Nanoconfined Redox Capacitor for Biosensing Signal Amplification

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 (Fig. 1(i)) by carrying out the electrofabrication and electrochemical signal measurements on nanoporous gold (NPG) (Fig. 1(ii)) patterned in a microfluidic channel (Fig. 2a). 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 (Fig. 1 (ii)), thereby enabling significantly higher capacity versus that obtained on a conventional redox capacitor (Fig. 2b). 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, including for measurement of human performance biomarkers.