Background of the Invention
Membrane-based test devices, particularly devices used
in diagnostic medicine, employ a variety of internal and external calibrators to
provide a qualitative or a quantitative result for an analyte of interest in a test
solution. One type of membrane-based test device is a lateral flow assay.
In general, lateral flow assays are membrane-based test
devices in which a sample that is suspected of containing the analyte of interest
is placed at or near one end of a membrane strip. The sample is carried to the opposite
end of the membrane strip by a liquid phase that traverses the membrane strip by
capillary action. While traversing the membrane strip, the analyte in the test sample,
if any, encounters one or more "capture" reagents with which it may react to produce
a detectable signal.
Home use assay devices such as pregnancy tests and the
like are now well established. Home use assays may be intended to detect physiological
changes in the human body, with the objective of promoting the health and well being
of an individual. Consumers are becoming increasingly health conscious, and it is
a significant advantage if the consumer is capable of monitoring his or her own
bodily functions, including levels of hormones and the like.
There are many different assays that are indicative of
physiological changes in the human body. Furthermore, there are many different assay
devices that operate by reading an assay strip or test sample. Some devices use
fluorescence emission, and others use light reflectance.
United States Patent No. 6,235,241 B1 to Catt et al.
("the Catt patent") is directed to an assay result reader used in conjunction
with an assay device. A commercially available device similar to that shown in the
Catt patent is known as a UNIPATH CLEAR PLAN Easy® Fertility Monitor. This
device is shown in Figure 1 herein, and comprises a fertility monitoring
device 21 with a removable hand held cover 22, which fits into a receiver
23 upon the housing 25. Bodily fluids are applied to the test strip
24, and the test strip 24 may be placed into the receiver
23, where the test strip 24 receives light that shines through a window
26 upon the test strip 24. Then, the level of reflected light is analyzed
to give a result.
One of the problems with fertility monitoring devices as
described is that they are not capable of providing a high degree of sensitivity,
in many Instances. That is, some analytes need to be monitored for medical purposes,
but do not require a high degree of sensitivity or a sophisticated instrument to
detect accurately and precisely the levels of analyte. Many currently available
home use reading devices have a low signal to noise ratio, which may be caused in
part by the undesirable introduction of excess amounts of stray or ambient light
into the viewing window. In conducting precise measurements using a reflectance-based
regime, it is critical that the amount of stray ambient light be reduced or eliminated
to achieve a high degree of sensitivity. It is therefore highly desirable to maximize
the signal to noise ratio, and increase the sensitivity of such reading devices.
Another reading device for home use is known as an ACCUCHECK®
Blood Glucose Meter manufactured and distributed by Boehringer Mannheim Diagnostics
of Indianapolis, Indiana 46250. The ACCUCHECK® device is a reflectance-based
instrument designed for home use in checking blood glucose levels. The instrument
does not employ a lateral flow assay. Instead, a user is instructed to place a drop
of blood upon a test pad. The reflectance sensor portion of the instrument contains
a removable holder, with two rectangular windows.
EP-A-0 308 770
discloses a reagent strip handling mechanism which includes the features
in the preamble to claims 1 and 13.
What is needed in the industry is a sensitive reading device
designed for lateral flow assay test strips. A reading device that provides an efficient
and reliable means for quickly placing a test strip into position to receive a reading
or result, while avoiding excess ambient and stray light would be desirable. A reading
device providing high sensitivity for detecting hormones and the like would be desirable.
A reading device having a window that achieves a high degree of efficiency in the
transmission and reflectance of light would be useful.
Summary of the Invention
According to the present invention there is provided a
lateral flow assay reading device as claimed in claim 1 and a method as claimed
in claim 13. The reading device is configured for detecting an assay result from
a membrane strip, in which the result is revealed by the binding of a detectable
analyte within a detection zone along the membrane strip. The assay reading device
comprises a housing and a receiving port within the housing. The receiving port
includes a light barrier structure, and admits a membrane strip directly from the
outside of the housing. That is, a membrane strip is inserted into the receiving
port. The receiving port is configured for minimizing the introduction of stray
or ambient light into the reading device.
A reading mechanism is also provided which includes a source
of electromagnetic radiation, and one or more sensors capable of detecting the Intensity
of reflected electromagnetic radiation. The source of radiation and the sensors
are positioned within the reading mechanism so that when the membrane strip is admitted
into the receiving port, the radiation impacts the detection zone upon the membrane
strip prior to impacting the sensor.
