PNA versus DNA in electrochemical gene sensing based on conducting polymers: study of charge and surface blocking effects on the sensor signal

Abstract

In this communication, we present an in-depth study of DNA/DNA, DNA/PNA and PNA/PNA hybridisation on a conducting polymer-modified electrode, measured by means of electrochemical impedance spectroscopy (EIS). DNA or PNA nucleic base sequence probes (where DNA stands for deoxyribonucleic acid and PNA for peptide nucleic acid) were covalently attached onto the sensor surface. As PNA is a non-charged variant of DNA, we investigate the effects of the surface charge and surface blocking by the surface confined probe/target nucleic bases complexes onto the kinetics of redox reaction of Fe(CN)₆^3−/4− couple occurring at the electrode/solution interface that provides electrochemical readout for hybridisation. A range of hybridisation detection experiments were performed, where the surface charge and surface charge density were varied, through varying the charged nature of the probe and the target (i.e. PNA or DNA) and the density of surface-bound PNA and DNA probes. To further the understanding of these effects on the measured electrochemical signal, kinetic studies of the hybridisation reactions were undertaken, and the equilibrium binding constants and binding rate constants for the hybridisation reactions were obtained. The study provides valuable insights to guide future designs of biosensors.