Mass Measurement of Single Intact Nanoparticles in a Cylindrical Ion Trap

Accurate nanoparticle mass characterization is a challenging task, especially at a single particle level. To solve this problem, a strategy for the mass measurement of single intact nanoparticle was proposed. A microscopy-based ion trap mass spectrometer was built up. To improve the detection sensitivity, a cylindrical ion trap with transparent conductive end-caps was used to increase the transmission of scattered light, and a vacuum ultraviolet lamp was used to increase the charge state of the isolated nanoparticle. By detecting the scattered light of the isolated nanoparticle, a series of secular frequencies were obtained, from which the corresponding mass-to-charge ratio of the nanoparticle was calculated. Finally, a Labview program was used to help deduce the charge state and absolute mass of the individual nanoparticle. Masses of gold nanoparticles with different sizes were accurately examined, which are (5.08 ± 0.44) × 10⁷ Da for 20 nm, (3.55 ± 0.34) × 10⁸ Da for 40 nm, and (1.22 ± 0.14) × 10⁹ Da for 60 nm, respectively. The mass of MOFs with irregular shapes was also determined, which is (6.48 ± 1.08) × 10⁹ Da. This method can provide the mass information on nanomaterials, thus opens up new possibility of characterizing nanoparticles at the single particle level.