Time-resolved energy transfer in DNA sequence detection using water-soluble conjugated polymers: The role of electrostatic and hydrophobic interactions

We have investigated the energy transfer processes in DNA sequence detection by using cationic conjugated polymers and peptide nucleic acid (PNA) probes with ultrafast pump-clump-emission spectroscopy. Pump-clump-emission spectroscopy provides femto-second temporal resolution and high sensitivity and avoids interference from the solvent response. The energy transfer from donor (the conjugated polymer) to acceptor (a fluorescent molecule attached to a PNA terminus) has been time resolved. The results indicate that both electrostatic and hydrophobic interactions contribute to the formation of cationic conjugated polymers/PNA-C/ DNA complexes. The two interactions result in two different binding conformations. This picture is supported by the average donor-acceptor separations as estimated from time-resolved and steady-state measurements. Electrostatic interactions dominate at low concentrations and in mixed solvents.