U.S. patent application number 10/132673 was filed with the patent office on 2003-06-26 for internal calibration system for flow-through assays.
This patent application is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Song, Xuedong, Wei, Ning.
Application Number | 20030119204 10/132673 |
Document ID | / |
Family ID | 21880091 |
Filed Date | 2003-06-26 |
United States Patent
Application |
20030119204 |
Kind Code |
A1 |
Wei, Ning ; et al. |
June 26, 2003 |
Internal calibration system for flow-through assays
Abstract
A flow-through assay for detecting the quantity of an analyte
residing in a test sample is provided. The flow-through assay
contains a porous membrane that is in fluid communication with
probe conjugates that contain a specific binding member and a
detectable probe. The porous membrane also defines a detection zone
and a calibration zone. The calibration zone includes two or more
calibration regions (e.g., lines, dots, etc.) containing differing
amounts of a binder that is configured to bind with the probe
conjugates. As a result, calibration signals are generated that can
be readily compared (visually, quantitatively, and the like) to a
detection signal to determine the presence or quantity of an
analyte in the test sample.
Inventors: |
Wei, Ning; (Roswell, GA)
; Song, Xuedong; (Roswell, GA) |
Correspondence
Address: |
DORITY & MANNING, P.A.
POST OFFICE BOX 1449
GREENVILLE
SC
29602-1449
US
|
Assignee: |
Kimberly-Clark Worldwide,
Inc.
|
Family ID: |
21880091 |
Appl. No.: |
10/132673 |
Filed: |
April 25, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10132673 |
Apr 25, 2002 |
|
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10035014 |
Dec 24, 2001 |
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Current U.S.
Class: |
436/514 |
Current CPC
Class: |
G01N 33/54386 20130101;
G01N 33/54393 20130101; G01N 33/558 20130101 |
Class at
Publication: |
436/514 |
International
Class: |
G01N 033/558 |
Claims
What is claimed is:
1. A flow-through assay for detecting the presence or quantity of
an analyte residing in a test sample, said flow-through assay
comprising a porous membrane, wherein said porous membrane is in
fluid communication with a probe conjugate that contains a specific
binding member and a detectable probe, said porous membrane
defining: a detection zone that contains a capture reagent that is
capable of binding to the analyte or the probe conjugate, wherein
said detection zone is capable of generating a detection signal
that represents the presence or absence of the analyte; a
calibration zone that contains a binder configured to bind with
said probe conjugate, said calibration zone including: i) a first
calibration region containing a first predetermined amount of said
binder, said first calibration region being capable of generating a
first calibration signal; ii) a second calibration region
containing a second predetermined amount of said binder that is
greater than said first predetermined amount of said binder, said
second calibration region being capable of generating a second
calibration signal, said second calibration signal having a greater
intensity than said first calibration signal; and wherein the
relative amount of the analyte within the test sample is determined
by comparing said detection signal to said first calibration signal
and said second calibration signal.
2. A flow-through assay as defined in claim 1, wherein said
detection signal is capable of being visually compared to said
first calibration signal and said second calibration signal.
3. A flow-through assay as defined in claim 1, wherein said
detection signal is capable of being compared to said first
calibration signal and said second calibration signal through the
use of an instrument.
4. A flow-through assay as defined in claim 1, wherein a
calibration curve is generated by plotting the intensity of said
first and second calibration signals versus known levels of the
analyte.
5. A flow-through assay as defined in claim 1, wherein said
calibration zone further includes a third calibration region
containing a third predetermined amount of said binder that is
greater than said second predetermined amount of said binder, said
third calibration region being capable of generating a third
calibration signal that has a greater intensity than said second
calibration signal.
6. A flow-through assay as defined in claim 1, wherein said first
and said second calibration regions are disposed in a direction
that is substantially parallel to the flow of the test sample
through said porous membrane.
7. A flow-through assay as defined in claim 1, wherein said binder
is a polyelectrolyte.
8. A flow-through assay as defined in claim 1, wherein said
detectable probe is selected from the group consisting of
chromogens, catalysts, fluorescent compounds, chemiluminescent
compounds, radioactive labels, direct visual labels, liposomes, and
combinations thereof.
9. A flow-through assay as defined in claim 8, wherein said
detectable probe comprises a latex microparticle.
10. A flow-through assay as defined in claim 1, wherein the
specific binding member of said probe conjugate is selected from
the group consisting of antigens, haptens, antibodies, and
complexes thereof.
11. A flow-through assay as defined in claim 1, wherein the capture
reagent is selected from the group consisting of antigens, haptens,
antibodies, and complexes thereof.
12. A flow-through assay as defined in claim 1, wherein the assay
is a sandwich-type assay.
13. A flow-through assay as defined in claim 1, wherein the assay
is a competitive-type assay.
14. A flow-through assay for detecting the presence or quantity of
an analyte residing in a test sample, said flow-through assay
comprising a porous membrane in fluid communication with a probe
conjugate containing a specific binding member and a detectable
probe, wherein said porous membrane defines: a detection zone, said
detection zone containing a capture reagent that is capable of
binding to the analyte, wherein said detection zone is capable of
generating a detection signal that represents the presence or
absence of the analyte; a calibration zone that contains a binder
configured to bind with said probe conjugate, said calibration zone
including: i) a first calibration line containing a first
predetermined amount of said binder, said first calibration line
being capable of generating a first calibration signal; ii) a
second calibration line containing a second predetermined amount of
said binder that is greater than said first predetermined amount of
said binder, said second calibration line being capable of
generating a second calibration signal, said second calibration
signal having a greater intensity than said first calibration
signal; iii) a third calibration line containing a third
predetermined amount of said binder that is greater than said
second predetermined amount of said binder, said third calibration
line being capable of generating a third calibration signal that
has a greater intensity than said second calibration signal; and
wherein the relative amount of the analyte within the test sample
is determined by comparing said detection signal to said first
calibration signal, said second calibration signal, and said third
calibration signal.
15. A flow-through assay as defined in claim 14, wherein said
detection signal is capable of being visually compared to said
first calibration signal, said second calibration signal, and said
third calibration signal.
16. A flow-through assay as defined in claim 14, wherein said
detection signal is capable of being compared to said first
calibration signal, said second calibration signal, and said third
calibration signal through the use of an instrument.
17. A flow-through assay as defined in claim 14, wherein a
calibration curve is generated by plotting the intensity of said
first, second, and third calibration signals versus known amounts
of the analyte.
18. A flow-through assay as defined in claim 14, wherein said
first, second, and third calibration lines are disposed in a
direction that is substantially parallel to the flow of the test
sample through said porous membrane.
19. A flow-through assay for detecting the presence or quantity of
an analyte residing in a test sample, said flow-through assay
comprising a porous membrane in fluid communication with probe
conjugates containing a specific binding member and a detectable
probe, said probe conjugates being configured to combine with the
analyte in the test sample when contacted therewith such that probe
conjugate/analyte complexes and uncomplexed probe conjugates are
formed, wherein said porous membrane defines: i) a detection zone
in which a capture reagent is substantially non-diffusively
immobilized on said porous membrane, said capture reagent being
capable of binding to said probe conjugate/analyte complexes,
wherein said detection zone is capable of generating a detection
signal; ii) a calibration zone that contains a binder configured to
bind with said uncomplexed probe conjugates, said calibration zone
including: a) a first calibration region containing a first
predetermined amount of said binder, said first calibration region
being capable of generating a first calibration signal; b) a second
calibration region containing a second predetermined amount of said
binder that is greater than said first predetermined amount of said
binder, said second calibration region being capable of generating
a second calibration signal, said second calibration signal having
a greater intensity than said first calibration signal; and wherein
the relative amount of the analyte within the test sample is
determined by comparing said detection signal to said first
calibration signal and said second calibration signal.
