CA2019980C - Analytical assay method - Google Patents
Analytical assay methodInfo
- Publication number
- CA2019980C CA2019980C CA002019980A CA2019980A CA2019980C CA 2019980 C CA2019980 C CA 2019980C CA 002019980 A CA002019980 A CA 002019980A CA 2019980 A CA2019980 A CA 2019980A CA 2019980 C CA2019980 C CA 2019980C
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- Prior art keywords
- analyte
- sample
- assay
- layer
- signal
- Prior art date
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
- G01N21/64—Fluorescence; Phosphorescence
- G01N21/6428—Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes"
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
- G01N33/50—Chemical analysis of biological material, e.g. blood, urine; Testing involving biospecific ligand binding methods; Immunological testing
- G01N33/52—Use of compounds or compositions for colorimetric, spectrophotometric or fluorometric investigation, e.g. use of reagent paper and including single- and multilayer analytical elements
- G01N33/525—Multi-layer analytical elements
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N2021/755—Comparing readings with/without reagents, or before/after reaction
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S435/00—Chemistry: molecular biology and microbiology
- Y10S435/97—Test strip or test slide
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S436/00—Chemistry: analytical and immunological testing
- Y10S436/80—Fluorescent dyes, e.g. rhodamine
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T436/00—Chemistry: analytical and immunological testing
- Y10T436/10—Composition for standardization, calibration, simulation, stabilization, preparation or preservation; processes of use in preparation for chemical testing
Abstract
A method for determining the amount of an analyte in a sample fluid utilizes a multilayer assay element which comprises at least one reagent layer and a light-blocking layer. The assay method includes the steps of optically reading a signal producing species, e.g. a fluorescent label, a first time before the sample fluid is applied to the assay element and a second time, at the same wavelength and in the same location within the assay element, after the sample fluid has been applied to the assay element and the sample analyte has interacted with the reagent(s) present in the assay element. The ratio of the two signals is taken and compared with that for known amounts of the analyte to determine the amount of analyte in the sample fluid.
Description
`~- 2019980 ANALYTICAL ASSAY METHOD
BACKGROUND OF THE INVENTION
The present invention relates to assays for the determination of analytes in fluids.
Many types of assay elements for the rapid analysis of analytes present in biological fluids are known in the art. Of 5 particular interest are dry multilayer analytical elements to which the sample, e.g., a drop of blood, serum or plasma, is applied and allowed to migrate or diffuse to a reagent layer or layers. As a result of the interaction between the analyte and the reagent(s) present, a detectable change is brought about in the element 10 corresponding to the presence of the analyte in the sample. The detectable change can be a color change which may be evaluated visually or read spectrophotometrically such as with a densitometer.
In another scheme based on the presence of fluorescent-labeled biologically active species, a fluorescent output signal can be 15 generated and read spectrofluorometrically. Such assay elements are of great interest because they can be adapted for use in automated analytical instruments.
` - 201~980 In the automated analytical hls~ lents a sample of a test fluid is typically provided in a sample cup and all of the assay method steps including pipetting of a measured volume of the sample onto an assay element, incubation and readout of the signal obtained 5 as a result of the interactions(s) between the reagent(s) and the sample analyte are carried out automatically. The assay element is typically transported from one station, e.g. the pipetting station, to another, e.g. the optical read station, by a transport means such as a rotating carousel to enable the test steps to be carried out 10 automatically.
Such automated analytical instruments are capable of processing many assay elements rapidly and it is necessary to achieve a very high level of precision for these assays. However, imprecisions in the results obtained can be caused by a number of factors. For 15 example, any element to element variation in the distance from the optical readout apparatus to the signal-generating species when readout of the signal is carried out will introduce imprecision into the results as will any element to element variation in the thickness of the layer in which the signal-generating species resides when it is 20 read.
The reagent layer(s) in thin film multilayer assay elements may be extremely thin, that is, on the order of about 0.01 mm or less. Accordingly, although such layers can be coated with a very high degree of precision nevertheless some slight variation in the 25 thickness of the reagent layers will exist on an element to element basis. Similarly, although the transport means e.g. a carousel, for the assay elements can be engineered within very exact tolerances, nevertheless there will exist some slight variations in the instrument position response for the respective assay element positions on the 30 transport means.
It is desirable therefore to have a methocl for compensating for signal imprecisions cause(J by varialiolls in rca~e _ 2 ~1 9g 80 74761-11 levels from element to element and variations in instrument position response as well those caused by other factors.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method for determining the presence of an analyte in a sample fluid comprising (a) distributing a sample of fluid across the surface of a multilayer assay element which comprises: i. a light-blocking layer which is permeable to said fluid; and ii. a reàgent layer comprising a signal generating species; (b) obtaining a readout signal by irradiating said reagent layer with electromagnetic radiation which is in the absorption region of said signal generating species; (c) taking the ratio of said readout signal from step (b) to a readout signal obtained by irradiating said reagent layer with the same electromagnetic radiation used in step (b) prior to distributing said fluid sample in step (a); and (d) comparing said ratio with that obtained for known amounts of said analyte to determine the amount of analyte in said sample.
