Single Plasmonic Particle with Exposed Sensing Hot Spot for Exploring Gas Molecule Adsorption in Nanolocalized Space

Single-particle (SP) sensing technology provides a methodology to explore the biochemical process in a micro/nanosize area (super-high resolution) with high sensitivity. Plasmonic nanoparticle is promising as a substrate for single-particle sensing. To realize specific sensing, a modification layer on the surface of the plasmonic nanoparticle is usually in need. However, a challenge stands in the way: the traditional coating of modification layer can deplete the highly enhanced electric field (EF) around the plasmonic particle and also, perhaps, hinder the analytes moving into the sensing hot spot with the most enhanced EF; thereby, the plasmonic particle cannot perform with super-high sensitivity. To solve this problem, we demonstrated an innovative single plasmonic particle sensing system in this work. In a convenient and controllable way, a single gold nanorod (AuNR) was successfully modified by monolayer WS2. There is an energy interaction between the AuNR and WS2, and thus, an exposed sensing hot spot with a nondepleted enhanced EF exists at the interface, which equips the as-prepared AuNR-WS, SP with the ability to detect small changes in the local dielectric environment. Meanwhile, the monolayer WS2 also acted as a specific modification layer for detecting different analytes. We applied the AuNR-WS2 SP to explore the adsorption kinetics of different gas molecules, including ammonia, ethanol, and acetone for the first time. Through monitoring the scattering spectra under a microscope in dark-field, AuNR-WS2 SP could successfully differentiate the three small molecules, and help to explore the adsorption kinetics of them. Our experimental results were consistent with theoretical simulation in SP's EF distribution and its scattering spectra under different dielectric environments. Additionally, this proposed interaction-based modification strategy was also applied to other plasmonic nanoparticles, such as AupAg nanocube and Au nanodisk, suggesting the universality of this innovative SP sensing system.