20. A flow-through assay for detecting the presence or quantity of
an analyte residing in a test sample, said flow-through assay
comprising a porous membrane in fluid communication with probe
conjugates that contain a specific binding member and a detectable
probe, wherein said porous membrane defines: i) a detection zone in
which a predetermined amount of capture reagent is substantially
non-diffusively immobilized on said porous membrane, said capture
reagent being capable of binding to said probe conjugates and to
the analyte, wherein said detection zone is capable of generating a
detection signal, and ii) a calibration zone that contains a binder
configured to bind with said probe conjugates unbound to said
capture reagents, said calibration zone including: a) a first
calibration region containing a first predetermined amount of said
binder, said first calibration region being capable of generating a
first calibration signal; b) a second calibration region containing
a second predetermined amount of said binder that is greater than
said first predetermined amount of said binder, said second
calibration region being capable of generating a second calibration
signal, said second calibration signal having a greater intensity
than said first calibration signal; and wherein the relative amount
of the analyte within the test sample is determined by comparing
said detection signal to said first calibration signal and said
second calibration signal.
21. A flow-through assay as defined in claim 20, wherein said
specific binding member is identical to the analyte.
22. A flow-through assay for detecting the presence or quantity of
an analyte residing in a test sample, said flow-through assay
comprising a porous membrane in fluid communication with probe
conjugates that contain a specific binding member and a detectable
probe, said probe conjugates being configured to combine with the
analyte in the test sample when contacted therewith such that probe
conjugate/analyte complexes and uncomplexed probe conjugates are
formed, wherein said porous membrane defines: i) a detection zone
in which a capture reagent is substantially non-diffusively
immobilized on said porous membrane, said capture reagent being
capable of binding to said uncomplexed probe conjugates, wherein
said detection zone is capable of generating a detection signal,
and ii) a calibration zone that contains a binder configured to
bind to said probe conjugate/analyte complexes and said probe
conjugates remaining unbound to said capture reagents, said
calibration zone including: a) a first calibration region
containing a first predetermined amount of said binder, said first
calibration region being capable of generating a first calibration
signal; b) a second calibration region containing a second
predetermined amount of said binder that is greater than said first
predetermined amount of said binder, said second calibration region
being capable of generating a second calibration signal, said
second calibration signal having a greater intensity than said
first calibration signal; and wherein the relative amount of the
analyte within the test sample is determined by comparing said
detection signal to said first calibration signal and said second
calibration signal.
23. A flow-through assay as defined in claim 22, wherein said
capture reagent is identical to the analyte.
Description
RELATED APPLICATIONS
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 10/035,014, filed on Dec. 24, 2001.
BACKGROUND OF THE INVENTION
[0002] Various analytical procedures and devices are commonly
employed in flow-through assays to determine the presence and/or
concentration of analytes that may be present in a test sample. For
instance, immunoassays utilize mechanisms of the immune systems,
wherein antibodies are produced in response to the presence of
antigens that are pathogenic or foreign to the organisms. These
antibodies and antigens, i.e., immunoreactants, are capable of
binding with one another, thereby causing a highly specific
reaction mechanism that can be used to determine the presence or
concentration of that particular antigen in a biological
sample.
[0003] There are several well-known immunoassay methods that use
immunoreactants labeled with a detectable component so that the
analyte can be detected analytically. For example, "sandwich-type"
assays typically involve mixing the test sample with antibodies to
the analyte. These antibodies are mobile and linked to a label or
probe, such as dyed latex, a colloidal metal sol, or a
radioisotope. This mixture is then contacted with a chromatographic
medium containing a band or zone of immobilized antibodies to the
analyte. The chromatographic medium is often in the form of a strip
resembling a dipstick. When the complex of the analyte and the
labeled antibody reaches the zone of the immobilized antibodies on
the chromatographic medium, binding occurs and the bound labeled
antibodies are localized at the zone. This indicates the presence
of the analyte. This technique can be used to obtain quantitative
or semi-quantitative results. Some examples of such sandwich-type
assays are described in. by U.S. Pat. Nos. 4,168,146 to Grubb, et
al. and 4,366,241 to Tom, et al.
[0004] An alternative technique is the "competitive-type" assay. In
a "competitive-type" assay, the label is typically a labeled
analyte or analyte-analogue that competes for binding of an
antibody with any unlabeled analyte present in the sample.
Competitive assays are typically used for detection of analytes
such as haptens, each hapten being monovalent and capable of
binding only one antibody molecule. Examples of competitive
immunoassay devices are described in U.S. Pat. Nos. 4,235,601 to
Deutsch, et al., 4,442,204 to Liotta, and 5,208,535 to Buechler, et
al.
[0005] Many of these assays rely upon calibration to provide valid
and meaningful results, particularly for semi-quantitative and
quantitative detections. Specifically, either external or internal
calibration systems are generally employed. In an external
calibration system, a standard curve is usually obtained from
standard samples containing a series of a known amount of analyte,
and the results obtained from the samples are then compared with
the standard curve to extract the presence and/or amount of the
analyte in the sample. The external calibration method is
relatively easy to design and simple to implement. However, it is
often subject to interference from environmental and batch-to-batch
variations, and is thus unreliable.
[0006] Conventional internal calibration systems, on the other
hand, typically utilize a membrane that has a calibration zone and
a detection zone on which the capturing reagent specific for the
analyte is immobilized. Unfortunately, the ability of the
calibration zone to provide a reliable and accurate comparison to
the detection zone is often limited. Moreover, most internal
calibration zones are relatively expensive, thereby making them
impractical for certain applications.
[0007] As such, a need currently exists for an accurate calibration
system for flow-through assays that is readily controllable and
inexpensive.
SUMMARY OF THE INVENTION
[0008] In accordance with one embodiment of the present invention,
a flow-through assay (e.g., sandwich, competitive, etc.) is
disclosed for detecting the presence or quantity of an analyte
residing in a test sample. The assay comprises a porous membrane
that is in fluid communication with a probe conjugate that contains
a specific binding member and a detectable probe. For example, in
some embodiments, the detectable probe is selected from the group
consisting of chromogens, catalysts, fluorescent compounds,
chemiluminescent compounds, radioactive labels, direct visual
labels, liposomes, and combinations thereof. In one particular
embodiment, the detectable probe comprises a latex
microparticle.
[0009] The porous membrane also defines a detection zone that
contains a capture reagent capable of binding to the analyte or the
probe conjugate. In some embodiments, for example, the capture
reagent is selected from the group consisting of antigens, haptens,
antibodies, and complexes thereof. The detection zone is capable of
generating a detection signal to indicate the presence or absence
of an analyte.
[0010] In addition, to assist in the determination of the amount of
analyte present within the test sample, the porous membrane also
defines a calibration zone that contains a binder configured to
bind with the probe conjugate. The calibration zone includes:
[0011] i) a first calibration region (e.g., line, dot, etc.)
containing a first predetermined amount of the binder, the first
calibration region being capable of generating a first calibration
signal; and
[0012] ii) a second calibration region (e.g., line, dot, etc.)
containing a second predetermined amount of the binder that is
greater than the first predetermined amount of the binder, the
second calibration region being capable of generating a second
calibration signal, the second calibration signal having a greater
intensity than the first calibration signal.
[0013] Once the calibration regions generate signals, they can then
be compared to the detection signal to determine the presence or
relative amount of analyte in the test sample. For example, in some
embodiments, the calibration signals can be visually observed and
compared to the detection signal. Moreover, the calibration signals
can also be compared to the detection signal through the use of an
instrument, such as a fluorescent reader, a color intensity reader,
and the like. If desired, a calibration curve can be developed by
plotting the intensity of the calibration signals versus known
amounts of the analyte. Once generated, the curve can then be used
to determine an unknown amount of the analyte within a test
sample.
[0014] To provide a greater degree of calibration accuracy, the
calibration zone can employ more than two calibration regions. For
instance, in some embodiments, the calibration zone further
includes a third calibration region (e.g., line, dot, etc.)
containing a third predetermined amount of the binder that is
greater than the second predetermined amount of the binder. The
third calibration region is capable of generating a third
calibration signal that has a greater intensity than the second
calibration signal. It should be understood, however, that any
number of calibration regions, such as four or five, may also be
used in the present invention.
