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

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.