New Parameter for Benchmarking Plasmonic Gas Sensors Demonstrated with Densely Packed Au Nanoparticle Layers

Localized surface plasmon resonance (LSPR) gas sensitivity is introduced as a new parameter to evaluate the performance of plasmonic gas sensors. A model is proposed to consider the plasmonic sensors' surface sensitivity and plasmon decay length and correlate the LSPR response, measured upon gas exchange, with an equivalent refractive index change consistent with adsorbed gas layers. To demonstrate the applicability of this new parameter, ellipsoidal gold nanoparticles (NPs) arranged in densely packed hexagonal lattices were fabricated. The main advantages of these sensors are the small and tunable interparticle gaps (18-29 nm) between nanoparticles (diameters: 72-88 nm), with their robust and scalable fabrication technology that allows the well-ordered arrangement to be maintained on a large (cm² range) area. The LSPR response of the sensors was tested using an LSPR sensing system by switching the gas atmosphere between inorganic gases, namely He/Ar and Ar/CO₂, at constant pressure and room temperature. It was shown that this newly proposed parameter can be generally used for benchmarking plasmonic gas sensors and is independent of the type and pressure of the tested gases for a sensor structure. Furthermore, it resolves the apparent disagreement when comparing the response of plasmonic sensors tested in liquids and gases.