WO2002008762A1 - Apparatus and method for evanescent light fluoroassays - Google Patents

Apparatus and method for evanescent light fluoroassays Download PDF

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Publication number
WO2002008762A1
WO2002008762A1 PCT/US2001/021634 US0121634W WO0208762A1 WO 2002008762 A1 WO2002008762 A1 WO 2002008762A1 US 0121634 W US0121634 W US 0121634W WO 0208762 A1 WO0208762 A1 WO 0208762A1
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WIPO (PCT)
Prior art keywords
analyte
waveguide
light
disposable cartridge
binding molecule
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PCT/US2001/021634
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French (fr)
Inventor
Arthur D. Boren
Alan C. Anderson
Jan W. Pawlak
Larry D. Wade
Timothy J. Stultz
Patrick E. Freudenthal
James M. T. Hines
Eric D. Miller
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Thaumdx, Llc
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Priority to US62063800A priority Critical
Priority to US09/620,638 priority
Application filed by Thaumdx, Llc filed Critical Thaumdx, Llc
Publication of WO2002008762A1 publication Critical patent/WO2002008762A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00Investigating or analysing materials by the use of optical means, i.e. using infra-red, visible or ultra-violet light
    • G01N21/62Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/64Fluorescence; Phosphorescence
    • G01N21/645Specially adapted constructive features of fluorimeters
    • G01N21/648Specially adapted constructive features of fluorimeters using evanescent coupling or surface plasmon coupling for the excitation of fluorescence
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/50Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
    • G01N33/53Immunoassay; Biospecific binding assay; Materials therefor
    • G01N33/543Immunoassay; Biospecific binding assay; Materials therefor with an insoluble carrier for immobilising immunochemicals
    • G01N33/54366Apparatus specially adapted for solid-phase testing
    • G01N33/54373Apparatus specially adapted for solid-phase testing involving physiochemical end-point determination, e.g. wave-guides, FETS, gratings

Abstract

An apparatus and method for evanescent light fluoroassays incorporate a waveguide in a disposable cartridge for the detection and quantification of analytes. The waveguide, preferably a planar waveguide, contains on one surface an analyte-binding molecule for binding an analyte from a fluid sample, such as a blood sample. The analyte is linked directly (for a competitive immunoassay) or indirectly, through an analyte-binding molecule, (for a sandwich immunoassay) to a fluorescent molecule. Alternatively, an analyte or analyte analog is bound to a surface of the waveguide. Analyte present in a fluid sample would compete with the analyte or analyte analog on the waveguide surface for a labeled analyte-binding molecule. The disposable cartridge (20) may contain a fluid sample in a tube, which is held on a platform comprising a light source (11), a means for holding the disposable cartridge (15), and a light detecting device (17). The system holds the disposable cartridge in place so that the waveguide (25) is properly aligned with the light source (11) and the light-detecting device (17). Air pressure, vacuum or capillary action may be used to move the fluid sample onto an assay area of the disposable cartridge, where the analyte reacts with the analyte-binding molecule on the waveguide surface. Upon passage of light through the waveguide, an evanescent field is created, which selectively excites fluorescent molecules bound to the waveguide. Light emitted by the fluorescent molecule is detected by the light-detecting device, and the amount of analyte in the fluid sample is determined. Upon completion of the measurement, the entire cartridge can be discarded. The apparatus and method may be used in competitive or sandwich-type immunoassays, nucleic acid assays and enzymatic hydrolysis assays.

Description

DESCRIPTION Apparatus And Method For Evanescent Light Fluoroassays

Field Of The Invention

The present invention is directed to a quantitative, qualitative, or semi-quantitative biosensor system for use in a broad range of clinical diagnostic, life science and drug discovery applications. More particularly, the present invention is directed to a quantitative biosensor system that uses evanescent light to excite a fluorescent molecule bound at a waveguide surface for rapid detection of a broad range of analytes in whole blood, serum, or plasma, as well as other unprocessed bodily fluids and solutions. Other applications that may benefit from such an in vitro assay system include pollution monitoring, life science research, agricultural and food testing, veterinary medicine, drug screening, and the detection of biological and chemical warfare agents.

Background Of The Invention

There is a great need for quick, reliable and cost-effective in vitro assay systems in a variety of medical, biological research, and chemical research fields. For example, in the case of hospital emergency rooms, effective treatment of many patients depends on rapid analysis of various clinical parameters to quickly and accurately determine the nature and extent of their medical problems. Patients being treated in clinics or individual doctors' offices would also benefit from such a system, in that the test results would be rapidly available to the doctor for diagnosis and treatment. Such patients then would not have to travel to a larger health care facility to have these tests performed, or have blood samples sent out to a central testing laboratory from which the results may not be available for several days.

Ideally, such an in vitro assay system would be capable of measuring sub- nanomolar concentrations of analytes in samples with minimal sample preparation and with a minimum number of analytical steps. The ability to measure sub-nanomolar concentrations of analytes is important because many analytes of physiological interest are found in biological fluids, such as blood or blood products, at such concentrations. The in vitro assay system should also ideally be capable of measuring a large number of different analytes, and be able to perform the analyses quickly, preferably within about five minutes. Furthermore, the system should be able to perform these assays for a minimal cost. Finally, the entire system should preferably be of a size that is capable of being easily incorporated into various point-of-care environments, such as the patient's bedside, emergency rooms, outpatient lab settings, physician offices and specialized hospital care units, such as intensive care units and coronary care units. The system also preferably could be used in various types of emergency vehicles, such as ambulances and hazardous materials response vehicles.

To measure sub-nanomolar concentrations of analytes, the most commonly employed clinical diagnostic methods employ antibodies in immunoassays. Clinical diagnostic immunoassays are of several different forms. One type of immunoassay is a competition immunoassay which can be performed using several different formats. For example, in one format, a labeled analyte or analyte analog is added to the sample suspected of containing analyte. This mixture is then applied to a solid phase which has an anti-analyte antibody immobilized thereon. The analyte in the sample (if any) competes with the labeled analyte or analyte analog for binding to the immobilized antibody. A high amount of analyte in the sample is indicated by a smaller amount of labeled analyte or analyte analog bound to the immoblized antibody. In another format of a competition immunoassay, labeled analyte or analyte analog is bound to an anti-analyte antibody, and the antibody is bound to a solid phase. As the sample suspected of containing analyte contacts the antibody, the unlabeled analyte in the sample displaces the labeled analyte bound to the antibody. The level of analyte in the sample is determined as a function of the amount of labeled analyte displaced from the solid phase. Thus, here as well, a high amount of analyte in the sample is indicated by a smaller amount of the labeled analyte left bound to the antibody. In another competitive immunoassay format, an analyte or analyte analog is bound to a solid phase, and a labeled anti-analyte antibody is pre-incubated with the sample suspected of containing analyte under conditions to allow analyte present in the sample to bind to the labeled antibody. This mixture is then incubated with the solid phase, and the analyte in the sample and the analyte or analyte analog bound to the solid phase compete for the labeled anti-analyte antibody. The level of analyte in the sample is determined as a function of the amount of labeled anti-analyte antibody displaced from the analyte and bound to the analyte or analyte analog on the surface of the solid phase. A high amount of analyte in the sample is indicated by a smaller amount of labeled anti-analyte antibody left bound to the analyte or analyte analog on the solid phase. Other format variations of the competitive immunoassay would be readily apparent to one skilled in the art.

A second type of clinical diagnostic immunoassay is a sandwich type immunoassay. This sandwich immunoassay may also include several different formats. For example, in one format, the sample is pre-incubated with a labeled anti-analyte antibody. Under the appropriate conditions, analyte present in the sample binds to the labeled antibody. After preincubation, the sample contacts a solid phase, to which is bound a second anti-analyte antibody, directed against an epitope that is different from or the same as that to which the first anti-analyte antibody is directed. A sandwich is formed, with the analyte between two antibodies, one bound to the solid phase and one bound to a label. In this case, the amount of label bound to the surface of the solid phase is proportional to the amount of analyte in the sample. In another format of a sandwich assay both the sample suspected of containing analyte and a labeled anti-analyte antibody are simultaneously put in contact with an anti-analyte antibody immobilized on a solid phase. In another format of the sandwich immunoassay, the sample suspected of containing analyte and the labeled anti-analyte antibody are applied sequentially to a solid phase containing an immobilized anti-analyte antibody. In both of these formats, the amount of label bound to the surface of the solid phase is proportional to the amount of analyte in the sample. Other format variations of the sandwich assay would be readily apparent to one skilled in the art.

So-called point-of-care diagnostic systems have evolved in response to health care cost containment pressures. These systems are designed for operation by non-laboratory professionals, so that the training required is minimal. Point-of-care systems enable the health care provider to make the correct diagnosis and take appropriate clinical action as quickly as possible, maximizing the effectiveness of treatment and minimizing the cost to both the patient and the health care system.

