Analysis of Fully On-Chip Microfluidic Electrochemical Systems under Laminar Flow

We demonstrated a functional on-chip multi-microelectrode array within a microfluidic channel as a fully on-chip electrochemical cell under laminar flow. A pair of working electrode (WE) and counter electrode (CE) with the small aspect ratio of width to length were parallel placed along the axial direction of flow, relying on the laminar nature of microscale flows to maintain sufficient separation of WE and CE. Thanks to the on-chip integrated reference electrode, the ohmic potential drop for the facing WE-CE configuration was experimentally examined to be negligible. Using a quasi-reversible probe, the COMSOL simulated diffusion limited voltammetric current was observed to deviate from the Levich equation when ignoring the lateral diffusion, as a result of the relatively high ratio of mass transfer to kinetics in the microfluidic chip compared to the disk electrode. The lateral diffusion was found to compensate the current distortion such that the limiting voltammetric response resembles the current predicted from the Levich equation. By considering these effects, the Koutecky-Levich method was used for the kinetic analysis of the microfluidic chips.