Redox-Induced Actuation of Microcantilevers Modified with Ferrocenylalkanethiolate Self-Assembled Monolayers

Abstract

The electrochemically-activated deflection of free-standing microcantilevers has received considerable interest for chemical sensing and nanoactuation. The development and optimization of this type of microcantilever transduction still requires a molecular-level understanding of the surface stress changes that cause the cantilever to bend. We present here the results of an on-going investigation of the electroactuation dynamics of gold-coated microcantilevers modified with model, redox-active ferrocenylalkanethiolate self-assembled monolayers. The microcantilever transducer enables the observation of the electrochemical transformation of the surface-confined ferrocenes to ferroceniums. We find that the ferrocenylalkanethiolate monolayer induces charge-normalized surface stress changes that are at least 10-fold greater than those generated by multilayers of the conducting polymers commonly used for electroactuation. The effects of the electrolyte anion and ferrocene coverage on the magnitude of the surface stress are presented. A physical model to explain the origin of the observed surface stress changes is described