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.

We present electronic excitation spectra of individual nanoparticles (NPs) in the gas phase obtained by messenger-mediated single nanoparticle action spectroscopy at cryogenic temperatures (cryo-SNAS). Single ∼100 nm diameter SiO 2 NPs, either colorless or dye-loaded, are trapped and coated with multiple layers of N 2 in a temperature-controllable modified quadrupole ion-trap at 100 K. The NP's mass is monitored quasi-continuously and nondestructively by light scattering. Absorption of electromagnetic radiation from a tunable (400−800 nm), quasi-continuous, supercontinuum laser leads to heating of the NP and subsequent evaporation of N 2 molecules. The average change in NP mass as a function of the irradiation wavelength then yields the cryo-SNAS spectrum without further correction. The obtained spectra are similar to direct absorption spectra of the corresponding NP suspensions but reveal narrower bands due to the lower NP temperature. These experiments demonstrate that cryo-SNAS allows the determination of photoabsorption spectra of single, free NPs independently of scattering processes.