Thus, the invention provides a method for determining the amount of an analyte in a sample fluid such as whole blood, plasma, serum, etc. The assay method is carried out with an assay element which includes at least one reagent layer and a light-blocking layer. The light-blocking layer provides an optical bound/free separation of a signal-generating species as a function of the amount of analyte in the sample fluid, The signal-generating species in the assay element is read optically a first time prior to delivering the sample fluid to the element.
Subsequently, after the sample fluid has been applied to the assay ;` 2 ~ 1 9 9 8 0 element and the interaction between the sample analyte and the reagent(s) present in the element has taken place, the ~ignal producing species is read optically a second time. Thi~ second optical reading is carried out by irradiating the same layer of the assay element as that read in the first optical reading and doing so at the same wavelength. The ratio of the second signal to the first signal is taken and compared with that for known amounts of the analyte to determine the amount of the analyte in the sample fluid.
By normalizing the signal obtained from the assay in this manner it is possible to compensate for variations in reagent levels because of variations in reagent layer thicknesses from element to element and also for variations in the analytical instrument position response. The compensation for such variations provides significantly improved precision in the assay method.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of various preferred embodiments -3a--`` 2019980 thereof taken in conjunction with the accompanying drawings wherein:
the Figure is a partially schematic cross-sectional view of an assay element which can be utilized in the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The assay elements which are utilized in the assay method of the invention may include any suitable signal-generating species. Any light radiation emitting or absorbing label, including a label which reacts with a reagent, which provides a detectable signal can be utilized as the signal-generating species. The label may be a fluorophore, a phosphor or a light absorbing material.
The assay method of the invention will be described in detail with respect to a preferred embodiment of an assay element which may be utilized therein. Referring now to the Figure there is seen an assay element 10 which is a thin film multilayer element 15 typically having a thickness of about 0.1 mm and comprised of a transparent support 12 which carries in succession a reagent layer 14, a light-blocking layer 16 and an optional top coat layer 18 which may serve as a reagent layer, a filter layer such as for proteins, an anti-abrasion layer, etc. The reagent layer 14 is very thin, typically having 20 a thickness of about 0.025 mm and includes an immunocomplex of a binding partner for the analyte of interest and a conjugate of a labeled analyte (the same as the sample analyte, an analogue thereof or a structurally similar material which will bind to the binding partner). The binding partner, an antibody when the sample analyte 25 is an antigen, is immobilized in the reagent layer 14 by being covalently bound to the surface of the support layer 12, which may be of any appropriate material such as a polyester or a polystyrene, or to a matrix material or by being physically held by the matrix material. The matrix material may be a hydrophilic gel material such 30 as gelatin, a polysaccharide, e.g. agarose, a derivatized polysaccharide, mixtures thereof, and the like. Light-blocking layer 16 may comprise any suitable material such as, for example, iron oxide, titanium - 2019~80 74761-11 dioxide or the like dispersed in a binder material such as a polysaccharide. The optional topcoat layer 18 may comprise an anti-abrasion layer of a material such as a polysaccharide or preferably may include buffers, blocking and displacing agents, etc.
The assay element 10 may also include a layer or other means (not shown) for distributing the sample fluid uniformly across the surface of the top layer of the element. Any suitable fluid distribution technique may be used including, for example, particulate layers, polymeric layers, fibrous layers, woven fabric layers and liquid transport systems which have been disclosed in the art as being suitable for this purpose. Many such liquid distribution systems and materials for providing a uniform distribution of a fluid sample across the surface of an assay element are known in the art and therefore extensive discussion of such materials and systems is not required here.
A particularly preferred fluid transport system is that described in Canadian Patent No. 1,310,887. The distribution means, whether a layer of fibrous material, etc. or a liquid transport system is preferably relatively thick in comparison to reagent layer 14.
In practice, the label which is present in reagent layer 14 is optically read prior to applying the sample to the assay element by irradiating layer 14 with the appropriate electro-magnetic radiation through transparent support layer 12 to obtain a first readout signal. The sample fluid is then distributed across the surface of the assay element and the fluid diffuses throughout layers 14, 16 and 18 as well as any fluid distribution 20199~
layer or liquid transport system present and an equilibrium is established. The analyte present in the sample will compete with the labeled analyte in reagent layer 14 for the available binding sites on the antibodies immobilized in layer 14, the labeled analyte being dissociated therefrom and replaced by the sample analyte in a ratio appropriately equal to the relative amounts of sample analyte and labeled analyte. Thus, depending upon the -5a-;- 2019980 amount of analyte in the sample, some percentage of the labeled analyte initially bound to the immobilized antibodies in layer 14 will be displaced therefrom and distributed throughout the remainder of the assay element, The amount of labeled analyte bound to the S immobilized antibodies in reagent layer 14 at any time is inversely proportional to the amount of sample analyte.
A second readout signal is obtained by again irradiating reagent layer 14 through support layer 12 with the same electromagnetic radiation used in the first optical read step to obtain a second signal which is inversely proportional to the amount of sample analyte~ that is, the signal decreases as the amount of sample analyte increases. Since reagent layer 14 is relatively thin in comparison to the combined thickness of layers 16 and 18 together with that of any fluid distribution layer or liquid transport system present and because light blocking layer 16 prevents any of the readout electromagnetic radiation from entering layer 18 or anything above it, the second signal obtained will be a function of the labeled analyte which is bound to the immobilized antibodies and a small percentage of the free labeled analyte which is distributed throughout the remainder of the assay element. In a preferred embodiment the ratio of the thickness of reagent layer 14 to the combined thickness of the light-blocking layer and the remainder of the assay element is from about 1:20 to about 1:100 or more.
