Patent Application
20110229913
The present invention relates to a method for amplifying a signal in an immunochromatographic assay for high-sensitive detection of an analyte and an immunochromatographic kit using the method, and more particularly, to a method for amplifying a signal in an immunochromatographic assay for high-sensitive detection of an analyte and an immunochromatographic kit using the method, which amplifies a signal by controlling a flow rate of indicators by discrimination between the size of a first indicator and the size of a second indicator binding to the first indicator in a sandwich assay method.
An immunochromatographic assay is a method that can test an analyte qualitatively and quantitatively within a short time by using the property that biological materials or chemical materials bind specifically to each other. Particularly, a sandwich-type immunoassay method is well known as immobilizing a first antibody, which is specific to a first epitope of an analyte to be tested for presence and concentration, to a solid support body and using a second antibody specific to a second epitope of the analyte.
An assay strip or an immunoassay kit, which is an assembly of the assay strip into a housing, is generally used as a kit for the immunochromatographic assay. When a fluid containing an analyte is applied to one side of a porous strip, the fluid flows due to a capillary phenomenon and an assay target binds to an immobilized antibody and an antibody containing an indicator, thus completing a sandwich-type assay method.
Generally, in an immunochromatographic kit, an antibody is immobilized to a membrane where a fluid sample can flow due to a capillary phenomenon, a sample pad and a conjugate pad are provided at the upstream side of the membrane, and an absorbing pad is connected to the downstream side of the membrane. The sample pad absorbs a liquid sample containing an analyte and provides a uniform flow, and an indicator, to which an antibody capable of binding selectively to the analyte is bound, is dried at the conjugate pad. An immobilized antibody binding selectively to an analyte and a material capable of binding to an antibody immobilized to an indicator are immobilized at the different positions of the membrane to form a detection site and a control site, respectively. An antibody immobilized to the membrane capable of binding selectively to the analyte and an antibody immobilized to the indicator may be configured to bind to the analyte in a sandwich type. The absorbing pad is formed of a material capable of absorbing a liquid sample. In the immunochromatographic kit, when a liquid sample containing an analyte is dropped on a sample pad, an indicator—antibody having a selectivity to the analyte and an antibody immobilized to a membrane bind to analyte in a sandwich type, thus forming a band that can be identified with the naked eye at the position of the membrane where the antibody is immobilized.
An immunochromatographic signal amplification method is disclosed in the related art that binds a primary conjugate body and an antigen, additionally binds a secondary conjugate body thereto, and they finally bind to an antibody immobilized to a membrane. However, because the detection sensitivity of the related art immunochromatographic method is low, it is difficult to detect a sample that requires a higher sensitivity.
Thus, the present inventors have completed the present invention by detecting the fact that the sensitivity of signal amplification increases when an antigen and a primary conjugate body bind to each other and they bind to an immobilized antibody in a sandwich reaction and then a secondary conjugate body binds thereto on an immunochromatography. In particular, the present invention performs signal amplification through one-time sample injection without separate mechanical control or artificial step-by-step reaction.
An aspect of the present invention provides a method for amplifying a signal in an immunochromatographic assay.
Another aspect of the present invention provides an immunochromatographic kit with an increased sensitivity by using the signal amplification method.
According to an aspect of the present invention, there is provided a method for amplifying a signal in an immunochromatographic assay, including: binding a primary conjugate body, which has a first antibody binding specifically to a first epitope of an analyte, a connector, and a first indicator to which the first antibody and the connector are bound, to the analyte; binding the analyte bound to the primary conjugate body to an immobilized second antibody binding specifically to a second epitope of the analyte; and binding a secondary conjugate body, which has a third antibody binding specifically to the connector of the primary conjugate body and a second indicator to which the third antibody is bound, to the connector of the primary conjugate body, wherein the primary conjugate body is disposed nearer to the immobilized second antibody than the secondary conjugate body, and the particle of the second indicator is larger than the particle of the first indicator, so that the secondary conjugate body reaches the immobilized second antibody later than the primary conjugate body.
