We present a DNA biosensor based on self assembled monolayers (SAMs) of thiol-derivatized Peptide nucleic acid (PNA) chains adsorbed on gold surfaces for recognizing complementary ssDNA. PNA molecules tend to realign their molecular axes parallel to the surface normal and form SAMs on gold surfaces at optimal concentrations. These BioSAMs of ssPNAs maintain their capability for recognising complementary ssDNA. We describe the combined use of PM-RAIRS and synchrotron radiation XPS for the detection and functional characterisation of ssPNA-DNA hybridisation behaviour on gold surfaces. RAIRS and XPS are powerful techniques for surface characterisation and molecular detection, which avoid fluorescent labelling of the target. Therefore, these results are interesting both from a fundamental point of view and for the development of optimized DNA-biosensors.