Water-soluble cationic polypyrrole, poly(N-(4-butyl-(1-methylimidazole)) pyrrole bromide) (PNBMIP-Br), was synthesized and applied for base pair mismatched oligonucleotides detection. Interactions between PNBMIP-Br and a series of oligonucleotides, including ss-DNA and base pair mismatched ds-DNA were studied by fluorometric spectra, circular dichroism spectra and voltammetric detection. The results showed that the electrostatic attraction and fluorescence resonance energy transfer of PNBMIP-Br/DNA complexes resulted in an amplification and effective recognition of the fluorescence signals. The results of cyclic voltammograms indicate that voltammetric detection is an effective method to distinguish ss-DNA and ds-DNA. (c) 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 1600-1605