PNA/dsDNA complexes: site specific binding and dsDNA biosensor applications

The ability of peptide nucleic acids (PNA) to form specific higher-order (i.e., three- and four-stranded) complexes with DNA makes it an ideal structural probe for designing strand-specific dsDNA biosensors. Higher-order complexes are formed between a dye-labeled charge-neutral PNA probe and complementary dsDNA. Addition of a light-harvesting cationic conjugated polymer (CCP) yields supramolecular structures held together by electrostatic forces that incorporate the CCP and the dye-labeled PNA/DNA complexes. Optimization of optical properties allows for excitation of the CCP and subsequent fluorescence resonance energy transfer (FRET) to the PNA-bound dye. In the case of noncomplementary dsDNA, complexation between the probe and target does not occur, and dye emission is weak. The binding between PNA and noncomplementary and complementary dsDNA was examined by several methods. Gel electrophoresis confirms specificity of binding and the formation of higher-order complexes. Nano-electrospray mass spectrometry gives insight into the stoichiometric composition, including PNA/DNA, PNA(2)/DNA, PNA/DNA(2), and PNA(2)/DNA(2) complexes. Finally, structural characteristics and binding-site specificity were examined using ion mobility mass spectrometry in conjunction with molecular dynamics. These results give possible conformations for each of the higher-order complexes formed and show exclusive binding of PNA to the complementary stretch of DNA for all PNA/DNA complexes. Overall, the capability and specificity of binding indicates that the CCP/PNA assay is a feasible detection method for dsDNA and eliminates the need for thermal denaturing steps typically required for DNA hybridization probe assays.