On-chip resistive microfluidic flow sensor with reduced analysis time using transient analysis

Abstract In the realm of microfluidics, a critical issue prevails: the majority of flow sensors are situated external to the microfluidic chip itself, resulting in an inherent deficiency of precise operational insights. Fields like drug development, concentration gradient generation, and proactive healthcare demand meticulous, dependable data for broader utilization. In our current work, we introduce a microfluidic flow sensor designed to gauge electrochemical resistance within a circuit comprising electrolytic fluid and inter-digitated electrodes. This sensor's design features a Si wafer substrate housing micropatterned Ti/Pt electrode seamlessly bonded to a polydimethylsiloxane microchannel using oxygen plasma. What sets this innovation apart is the placement of microelectrodes within the microchannel, enabling on-chip flow rate measurements. Employing aqueous NaCl with variable solute concentrations ranging from 0.1 M to 0.4 M, we optimized the microchannel dimensions to accommodate flow rates spanning 0-500 µL/min. The sensor achieves a limit of detection (LOD) at 1 µL/min and boasts a resolution of 5 µL/min for lower flow rates (0 to 100 µL/min), while maintaining a resolution of 100 µL/min for higher flow rates (100 to 500 µL/min). Moreover, we have implemented an algorithm based on the trapezoidal rule, enabling flow rate prediction within 5 seconds. With its capability to swiftly and accurately measure flow rates across a wide spectrum, this proposed device emerges as an invaluable tool for applications mandating continuous flow rate monitoring.