Detection of myocardial infarction (MI) is an example of the types of assays to which such point-of-care devices may be directed. Cardiovascular disease is the leading cause of morbidity and mortality in the United States. Seventy million Americans are affected by heart disease each year, at a cost of $91 billion. The majority of deaths are attributed to acute myocardial infarction. However, diagnosis of MI can be difficult, because of the varying clinical presentations of MI. As a result, many patients without MI are needlessly admitted to the cardiac care unit for evaluation to rule out MI. Even where MI is correctly diagnosed, patients are often kept in the cardiac care unit longer than is necessary, and thereby occupy hospital resources needlessly. Further, due to the difficulty of diagnosis, many other patients are incorrectly discharged after suffering an MI. It is estimated that the annual cost of inappropriate admission or discharge of MI patients is $4 billion. Therefore, quick, accurate and inexpensive monitoring systems are essential to keep the cost of care of MI patients to a mimmum.

In addition, current MI intervention protocols call for the restoration of blood flow to the heart as soon as possible to minimize the damage to heart muscle. Maximum benefit is derived from current early intervention protocols by initiation of treatment within 4-6 hours of onset of chest pain, to provide reperfusion and a positive clinical outcome. Accordingly, rapid and accurate diagnosis of MI is essential for an optimal outcome of the therapeutic protocols. The diagnosis of MI may include analysis of certain blood protein markers that have been shown to be associated with cellular necrosis initiated by a cardiac ischemic event. Marker proteins that are often used in the diagnosis of MI include the MB isoenzyme of creatine kinase (CK-MB), myoglobin, and troponin I. Simultaneous detection of these proteins in the blood assists the physician in the diagnosis of MI.

CK-MB is an 82 kDa isoenzyme of creatine kinase that is found in high concentrations (although not exclusively) in the myocardium. Typically, concentrations of CK-MB in free circulation rise within 3-6 hours of the onset of chest pain associated with MI, reach peak concentrations in 12-24 hours, and return to normal levels within 3 days. While the blood concentration of CK-MB can be elevated as a result of other events, such as strenuous exercise or muscle trauma, nonetheless CK-MB measurements, usually in conjunction with other markers, are relied upon in the diagnosis of MI.

Myoglobin is a 17 kDa heme-bearing protein which is found in all muscle cells and which functions in the transport of oxygen in and out of muscle cells. Following ischemia associated with MI, the myoglobin concentration in circulation rises relatively quickly, becoming detectable after just 2-4 hours, reaching a peak concentration after 9-12 hours and returning to normal within 36 hours. Because it is found in all muscle cells, an increase in the concentration of myoglobin in the blood may be associated with other conditions that produce muscle damage, such as muscle trauma, surgery, exercise and degenerative muscle diseases. Therefore, myoglobin is useful in the exclusion of MI in the early hours following the onset of chest pain.

Troponin is a protein complex that interacts with intracellular calcium to regulate muscle contraction. Troponin I, troponin T, and troponin C are distinct polypeptides that make up the troponin complex. The cardiac isotype of troponin I has 31 MIno-terminal residues not found in the two skeletal isotypes of troponin I, which allow the cardiac isotype to be specifically detected in the blood. The circulatory levels of cardiac troponin I begin to increase 4-8 hours after onset of chest pain, reach peak levels at 12-16 hours, and decline over the following 5-9 days. Because of the specificity of the cardiac isotype, cardiac troponin I measurement can be useful in the detection of MI where skeletal muscle injury is also present.

CK-MB, myoglobin, and troponin I measurements are often used together to diagnose MI. However, it is recognized that other antigens that relate to MI could also possibly be used, and that these three antigens are not necessarily the only ones employed in the diagnosis of MI. The Triage® Cardiac System (Biosite Diagnostics, Inc., San Diego, CA, USA) is an example of a handheld point-of-care cardiac marker test that is intended to detect an MI in about 15 minutes. The Triage® Cardiac System comprises a disposable sample panel capable of detecting three common cardiac markers and a specialized reader that measures the test output from the sample panel and displays the results. The user obtains a blood sample from the patient and applies a premeasured portion to the sample panel. The sample panel then is inserted into the specialized reader, and the reader displays the quantitative values of the three markers.

The Stratus® CS STAT Fluorometric Analyzer (Dade-Behring, Deerfield, IL, USA) is an example of a benchtop or countertop fluorometric analyzer that also measures the concentration of three common cardiac markers. The Stratus® CS STAT requires 14 minutes to measure one of the three commonly detected cardiac markers used in MI evaluation, and takes 24 minutes to measure all three. Unlike the Triage® Cardiac System described above, the Stratus® CS STAT system is a nonportable, benchtop instrument that is intended to remain in place at a particular station within the hospital or clinic. The operator obtains a blood sample from the patient and inserts a cannula from the instrument into the sample tube. The operator then loads a test pack into the instrument. The instrument automatically centrifuges the sample and carries out the test.

Each of these systems have particular drawbacks. For example, the Triage® Cardiac System requires that a blood sample be obtained, and then a portion of that sample be withdrawn by the operator from the sample tube for application to the sample panel. This step exposes the operator to the blood sample, increasing the risk of infection transmission from the sample to the operator. Furthermore, the system requires a filtration step to separate the red blood cells from the plasma. This separation step introduces an additional source of potential error into the method. The Stratus® CS STAT system does not require withdrawal of a blood sample from the sample tube for application to the instrument. However, this instrument requires that the sample be centrifuged, which adds additional complexity and introduces an additional source of error into the process. Thus, there is a great need for a point-of-care device that eliminates exposure of the operator to the sample or exposure of the sample to contMInation, and further does not require any separation or washing steps.

Immunoassays that employ antibodies, or analytes or analyte analogs, bound to a solid phase, such as those described above, typically require one or more washing steps to separate the unbound labeled molecules from the bound labeled molecules, in order to eliminate interference from unbound label and attain the desired level of specificity. This wash step is more critical when testing for analytes present in sub-nanomolar concentrations, since background label could make detection of bound analyte difficult. However, such washing steps increase the complexity of the system, and usually require care on the part of the operator to produce consistent and accurate results. Furthermore, it is often the case that other components in the sample interfere with such immunoassays, and variations in the amounts and character of these components can lead to error in the measurement of the analyte. Typically, such interfering components, where present, are removed by a separation step, which adds additional undesirable complexity to the assay procedure and provides an additional source of error. Therefore, it would be desirable to have a clinical diagnostic system that does not require any washing or separation steps.

One approach that reduces or eliminates the need for washing or separation steps in a solid-phase immunoassay is to take advantage of the phenomenon of evanescent field generation associated with total internal reflection (TIR). Total internal reflection occurs when light is passed through an optical waveguide having a higher index of refraction than the surrounding medium, e.g., a silica waveguide in an aqueous medium. In this situation, a beam of light travelling down such a waveguide and striking the interface between the waveguide and the medium will either be refracted into the medium or reflected totally back into the waveguide, depending on the angle of incidence. In the latter case, the incident and reflected beams will interfere, producing a standing wave in the waveguide perpendicular to the direction of travel of the incident beam. The standing wave has a finite electromagnetic field amplitude that is maximal at the interface between the waveguide and the medium, but which decays exponentially as it moves away from the interface and into the surrounding medium. This decaying electromagnetic field in the surrounding medium is referred to as the evanescent field. Where the surrounding field is an aqueous medium and the waveguide is either glass or a similar silica-based material or an optical plastic such as polystyrene, the evanescent field generally extends out from the waveguide into the aqueous medium to a distance of between about 100-200 nm. This distance is slightly greater than a thickness of a protein layer on the waveguide.

The evanescent field can be employed to selectively excite fluorescent label molecules bound to the exterior surface of the waveguide, i.e., the surface of the waveguide that is in contact with the surrounding medium. In particular, the fluorescent label molecules may be bound to the exterior surface of the waveguide via antibodies or other analyte-binding molecules, or via analytes or analyte analogs. The evanescent field extends far enough out into the aqueous medium to excite the fluorescent molecules bound to the surface of the waveguide, without exciting the unbound fluorescent label molecules in the bulk medium. Thus, any light emitted as a consequence of the excitation of the fluorescent label molecules is due only to those fluorescent label molecules bound at the waveguide surface.

Evanescent immunoassays have been demonstrated in at least three different optical geometries. The first employs single-reflection TIR using evanescence for excitation and a collimating lens to collect transmitted fluorescence. The second uses optical fibers for both evanescent excitation and emission. The third employs planar waveguides with evanescent excitation, and collection by either transmittance or evanescence.

