Characterization of Upconversion Nanoparticles by Single-Particle ICP-MS Employing a Quadrupole Mass Filter with Increased Bandpass

Abstract

This work introduces new methods to characterize dispersions of small-diameter or low-mass-fraction nanoparticles (NPs) by single-particle inductively coupled plasma-mass spectrometry (SP ICP-MS). The optimization of ion extraction, ion transport, and the operation of the quadrupole with increased mass bandwidth improved the signal-to-noise ratios significantly and decreased the size detection limits for all NP dispersions investigated. As a model system, 10.9 ± 1.0 nm Au NPs were analyzed to demonstrate the effects of increasing ion transmission. Specifically, increasing the mass bandwidth of the quadrupole improved the size detection limit to 4.2 nm and enabled the resolution of NP signals from ionic background and noise. Subsequently, the methods were applied to the characterization of lanthanide-doped upconversion nanoparticles (UCNPs) by SP ICP-MS. Three different types of UCNPs (90 nm NaYF4: 20% Yb, 2% Er; 20 nm NaGdF4: 20% Yb, 1% Er; 15 nm NaYF4: 20% Yb, 2% Er) were investigated. Y showed the best signal-to-noise ratios with optimized ion extraction and transport parameters only, whereas the signal-to-noise ratios of Gd, Er, and Yb were further improved by increasing the mass bandwidth of a quadrupole mass filter. The novel methods were suitable for detailed characterization of diluted UCNP dispersions including particle stoichiometries and size distributions. A Poisson model was further applied to assess particle–particle interactions in the aqueous dispersions. The methods have considerable potential for the characterization of small-diameter and/or low-mass-fraction nanoparticles.

Single Particle Inductively Coupled Plasma Mass Spectrometry with Nanosecond Time Resolution

“…Argon was also used as cooling gas and auxiliary gas with flow rates of 14 L min -1 and 0.8 L min -1 , respectively. The mass resolution of the quadrupole was slightly decreased to obtain higher sensitivity for the 197 Au + ion trace, an approach which was adapted from Meyer et al 28 Data Acquisition and Data Processing…”

“…8 With a dwell time of 50 µs, Lamsal et al could quantify platinum nanoparticles with a diameter of 10 nm. 16 Montaño et al evaluated the advantage of utilizing dwell times from 25-100 µs for the detection of SiO2 NP over the previously common method of removing the polyatomic spectral interference of 14 N 14 N + on 28 Si + by use of a collision or reaction gas. 17 Additionally, Kálomista et al were able to distinguish gold nanorods from spherical gold NP by comparing the shape of the oversampled ion cloud profiles of both particle types, as well as to determine the structure and composition of Au-Ag bimetallic nanoparticles.…”

Analytical applications of single particle inductively coupled plasma mass spectrometry: a comprehensive and critical review

“…The analysis of pristine nanoparticles is regarded as the least complex scenario, since there is no matrix in which they are contained. Engineered nanomaterials commonly produced at laboratories for research or industrial purposes, 61,[63][64][65][66][67][68][69][70][71][72]75,76 but also commercial suspensions, 60,62,73,74 have been considered in this section. Table 2 summarizes the applications of SP-ICP-MS to the analysis of such pristine nanoparticles.…”

“…Complex nanomaterials, like up-conversion nanoparticles (NaYF 4 and NaGdF 4 doped with Yb or Er), could also be characterised by decreasing the element mass per particle detection limit; this could be done by reducing the resolution of the quadrupole and hence increasing the transmission of ions. 70 Although carbon nanotubes are not directly detectable by SP-ICP-MS, their metal impurities have been used as proxies for their detection. In that way, the yttrium contained in nanotubes allowed their detection, 73,74 although the concentration was underestimated due to the difficulties of detecting nanotubes with low loads of yttrium.…”

“…In that way, the yttrium contained in nanotubes allowed their detection, 73,74 although the concentration was underestimated due to the difficulties of detecting nanotubes with low loads of yttrium. The characterisation of pristine nanoparticle by SP-ICP-MS has been complemented by electron microscopy techniques for size and shape characterisation 57,61,64,65,[68][69][70]73,74 and XRD 68,69,72,75 for confirmation of their nature through their crystalline structure.…”