According to another aspect of the present invention, there is provided a method for amplifying a signal in an immunochromatographic assay, including: binding a primary conjugate body, which has a first antibody binding specifically to a first epitope of an analyte and a first indicator to which the first antibody is bound, to the analyte; binding the analyte bound to the primary conjugate body to an immobilized second antibody binding specifically to a second epitope of the analyte; and binding a secondary conjugate body, which has a third antibody binding specifically to the first antibody of the primary conjugate body and a second indicator to which the third antibody is bound, to the first antibody of the primary conjugate body, wherein the primary conjugate body is disposed nearer to the immobilized second antibody than the secondary conjugate body, and the particle of the second indicator is larger than the particle of the first indicator, so that the secondary conjugate body reaches the immobilized second antibody later than the primary conjugate body.
According to another aspect of the present invention, there is provided an immunochromatographic kit including: a sample pad to which a liquid sample containing an analyte is applied; a conjugate pad including a primary conjugate body having a first antibody binding specifically to a first epitope of an analyte, a connector, and a first indicator to which the first antibody and the connector are bound, and a secondary conjugate body having a third antibody binding specifically to the connector of the primary conjugate body and a second indicator to which the third antibody is bound, wherein the primary conjugate body is disposed nearer to an immobilized second antibody than the secondary conjugate body and the second indicator is larger than the first indicator so that the secondary conjugate body reaches the immobilized second antibody later than the primary conjugate body; a membrane including a detection site immobilizing thereto the second antibody binding specifically to a second epitope of the analyte to which the primary conjugate body is bound, and a control site for error detection; and an absorbing pad absorbing the liquid sample by a capillary phenomenon.
According to another aspect of the present invention, there is provided an immunochromatographic kit including: a sample pad to which a liquid sample containing an analyte is applied; a conjugate pad including a primary conjugate body having a first antibody binding specifically to a first epitope of an analyte and a first indicator to which the first antibody is bound, and a secondary conjugate body having a third antibody binding specifically to the first antibody of the primary conjugate body and a second indicator to which the third antibody is bound, wherein the primary conjugate body is disposed nearer to an immobilized second antibody than the secondary conjugate body and the second indicator is larger than the first indicator so that the secondary conjugate body reaches the immobilized second antibody later than the primary conjugate body; a membrane including a detection site immobilizing thereto the second antibody binding specifically to a second epitope of the analyte to which the primary conjugate body is bound, and a control site for error detection; and an absorbing pad absorbing the liquid sample by a capillary phenomenon.
The signal amplification method of the present invention immobilizes a primary conjugate body to a capture antibody together with an antigen and then binds a secondary conjugate body to the primary conjugate body, thereby providing a good signal amplification effect. Also, the use of the signal amplification method makes it possible to fabricate an immunochromatographic kit with an increased sensitivity.
Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
In this specification, the term ‘connector’ represents a material that binds specifically to a third antibody by an antigen-antibody reaction so that a secondary conjugate body can bind to a primary conjugate body. In the present invention, the primary conjugate body contains a first antibody, a connector, and a first indicator. However, if the first antibody can bind to a third antibody of a secondary conjugate body, the primary conjugate body may not contain the connector. Herein, the primary conjugate body is immobilized to a capture antibody while flowing through a strip after binding to an antigen. In the present invention, the secondary conjugate body contains a second indicator and a third antibody specific to the connector of the primary conjugate body. Herein, the third antibody binds specifically to a connector of the primary conjugate body to amplify a signal. However, if the third antibody can bind specifically to the first antibody and thus the primary conjugate body does not contain the connector, the third antibody binds to the first antibody of the primary conjugate body to amplify a signal.
In a signal amplification method of the present invention, a primary conjugate body containing a first antibody and a first indicator binds to an antigen in an immunochromatograph and then binds to a second antibody (i.e., an immobilized capture antibody) in a sandwich reaction and then a secondary conjugate body containing a third antibody and a second indicator binds to the primary conjugate body to amplify a signal. In particular, the signal amplification method of the present invention increases the sensitivity of the signal amplification by controlling the flow rate of the secondary conjugate body by controlling the indicator size of the secondary conjugate body to be larger than the indicator size of the primary conjugate body.
