Self-powered piezoelectric microfluidic flow sensor for low-flow monitoring of metal-ion solutions

Microfluidic technology enables precise manipulation of fluids at the microscale, where accurate flow velocity measurement is crucial for controlling mass transport, ion migration, and electrochemical responses. However, existing pressure sensors mainly respond to high-frequency dynamics or require external excitation, which limits stable detection under low-frequency or low-flow conditions. Here, we present a self-powered piezoelectric microfluidic flow sensor that detects flow rates as low as ∼3 µL min^-1 over a broad measurable range of 3-203 µL min^-1. Using a commercial piezoelectric film coupled with a PDMS membrane, the device converts diaphragm deformation into voltage signals without external power, achieving a high sensitivity 0.79 mV (µL min^-1)^-1, rapid response (0.1) ms, and excellent stability. The proposed sensor also offers low cost and scalable integration, showing strong potential for portable lab-on-a-chip applications.