Advanced Potentiometric Configuration to Enhance Stability and Reliability of AlGaN/GaN HEMT-Based Water-Gated pH Sensor

Abstract

High-electron mobility transistor (HEMT) sensors show great promise for achieving direct, real-time, and label-free detection. Leveraging the distinctive characteristics of the two-dimensional electron gas (2DEG), HEMT sensors can amplify current fluctuations related to potential changes when molecules are introduced, making them extremely sensitive to surface charge variations. The introduction of a water-gated HEMT (WGHEMT) sensor represents a significant advancement, enabling precise detection of pH levels across a broad spectrum, from acidic pH 2 to basic pH 12. Comprising an inner and outer pool with an ion-selective membrane situated in between, the WGHEMT pH sensor exhibits excellent voltage and current sensitivity of 43.71 mV pH−1 and 144.42 μA pH−1, respectively. It features a rapid response time of 12 s and demonstrates remarkable stability and reliability, with coefficients of variation (C.V.) of 0.29%, 0.12%, 0.26%, 0.24%, 0.28%, and 0.28% for pH 2, pH 4, pH 6, pH 8, pH 10, and pH 12, respectively. The sensor maintains its performance with only 10% degradation after 5 months of repeated measurements and exposure to various pH levels. The WGHEMT pH sensor’s excellent sensitivity, linearity, hysteresis, rapid response time, stability, and reliability highlight its potential for practical deployment in real-world applications.