored in a memory or they may be transmitted to thedata analyzer46 for processing.
• As shown inFIGS. 5A and 5B, the reflected or fluorescing light from thetest region16 is received by only asubset80 of thelight detectors70 in thearray68. Similarly, the reflected or fluorescing light from thecontrol region18 is received by only asubset82 of thelight detectors70 in thearray68. Thus, the signals from the light detectors in thesubsets80,82 provide relatively low noise light intensity measurements of the light reflected or fluorescing from thetest region16 and thecontrol region18, respectively.
• The data analyzer46 is operable to process the signals that are generated by the individuallight detectors70 to identify the ones of the light intensity measurements that are obtained from the regions of interest (e.g., thetest region16 and the control region18). Referring toFIG. 6, in one illustrative example, thelight detector array68 produces a set of light intensity signals that are represented by a three-dimensional surface84. In this example, thesurface84 includeshigher intensity measurements86,88 from locations of thedetection zone15 corresponding to thesubsets80,82 of thelight detectors70 in thelight detector array68. With respect to this example, thedata analyzer46 may identify the light intensity measurements that are obtained from thetest region16 and thecontrol region18 by thresholding thesurface84 at anintensity threshold level90. In some implementations, the threshold that is used in the thresholding process is constant across the strip or region of interest. For example, in some implementations, the threshold may be slanted or have local variations to account for variations in illumination or diffusion of the analytes. The ones of the light intensity measurements that are above thethreshold level90 are identified as having come from thetest region16 and thecontrol region18. Additional information, such as the relative positions of thelight detector array68 from which the identified ones of the light intensity measurements were obtained, may be used by thedata analyzer46 to correlate the identified light intensity measurements with thetest region16 and thecontrol region18.
III. Position Markers on a Test Strip and Reading Same
• A. Overview
• In some embodiments, thetest strip50 includes one or more reference features that serve as position markers, which are aligned with respect to regions of interest in the test strip. These embodiments enable the levels of noise (e.g., noise caused by reflection of light or intrinsic fluorescence from materials in the test strip) in lateral flow assay measurements to be reduced by restricting the measurements to the regions of interest on the test strip based on measurements obtained from the reference features. In this way, these embodiments increase the signal-to-noise levels of these measurements and, thereby, increase measurement sensitivity and reduce the incidence of erroneous results for low concentrations of analytes.
• FIG. 7 shows an embodiment of a method by which the diagnostic test system40 (FIG. 3) reads a test strip having at least one position marker.
• In accordance with this method, thereader44 obtains light intensity measurements from the test strip (FIG. 7, block92). In the implementation shown inFIG. 5A, thelight source66 illuminates the exposed portion of thedetection zone15, including thetest region16 and thecontrol region18 of thetest strip50, withlight76. The illuminatinglight76 may be broadband or narrowband and may be polarized or non-polarized. Thelight detector array68 then obtains separable localized light intensity measurements from the illuminated regions of thedetection zone15.
• The data analyzer46 identifies ones of the light intensity measurements that are obtained from a region of interest (e.g., thetest region16 or the control region18) based on at least one measurement that is obtained from the at least one position marker (FIG. 7, block94). In this process, thedata analyzer46 may identify the ones of the light intensity measurements that are obtained from a region of interest based on predetermined information about the spatial relationship between the region of interest and the at least one position marker.
• In general, each of the position markers may be implemented by any type of feature that has a different optical, electrical, or mechanical characteristic than the adjacent regions of the test strip surface.
• B. Optical Position Markers
• In some implementations, an optical position marker may have a detectable optical response that is different from the optical response of adjacent surface regions. For example, an optical position marker may have a greater reflection or emission than adjacent surface regions with respect to light within a specified wavelength range (e.g., the visible wavelength range: 390 nm to 770 nm). In other implementations, an optical position marker may have a lower reflection or emission than adjacent surface regions with respect to light within the specified wavelength range. In some implementations, the optical position marker is capable of fluorescent emission within a first wavelength range, whereas the adjacent surface regions are capable of fluorescent emission within a second wavelength range different from the first wavelength range or with an intensity that is significantly lower than the intensity of fluorescent emission by the optical position marker within the first wavelength range.
• FIG. 8 shows an embodiment of a method by which thedata analyzer46 identifies ones of the light intensity measurements that are obtained from a region of interest in thedetection zone15 based on intensity measurements that are obtained from at least one optical position marker that is aligned with respect to the region of interest along thelateral flow direction51.