[0015] The geometric disposition of the calibration regions can
also be selected to increase or decrease the time required for
calibration. For example, in one embodiment, at least one of the
calibration regions is disposed in a direction that is
substantially perpendicular to the flow of the test sample through
the porous membrane. Moreover, in another embodiment, at least one
of the calibration regions is disposed in a direction that is
substantially parallel to the flow of the test sample through the
porous membrane. Such a parallel disposition can allow simultaneous
calibration of multiple calibration regions.
[0016] In accordance with another embodiment of the present
invention, a flow-through assay for detecting the presence or
quantity of an analyte residing in a test sample is disclosed. The
flow-through assay comprises a porous membrane that is in fluid
communication with probe conjugates that contain a specific binding
member and a detectable probe. The probe conjugates are configured
to combine with the analyte in the test sample when contacted
therewith such that probe conjugate/analyte complexes and
uncomplexed probe conjugates are formed. Further, the porous
membrane defines a detection zone. A capture reagent is
substantially non-diffusively immobilized on the porous membrane
within the detection zone. The capture reagent is capable of
binding to the probe conjugate/analyte complexes to generate a
detection signal. The porous membrane also defines a calibration
zone that contains a binder configured to bind with the uncomplexed
probe conjugates. The calibration zone includes first and second
calibration lines that generate calibration signals. The relative
amount of the analyte within the test sample is determined by
comparing the detection signal to the first calibration signal and
the second calibration signal.
[0017] In accordance with another embodiment of the present
invention, a flow-through assay for detecting the presence or
quantity of an analyte (e.g., antigen) residing in a test sample is
disclosed. The flow-through assay comprises a porous membrane that
is fluid communication with probe conjugates containing a specific
binding member and a detectable probe. For example, in one
embodiment, the specific binding member is identical to the
analyte. The porous membrane defines a detection zone in which a
predetermined amount of capture reagent is substantially
non-diffusively immobilized on the porous membrane. The capture
reagent (e.g., antibody) is capable of binding to the analyte
(e.g., antigen) such that the analyte of the test sample and probe
conjugates compete for the predetermined amount of capture reagent.
The detection zone is capable of generating a detection signal. The
porous membrane also defines a calibration zone that contains a
binder configured to bind with the probe conjugates unbound to the
capture reagents. The calibration zone includes first and second
calibration regions that generate calibration signals. The relative
amount of the analyte within the test sample is determined by
comparing the detection signal to the first calibration signal and
the second calibration signal.
[0018] In accordance with still another embodiment of the present
invention, a flow-through assay for detecting the presence or
quantity of an analyte (e.g., antigen) residing in a test sample is
disclosed. The assay comprises a porous membrane in communication
with probe conjugates that contain a specific binding member (e.g.,
antibody) and a detectable probe. The probe conjugates are
configured to combine with the analyte in the test sample when
contacted therewith such that probe conjugate/analyte complexes and
uncomplexed probe conjugates are formed. The porous membrane
defines a detection zone in which a capture reagent is
substantially non-diffusively immobilized on the porous membrane.
The capture reagent (e.g., antigen) is capable of binding to the
uncomplexed probe conjugates, wherein the detection zone is capable
of generating a detection signal. The porous membrane also defines
a calibration zone that contains a binder configured to bind with
the bind with the probe conjugates unbound to the capture reagents.
The calibration zone includes first and second calibration regions
that generate calibration signals. The relative amount of the
analyte within the test sample is determined by comparing the
detection signal to the first calibration signal and the second
calibration signal.
[0019] Other features and aspects of the present invention are
discussed in greater detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] A full and enabling disclosure of the present invention,
including the best mode thereof, directed to one of ordinary skill
in the art, is set forth more particularly in the remainder of the
specification, which makes reference to the appended figures in
which:
[0021] FIG. 1 is a top view of one embodiment of the present
invention, showing a flow-through assay having three calibration
lines in a calibration zone;
[0022] FIG. 2 is a perspective schematic view of one embodiment of
a flow-through assay of the present invention, showing the membrane
strip after a test sample containing analyte has been applied to
the sampling pad;
[0023] FIG. 3 illustrates the lateral assay shown in FIG. 2, but
with the test sample migrated through the assay;
[0024] FIG. 4 is a top view of another embodiment of the present
invention, in which FIG. 4A shows calibration lines substantially
parallel to the flow of the analyte and FIG. 4B shows calibration
dots substantially parallel to the flow of the analyte;
[0025] FIG. 5 shows a calibration curve that may be used in one
embodiment of the present invention;
[0026] FIG. 6 shows a calibration curve for CRP detection as
discussed in Example 3;
[0027] FIG. 7 shows a calibration curve for LH detection as
discussed in Example 4; and
[0028] FIG. 8 shows a calibration curve for pre-albumin detection
as discussed in Example 5.
[0029] Repeat use of reference characters in the present
specification and drawings is intended to represent same or
analogous features or elements of the invention.
DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS
[0030] Definitions
[0031] As used herein, the term "analyte" generally refers to a
substance to be detected. For instance, analytes can includes
antigenic substances, haptens, antibodies, and combinations
thereof. Analytes include, but are not limited to, toxins, organic
compounds, proteins, peptides, microorganisms, amino acids, nucleic
acids, hormones, steroids, vitamins, drugs (including those
administered for therapeutic purposes as well as those administered
for illicit purposes), bacteria, virus particles and metabolites of
or antibodies to any of the above substances. Specific examples of
some analytes include ferritin; creatinine kinase MIB (CK-MB);
digoxin; phenytoin; phenobarbitol; carbamazepine; vancomycin;
gentamycin; theophylline; valproic acid; quinidine; leutinizing
hormone (LH); follicle stimulating hormone (FSH); estradiol,
progesterone; IgE antibodies; vitamin B2 micro-globulin; glycated
hemoglobin (Gly. Hb); cortisol; digitoxin; N-acetylprocainamide
(NAPA); procainamide; antibodies to rubella, such as rubella-IgG
and rubella IgM; antibodies to toxoplasmosis, such as toxoplasmosis
IgG (Toxo-IgG) and toxoplasmosis IgM (Toxo-IgM); testosterone;
salicylates; acetaminophen; hepatitis B virus surface antigen
(HBsAg); antibodies to hepatitis B core antigen, such as
anti-hepatitis B core antigen IgG and IgM (Anti-HBC); human immune
deficiency virus 1 and 2 (HIV 1 and 2); human T-cell leukemia virus
1 and 2 (HTLV); hepatitis B e antigen (HBeAg); antibodies to
hepatitis B e antigen (Anti-HBe); thyroid stimulating hormone
(TSH); thyroxine (T4); total triiodothyronine (Total T3); free
triiodothyronine (Free T3); carcinoembryoic antigen (CEA); and
alpha fetal protein (AFP). Drugs of abuse and controlled substances
include, but are not intended to be limited to, amphetamine;
methamphetamine; barbiturates, such as amobarbital, secobarbital,
pentobarbital, phenobarbital, and barbital; benzodiazepines, such
as librium and valium; cannabinoids, such as hashish and marijuana;
cocaine; fentanyl; LSD; methaqualone; opiates, such as heroin,
morphine, codeine, hydromorphone, hydrocodone, methadone,
oxycodone, oxymorphone and opium; phencyclidine; and propoxyhene.
Other potential analytes may be described in U.S. Pat. No.
4,366,241 to Tom et al.
[0032] As used herein, the term "test sample" generally refers to a
material suspected of containing the analyte. The test sample can
be used directly as obtained from the source or following a
pretreatment to modify the character of the sample. The test sample
can be derived from any biological source, such as a physiological
fluid, including, blood, saliva, ocular lens fluid, cerebral spinal
fluid, sweat, urine, milk, ascites fluid, raucous, synovial fluid,
peritoneal fluid, amniotic fluid or the like. The test sample can
be pretreated prior to use, such as preparing plasma from blood,
diluting viscous fluids, and the like. Methods of treatment can
involve filtration, distillation, concentration, inactivation of
interfering components, and the addition of reagents. Besides
physiological fluids, other liquid samples can be used such as
water, food products and the like for the performance of
environmental or food production assays. In addition, a solid
material suspected of containing the analyte can be used as the
test sample. In some instances it may be beneficial to modify a
solid test sample to form a liquid medium or to release the
analyte.
