Interplay between the potential waveform and diffusion layer dynamics determines the time-response of voltammetric detection in microchannels
The diffusion layer is a critical factor affecting the temporal response of electrochemical devices. In this article, we have investigated the effect of the relaxation of the diffusion layer during the potentiodynamic sensing of ferrocenemethanol (FcMeOH) in microchannels and compared these results to amperometry. First, the effect of the relaxation of the diffusion layer is described, both theoretically and experimentally. Then, chronoamperometric and voltammetric measurements were considered, and the rate of current increase as a plug of FcMeOH is injected into the device was studied for both cases. It was found that, for the oxidation of FcMeOH, the waveform maximising the duration of the anodic phase provided an improved response for potentiodynamic methods, even though amperometry was always found to show the best results. This was further established by extracting the impulse response and modulation transfer functions, which characterize the time and frequency responses, respectively, of the fluidic/electrochemical system. These findings can help designing potential waveforms improving the time response of the device, in systems where high temporal resolution is needed. This is particularly appropriate to bioelectrochemical analyses, where release and uptake phenomena can occur on the millisecond timescale. (C) 2015 Elsevier Ltd. All rights reserved.