Abstract
In the past decade, the development of single particle–inductively coupled plasma mass spectrometry (SP-ICPMS) has revolutionized the field of nanometallomics. Besides differentiation between dissolved and particulate metal signals, SP-ICPMS can quantify the nanoparticle (NP) number concentration and size. Because SP-ICPMS is limited to characterization of NPs in solution, we show how solid sampling by laser ablation (LA) adds spatial-resolution characteristics for localized NP analysis in biomaterials. Using custom-made gelatin standards doped with dissolved gold and commercial or synthesized gold nanoparticles, LA-SP-ICPMS conditions such as laser fluence, beam size, and dwell time were optimized for NP analysis to minimize NP degradation, peak overlap, and interferences from dissolved gold. A data-processing algorithm to retrieve the NP number concentration and size was developed for this purpose. As a proof-of-concept, a sunflower-root-sample cross-section, originating from a sunflower plant exposed to gold NPs, was successfully imaged using the optimized LA-SP-ICPMS conditions for localized NP characterization.
Highlights
W ith the growing use of nanoparticles (NPs) in different fields such as energy production,[1] biology, medicine,[2,3] and consumer goods,[4] more and more concerns have been raised about their safety.[5]
The raw data collected by laser ablation (LA)-SP-ICPMS requires substantial processing and an in-depth understanding of the events occurring both during the laser-ablation process and in the ICPMS detection step
This detection-efficiency factor can be defined as DEF =/(mean number of particles per shot in the mass ablated)
Summary
The optimized method was used to measure gold-NP size, number concentration, and localization in roots of sunflower plants grown hydroponically with gold NPs added. This dilution step will affect the peak density, so the particle number concentration in the gelatin needs to be sufficiently high to perform this step. When the NP number concentration is high, and no further instrumental dilution is possible, the probability to encounter more than one peak in the integration window increases, and inaccurate NP analysis ensues.[33] To show this effect, a gelatin standard with 40 nm gold NPs and a NP number concentration of 9.0 × 1010 g−1 was ablated (beam size, 85 μm (round mask); repetition rate, 20 Hz; scanning speed, 40 μm s−1), and the counts associated with 197Au were accumulated with integration windows of 100, 500, and 1000 μs.
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