A calorimetric flow sensor for ultra-low flow applications using electrochemical impedance

We present a calorimetric flow sensor which utilizes electrochemical impedance (EI) measurement to sense flow-mediated heat transfer. Sensors were fabricated from thin-film platinum and Parylene C, rendering them biocompatible, flexible, and corrosion-resistant. A novel sensing method based on asymmetric impedance dips during heater pulsing allowed flow measurement at ultra-low flow velocities (less than 200 μm/s), and simultaneous EI measurement from multiple electrode pairs using a custom multiplexer setup enabled highly sensitive, bidirectional flow transduction. Sensors tested in phosphate-buffered saline achieved a 2σ resolution of 19.1 μm/s, which represents a greater than 4x improvement over previously reported EI-based sensors. The sensor's biocompatible and flexible construction is ideal for microfluidics, lab-on-chip, and in vivo applications.