U.S. Patent No. 4,582,809 (Block et al.) discloses a method and apparatus for a fluorescent immunoassay that employs an evanescent field created in an optical fiber that is immersed in a sample solution. U.S. Patent 5,492,674 (Meserol) also describes an evanescent field fluorescent immunoassay device that employs an optical fiber. U.S. Patents 5,512,492; 5,677,196; 5,846,842; and 5,919,712 (Herron et al.) disclose apparatuses and methods for an evanescent-light immunofluorescence assay capable of detecting analytes in solution. The use of a planar waveguide in such assays is described. Because a planar waveguide has a width, the light source for the waveguide cannot be a normal spot beam, but has to be altered so that a line of light is incident on the end of the waveguide. Evanescent immunoassays that employ planar waveguides require a very- even light source to avoid errors associated with uneven illumination. That is, planar waveguides must be illuminated evenly throughout the waveguide, or any differences in illumination may be mistaken for differences in the amount of analyte bound to the waveguide. Furthermore, the light source must be introduced into the waveguide at a critical angle to maximize the total internal reflectance that occurs within the waveguide and which leads to the generation of the evanescent field. In the normal situation, only a portion of the fluorescent molecules bound at the surface of the waveguide are excited by the illuminating light. Thus, there remains a preponderance of bound fluorescent molecules that can be illuminated if the light intensity varies across the waveguide. As a result, an even light source is essential for accurate quantitation of analytes in an evanescent field fluoroimmunoassay.

By using a light detector that is capable of measuring light emitted from the waveguide surface in a direction that is perpendicular to the surface of the planar waveguide, multiple samples in a high-density, spatially resolved format may be assayed simultaneously in an evanescent field fluoroimmunoassay. The advantage of such a format lies in the ability to process a large number of samples in a high-throughput manner. In such a format, the system takes a statistical sampling of data to calibrate the assay and the instrument. The precision of such a system is dependent on the uniformity of the illumination density. The multiple readings taken from various points on the waveguide require that the illumination density across the waveguide be uniform, or errors in calibration and measurement will be inevitable.

Previous attempts to use evanescent immunoassays that incorporate disposable cartridges have suffered from the difficulty in precisely aligning the waveguide, which is incorporated in the disposable cartridge, with the light input, which is derived from a light source mounted in the instrument. The light input to the waveguide must be precisely and reproducibly aligned, because deviations in the amount of light entering the waveguide can produce large errors in the calculated amounts of analyte. For example, the Herron et al. patents disclosed above taught the use of a focusing lens that could move in two dimensions to align the light entering the waveguide, and the use of an integral semi- cylindrical lens for capturing the incident light. Obviously, a drawback to this system is that any error in focusing by the operator could lead to an incorrect result. The apparatuses disclosed by Block et al. and Meserol each employed an optical fiber, which cannot be used for running multiple assays on the same surface. Thus, to date, no instrument, method or system that employs an evanescent field-dependent immunoassay has been able to reliably incorporate disposable cartridges containing planar waveguides. The present invention fulfills this need.

Summary Of The Invention

An apparatus and method for evanescent light fluoroassays incorporate a waveguide in a disposable cartridge for the detection and quantification of analytes. The waveguide, which is preferably a planar waveguide, contains on one surface an analyte- binding molecule for binding an analyte of interest from a fluid sample, such as a blood sample. ' The analyte is linked directly (for a competitive immunoassay) or indirectly, through an analyte-binding molecule (for a sandwich immunoassay) to a fluorescent molecule. Alternatively, an analyte or analyte analog is bound to a surface of the waveguide. In this case, an analyte present in a fluid sample would compete with the analyte or analyte analog on the waveguide surface for a labeled analyte-binding molecule. The disposable cartridge may contain a fluid sample in a fluid sample tube, and is held on a platform that comprises a light source, such as a laser, a halogen bulb, and the like, and a light detecting device, such as a CCD camera, a photodetector, a photodiode array, and the like. The light detecting device is capable of measuring emitted light that is perpendicular to the planar waveguide, which permits multiple spatially resolved assays to be read simultaneously. The system holds the disposable cartridge in place in the instrument so that the waveguide is properly aligned with the light source and the light-detecting device. The disposable cartridge may be held in place by any appropriate means, i.e., a tray in the instrument. Air pressure, vacuum, or capillary action may be used to move the fluid sample onto an assay area of the disposable cartridge, where, for example, the analyte reacts with the analyte-binding molecule on the waveguide surface. Upon passage of light through the waveguide, an evanescent field is created, which selectively excites fluorescent molecules bound to the surface of the waveguide. Light emitted by the fluorescent molecule is detected by the light-detecting device, and the amount of analyte in the fluid sample is determined. The amount of analyte in the solution is determined by taking multiple measurements of the emitted light over a period of time, which produces measurement data more quickly than the conventional endpoint measurement. Upon completion of the measurement, the entire cartridge can be discarded. The apparatus and method are suitable for use in either competitive or sandwich-type immunoassays. In one embodiment of the present invention, an instrument for detecting and/or quantifying an analyte in a biological fluid comprises a disposable cartridge, the disposable cartridge including a waveguide, the waveguide having an analyte-binding molecule on at least one surface thereof, the analyte-binding molecule being effective to bind to an analyte indirectly or directly bound to a fluorescent molecule, a light source, the light source being capable of directing light through the waveguide, the light having a wavelength effective to excite the fluorescent molecule, an optic system, the optics system comprising a light detection means and being capable of detecting light emitted in a perpendicular direction from the waveguide surface, and a means, such as a cartridge tray, for holding the disposable cartridge within the instrument, the cartridge tray, for example, comprising a kinematic mount for aligning the waveguide in the disposable cartridge with the light, whereby when the light is directed through the waveguide, an evanescent field is created by total internal reflection, the evanescent field being capable of exciting the fluorescent molecule when the fluorescent molecule is bound to the analyte-binding molecule and thereby producing an emission from the excited fluorescent molecule that is capable of being detected by the light detection means.

In an alternative embodiment, the instrument comprises a waveguide having an analyte or analyte analog bound on at least one surface of the waveguide in place of the analyte-binding molecule. In this case, analyte in the fluid sample competes with the analyte or analyte analog bound on the waveguide for an analyte-binding molecule bound to a fluorescent molecule.

In another embodiment of the present invention, a disposable cartridge for use in an instrument for detecting and/or quantifying one or more analytes in a fluid sample comprises a waveguide, the waveguide having an analyte-binding molecule on at least one surface thereof, the analyte-binding molecule being effective to bind to an analyte indirectly or directly bound to a fluorescent molecule, and may include a receptacle for a sample tube and a means for piercing the sample tube, the means for piercing including an inlet to a flow path connecting the inlet to the at least one surface of the waveguide bearing an analyte-binding molecule.

In an alternative embodiment, the disposable cartridge comprises a waveguide having an analyte or analyte analog bound on at least one surface of the waveguide in place of the analyte-binding molecule. In this case, analyte in the fluid sample competes with the analyte or analyte analog bound on the waveguide for an analyte-binding molecule bound to a fluorescent molecule.

In another embodiment of the present invention, a method for detecting and/or quantitating an analyte in a fluid sample comprises the steps of collecting a fluid sample into a closed sample tube, placing the closed sample tube containing the fluid sample in a receptacle in a disposable cartridge, the receptacle having a means for piercing the closed sample tube, the means for piercing being effective to permit all or a portion of the fluid sample to contact a surface of an assay region of a waveguide in the disposable cartridge, the waveguide having an analyte-binding molecule on at least one surface thereof, piercing the closed sample tube, contacting the surface of the waveguide bearing the analyte- binding molecule with all or a portion of the fluid sample under conditions whereby the analyte present in the fluid sample binds to the analyte-binding molecule, and the binding of the analyte to the analyte-binding molecule produces a change in an amount of a fluorescent molecule bound directly or indirectly to the analyte, directing a line of light through the waveguide, the waveguide being made of a material having a refractive index greater than that of the fluid sample in contact with the waveguide, whereby an evanescent field is created, the evanescent field extending out from the surface of the waveguide into the fluid sample, and exciting the fluorescent molecules bound directly or indirectly to the analyte-binding molecule to produce a light emission, and detecting and/or quantitating binding of the analyte to the analyte-binding molecule through detection and/or quantitation of the light emission.

In an alternative embodiment, the method comprises a waveguide having an analyte or analyte analog bound on at least one surface of the waveguide in place of the analyte-binding molecule. In this case, the method involves contacting the surface of the waveguide bearing the analyte or analyte analog with all or a portion of the fluid sample under conditions whereby the analyte present in the fluid sample competes with the analyte or analyte analog on the waveguide surface for analyte-binding molecule labeled with a fluorescent molecule.

The above and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings.

