Abstract: This invention provides a method for detecting a target nucleic acid which comprises forming a reaction mixture which includes the target nucleic acid and an amount of a complementary single-stranded nucleic acid probe which is greater than the target molecule, under conditions which allow the probe and the target nucleic acid to hybridize to each other and form a double stranded target-probe complex, nicking the hybridized probe at least once within a predetermined sequence so as to form at least two probe fragments hybridized to the target nucleic acid, resulting in the probe fragments to become single-stranded and allowing the target nucleic acid to become hybridized to another probe; and identifying probe fragments, thereby detecting the target nucleic acid. This invention also provides a method for detecting a target nucleic acid.