A Disposable Solid-State EGFET Chip Integrated With a Mini-Readout System for Multi-Ion and Urea Detection

In recent years, owing to the demands of point-of-care tests (POCTs), sensors with the advantages of low cost, small dimensions, and precise detection have been widely developed. Extended-gate field-effect transistor (EGFET) devices stand out due to their simplified fabrication and excellent sensing performance. This study optimizes titanium nitride (TiN) sputtering as a gate material for a high-performance sensing membrane and integrates a custom-made quasi-reference electrode (C-qRE) onto the EGFET chip to develop a portable platform for detecting urinary tract stone-related biomarkers, including calcium ions (Ca<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup>) and urea. The optimized TiN membrane, fabricated under a nitrogen flow ratio of 60%, achieved a pH sensitivity of 59.4 mV/pH with linearity of 100%, and minimized drift (0.8 mV/hour) and hysteresis (1 mV). Calcium ion detection showed 27.2 mV/pCa sensitivity with 99.9% linearity, while urea detection demonstrated 32.9 mV/mM sensitivity across 0.3–3.7 mM. The C-qRE maintained pH sensitivity of 57.2 mV/pH over 240 days. Furthermore, a multiplexed constant-voltage constant-current (CVCC) readout system was implemented to enable simultaneous measurement of multiple sensors, providing a compact and reliable alternative to conventional systems. This novel EGFET-based device integrates a semiconductor quasi-reference electrode for multimarker detection, offering high sensitivity, stability, and portability, and holds significant promise for clinical and home monitoring, representing a major advance in POCT diagnostics.