DETAILED DESCRIPTION
[0033] Reference now will be made in detail to various embodiments
of the invention, one or more examples of which are set forth
below. Each example is provided by way of explanation of the
invention, not limitation of the invention. In fact, it will be
apparent to those skilled in the art that various modifications and
variations can be made in the present invention without departing
from the scope or spirit of the invention. For instance, features
illustrated or described as part of one embodiment, can be used on
another embodiment to yield a still further embodiment. Thus, it is
intended that the present invention covers such modifications and
variations as come within the scope of the appended claims and
their equivalents.
[0034] In general, the present invention is directed to an internal
calibration system for flow-through assays. In particular, the
present invention employs the use of a calibration zone that
contains two or more distinct calibration regions (e.g., lines,
dots, etc.). The calibration regions contain a different amount of
a binder so that one region is capable of generating a calibration
signal that is less intense than the calibration signal generated
by the other regions. In one embodiment, a calibration curve can be
developed for the level of binder in each calibration region for
comparison to a detection signal. It has been discovered that the
internal calibration system provides an accurate, inexpensive, and
readily controllable method of determining the presence of an
analyte in a test sample.
[0035] Referring to FIGS. 1-3, for instance, one embodiment of a
sandwich-type flow-through assay 20 that can be formed according to
the present invention will now be described in more detail. As
shown, the assay 20 is contains a porous membrane 23 optionally
supported by a rigid material (not shown). In general, the porous
membrane 23 can be made from any of a variety of materials through
which the test sample is capable of passing. For example, the
materials used to form the porous membrane 23 can include, but are
not limited to, natural, synthetic, or naturally occurring
materials that are synthetically modified, such as polysaccharides
(e.g., cellulose materials such as paper and cellulose derivatives,
such as cellulose acetate and nitrocellulose); silica; inorganic
materials, such as deactivated alumina, diatomaceous earth,
MgSO.sub.4, or other inorganic finely divided material uniformly
dispersed in a porous polymer matrix, with polymers such as vinyl
chloride, vinyl chloride-propylene copolymer, and vinyl
chloride-vinyl acetate copolymer; cloth, both naturally occurring
(e.g., cotton) and synthetic (e.g., nylon or rayon); porous gels,
such as silica gel, agarose, dextran, and gelatin; polymeric films,
such as polyacrylamide; and the like. In one particular embodiment,
the porous membrane 23 is formed from nitrocellulose and/or
polyester sulfone materials. It should be understood that the term
"nitrocellulose" refers to nitric acid esters of cellulose, which
may be nitrocellulose alone, or a mixed ester of nitric acid and
other acids, such as aliphatic carboxylic acids having from 1 to 7
carbon atoms.
[0036] To initiate the detection of an analyte 40 within the test
sample, a user may directly apply the test sample to a portion of
the porous membrane 23 through which it can then travel to reach
one or more detection and calibration zones (described below).
Alternatively, the test sample may first be applied to a sampling
pad that is in fluid communication with the porous membrane 23. For
example, as shown in FIGS. 1-3, the lateral flow assay 20 can
contain a sampling pad 21 generally configured to receive the test
sample. Some suitable materials that can be used to form the
sampling pad 21 include, but are not limited to, nitrocellulose,
cellulose, porous polyethylene pads, and glass fiber filter paper.
If desired, the sampling pad 21 may also contain one or more assay
pretreatment reagents, either diffusively or non-diffusively
attached thereto.
[0037] In the illustrated embodiment, the test sample travels from
the sampling pad 21 to a conjugate pad 22 (as shown by the
directional arrow 29 in FIG. 1) that is placed in communication
with one end of the sampling pad 21. The conjugate pad 22 is formed
from a material through which the test sample is capable of
passing. For example, in one embodiment, the conjugate pad 22 is
formed from glass fibers.
[0038] Besides simply allowing the test sample to pass
therethrough, the conjugate pad 22 also typically performs other
functions as well. For example, in some embodiments, various probes
41 (see FIG. 2) are releasibly applied to the conjugate pad 22.
While contained on the conjugate pad 22, these probes 41 remain
available for binding with the analyte 40 as the analyte 40 passes
from the sample pad 21 through the conjugate pad 22. Upon binding
with the analyte 40, the probes 41 can later serve to identify
(e.g., visually, etc.) the presence of the analyte 40 in the
detection zone of the assay 20.
[0039] Any substance generally capable of producing a signal that
is visually detectable or detectable by an instrumental device may
be used as the probes 41. Various suitable probes can include
chromogens; catalysts; fluorescent compounds; chemiluminescent
compounds; radioactive labels; direct visual labels, including
colloidal metallic and non-metallic particles (e.g., gold), dye
particles, enzymes or substrates, or organic polymer latex
particles; liposomes or other vesicles containing signal producing
substances; and the like. For instance, some enzymes suitable for
use as probes are disclosed in U.S. Pat. No. 4,275,149 to Litman,
et al., which is incorporated herein in its entirety by reference
thereto for all purposes. One example of an enzyme/substrate probe
system is the enzyme alkaline phosphatase and the substrate nitro
blue tetrazolium-5-bromo-4-chloro-3-indolyl phosphate, or
derivative or analog thereof, or the substrate
4-methylumbelliferyl-phosp- hate. In an alternative probe system,
the probe can be a fluorescent compound where no enzymatic
manipulation is required to produce a detectable signal.
Fluorescent molecules, such as fluorescein, phycobiliprotein,
rhodamine and their derivatives and analogs, are suitable for use
as probes in this reaction. Commercially available examples of such
fluorescent materials include fluorescent carboxylated microspheres
sold by Molecular Probes, Inc. under the trade names "FluoSphere"
(Red 580/605) and "TransfluoSphere" (543/620), as well as "Texas
Red" and 5- and 6-carboxytetramethylrhodamine, which are also sold
by Molecular Probes, Inc.
[0040] A visually detectable, colored microparticle (sometimes
referred to as "beads" or "microbeads") can also be used as a
probe, thereby providing for a direct colored readout of the
presence or concentration of the analyte in the sample without the
need for further signal producing reagents. In some instances, the
particles that are used in a quantitative assay can also contribute
a signal (e.g., light absorption) that would cause the zone in
which the particles are located to have a different signal than the
rest of the membrane 23.
[0041] The type of microparticles utilized for the probes 41 may
also vary. For instance, naturally occurring microparticles, such
as nuclei, mycoplasma, plasmids, plastids, mammalian cells (e.g.,
erythrocyte ghosts), unicellular microorganisms (e.g., bacteria),
polysaccharides (e.g., agarose), and the like, can be used.
Further, synthetic microparticles may also be utilized. For
example, in one embodiment, synthetic latex microparticles that are
colored with a dye are utilized as the probes 41. Although any
latex microparticle capable of adsorbing or covalently bonding to a
binding partner may be used in the present invention, the latex
microparticles are typically formed from polystyrene, butadiene
styrenes, styreneacrylic-vinyl terpolymer, polymethylmethacrylate,
polyethylmethacrylate, styrene-maleic anhydride copolymer,
polyvinyl acetate, polyvinylpyridine, polydivinylbenzene,
polybutyleneterephthalate, acrylonitrile, vinylchloride-acrylates,
and the like, or an aldehyde, carboxyl, amino, hydroxyl, or
hydrazide derivative thereof. Other suitable microparticles may be
described in U.S. Pat. Nos. 5,670,381 to Jou, et al. and 5,252,459
to Tarcha, et al., which are incorporated herein in their entirety
by reference thereto for all purposes. Commercially available
examples of suitable colored, latex microparticles include
carboxylated latex beads sold by Bang's Laboratory, Inc.
