Sensitivity-enhanced detection of ethanol gas using MoO₃ nanoflake-functionalized laser-induced graphene in a planar...

Recent advancements in sensor technology have heightened the demand for more sensitive gas detection methods, crucial for improving environmental monitoring and industrial safety applications. This study investigates the potential of a hybrid of laser-induced graphene (LIG) and MoO₃ nanoflakes via a planar microwave resonator for detecting ethanol gas with high sensitivity. To implement the proposed sensor, a rectangular-shaped graphene layer was patterned on a polyimide substrate using a computer-controlled CO₂ laser and functionalized with MoO₃ nanoflakes. The LIG/MoO₃ hybrid was attached to the high-field distribution zone of a planar microwave resonator, which consisted of electromagnetically coupled split-ring resonators (SRRs), thereby improving the detection sensitivity for ethanol gas. As a proof of concept, a prototype of the microwave resonator sensor interfaced with a LIG/MoO₃ hybrid was developed and tested for its ability to detect different volatile organic compounds (VOCs) and monitor a wide range of ethanol concentrations. Integrating the resonator sensor with a LIG/MoO₃ hybrid achieved rapid (~ 45 s), linear, and sensitive (193 kHz/ppm) detection and characterization of ethanol gas (25 to 800 ppm) using shifts in its baseline resonant frequency of 4.067 GHz. Additionally, functionalizing the LIG interface with MoO₃ nanoflakes resulted in a gas sensing response that was boosted by a factor of up to 1.825 times the sensitivity compared to LIG and MoO₃ as gas-sensitive interfaces. The achieved results demonstrate the potential of LIG/M_OO₃-interfaced microwave resonator sensor in detecting and characterizing ethanol gas for environmental quality monitoring.