The Combined Influence of Interfacial Reaction Resistance and Fluid Flow on Microelectrode Sensors

Abstract

The influence of convection and interfacial‐reaction resistance on the response of microsensors, including the effects of: (i) fluid flow rates; (ii) reactant (to be sensed) concentration and diffusion coefficient; (iii) fluid conduit and microsensor size; and (iv) sensor potential and interfacial‐reaction resistance, are clarified. For steady‐state convective diffusion to a microdisk sensor, it is shown that sensor response is a monotonic function of two dimensionless groups: the Péclet number Pe, which characterizes the magnitude of convective transport relative to that of diffusion, and the group tan (θ¯), which provides a measure of diffusive‐transport resistance relative to that of the interfacial charge‐transfer reaction. A singular‐perturbation solution provides the sensor response vs. Pe and θ¯ for small Pe, corresponding to slow fluid flows and small disks, and numerical calculations extend the analysis to higher Pe values. The analysis suggests a method for increasing the signal‐to‐noise ratio through altering the sensor bias potential.