Parts-per-Trillion-Level Acetone Gas Detection Using a Suspended Graphene/SiO₂ SAW Breath and Skin Gas Sensor:...

Detection of parts-per-trillion (ppt)-level acetone gas molecules at room temperature using suspended graphene on SiO₂ micropillars has rarely been achieved using solid-state devices or surface acoustic wave (SAW) sensors. This paper presents the effect of SiO₂ micropillars and suspended graphene as a guiding and sensing layer to detect acetone gas. The integration of suspended graphene with SiO₂ micropillars introduces a coupled resonance effect arising from the interaction between the mechanical vibrations of the graphene and the acoustic vibrations of the micropillars. This effect leads to the formation of hybrid resonance modes when the natural frequencies of the vibrations align. This coupling mechanism amplifies the displacement and energy of the Love wave propagating along the surface of the sensor, enhancing its overall performance. Additionally, the interaction of the Love waves with the SiO₂ micropillars and the suspended graphene generates characteristic dips in the transmission spectra. These dips correspond to the excitation of specific flexural and torsional resonance modes within the structure. A custom-fabricated SAW device, featuring micropillars with a diameter of 4 μm and heights of 1.0 and 1.2 μm, demonstrated exceptionally high sensitivity toward acetone gas at a concentration of 500 ppt. Moreover, the suspended graphene exhibited rapid response and recovery times across a wide range of acetone concentrations.