Selective and Real-Time Ion Monitoring with Integrated Floating-Gate Organic Electrochemical Transistor Sensing Circuits

Ion-selective transistor-based sensors play a pivotal role in quantifying ion concentrations in aqueous media. Existing solutions rely on direct coupling between ion-selective membrane and channel, requiring bulky electrolyte reservoirs or complex technological approaches and material interfaces. This work introduces a transformative paradigm with ion-selective floating-gate organic electrochemical transistors (ISFG-OECTs) and their integration in sensing circuits. ISFG-OECTs feature spatial separation between ion-selective gating and ionic-electronic current modulation. Leveraging volumetric capacitance and solid-state ionic liquid, efficient ionic coupling with the channel is obtained. These distinctive features make them an ideal solution for streamlined materials integration, eliminating the need for liquid reservoirs. Theoretical foundations and design guidelines for efficient ISFG-OECT implementation are elucidated. Experimental results demonstrate the effectiveness of ISFG-OECTs in both transistor-sensors and current-driven circuit configurations, revealing highly selective detection of K⁺ ions with a limit of detection as low as 11 × 10⁻⁶ m, even in the presence of interfering Na⁺ ions at concentrations two orders of magnitude higher. The proposed approach is simple, reliable, and scalable, offering opportunities for a broad range of fields, such as medical diagnostics, precision agriculture, and environmental monitoring.