[0042] When utilized, the mean diameter of particulate probes 41
may generally vary as desired depending on factors such as the type
of particle chosen, the pore size of the membrane, and the membrane
composition. For example, in some embodiments, the mean diameter of
the particulate probes 41 ranges from about 0.01 microns to about
100 microns, and in some embodiments, from about 0.1 microns to
about 75 microns. In one particular embodiment, the particulate
probes 41 have a mean diameter of about 0.3 microns. In such
instances, the membrane 23 can have a pore size of from about 0.1
to about 0.3 microns.
[0043] When deposited on the conjugate pad 22, the probes 41 may be
capable of directly bonding (covalently or non-covalently) with the
analyte 40. However, it is often desired to modify the probes 41 in
some manner so that they are more readily able to bond to the
analyte 40. In such instances, the probes 41 can be modified with
certain specific binding members 90 that are non-covalently (e.g.,
adsorbed) and/or covalently attached thereto to form probe
conjugates 42.
[0044] Specific binding members generally refer to a member of a
specific binding pair, i.e., two different molecules where one of
the molecules chemically and/or physically binds to the second
molecule. For instance, immunoreactive specific binding members can
include antigens, haptens, antibodies, and complexes thereof,
including those formed by recombinant DNA methods or peptide
synthesis. An antibody can be a monoclonal or polyclonal antibody,
a recombinant protein or a mixture(s) or fragment(s) thereof, as
well as a mixture of an antibody and other specific binding
members. The details of the preparation of such antibodies and
their suitability for use as specific binding members are well
known to those skilled in the art.
[0045] Other common specific binding pairs include but are not
limited to, biotin and avidin, carbohydrates and lectins,
complementary nucleotide sequences (including probe and capture
nucleic acid sequences used in DNA hybridization assays to detect a
target nucleic acid sequence), complementary peptide sequences
including those formed by recombinant methods, effector and
receptor molecules, hormone and hormone binding protein, enzyme
cofactors and enzymes, enzyme inhibitors and enzymes, and the like.
Furthermore, specific binding pairs can include members that are
analogs of the original specific binding member. For example, a
derivative or fragment of the analyte, i.e., an analyte-analog, can
be used so long as it has at least one epitope in common with the
analyte.
[0046] The specific binding members 90 can generally be attached to
the probes 41 using any of a variety of well-known techniques. For
instance, when using latex microparticles as the probes 41,
covalent attachment of the specific binding members 90 thereto can
be accomplished using carboxylic, amino, aldehyde, bromoacetyl,
iodoacetyl, thiol, epoxy and other reactive or linking functional
groups, as well as residual free radicals and radical cations,
through which a protein coupling reaction can be accomplished. A
surface functional group can also be incorporated as a
functionalized co-monomer because the surface of the latex
microparticle can contain a relatively high surface concentration
of polar groups. In addition, although latex microparticle probes
are typically functionalized after synthesis, in certain cases,
such as poly(thiophenol), the microparticles are capable of direct
covalent linking with a protein without the need for further
modification.
[0047] Thus, referring again to FIGS. 2 and 3, a test sample
containing an analyte 40 can initially be applied to the sampling
pad 21. From the sampling pad, the test sample can then travel to
the conjugate pad 22, where the analyte 40 binds to the specific
binding member 90 of a probe conjugate 42 to form a probe
conjugate/analyte complex 49. Moreover, because the conjugate pad
22 is in fluid communication with the porous membrane 23, the probe
conjugate/analyte complex 49 can migrate from the conjugate pad 22
to a detection zone 31 present on the porous membrane 23.
[0048] The detection zone 31 may contain an immobilized capture
reagent 45. Although not required, it may be desired that the
capture reagents 45 be formed from the same class or category of
materials (e.g., antibodies) as the specific binding members 90
used to form the probe conjugates 42. These capture reagents 45
serve as stationary binding sites for the probe conjugate/analyte
complexes 49. In some instances, the analytes 40, such as
antibodies, antigens, etc., have two binding sites. Upon reaching
the detection zone 31, one of these binding sites is occupied by
the specific binding member 90 of the probe conjugate/analyte
complex 49. However, the free binding site of the analyte 40 can
bind to the immobilized capture reagent 45. Upon being bound to the
immobilized capture reagent 45, the probe conjugate 42 of a newly
formed ternary complex 50 signals the presence of the analyte 40,
either visually or through other methods of detection (e.g.,
instruments, etc.). Thus, to determine whether a particular analyte
40 is present within a test sample, a user can simply analyze the
detection zone 31.
[0049] However, although a detection zone may indicate the presence
of an analyte, it is often difficult to determine the relative
concentration of the analyte within a test sample using solely a
detection zone. Thus, in accordance with the present invention, the
assay also includes a calibration zone that may be compared to the
detection zone for determining the concentration of a particular
analyte within a test sample. For instance, referring again to
FIGS. 1-3, one embodiment of a flow-through assay 20 that includes
a calibration zone 32 is illustrated. In this embodiment, the
calibration zone 32 is formed on the porous membrane and is
positioned downstream from the detection zone 31. The control zone
32 is provided with a binder 47 that is capable of binding to any
remaining probes 41 and/or probe conjugates 42 that pass through
the length of the membrane 23. In particular, upon being contacted
with the test sample, any probes 41 and/or probe conjugates 42 that
do not bind to the analyte 40 migrate through the detection zone 31
with the complexes 49. In the detection zone 31, as set forth
above, the complexes 49 bind to capture reagents 45 and remain
immobilized. However, the unbound probes 41 and/or probe conjugates
42 continue to migrate through the detection zone 31 and enter the
calibration zone 32 of the porous membrane 23. At the calibration
zone 32, these unbound probes 41 and/or probe conjugates 42 then
bind to the binders 47. When immobilized in the calibration zone
32, the probes 41 and/or probe conjugates 42 are observable, either
visually or by other methods, so that a user can compare the signal
intensity in the detection zone 31 to the signal intensity in the
calibration zone 32.
[0050] The calibration zone 32 may generally provide any number of
distinct calibration regions so that a user can better determine
the concentration of a particular analyte within a test sample. In
most embodiments, for example, the calibration zone 32 includes two
or more calibration distinct calibration regions (e.g., lines,
dots, etc.). For instance, in the illustrated embodiment, at least
three calibration regions 25, 26, and 27 in the form of lines are
utilized. As shown in FIGS. 1-3, the calibration regions 25, 26,
and/or 27 may be disposed in the form of lines in a direction that
is substantially perpendicular to the flow of the test sample
through the assay 20.
[0051] Likewise, in some embodiments, such as shown in FIG. 4A, the
calibration regions 25, 26, and/or 27 can be disposed in the form
of lines in a direction that is substantially parallel to the flow
of the test sample through the assay. In yet another embodiment,
such as shown in FIG. 4B, three calibration regions 25a, 26a, and
27a are disposed in the form of dots in a direction that is
substantially parallel to the flow of the test sample through the
assay. In such instances, a user may be able to compare the
calibration signal to the detection signal in a lesser amount of
time because each of the calibration regions simultaneously
generate a calibration signal.
[0052] The calibration regions 25, 26, and 27 may be pre-loaded on
the porous membrane 23 with different amounts of the binder 47 so
that a different signal intensity is generated by each calibration
region 25, 26, and 27 upon migration of the probes 41 and/or probe
conjugates 42. The overall amount of binder 47 within each
calibration region can be varied by utilizing calibration regions
of different sizes and/or by varying the solution concentration or
volume of the binder 47 in each calibration region. Generally
speaking, the concentration of a binder 47 within a given
calibration region can range from about 0.01% to about 25% by
weight of the solution.
[0053] If desired, an excess of probe molecules can be employed in
the assay 20 so that each calibration region 25, 26, and 27 reaches
its full and predetermined potential for signal intensity. That is,
the amount of probes 41 that are deposited upon calibration regions
25, 26, and 27 are predetermined because the amount of the binder
47 employed on the calibration regions 25, 26, and 27 is set at a
predetermined and known level. A comparison may be made between the
intensity levels of the calibration regions 25, 26, and 27 and the
detection line 24 to calculate the amount of analyte 40 present in
the test sample. This comparison step may occur visually, with the
aid of a reading device, or using other techniques.