A process of an immunochromatographic signal amplification method according to the present invention will be described below in detail with reference to the accompanying drawings. The primary conjugate body 8, which has the first antibody 1 capable of binding specifically to a first epitope of the analyte 4, the connector 2, and the first indicator 3 to which the first antibody 1 and the connector 2 are bound, binds to the analyte 4; while flowing through a strip, the analyte 4 bound to the primary conjugate body 8 binds to the immobilized second antibody 5 binding specifically to a second epitope of the analyte 4; and then the secondary conjugate body 9, which has the third antibody 6 binding specifically to the connector 2 of the primary conjugate body 8, and the second indicator 7 to which the third antibody 6 is bound, binds to the connector 2 of the primary conjugate body 8. Herein, the primary conjugate body 8 is disposed nearer to the immobilized second antibody 5 than the secondary conjugate body 9, and the particle of the second indicator 7 is larger than the particle of the first indicator 3. Thus, the secondary conjugate body 9 reaches the immobilized second antibody 5 later than the primary conjugate body 8, thereby amplifying an immunochromatographic signal.
The connector 2 included in the primary conjugate body 8 may be a bovine serum albumin (BSA) or a human serum albumin (HAS), and the third antibody 6 may be an anti-BSA or an anti-HSA. However, the connector 2 and the third antibody 6 are not limited thereto. For example, the connector 2 and the third antibody 6 may comprise any substances which react selectively each other such as a peptide-antibody binding and a biotin-avidin binding that enables the secondary conjugate body 9 to bind to the primary conjugate body 8, while not to bind to the analyte 4. For example, according to the present invention, a serum albumin (specifically a BSA) may be used as the connector 2 and the secondary conjugate body 9 may be produced using another serum albumin that is not used to produce the primary conjugate body 8. However, because the connector 2 is included in the primary conjugate body 8 to enable the secondary conjugate body 9 to bind to the primary conjugate body 8, the connector 2 may not be included if the third antibody 6 and the first antibody 1 can bind specifically to each other. The case where the third antibody 6 and the first antibody 1 can bind specifically to each other includes the case where the third antibody 6 recognizes the first antibody 1 as an antigen thus bind to the first antibody 1. As described above, the present invention may include any structure that enables the secondary conjugate body 9 to bind to the primary conjugate body 8.
The analyte 4 capable of being detected by the method of the present invention may be any analyte that can bind to the first antibody 1 and the second antibody 5 by an immunoreaction, i.e., an antigen-antibody reaction to form a sandwich-type immune complex. Examples of the analyte 4 include proteins, deoxyribo nucleic acids (DNAs), environmental pollutants including environmental hormones, disease factors such as viruses and food poisoning bacteria, and pathogenic poisonous substances.
In the present invention, the antibody and the antigen may be any substances that can bind specifically to the analyte 4 by an antigen-antibody reaction. If the analyte 4 is an antibody, a substance binding specifically to the antibody may be used as an antigen. According to the analyte 4, the antigen and antibody may be any well-known antigen and antibody.
In the present invention, examples of a coloring substance generating an ‘indicator’ signal include a color former, a fluor, and a colored latex particle. For example, the coloring substance may be a gold colloid or a quantum dot. The first indicator 3 of the primary conjugate body 8 and the second indicator 7 of the secondary conjugate body 9 may be different from each other. However, in consideration of the problems in fabrication, the first indicator 3 and the second indicator 7 may be identical to each other.
As can be seen from an embodiment 3 and
An immunochromatographic kit of the present invention uses the above signal amplification method. The immunochromatographic kit of the present invention includes: a sample pad to which a liquid sample containing an analyte is applied; a conjugate pad including a primary conjugate body having a first antibody binding specifically to a first epitope of an analyte, a connector, and a first indicator to which the first antibody and the connector are bound, and a secondary conjugate body having a third antibody binding specifically to the connector of the primary conjugate body and a second indicator to which the third antibody is bound, wherein the primary conjugate body is disposed nearer to an immobilized second antibody than the secondary conjugate body and the second indicator is larger than the first indicator so that the secondary conjugate body reaches the immobilized second antibody later than the primary conjugate body; a membrane including a detection site immobilizing thereto the second antibody binding specifically to a second epitope of the analyte to which the primary conjugate body is bound, and a control site for error detection; and an absorbing pad absorbing the liquid sample by a capillary phenomenon.
The pad used to fabricate the immunochromatographic kit of the present invention may be formed of any natural porous material or any synthetic porous material. For example, the pad may be formed of a nitrocellulose.
The sample pad 10 is a portion that first absorbs a liquid sample containing an analyte. One end of the membrane 12 may be used as the sample pad 10, or a separate member may be used as the sample pad 10. The sample pad 10 absorbs a sample containing an analyte, and moves the analyte to the conjugate pad 11 by a capillary phenomenon.
