Pushing down the Limit of Ammonia Detection of ZnO-Based Chemiresistive Sensors with Exposed Hexagonal Facets at Room Temperature

High Resolution Image Download MS PowerPoint Slide Trace-level ammonia (NH 3 ) detection at room temperature (RT) is vital for environmental monitoring and noninvasive medical diagnostics. However, to achieve sufficient performance, most existing sensors require external stimuli such as light illumination, piezoelectric activation, doping or heterostructure engineering. In contrast, we report a highly responsive and flexible NH 3 sensor based on morphology-engineered ZnO nanoflowers (ZF), synthesized via a simple solution-based method. The nanoflower architecture, composed of radially aligned nanorods exposing abundant hexagonal facets, provides a high surface area and a dense array of active sites for gas adsorption, enabling sensing without any additional external stimulus or material modification. The sensor exhibits a theoretical limit of detection (LoD) of 16 ppb and a limit of quantification (LoQ) of 53 ppb, with experimental detection down to 200 ppb. Operating at RT (300 K), it delivers ultrafast response ( T r ) and recovery times ( T re ) of 0.5 and 1 s, respectively. Excellent selectivity was observed, with minimal interference from acetone, ethanol, isopropanol, and even under high humidity (∼90%). Mechanical robustness was demonstrated by bending the device to a 1.5 mm radius, with no sensitivity or signal stability loss. A response of ∼2500 was recorded for 10 ppm of NH 3 . These results establish the ZF-based sensor, achieved solely through morphology tuning, as a promising platform for real-time, low-level NH 3 detection in diverse fields.