Ultra-sensitive and accurate multi-ion detection in biofluids via organic electrochemical transistors

As an emerging ionic sensor with low-voltage operation (<1 V), biocompatibility, and stable operation in aqueous environments, organic electrochemical transistors (OECTs) have attracted significant research interest for various biofluid-related ion detection, where minor ion concentration variations can effectively reflect health or pathology states. However, OECT-based ion sensors are currently limited by restricted device transconductance g_m and stabilites, which severely hinder their applications in actual ion sensing scenarios. Here, ultra-sensitive multi-ion sensors based on high-performance n-type vertical OECTs (accumulation mode, g_m = 58 mS) for Na⁺, K⁺, and Ca²⁺ detection in a practical biofluid (effluent from continuous renal replacement therapy), are demonstrated with high accuracy and stability, which are comparable to conventional Roche method. High current sensitivities (14.0 mA/dec for Na⁺, 1.73 mA/dec for K⁺, 4.09 mA/dec for Ca²⁺, which is more than one order of magnitude larger than ever reported for ion-sensitive transistors), and accuracy (inaccuracy <18.5 %), fast response times (<10 s), and reversible sensing capability are accomplished by coupling micrometer size vertical channel structure with optimized ion-selective membranes. This work introduces a general approach for reliable ion detection and could be effectively extended to other biosensors with high sensitivity and accuracy.