In another embodiment of the invention, a test kit. Including
a lateral flow assay reading device as claimed in claim 1 and a porous liquid permeable
membrane strip is provided.
In yet another embodiment of the invention, a system for
conducting a lateral flow assays is be provided for detecting the quantity of analyte
that resides in a test liquid. The system includes a probe configured for generating
a detectable signal, and a membrane strip designed for mobilizing a test liquid.
The membrane strip includes a detection zone. Furthermore, a reading device as previously
described is employed, with a receiving port and light barrier structure configured
for minimizing stray light Into the reader. An assay result having increased sensitivity
is achieved by way of the invention.
Brief Description of the Drawings
A full and enabling disclosure of this invention, including
the best mode shown to one of ordinary skill in the art, is set forth in this specification.
The following Figures illustrate the invention:
Detailed Description of the Invention
- Figure 1 is a perspective view of the CLEAR PLAN EASY® Fertility
Monitor previously discussed;
- Figure 2 is a perspective view of one embodiment of the reading device
of the invention, showing the light barrier structure and receiving port;
- Figure 3 shows a perspective view of the reading device in which the
receiving port 45 has been exploded upwards to reveal details;
- Figure 3a Is a view of the underside of the top plate, showing interaction
of the pressure plate with the top plate in the receiving port;
- Figure 4 shows a cross sectional view of the receiving port in one embodiment
of the invention, as taken along line 4-4 of Figure 2;
- Figure 5 shows an alternate embodiment of the reading device of the invention
having a channel on the upper surface of the reading device configured to receive
a membrane test strip;
- Figure 5a shows a cross sectional view of the membrane strip receiving
portion of the reading device as taken along lines 5a-5a in Figure
- Figure 5b shows a design layout for the electronics of the reading device,
including a microcontroller, LCD display, and the like;
- Figure 6 shows a closer view of the membrane strip receiving portion
of the embodiment previously shown in Figure 5, showing one particular application
in which the membrane strip includes a nub that interlocks into one or more notches;
- Figure 7 shows a cross sectional view of the structure shown in Figure
6, as taken along lines 7-7 in Figure 6.
Reference now will be made to the 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 as a 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 this invention without departing from the scope 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 cover such modifications and variations as come within
the scope of the appended claims and their equivalents.
In the invention, an optical reflectance meter or reading
device is provided. The reading device may be used with lateral flow assays to provide
quantitative results. The metering device may be designed to provide improved sensitivity
and increased accuracy. The method and system of the invention may serve as a more
accurate and sensitive alternative to direct visual examination of a membrane assay
The reading device of the invention may include various
components including a light source such as a light emitting diode ("LED") or laser,
a light beam modulator, mirror, lenses, photo diodes, sample holders and other optional
components, as further described herein. In any event, the sample holder provides
for easy insertion of membrane test strips, with a minimal amount of pass through
of ambient or stray light, thus reducing the noise level. A reading device having
an improved signal to noise ratio Is provided, with greater sensitivity. The sample
holder may include a mechanical design having a spring-loaded member. In some applications,
at least two different stop positions are provided for the same membrane test strip
wherein the first stop position may be used to provide a reference reading, and
a second stop position may be used to read actual samples in a detection area or
a detection zone.
One embodiment of the invention is further illustrated
in Figure 2, wherein a reading device 40 receives a membrane strip
41 into a receiving port 45 to provide a result. A light barrier structure
28 also is shown. A detection zone 42 upon the membrane strip
41 is located some distance from a reference zone 43, which gives
a base line reference or calibration reading. In the particular embodiment shown,
the detection zone 42 is provided towards-the outside, while the reference
zone 43 is towards the inside, but it should be recognized that the positions
of these respective zones could be reversed from that which is shown in Figure
The reading device 40 may include a housing exterior
44, and on/off switch 49, and housing interior (not shown in Figure
2). In Figure 2, an LCD display 60 is shown.
