Gas Detection With Switchable Selectivity in a Functionalized-Graphene Integrated Microrod Resonator

Whispering gallery mode microresonators significantly enhance light-matter interactions, making them ideal platforms for a wide range of applications, including lasers, nonlinear converters, modulators, and sensors. Recently, the integration of sensitive materials such as graphene within optical microcavities has overcome the inert nature of the traditional optical microresonators, paving the way for highly sensitive biochemical detection. However, challenges such as Q factor deterioration, complex mode analysis, and demanding operation processes remain, resulting in intricate experimental setups, high excitation thresholds, and issues with device reliability and portability. Besides, the selectivity in the sensing process is also a challenge which relates to the material property. In this work, we present a gas sensor by combining functionalized graphene with a microrod resonator, addressing these challenges with the low threshold, simple structure, easy operation, high sensitivity, and switchable selectivity. By monitoring the shift of the resonant mode caused by the adsorption of gas molecules, we achieve the 1.1 ppb level detection of NH₃ and CO₂ in the P-doped graphene based microresonator and demonstrate 4 ppb level detection of NO₂ with high selectivity by changing the doping state of graphene from P to N. Our approach showcases the advantages of low cost, high sensitivity, and switchable selectivity, providing a promising solution for flexible and high-performance chemical sensing systems.