Balanced sensitivity and detection range in ion-selective OECTs by gate bias modulation

Due to their biocompatibility, low operating voltage, and substantial signal amplification capability, ion-selective organic electrochemical transistors (IS-OECTs) show tremendous potential for biofluid-related ion detections. However, IS-OECT performances are severely limited by the nonlinear correlation of effective ion-selective membranes (ISMs) potential and effective gate bias demonstrating maximum transconductance (g_m), which results in tremendously unstable and degraded current sensitivity (S_I) in wide ion concentration ranges. Here, by introducing gate bias modulation to ensure the IS-OECTs yield consistent high g_m in all ion concentration subranges, a wider detection range and an ultrahigh sensitivity can be simultaneously achieved. Specifically, ascribed to the gate bias modulated from 0.7 to 0.95 V, Ca²⁺ and NH₄⁺-IS-OECTs based on small footprint (640 µm²) n-type vertical OECTs (vOECTs) possess approximately 3 mA/dec over a wide ionic range of 10⁻⁵ to 10⁻¹ M, respectively, which is the highest S_I when compared to ever reported for Ca²⁺ and NH₄⁺ ion-sensitive transistors. This work introduces a general approach for ultrahigh sensitivity and wide detection range IS-OECTs, and could be extended to other transistor-based biomolecule and ion sensors, offering valuable insights for advancing high-performance bioelectronics.