The paper reports on the investigation of the electrochemical behavior of a thin gold him electrode coated with silicon dioxide (SiOx) layers of increasing thickness. Stable thin films of amorphous silica (SiOx) were deposited on glass slides coated with a 5 nm adhesion layer of titanium and 50 nm of gold, using plasma-enhanced chemical vapor deposition (PECVD) technique. Scanning electrochemical microscopy (SECM) and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical behavior of the interfaces. In the case of SECM, the influence of the SiOx thicknesses on the electron transfer kinetics of three redox mediators was investigated. Normalized current-distance curves (approach Curves) were fitted to the theoretical model in order to find the effective heterogeneous first order rate constant (k(eff)) at the sample. EIS was in addition used to confirm the diffusion barrier character of the SiOx interlayer. (c) 2008 Elsevier Ltd. All rights reserved.