Immunochromatography-assisted device

Details Immunochromatography-assisted device Immunochromatography-assisted device

1998-09-16

2001-02-27

Chin, Christopher L. (Department: 1641)

Chemistry: analytical and immunological testing

Involving an insoluble carrier for immobilizing immunochemicals

C435S007100, C435S007500, C435S007920, C435S970000, C436S501000, C436S514000, C436S523000, C436S536000, C436S532000, C436S169000, C436S810000, C436S823000, C422S051000, C422S051000, C422S051000, C422S067000

Reexamination Certificate

active

06194225

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an extracorporeal diagnostic drug or a portable diagnostic device for detecting microorganisms in water and a trace amount of markers in the humor. More specifically, the present invention is intended to improve the performance of an immunochromatography-assisted device which facilitates simple and rapid measurements of such substances at small-scale clinics with no installation of analytical equipment and by the subjects studied.
Extracorporeal diagnostic drugs for detecting a trace amount of markers in the body fluids such as urine, sweat and blood have recognized importance as the major aids for clinical diagnosis and home care medicine. Immunochromatography is a basic technology for extracorporeal diagnostic drugs which best use specific reaction of an antibody. Among them, the most typical and widely applied immunochromatography-assisted device in the market as a general medicine is pregnancy testing drug. When pregnant, women secret human chorionic gonadotropin (hCG) from the placenta, which is later excreted in urine. Upon introduction of a female urine sample, a pregnancy tester determines whether the urine is positive or negative for pregnancy usually within 3 minutes or so, facilitating easy evaluation of pregnancy by any non-skilled ordinary person. A representative structure of such immunochromatography-assisted device is disclosed in the U.S. Pat. No. 5,602,040, for example.
In the following, the structure and operation of a most simple immunochromatography-assisted device will be described, taking the pregnancy tester as an example.
FIG. 1
illustrates the structure of a porous carrier for use in a typical immunochromatography-assisted device. The most widely used porous carrier is a sheet of nitrocellulose because the material readily allows fixation of an antibody. However, if the porous carrier
1
is formed with this material entirely, the flow rate of a sample reduces prominently. Therefore, it is preferable for the carrier to be formed with nitrocellulose only for a determining part and with a glass filter which allows a sample to flow more rapidly for the rest. A sample introducing part
2
located at one end of the carrier is made of a porous carrier such as glass filter that inherently absorbs a sample rapidly but is weak in retaining the sample, thus permitting a rapid and smooth passage of the sample toward a reaction-related part. If the porous carrier
1
is to be accommodated in a hollow case, the sample introducing part
2
is formed relatively long so as to partially expose it from the case to allow direct introduction of a urine sample into the sample introducing part
2
. Alternatively, if the entire sample introducing part
2
is to be accommodated in the case, the case should have an aperture through which a sample is introduced into the sample introducing part.
A labelled part
3
is formed by impregnating a glass filter with an aqueous solution of an anti-hCG antibody which is adsorbed on colloidal gold or colored latex, followed by freezing and drying it. A determining part
4
is produced by dropping an aqueous solution of another antibody on a nitrocellulose sheet in an arbitrary shape, followed by drying and rinsing it. The very strong non-specific adsorption property of nitrocellulose ensures tight adhesion of the antibody to the nitrocellulose sheet. After fixation of the antibody, the nitrocellulose sheet may be surface-treated with bovine serum albumin (hereinafter abbreviated to “BSA”), for example, in order to prevent coloring of the background due to the non-specific adsorption property of nitrocellulose during antigen-antibody reaction for detection. This surface treatment is called blocking. A fluid absorbing part
5
located at the other end of the porous carrier is formed with a material such as glass filter which is excellent in fluid absorption and fluid absorbing capacity, for the purpose of rapid absorption of excess sample.
As a sample, female urine is introduced into the sample introducing part
2
in an amount as determined based on the shape of the immunochromatography-assisted device (normally 0.1 to 2 ml). The sample passes through the determining part
4
via the labelled part
3
toward the fluid absorbing part
5
. When the sample passes around the labelled part
3
, the labelled antibody which is carried on the labelled part
3
dissolves in water in the sample and is transferred toward the determining part
4
together with the sample. Subsequently, the labelled antibody dissolved in water arrives at the determining part
4
. At that time, if the urine is positive for pregnancy, the labelled antibody reacts with the fixed antibody present at the determining part
4
via an antigen in the urine sample based on the specific antigen-antibody binding reaction, which causes the determining part
4
to be colored, If negative, such reaction would not occur and the labelled antibody uneventfully passes the determining part
4
to be absorbed in the fluid absorbing part. In this way, the presence or absence of an antigen in an aqueous sample solution can be determined.
In such immunochromatography-assisted device as described above, coloring of the part other than the antibody in a fixed phase present at the determining part (background coloring) and coloring of the antibody in the fixed phase in the absence of an analyte (blank coloring) reduce the S/N ratio during detection and become a factor for causing a malfunction. Background coloring is caused by a hydrophobic bond between a visualized antibody in a mobile phase and the porous carrier. On the other hand, blank coloring is caused by electrical interaction between the negative-charged antibody in the mobile phase and the positive-charged antibody in the fixed phase.
Normal samples for use in detection are free of such substance as surfactant, pH buffer or the like that offsets a hydrophobic bond and electrical interaction. Therefore, the conventional immunochromatography-assisted device has drawbacks of development of not a little background coloring and occasional development of blank coloring. These drawbacks are particularly prominent when the antibody in the mobile phase is visualized with an organic dye.
Such immunochromatography-assisted device can be improved for its detectability by increasing the amount or concentration of the labelled antibody to be carried on the labelled part. However, this method disadvantageously increases the time until visual confirmation of background decoloring by sufficient depletion of the labelled antibody. In other words, an improvement in detectability contradicts a reduction in reaction time. If the antigen contained in a sample is over excess, the overall antibody in the mobile phase has to participate in antigen-antibody reaction, causing depletion of the mobile phase antibody at the determining part, which results in a malfunction of the device such that the amount of antigen is small seemingly. This is why a dynamic range in which reaction takes place essentially is preset in immunochromatography. The dynamic range for developing reaction is generally 50 to 100,000 IU/L with respect to the pregnancy tester.
Moreover, if an immunochromatography-assisted device is configured so as to ensure movement of a sample toward the determining part via the labelled part, hCG reacts with the labelled antibody before it reacts with the fixed antibody. Such structure is disadvantageous in detecting a low concentration of antigen as an analyte.
BRIEF SUMMARY OF THE INVENTION
In view of the above-mentioned drawbacks of the prior art device, the object of the present invention is to provide an immunochromatography-assisted device facilitating accurate and rapid detection of an antigen contained in a liquid sample by eliminating coloring of the background and blank coloring which may cause a malfunction during detection.
Another object of the present invention is to provide an epoch-making immunochromatography-assisted device for realizing improved detectability and reduced re

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