Resonant electron tunneling through azurin in air and liquid by scanning tunneling microscopy

Electron transfer through the redox metalloprotein azurin immobilized on Au (111) by its disulphide bridge is studied by scanning tunneling microscopy (STM) in buffer solution and (for the first time) in air. STM analysis gives evidences of a stable and robust binding of the molecules in both cases. Bright spots, associated with azurin molecules, are clearly visible in STM images. The image contrast of adsorbed azurin is highly affected by the bias potential with proteins visible only for some well-defined voltage values. This experimental demonstration of the possibility to induce tunneling through azurin in air could disclose very interesting perspectives for the development of protein-based hybrid nanodevices operating in nonliquid environments.