Theory and experiments of transport at channel microband electrodes under laminar flows. 1. Steady-state regimes at a single electrode.

Integration of microelectrodes in microfluidic devices has attracted significant attention during the past years, in particular for analytical detections performed by direct or indirect electrochemical techniques. In contrast there is a lack of general theoretical treatments of the difficult diffusion-convection problems which are borne by such devices. In this context, we investigated the influence of the confining effect and hydrodynamic conditions on the steady-state amperometric responses monitored at a microband electrode embedded within a microchannel. Several convective-diffusive mass transport regimes were thus identified under laminar flow on the basis of numerical simulations performed as a function of geometrical and hydrodynamic parameters. A rationalization of these results has been proposed by establishing a zone diagram describing all the limiting and intermediate regimes. Concentration profiles generated by the electrode across the microchannel section were also simulated according to the experimental conditions. Their investigation allowed us to evaluate the thickness of the diffusive-convective layer probed by the electrode as well as the distance downstream from which the solution becomes again homogeneous across the whole microchannel section. Experimental checks of the theoretical principles delineated here have validated the present results. Experiments were performed at microband electrodes integrated in microchannels with aqueous solutions of ferrocene methanol under pressure-driven flow.