Scanning tunneling spectroscopy investigation of self-assembled plastocyanin mutants onto gold substrates under controlled environment Original Research Article

The study of the electronic conduction through plastocyanin (PC) mutants assembled on a gold surface has been addressed by scanning tunneling spectroscopy. The two mutants exploit a single thiol group (PCSH) or a disulfide bridge (PCSS) to covalently bind at gold surface. The I–V measurements were performed by positioning the STM tip on top of a single molecule and sweeping the bias potential between ±1 V, under both ambient and controlled atmosphere. For PCSS, under ambient conditions, asymmetric I–V characteristics were obtained, which disappear under nitrogen atmosphere. PCSH, instead shows a symmetric I–V relation in air and under nitrogen environment. Here, as factors underlying this distinct electron conductive behaviour, a potential role for hydration water molecules and for copper redox levels are discussed.