The conjugate pad 11 has a secondary conjugate body and a primary conjugate body that are in a dry state. When the conjugate pad 11 absorbs a liquid sample containing an analyte, the secondary conjugate body and the primary conjugate body become fluid and move to the membrane 12. The primary conjugate body is disposed nearer to an immobilized second antibody than the secondary conjugate body, and the particle of the second indicator is produced to be larger than the particle of the first indicator, so that the secondary conjugate body develops on the strip slower than the primary conjugate body.
As can be seen from the embodiment 3 and
As illustrated in
It can be seen from an embodiment 4 that the signal amplification effect is enhanced when the contact between a primary conjugate body and a secondary conjugate body are further controlled by separating the primary conjugate body and the secondary conjugate body by means of two separate conjugate pads. In result, the signal amplification effect is good when the first conjugate pad and the secondary conjugate body are separated by means of two conjugate pads (see
The membrane 12 may be formed of a substance coated with nitrocellulose particles. The membrane 12 may be formed of any substance that can maintain a sufficient reaction time between an antigen and an antibody at a lateral flow rate of about 180 sec/cm and thus can secure the fluidity of a liquid sample. The membrane 12 includes: a detection site immobilizing thereto a second antibody bonding specifically to a second region of an analyte to which a primary conjugate body is bound; and a control site detecting the presence of a reaction due to an error as a contrast group thereof. The detection site shows the result for determination of a test result. The control site is configured to detect an error of a capture antibody and a gold nano-particle conjugate body, and is used to detect whether mobile substances react to the detection site/the control site without an error.
The absorbing pad 15 may be any pad that can sufficiently absorb post-reaction residuals.
Hereinafter, the present invention will be described in more detail with reference to embodiments. These embodiments are merely exemplary, and the present invention is not limited by the embodiments.
1. Composition of Primary Conjugate Body
A 0.1 mL 0.1 M borate buffer (pH 8.5) was added into a 1 mL gold nano-particle colloid solution (BBInternational, 10 nm), a 1 mg/mL first antibody 10 uL was added thereinto, and they were reacted for 30 minutes. After the reaction, a 0.1 ml solution obtained by dissolving a 1% (w/v) bovine serum albumin (BSA) (Sigma) as a connector in a phosphate buffered saline (PBS) (Gibco) was added thereinto, and they were reacted at the normal temperatures for 15 minutes. After the reaction, it was centrifuged at 10,000 rpm at 4° C. for 20 minutes to disperse in a 1 mL BSA (Sigma) solution dissolved in a 10 mM PBS at a 1 mg/mL concentration. The centrifuging/dispersing process was repeated once again, and it was again centrifuged to disperse in a 1 mL PBS, thereby fabricating a primary conjugate body.
The first antibody may be 4T21, 560 (HyTest) for immunoassay of a troponin I, and may be M012607 (Fitzgerald) for immunoassay of a myoglobin.
2. Composition of Secondary Conjugate Body
A 0.1 mL 0.1 M borate buffer (pH 8.5) was added into a 1 mL gold nano-particle colloid solution (BBInternational, 10, 20, 40, 60 nm), an anti-BSA antibody (Genetex) 10 uL as a 1 mg/mL third antibody was added thereinto, and they were reacted for 30 minutes. After the reaction, a 0.1 ml solution obtained by dissolving a 1% (w/v) human serum albumin (HSA) (Sigma) in a distilled water was added thereinto, and they were reacted at the normal temperatures for 15 minutes. After the reaction, it was centrifuged at 10,000 rpm at 4° C. for 20 minutes to disperse in a 1 mL solution dissolved in a PBS at a 1 mg/mL HSA concentration. The centrifuging/dispersing process was repeated twice, thereby fabricating a secondary conjugate body.
1. Method of Fabricating Immunochromatograph
A nitrocellulose membrane (Millipore, 180 sec) and an absorbing pad (Millipore) were adhered to a plastic pad (Millipore). Thereafter, using a dispenser system (Zeta Co.), a capture antibody (second antibody) 1 mg/mL solution dissolved in a PBS and a goat anti-mouse IgG antibody (Sigma, M8642) 1 mg/mL solution dissolved in a PBS as a contrast group were scribed on the membrane at a speed of 6 cm/sec, thereby forming a detection site and a control line. After the membrane was dried, it was cut by a cutter at intervals of 3 mm.