In Figure 3, the light barrier structure
28 is shown in a view with the components exploded upwards from the housing
exterior 44 of the reading device 40. The top plate 50 is also
shown. The device shown in Figure 3 corresponds to the device shown In Figure
2, and is essentially the same embodiment. The receiving port 45 is
bounded on its lower edge by bottom plate 56, and on its upper edge by top
plate 50. Within the receiving port 45 there is a pressure plate
51, under which the membrane strip 41 is inserted. The pressure plate
51 is held by spring 52 in a resilient engagement with the membrane
strip 41 (not shown in Figure 3). The membrane strip 41 is
held over aperture 54, which happens to be circular in Figure 3. However,
the aperture could be of many different shapes and sizes, and most preferably approximates
the size and/or shape of the zone of interest upon the membrane strip
41 that is to be examined. The channel 53 forms the conduit through
which the membrane strip 41 is inserted. Screws 55a-d holds the top
plate 50 down upon the housing 44.
In Figure 3a, the underside of top plate
50 is shown, revealing a recess 58. Within the recess 58 resides
the pressure plate 51, which is held in springing engagement by spring
52. Also shown is a light-absorbing member 57, which rests upon the
top or upper surface of membrane strip 41 (see Figure 2). The light-absorbing
member 57 acts as a low reflectance specimen in contact with the aperture
54 that allows the instrument to be calibrated to eliminate the effects of
internal reflections within the sensor housing. In practice, such calibration can
be performed automatically by the microprocessor when power is first applied to
the instrument. Furthermore, the light absorbing member 57 absorbs any light
which is transmitted completely through the membrane strip 41, so that such
light is not reflected back downward towards the sensor 92 (see Figure
5a). In this way, the sensitivity and signal to noise ratio of the
reading device 40 is maximized.
The light-absorbing member 57 may include almost
any type of material that is capable of absorbing light, such as a black or dark
colored flocking, plastic, metal, felt, or other material. For example, materials
that are used in the photography arts that are known to absorb light could be employed.
Such materials may be flexible and/or conformable, and may be comprised of felt.
There is no particular size or shape that is preferred for a light-absorbing member
57, but it is important that the light-absorbing member 57 cover completely
the area under which the membrane strip 41 is being impacted by light from
its underside. One optional feature of the light-absorbing member 57 would
be to provide a flexible or conformable form fit to the test strip, by using felt
or drapable material.
Figure 4 shows a cross section of the light barrier
structure 28 with receiving port 45 as shown in lines 4-4 of
Figure 2. The receiving port 45 comprises a pressure plate
51 that fits between a top plate 50 and a bottom plate 56.
A membrane strip 41 is inserted below the pressure plate 51, where
the detection zone 42 of the membrane strip 41 may be placed directly
over a light pathway 59. Light generated by a light source (now shown in
Figure 4) such as a light emitting diode (LED) passes upwards along arrow
59a and is reflected downward from membrane strip 41 along arrow
59b as seen in Figure 4.
The internal light emitting and sensing components of the
reading device shown in Figures 2-4 is essentially the same as that shown
in Figures 5-5a.
It is important to the sensitivity of the reading device
40 that the light aperture located immediately below the membrane strip
41 is of a size that approximates the size of detection zone 42 upon
the membrane strip 41. In other applications, the aperture (not shown in
Figure 4) may be slightly larger than the detection zone 42. In some cases,
the aperture could be about 1.3 or even 1.8 times larger in area than the detection
zone 42. However, it has been found that the closer the aperture corresponds
to the size of the detection zone 42 upon the membrane strip 41, the higher
the signal to noise ratio that can be achieved by the reading device 40,
and the more sensitive will be the reading device 40. Furthermore, the membrane
strip 41 also may include a reference zone 43 at another location
upon the membrane strip 41. The reference zone 43 may be placed over
the light pathway 59 in order to obtain a reference reading or a calibration
of the reading device 40. Then, in a second step, the detection zone
42 may be placed over the light pathway 59 to obtain the sample reading.
A spring 52 is shown in cross section above the light-absorbing member
57, which fits just above the membrane strip 41. The light-absorbing
member 57 is capable of absorbing light that may undesirably enter the receiving
port 45 from outside. Furthermore, the light-absorbing member 57 is
capable of absorbing light that may proceed through the light pathway
59, and be transmitted completely through the membrane strip 41. This
prevents reflection downward of stray light, improving sensitivity.
