Nano-Bio Electronic Devices Based on DNA Bases and Proteins

A key challenge of the current research in nanoelectronics is the realization of biomolecular devices. The biomolecules have specific functionalies that can be exploited for the implementation of electronic and optoelectronic devices. Different nanotechnological strategies have been pursued to implement the biomolecular devices, following a bottom-up or a topdown approach depending on the used biomolecule and on its functionality. In this paper we present our results on the implementation of nano-biomolecular devices based on modified DNA nucleosides and metalloproteins. The first kind of devices is based on a DNA base, the guanosine, which is engineered in two different modified forms: the lipophilic deoxyguanosine derivative 1, and the lipophilic 8-oxodeoxiguanosine. These biomolecules show strong electron-donor properties and internal dipole. Moreover these modified nucleosides exhibit self-assembly and self-recognition properties, resulting in the formation of two-dimensional ordered supramolecular structures in the solid state. The aggregates show a clear semiconductor behaviour with blue band-gap and coherent band transport. These are used, in combination with nanopatterned metallic contacts separated by narrow gaps between 200 nm and 30 nm, to fabricate novel biomolecular electronic devices with excellent photodiode behaviour and metal/semiconductor/metal characteristics at room temperature. A three terminal device, like field effect transistor based on a deoxyguanosine derivative (a DNA base), is demonstrated. A totally different approach is followed for the implementation of devices based on proteins. The use of electron-transfer proteins, such as the blue copper protein azurin (Az), is particularly attractive because of its natural redox properties and their self assembly capabilities. Our results about the fabrication, characterization and modelling of devices based on this redox protein are presented.. The charge transfer process in protein devices depends on their redox centers (the metal atom) and their orientation in the solid state, achieved through different immobilization methods. A biomolecular electron rectifier is demonstrated by interconnecting two gold nanoelectrodes with an azurin monolayer immobilized on SiO2. The device exhibits a clear rectifying behavior with discrete current. steps in the positive wing of the current-voltage curve, which are ascribed to resonant tunnelling through the redox active center. The basic properties of Azurin-based three terminal devices are also reported. A prototype of biomolecular transistor in the solid state and operating in air, based on such class of proteins is presented.