ZIF-8 functionalized smiley-shaped resonator for high-sensitivity ethanol gas detection via Fano resonance in a MIM waveguide.

We present a Fano resonance-based metal-insulator-metal (MIM) waveguide sensor functionalized with a metal-organic framework (MOF) for low-concentration ethanol gas detection. The device features a smiley-shaped resonator and a bus waveguide with a baffle. Its resonant cavity is filled with ZIF-8, a MOF with high ethanol adsorption selectivity. Fano resonance arises from the interference between a broad continuum state provided by the Ag baffle and a discrete state provided by the smiley-shaped resonator. This leads to an asymmetric line profile that enhances sensitivity. By integrating Fano resonance in the MIM waveguide with ZIF-8's ethanol adsorption capability, the sensor achieves the detection of low-concentration ethanol gas. Simulations show that as ethanol concentration increases from 25 to 100 ppm, the refractive index of ZIF-8 changes by Δn=0.00717, inducing a 3.7 nm redshift, yielding a sensitivity of 54.4 pm/ppm. The sensor achieves a detection limit of 25 ppm.