Electrochemical and spectroscopic characterization of self-assembled monolayers: Electrode modification for cardiac pacing applications

Abstract

New biomaterials for permanent cardiac pacemaking electrode applications based on Au surfaces chemically modified with self-assembled monolayers (SAMs) have been developed. The research described herein focuses on four areas related to understanding the extraordinary pacing exhibited by modified pacemaker electrodes. SAM-modified pacemaker electrodes were fabricated and tested in canines for chronic and acute cardiac pacing. In addition to having electrical properties suitable for pacing the heart, SAM-modified electrodes are proven superior to control electrodes in pacing performance. The data suggest that the biocompatibility of electrically conductive materials can be controlled at the molecular level with monolayer organic surface films. The development of a small rodent model for studying cardiac pacing was explored as an alternative to using canines in clinical studies. Rodents, not previously used for such studies, were demonstrated to be excellent mammals for testing initial electrode modification strategies. Myocardial tissue resistance in a living mammalian heart was determined using chronoamperometry and cyclic voltammetry of Ru(NH3 Pacemaker systems represent complete electrochemical cells. Thus, modified pacemaker electrodes are simply examples of chemically modified electrodes, an area of electrochemistry which has been studied extensively over the past two decades. For these types of systems, the interfacial chemistry occurring in the vicinity of the SAM is crucial to its function. Therefore, investigations into the stability, order, and orientation of SAMs at the metal electrode surface, and solvent behavior at the outer edge of the SAMs were undertaken. Such fundamental information is critical in understanding the biocompatibility of these modified pacemaker electrodes, and potentially, in understanding the mechanism for the pacing efficacy of the electrode modification. Surface Raman spectroscopy using an emersion approach was developed as an exceptional technique for probing the structural order and stability of SAMs on Ag and Au after exposure to solvent, electrolyte, and potential. Finally, the stability of these SAM-modified pacemaker electrodes to air and mechanical stress was investigated. Raman spectroscopy, cyclic voltammetry and x-ray photoelectron spectroscopy were utilized to better understand the shelf-life of modified electrodes.