Patent ID: 7361489

Claim:
A method for detecting a target nucleic acid in a nucleic acid containing sample comprising: (a) contacting the nucleic acid containing sample with a circular oligonucleotide probe under conditions that allow hybridization between complementary sequences in the target nucleic acid and the circular oligonucleotide probe; (b) adding at least one forward primer comprising a sequence complementary to a portion of the circular oligonucleotide probe, under conditions where the forward primer is extended around the circular oligonucleotide probe for multiple revolutions to form a single-stranded DNA molecule comprising repeating units complementary to the sequence of the circular probe; (c) adding at least one oligonucleotide primer pair comprising a first primer and a second primer, wherein (i) the first primer of the pair comprises (A) a first sequence on its 3′ end that is substantially identical to a portion of the circular oligonucleotide probe, (B) a second sequence that is complementary to the second primer of the pair, and (C) a signal generating moiety selected from the group consisting of a fluorescent agent and a chemiluminescent agent; (ii) the second primer of the pair comprises (A) a sequence that is complementary to the first primer and (B) a moiety capable of quenching, masking or inhibiting the activity of the signal generating moiety when located adjacent to, or in close proximity to the signal generating moiety; and (iii) when the first primer and the second primer are bound to one another, a signal generated by the signal generating moiety is inhibited; (d) adding at least one reverse primer comprising a sequence that is substantially identical to a portion of the circular oligonucleotide probe and wherein the forward primer, reverse primer, and the first primer and the second primer of the oligonucleotide primer pair are not identical; (e) adding a DNA polymerase having strand displacement activity and lacking 3′ to 5′ exonuclease activity; and (f) amplifying the circular oligonucleotide probe using ramification-extension amplification method (RAM) thus producing an amplification product comprising a sequence that is substantially identical to a sequence in the circular probe, and separating the signal generating moiety selected from the group consisting of a fluorescent agent and a chemiluminescent agent from the quenching, masking or inhibitory moiety by the action of the DNA polymerase having strand displacement activity and lacking 3′ to 5′ exonuclease activity during the amplification method, wherein detection of the signal indicates the presence of the target nucleic acid in the nucleic acid containing sample.