[0054] Calibration and sample testing may be conducted under
approximately the same conditions at the same time, thus providing
reliable quantitative results, with increased sensitivity. The
assay 20 may also be employed for semi-quantitative detection.
Specifically, when multiple calibration regions 25, 26, and 27
provide a range of signal intensities, the signal intensity of the
detection zone 31 can be compared (e.g., visually) with the
intensity of the calibration regions 25, 26, and 27. Based upon the
intensity range in which the detection zone 31 falls, the general
concentration range for the analyte 40 may be determined. If
desired, the signal ratio between the detection zone 31 and the
calibration regions 25, 26, and 27 may be plotted versus analyte
concentration for a range of known analyte concentrations to
generate a calibration curve, such as shown in FIG. 5. To determine
the quantity of an unknown test sample, the signal ratio may then
be converted to analyte concentration according to the calibration
curve. Moreover, when using fluorescence to determine the amount of
analyte 40 in a test sample, a receiver or a receiving device can
be used to measure the amount of fluorescence generated in the
detection zone 31 and the calibration zone 32, and thereafter make
the appropriate comparison to determine the quantity of analyte in
a given test sample.
[0055] The binders 47 utilized in the calibration zone 32 can
generally be formed from a variety of different materials capable
of forming a chemical or physical bond with the probes 41 and/or
probe conjugates 42. For example, in some embodiments, the binders
47 can contain a biological capture reagent that is the same or
different than the capture reagents 45. Such biological capture
reagents are well known in the art and can include, but are not
limited to, antigens, haptens, antibodies, and complexes
thereof.
[0056] In addition, it may also be desired to utilize various
non-biological materials for the binders 47. For instance, in some
embodiments, the binders 47 can include a polyelectrolyte that can
bind to the probes 41 and/or probe conjugates 42. The
polyelectrolytes can have a net positive or negative charge, as
well as a net charge that is generally neutral. For instance, some
suitable examples of polyelectrolytes having a net positive charge
include, but are not limited to, polylysine (commercially available
from Sigma-Aldrich Chemical Co., Inc. of St. Louis, Mo.),
polyethylenimine; epichlorohydrin-functionalized polyamines and/or
polyamidoamines, such as poly(dimethylamine-co-epichlorohydrin);
polydiallyidimethyl-ammonium chloride; cationic cellulose
derivatives, such as cellulose copolymers or cellulose derivatives
grafted with a quaternary ammonium water-soluble monomer; and the
like. In one particular embodiment, CelQuat.RTM. SC-230M or H-100
(available from National Starch & Chemical, Inc.), which are
cellulosic derivatives containing a quaternary ammonium
water-soluble monomer, can be utilized. Moreover, some suitable
examples of polyelectrolytes having a net negative charge include,
but are not limited to, polyacrylic acids, such as
poly(ethylene-co-methacrylic acid, sodium salt), and the like. It
should also be understood that other polyelectrolytes may also be
utilized in the present invention, such as amphiphilic
polyelectrolytes (i.e., having polar an non-polar portions). For
instance, some examples of suitable amphiphilic polyelectrolytes
include, but are not limited to, poly(styryl-b-N-methyl 2-vinyl
pyridinium iodide) and poly(styryl-b-acrylic acid), both of which
are available from Polymer Source, Inc. of Dorval, Canada.
[0057] Although any polyelectrolyte may generally be used, the
polyelectrolyte selected for a particular application may vary
depending on the nature of the probes/probe conjugates, the porous
membrane, and the like. In particular, the distributed charge of a
polyelectrolyte allows it to bind to substances having an opposite
charge. Thus, for example, polyelectrolytes having a net positive
charge are often better equipped to bind with probes 41 and/or
probe conjugates 42 that are negatively charged, while
polyelectrolytes that have a net negative charge are often better
equipped to bind to probes 41 and/or probe conjugates 42 that are
positively charged. Thus, in such instances, the ionic interaction
between these molecules allows the required binding to occur within
the calibration zone 32. Nevertheless, although ionic interaction
is primarily utilized to achieve the desired binding in the
calibration zone 32, it has also been discovered that
polyelectrolytes can also bind with probes 41 and/or probe
conjugates 42 having a similar charge.
[0058] Because the polyelectrolyte is designed to bind to the
probes 41 and/or probe conjugates 42 to provide a calibration
signal, it is typically desired that the polyelectrolyte be
substantially non-diffusively immobilized on the surface of the
porous membrane 23. Otherwise, the probes 41 and/or probe
conjugates 42 would not be readily detectable by a user seeking to
calibrate the assay. Thus, the polyelectrolytes can be applied to
the porous membrane 23 in such a manner that the polyelectrolytes
do not substantially diffuse into the matrix of the porous membrane
23. In particular, the polyelectrolytes typically form an ionic
and/or covalent bond with functional groups present on the surface
of the porous membrane 23 so that they remain immobilized thereon.
Although not required, the formation of covalent bonds between the
polyelectrolyte and the porous membrane 23 may be desired to more
permanently immobilize the polyelectrolyte thereon.
[0059] For example, in one embodiment, the monomers used to form
the polyelectrolyte are first formed into a solution and then
applied directly to the porous membrane 23. Various solvents (e.g.,
organic solvents, water, etc.) may be utilized to form the
solution. Once applied, the polymerization of the monomers is
initiated using heat, electron beam radiation, free radical
polymerization, and the like. In some instances, as the monomers
polymerize, they form covalent bonds with certain functional groups
of the porous membrane 23, thereby immobilizing the resulting
polyelectrolyte thereon. For example, in one embodiment, an
ethyleneimine monomer can form a covalent bond with a carboxyl
group present on the surface of some porous membranes (e.g.,
nitrocellulose).
[0060] In another embodiment, the polyelectrolyte can be formed
prior to application to the porous membrane 23. If desired, the
polyelectrolyte may first be formed into a solution using organic
solvents, water, and the like. Thereafter, the polyelectrolytic
solution is applied directly to the porous membrane 23 and then
dried. Upon drying, the polyelectrolyte may, as described above,
form an ionic bond with certain functional groups present on the
surface of the porous membrane 23 that have a charge opposite to
the polyelectrolyte. For example, in one embodiment,
positively-charged polyethyleneimine can form an ionic bond with
negatively-charged carboxyl groups present on the surface of some
porous membranes (e.g., nitrocellulose).
[0061] In addition, the polyelectrolyte may also be crosslinked to
the porous membrane 23 using various well-known techniques. For
example, in some embodiments, epichlorohydrin-functionalized
polyamines and/or polyamidoamines can be used as a crosslinkable,
positively-charged polyelectrolyte. Examples of these materials are
described in U.S. Pat. Nos. 3,700,623 to Keim and 3,772,076 to
Keim, 4,537,657 to Keim, which are incorporated herein in their
entirety by reference thereto for all purposes and are believed to
be sold by Hercules, Inc., Wilmington, Del. under the Kymene.TM.
trade designation. For instance, Kymene.TM. 450 and 2064 are
epichlorohydrin-functionalized polyamines and/or polyamidoamines
that contain epoxide rings and quaternary ammonium groups that can
form covalent bonds with carboxyl groups present on certain types
of porous membranes (e.g., nitrocellulose) and crosslink with the
polymer backbone of the porous membrane when cured. In some
embodiments, the crosslinking temperature can range from about
50.degree. C. to about 120.degree. C. and the crosslinking time can
range from about 10 to about 600 seconds.
[0062] Although various techniques for non-diffusively immobilizing
polyelectrolytes on the porous membrane 23 have been described
above, it should be understood that any other technique for
non-diffusively immobilizing polyelectrolytic compounds can be used
in the present invention. In fact, the aforementioned methods are
only intended to be exemplary of the techniques that can be used in
the present invention. For example, in some embodiments, certain
components may be added to the polyelectrolyte solution that can
substantially inhibit the diffusion of such polyelectrolytes into
the matrix of the porous membrane 23.
