Wrap-around sensors for electrical detection of particles in microfluidic channels

Microfluidic devices with integrated electrical sensors have been widely employed in the detection and characterization of particles suspended in liquids. Conventionally, electrical sensors in microfluidic devices are composed of electrodes all patterned on the same surface in a coplanar arrangement. While simplifying the fabrication of electrical sensors within microfluidic channels considerably, the use of coplanar electrodes leads to non-uniform electric fields within the channel and complicates scaling of electrical sensor networks by constraining the routing of different traces within the same plane. The alternative of integrating counter-facing parallel electrodes into microfluidic channels to alleviate those limitations requires a complex fabrication process. In this work, we present a robust and straightforward approach to creating 3D electrical sensors in microfluidic devices fabricated using soft lithography. By placing a blanket electrode on the microfluidic channel walls, our electrical sensor wraps around the flow channel to (i) provide higher sensitivity than their coplanar counterparts, (ii) extend the sensing volume beyond the vicinity of a surface and (iii) simplify the creation of electrical sensor networks with complex geometries by relaxing the routing constraints on traces. Practical implementation of 3D electrical sensors in microfluidic channels offers the potential to enhance the utility of electrical sensing without impacting the frugality of fluidic components in designing integrated microfluidic systems as quantitative platforms.