Capabilities of Single Particle Inductively Coupled Plasma Mass Spectrometry for the Size Measurement of Nanoparticles: A Case Study on Gold Nanoparticles

The increasing application of engineered nanomaterials (ENMs) in consumer and medical products has motivated the development of single-particle inductively coupled plasma mass spectrometry (spICP-MS) for characterizing nanoparticles under realistic environmental exposure conditions. Recent studies have established a set of metrological criteria and evaluated the feasibility of spICP-MS for sizing or quantifying various highly commercialized ENMs. However, less is known about the performance of spICP-MS for detecting nanoparticles with sizes greater than 80 nm. This paper presents a systematic study on spICP-MS for accurate size measurement of gold nanoparticles from 10 to 200 nm. We show that dwell time contributes significantly to the quality of data, with the optimal dwell time that limits split particle events, particle coincidences and false positives being 10 ms. A simple approach to correct for split particle events is demonstrated. We show that transient features of single particle events can be temporally resolved on a conventional quadrupole ICP-MS system using a sufficiently short dwell time (0.1 ms). We propose an intensity-size diagram for estimating the linear dynamic size range and guiding the selection of ICP-MS operating conditions. The linear dynamic size range of the ICP-MS system under standard (highest) sensitivity conditions is 10 to 70 nm but can be further extended to 200 nm by operating in less sensitive modes. Finally, the ability of spICP-MS to characterize heterogeneous forms of metal containing nanoparticles is evaluated in mixtures containing both dissolved and poly disperse nanoparticulate Au

Separation, Sizing, and Quantitation of Engineered Nanoparticles in an Organism Model Using Inductively Coupled Plasma Mass Spectrometry and Image Analysis

For environmental studies assessing uptake of orally ingested engineered nanoparticles (ENPs), a key step in ensuring accurate quantification of ingested ENPs is efficient separation of the organism from ENPs that are either nonspecifically adsorbed to the organism and/or suspended in the dispersion following exposure. Here, we measure the uptake of 30 and 60 nm gold nanoparticles (AuNPs) by the nematode, Caenorhabditis elegans, using a sucrose density gradient centrifugation protocol to remove noningested AuNPs. Both conventional inductively coupled plasma mass spectrometry (ICP-MS) and single particle (sp)­ICP-MS are utilized to measure the total mass and size distribution, respectively, of ingested AuNPs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) imaging confirmed that traditional nematode washing procedures were ineffective at removing excess suspended and/or adsorbed AuNPs after exposure. Water rinsing procedures had AuNP removal efficiencies ranging from 57 to 97% and 22 to 83%, while the sucrose density gradient procedure had removal efficiencies of 100 and 93 to 98%, respectively, for the 30 and 60 nm AuNP exposure conditions. Quantification of total Au uptake was performed following acidic digestion of nonexposed and Au-exposed nematodes, whereas an alkaline digestion procedure was optimized for the liberation of ingested AuNPs for spICP-MS characterization. Size distributions and particle number concentrations were determined for AuNPs ingested by nematodes with corresponding confirmation of nematode uptake <i>via</i> high-pressure freezing/freeze substitution resin preparation and large-area SEM imaging. Methods for the separation and <i>in vivo</i> quantification of ENPs in multicellular organisms will facilitate robust studies of ENP uptake, biotransformation, and hazard assessment in the environment

Development of a Standard Reference Material for Metabolomics Research

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health (NIH), has developed a Standard Reference Material (SRM) to support technology development in metabolomics research. SRM 1950 Metabolites in Human Plasma is intended to have metabolite concentrations that are representative of those found in adult human plasma. The plasma used in the preparation of SRM 1950 was collected from both male and female donors, and donor ethnicity targets were selected based upon the ethnic makeup of the U.S. population. Metabolomics research is diverse in terms of both instrumentation and scientific goals. This SRM was designed to apply broadly to the field, not toward specific applications. Therefore, concentrations of approximately 100 analytes, including amino acids, fatty acids, trace elements, vitamins, hormones, selenoproteins, clinical markers, and perfluorinated compounds (PFCs), were determined. Value assignment measurements were performed by NIST and the Centers for Disease Control and Prevention (CDC). SRM 1950 is the first reference material developed specifically for metabolomics research