Are redox probes a useful indicator of film stability? An electrochemical, AFM and XPS study of electrografted amine films on carbon

The electrochemical response of solution-based redox probes is commonly used to detect and monitor the formation and stability of films grafted to conducting substrates. In this work we examine redox probe responses at films grafted to glassy carbon (GC) and pyrolysed photoresist film (PPF) by electrooxidation of aliphatic primary amines. Cyclic voltammograms are obtained before and after soaking the modified surfaces in phosphate buffer and acetonitrile. For conditions where films exhibit large changes in electrochemical blocking properties, AFM measurements of film thickness and surface roughness, and XPS measurements of surface composition, are used to monitor the stability of the films. No changes in film structure or composition can be detected, demonstrating that electrochemical loss of blocking properties cannot be equated with large-scale loss of surface film. The origin of changes in probe response is discussed.