Brief Description Of The Drawings

Figure 1 is a schematic representation of the clinical diagnostic platform according to the preferred embodiment of the present invention. Figure 2 is an exploded schematic representation of the disposable cartridge according to the preferred embodiment of the present invention. Figure 3 is a second exploded schematic representation of the disposable cartridge according to the preferred embodiment of the present invention, showing the path of flow of air and sample in the disposable cartridge.

Figure 4 is a schematic representation of the cartridge tray that holds the disposable cartridge in place, according to the preferred embodiment of the present invention.

Figure 5 is a graph of the results obtained for the measurement of the intensity of light emission as a function of Tnl concentration for the same blood sample measured in three separate channels of the disposable cartridge, illustrating the reproducibility of the preferred method of the present invention. Figure 6 is a graph of the results obtained for the measurement of the intensity of light emission as a function of Tnl concentration for a blood sample and a plasma sample as performed by the preferred method of the present invention.

Figure 7 is a chart that shows the mean CV% of the preferred method of the present invention when used to measure amounts of added Tnl in whole blood. Figure 8 is a schematic representation of the indirect analyte labelling method for use in the preferred method of the present invention. Phycotags = Cy5 or other fluorescent molecule having at least equivalent photoefficiency; Indirect Label = a phycobiliprotein, such as APC, or a phycobilisome, such as PBXL-1, PBXL-2, PBXL-3, or PBXL-4, or combinations thereof; RAb = second anti-analyte antibody; CAb = first anti-analyte antibody.

Figure 9 is a schematic representation of a waveguide array according to a preferred embodiment of the present invention, showing three assay channels, each containing a 4x17 array of sensing regions.

Detailed Description Of The Preferred Embodiments The present invention is an instrument and assay method that takes advantage of the phenomenon of evanescent fluorescence to detect analytes in a fluid sample. The instrument comprises an biosensor platform and disposable cartridges, and further may include sample tubes incorporating assay reagents that may be lyophilized. The biosensor platform includes a light source for exciting a fluorescent label, light detection means for detecting light emitted from the label, and a means, e.g., a cartridge tray that includes a kinematic mount, for holding the disposable cartridge in precise alignment, so that the light input from the biosensor platform is precisely aligned with a planar waveguide in the disposable cartridge. The light source is preferably a laser light source, and the light detection means is preferably a CCD camera. The light detection means is oriented so that it is capable of detecting light emitted from the waveguide surface in a direction that is perpendicular to the planar waveguide. As a result, spatially resolved assay areas can be simultaneously measured. The light detection means may itself be perpendicular to the planar waveguide; alternatively, the light emitted from the waveguide surface in a perpendicular direction may be redirected, using mirrors or other optical elements, to the light detection means. The biosensor platform may also include an onboard computer to convert the output from the light detection means into analyte concentrations, a pump or other means to move sample out of the sample collection tube and into the assay area, and a touch screen interface with the operator. In addition, various peripheral devices, such as a printer and a bar code scanner, may also be included. The instrument may be used in various analyte detection formats, including, for example, sandwich immunoassays, competitive immunoassays, direct DNA probe hybridization assays, sandwich DNA probe hybridization assays, enzymatic assays, bDNA quantification, and fluorescent dye energy transfer reactions.

The disposable cartridge contains a waveguide to which an analyte-binding molecule, an analyte, or an analyte analog is bound in an assay area. For clinical applications, planar waveguides are preferred over other geometries for several reasons. First, the exciting light is concentrated into a very small volume, producing a high level of evanescent excitation. Second, the planar configuration enables the construction of a multichannel device for simultaneous running multiple assays. Lastly, the planar configuration is amenable to microfabrication techniques, which can reduce the cost of such assays. It is this planar waveguide that forms the basis of the EPW™ technology employed in the present invention. The planar waveguide can be arranged so that multiple assays can be performed simultaneously on the assay area of the waveguide.

The disposable cartridge may further include a groove for holding a sample tube in place on the disposable cartridge, and a flow path for movement of the sample from the sample tube into the assay area on the waveguide. The waveguide may be made of any material through which light may be transmitted and which has a refractive index greater than that of the sample medium, which in most cases will be water or some other aqueous medium, so as to create an evanescent field that can excite fluorescent molecules bound directly or indirectly to the waveguide surface at the waveguide/medium interface. Such waveguides have in the past been made of silica substrates, such as quartz. However, such quartz waveguides may not be suitable for use in disposable clinical assay cartridges, because of the high cost of materials and labor involved in making such waveguides. More recently, it has been discovered that polystyrene has the required properties for use as a waveguide. Polystyrene is inexpensive and is amenable to common high-throughput methods, such as injection molding. The low production costs associated with the use of polystyrene make it an ideal material for use as a waveguide in evanescent field clinical assays. Thin film waveguides (~1 μm thick) may also be advantageously employed in the apparatus and methods of the present invention. Such thin-film waveguides comprise a relatively thick substrate having one or more thin film waveguide channels deposited thereon. The substrate and waveguide are both comprised of optically transmissive material, with the thin film waveguide having a refractive index greater than that of the substrate. See U.S. Patents 5,832,165 and 5,814,565 to Reichert et al. Thin film waveguides have an advantage of higher evanescent intensity and greater reflection density (i.e., on the order of 500-1,000 reflections/cm) than that obtainable using thick- film waveguides. Plowman and Reichert assessed the usefulness of a siliconoxynitride thin-film integrated optic waveguide for use in a fluoroimmunoassay. T.E. Plowman and W.M. Reichert, 1996 Biosensors and Bioelectronics, 11(1/2):149-160. They reported that using a thin-film waveguide, they were able to detect femtomolar (10"15) concentrations of analyte. These advantages of thin film waveguides may render them suitable for use in such evanescent planar waveguide-based assay devices. The incident light is preferably excitation light at a wavelength between 290-1,800 nm in wavelength, preferably 460-700 n . The incident light has a power between 0.1- 500 mW, more preferably between 5-60 mW. In one preferred embodiment, the light source is a red light laser diode (635-660 nm) at a power of 10-30 mW. High efficiency coupling by the light source means that less power is required to maintain a given power level. The light beam is formed into a line of light by any of a number of methods, but most preferably by use of a resonator. Other methods that can be used include, for example, the use of a line-generating lens in conjunction with a focusing lens or the use of a diffractive optic. Preferably, the energy across the width of the light line is kept constant by varying the power input to the light source. An evanescent light field is created upon passage of the light through the waveguide in TIR mode, which excites the fluorescent molecules bound to the surface of the waveguide. However, because the evanescent field decays rapidly as it deviates from the waveguide surface, unbound fluorescent molecules are not excited by the evanescent field. The emissions from the excited fluorescent molecules are detected by the light detector on the diagnostic biosensor platform and measured.

The light detector is oriented so as to enable the collection of light emitted in a direction perpendicular to the surface of the planar waveguide. This enables the measurement of a large number of spatially resolved assay areas. If the light detector was instead oriented parallel to the planar waveguide surface, a discrete beam would have to be used for each assay area. The light detector itself may be positioned directly above the waveguide surface. More preferably, the light detector need not be positioned directly above the waveguide surface and optical elements, such as one or more mirrors, may be used to direct the emitted light to the light detector.

In one embodiment, the waveguide is a polystyrene unit. The polystyrene waveguide is preferably formed as a unitary piece by injection molding, but may be formed in multiple pieces or by any other appropriate method. The polystyrene waveguide is preferably on the order of about 500-1,000 μm in thickness, and can be of any desired length and width. Preferably, the waveguide is of a size that permits the creation of multiple channels for reaction with sample. This permits the establishment of various controls and calibration mixtures in combination with the measurement of multiple analytes in the sample. In one embodiment, the waveguide has dimensions of 2.5 cm by 25.0 cm, and accommodates three channels, each containing four separate sensing regions, for a total of 12 separate sensing regions in the assay area. In another embodiment, the waveguide has three channels, each containing an array of separate sensing regions in the form of dots containing assay components. Each of the channels may comprise an array of separate sensing regions, and each channel may contain an analyte-binding molecule for a different analyte. Thus, in this embodiment, a single sample could have up to three different analytes measured. Many different geometries can be contemplated to accommodate any desired number and size of sensing regions deemed desirable.

