chemiresistive

Chemiresistive sensors are chemical sensors that detect target species by measuring changes in the electrical resistance of a sensing material when it interacts with the chemical environment. The sensing layer, typically nanostructured, lies between two electrodes; adsorption of gas or liquid-phase analytes alters surface charge, carrier density, and depletion-region width, producing a measurable change in resistance. The direction and magnitude of the response depend on the material type (n-type or p-type) and the analyte’s chemical nature.

Common sensing materials include metal oxides such as SnO2, ZnO, and WO3; conducting polymers like polyaniline and polypyrrole; and carbon-based materials such as graphene and carbon nanotubes. Hybrid materials and nanostructured morphologies are often used to improve sensitivity and response speed.

Device architectures range from simple interdigitated electrode configurations with a sensing film to chemiresistive field-effect transistors (ChemFETs) where a conducting channel modulates current under analyte exposure. Performance metrics include the baseline resistance, the relative resistance change (ΔR/R0) in response to a specific analyte, response time, recovery time, and limit of detection. Operating conditions, especially temperature and humidity, strongly influence performance.

Applications span environmental monitoring, industrial safety (toxic or flammable gas detection), and medical diagnostics (breath or volatile markers). Selectivity is a major design challenge, often addressed through material functionalization, composite and heterostructure engineering, and advanced signal processing.

Limitations include cross-sensitivity, drift, and power consumption, particularly for high-temperature metal-oxide sensors. Ongoing research seeks room-temperature operation, improved stability, and better selectivity through nanostructuring and integrating chemiresistive sensing with other transduction mechanisms.