| Dec 13, 2025 |
Graphene integrated silica microrod sensor converts gas adsorption into optical shifts, achieving parts per billion sensitivity with doping controlled selectivity at low power.
(Nanowerk News) Monitoring trace gases with high sensitivity and selectivity is essential for environmental safety and smart monitoring systems. Whispering-gallery-mode (WGM) optical microcavities have emerged as a powerful platform for such applications, owing to their ultrahigh quality (Q) factors and exceptional sensitivity to minute refractive-index changes.
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However, challenges such as Q-factor deterioration, complex mode analysis, demanding operation processes, and limited selectivity still remain, leading to intricate experimental setups, high excitation thresholds, and reduced device reliability and portability.
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To address these limitations, the research team led by Professor Baicheng Yao from the University of Electronic Science and Technology of China designed and fabricated a graphene-integrated silica microrod resonator, establishing a compact platform capable of converting gas adsorption into measurable resonance shifts (Photonic Sensors, “Gas Detection With Switchable Selectivity in a Functionalized-Graphene Integrated Microrod Resonator”).
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| (a) The schematic diagram of the gas sensing principle based on a graphene-integrated microrod resonator. (b) The optical microscope image of the graphene-integrated microrod resonator. (c)-(d) The preparation processes of P-doped and N-doped graphene, as well as their mechanisms for selectively sensing gas molecules. (e)-(f) The Raman spectra of graphene before and after N doping. (Image: CAS)
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The team prepared the microrod resonators through laser machining and obtained monolayer graphene via mechanical exfoliation, followed by precise integration of the graphene onto the microrod surface to ensure strong interaction between the cavity mode and graphene. In addition, they modified the doping state of the graphene through vapor-phase doping, and the Raman spectroscopy confirmed both its monolayer structure and its doping characteristics.
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The researchers then constructed a tapered-fiber-coupled experimental system and placed the device inside a sealed gas chamber to quantify its resonance response to different gases. By exposing the microrod to calibrated concentrations of NH₃, CO₂, and NO₂, they monitored the wavelength shifts of multiple cavity modes and evaluated the concentration-dependent characteristics of each gas.
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Using this approach, the sensor achieved ppb-level sensitivity with a best detection limit of 1.1 ppb, while requiring only extremely low probe power, demonstrating its excellent gas-sensing performance.
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A major contribution of this work lies in enabling switchable selectivity through graphene doping engineering. Rather than altering the device structure, the researchers tuned the gas-sensing characteristics by converting graphene from P-type to N-type using diethylenetriamine (DETA). They systematically compared the sensitivities and detection limits of the two doping states for all three gases, demonstrating that P-doped graphene favors NH₃ and CO₂ detection, whereas N-doped graphene significantly enhances the response to NO₂. The team further verified the repeatability and recovery behavior of both configurations, confirming their suitability for long-term sensing applications.
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With its simple construction, low-power operation, and doping-enabled switchable selectivity, the functionalized-graphene microrod resonator provides a versatile sensing platform for next-generation environmental monitoring, industrial safety assessment, and smart IoT systems.
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