Study of the deposition of amine terminal groups on Au surfaces for the development of amperometric genosensors

The development of efficient enzyme biosensors, immunosensors, and genosensors is attracting the interest of scientific community, due to the need of fast responses in such an important field as that of human health. With this respect, electrochemical biosensors can also satisfy the increasing demand of low cost and easy-to-use devices. The stable anchoring of recognition elements on the electrode surface has been generally achieved by functionalising the bio-molecule with thiol terminal groups, thanks to their high affinity with Au substrates. In the present communication we show the capability of amino terminal groups to stably interact with Au surfaces. To this aim, the deposition of hexylamine on flat Au surfaces has been studied through spectroscopic and electrochemical investigations. In particular, photoemission, X-ray absorption and vibrational spectroscopies allowed us to clarify the mechanism of the amine interaction with Au substrates, which constitutes quite a debated aspect. The stability of the adsorbed molecules on the surface and the reproducibility of the surface functionalisation have been checked through the deposition of amino derivatives bearing a ferrocene electroactive moiety. These investigations have been exploited in the development of amperometric genosensors based on peptide nucleic acids (PNA) as recognition elements: PNA molecules functionalised with a lysine terminal group have been deposited on Au substrates and the occurrence of DNA hybridisation has been detected electrochemically. Finally, the advantages of the use of Au nanostructured surfaces, replacing the most widely used smooth ones, have been ascertained and discussed.