Monolayers of cysteine linked peptide nucleic acid (PNA) assembled on gold electrodes were investigated for the sensing of DNA recognition. The monolayer was characterized by cyclic voltammetry (CV). The electron transfer through the monolayers was investigated using electrochemical impedance spectroscopy (EIS) in the presence of target DNA and redox marker ions [Fe(CN)(6)](3-/4-) as hybridization indicator. The EIS spectra in the form of Nyquist plots were analyzed with a Randles circuit, and the electron transfer resistance, R-ct, was used to monitor the sensing of the target DNA. The results showed that without any modification to the target DNA, the complementary and the mismatch can be discriminated effectively at PNA self assembled monolayers (SAMs). Therefore, this work can provide another view on using PNA SAMs as a probe candidate for label-free detection of DNA recognition. (c) 2007 Elsevier B.V. All rights reserved.