The electrostatic complexes of double-stranded deoxyribonucleic acid (dsDNA) and a cationic conjugated polyelectrolyte, poly{(4,4′-(1,4-phenylene)bis(2,6-diphenylpyridinium))-co-para-biphenylene ditosylates} (PPT), were investigated by spectral methods. The binding constant of PPT with calf thymus DNA (ctDNA) is estimated to be 9.3 × 105 M−1, which was determined by UV-vis spectral titration. Fluorescence emission of PPT in phosphate buffer solutions (5.0 μM) can be drastically quenched to about one-fourth of its original intensity in the presence of a trace amount (0.28 μM) of ctDNA with a large Stern–Volmer constant (KSV = 8.79 × 106 M−1). The fluorescence quenching efficiency is related to the target concentration, which allows the quantitative detection of the target sequence in a sample. A linear detection range from 1.5 to 280 nM was obtained under the optimized experimental conditions with a detection limit down to the 10−9 M range. Furthermore, strong electrostatic attraction may be the main driving force for PPT/ctDNA binding, which was proposed according to the results of circular dichroism and melting transition study of ctDNA in the presence of PPT. This investigation provides an insight into designing a novel conjugated polyelectrolyte for biomolecular sensing.