In a particular embodiment, the array is a 4x17 array (Fig. 9). That is, in this embodiment, each of three channels 51, 52, 53 may contain four rows, each row containing seventeen sensing regions, for a total of 204 sensing regions. One of the four rows in each channel is used for electronic quality control of the instrument, as described below. A second one of the four rows is used for onboard chemistry calibration. This row contains defined concentrations of analyte, either all at the same concentration or at different concentrations. If different concentrations are used, then the change in signal intensity associated with each different concentration is measured over time, and the slopes of these curve can be plotted against the concentration to provide a curve that measurement of the analyte concentration in the sample. The remaining two rows are used for sample analyte measurement. The instrument electronic quality control is checked by measurement of light reflected back from pits or depressions in the dots of one of the rows. The surface of the plastic is deformed (i.e., etched, roughened or gouged) so that the light passing through the waveguide is reflected out of the waveguide at these points, producing a series of bright dots along the surface of the waveguide. The intensity of the light reflected out of these dots is measured by the light detector and compared to an expected reflected light level stored in the memory of the instrument. If the intensity measured from the dots is equal to the expected reflected light level, the ratio will be unity. If the intensity is less than that expected, the ratio will be less than unity. If the ratio of the measured light level reflected from the waveguide to the expected light level is less than a predetermined value, the cartridge will be rejected and an instrument error message displayed to the operator. This quality control check effectively monitors the light source, the optical elements and their alignment, and the light detector with a single measurement, because any defect in any one of these will affect either the amount of light passing through the waveguide or the amount of light measured by the light detector.

If the ratio of the measured light level reflected from the waveguide to the expected light level is not below a predetermined value, but still differs from unity by a measurable level, then the difference will be added to each measurement made by the instrument from that waveguide. In this way, small errors in a measurement caused by variables in the instrument can be corrected in each measurement obtained by the instrument. However, if the difference is greater than the predetermined value, that is, if the ratio of measured to expected reflected light is less than the predetermined minimal ratio, the test will be halted and an instrument error message displayed.

A second row of dots is employed for checking the quality of the assay components on the surface of the waveguide. These dots contain one or more predetermined concentrations of analyte bound to the surface of the waveguide. Different concentrations of analyte may be loaded onto the waveguide to permit creation of a standard curve for the onboard chemistry calibration. For example, in the case of the 4x17 array described above, dots 1-9 of the onboard chemistry calibration row may contain relatively low levels of the analyte, and dots 10-17 may contain relatively higher levels of the analyte. Any desired combination of analyte levels may be used to generate the data for the onboard chemistry calibration. When the sample passes over the waveguide, unbound labeled antibody binds to the analyte in these dots, and produces a signal that is measured by the light detector. The measurements thus obtained are used to draw a standard curve, and the standard curve obtained from the measured data is compared to an expected standard curve held in the memory of the computer. In this case, because the analytes and antibodies differ from assay to assay, the expected standard curve is input to the memory of the onboard computer by scanning a bar code label on the cartridge containing information about the standard curve. If the assay components are in perfect condition, the slopes of the measured and standard curves will be identical, and a ratio of the slopes will be unity. However, if the slope of the measured curve deviates from unity by more than a predetermined amount, the cartridge will be rejected. As in the case of the instrument electronic quality control described above, if the slope of the measured curve deviates from unity, but by an amount less than the predetermined amount, then the measurements will be adjusted accordingly to account for the difference. In this manner, the change in the quality of the assay components will be compensated for by the addition or subtraction of an appropriate value to each measurement.

The series of dots containing the assay components can be laid onto the waveguide by any of a number of methods known to those of skill in the art. For example, each dot can be laid down onto the surface using a syringe pump or an inkjet printer. Alternatively, a "quill" method may be used, whereby a sharp pointed device is dipped into a assay component solution and then the solution transferred to the waveguide surface. It is also possible to use a template and spray the assay components onto the surface. The planar waveguide in the disposable cartridge provides a solid surface for immobilization of analyte-binding molecules and acts as the transmission medium for light, which serves to excite fluorescent molecules bound directly or indirectly by the analyte-binding molecules. Alternatively, analyte or analyte analog molecules may be bound to the waveguide surface. The analyte-binding molecules bound to the surface of the waveguide are preferably antibodies, but may be any molecule that binds specifically and with sufficient affinity to the analyte of interest. More specifically, the analyte- binding molecules may be polyclonal antibodies, monoclonal antibodies, derivatives of monoclonal antibodies, receptor bodies, nucleic acids, and the like. Derivatives of monoclonal antibodies could be any that are known to those of skill in the art, but include, without limitation, an F(ab), an F(ab')2, an scFv fragment, and an Fv. The analyte-binding molecules may be bound to the surface of the waveguide through simple physical adsorption or through specific chemical attachment. Where the analyte-binding molecule is an antibody, and is bound to the surface via simple adsorption, the binding of the antibody may be improved by a simple acid pretreatment step. For a description of the acid pretreatment method, see I.-N. Chang, et al., "Adsorption mechanism of acid pre- treated antibodies on dichlorodimethylsilane-treated silica surfaces," J. Coloid Interface Sci, July, 1995 and I.-N. Chang and J.N. Herron, "Orientation of acid pretreated antibodies on hydrophobic dichlorodimethylsilane-treated silica surfaces," Langmuir, July 1995, the entireties of which are hereby incorporated by reference. Specific chemical attachment can be accomplished by a variety of ways known to those of skill in the art. For example, an antibody may be bound to the surface through an streptavidin/biotin method. In this method, the streptavidin is bound to the waveguide surface by first mixing the streptavidin with a photoreactive agent, and then applying the mixture to the waveguide. After drying, the mixture is activated by exposure to ultraviolet light. The streptavidin is thereby irreversibly bound to the surface of the waveguide. Thereafter, the analyte-binding molecule, having been previously biotinylated, is incubated with the streptavidin-coated waveguide for a sufficient period of time to permit binding of the biotin group to the streptavidin. Specific chemical attachment can be accomplished through the use of "caged" compounds, which are a class of compounds that can bind to the analyte-binding molecule and mediate binding of the analyte-binding molecule to the waveguide surface and, in some cases, also cross-linking of the analyte-binding molecules bound to the waveguide. Examples of such molecules are the psoralens and derivatives of the psoralens, such as N-hydroxysuccinMIde esters of psoralens. Such compounds are preferably those that are activated by light at wavelengths above 320 nm, and more preferably light in a range between 350-360 nm. At these wavelengths, proteinaceous analyte-binding molecules do not absorb light, and thus are not affected. In another method, the analyte-binding molecule may be bound to the surface using methods based on the use of a fMIly of tri-block polymers of the form PEO-PPO- PEO, where PEO = poly(ethylene oxide) and PPO = poly(propylene oxide). These polymers are sold under the name Pluronics™ (BASF, Mount Olive, NJ). The PPO polymer blocks are significantly more hydrophobic than the PEO polymer blocks, and adsorb more readily to non-polar surfaces such as polystyrene. This leaves the PEO blocks available for binding to the analyte-binding molecules, either by photochemical crosslinking agents or by chemical crosslinking agents well known to those of skill in the art. Other methods for specific attachment of the analyte-binding molecule to the surface of the waveguide would be known to those of skill in the art. The fluorescent molecule used in the assays may be any that can be excited by light emitted by the light source to emit light through fluorescence. Examples of such molecules include fluorescein dyes, rhodMIne dyes, cyanine dyes, and the like. Preferably, the fluorescent molecule is cyanine 5 (Cy5, Amersham Life Science Inc., Arlington Heights, IL). The fluorescent molecule may be either directly attached to the analyte or to an analyte analog (in the case of competitive immunoassays) or to the second anti-analyte antibody (in the case of sandwich-type immunoassays). Alternately, and more preferably, an indirect label method may be used, where a fluorescent molecule-binding molecule is bound to the analyte or second anti-analyte antibody, and fluorescent molecules are bound to the fluorescent molecule-binding molecule, as shown in Fig. 8. This method has the advantage of amplifying the signal obtained from each bound analyte molecule. Examples of such fluorescent molecule-binding molecules include APC (Prozyme, Inc., San Leandro, CA) and PBXL-3 (Martek Biosciences Corp., Columbia, MD).

Multiple measurements are taken from each assay over time, instead of the conventional endpoint measurement procedure. The slope of the curve of emission signal versus time is plotted and the resulting slope converted to an analyte concentration. This procedure gives an measurement of the analyte concentration more quickly than is possible using the conventional endpoint measurement. The output from the CCD camera may be converted to an analyte concentration result in the following manner. For each assay, the instrument records a number of images over time to form a "movie" of successive images. The first image recorded is subtracted from each subsequent image, leaving a movie representing change from time t=0. A three-dimensional (3x3x3 pixel neighborhood) median filter is run on the stack, followed by a one-dimensional Fourier transform on each row of pixels down the length of each wavelength channel. The peak values from all pixel rows in a given channel are summed, and the peak sums are curve fitted vs. time using the formula ink . -to . I = R ' e - (1 " g > + / k o where I is the intensity from the processed images, R is the rate variable (unknown), m is a constant for the time point at which the rate is measured, k is a constant that determines the degree of curvature, and t is the time variable. The above equation is solved for R, producing the raw assay result which is compared to a standard curve to convert to an analyte concentration result.