• In accordance with this embodiment, thedata analyzer46 identifies ones of the light intensity measurements that are obtained from the at least one optical position marker (FIG. 8, block96).
• The data analyzer46 may identify the light intensity measurements that are obtained from the at least one optical position marker in any of a wide variety of different ways that depend on the implementation of the optical position marker and the other regions in the detection zone. As explained above, each of is the optical position markers may be implemented by any type of feature on a surface of thetest strip50 that has a different optical characteristic than the adjacent regions of the test strip surface. In some implementations, the optical position markers are composed of quantum dots that exhibit fluorescent emission with narrow wavelength ranges or other optically recognizable media. The optical position markers may be formed on the exposed surface of thetest strip50 in any of a wide variety of different ways, including silk screening and other printing or deposition methods. The data analyzer46 may identify the ones of the light intensity measurements that correspond to the optical position marker by identifying the light intensity measurements that have one or more predetermined attributes, such as exhibiting a characteristic pattern of light intensity variations across the test strip along the lateral flow direction or having the highest relative intensities within a specified wavelength range.
• After identifying the light intensity measurements that are obtained from the at least one optical position marker (FIG. 8, block96), thedata analyzer46 identifies ones of the light intensity measurements that are obtained from the region of interest based on a rule correlating imaged positions of the at least one optical position marker and the region of interest (FIG. 8, block98). In some implementations, the at least one optical position marker encodes at least one position along the lateral flow direction. In these implementations, thedata analyzer46 infers the imaged position of the region of interest based on the positions that are encoded by the optical position markers. For example, the encoded position may correspond to one or both of the beginning and ending locations of the region of interest along the lateral flow direction. In these implementations, thedata analyzer46 may infer that the region of interest is located after, before or between the locations demarcated by the at least one optical position marker.
• FIG. 9 shows an implementation of thetest strip50 that includes an exemplary set ofoptical position markers100 that are spaced regularly along the edge of thetest strip50. Theoptical position markers100 include features that have a different reflection or emission characteristic than the surface of thetest strip50. As a result, the measurements that are obtained near the edge of thetest strip50 vary in intensity in accordance with the pattern of theoptical position markers100. In this way, theoptical position markers100 encode positions along thetest strip50 in thelateral flow direction51. With respect to the implementation shown inFIG. 9, thedata analyzer46 may determine the encoded positions along the lateral flow direction by incrementing a position counter with each intensity variation cycle (e.g., peak-to-valley) in the light intensity measurements obtained from the edge of thedetection zone15.
• In these implementations, thedata analyzer46 correlates the light intensity measurements with the positions along thetest strip50 in thelateral flow direction51. The location correlation information may be stored in a lookup table that is indexed by the position counter value. Based on this information and on the predetermined information correlating the locations of the regions of interest with the light intensity contrast pattern produced by theoptical position markers100, thedata analyzer46 can identify the ones of the light intensity measurements corresponding to the regions of interest.
• In other implementations, theoptical position markers100 may encode position information in variations in the lengths of the optical position markers along thelateral flow direction51. Alternatively, theoptical position markers100 may encode position information in variations in the spacing between adjacent ones of theoptical position markers100 along thelateral flow direction51.
• FIG. 10 shows an implementation of thetest strip50 that includes an exemplary set ofoptical position markers102,104,106,108 that are positioned adjacent to thetest region16 and thecontrol region18. In particular, theoptical position marker102 is positioned adjacent to anupstream edge110 of thetest region16 and theoptical position marker104 is positioned adjacent to adownstream edge112 of thetest region16. Similarly, theoptical position marker106 is positioned adjacent to anupstream edge114 of thecontrol region18 and theoptical position marker108 is positioned adjacent to adownstream edge116 of thecontrol region18. In the illustrated embodiment, the optical position markers102-108 are beside one edge of thedetection zone15.
• In the illustrated embodiment, the optical position markers102-108 have square shapes. In general, however, the optical position markers102-108 may have any type of shape, including a polygonal (e.g., rectangular) shape and a curved (e.g., elliptical or circular) shape.