The ratio of the second signal to the first signal is taken and compared with that for known amounts of the analyte to determine the amount of analyte in the sample fluid. The ratio may be used as obtained or it may be multiplied by some constant, dependent upon the particular assay, to provide a signal which falls in some desired range.
In commercial use the assay is preferably carried out in an automated analytical instrument which performs the analysis automatically and records the result. By practicing the assay method 20~9980 `_ of the invention variations in the instrument position response and in the thickness of the reagent layer from element to element can be compensated for and significantly better precision obtained.
The invention will now be described further in detail S with respect to specific preferred embodiments by way of examples, it being understood that these are intended to be illustrative only and the invention is not limited to the materials, procedures, etc. recited therein.
EXAMPLE I
10 - An assay element was prepared comprising a transparent polyethylene terephthalate support having coated thereon in succession:
1. a reagent layer comprising about 500 mg/m2 of a 3:1 mixture of agarose and glyoxyl agarose; about 72 mg/m2 of bis 15 tris propane buffer; about 10 mg/m2 of an antibody raised against theophylline; and about 0.07 mg/m2 of a fluorescent labeled theophylline conjugate represented by the formula .
~3 o3S(CH2)2HNOCCI H2 CH2CONH(CH2)2S03 ~o NH(CH3)~
N ~ N-C [CH2]3 ~,~f 2. a light-blocking layer comprising about 6000 mg/m2 of iron oxide, about 2000 mg/m2 of agarose and about 50.4 20 mg/m2 of 2'-morpholino ethane sulfonic acid (pH 5.7); and 201~980 3. a topcoat layer comprising about 2000 mg/m2 of agarose.
Test samples containing different levels of theophylline in a buffer solution were prepared. The buffer solution was made up S of 50 mM of hydroxyethyl piperazine ethyl sulfonate (HEPES) buffer, pH 7.2, 150 mM of sodium chloride, 10 mM of EDTA and 1% of Polygeline. Each sample was run in quadruplicate.
Each assay element was inserted into a laboratory analytical instrument and conditioned at 37C for about two minutes.
10 The test element was then irradiated through the transparent support with 550 nm light and the fluorescent emission measured at 580 nm.
The test sample, about 10,ul, was then applied to the assay element which was incubated for an additional six minutes and then read again. The data obtained are shown in Table I. Each value shown 15 is the average of four readings from the four quadruplicates run for each test sample. The normalized signal value was obtained by taking the values obtained from dividing the wet reading by the dry reading and multiplying them by a constant which in this case was 1.166.
TABLE I
DRY DRY WET WET NORMALIZED NORMALIZED
THEOPHYLLINE SIGNAL CVSIGNAL CV SIGNAL CV
(~g/dl) (V) (%) (V)(%) (V) (%) 2.5 1.192 7.5 1.256 8.6 1.229 1.3 5.0 1.174 7.2 1.016 10.0 1.008 4.1 20.0 1.176 7.9 0.683 11.0 0.678 5.2 40.0 1.180 11.2 0.561 22.0 0.551 10.8 It is seen that normalizing the signal in accordance witl the method of the invention provides significantly improved precision.
, . . .
` 2019980 `
Also, the data show that the improved precision was obtained at theophylline levels across the assay range (2.5 - 40.0 ~g/dl).
EXAMPLE II
An assay element similar to that illustrated in Example 5 I was prepared wherein the reagent layer included about 20 mg/m2 of an antibody raised against phenytoin and about 0.15 mg/m2 of a conjugate consisting of phenytoin bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0, 5 and 40 ,ug/dl respectively 10 of phenytoin were prepared in a buffer solution which was the same as that described in Example I with the exceptions that it contained about 2% BSA, about 0.01~o NaN3 and about 0.01% PNS and did not contain Polygeline.
The assay procedure was the same as that previously 15 described. Eighteen assays were run for each concentration. The data obtained are shown in Table II. The normalized signal value was obtained by multiplying the ratio of the wet to dry readings by 3.836.
TABLE II
DRY DRY WET WET NORMALIZED NORMALIZED
PHENYTOIN SIGNAL CV SIGNAL CV SIGNAL CV
(~g/dl (V) (%) (V) (~) (V) (~) 0 3.682 5.4 6.806 4.87.090 1.7 3.724 2.8 5.542 2.65.710 1.4 3.533 3.8 3.417 8.93.711 7.9 It can be seen that normalizing the signal according to the invention gave significantly improved precision.
EXAMPLE III
An assay element similar to that illustrated in Example I was prepared wherein the reagent layer included about 15 mg/m2 of an antibody raised against phenobarbital and about 0.15 mg/m2 of S a conjugate consisting of phenobarbital bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0 and 5 ~g/dl, respectively, of phenobarbital in pooled human serum were prepared. The assay procedure was the same as that previously described. Three assays 10 were carried out for each concentration. The results obtained are shown in Table III. The normalized signal value was obtained by multiplying the ratio of the wet to dry readings by 3Ø
TABLE III
PHENO- DRY DRY WET WET NORMALIZED NORMALIZED
BARBITAL SIGNAL CV SIGNAL CV SIGNAL CV
(~g/dl) (V) (~) (V) (~) (V) (%) 0 4.112 5.13 5.002 6.08 3.648 1.24 3.886 10.66 3.462 11.56 2.671 1.05 The results show that normalizing the signal according 5 to the invention provided significantly improved precision.
