Electrofabricated biomaterial-based capacitor on nanoporous gold for enhanced redox amplification

Abstract

Redox reactions are widely utilized as a transduction modality for biological to electrical communication. Biomaterial-based redox capacitors are emerging as a promising bio-device interface, since the redox-cycling current from interaction of a pair of mediators with the redox capacitor film can be amplified when the redox potentials of the mediators bracket that of the capacitor. We present a method to further amplify the signal responses of a standard catechol-chitosan redox capacitor by carrying out the electrofabrication and electrochemical signal measurements on nanoporous gold (NPG) patterned in a microfluidic channel. Specifically, a pH-responsive chitosan film is electrodeposited on an NPG covered gold electrode, which is electrochemically grafted with catecholic species and modified by a self-assembled monolayer of mercapto-hexanol to enable electrochemical measurements under ambient conditions. The resulting nanoporous architecture of the “NPG/redox-capacitor” enhances the spatial extent across the film depth that is available to the redox mediator for electron transfer interactions with the electrode before escape into the bulk film, thereby enabling significantly higher capacity versus that obtained on a conventional redox capacitor. The sensitivity and biocompatibility of this NPG/redox-capacitor are validated on a micro-device platform by demonstrating its ability to quantitatively detect the redox active bacterial metabolite: pyocyanin, directly from growth cultures of the opportunistic pathogen: Pseudomonas aeruginosa. Due to the capability for microfluidic integration, we envision that this NPG/redox-capacitor electrofabrication strategy can widely impact studies on biological to electrical communication.