"Solid-state proteins" for nanobioelectronic applications

The use of proteins as electron-conductive materials for bioelectronic/biosensing applications has recently attracted great attention, thanks to the possibility of exploiting their self-assembling capabilities and their specific functionalities at the nanoscale. However, a crucial point is the structural stability of biological macromolecules when used in the solid state and at ambient conditions. In particular, investigations about ageing effects as well as resistance to high electric fields are of fundamental and applicative interest (e.g. biomolecular electronic devices). In this work, we have studied the metalloprotein azurin in both respects. Protein films were maintained at ambient conditions through several weeks, and their conformational changes were investigated by fluorescence spectroscopy. The experimental evidence indicates a weak initial conformational rearrangement, followed by longterm stability. The ageing effects were studied on wild type azurin, as well as on two protein derivatives (apo- and zinc-form): interestingly, the results obtained in the solid state were consistent with the expected structural stability of the three species. Moreover, upon rehydration of the biomolecular films at the end of the investigated period (approximately one month), azurin returns to exhibit a native-like conformation. ''Solid-state proteins'' were also investigated with respect to their resistance to high external electric fields (up to 107 V/m) by means of lm-sized interdigitated electrodes. Fluorescence experiments reveal that no significant field-induced conformational alteration occurs. Such results are also discussed and supported by theoretical predictions of the inner protein fields, based on X-ray structural data.