One alternate embodiment of the invention is shown In Figure
5, A light barrier structure 81 is provided, below an LCD display
74. The light barrier structure is bounded from above by top plate
72, and from below by bottom plate 78. A reading device
65 is comprised of a housing 73 having a receiving port 64 bounded
upon the top by a hood 66. The receiving port 64 consists in part
of a channel 68 that runs vertically as shown in Figure 5. An aperture
69, (which in Figure 5 happens to be in the shape of a rectangle)
is located In the bottom of the channel 68. A first notch 70 and a
second notch 71 are provided as locating points to receive a membrane strip
having nub 77 which will be seen in Figure 5a. Screws 67a and
67b hold the hood 66 down upon the top plate 72. The function
of the hood 66 is to reduce the amount of ambient light that impacts near
the aperture 69, increasing the sensitivity of the reading device
65, and improving the signal to noise ratio of results obtained. An on/off
switch 75 is shown near the right side of the housing 73.
Figure 5a is a basic schematic taken in cross section
along lines 5a-5a of Figure 5 showing the basic internal architecture
of the reading device 65 employed in the invention. Screws 67a-b hold
down a top plate 72 upon bottom plate 78, and also function to hold
hood 66 to plate 72. In cross section, one can see a light-absorbing member
80 that is positioned above membrane strip 76. A nub 77 fits
into first notch 70 to register the membrane strip 76 in the appropriate
position to receive light 91 from a light emitting diode (LED)
90. The light 91 travels to the membrane strip 76, and then
is reflected downward along light pathway 93 to a sensor 92. In some
applications, the sensor 92 is a diode. A housing 73 is also seen,
and may include other components that are not shown in Figure 5a.
A basic schematic diagram of a reading device
65 is shown in Figure 5b. In Figure 5b, an LCD display
74 having 16 characters is shown on the right side of Figure 5b. The
LCD display 74 is connected to a micro controller 95. The microcontroller
95 directs the activities of the reading device 65, and regulates
the light energy output of the light emitting diode (LED) 90, as shown in
the lower left portion of Figure 5b.
Likewise, a photo diode 92 receives light energy,
and converts such energy to signals that are transmitted to a preamplifier
79, and then to the microcontroller 95. Eventually, the data output
or result of an assay is illuminated on the LCD display 74, shown in Figure
The wavelength of the illumination radiation should be
chosen to fall within the wavelength range over which the detector (photodiode)
has appreciable responsivity (typically 400 nm to 1000 nm for a silicon photodiode.
Furthermore, the wavelength of the illuminating radiation should be chosen to be
near the maximal absorption wavelength of the detectable material used as the label
in the lateral flow assay.
It is generally accepted that the detectable material used
as a label or probe in the assay is one that will interact with light in the visible
or near visible range, by absorption. For example, if the probe is a substance that
appears blue to the naked eye when concentrated, the ideal electromagnetic radiation
would likely be yellow. Particulate direct labels, including metallic and gold sols,
non-metallic elemental sols (i.e. selenium or carbon) and colored latex (polystyrene)
particles are suitable examples, as further described herein.
The source of light represented by the light emitting diode
90 may be comprised entirely of commercially available components. Suitable examples
are commercially available LED's, preferably chosen to provide a suitable wavelength
of light that is strongly absorbed by the detectable material concentrated in the
detection zone 42. If desired, an array of LED's, which are energized in turn, could
Figure 6 shows a more detailed view of the top plate 72
of one embodiment of the invention, which is seen in Figure 5. A membrane strip
76 having a nub 77 is registered into first notch 70 as shown. In some embodiments
of the invention, the nub 77 registers with the first notch 70 to take a reading
from a reference zone 83 on the membrane strip 76. Then, once a reference or calibration
reading is obtained, the membrane strip 76 may be lifted up and the position changed
so that the nub 77 is integrated into the second notch 71. A detection zone 82 is
shown on membrane strip 76. The detection zone 82 would then be placed over the
aperture (aperture is not shown in Figure 6) to obtain the test sample reading.
The channel 68 into which the membrane strip 76 is placed is shown in Figure 6.
Figure 7 shows a cross sectional view along lines 7-7 of
Figure 6. Screws 67a-b holds the hood 66, and a top plate 72 to a bottom plate 78.
