Polyaniline, PANI, films have been deposited on gold disc electrodes by vapour deposition using an Fe (III) tosylate oxidant. Gold nanoparticles were then electrodeposited to give a nanocomposite material, PANI-AuNP. UV-visible and Raman spectroscopy indicate that film contains PANI in both the base and salt states. Thiolated capture strand DNA, that is complementary to a section of the sequence from the pathogen Staphylococcus aureus that causes mammary gland inflammation, was then immobilized onto the gold nanoparticles and any exposed underlying gold electrode. Following hybridisation of the target, a probe strand, labelled with horse radish peroxidase was hybridized to the section of the target not bound to the capture strand. The concentration of the target was determined by measuring the current required to reduce benzoquinone generated by the HRP label. Semi-log plots of the pathogen DNA concentration vs. faradaic current are linear from 150 pM to 1 mu M and pM concentrations can be detected without the need for molecular, e.g., PCR or NASBA, amplification. (C) 2013 Elsevier B.V. All rights reserved.