Low-molecular Sensing Technologies Using Metal Nanosheets with Low-energy and High-selectivity

In order to establish a safer and secure society utilizing IoT devices, gas sensors have been increasingly demanded for healthcare, safety, and environmental monitoring applications. Conventional chemiresistive sensors, however, suffer from high energy consumption due to external heaters, low selectivity, and low stability. Here, we review a series of noble metal nanosheet sensors that satisfy the above requirements by utilizing the metal itself as both receptor and transducer. Platinum (Pt) nanosheets demonstrated reliable hydrogen (H2) detection under high humidity, with sub-ppm sensitivity and immunity to water interference, unlike conventional. Density of states investigated by the density functional theory revealed that the resistance changes are due to the difference between oxygen- and hydrogen-induced electron scattering. Integrated Pt and PtRh nanosheets enabled simultaneous detection of hydrogen and ammonia by exploiting self-heating effects to achieve optimal operating temperatures. Although self-heating effects contribute to reduce the power consumption necessary to achieve temperature necessary to stimulate chemical reactions, power consumption was further reduced by scaling the device dimensions and pulsed operation of self heating without significant signal loss of sensor responses. Palladium-nanodot-functionalized suspended graphene nanosheets exhibited multifunctionality, switching their functionality between hydrogen and humidity sensing depending on applied bias. Gold (Au) nanosheets with TiN adhesion layers provided ppb-level detection of hydrogen sulfide (H2S), with excellent selectivity, reproducibility, and long-term stability, achieving a limit of detection of 0.5 ppb. These results establish metal nanosheet sensors as a promising platform for breath analysis and IoT-based molecular sensing.