• In some implementations, thedata analyzer46 is operable to identify the light intensity measurements that are obtained from the optical position markers102-108 based on the sizes, shapes, and/or locations of the optical position markers102-108. For example, thedata analyzer46 may identify the light intensity measurements by locating square regions in an image of thedetection zone15 that is captured by thelight detector array68. In other implementations, thedata analyzer46 may identify the light intensity measurements that are obtained from the optical position markers102-108 based on one or more attributes (e.g., relative intensity, wavelength, or decay profile) of the light reflected or fluorescing from the optical position markers102-108.
• The data analyzer46 readily may determine the bounds of the regions ofinterest16,18 based on the edges of the optical position markers102-108 in an image that is captured by thelight detector array68. For example, with respect to the implementation illustrated inFIG. 10, thedata analyzer46 identifies thetest region16 as the transverse region between theoptical position markers102,104 and identifies thecontrol region18 as the transverse region between theoptical position markers106,108. If only the upstreamoptical position markers102,106 were present, thedata analyzer46 would be configured to identify the regions ofinterest16,18 as corresponding to the transverse regions immediately following theoptical position markers102,106 with respect to the lateral flow direction. Similarly, if only the downstreamoptical position markers104,108 were present, thedata analyzer46 would be configured to identify the regions ofinterest16,18 as corresponding to the transverse regions immediately preceding theoptical position markers104,108 with respect to thelateral flow direction51.
• In the implementation of thetest strip50 that is illustrated inFIG. 10, the optical position markers102-108 are located beside an edge of thedetection zone15.FIG. 11 shows another implementation of thetest strip50 in which theoptical position markers118,120,122,124 are located centrally over the flow path in thedetection zone15. The optical position markers118-124 are elongate in the transverse direction perpendicular to thelateral flow direction51. In other respects, the optical position markers118-124 may be implemented in the same way as the optical position markers102-108.
• FIG. 12A shows an embodiment of thetest strip50 in which respective optical position markers are formed by the spatial arrangement of the immobilized test reagent in thetest region16 and the spatial arrangement of the immobilized test reagent in thecontrol region18. In particular, thetest region16 includes three discrete, spaced-apartcode areas126,128,130 in which the test reagent is immobilized. Similarly, thecontrol region18 includes three discrete, spaced-apartcode areas132,134,136 in which the control reagent is immobilized. Each of the code areas126-136 has a rectangular shape with the same length (L) but varying width. In this exemplary embodiment, each of the code areas has a width that is an integer multiple of a unit width (w). For example, the widths of thecode areas126,130,134, and136 are equal to the unit width w, whereas the widths of thecode areas128,132 are equal to 3 w. The position information is encoded in the varying widths of the code areas of thetest region16 and thecontrol region18.
• FIG. 12B shows a graph of aggregate light intensity plotted as a function of position along thelateral flow direction51 of test strip shown inFIG. 12A. With respect to this example, thelight detector array68 of thediagnostic test system20 shown inFIG. 5A captures a first signaturelight code pattern138 from the code areas126-130 of thetest region16 and a secondsignature light pattern140 from the code areas132-136 of thecontrol region18. The data analyzer46 determines the widths of the code areas126-136 from thesignature light patterns138,140 and translates the widths into code values that uniquely identify thetest region16 and thecontrol region18. For example, from thesignature light pattern138, thedata analyzer46 determines that the widths of the code areas126-130 are w, 3 w, and w and translates these widths into the code value131. From thesignature light pattern140, thedata analyzer46 determines that the widths of the code areas132-136 are 3 w, w, and w and translates these widths into the code value311. In some embodiments, the code values identifying thetest region16 and thecontrol region18 are stored in a lookup table, which thedata analyzer46 may query to determine the locations of thetest region16 and thecontrol region18.
• In general, the immobilized test reagent and the immobilized control reagent may be arranged in any one-dimensional or two-dimensional pattern that uniquely identifies thetest region16 and thecontrol region18, respectively. In some implementations, the immobilized reagents of the test andcontrol regions16,18 are spatially arranged to form one- or two-dimensional bar code symbols. In some embodiments, the bar codes symbols are patterns of parallel bars and spaces of various widths that represent data elements or characters. Typically, the bars represent strings of binary ones and the spaces represent strings of binary zeros. A one-dimensional bar code symbol (e.g., a UPC bar code symbol) typically contains a series of bars and spaces that vary only in a single dimension. In two-dimensional bar codes (e.g., a PDF417 bar code symbol, a Code1 bar code symbol, and a Maxicode bar code symbol), the bar code patterns vary in two dimensions. With respect these embodiments, thediagnostic test system40 implements the bar code decoding process corresponding to the bar coding method that is used to create the code areas of the test andcontrol regions16,18.
• In addition to identifying the locations of the test andcontrol regions16,18 in thedetection zone15, the code areas may encode additional information relating to the test strip in general (e.g., date and place of manufacture), the test and control regions in particular (e.g., the type of target analyte that may be assayed), or to methods of reading the test strip (e.g., predetermined calibration values or scaling values for adjusting the measurement results or interpreting the measurement results).
