A method for assessing a sample for target nucleic acid, said method comprising: (a) contacting said sample with a probe nucleic acid, the probe nucleic acid comprising: (i) an amplifying restriction endonuclease and (ii) a nucleotide sequence complementary to a sequence of said target nucleic acid; under conditions wherein, if said target nucleic acid is present in said sample, at least a portion of said target nucleic acid hybridizes to at least a portion of said probe nucleic acid to form a double-stranded portion of nucleic acid comprising a restriction endonuclease cut site, (b) contacting said double-stranded portion of nucleic acid with a recognition restriction endonuclease having the ability to cut said double-stranded portion of nucleic acid at said restriction endonuclease cut site under conditions wherein said recognition restriction endonuclease cleaves said double-stranded portion of nucleic acid at said restriction endonuclease cut site, thereby separating a portion of said probe nucleic acid comprising said amplifying restriction endonuclease from at least another portion of said probe nucleic acid, (c) contacting said portion of said probe nucleic acid comprising said amplifying restriction endonuclease with a signal expansion nucleic acid, the signal expansion nucleic acid comprising: (i) a label, (ii) said amplifying restriction endonuclease, and (iii) a double-stranded portion of nucleic acid comprising a restriction endonuclease cut site of said amplifying restriction endonuclease; under conditions wherein said amplifying restriction endonuclease cleaves said signal expansion nucleic acid at said restriction endonuclease cut site of said amplifying restriction endonuclease, thereby separating a portion of said signal expansion nucleic acid comprising said label and said amplifying restriction endonuclease from at least another portion of said signal expansion nucleic acid, and (d) determining the presence or absence of said portion of said signal expansion nucleic acid, wherein the presence of said portion of said signal expansion nucleic acid indicates that said sample contains said target nucleic acid, and wherein the absence of said portion of said signal expansion nucleic acid indicates that said sample does not contain said target nucleic acid. (a) contacting said sample with a probe nucleic acid, the probe nucleic acid comprising: (i) an amplifying restriction endonuclease and (ii) a nucleotide sequence complementary to a sequence of said target nucleic acid; under conditions wherein, if said target nucleic acid is present in said sample, at least a portion of said target nucleic acid hybridizes to at least a portion of said probe nucleic acid to form a double-stranded portion of nucleic acid comprising a restriction endonuclease cut site, (b) contacting said double-stranded portion of nucleic acid with a recognition restriction endonuclease having the ability to cut said double-stranded portion of nucleic acid at said restriction endonuclease cut site under conditions wherein said recognition restriction endonuclease cleaves said double-stranded portion of nucleic acid at said restriction endonuclease cut site, thereby separating a portion of said probe nucleic acid comprising said amplifying restriction endonuclease from at least another portion of said probe nucleic acid, (c) contacting said portion of said probe nucleic acid comprising said amplifying restriction endonuclease with a signal expansion nucleic acid, the signal expansion nucleic acid comprising: (i) a label, (ii) said amplifying restriction endonuclease, and (iii) a double-stranded portion of nucleic acid comprising a restriction endonuclease cut site of said amplifying restriction endonuclease; under conditions wherein said amplifying restriction endonuclease cleaves said signal expansion nucleic acid at said restriction endonuclease cut site of said amplifying restriction endonuclease, thereby separating a portion of said signal expansion nucleic acid comprising said label and said amplifying restriction endonuclease from at least another portion of said signal expansion nucleic acid, and (d) determining the presence or absence of said portion of said signal expansion nucleic acid, wherein the presence of said portion of said signal expansion nucleic acid indicates that said sample contains said target nucleic acid, and wherein the absence of said portion of said signal expansion nucleic acid indicates that said sample does not contain said target nucleic acid.