The second antibody, i.e., the capture antibody, may be a troponin capture antibody (Hytest) for immunoassay of a troponin I, and may be a myoglobin capture antibody M09983110 (Fitzgerald) for immunoassay of a myoglobin.
After a sample pad (Millipore, C068) was immersed in a 0.5% Tween 20, a 5% Sucrose, a 0.05% Dextran, a 5% sodium azide aqueous solution, it was dried and cut to about 10×3 mm.
As illustrated in
2. Method of Fabricating Conjugate Pad
Conjugate pads were fabricated by discrimination between a first conjugate pad and a second conjugate pad. For the primary and second conjugate pads, a GFC (Millipore Co.) was cut to 5×3 mm, and they were dried after being coated with the primary conjugate body and the secondary conjugate body of the embodiment 1 by 5 μL.
A primary conjugate body using gold nano-particles with a diameter of 10 nm or 20 nm, and gold nano-particles forming a secondary conjugate body were fabricated in various sizes (10, 20, 40, 60 nm), and the signal amplification effects depending on the gold nano-particle sizes were observed.
The immunochromatographic kit was immersed in a 96 well plate where a serum (Linear chemicals, Cromatest) 70 μL dissolving a troponin I at a predetermined concentration was immersed, and a measurement was performed. The result of the case of the primary conjugate body having a nano-particle diameter of 10 nm is illustrated in Table 1 and
As a result of detection of the measurement result after 10 minutes on the basis of the K/S values (=(1−Rd)2/2Rd; Rd: Relative Diffusion Reflectance, K: Absorption Coefficient of Sample, S: Scattering Coefficient), the sensitivity of a combination of a primary conjugate body with a 10 nm gold nano-particle size and a secondary conjugate body with a 40 nm gold nano-particle size increased highest in comparison with those of the other combinations, and the sensitivity increased two or more times of a log value (about 100 times) in comparison with the case of not amplifying a signal.
(1) Fabrication of Conjugate Pad
A conjugate pad was fabricated in the following way in order to observe the signal amplification effect of the case where a conjugate pad is fabricated such that a primary conjugate body and a secondary conjugate body do not contact each other. An immunochromatograph not enhancing was fabricated as a contrast group. Herein, a conjugate pad was cut to 5×3 mm by means of a GFC pad (Millipore), and then it was dried after being coated with a primary conjugate body fabricated using an antibody corresponding to the analyte in the embodiment 1.
1) For fabrication of a conjugate pad where a primary conjugate body and a secondary conjugate body do contact, two conjugate pads (GFC, Millipore GFC203000) were cut to 5×3 mm, and then they were dried after being respectively coated the primary conjugate body and the secondary conjugate body fabricated according to the embodiment 1. If the conjugate pads are entirely coated, there is a possibility that the overlaps between the two conjugate pads may contact each other so that the primary conjugate body and the secondary conjugate body are mixed during the inflow of a liquid sample containing an analyte.
2) For fabrication of a conjugate pad where a primary conjugate body and a secondary conjugate body do not contact, using the primary conjugate body and the secondary conjugate body fabricated according to the embodiment 1, the primary conjugate body was coated to 5 μL according to the method of the embodiment 2 and were dried to fabricate a first conjugate pad. Using a Fusion 5™ pad (Whatman Co.) as a second conjugate pad, the secondary conjugate body was formed in a line to fabricate an immunochromatograph, and an experiment was performed. The structure of the immunochromatographic kit using the conjugate pads is identical to that of
(2) Troponin I Assay
The so-fabricated immunochromatograph and the contrast group immunochromatograph were immersed in a 96 well plate where a plasma (Linear chemicals, Cromatest) 70 μL dissolving a troponin I antigen at a predetermined concentration was immersed, and a measurement was performed.
As a result of detection of the measurement result after 10 minutes, as can be seen from
(3) Myoglobin Assay
In the above method, the myoglobin of the case of not amplifying a signal and the myoglobin of the case of using the Fusion 5™ pad as the second conjugate pad to amplify a signal were assayed. The first antibody of the primary conjugate body and the second antibody, i.e., the capture antibody were anti-myoglobin antigens of Fitzgerald product.
As a result of detection of the measurement result after 10 minutes, as can be seen from
While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/KR2008/007049 | 11/28/2008 | WO | 00 | 5/27/2011 |
