Optimizing the cationic conjugated polymer-sensitized fluorescent signal of dye labeled oligonucleotide for biosensor applications.

Methods for real time， highly selective and sensitive polynucleotide detection are of vast scientific and economic importance. Fluorescence resonance energy transfer (FRET)-based assays which take advantage of the collective response of water-soluble conjugated polymers (CPs) and the self-assembly characteristic of aqueous polyelectrolytes have been widely used for the detection of DNA， RNA， protein and small molecules. The detection sensitivity of CP-based biosensor is dependent on the signal amplification of dye emission upon excitation of CP relative to that upon direct excitation of the dye. Using cationic polyfluorene derivatives and chromophore (fluorescein or Texas Red) labeled single-stranded DNA molecules (ssDNA-C*) as donor/acceptor pairs， we show that in addition to the spectral overlap， orientation and distance between the donor and the acceptor， the energy levels and fluorescence quenching of the donor/acceptor within the polymer/DNA-C* complexes are also important factors that affect the signal output of dye emission.