The cartridges are designed to be read in an instrument that contains the light source system and the optics system, as well as other systems desirable for the performance of the assays and the collection and reporting of the results. The instrument may include a touch screen in place of the conventional keyboard and mouse for input from the operator. The touch screens also make navigation simple and limit the possibility for operator error. A bar code reader may also be incorporated to input reagent calibration data, patient chart data and operator ID information. The bar code reader may be a pen- type scanner or a handheld gun scanner. A printer, either remote or built-in, may be included to provide hard copy output of results as they are generated. The instrument may also interface with one or more of a hospital information system, a laboratory information system, or a PC, preferably through data ports. Such connection facilitates the collection and storage of patient information, as well as correct billing of clinical tests to the patient or the patient's health insurer.

Example 1 - Preferred Instrument Embodiment Figures 1-3 show a particular embodiment of the instrument described herein. A clinical diagnostic platform 10 is shown in Figure 1. Light is emitted from a conventional laser source 11, and first strikes an oscillating resonator 12. Laser 11 is preferably a laser diode emitting at 28 ± 2 mW at 660 nm. The laser diode is cooled by a TE cooler to a fixed temperature ± 5° C in a range between 15 and 25° C. Oscillating resonator 12 moves back and forth at a frequency of about 100 Hz to create a line of laser light from the output of laser 11. The line of laser light is passed through a plano-convex lens 13 to generate a flat, parallel and uniform beam of fixed width which is then reflected off a mirror 14 and enters waveguide 25 in a disposable cartridge 20. Disposable cartridge 20 is held in a cartridge tray 15 through a kinematic mount. Preferably, the angle of incidence to the waveguide is 20° ± 5 °. This promotes the coupling of higher order modes, resulting in increased electric field intensity at the waveguide surface. The light emitted by the bound fluorescent molecules is reflected off a second mirror 16 and enters a CCD camera 17.

In a preferred embodiment, CCD camera 17 is a standard astronomical CCD camera (Santa Barbara Instrument Group, Santa Barbara, CA), having a nominal CCD resolution of 382x255 pixels. The lens of CCD camera 17 has a focal length of 25 mm, with a f/16 fixed aperture and adjustable focus. A closeup adapter is used to obtain an acceptable level of near field focus. A band pass filter is used to block the laser light while permitting passage of light emitted by the fluorescent molecule. This greatly improves the signal/noise ratio, and becomes particularly important at low levels of emission.

The movement of oscillating resonator 12 is not even, which causes the energy output of the line of laser light to be uneven across the laser light line. More particularly, the speed of oscillating resonator is at its maximum in the center of the line, and at its minimum (=0) at each end. As a result, the energy output is greater at each end that it is in the middle, where the energy output is at a minimum due to the speed of oscillating resonator 12 at this point. To create a line of laser light having an equivalent energy throughout its width, the driving wave of oscillating resonator 12 is fed back into the power input to laser 11. As the speed of oscillating resonator 12 increases, i.e., as the line of light is drawn from one end toward the center, the power input to laser 11 is increased. Similarly, as the speed of oscillating resonator 12 decreases, i.e., as the line of light is drawn from the center toward the end, the power input is reduced. In this way, the output of laser 11 compensates for the variations in speed and therefore light energy that are due to the action of oscillating resonator 12. Preferably, the power distribution along the width of the line of laser light varies by < 15%, and more preferably by < 1%. The instrument is under the control of a single onboard computer (not shown) with a Celeron 433 MHz (or equivalent, or better) processor. The computer preferably has a PC/104 bus port that accepts the A/D / D/A digital I/O board. A hard disk (10.2 GB minimum) and a speaker may be attached to the computer, and any number of external connectors for connecting peripheral devices, as desired. Examples include COM3, Ethernet, and USB connectors, and mouse, monitor, printer and keyboard connectors. An interface board provides power distribution and computer monitoring of all voltages. This board is powered by the input from the power supply, and supplies power for the computer and the two onboard pumps.

Referring now to Figs. 2-3, in a preferred embodiment disposable cartridge 20 comprises a bottom piece 21, a base piece 22, and a cover 23. Bottom piece 21, base piece 22, and cover 23 are all preferably made from an inexpensive, strong plastic material, such as, for example, acrylonitrile butadienestyrene (ABS). As shown in Fig. 2, base piece 22 fits atop bottom piece 21, and cover 23 fits over and encompasses both base piece 22 and bottom piece 21. Preferably, cover piece 23 is held in place using snap tabs on one piece and corresponding slots on the other. Disposable cartridge 20 has three projections 41 on the bottom of bottom piece 21.

These projections match notches 42 in the bottom of cartridge tray 15 (Figure 4), which is held in a drawer that pulls out from the interior of clinical diagnostic platform 10. Each disposable cartridge 20 fits into cartridge tray 15 with projections 41 on the bottom of bottom piece 21 falling into one of notches 42 to form a kinematic mount. This ensures that disposable cartridge 20 is reproducibly placed in the cartridge tray. In addition, a vacuum is formed in the cartridge tray through diaphragm 18 to pull disposable cartridge 10 into the cartridge tray and hold it in place. Once disposable cartridge 20 is in place in cartridge tray 15, cartridge tray 15 withdraws into the interior of clinical diagnostic platform 10 until projections 43 on each corner and at the top of the back side of cartridge tray 15 fit into depressions 44 in the back side of the drawer. Depressions 44 are oriented at angles, as shown in Figure 4. In this manner, disposable cartridge 20 is always maintained in the proper orientation both within cartridge tray 15 and clinical diagnostic platform 10, so that waveguide 35 and the laser light input are in perfect alignment.

Base piece 22 includes an inlet 24 for holding in place a needle assembly 25. Needle assembly 25 includes a hub 26 and at least two needles (18 and 19) that are capable of piercing a stopper of a blood collection tube 27. Hub 26 is made of any appropriate strong, inexpensive material, such as polycarbonate. Each needle (preferably stainless steel) is tightly connected to an inlet channel (28 and 29 in Fig. 3) in base piece 22 through a hub receptacle 30. One needle (18 in Fig. 2) acts to introduce air into blood collection tube 27 to force sample out of blood collection tube 27 into inlet channel 28 via the second needle (19 in Fig. 2).

Inlet channels 28 and 29 communicate directly with bottom piece channels 31 and 32, respectively. Air enters bottom piece channel 31 through a flexible air inlet 39 (Figure 4) in the bottom of bottom piece 21 and thereafter passes through needle 18 into blood collection tube 27 via inlet channel 28. Sample fluid passes out of blood collection tube 27 into inlet channel 29, then into bottom piece channel 32 and eventually reaches outlet 33. Base piece 22 further includes a sample well 34, which may be optionally divided into a plurality of channels. At one end of sample well 34, sample fluid exits from outlet

33 and enters sample well 34. At the other end of sample well 34 are a plurality of outlet channels leading to a disposal chamber 37 in bottom piece 21. A porous polyethylene ("Porex") plug 38 in each of the plurality of outlet channels permits passage of air, but resists passage of sample fluid into disposal chamber 35. Base piece 22 sits snugly atop disposal chamber 35 and keeps fluid in disposal chamber 37 from leaking out of disposable cartridge 20.

A waveguide 35 sits atop sample well 34. Sample fluid is kept from escaping sample well 34 by a channel gasket 36 that surrounds sample well 34. Channel gasket 36 is preferably made of silicone, but can be any appropriate type of inert plastic or rubber material that is effective to prevent leakage of the fluid sample out of sample well 34. As discussed above, waveguide 35 may be made of any appropriate material having an index of reflection greater than that of the sample fluid, but is most preferably made of polystyrene.

Cover 23 preferably includes a plurality of slots 39 that match the number of channels in sample well 34. Slots 39 may be either open or covered by a transparent or translucent sheet that permits passage of the light emitted upon excitation of a fluorescent molecule. To use the cartridge, blood is first drawn from the patient into blood collection tube

27. Blood collection tube 27 contains all necessary assay reagents, such as, for example, antibody, fluorescent label, buffers, ions, and so on, preferably in a lyophilized state. The contents of blood collection tube 27 are then mixed, and the tube then is inserted into disposable cartridge 20 by pushing the tube onto needles 18 and 19 of needle assembly 25. Disposable cartridge 10 is then placed onto cartridge tray 15. Air is pumped into blood collection tube 27 to push the mixed blood sample onto sample well 34 for analysis. Analytes present in the mixed blood sample are bound to the surface of waveguide 35 via the analyte-binding molecule.

Preferably, air is pumped into blood collection tube 27 using a small electric piston or diaphragm pump (not shown). The pump further preferably includes or is linked to a pressure sensor. The pump acts to expel fluid sample out of blood collection tube 27, through inlet channel 29 and bottom piece channel 32, out outlet 33 and into sample well

34 until the fluid sample reaches the outlet channels containing the porous ethylene plugs. As long as only air is passing through the porous ethylene plugs, the pressure in the flow path does not rise substantially. However, when the mixed blood sample reaches the porous material, its further passage is blocked, and the pressure in the flow path begins to rise until the pressure sensor is activated and turns off the pump. In this fashion, correct and reproducible filling of sample well 34 is assured.

