Ultrasensitive dual-channel chemosensory synapse based on gas-induced ion flux and hole generating electrochemical transistor

Hazardous gases, such as nitrogen dioxide (NO₂), generally have minimal immediate effects on organs like the lungs and liver at transient low concentrations. However, prolonged exposure can cause irreversible damage, leading to respiratory diseases such as bronchitis, pulmonary edema, and lung cancer. Despite the dangers of long-term exposure to low concentrations of NO₂, most sensors use field-effect transistors (FETs) designed for detecting high concentrations. These sensors lack the memory capabilities needed to detect cumulative low concentrations and consume high power, limiting their applications in wearable devices. Inspired by biological chemo neural synapse, artificial olfactory systems using organic electrochemical transistor (OECT)-based synaptic devices have been developed to detect and memorize cumulative gas concentrations while operating at low voltages. However, current OECT-based sensors suffer from low sensitivity and slow response time, which hinder their ability to detect low gas concentrations effectively. This is due to the requirement of high gas concentrations to initiate electrochemical doping in the semiconductor channel, as well as slow ion dynamics within the system. A common approach to overcoming these limitations involves the modulation of synaptic plasticity via electrical pulsing under exposure to chemical gas, thus causing the ion flux to be dominated by the external voltage rather than by the chemical gas sensor.
Here, inspired by the dual chemosensory system and millions of olfactory receptors of the canine olfactory system that enable it to detect and memorize very low chemical concentrations with high sensitivity and accuracy, we present the design of a novel dual-channel OECT-based chemosensory synaptic device. This device allows independent and simultaneous modulation of gas-induced ion flux and gas-induced hole generation. To achieve this, we engineered an amine-functionalized semiconducting polymer gel (NH₂-SPG) with exposed surface area, where the NH₂ groups act as artificial chemical receptors interacting directly and strongly with electron withdrawing NO₂ gas molecules, enhancing sensitivity and fast response time. Notably, the gas-induced ion dynamics between the electrolyte and semiconductor channel enable excellent gas memory properties, as well as additional hole generation for synergistic high sensitivity. This strategic dual-channel design integrates FET- and single-channel OECT-based gas sensing mechanisms into one device, achieving both exceptional sensitivity and excellent memory properties, enabling the detection of cumulative low concentrations of hazardous gases.