Triggering Mechanism for DNA Electrical Conductivity: Reversible Electron Transfer between DNA and Iron Oxide Nanoparticles

A new category of iron oxide nanoparticles (SAMNs, γ-Fe2O3) allows the intimate chemical and electrical contact with DNA by direct covalent binding. On these basis, different DNA-nanoparticle architectures were developed and used as platform for studying electrical properties of DNA. The macroscopic three-dimensional nano-bio-conjugate, constituted of 5% SAMNs, 70% water and 25% DNA, showed high stability, electrochemical reversibility and, moreover, electrical conductivity (70-80 Ω cm-1). Reversible electron transfer at the interface between nanoparticles and DNA was unequivocally demonstrated by Mössbauer spectroscopy, which showed the appearance of Fe(II) atoms on nanoparticles following nano-bio-conjugate formation. This represent the first example of permanent electron exchange by DNA, as well as, of DNA conductivity at a macroscopic scale. Finally, the most probable configuration of the binding was tentatively modelled by density functional theory (DFT/UBP86/6-31+G*), showing the occurrence of electron transfer from the organic orbitals of DNA to surface exposed Fe(III) on nanoparticles, as well as the generation of defects (holes) on the DNA bases. The unequivocal demonstration of DNA conduction provides a new perspective in the five decades long debate about electrical properties of this biopolymer, further suggesting novel approaches for DNA exploitation in nano-electronics.