High-performance and dual-modal gigahertz sensing for toxic gases with spoof localized surface plasmons

Abstract Gigahertz (GHz) sensors based on spoof localized surface plasmon (SLSP) resonances have been demonstrated to detect various bio/chemical substances. However, quantitatively and contactlessly measuring tiny refractive index changes of toxic gases in GHz regime is still absent. Here, we propose a design of SLSP-based GHz sensors composed of a one-dimensional array of textured cylinders that are hollowed out to allow toxic gases flow. The textured cylinder supports multi-order SLSP resonances and the magnetic fields are localized in the gas region when the SLSPs are excited, resulting that the resonances frequencies and linewidths are sensitive to the refractive index changes of the gas. The sensing performance assessment shows that the device achieves sensitivities exceeding 3000 MHz RIU –1 (RIU: refractive index unit). In particular, due to the high-Q factor and strong localized field, the 4th- and 5th-order SLSP resonances induce ultra-high figure-of-merits (FOMs) up to 771 and 6137.65, respectively, indicating a feasible approach to measure toxic gases with refractive index changes of approximately 0.0015. Our work offers a GHz sensing platform achieving high sensitivities and FOMs, and has great potential in various sensing applications.