Enhanced electrocatalytic behaviour of gold electrodes modified with ZnO nanoparticles through organophosphonate chemistry

Stable immobilization and homogenous distribution of ZnO nanostructures on solid substrates can play a fundamental role in developing nanostructured biosensing devices. In this work we studied how phosphonic acid-terminated self-assembled monolayers (SAMP of 1) can enhance the electrocatalytic behaviour of ZnO nanoparticles (NPs) immobilized on gold surface. It is well known that alkanethiols can form uniform and conformal monolayers on gold through the thiol group and it has already been shown that ZnO surface can be modified by organophosphonates. Here we focus on the application of this chemistry as a tool for the fabrication of designed architectures of ZnO nanostructures on gold electrodes. Successful surface modification was verified by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Our results indicate the formation of highly stable arrays of ZnO nanoparticles. As a proof of concept, the novel electrodes developed were tested in electrochemical assays for the detection of the transgenic protein neomycin phosphotransferase II (NPTII), showing enhanced electrocatalytic stability in immunosensor applications. The target protein could be detected down to nanomolar level by using the difference in charge transfer resistance (ARct) recorded in impedance spectroscopy measurements.