Redox Cycling in Nanopore-Confined Recessed Dual-Ring Electrode Arrays

Abstract

A redox cycling geometry based on an array of nanopore-confined recessed dual-ring electrodes (RDREs) has been devised to amplify electrochemical signals and enhance the sensitivity of electroanalytical measurements. The RDRE arrays were fabricated using layer-by-layer deposition followed by focused ion beam milling. A characteristic feature of the nanoscale dual-ring geometry is that electrochemical reactions occurring at the bottom-ring electrode can be tuned by modulating the potential at the top-ring electrode. Thus, the resulting device was operated in generator–collector mode by holding the top-ring electrodes at a constant potential and performing cyclic voltammetry by sweeping the bottom-ring potential in aqueous Fe(CN) 6 3–/4– . The enhanced (∼23×) limiting current, achieved by cycling the redox couple between top- and bottom-ring electrodes with high collection efficiency, was compared with that obtained in the absence of self-induced redox cycling (SIRC). Measured shifts in Fe(CN) 6 3–/4– concentration distributions were found to be in excellent agreement with finite-element simulations. The SIRC effect in the RDRE array was also characterized by electrochemical experiments before and after oxygen plasma treatment. The plasma-treated RDRE array exhibited a significant signal amplification, with the faradaic current being augmented by a factor of ∼65 as a result of efficient redox cycling of electroactive species in the nanopores. The amplification factor of the devices was optimized by controlling the interpore distance, with larger pore density arrays exhibiting larger amplification factors.