Nanostructured surfaces for amperometric and impedimetric biosensors

The development of efficient enzyme biosensors, immunosensors, and genosensors is attracting the interest of scientific community due to many problems related to human health. With this respect, electrochemical biosensors can meat the increasing demand of low cost and easy-to-use devices. The stable anchoring of recognition elements on the electrode surface has been generally obtained by functionalising the bio-molecule with thiol terminal groups, due to their high affinity with Au substrates. In the present communication we check the capability of amino terminal groups in achieving stable interaction with Au surfaces. To such a scope, we have used amino derivatives bearing a ferrocene electroactive moiety as a probe. The stability of the adsorbed molecules on the surface and the reproducibility of the deposition procedure have been checked using electrochemical techniques, by exploiting the signal relative to ferrocene reversible oxidation. In order to maximise the number of biological recognition elements anchored on the electrode surface, Au nanostructured surfaces have been developed. In particular, chemically synthesised Au nanoparticles have been stably fixed on Au planar substrates through a dithiol interlayer film, constituting a Self Assembled Monolayer with significant electronic conductivity. The physical-chemical characteristics of the resulting Au nanostructure, by varying the deposition parameters, have been studied through electrochemical and impedance spectroscopic investigations. The Au nanostructured surface has been tested for developing DNA sensors based on peptide nucleic acids (PNA) as recognition elements. In this case, the possibility to use a simple amino group as anchoring moiety, with respect to the commonly used thiol group, should be preferred, since the synthesis of the relevant PNA derivatives results easier. The selective recognition of target DNA sequence has been verified by recording both amperometric and impedimetric signal. The advantage of the use of Au nanostructured surfaces with respect to bare Au, in terms of sensitivity of the signal, has been ascertained