A cryogenic single nanoparticle action spectrometer

A nanoparticle (NP) mass spectrometer designed to perform action spectroscopy on single NPs at cryogenic temperatures is described. NPs from an electrospray ion source with masses ranging from 460 to 740 MDa are injected and trapped in a temperature controllable (8-350 K) split-ring electrode ion-trap characterized by improved optical access and trapping potential. After excess NPs are ejected from the trap, the mass-to-charge ratio and subsequently the absolute mass of the trapped NP are determined nondestructively using Fourier transformation and resonant excitation methods. The setup allows us to monitor the mass variation of a single NP as a function of the ion-trap temperature, collision-gas pressure, and irradiation laser power. Ion-trap temperature controlled N₂ adsorption at cryogenic temperatures onto a single, ∼90 nm diameter SiO₂ NP is demonstrated and characterized. We further show that laser irradiation at 532 nm leads to power-dependent changes in the effective N₂ adsorption rate of the particle, which can be monitored and ultimately exploited to measure absorption spectra of a single NP.