Device assembly. In order to assemble the device, the lid was either affixed to the base via 6 machine screws or using a clip (figures 2 and S1). HPLC fittings were inserted into each screw thread to accommodate the inlet from the pumps, electrodes and the outlet. Once fully assembled, the device was placed into a custom-made Faraday cage and electrolyte solution was pumped into the device. The PDMS was poured onto side of the lid with the ridge, such that the PDMS covered the entire lid surface and was <1mm in thickness.