• C. Electrical Position Markers
• In some embodiments, thetest strip50 includes electrical position markers that are aligned with respective regions of interest on the test strip. With respect to these embodiments, thedata analyzer46 identifies the ones of the light intensity measurements that are obtained from the respective regions of interest based on predetermined information about the spatial relationship between the regions of interest and the corresponding electrical position markers.
• FIG. 13A shows an implementation of thetest strip50 that includes an exemplary set ofelectrical position markers140,142,144,146 that are spaced along the edge of thetest strip50. The electrical position markers140-146 include features that have a different electrical characteristic than the adjacent areas on the surface of thetest strip50. As a result, the measurements that are obtained near the edge of thetest strip50 vary in electrical response in accordance with the pattern of the electrical position markers140-146. With respect to these embodiments, the diagnostic test system40 (FIG. 3) includes a detection system that is capable of detecting the electrical position markers. In general, any type of electrical conductor detection method may be used to detect the electrical position markers, including current, voltage, resistance, and capacitance based measurement methods.
• FIG. 13B snows an embodiment of adetection system148 on a portion of an embodiment of the test strip shown inFIG. 13A. Thedetection system148 includes adetector150, a firstelectrical contact152, and a secondelectrical contact154. The first and secondelectrical contacts152,154 are electrically connected to thedetector150 and are separated from one another by anair gap156, which forms an open circuit. Thedetector150 may include any type of circuit (e.g., an ohmmeter, a voltmeter, and an ammeter) that is capable of detecting when an electrical connection is formed across theair gap156. In these embodiments, the top surface of the test strip is formed of a material with a high electrical resistance except at the locations of the electrical position markers140-146.
• In operation, at least one of thedetection system148 and thetest strip50 is moved relative to the other in a direction parallel to thelateral flow direction51. The first and secondelectrical contacts152,154 slide over the top surface of the test strip. In some implementations, the first and secondelectrical contacts152,154 are urged (e.g., by springs) against the top surface of the test strip. In the position shown inFIG. 13B, the first and secondelectrical contacts152,154 are connected only by the material of the top surface of the test strip. In this position, thedetector150 is configured to determine that there is an open circuit between the first and secondelectrical contacts152,154. In the position shown inFIG. 13C, on the other hand, the first and secondelectrical contacts152,154 are connected by theelectrical position marker146. In this position, thedetector150 is configured to determine that there is a closed circuit between the first and secondelectrical contacts152,154.
• Thedetector150 may determine whether there is an open circuit or a closed circuit between the first and secondelectrical contacts152,154 by comparing an electrical measurement (e.g., current, voltage, or resistance) between the first and secondelectrical contacts152,164 to a threshold value. For example, the detector may determine that there is an open circuit between the first and secondelectrical contacts152,154 when the measured electrical resistance value is greater than or equal to a threshold resistance value and that there is a closed circuit between the first and secondelectrical contacts152,154 when the measured electrical resistance value is below the threshold value.
• In the embodiment shown inFIG. 13A, the electrical position markers140-146 are aligned with the upstream and downstream edges of thetest region16 and thecontrol region18 along thelateral flow direction51. In this way, thedata analyzer46 readily may determine that the test andcontrol regions16,18 are located between the detected positions of theelectrical position markers140,142 and144,146, respectively.
• In other embodiments, the electrical position markers may encode position information in different ways. For example, in some embodiments, the electrical position markers may be positioned at regularly spaced locations along the edge of thetest strip50. As a result, the electrical measurements that are obtained near the edge of thetest strip50 vary in value in accordance with the pattern of the electrical position markers. In this way, the electrical position markers encode positions along thetest strip50 in thelateral flow direction51. With respect to these embodiments, thedata analyzer46 may determine the encoded positions along thelateral flow direction51 by incrementing a position counter with each measurement variation cycle (e.g., peak-to-valley) in the electrical measurements obtained from the edge of thedetection zone15.
• D. Mechanical Position Markers
• In some embodiments, thetest strip50 includes mechanical position markers that are aligned with respective regions of interest on the test strip. With respect to these embodiments, thedata analyzer46 identifies the ones of the light intensity measurements that are obtained from the respective regions of interest based on predetermined information about the spatial relationship between the regions of interest and the corresponding mechanical position markers.
