Spatial sensitivity analysis of fluid mixing in a plate-and-frame microreactor channel via electric impedance spectroscopy with switchable working electrodes

Abstract

A wide variety of multiphase and mixing processes are performed in microfluidic systems, ranging from cell handling or protein separations to suspension catalysis or nanoparticle synthesis. While the utility of microfluidic devices in these areas has been demonstrated, there is still much which is unknown about precise local processes; for example, local mass transport. Electrical impedemetric sensing provides one possible non-invasive means of garnering this information. Indeed, such methods have been widely reported in lab-on-a-chip systems for biological applications, where fabrication and packaging on glass and PDMS substrates is relatively simple. Impedimetric monitoring is, however, much less common in plate-and-frame microreactors, which are more often used for chemical/thermal processes under harsh conditions. Here we present a methodology for integrating an impedance sensor into a plate-and-frame microreactor module for tracking phase distributions within the channel. A simple proof-of-concept test case based on parallel laminar flow of water and ethylene glycol is demonstrated. A sensor block with switchable working electrodes is installed in the cover of a microchannel and the metal channel wall machined in a base plate serves as a counter-electrode. Custom electrode geometries may be designed for selectively probing spatially resolved sub-volumes within a channel. A key feature of the work is the use of a low-cost, commercially available integrated circuit to perform impedance measurements with significant sensitivity to the water/EG mixing ratio. This represents an inexpensive and portable measurement device which may make the numbering-up of such sensors more practical in industrial settings.