EXAMPLE IV
An assay element similar to that illustrated in Example I was prepared wherein the reagent layer included about 0.5 mg/m2 of an antibody raised against T4 and about 0.01 mg/m2 of a 20 conjugate consisting of T4 bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0.0, 2.5 and 10.0 ~g/dl, respectively, of T4 in plasma (stripped of T4) were prepared. The assay proceclure was the same as that previously ~lescribe(J. rl~welve ` 2019980 -assays were carried out for each concentration. The results are shown in Table IV. The normalized signal value was obtained by multiplying the ratio of the wet to dry reaclingc by 3Ø
TABLE IV
DRY DRY WET WET NORMALIZED NORMALIZED
(~g/dl) (V) (%) (V) (%) (V)(%) 0 2.573 3.85 2.735 3.67 3.190 1.40 2.5 2.552 4.80 2.522 5.00 2.965 1.52 10.0 2.512 4.42 1.907 5.97 2.276 2.14 The data show that significantly improved precision was obtained by norm~ ing the signal according to the invention.
Although the invention has been described with respect to specific preferred embodiments it is not intended to be limited thereto but rather those skilled in the art will recognize that 10 variations and modification may be made therein which are within the spirit of the invention and the scope of the appended claims.
BACKGROUND OF THE INVENTION
The present invention relates to assays for the determination of analytes in fluids.
Many types of assay elements for the rapid analysis of analytes present in biological fluids are known in the art. Of 5 particular interest are dry multilayer analytical elements to which the sample, e.g., a drop of blood, serum or plasma, is applied and allowed to migrate or diffuse to a reagent layer or layers. As a result of the interaction between the analyte and the reagent(s) present, a detectable change is brought about in the element 10 corresponding to the presence of the analyte in the sample. The detectable change can be a color change which may be evaluated visually or read spectrophotometrically such as with a densitometer.
In another scheme based on the presence of fluorescent-labeled biologically active species, a fluorescent output signal can be 15 generated and read spectrofluorometrically. Such assay elements are of great interest because they can be adapted for use in automated analytical instruments.
` - 201~980 In the automated analytical hls~ lents a sample of a test fluid is typically provided in a sample cup and all of the assay method steps including pipetting of a measured volume of the sample onto an assay element, incubation and readout of the signal obtained 5 as a result of the interactions(s) between the reagent(s) and the sample analyte are carried out automatically. The assay element is typically transported from one station, e.g. the pipetting station, to another, e.g. the optical read station, by a transport means such as a rotating carousel to enable the test steps to be carried out 10 automatically.
Such automated analytical instruments are capable of processing many assay elements rapidly and it is necessary to achieve a very high level of precision for these assays. However, imprecisions in the results obtained can be caused by a number of factors. For 15 example, any element to element variation in the distance from the optical readout apparatus to the signal-generating species when readout of the signal is carried out will introduce imprecision into the results as will any element to element variation in the thickness of the layer in which the signal-generating species resides when it is 20 read.
The reagent layer(s) in thin film multilayer assay elements may be extremely thin, that is, on the order of about 0.01 mm or less. Accordingly, although such layers can be coated with a very high degree of precision nevertheless some slight variation in the 25 thickness of the reagent layers will exist on an element to element basis. Similarly, although the transport means e.g. a carousel, for the assay elements can be engineered within very exact tolerances, nevertheless there will exist some slight variations in the instrument position response for the respective assay element positions on the 30 transport means.
It is desirable therefore to have a methocl for compensating for signal imprecisions cause(J by varialiolls in rca~e _ 2 ~1 9g 80 74761-11 levels from element to element and variations in instrument position response as well those caused by other factors.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a method for determining the presence of an analyte in a sample fluid comprising (a) distributing a sample of fluid across the surface of a multilayer assay element which comprises: i. a light-blocking layer which is permeable to said fluid; and ii. a reàgent layer comprising a signal generating species; (b) obtaining a readout signal by irradiating said reagent layer with electromagnetic radiation which is in the absorption region of said signal generating species; (c) taking the ratio of said readout signal from step (b) to a readout signal obtained by irradiating said reagent layer with the same electromagnetic radiation used in step (b) prior to distributing said fluid sample in step (a); and (d) comparing said ratio with that obtained for known amounts of said analyte to determine the amount of analyte in said sample.
Thus, the invention provides a method for determining the amount of an analyte in a sample fluid such as whole blood, plasma, serum, etc. The assay method is carried out with an assay element which includes at least one reagent layer and a light-blocking layer. The light-blocking layer provides an optical bound/free separation of a signal-generating species as a function of the amount of analyte in the sample fluid, The signal-generating species in the assay element is read optically a first time prior to delivering the sample fluid to the element.