[0063] Beside the above-mentioned components, the flow-through
assay 20 may also contain additional components. For example,
referring again to FIGS. 1-3, the assay 20 can also contain a
wicking pad 28. The wicking pad 28 generally receives fluid that
has migrated through the entire porous membrane 23. As is well
known in the art, the wicking pad 28 can assist in promoting
capillary action and fluid flow through the membrane 23.
[0064] Although various embodiments of assay configurations have
been described above, it should be understood, that an assay of the
present invention may generally have any configuration desired, and
need not contain all of the components described above. Further,
other well-known components of assays not specifically referred to
herein may also be utilized in the present invention. For example,
various assay configurations are described in U.S. Pat. Nos.
5,395,754 to Lambotte, et al.; 5,670,381 to Jou, et al.; and
6,194,220 to Malick, et al., which are incorporated herein in their
entirety by reference thereto for all purposes. In addition, it
should also be understood that competitive assays may also be
formed according to the present invention. Techniques and
configurations of competitive assays are well known to those
skilled in the art.
[0065] For instance, in one embodiment, the flow-through assay 20
described above and illustrated in FIGS. 1-3 can be easily modified
to form a competitive assay by utilizing probe conjugates 42 that
contain specific binding members 90 identical to the analyte 40. As
a result, the analyte 40 and probe conjugates 42 will compete for a
predetermined number of capture reagents 45 in the detection zone
31. Generally speaking, because the analyte 40 is unbound, it will
move faster through the porous membrane and occupy a greater number
of binding sites in the detection zone 31. Any unbound probe
conjugates 42 will then travel to the calibration zone 32 where
they can bind with the binder 47. The signal thus generated in the
calibration zone 32 can be compared to the signal generated in the
detection zone 31, wherein the relative amount of analyte in the
test sample is inversely proportional to the intensity of the
detection signal and directly proportional to the intensity of the
calibration signal.
[0066] Likewise, in another embodiment, a competitive assay can be
formed by utilizing capture reagents 45 that are identical to the
analyte 40. Thus, in this embodiment, the probe conjugates 42
initially bind to the analyte 40 to form ternary complexes 49. The
unbound probe conjugates 42 and ternary complexes 49 then migrate
to the detection zone 31, where the unbound probe conjugates 42
bind to the capture reagent 45. Any remaining unbound probe
conjugates 42 and the ternary complexes 49 will then migrate to the
calibration zone 32, where they compete for a predetermined amount
of the binder 47. The signal thus generated in the calibration zone
32 can be compared to the signal generated in the detection zone
31, wherein the relative amount of analyte in the test sample is
inversely proportional to the intensity of the detection signal and
directly proportional to the intensity of the calibration
signal.
[0067] The present invention may be better understood with
reference to the following examples.
EXAMPLE 1
[0068] The ability of an internal calibration zone of the present
invention to calibrate a sandwich assay was demonstrated.
Initially, Millipore SX porous membrane samples made of
nitrocellulose were laminated onto corresponding supporting cards
having a length of approximately 30 centimeters. Aqueous solutions
of polyethylenimine were then stripped onto the membrane (1.times.,
10.times., and 100.times. dilution of 7.4% polyethyleneimine
solution) to form three separate calibration lines of different
concentrations. After application of the polyethylenimine, the
membranes were dried for 1 hour at a temperature of 37.degree.
C.
[0069] A cellulosic fiber wicking pad (Millipore Co.) was attached
to one end of the membrane. The other end of the membrane was
inserted into a variety of probe and probe conjugate suspensions.
In particular, the following probes were tested:
1 Particle Size Net Probe Color (microns) Charge Vendor Colored
Blue 0.3 Positive Bang's Carboxylate Laboratory, Inc. Latex Beads
Fluorescent Red 0.5 Positive Molecular Probes, Carboxylate Inc.
Latex Beads
[0070] The assays were also inserted into suspensions of probe
conjugates. In particular, the above-mentioned probes were
conjugated with anti-C-reactive protein monoclonal antibody
(anti-CRP Mab), anti-leutinizing hormone monoclonal antibody
(anti-LH Mab), and anti-prealbumin polyclonal antibody (anti-Pab)
using well-known techniques. For instance, a 100-microliter
suspension of the 0.5-micron fluorescent carboxylated microspheres
(available from Molecular Probes, Inc.) was initially washed two
times with a phosphate buffer saline (PBS) and then re-suspended in
200 microliters of PBS. To the suspension, 5 mg carbodiimide was
added and the mixture was mixed gently for 1 hour. The microspheres
were then washed twice with a borate buffer and then washed. The
microspheres were re-suspended in a 185-microliter borate buffer.
15 microliters of .alpha.-LH monoclonal antibody (9.7 mg/ml) was
then added to the suspension and allowed to react for 3 hours under
gentle mixing. Thereafter, 200 microliters of a 1M ethanolamine
aqueous solution was added to the reaction mixture for 20 minutes.
The microspheres were then washed two times using PBS and stored in
PBS.
[0071] The probe and probe conjugate suspensions contained water
and 1.6% polyoxyethylene sorbitan monolaurate (a nonionic
surfactant available from Sigma-Aldrich under the name "Tween 20").
The resulting concentration of the probes ranged from 0.001-5 mg/ml
and the concentration of the probe conjugates range from 0.2-10
mg/ml.
[0072] After about 5 minutes, the stripped calibration lines were
then observed to determine if the probes/probes conjugates were
visually detectable. The line containing the 1.times. diluted
solution exhibited the highest signal intensity, while the line
containing the 100.times. diluted exhibited the lowest signal
intensity.
EXAMPLE 2
[0073] The ability of an internal calibration zone of the present
invention to calibrate a half-dipstick sandwich assay was
demonstrated. Initially, Millipore SX porous membrane samples made
of nitrocellulose were laminated onto corresponding supporting
cards having a length of approximately 30 centimeters. 7.4%
polyethylenimine aqueous solutions (1.times., 10.times., and
100.times. diluted samples) were then stripped onto the Millipore
SX membrane to form three calibration lines of different
concentrations.
[0074] Anti-C-reactive protein (anti-CRP) monoclonal antibody (Mab
A5804, 1 mg/ml, obtained from BiosPacific, Inc.) was stripped onto
the membrane to form a detection line. The membrane was dried for 1
hour at a temperature of 37.degree. C. A cellulosic fiber wicking
pad (Millipore Co.) was attached to one end of the membrane. The
laminated membrane was then cut into small half dipsticks.
[0075] The end of the membrane opposite to the wicking pad was
applied to a test well that contained C-reactive protein (CRP),
Tween 20, anti-CRP Mab conjugated to blue latex beads (anti-CRP
Mab-beads), and water. The mixture in the well migrated along the
half dipstick to the detection line, calibration lines, and wicking
pad of the dipstick.
[0076] The CRP analyte was captured by the anti-CRP Mab-beads at
the detection line, while any remaining unbound anti-CRP Mab-beads
were captured by the calibration lines. Thus, after about 5
minutes, one blue line was observed on the detection line, while
three blue lines were observed on the calibration lines. The line
containing the 1.times. diluted solution exhibited the highest
signal intensity, while the line containing the 100.times. diluted
exhibited the lowest signal intensity.
EXAMPLE b 3
[0077] The ability of an internal calibration zone of the present
invention to calibrate a half-dipstick sandwich assay was
demonstrated. Initially, HF 09002 porous membrane samples made of
nitrocellulose were laminated onto corresponding supporting cards
having a length of approximately 30 centimeters. 0.14% (calibration
#1), 0.64% (calibration #2), and 1.4% (calibration #3)
polyethylenimine aqueous solutions (1.times., 10.times., and
100.times. diluted samples) were then stripped onto the membrane to
form three calibration lines of different concentrations.
[0078] Anti-C-reactive protein (anti-CRP) monoclonal antibody (Mab
A5804, 1 mg/ml, obtained from BiosPacific, Inc.) was stripped onto
the membrane to form a detection line. The membrane was dried for 1
hour at a temperature of 37.degree. C. A cellulosic fiber wicking
pad (Millipore Co.) was attached to one end of the membrane. The
laminated membrane was then cut into small half dipsticks.