After the assay is completed, the cartridge with the attached tube is safely disposed. The sample and all solutions remain in the cartridge - once the sample tube is attached to the cartridge, there is no possibility of operator injury or exposure to the fluid sample, nor is there any chance of contMInation of the sample. Using the cartridge and the system of the present invention, the risk of performing the assay is limited to the exposure when the blood is drawn from the patient. The use of positive pressure to move the sample from the evacuated tube to the assay area requires no user interaction and ensures a smooth, bubble-free sample in the assay area.

Example 2 - Measurement of CK-MB, myoglobin and troponin I

The LifeLite™ Cardiac Panel is a three-test disposable cartridge for the simultaneous measurement of CK-MB, myoglobin and troponin I in the instrument of the preferred embodiment, in order to detect an MI. As described above, blood is drawn from a patient suspected of suffering an MI into a sample tube specific for the Cardiac Panel test. The sample tube contains, preferably in lyophilized form, the assay reagents necessary to detect and measure the analytes CK-MB, myoglobin and troponin I. Included in these assay reagents are fluorescent label-anti-analyte antibody conjugates. The fluorescent label is preferably Cy5, and the anti-analyte antibodies are antibodies directed against the analytes CK-MB, myoglobin and troponin I. After mixing, the sample tube is affixed onto the LifeLite™ Cardiac Panel disposable cartridge. Information about the patient and the disposable cartridge is entered into the instrument by reading a bar code label on the cartridge and sample tube, and the disposable cartridge is loaded into the cartridge tray of the instrument. The operator initiates the test run sequence. The test is completed in five minutes or less.

Preferably, the dynamic range of the instrument is 0.1-100 ng/ml for Tnl, 0.5-300 ng/ml for CK-MB, and 1.5-1000 ng/m for myoglobin, with a CV of < 10%. Data obtained, using the method and instrument of the preferred embodiment, from a sample of whole blood spiked with increasing amounts of troponin I (Tnl) are shown in Figs. 5-7. Fig. 5 is a graph of the signal intensity plotted against the concentration of Tnl added to the blood sample, and illustrates the linearity of response of the assay over a broad range of Tnl concentrations, from 0.5 ng/ml to 5 ng/ml. Fig. 6 shows the intensity of signal as a function of the concentration of Tnl added to the blood sample, in the cases of a blood sample and a plasma sample. Fig. 6 illustrates that the linearity of the response is not affected by the use of the whole blood in place of plasma, highlighting the fact that the method employed is insensitive to the presence of red blood cells, and thus a separation step is not required. Figure 7 is a table showing the reproducibility of the method when three different channels are employed. The coefficient of variation (CV%) is not greater than 12% for any measurement. Thus, the method of this invention is able to reproducibly measure the concentration of analytes in the samples. The in vitro clinical diagnostic instrument of the present invention can be used for direct whole blood testing, without any need for separation or removal of red blood cells. The disposable testing cartridges enable the operator to perform the entire assay without any exposure of the operator to the sample. This latter feature is particularly important when dealing with bodily samples, particularly human blood, that may contain infectious agents that pose a risk to the operator. In addition, because the sample tubes are immediately loaded directly onto the disposable assay cartridge, and the sample is moved directly to the assay area by air pressure, there is no possibility of sample contMInation. The system can also be used to measure a broad range of analytes, including, for example, small molecules, such as various blood-borne hormones, including human chorionic gonadotropin (hCG), drugs (i.e., digoxin, theophylline, phenytoin (i.e., Dilantin®), carbamazepine (i.e., Tegretol®), and phenobarbital), other proteins, infectious organisms, large particles (i.e., spores), and various parameters in blood, such as blood gases, blood pH and electrolytes. Examples of infectious organisms that can be detected may include, for example, C. difficile (A+B), HIV, CMV, HSV, mycoplasma, H. pylori, rotavirus, respiratory viruses (i.e., influenza A, influenza B, and respiratory syncitial virus (RSV)), and chlamydia and gonococcus. The system can simultaneously conduct multiple assays on a single patient sample, and may be used in a variety of assay formats, such as sandwich-type immunoassays, competitive immunoassays, nucleic acid assays, and enzymatic hydrolysis assays. The system is capable of simultaneously measuring multiple analytes, and is also capable of performing different assays of the same analyte in a single sample. The system also is capable of performing simultaneous standardization procedures, which ensures accurate results.

Various patents and publications are cited herein, and their disclosures are hereby incorporated by reference in their entireties. The present invention is not intended to be limited in scope by the specific embodiments described herein. Although the present invention has been described in detail for the purpose of illustration, various modifications of the invention as disclosed, in addition to those described herein, will become apparent to those of skill in the art from the foregoing description. Such modifications are intended to be encompassed within the scope of the present claims.

