Effects of Counter Electrode Induced Redox Cycling on Fe(III) Reduction within Microfluidic Electrochemical Cells

Abstract

In this paper we demonstrated a functional on-chip multi-microelectrode array within microfluidic channels as an fully on-chip electrochemical cell. The response of Pt electrodes within the multi-microelectrode array in the microfluidic channel filled with stagnant Fe(III) solution was characterized using cyclic voltammetry. We found that the mass transport is confined by the small channel dimensions. Furthermore, the interaction between closely-spaced working electrode (WE)-counter electrode (CE) pairs induced the so-called redox cycling, as a result of the overlap of their diffusion regions. The redox cycling modified the electrochemical response of the micro system, resulting in a larger peak separation and higher steady-state current plateaus compared to a bulk system. These experimental findings were validated by using the COMSOL simulations, which also visualize the underlying concentration profiles: thin-layer behavior in the absence of redox cycling and a steep concentration profile in the presence redox cycling, where the depletion-layer width is exactly identical to the WE-CE distance. This analysis from a particular geometry provides an example for the analysis of general micro systems. This work indicates that redox cycling at the WE-CE mode can enhance the current response of amperometric biosensors.