Subsequently, after the sample fluid has been applied to the assay ;` 2 ~ 1 9 9 8 0 element and the interaction between the sample analyte and the reagent(s) present in the element has taken place, the ~ignal producing species is read optically a second time. Thi~ second optical reading is carried out by irradiating the same layer of the assay element as that read in the first optical reading and doing so at the same wavelength. The ratio of the second signal to the first signal is taken and compared with that for known amounts of the analyte to determine the amount of the analyte in the sample fluid.
By normalizing the signal obtained from the assay in this manner it is possible to compensate for variations in reagent levels because of variations in reagent layer thicknesses from element to element and also for variations in the analytical instrument position response. The compensation for such variations provides significantly improved precision in the assay method.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description of various preferred embodiments -3a--`` 2019980 thereof taken in conjunction with the accompanying drawings wherein:
the Figure is a partially schematic cross-sectional view of an assay element which can be utilized in the method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The assay elements which are utilized in the assay method of the invention may include any suitable signal-generating species. Any light radiation emitting or absorbing label, including a label which reacts with a reagent, which provides a detectable signal can be utilized as the signal-generating species. The label may be a fluorophore, a phosphor or a light absorbing material.
The assay method of the invention will be described in detail with respect to a preferred embodiment of an assay element which may be utilized therein. Referring now to the Figure there is seen an assay element 10 which is a thin film multilayer element 15 typically having a thickness of about 0.1 mm and comprised of a transparent support 12 which carries in succession a reagent layer 14, a light-blocking layer 16 and an optional top coat layer 18 which may serve as a reagent layer, a filter layer such as for proteins, an anti-abrasion layer, etc. The reagent layer 14 is very thin, typically having 20 a thickness of about 0.025 mm and includes an immunocomplex of a binding partner for the analyte of interest and a conjugate of a labeled analyte (the same as the sample analyte, an analogue thereof or a structurally similar material which will bind to the binding partner). The binding partner, an antibody when the sample analyte 25 is an antigen, is immobilized in the reagent layer 14 by being covalently bound to the surface of the support layer 12, which may be of any appropriate material such as a polyester or a polystyrene, or to a matrix material or by being physically held by the matrix material. The matrix material may be a hydrophilic gel material such 30 as gelatin, a polysaccharide, e.g. agarose, a derivatized polysaccharide, mixtures thereof, and the like. Light-blocking layer 16 may comprise any suitable material such as, for example, iron oxide, titanium - 2019~80 74761-11 dioxide or the like dispersed in a binder material such as a polysaccharide. The optional topcoat layer 18 may comprise an anti-abrasion layer of a material such as a polysaccharide or preferably may include buffers, blocking and displacing agents, etc.
The assay element 10 may also include a layer or other means (not shown) for distributing the sample fluid uniformly across the surface of the top layer of the element. Any suitable fluid distribution technique may be used including, for example, particulate layers, polymeric layers, fibrous layers, woven fabric layers and liquid transport systems which have been disclosed in the art as being suitable for this purpose. Many such liquid distribution systems and materials for providing a uniform distribution of a fluid sample across the surface of an assay element are known in the art and therefore extensive discussion of such materials and systems is not required here.
A particularly preferred fluid transport system is that described in Canadian Patent No. 1,310,887. The distribution means, whether a layer of fibrous material, etc. or a liquid transport system is preferably relatively thick in comparison to reagent layer 14.
In practice, the label which is present in reagent layer 14 is optically read prior to applying the sample to the assay element by irradiating layer 14 with the appropriate electro-magnetic radiation through transparent support layer 12 to obtain a first readout signal. The sample fluid is then distributed across the surface of the assay element and the fluid diffuses throughout layers 14, 16 and 18 as well as any fluid distribution 20199~
layer or liquid transport system present and an equilibrium is established. The analyte present in the sample will compete with the labeled analyte in reagent layer 14 for the available binding sites on the antibodies immobilized in layer 14, the labeled analyte being dissociated therefrom and replaced by the sample analyte in a ratio appropriately equal to the relative amounts of sample analyte and labeled analyte. Thus, depending upon the -5a-;- 2019980 amount of analyte in the sample, some percentage of the labeled analyte initially bound to the immobilized antibodies in layer 14 will be displaced therefrom and distributed throughout the remainder of the assay element, The amount of labeled analyte bound to the S immobilized antibodies in reagent layer 14 at any time is inversely proportional to the amount of sample analyte.
A second readout signal is obtained by again irradiating reagent layer 14 through support layer 12 with the same electromagnetic radiation used in the first optical read step to obtain a second signal which is inversely proportional to the amount of sample analyte~ that is, the signal decreases as the amount of sample analyte increases. Since reagent layer 14 is relatively thin in comparison to the combined thickness of layers 16 and 18 together with that of any fluid distribution layer or liquid transport system present and because light blocking layer 16 prevents any of the readout electromagnetic radiation from entering layer 18 or anything above it, the second signal obtained will be a function of the labeled analyte which is bound to the immobilized antibodies and a small percentage of the free labeled analyte which is distributed throughout the remainder of the assay element. In a preferred embodiment the ratio of the thickness of reagent layer 14 to the combined thickness of the light-blocking layer and the remainder of the assay element is from about 1:20 to about 1:100 or more.
The ratio of the second signal to the first signal is taken and compared with that for known amounts of the analyte to determine the amount of analyte in the sample fluid. The ratio may be used as obtained or it may be multiplied by some constant, dependent upon the particular assay, to provide a signal which falls in some desired range.