[0079] The end of the membrane opposite to the wicking pad was
applied to three test wells that contained Tween 20, an excess
amount of anti-CRP Mab conjugated to blue latex beads (anti-CRP
Mab-beads), and water. The test wells also contained different
concentrations of C-reactive protein (CRP). In particular, the
solutions contained 0 nanograms (ng), 0.54 ng, 5.4 ng, and 54 ng of
CRP, respectively.
[0080] The mixture in the wells migrated along each half dipstick
to the detection line, calibration lines, and wicking pad of the
dipstick. The CRP analyte was captured by the anti-CRP Mab-beads at
the detection line, while any remaining unbound anti-CRP Mab-beads
were captured by the calibration lines. Thus, for each sample, one
blue line was observed on the detection line, while three blue
lines were observed on the calibration lines. The line containing
the 1.4% polyethyleneimine solution exhibited the highest signal
intensity, while the line containing the 0.14% polyethyleneimine
solution exhibited the lowest signal intensity. Based on analysis,
it was determined that calibration line #1 contained 0.54 ng of
CRP, calibration line #2 contained 5.4 ng of CRP, and calibration
line #3 contained 54 ng of CRP.
[0081] Thus, when an unknown test sample is tested, CRP
concentration can be visually determined by comparing the detection
line with the three calibration lines. In particular, when the
detection line intensity is visually determined to have an
intensity between the intensity of calibration lines #2 and #3, the
CRP concentration is between 5.4 and 54 ng. Likewise, when the
detection line intensity is visually determined to have an
intensity between the intensity of calibration lines #1 and #2, the
CRP concentration is between 0.54 and 5.4 ng. Further, a detection
line having an intensity less than the intensity of the calibration
line #1 has a CRP concentration less than 0.54 ng, while a
detection line having an intensity greater than the intensity of
the calibration line #3 has a CRP concentration greater than 54
ng.
[0082] The calibration line intensity can also be measured by an
instrument, such as an assay reader. For example, a calibration
curve (shown in FIG. 6) was developed using the line intensities of
calibration lines #1-#3 and their CRP concentrations. The
mathematical equation generated by the calibration curve can be
inputted into an instrument that is able to read intensity for
detection of CRP in a test sample.
EXAMPLE 4
[0083] The ability of an internal calibration zone of the present
invention to calibrate a half-dipstick sandwich assay was
demonstrated. Initially, SHF 075 porous membrane samples made of
nitrocellulose were laminated onto corresponding supporting cards
having a length of approximately 30 centimeters. Varying
concentrations of CelQuat.RTM. H-100 (a cellulosic derivative
available from National Starch & Chemical, Inc.) were stripped
onto the membrane to form three calibration lines having different
concentrations. In particular, the concentrations utilized were 2.5
parts CelQuat.RTM. H-100 per million of the solution (ppm)
(calibration #1), 5 ppm (calibration #2), and 20 ppm (calibration
#3).
[0084] Anti-.beta.-utilizing hormone (anti-.beta.-LH) monoclonal
antibody (Mab, 1 mg/ml, obtained from Fitzgerald Industries Intl.,
Inc.) was stripped onto the membrane to form a detection line. The
membrane was dried for 1 hour at a temperature of 37.degree. C. A
cellulosic fiber wicking pad (Millipore Co.) was attached to one
end of the membrane. The laminated membrane was then cut into small
half dipsticks.
[0085] The end of the membrane opposite to the wicking pad was
applied to a test well that contained Tween 20,
anti-.alpha.-leutinizing hormone (anti-.alpha.-LH) Mab conjugated
to blue latex beads (anti-.alpha.-LH Mab-beads), and water. The
mixture also contained varying concentrations of .beta.-leutinizing
hormone (LH). In particular, the concentrations tested were 0 ppm,
20 ppm, and 100 ppm, which corresponded to solutions containing 0
nanograms (ng), 20 ng, and 100 ng of LH, respectively.
[0086] The mixture in the wells migrated along each half dipstick
to the detection line, calibration lines, and wicking pad of the
dipstick. The LH analyte was captured by the anti-.alpha.-LH
Mab-beads at the detection line, while any remaining unbound
anti-.alpha.-LH Mab-beads were captured by the calibration lines.
Thus, for each sample, one blue line was observed on the detection
line, while three blue lines were observed on the calibration
lines. The line containing the 20 ppm CelQuat.RTM. solution
exhibited the highest signal intensity, while the line containing
the 2.5 ppm CelQuat.RTM. solution exhibited the lowest signal
intensity. Based on analysis, it was determined that calibration
line #1 contained 20 ng of LH and calibration line #3 contained 100
ng of LH. Moreover, using an instrument capable of reading line
intensity, it was determined that calibration lines #1, #2, and #3
had a line intensity of 1, 2, and 4, respectively.
[0087] A calibration curve (shown in FIG. 7) was then developed
using the line intensities of calibration lines #1-#3 and their LH
concentrations. The mathematical equation generated by the
calibration curve was then inputted into an instrument. A test
sample containing an unknown level of LH was then applied to a
membrane formed as described above. Using the instrument, it was
determined that the intensity of the detection signal was about
1.5. As a result, it was determined that the concentration of the
LH in the unknown test sample was about 36 ng.
EXAMPLE 5
[0088] The ability of an internal calibration zone of the present
invention to calibrate a half-dipstick competitive assay was
demonstrated. Initially, HF 120 porous membrane samples made of
nitrocellulose were laminated onto corresponding supporting cards
having a length of approximately 30 centimeters. Varying
concentrations of CelQuat.RTM. H-100 (a cellulosic derivative
available from National Starch & Chemical, Inc.) were stripped
onto the membrane to form three calibration lines having different
concentrations. In particular, the concentrations utilized were 2.5
parts CelQuat.RTM. H-100 per million of the solution (ppm)
(calibration #1), 5 ppm (calibration #2), and 20 ppm (calibration
#3).
[0089] Pre-albumin (1 mg/ml, obtained from Biogenesis, Inc.) was
stripped onto the membrane to form a detection line. The membrane
was dried for 1 hour at a temperature of 37.degree. C. A cellulosic
fiber wicking pad (Millipore Co.) was attached to one end of the
membrane. The laminated membrane was then cut into small half
dipsticks.
[0090] The end of the membrane opposite to the wicking pad was
applied to a test well that contained 30 microliters of 2% Tween
20, 10 microliters of red fluorescent microspheres conjugated with
anti-prealbumin polyclonal antibody, and water. The mixture also
contained varying concentrations of pre-albumin in phosphate buffer
saline. In particular, the concentrations tested were 0 micrograms,
75 micrograms and 125 micrograms.
[0091] It was observed that the three calibration lines turned
different intensities of red, where the calibration line #3 has the
highest and line #1 has the lowest intensity. The intensity of the
detection line in this competitive assay was inversely proportional
to the test pre-albumin concentration. When there was no
pre-albumin, the conjugate was captured by the detection line and
the three calibration lines. With an increased amount of
pre-albumin antigen, the detection line became less intense.
[0092] The line intensity was then read by a fluorescence reader
and used to generate a calibration curve. The results are shown
below in Table 1.
2TABLE 1 Calibration for Pre-albumin Detection with Line Intensity
Signal Intensity Calibration #1 1 1 1 Calibration #2 10 10 10
Calibration #3 20 20 20 Detection Line 20 10 0
[0093] For the detection line, the signal intensity values of 20,
10, and 0 was determined to correspond to pre-albumin amounts of 0
micrograms, 75 micrograms, and 125 micrograms, respectively. A
calibration curve generated from this data is also shown in FIG. 8.
Using this calibration curve, the presence and/or amount of an
unknown level of pre-albumin can be determined.
[0094] While the invention has been described in detail with
respect to the specific embodiments thereof, it will be appreciated
that those skilled in the art, upon attaining an understanding of
the foregoing, may readily conceive of alterations to, variations
of, and equivalents to these embodiments. Accordingly, the scope of
the present invention should be assessed as that of the appended
claims and any equivalents thereto.
* * * * *