Redox Cycling in Individually Encapsulated Attoliter-Volume Nanopores

Redox cycling electrochemistry in arrays of individually encapsulated attoliter-volume ( V ∼ 10 aL) nanopores is investigated and reported here. These nanopore electrode array (NEA) structures exhibit distinctive electrochemical behaviors not observed in open NEAs, which allow free diffusion of redox couples between the nanopore interior and bulk solution. Confined nanopore environments, generated by sealing NEAs with a layer of poly(dimethylsiloxane), are characterized by enhanced currents-up to 250-fold compared with open NEAs-owing to effective trapping of the redox couple inside the nanopores and to enhanced mass transport effects. In addition, electrochemical rectification ( ca. 1.5-6.3) was observed and is attributed to ion migration. Finite-element simulations were performed to characterize the concentration and electric potential gradients associated with the disk electrode, aqueous medium, and ring electrode inside the nanopores, and the results are consistent with experimental observations. The additional signal enhancement and redox-cycling-based rectification behaviors produced in these self-confined attoliter-volume nanopores are potentially useful in devising ultrasensitive sensors and molecular-based iontronic devices.