• FIG. 14A shows an implementation of thetest strip50 that includes an exemplary set ofmechanical position markers160,162,164,166 that are spaced along the edge of thetest strip50. The mechanical position markers160-166 include features that have a different surface profile than the adjacent areas on the surface of thetest strip50. As a result, the measurements that are obtained near the edge of thetest strip50 vary in mechanical response in accordance with the pattern of the mechanical position markers160-166. With respect to these embodiments, the diagnostic test system40 (FIG. 3) includes a detection system that is capable of detecting the mechanical position markers. In general, any type of detection method that is responsive to variations in surface profile may be used to detect the mechanical position markers, including spring contact based methods and mechanical transducer based methods.
• FIG. 14B shows an embodiment of adetection system168 on a portion of an embodiment of the test strip shown inFIG. 14A. Thedetection system168 includes adetector170, a firstelectrical conductor172, and a secondelectrical conductor174. The first and secondelectrical conductors172,174 are electrically connected to thedetector170 and are separated from one another by the substrate of thetest strip50. The firstelectrical conductor172 is attached to a spring-loadedpiston176 and the secondelectrical conductor174 is an electrically conducting support member for thetest strip50. In other embodiments, the firstelectrical conductor172 may be implemented by an electrically conducting brush electrode. Thedetector170 may include any type of circuit (e.g., an ohmmeter, a voltmeter, and an ammeter) that is capable of detecting when the first and second electrical conductors are electrically connected together. In these embodiments, the test strip is formed of a material with a high electrical resistance and the mechanical position markers160-166 correspond to respective holes that extend through thesubstrate22 of thetest strip50.
• In operation, at least one of thedetection system168 and thetest strip50 is moved relative to the other in a direction parallel to thelateral flow direction51. The firstelectrical conductor172 slides over the top surface of thetest strip50, which is supported by the secondelectrical conductor174. The firstelectrical conductor172 is urged by aspring177 against the top surface of thetest strip50.
• In the position shown inFIG. 14B, the first and secondelectrical conductors172,174 are connected only by the high resistance material of thetest strip50. In this position, thedetector170 is configured to determine that there is an open circuit between the first and secondelectrical conductors172,174. In the position shown inFIG. 14C, on the other hand, the firstelectrical conductor172 extends through themechanical position marker166 and directly contacts the secondelectrical conductor174. In this position, thedetector170 is configured to determine that there is a closed circuit between the first and secondelectrical conductors172,174.
• Thedetector170 may determine whether there is an open circuit or a closed circuit between the first and secondelectrical conductors172,174 by comparing an electrical measurement (e.g., current, voltage, or resistance) between the first and secondelectrical conductors172,174 to a threshold value. For example, the detector may determine that there is an open circuit between the first and secondelectrical conductors172,174 when the measured electrical resistance value is greater than or equal to a threshold resistance value and that there is a closed circuit between the first and secondelectrical conductors172,174 when the measured electrical resistance value is below the threshold value.
• In the embodiment shown inFIG. 14A, the mechanical position markers160-166 are aligned with the upstream and downstream edges of thetest region16 and thecontrol region18 along thelateral flow direction51. In this way, thedata analyzer46 readily may determine that the test andcontrol regions16,18 are located between the detected positions of themechanical position markers160,162 and164,166, respectively.
• In other embodiments, the mechanical position markers may encode position information in different ways. For example, in some embodiments, the mechanical position markers may be positioned at regularly spaced locations along the edge of thetest strip50. As a result, the electrical measurements that are obtained near the edge of thetest strip50 vary in value in accordance with the pattern of the mechanical position markers. In this way, the mechanical position markers encode positions along thetest strip50 in thelateral flow direction51. With respect to these embodiments, thedata analyzer46 may determine the encoded positions along thelateral flow direction51 by incrementing a position counter with each measurement variation cycle (e.g., peak-to-valley) in the electrical measurements obtained from the edge of thedetection zone15.
• In other embodiments, the first and secondelectrical conductors172,174 of thedetection system168 are replaced by a mechanical transducer (e.g., a stylus connected to a piezoelectric element) is dragged across the top surface of the test strip. In particular, the mechanical transducer generates signals corresponding to its movement in a direction normal to the surface of the test strip. The vertical motion of the stylus compresses the piezoelectric element, which generates a voltage response that varies linearly with the movement of the stylus. These signals indicate the surface profile variations across the surface of thetest strip50. With respect to these embodiments, the mechanical position markers may be implemented by holes, notches, dimples, or bumps on the top surface of thetest strip50.
III. Calibration Regions on a Test Strip and Reading Same
