|Vanessa Frascerra, Giuseppe Maruccio, Loretta L. del Mercato, Valentina Arima, Pier Paolo Pompa, Franco Calabi, Roberto Cingolani and Ross Rinaldi
National Nanotechnology Laboratory of Istituto Nazionale di Fisica della Materia, Dipartimento di Ingegneria dell'Innovazione, Università di Lecce, Via per Arnesano, 73100 Lecce, Italy
Scanning probe microscopy (SPM) has demonstrated to be very useful to image and investigate biological molecules. Here, a SPM study of the stability of the metalloprotein Azurin in air is reported. Due to its electron transfer properties, Azurin and its physiological partners are very interesting for the fabrication of planar biosensors, with enhanced sensitivity and selectivity, exploiting a monolayer of proteins that should act as an optimal surface for the analyte molecules to react with. For this purpose it is fundamental that the immobilized protein preserves its conformation and properties, especially at ambient conditions.
First, STM allows us to achieve a very high resolution and to probe the electronic properties of Au (111)-immobilized Azurin, both in buffer solution and in air. Our results demonstrate that immobilized proteins preserve their electron transfer function. Secondly, force-distance spectroscopy has been used to measure the interaction between tip and azurin immobilized on SiO2 by mercaptosilanes. The force curves show that the adhesion of the tip to the azurin is weaker than to the SiO2 and silanized surface. The mechanical properties of azurin could be deduced by analyzing these curves and correlated with the native state of the protein.