A membrane strip 76 is provided in the channel 68, so that the nub 77 is fitted
into first notch 70. The light-absorbing member 80 is positioned over the membrane
strip 76 in Figure 7. The light-absorbing member 80 may include those materials
described for component 57, including almost any type of material that is capable
of absorbing light, such as a black or dark colored flocking, felt, plastic, metal,
or other material.
The membrane-based device of the invention comprises several
components, including a membrane, a sample pad, a conjugate pad and a wicking pad,
or a combination of these items. The membrane typically includes at least two zones,
that is, one or more detection zone(s) and one or more control or reference zone(s).
A sample pad contacts one end of the conjugate pad.
One design of the assay device includes a liquid sample
flow direction having a sample pad, conjugate pad, detection zone, and a pad, typically
provided in that order from one end to the other end. In general, the wicking pad
assists in promoting capillary action and fluid flow one-way through the membrane
strip. The pad "pulls" the liquid containing the analyte along the membrane from
one end of the membrane to another end of the membrane.
Probes used in the invention may comprise beads or particles.
Such beads or particles may be comprised of latex, or other suitable material, as
further described herein. In some applications, plain particles are used, while
other applications may employ particles with capture reagents and/or antibodies
conjugated upon the outer surface of the particle. The particles are typically colored
with a dye that is visible to the eye, or to a detection apparatus. In other embodiments,
the particles may include light absorbing materials such as metal sols, gold, or
silver particles. Gold nanoparticles have been found to be suitable in some applications.
In one application of the invention a system for conducting
a lateral flow assay is provided to detect the quantity of analyte that resides
in a test liquid. The system comprises employing a probe analyte conjugate complex
that is capable of generating a detectable signal. Furthermore, a membrane strip
is provided and configured for mobilizing a test liquid which contains both a probe
and an analyte conjugate. The membrane strip comprises a detection zone, in which
the detection zone has deposited thereon a first capture reagent. The first capture
reagent is immobilized upon the detection zone, and is configured for attaching
to probe analyte conjugates to immobilize the probe analyte conjugates, thereby
forming a sandwich complex within the detection zone.
A detection line may contain an immobilized second capture
reagent (i.e.: antibody or other conjugating species), which serves to immobilize
the unbound probes by binding to form a control probe complex (i.e.: immobile species)
on a capture line. When significant numbers of the probe are immobilized in this
way, a visibly distinctive line appears at one or more detection lines on the membrane
strip. The control line may be embedded with a predetermined amount of second capture
In some instances, a comparison is made between the intensity
levels of the calibration or control lines (or zone), or some other reference standard,
and the detection line of the membrane strip, to calculate the amount of analyte
present in a sample. This comparison step is accomplished with the reading device
further described herein.
The membrane strip employed in the assay may be a cellulose
ester, with nitrocellulose usually providing good results, but the invention is
not limited to such compositions for the membrane strip.
It is to be understood that the invention can be configured
for detecting a broad range of analytes, including therapeutic drugs, drugs of abuse,
hormones, vitamins, glucose proteins (including antibodies of all classes), peptides,
steroids, bacteria or bacterial infection, fungi, viruses, parasites, components
or products of bacteria, allergens of all types, antigens of all types, products
or components of normal or malignant cells, and the like.
The following analytes are examples of analytes that may
be tested using the present invention: T.sub.4, T.sub.3, digoxin, hCG, insulin,
theophylline, luteinizing hormone, organisms causing or associated with various
disease states, such as streptococcus pyogenes (group A), Herpes Simplex I and II,
cytomegalovirus, chlamydiae, and others known in the art.
United States Patent No. 4,366,241
(Tom et al.) lists at columns 19-26 a variety of potential analytes of
interest that are members of an immunologic pair, including proteins, blood clotting
factors, hormones, microorganisms, pharmaceutical agents, and vitamins. Any of these
analytes are suitable for use as the analyte in present invention.
