Using electrochemical coupling between parallel microbands for in situ monitoring of flow rates in microfluidic channels

Extensive development of analytical and bioanalytical applications is based on microfluidic transport of analyte species, which is generally difficult to quantify experimentally. The transport of a reversible redox species at paired microband electrodes operating in generator–collector mode was investigated within a linear microchannel in the presence or in the absence of a gravity pressure driven flow. A solution of 1 mM ruthenium (III) hexaammine in 0.1 M KNO3 has been used as a model system. The device used consists of a top layer of poly(dimethylsiloxane) (PDMS) containing the microchannel fixed onto a glass layer where a series of identical parallel platinum microband electrodes had been microfabricated. The micrometric microchannel height was selected to be in the same range as that of the microband width so that the diffusion length of the redox species could be geometrically constrained by the microchannel wall. The pure diffusional transport properties, taking place in this restricted volume in the absence of any flow, were characterized quantitatively by numerical simulations, based on a model developed previously. Under a pressure driven flow, the generator–collector assembly is adequate to evaluate in situ the average velocity rate of the flow.