Amplification of assay reporters by nucleic acid replication

Chemistry: molecular biology and microbiology – Measuring or testing process involving enzymes or... – Involving nucleic acid

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435 5, 435 912, 435 71, 435 72, 435 79, 536 243, 536 2432, 536 2433, 536 266, C12Q 168, C12Q 170, C07H 2104, G01N 3353

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059855487

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

This invention relates to a method for the amplified detection of an analyte in fluid, wherein amplification is achieved by replicating a target nucleic acid sequence which has been immobilized in response to analyte.


BACKGROUND OF THE INVENTION

The introduction of immunoassays in the 1960s and 1970s greatly increased the number of analytes amenable to precise and accurate measurement. Radio immunoassays (RIAs) and immunoradiometric (IRMA) assays utilize radioisotopic labeling of either an antibody or a competing antigen to measure an analyte. Detection systems based on enzymes or fluorescent labels were then developed as an alternative to isotopic detection systems. D. L. Bates, Trends in Biotechnology, 5(7), 204 (1987), describes one such method based upon enzyme amplification. In this method a secondary enzyme system is coupled to a primary enzyme label, for example, the primary enzyme can be linked catalytically to an additional system such as a substrate cycle or an enzyme cascade. Enzyme amplification results from the coupling of catalytic processes, either by direct modification or by interaction with the product of the controlling enzyme.
U.S. Pat. No. 4,668,621 describes utilization of an enzyme-linked coagulation assay (ELCA) in an amplified immunoassay using a clotting cascade to enhance sensitivity. The process involves clot formation due to thrombin activated fibrin formation from soluble fibrinogen and labeled solubilized fibrinogen. Amplification of the amount of reportable ligand attached to solid phase is obtained only by combining use of clotting factor conjugates with subsequent coagulation cascade reactions.
Substrate/cofactor cycling is another variation of enzyme-mediated amplification, and is based on the cycling of a cofactor or substrate which is generated by a primary enzyme label. The product of the primary enzyme is a catalytic activator of an amplifier cycle which responds in proportion to the concentration of substrate and hence the concentration of the enzyme label. An example of this type of substrate cycling system is described in U.S. Pat. No. 4,745,054.
Vary et al., Clin Chem., 32, 1696 (1986) describes an enzyme amplification method suited to nucleic acid detection. This method is a strand displacement assay which uses the unique ability of a polynucleotide to act as a substrate label which can be released by a phosphorylase.
Bobrow et al., J. of Immunol. Methods, 125, 279 (1989) discloses a method to improve detection or quantitation of an analyte by catalyzed reporter deposition. Amplification of the detector signal is achieved by activating a conjugate consisting of a detectably labeled substrate specific for the enzyme system, wherein said conjugate then reacts with the analyte-dependent enzyme activation system to form an activated conjugate which deposits wherever receptor for the conjugate is immobilized.
Nucleotide hybridization assays have been developed as a means for detection of specific nucleic acid sequences. U.S. Pat. No. 4,882,269 discloses an amplified nucleic acid hybridization assay in which a target nucleic acid is contacted with a complementary primary probe having a polymeric tail. A plurality of second signal-generating probes capable of binding to the polymeric tail are added to achieve amplified detection of the target nucleic acid. Variations of this methodology are disclosed in PCT Application WO 89/03891 and European Patent Application 204510, which describe hybridization assays in which amplifier or multimer oligonucleotides are hybridized to a single-stranded nucleic acid unit which has been bound to the targeted nucleic acid segment. Signal amplification is accomplished by hybridizing signal-emitting nucleic acid bases to these amplifier and multimer strands. In all of these disclosures amplification is achieved by mechanisms which immobilize additional sites for attachment of signal-emitting probes.
In contrast, the present invention utilizes a fundamentally different concept in achieving signal amplification. In

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