• A. Overview
• In some embodiments, one or more of the reference features on thetest strip50 are calibration regions that provide a reference optical response that may be used by embodiments of thediagnostic test system10 to calibrate one or more components of a diagnostic test system and the assay measurements obtained by such a system and, thereby, increase the accuracy of the lateral flow assay results.
• In general, the calibration regions may be laid out in thedetection zone15 of thetest strip50 in any of a wide variety of ways. In some implementations, the calibration regions are positioned near the regions of interest in order to reduce the effects of temperature or manufacturing variations across thetest strip50. In some of these implementations, the calibration regions are laid out adjacent to one or more of the regions of interest in thedetection zone15 of thetest strip50. For example, in one exemplary embodiment, the calibration regions may be laid out in the same way as the optical position markers102-108 in the implementation shown inFIG. 10 or the same way as the optical position markers118-124 in the implementation shown inFIG. 11.
• In implementations of thetest strip50 that include a test region and one or more additional capture regions (e.g., another test region or a control region), one or more the additional capture regions may serve as a calibration region for calibrating one or more components of a diagnostic test system and/or calibrating the assay measurements obtained from the test region.
• B. Measurement Calibration Regions
• In some embodiments, the calibration regions are calibrated to provide a reference optical response that may be used by thedata analyzer46 to calibrate the light intensity measurements that are obtained from the regions of interest.
• FIG. 15 shows an embodiment of a method by which thediagnostic test system10 calibrates the light intensity measurements that are obtained from a region of interest.
• In accordance with this method, thedata analyzer46 determines a measurement calibration value from at least one light intensity measurement that is obtained from a calibration region (FIG. 15, block180). The measurement calibration value may correspond to a statistical measure (e.g., a peak intensity value or average intensity value) that is computed from the light intensity measurements that are obtained from the calibration region.
• The data analyzer46 then determines an amount of a target substance (e.g., the target analyte captured by thetest region16 or the label captured by the control region18) based on the light intensity measurements that are obtained from the region of interest and the determined measurement calibration value (FIG. 15, block182).
• In some implementations, at least one calibration region contains a calibrated amount of the test label32 such that the optical response (e.g., reflected light intensity or fluorescent emission intensity) of the calibration region corresponds to a known quantity (e.g., number or density) of the test label32. The data analyzer46 may then scale the optical responses from thetest region16 and thecontrol region18 based on the optical response of the calibration region to obtain measures of the quantity of the analyte captured by thetest region16 or the quantity of the label captured by thecontrol region18.
• In some implementations, thetest strip50 includes multiple calibration regions having different respective calibrated amounts of the same label. With respect to these implementations, thedata analyzer46 generates from the optical responses of the calibration regions a calibration curve mapping light intensities to measures of the quantities of the label. The data analyzer46 may then map the light intensity measurements that are obtained from the regions of interest to a measure of the amount of a captured substance of interest (e.g., the target analyte captured in thetest region16 or the label captured by the control region18).
• In some implementations, thelabeling zone14 of thetest strip50 contains different colored labels that specifically bind to different respective analytes that may be present in the fluid sample. In these implementations, thetest strip50 may include one or more calibration regions that contain calibrated amounts of the different labels. In these implementations, thetest strip50 may include a separate calibration region for each label. Alternatively, thetest strip50 may contain one or more calibration regions each of which contains calibrated amounts of multiple different labels. The calibrated amounts of the different labels may be intermixed and distributed across the same calibration region or they may be located within different respective sub-areas of the same calibration region.
• C. Detection Calibration Regions
• In some embodiments, the calibration regions provide a reference optical response that may be used by thedata analyzer46 to calibrate one or more operational parameters of the detection system of thereader44.
• In this regard, thedata analyzer46 may optimize the wavelength characteristics of the components of the detection system that distinguish among the different light colors that are emitted by different labels on thetest strip50. For example, thedata analyzer46 may generate a signal that adjusts the wavelength passband of a tunable optical filter of the detection system to maximize the detected intensity of light received from a calibration region.
• The data analyzer46 also may adjust (e.g., normalize) the response of the detection system for the characteristic wavelengths of light received from the calibration regions. For example, thedata analyzer46 may generate a signal that adjusts the response of the detection system so that it produces a predetermined output value (e.g., a predetermined current value or a predetermined voltage value) in response to light obtained from the calibration region. The data analyzer46 may generate a respective response adjustment signal for each wavelength range of interest (e.g., for the characteristic wavelength of each label carried by the test strip50).