Claims

Claims
1. An instrument for detecting and/or quantifying an analyte in a fluid sample, comprising: a disposable cartridge, said disposable cartridge including a waveguide; said waveguide having an analyte-binding molecule on at least one surface thereof, said analyte-binding molecule being effective to bind to an analyte indirectly or directly bound to a fluorescent molecule; a light source, said light source being capable of directing light through said waveguide, said light having a wavelength effective to excite said fluorescent molecule; an optic system, said optics system comprising a light detection means and being capable of detecting light emitted in a perpendicular direction from said waveguide surface; and a means for aligning said waveguide in said disposable cartridge with said light, whereby when said light is directed through said waveguide, an evanescent field is created by total internal reflection, said evanescent field being capable of exciting said fluorescent molecule when said fluorescent molecule is bound to said analyte-binding molecule and thereby producing an emission from said excited fluorescent molecule that is capable of being detected by said light detection means.
2. An instrument for detecting and/or quantifying an analyte in a fluid sample, comprising: a disposable cartridge, said disposable cartridge including a waveguide; said waveguide having an analyte or analyte analog on at least one surface thereof, said analyte or analyte analog being effective to bind to an analyte-binding molecule bound to a fluorescent molecule; a light source, said light source being capable of directing light through said waveguide, said light having a wavelength effective to excite said fluorescent molecule; an optic system, said optics system comprising a light detection means and being capable of detecting light emitted in a perpendicular direction from said waveguide surface; and a means for aligning said waveguide in said disposable cartridge with said light, whereby when said light is directed through said waveguide, an evanescent field is created by total internal reflection, said evanescent field being capable of exciting said fluorescent molecule when said fluorescent molecule is bound to said analyte-binding molecule and thereby producing an emission from said excited fluorescent molecule that is capable of being detected by said light detection means.
3. The instrument of either of claims 1 or 2, wherein said means for aligning includes a cartridge tray having a kinematic mount.
4. The instrument of either of claims 1 or 2, wherein said waveguide is a planar waveguide.
5. The instrument of either of claims 1 or 2, wherein said planar waveguide is a unitary piece of polystyrene plastic.
6. The instrument of either of claims 1 or 2, wherein said light detection means is a CCD camera.
7. The instrument of either of claims 1 or 2, wherein said light source is a laser, and said light is laser light.
8. The instrument of either of claims 1 or 2, further comprising an air pump, said air pump connecting to a sample tube held on said disposable cartridge and being effective to displace all or a portion of a fluid sample in said sample tube into an assay area portion of said disposable cartridge.
9. The instrument of either of claims 1 or 2, wherein said means for aligning holds said disposable cartridge at a predetermined position in a cartridge tray having a kinematic mount.
10. The instrument of claim 9, wherein said means for aligning holds said disposable cartridge at a predetermined position in said instrument.
11. The instrument of either of claims 1 or 2, wherein said optic system further comprises a resonator, said resonator being effective to spread said light emitted by said light source into a light line having a width at least as great as a width of said waveguide.
12. The instrument of claim 11 , wherein said resonator oscillates at a frequency of about lOO Hz.
13. The instrument of claim 11, further comprising a means for altering power input to said light source, said means for altering power input to said light source being effective to maintain a level of light energy across said light line that varies across said width of said light line by < 15%.
14. The instrument of claim 11, further comprising a means for altering power input to said light source, said means for altering power input to said light source being effective to maintain a level of light energy across said light line that varies across said width of said light line by < 1%.
15. The instrument of either of claims 1 or 2, further comprising: a resonator in said optic system, said resonator being effective to spread said light emitted by said light source into a light line having a width at least as great as a width of said waveguide; and a means for altering power input to said light source, said means for altering power input to said light source being effective to maintain a level of light energy across said light line that varies across said width of said light line by < 15%.
16. The instrument of either of claims 1 or 2, further comprising: a resonator in said optic system, said resonator being effective to spread said light emitted by said light source into a light line having a width at least as great as a width of said waveguide; a means for altering power input to said light source, said means for altering power input to said light source being effective to maintain a level of light energy across said light line that varies across said width of said light line by < 15%; a means for aligning said disposable cartridge at a predetermined position in a cartridge tray having a kinematic mount; and a means for aligning said cartridge tray at a predetermined position in said instrument.
17. A disposable cartridge for use in an instrument for detecting and/or quantifying one or more analytes in a fluid sample, comprising: a waveguide; said waveguide having an analyte-binding molecule on at least one surface thereof, said analyte-binding molecule being effective to bind to an analyte bound indirectly or directly to a fluorescent molecule.
18. A disposable cartridge for use in an instrument for detecting and/or quantifying one or more analytes in a fluid sample, comprising: a waveguide; said waveguide having an analyte or analyte analog on at least one surface thereof, said analyte or analyte analog being effective to bind to an analyte-binding molecule indirectly or directly bound to a fluorescent molecule.
19. The disposable cartridge of either of claims 17 or 18, wherein said waveguide is a planar waveguide.
20. The disposable cartridge of either of claims 17 or 18, wherein said planar waveguide is a unitary piece of polystyrene plastic.
21. The disposable cartridge of either of claims 17 or 18, wherein said waveguide is separated into a plurality of channels.
22. The disposable cartridge of claim 21, wherein each of said channels comprises a different analyte-binding molecule.
23. The disposable cartridge of either of claims 17 or 18, wherein said waveguide is a thin film waveguide deposited on a substrate, said thin film waveguide having an index of refraction greater than that of said substrate.
24. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is a member selected from the group consisting of a polyclonal antibody, a monoclonal antibody, a derivative of a monoclonal antibody, a receptor body, and a nucleic acid.
25. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is a derivative of a monoclonal antibody selected from the group consisting of an F(ab), an F(ab')2. an scFv fragment, and an Fv.
26. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is a monoclonal antibody.
27. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for a member of the group consisting of a peptide, a polypeptide, a protein, or a polynucleotide.
28. The disposable cartridge of either of claims 17 or 18, further comprising a porous material plug, said plug being located substantially at the end of said flow path, said plug permitting preferential passage of air but not said fluid sample.
29. The disposable cartridge of either of claims 17 or 18, wherein: said waveguide is a planar waveguide; said waveguide is separated into a plurality of channels, each of said channels comprising a different analyte-binding molecule; and each of said analyte-binding molecules is a monoclonal antibody.
30. The disposable cartridge of either of claims 17 or 18, wherein said an analyte-binding molecule is specific for at least one member selected from the group consisting of myoglobin, troponin I and creatine kinase MB.
31. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for an infectious organism.
32. The disposable cartridge of claim 31, wherein said infectious organism is a member selected from the group consisting of C. difficile (A+B), HIV, CMV, HSV, mycoplasma, H. pylori, and rotavirus.
33. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for a respiratory virus.
34. The disposable cartridge of claim 33, wherein said respiratory virus is a member selected from the group consisting of influenza A, influenza B, and respiratory syncitial virus (RSV).
35. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for human chorionic gonadotropin (hCG).
36. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for at least one member of the group consisting of digoxin, theophylline, phenytoin, carbamazepine, and phenobarbital.
37. The disposable cartridge of either of claims 17 or 18, wherein said analyte- binding molecule is specific for a member of the group consisting of chlamydia and gonococcus.
38. The disposable cartridge of either of claims 17 or 18, wherein: said waveguide is a planar waveguide, said planar waveguide being separated into a plurality of channels; and one or more of said channels includes a plurality of sensing regions, each of said sensing regions containing an analyte-binding molecule bound to said planar waveguide.
39. The disposable cartridge of claim 38, wherein: said sensing regions in at least one of said channels contain no analyte- binding molecule and are deformations in said waveguide that are capable of reflecting light out of said waveguide.
40. The disposable cartridge of claim 38, wherein: said sensing regions in at least one of said channels contain predetermined amounts of said analyte bound to said waveguide, whereby the function of assay components can be monitored.
41. The disposable cartridge of either of claims 17 or 18, further comprising a receptacle for a sample tube, said sample tube containing said fluid sample.
42. The disposable cartridge of either of claims 17 or 18, further comprising a means for piercing a sample tube, said sample tube containing said fluid sample; said means for piercing including an inlet to a flow path connecting said inlet to said at least one surface of said waveguide bearing an analyte-binding molecule.
43. The disposable cartridge of claim 42, wherein said means for piercing is a needle.
44. A method for detecting and/or quantitating an analyte in a fluid sample, comprising the steps of: collecting a fluid sample into a closed sample tube; contacting a surface of a waveguide bearing an analyte-binding molecule with all or a portion of said fluid sample, said analyte-binding molecule being bound to an analyte or analyte analog labeled with a fluorescent molecule, under conditions whereby an analyte present in said fluid sample binds to said analyte-binding molecule, and said binding of said analyte to said analyte-binding molecule produces a change in an amount of said labeled analyte or analyte analog bound to said analyte-binding molecule; directing a line of light of uniform intensity through said waveguide, said waveguide being made of a material having a refractive index greater than that of said bodily fluid sample in contact with said waveguide, whereby an evanescent field is created, said evanescent field extending out from said surface of said waveguide into said fluid sample, and exciting said fluorescent molecules bound directly or indirectly to said analyte-binding molecule to produce a light emission; and detecting and/or quantitating binding of said analyte to said analyte-binding molecule through detection and/or quantitation of said light emission.
45. A method for detecting and/or quantitating an analyte in a fluid sample, comprising the steps of: collecting a fluid sample into a closed sample tube, said closed sample tube containing an analyte-binding molecule labeled with a fluorescent molecule; contacting a surface of a waveguide bearing an analyte-binding molecule with all or a portion of said fluid sample, under conditions whereby an analyte present in said fluid sample binds to both said analyte-binding molecule on said surface of said waveguide and to said analyte-binding molecule labeled with a fluorescent molecule; directing a line of light of uniform intensity through said waveguide, said waveguide being made of a material having a refractive index greater than that of said bodily fluid sample in contact with said waveguide, whereby an evanescent field is created, said evanescent field extending out from said surface of said waveguide into said fluid sample, and exciting said fluorescent molecules bound to said analyte-binding molecule to produce a light emission; and detecting and/or quantitating binding of said analyte to said analyte-binding molecule through detection and/or quantitation of said light emission.
46. A method for detecting and/or quantitating an analyte in a fluid sample, comprising the steps of: collecting a fluid sample into a closed sample tube; contacting said surface of said waveguide bearing said analyte or analyte analog with all or a portion of said fluid sample under conditions whereby said analyte present in said fluid sample binds to an analyte-binding molecule bound directly or indirectly to a fluorescent molecule, and said analyte present in said fluid sample competes with said analyte or analyte analog on said waveguide surface for binding to said analyte- binding molecule; directing a line of light of uniform intensity through said waveguide, said waveguide being made of a material having a refractive index greater than that of said bodily fluid sample in contact with said waveguide, whereby an evanescent field is created, said evanescent field extending out from said surface of said waveguide into said fluid sample, and exciting said fluorescent molecules bound directly or indirectly to said analyte-binding molecule to produce a light emission; and detecting and/or quantitating binding of said analyte to said analyte-binding molecule through detection and/or quantitation of said light emission.
47. The method of any of claims 44,45, or 46, wherein said detection and or quantitation of said light emission is detection and/or quantitation of light emitted perpendicularly to said waveguide.
48. The method of any of claims 44,45, or 46, wherein said line of light of uniform intensity varies by not more than 15% across a width of said line.
49. The method of any of claims 44,45, or 46, wherein said line of light of uniform intensity varies by not more than 1% across a width of said line.
50. The method of any of claims 44,45, or 46, wherein said disposable cartridge is aligned at a predetermined position in said cartridge tray and at a predetermined position in said instrument, whereby said line of light is incident on said waveguide across a width of said waveguide.
51. The method of any of claims 44,45, or 46, wherein said step of collecting a fluid sample into a closed sample tube includes collecting said fluid sample into a first tube, and thereafter transferring said fluid sample to said closed sample tube.
52. The method of any of claims 44,45, or 46, wherein said measurement of said light emission is performed by: measuring an amount of said light emission at a plurality of time points; making a curve of the amount of said light emission against time; calculating a slope of said curve; and determining a concentration of said analyte by relating said slope to a standard curve of analyte concentration against a slope of light emission.
PCT/US2001/021634 2000-07-21 2001-07-10 Apparatus and method for evanescent light fluoroassays WO2002008762A1 (en)

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