In commercial use the assay is preferably carried out in an automated analytical instrument which performs the analysis automatically and records the result. By practicing the assay method 20~9980 `_ of the invention variations in the instrument position response and in the thickness of the reagent layer from element to element can be compensated for and significantly better precision obtained.
The invention will now be described further in detail S with respect to specific preferred embodiments by way of examples, it being understood that these are intended to be illustrative only and the invention is not limited to the materials, procedures, etc. recited therein.
EXAMPLE I
10 - An assay element was prepared comprising a transparent polyethylene terephthalate support having coated thereon in succession:
1. a reagent layer comprising about 500 mg/m2 of a 3:1 mixture of agarose and glyoxyl agarose; about 72 mg/m2 of bis 15 tris propane buffer; about 10 mg/m2 of an antibody raised against theophylline; and about 0.07 mg/m2 of a fluorescent labeled theophylline conjugate represented by the formula .
~3 o3S(CH2)2HNOCCI H2 CH2CONH(CH2)2S03 ~o NH(CH3)~
N ~ N-C [CH2]3 ~,~f 2. a light-blocking layer comprising about 6000 mg/m2 of iron oxide, about 2000 mg/m2 of agarose and about 50.4 20 mg/m2 of 2'-morpholino ethane sulfonic acid (pH 5.7); and 201~980 3. a topcoat layer comprising about 2000 mg/m2 of agarose.
Test samples containing different levels of theophylline in a buffer solution were prepared. The buffer solution was made up S of 50 mM of hydroxyethyl piperazine ethyl sulfonate (HEPES) buffer, pH 7.2, 150 mM of sodium chloride, 10 mM of EDTA and 1% of Polygeline. Each sample was run in quadruplicate.
Each assay element was inserted into a laboratory analytical instrument and conditioned at 37C for about two minutes.
10 The test element was then irradiated through the transparent support with 550 nm light and the fluorescent emission measured at 580 nm.
The test sample, about 10,ul, was then applied to the assay element which was incubated for an additional six minutes and then read again. The data obtained are shown in Table I. Each value shown 15 is the average of four readings from the four quadruplicates run for each test sample. The normalized signal value was obtained by taking the values obtained from dividing the wet reading by the dry reading and multiplying them by a constant which in this case was 1.166.
TABLE I
DRY DRY WET WET NORMALIZED NORMALIZED
THEOPHYLLINE SIGNAL CVSIGNAL CV SIGNAL CV
(~g/dl) (V) (%) (V)(%) (V) (%) 2.5 1.192 7.5 1.256 8.6 1.229 1.3 5.0 1.174 7.2 1.016 10.0 1.008 4.1 20.0 1.176 7.9 0.683 11.0 0.678 5.2 40.0 1.180 11.2 0.561 22.0 0.551 10.8 It is seen that normalizing the signal in accordance witl the method of the invention provides significantly improved precision.
, . . .
` 2019980 `
Also, the data show that the improved precision was obtained at theophylline levels across the assay range (2.5 - 40.0 ~g/dl).
EXAMPLE II
An assay element similar to that illustrated in Example 5 I was prepared wherein the reagent layer included about 20 mg/m2 of an antibody raised against phenytoin and about 0.15 mg/m2 of a conjugate consisting of phenytoin bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0, 5 and 40 ,ug/dl respectively 10 of phenytoin were prepared in a buffer solution which was the same as that described in Example I with the exceptions that it contained about 2% BSA, about 0.01~o NaN3 and about 0.01% PNS and did not contain Polygeline.
The assay procedure was the same as that previously 15 described. Eighteen assays were run for each concentration. The data obtained are shown in Table II. The normalized signal value was obtained by multiplying the ratio of the wet to dry readings by 3.836.
TABLE II
DRY DRY WET WET NORMALIZED NORMALIZED
PHENYTOIN SIGNAL CV SIGNAL CV SIGNAL CV
(~g/dl (V) (%) (V) (~) (V) (~) 0 3.682 5.4 6.806 4.87.090 1.7 3.724 2.8 5.542 2.65.710 1.4 3.533 3.8 3.417 8.93.711 7.9 It can be seen that normalizing the signal according to the invention gave significantly improved precision.
EXAMPLE III
An assay element similar to that illustrated in Example I was prepared wherein the reagent layer included about 15 mg/m2 of an antibody raised against phenobarbital and about 0.15 mg/m2 of S a conjugate consisting of phenobarbital bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0 and 5 ~g/dl, respectively, of phenobarbital in pooled human serum were prepared. The assay procedure was the same as that previously described. Three assays 10 were carried out for each concentration. The results obtained are shown in Table III. The normalized signal value was obtained by multiplying the ratio of the wet to dry readings by 3Ø
TABLE III
PHENO- DRY DRY WET WET NORMALIZED NORMALIZED
BARBITAL SIGNAL CV SIGNAL CV SIGNAL CV
(~g/dl) (V) (~) (V) (~) (V) (%) 0 4.112 5.13 5.002 6.08 3.648 1.24 3.886 10.66 3.462 11.56 2.671 1.05 The results show that normalizing the signal according 5 to the invention provided significantly improved precision.
