When an oxy-peptide nucleic acid that contains pyrrolidine rings (pyrrolidine-based oxy-PNA = POPNA) hybridized with its complementary DNA, a fluorophore, DiSC(2)(5), bound specifically to the hybrid in aqueous solution. Free DiSC(2)(5) did not fluoresce by itself, but the bound DiSC(2)(5) showed strong fluorescence. The fluorescence was observed only on a fully-matched POPNA-DNA hybrid, but not on hybrids with even single mismatches. This finding provides bases for highly sensitive and highly specific detection of single nucleotide polymorphisms.