Microfluidic Solid-State pH Sensor for Dynamic Monitoring of Extracellular pH in Live Cell Cultures

Accurate, real-time monitoring of the extracellular acidification is crucial for understanding the dynamics of cellular metabolism. Here, we present a microfluidic device with a solid-state potentiometric pH sensor for monitoring the extracellular acidification rate (ECAR) in live cell culture. The sensor employs a two-electrode configuration made up of Ag/AgCl and RuO₂ electrodes. The sensor showed excellent analytical capabilities, a consistent Nernst response with high sensitivity (-93 mV/pH), repeatability, and reproducibility. Integrated within a PDMS-based microfluidic culture chamber, the device enables noninvasive, continuous pH monitoring with minimal sample volume. ECAR measurements performed on HeLa cells demonstrate the platform's ability to detect both basal and stress-induced acidification, including rapid responses to glucose, oligomycin, and 2-deoxyglucose treatments. The system's high performance with as few as 300-500 cells underscores its utility for metabolic profiling in rare or limited biological samples. This compact, scalable platform offers a powerful tool for real-time metabolic analysis with broad applications in cancer research, drug screening, and bioenergetic diagnostics.