Other examples of preferred ligands or analytes that may
be detected include the following: human bone alkaline phosphatase antigen (HBAPAg);
human chorionic gonadotropin (hCG); human luteinizing hormone (hLH); human follicle
stimulating hormone (hFSH); creatine phosphokinase MB isoenzyme; ferritin; carcinoembryonic
antigen (CEA); prostate specific antigen (PSA); CA-549 (a breast cancer antigen);
hepatitis B surface antigen (HBsAg); hepatitis B surface antibody (HBsAb); hepatitis
B core antigen (HBcAg); hepatitis B core antibody (HBcAb); hepatitis A virus antibody;
an antigen of human immunodeficiency virus HIV I, such as gp 120, p66, p41, p31,
p24 or p17; the p41 antigen of HIV II; and the respective antiligand (preferably
a monoclonal antibody) to any one of the above ligands. The HIV antigens are described
more fully in
United States Pat. No. 5,120,662
Gelderblom et al., Virology 156: 171-176 1987
As used herein, the term "probe" refers generally to a
structure that is capable of carrying an analyte in a lateral flow assay to a detection
area or zone, which may or may not be in the form of a particle or microparticle.
Furthermore, as used herein the term "probe-conjugate" refers to a species that
is capable of carrying an analyte in a lateral flow assay to form a probe-conjugate
complex, which binds a first capture reagent in a detection zone of a membrane strip
to become a "sandwich complex" in the detection zone.
As used herein, the term "microparticle" is a more specific
reference to a particular type of probe, and may include any beads or probes to
which an antibody may be bound, whether covalently, or non-covalently such as by
adsorption. An additional requirement for some particles that are used in a quantitative
assay is that the particle contributes a signal, usually light absorption, which
would cause the zone in which the particles were located to have a different signal
than the rest of the membrane,
Optionally, metallic particles or metal could be used as
the probe in the invention. These particles are commercially available as microspheres
of substantially uniform diameter from companies such as British Biocell International,
of Cardiff, United Kingdom.
By the phrase "membrane" or "membrane strip" as used herein
is meant a test device or strip that employs a membrane and one or more reagents
to detect the concentration of an analyte of interest in a test solution, preferably
an aqueous test solution. At least one of the reagents associated with the membrane
device is a binding partner of the analyte of interest.
Latex microparticles for use In the present invention are
commercially available as polymeric microspheres of substantially, uniform diameter
(hereinafter "polymeric microspheres"), such as from Bangs Laboratories of Carmel,
Indiana, or Dow Chemical Co. of Midland, Michigan. Although any polymeric microsphere
that is capable of adsorbing or of being covalently bound to a binding partner may
be used in the present invention, the polymeric microspheres typically are composed
of one or more members of the group consisting of 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.
The underivatized polymeric microspheres, such as polystyrene,
are hydrophobic and passively adsorb other hydrophobic molecules, including most
proteins and antibodies. Techniques for adsorbing a protein or polypeptide on a
hydrophobic particle are provided in the publication by
Cantarero, et al. "The Absorption Characteristics of Proteins for Polystyrene
and Their Significance in Solid Phase Immunoassays," Analytical Biochemistry 105,
Bangs, "Latex Immunoassays," J. Clin. Immunoassay, 13 127-131 (1980)
Various procedures for adsorbing molecules on polymeric
microspheres are also described, in general terms, in
Bangs, L. B., "Uniform Latex Particles," presented at a workshop at the 41st
National Meeting, Amer. Assoc. Clin. Chem., 1989
, and available in printed form from Seragen Diagnostics Inc., Indianapolis,
Ind.; or Galloway, R. J., "Development of Microparticle Tests and Immunoassays,
" i.e., Seradyn Inc. of Indiana
The test solution may be a component of a biological fluid,
such as extracted, diluted, or concentrated from a plant or animal, preferably a
mammal, more preferably a human. Especially preferred biological fluids are serum,
plasma, urine, ascites fluid, peritoneal fluid, amniotic fluid, synovial fluid,
cerebrospinal fluid and the like, or a concentrate or dilution thereof.
In the practice of the invention, calibration and sample
testing may be conducted under essentially exactly the same conditions at the same
time, thus providing highly reliable quantitative results, and increased sensitivity.
The invention also may be employed for semi-quantitative
detection. As the multiple control lines provide a range of signal intensities,
the signal intensity of the detection line can be compared (i.e. such as for example,
visually) with the control lines. Based on the intensity range the detection line
falls, the possible concentration range for the analyte may be determined. The probes
may be latex beads labeled with any signal generating species or the labeled latex
beads further conjugated with antibodies.
It is understood by one of ordinary skill in the art that
the present discussion is a description of exemplary embodiments only, and is not
intended as limiting the broader aspects of the present invention, which broader
aspects are embodied in the exemplary constructions. The scope of the invention
is defined by the appended claims.