STM and cyclic voltammetric investigation of recombinant azurin-gold nanoparticle hybrids

Here, we developed a method for the formation of redox metalloprotein azurin (Az) and gold nanoparticle (Au-NP) hybrid and evaluated its electrical and electrochemical properties using a combination of scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS). A cysteine residue was introduced in Az to directly coordinate with the Au surface without the use of any additional linkers, followed by the binding of Au-NP to Az. Electrochemical experiments were performed to determine the redox behavior of the Az-Au-NP hybrid system, which showed a pair of voltammetric peaks at 150 and 50 mV for oxidation and reduction respectively. The hybrid system showed an enhanced reduction current when compared with its individual components. The tunneling current-voltage (I-V) characteristics and their derivative (dI/dV-V) curves exhibited a clear gap and peak structure around the gap, with limited fluctuations in the I-V curves, which were statistically characterized. The hybrid system was found to exhibit semiconducting behavior with a band gap that varied from 1.4 to 2.0 eV. From the observed results, the Au/Az-Au-NP hybrid system based on the combined STM/STS technique can be used in the development of future nanobiodevices.