Integrated Field's metal microelectrodes based microfluidic impedance cytometry for cell-in-droplet quantification

Microfluidic impedance cytometry (MIC) provides a non-optical and label-free method for single cell detection and classification in microfluidics. However, the cleanroom intensive infrastructure required for MIC electrode fabrication limits its wide implementation in microfluidic analysis. To bypass the conventional metal (platinum) electrode fabrication protocol, we fabricated coplanar 'in-contact' Field's metal (icFM) microelectrodes in multilayer elastomer devices with a single photolithography step. Our icFM microelectrodes displayed excellent and comparable performance to the platinum electrodes for detection of single erythrocytes with a lock-in amplifier based MIC setup. We further characterized it for water-in-oil droplets generated in a T-junction microfluidic channel and found high sensitivity and long-term operational stability of these electrodes. Finally, to facilitate droplet based single cell analysis, we demonstrate detection and quantification of single cells entrapped in aqueous droplets.