Plasmon resonance detection of water adsorption isotherms

Plasmonic nanoparticles are highly sensitive to any change in the optical properties of the surrounding medium, such as those provoked by the adsorption or desorption of molecules over metal surfaces, which makes them promising candidates for various sensing applications, including environmental monitoring. In our work we investigate the localized surface plasmon resonance (LSPR) response of two different types of silver nanoparticles (nanospheres and nanoplates) chemically grafted onto transparent substrates and exposed to increasing quantities of water vapor inside a vacuum chamber. Through an “in situ” UV–Vis spectrophotometer, we demonstrate that the LSPR properties of metal nanoparticles can be used to monitor the adsorption and desorption of water vapor over a metal surface, with the support of the Finite-Difference Time-Domain simulations. We investigate and compare the sensitivities of different plasmonic substrates, finding that silver nanoplates are the most sensitive to water vapor adsorption. Exploring how water adsorption on metal nanoparticles impacts the LSPR properties could provide key insights for optimizing plasmonic humidity sensors.