Moisture

Engineering

Breath gas analysis

Materials science

Chromatography

Relative humidity

Ammonia

Humidity

Chemical engineering

Odor

Physical chemistry

Physics

Nanotechnology

Organic chemistry

Overlayer

Composite material

Evaporation

Chemistry

Meteorology

Optoelectronics

ACS Applied Materials & Interfaces

Ammonia (NH3) is an irritant gas with a unique pungent odor; sub-parts per million-level breath ammonia is a medical biomarker for kidney disorders and Helicobacter pylori bacteria-induced stomach infections. The humidity varies in both ambient environment and exhaled breath, and thus humidity dependence of gas-sensing characteristics is a great obstacle for real-time applications. Herein, flexible, humidity-independent, and room-temperature ammonia sensors are fabricated by the thermal evaporation of CuBr on a polyimide substrate and subsequent coating of a nanoscale moisture-blocking CeO2 overlayer by electron-beam evaporation. CuBr sensors coated with a 100 nm-thick CeO2 overlayer exhibits an ultrahigh response (resistance ratio) of 68 toward 5 ppm ammonia with excellent gas selectivity, rapid response, reversibility, and humidity-independent sensing characteristics at room temperature. In addition, the sensing performance remains stable after repetitive bending and long-term operation. Moreover, the sensors exhibit significant response to the simulated exhaled breath of patients with H. pylori infection; the simulated breath contains 50 ppb NH3. The sensors thus show promising potential in detecting sub-parts per million-level NH3, regardless of humidity fluctuations, which can open up new applications in wearable devices for in situ medical diagnosis and indoor/outdoor environment monitoring.

Flexible Room-Temperature NH<sub>3</sub> Sensor for Ultrasensitive, Selective, and Humidity-Independent Gas Detection

Flexible Room-Temperature NH3 Sensor for Ultrasensitive, Selective, and Humidity-Independent Gas Detection

Flexible Room-Temperature NH₃ Sensor for Ultrasensitive, Selective, and Humidity-Independent Gas Detection