EXAMPLE IV
An assay element similar to that illustrated in Example I was prepared wherein the reagent layer included about 0.5 mg/m2 of an antibody raised against T4 and about 0.01 mg/m2 of a 20 conjugate consisting of T4 bound to the fluorescent moiety illustrated in Example I.
Test samples containing 0.0, 2.5 and 10.0 ~g/dl, respectively, of T4 in plasma (stripped of T4) were prepared. The assay proceclure was the same as that previously ~lescribe(J. rl~welve ` 2019980 -assays were carried out for each concentration. The results are shown in Table IV. The normalized signal value was obtained by multiplying the ratio of the wet to dry reaclingc by 3Ø
TABLE IV
DRY DRY WET WET NORMALIZED NORMALIZED
(~g/dl) (V) (%) (V) (%) (V)(%) 0 2.573 3.85 2.735 3.67 3.190 1.40 2.5 2.552 4.80 2.522 5.00 2.965 1.52 10.0 2.512 4.42 1.907 5.97 2.276 2.14 The data show that significantly improved precision was obtained by norm~ ing the signal according to the invention.
Although the invention has been described with respect to specific preferred embodiments it is not intended to be limited thereto but rather those skilled in the art will recognize that 10 variations and modification may be made therein which are within the spirit of the invention and the scope of the appended claims.
Claims (7)
1. A method for determining the presence of an analyte in a sample fluid comprising (a) distributing a sample of fluid across the surface of a multilayer assay element which comprises:
i. a light-blocking layer which is permeable to said fluid; and ii. a reagent layer comprising a signal generating species.
(b) obtaining a readout signal by irradiating said reagent layer with electromagnetic radiation which is in the absorption region of said signal generating species;
(c) taking the ratio of said readout signal from step (b) to a readout signal obtained by irradiating said reagent layer with the same electromagnetic radiation used in step (b) prior to distributing said fluid sample in step (a); and (d) comparing said ratio with that obtained for known amounts of said analyte to determine the amount of analyte in said sample.
i. a light-blocking layer which is permeable to said fluid; and ii. a reagent layer comprising a signal generating species.
(b) obtaining a readout signal by irradiating said reagent layer with electromagnetic radiation which is in the absorption region of said signal generating species;
(c) taking the ratio of said readout signal from step (b) to a readout signal obtained by irradiating said reagent layer with the same electromagnetic radiation used in step (b) prior to distributing said fluid sample in step (a); and (d) comparing said ratio with that obtained for known amounts of said analyte to determine the amount of analyte in said sample.
2. The method as defined in claim 1 wherein said assay element further includes a support which is transparent to said electromagnetic radiation.
3. The method as defined in claim 1 wherein said reagent layer includes an immobilized binding partner for said analyte and said signal generating species comprises a conjugate of a label bound to a moiety which is capable of binding to said binding partner.
4. The method as defined in claim 3 wherein said moiety bound to said label is said analyte or an analogue thereof.
5. The method as defined in claim 3 wherein said label is fluorescent.
6. The method as defined in claim 2 wherein said assay element further includes a top layer arranged above said light blocking layer.
7. The method as defined in claim 2 wherein the ratio of the thickness of said reagent layer to that of the remainder of said assay element is from about 1:20 to about 1:100 or more.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/382,555 US5166079A (en) | 1989-07-19 | 1989-07-19 | Analytical assay method |
| US382,555 | 1989-07-19 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2019980A1 CA2019980A1 (en) | 1991-01-19 |
| CA2019980C true CA2019980C (en) | 1994-08-23 |
Family
ID=23509484
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002019980A Expired - Fee Related CA2019980C (en) | 1989-07-19 | 1990-06-27 | Analytical assay method |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US5166079A (en) |
| EP (1) | EP0434800B1 (en) |
| JP (1) | JPH0743382B2 (en) |
| AT (1) | ATE97487T1 (en) |
| CA (1) | CA2019980C (en) |
| DE (1) | DE69004673T2 (en) |
| DK (1) | DK0434800T3 (en) |
| ES (1) | ES2048495T3 (en) |
| WO (1) | WO1991001490A1 (en) |
Families Citing this family (19)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991019187A1 (en) * | 1990-06-04 | 1991-12-12 | Pb Diagnostic Systems, Inc. | Analytical assay |
| JPH06222057A (en) * | 1993-01-27 | 1994-08-12 | Kyoto Daiichi Kagaku:Kk | Analytical composition |
| DE4331596A1 (en) * | 1993-09-17 | 1995-03-23 | Boehringer Mannheim Gmbh | Method for the quantitative analysis of sample liquids |