• D. Illumination Calibration Regions
• In some embodiments, the calibration regions provide a reference optical response that may be used by thedata analyzer46 to calibrate one or more operational parameters of the illumination system of thereader44.
• FIG. 16 shows an embodiment of thetest strip50 that includes first and second illuminationsource calibration regions184,186. Each of the first and second illuminationsource calibration regions184,186 has a reflection or emission that is greater than the adjacent surface regions of the test strip with respect to light within a target wavelength range. In some implementations, the first and second illuminationsource calibration regions184,186 have reflectivities that are greater than 90% with respect to light within the visible wavelength range (i.e., 390 nm to 770 nm). In these implementations, the first and second illuminationsource calibration regions184,186 are formed of thin films of a metal (e.g., aluminum or gold). In other implementations, the first and second illuminationsource calibration regions184,186 include immobilized fluorescent particles (e.g., quantum dots) with secondary fluorescent emissions that may be used to calibrate one or more operational parameters of the illumination system of thereader44.
• FIG. 17 shows an embodiment of a method by which thedata analyzer46 calibrates an illumination source of thereader44.
• In accordance with this method, thedata analyzer46 determines an illumination source output measure from at least one light intensity measurement obtained from the illumination source calibration region (FIG. 17, block190). In some implementations, the illumination source calibration source corresponds to a statistical measure (e.g., a peak intensity value or average intensity value) that is computed from the light intensity measurements that are obtained from the illumination source calibration region.
• The data analyzer46 generates a signal for calibrating the illumination source based on the illumination source output measure (FIG. 17, block192). In some implementations, thedata analyzer46 compares the illumination source output measure to a reference value. The data analyzer46 may generate a control signal that increases the light intensity output of the illumination source when the illumination source output measure is below the reference value and decreases the light intensity output of the illumination source when the illumination source output measure is above the reference value. In some implementations, thedata analyzer46 may iteratively determine the illumination source output measure and generate the illumination control signal until the illumination source output measure is within a specified range of the reference value.
• In the embodiment shown inFIG. 16, the first illuminationsource calibration region184 is located upstream of thetest region16 and the second illuminationsource calibration region186 is located downstream of thecontrol region18. In this way, thedata analyzer46 may detect variations in the output of the illumination source across thedetection zone15. In some implementations, thedata analyzer46 may scale the light intensity measurements obtained for the regions of interest based on the differences between the illumination source output measures determined for the first and second illuminationsource calibration regions184,186. The amount by which the light intensity measurements are scaled may be determined empirically and stored in a lookup table or represented by a parametric curve or some other function of the illumination source output measures.
IV. Conclusion
• The embodiments that are described above provide lateral flow assay test strips that have one or more reference features. In some embodiments, the reference features are position markers that are aligned with respect to regions of interest in the test strip and may be used by embodiments of the diagnostic test system to identify light intensity measurements obtained from regions of interest. In some embodiments, the reference features are calibration regions that provide a reference optical response that may be used by embodiments of the diagnostic test system to calibrate one or more components of a diagnostic test system and the assay measurements obtained by such a system. In these ways, the embodiments described above improve the accuracy and precision with which analytes in a fluid sample may be assayed.
• Other embodiments are within the scope of the claims.
• For example, the embodiments are described above in connection with an implementation of thediagnostic test system10 that includes a two-dimensional array oflight detectors70. These embodiments also may be integrated with different implementations of thediagnostic test system10, including implementations in which thereader44 includes a one-dimensional array of light detectors and a mechanism for imparting relative motion between the optical inspection components of the reader and the test strip-.
• Some implementations of thetest strip50 may include two or more of the different types of reference features that are described above.
• In the embodiments described above, the test regions, control regions, calibration regions, and position markers are shown as having rectangular shapes in the plane of thedetection zone15. In general, however, these features may have any type of shape, including a polygonal (e.g., rectangular) shape and a curved (e.g., elliptical or circular) shape.