| US5492360A (en) * | 1994-04-11 | 1996-02-20 | Davidson Textron Inc. | Tether tear strap and trim panel having same |
| US5601997A (en) | 1995-02-03 | 1997-02-11 | Tchao; Ruy | Chemotaxis assay procedure |
| US7098041B2 (en) * | 2001-12-11 | 2006-08-29 | Kimberly-Clark Worldwide, Inc. | Methods to view and analyze the results from diffraction-based diagnostics |
| US20030119203A1 (en) | 2001-12-24 | 2003-06-26 | Kimberly-Clark Worldwide, Inc. | Lateral flow assay devices and methods for conducting assays |
| US6837171B1 (en) | 2002-04-29 | 2005-01-04 | Palmer/Snyder Furniture Company | Lightweight table with unitized table top |
| US7285424B2 (en) | 2002-08-27 | 2007-10-23 | Kimberly-Clark Worldwide, Inc. | Membrane-based assay devices |
| US7432105B2 (en) * | 2002-08-27 | 2008-10-07 | Kimberly-Clark Worldwide, Inc. | Self-calibration system for a magnetic binding assay |
| US7781172B2 (en) | 2003-11-21 | 2010-08-24 | Kimberly-Clark Worldwide, Inc. | Method for extending the dynamic detection range of assay devices |
| US7713748B2 (en) | 2003-11-21 | 2010-05-11 | Kimberly-Clark Worldwide, Inc. | Method of reducing the sensitivity of assay devices |
| US20050112703A1 (en) | 2003-11-21 | 2005-05-26 | Kimberly-Clark Worldwide, Inc. | Membrane-based lateral flow assay devices that utilize phosphorescent detection |
| US7943395B2 (en) | 2003-11-21 | 2011-05-17 | Kimberly-Clark Worldwide, Inc. | Extension of the dynamic detection range of assay devices |
| US7815854B2 (en) | 2004-04-30 | 2010-10-19 | Kimberly-Clark Worldwide, Inc. | Electroluminescent illumination source for optical detection systems |
| US7796266B2 (en) | 2004-04-30 | 2010-09-14 | Kimberly-Clark Worldwide, Inc. | Optical detection system using electromagnetic radiation to detect presence or quantity of analyte |
| EP1742039A1 (en) * | 2005-07-07 | 2007-01-10 | F. Hoffmann-La Roche Ltd. | Method for the determination of the concentration of a non-volatile analyte |
| CN102224260B (en) * | 2008-09-24 | 2015-11-25 | 施特劳斯控股公司 | For test kit and the device of detect analytes |
| WO2010119098A1 (en) * | 2009-04-15 | 2010-10-21 | Stefan Wennmalm | Inverse-fluorescence correlation spectroscopy |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55164356A (en) * | 1979-06-08 | 1980-12-22 | Fuji Photo Film Co Ltd | Multi-layer analysis sheet for liquid sample analysis |
| JPS5639465A (en) * | 1979-09-10 | 1981-04-15 | Olympus Optical Co Ltd | Detecting method of immunological agglutination |
| JPS5977356A (en) * | 1982-06-30 | 1984-05-02 | Fuji Photo Film Co Ltd | Multilayer analysis element for fluorescent assay and fluorescent assay using the same |
| US4459358A (en) * | 1982-12-29 | 1984-07-10 | Polaroid Corporation | Multilayer element for analysis |
| JPS59170768A (en) * | 1983-03-17 | 1984-09-27 | Fuji Photo Film Co Ltd | Multilayered analyzing element for non-isotope assay and assay method using said element |
| JPS6111642A (en) * | 1984-06-28 | 1986-01-20 | Fuji Photo Film Co Ltd | Chemical analysis instrument |
| WO1987000023A1 (en) * | 1985-07-03 | 1987-01-15 | International Biomedics, Inc. | Methods of measuring oxygen concentration |
| JPH076917B2 (en) * | 1986-09-01 | 1995-01-30 | 富士写真フイルム株式会社 | Calibration method correction method in dry analysis method |
| US4954435A (en) * | 1987-01-12 | 1990-09-04 | Becton, Dickinson And Company | Indirect colorimetric detection of an analyte in a sample using ratio of light signals |
| JPS6463864A (en) * | 1987-09-03 | 1989-03-09 | Fuji Photo Film Co Ltd | Immunoassay |
| AU621935B2 (en) * | 1988-11-23 | 1992-03-26 | Dade Behring Marburg Gmbh | Biological diagnostic assay system |
-
1989
- 1989-07-19 US US07/382,555 patent/US5166079A/en not_active Expired - Lifetime
-
1990
- 1990-06-19 DE DE90910067T patent/DE69004673T2/en not_active Revoked
- 1990-06-19 EP EP90910067A patent/EP0434800B1/en not_active Revoked
- 1990-06-19 JP JP2509125A patent/JPH0743382B2/en not_active Expired - Fee Related
- 1990-06-19 AT AT90910067T patent/ATE97487T1/en active
- 1990-06-19 WO PCT/US1990/003453 patent/WO1991001490A1/en not_active Application Discontinuation
- 1990-06-19 DK DK90910067.9T patent/DK0434800T3/en active
- 1990-06-19 ES ES90910067T patent/ES2048495T3/en not_active Expired - Lifetime
- 1990-06-27 CA CA002019980A patent/CA2019980C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0434800B1 (en) | 1993-11-18 |
| DE69004673D1 (en) | 1993-12-23 |
| JPH0743382B2 (en) | 1995-05-15 |
| DE69004673T2 (en) | 1994-03-10 |
| ATE97487T1 (en) | 1993-12-15 |
| DK0434800T3 (en) | 1993-12-27 |
| ES2048495T3 (en) | 1994-03-16 |
| US5166079A (en) | 1992-11-24 |
| EP0434800A1 (en) | 1991-07-03 |
| WO1991001490A1 (en) | 1991-02-07 |
| JPH04500860A (en) | 1992-02-13 |
| CA2019980A1 (en) | 1991-01-19 |
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