Claims (15)

1-30. (canceled)

31. A diagnostic test system, comprising:

a housing comprising a port constructed and arranged to receive a test strip that comprises a flow path for a fluid sample, a sample receiving zone coupled to the flow path, a label that specifically binds a target analyte, a detection zone coupled to the flow path and comprising a test region exposed for optical inspection and having an immobilized test reagent that specifically binds the target analyte, and at least one reference feature;

a reader operable to obtain light intensity measurements from exposed regions of the test strip when the test strip is loaded in the port; and

a data analyzer operable to perform operations comprising at least one of (a) identifying ones of the light intensity measurements obtained from the test region based on at least one measurement obtained from the at least one reference feature, and (b) generating a control signal modifying at least one operational parameter of the reader based on at least one measurement obtained from the at least one reference feature.

32. The system ofclaim 31, wherein the reference feature is aligned with respect to the test region, and the data analyzer is operable to determine ones of the light intensity measurements obtained from the at least one reference feature.

33. The system ofclaim 32, wherein the data analyzer is operable to identify the ones of the light intensity measurements obtained from the test region based on a rule correlating imaged positions of the determined ones of the light intensity measurements obtained from the at least one reference feature and light intensity measurements obtained from the test region.

34. The system ofclaim 31, wherein the reference feature comprises an encoding of position in the detection zone formed by a spatial arrangement of the immobilized test reagent in the test region.

35. The system ofclaim 31, further comprising a detection system operable to detect the reference feature, and wherein the data analyzer is operable to identify ones of the light intensity measurements obtained from the test region by correlating detection of the reference feature by the detection system with the obtaining of the light intensity measurements by the reader.

36. The system ofclaim 35, wherein the reference feature comprises an electrical conductor on a surface of the test strip.

37. The system ofclaim 35, wherein the reference feature comprises a mechanical feature having a different surface profile on the test strip than adjacent areas of the test strip.

38. The system ofclaim 37, further comprising a mechanical transducer configured to generate signals indicative of surface profile variations across the test strip.

39. The system ofclaim 31, wherein the at least one reference feature produces a series of contrast variations along the flow path, the reader is operable to obtain from the at least one reference feature a series of light intensity measurements encoding positions along the flow path, and the data analyzer is operable to decode the series of light intensity measurements into positions along the flow path and identify the ones of the light intensity measurements obtained

from the test region based on the positions decoded from the series of light intensity measurements.

40. The system ofclaim 31, wherein the reference feature is adjacent to the test region, and the data analyzer is operable to identify the ones of the light intensity measurements obtained from the test region based on light intensity measurements obtained from the reference feature.

41. The system ofclaim 31, wherein the reference feature is calibrated to provide at least one reference optical response to illumination with a specified wavelength range, and the data analyzer is operable to determine an amount of the analyte captured in the test region based on the at least one light intensity measurement obtained from the reference feature and at least one light intensity measurement obtained from the test region.

42. The system ofclaim 31, wherein:

the at least one reference feature comprises a first reference feature over the flow path upstream of and adjacent to the test region, and a second reference feature over the flow path downstream of and adjacent to the test region; and

the data analyzer is operable to determine a measurement calibration value from light intensity measurements obtained from the first and second reference features and to determine an amount of the analyte based on the light intensity measurements obtained from the test region and the determined measurement calibration value.

43. The system ofclaim 31, wherein the at least one reference feature comprises an illumination source calibration region, the reader comprises an illumination source operable to illuminate the test strip when the test strip is loaded in the port, and the data analyzer is operable to generate a signal for calibrating the illumination source based on the at least one light intensity measurement obtained from the illumination source calibration region.

44-55. (canceled)

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