One of the key challenges in the field of nanoparticle (NP) analysis is in producing reliable and reproducible characterisation data for nanomaterials. This study looks at the reproducibility using a relatively new, but rapidly adopted, technique, Nanoparticle Tracking Analysis (NTA) on a range of particle sizes and materials in several different media. It describes the protocol development and presents both the data and analysis of results obtained from 12 laboratories, mostly based in Europe, who are primarily QualityNano members. QualityNano is an EU FP7 funded Research Infrastructure that integrates 28 European analytical and experimental facilities in nanotechnology, medicine and natural sciences with the goal of developing and implementing best practice and quality in all aspects of nanosafety assessment. This study looks at both the development of the protocol and how this leads to highly reproducible results amongst participants. In this study, the parameter being measured is the modal particle size.

As silver nanoparticles (AgNPs) are used in a wide array of commercial products and can enter the human body through oral exposure, it is important to understand the fundamental physical and chemical processes leading to changes in nanoparticle size under the conditions of the gastrointestinal (GI) tract. Rapid AgNP growth was observed using nanoparticle tracking analysis with 30 s resolution over a period of 17 min in simulated gastric fluid (SGF) to explore rapid kinetics as a function of pH (SGF at pH 2, 3.5, 4.5 and 5), size (20 and 110 nm AgNPs), and nanoparticle coating (citrate and PVP). Growth was observed for 20 nm AgNP at each pH, decreasing in rate with increasing pH, with the kinetics shifting from second-order to first-order. The 110 nm AgNP showed growth at ≤3.5 pH, with no growth observed at higher pH. This behavior can be explained by the generation of Ag+ in acidic environments, which precipitates with Cl−, leading to particle growth and facilitating particle aggregation by decreasing their electrostatic repulsion in solution. These results highlight the need to further understand the importance of initial size, physicochemical properties, and kinetics of AgNPs after ingestion to assess potential toxicity.

Consumer exposure to silver nanoparticles (AgNP) via ingestion can occur due to incorporation of AgNP into products such as food containers and dietary supplements. AgNP variations in size and coating may affect toxicity, elimination kinetics or tissue distribution. Here, we directly compared acute administration of AgNP of two differing coatings and sizes to mice, using doses of 0.1, 1 and 10 mg/kg body weight/day administered by oral gavage for 3 days. The maximal dose is equivalent to 2000× the EPA oral reference dose. Silver acetate at the same doses was used as ionic silver control. We found no toxicity and no significant tissue accumulation. Additionally, no toxicity was seen when AgNP were dosed concurrently with a broad-spectrum antibiotic. Between 70.5% and 98.6% of the administered silver dose was recovered in feces and particle size and coating differences did not significantly influence fecal silver. Peak fecal silver was detected between 6- and 9-h post-administration and <0.5% of the administered dose was cumulatively detected in liver, spleen, intestines or urine at 48 h. Although particle size and coating did not affect tissue accumulation, silver was detected in liver, spleen and kidney of mice administered ionic silver at marginally higher levels than those administered AgNP, suggesting that silver ion may be more bioavailable. Our results suggest that, irrespective of particle size and coating, acute oral exposure to AgNP at doses relevant to potential human exposure is associated with predominantly fecal elimination and is not associated with accumulation in tissue or toxicity.

Detection of single walled carbon nanotubes (CNTs) was performed using single particle-inductively coupled plasma-mass spectrometry (spICPMS). Due to the ambiguities inherent in detecting CNTs by carbon analysis, particularly in complex environmental matrices, this study focuses on using trace catalytic metals intercalated in the CNT structure as proxies for the nanotubes. Using a suite of commercially available CNTs, the monoisotopic elements Co and Y were found to be the most effective for differentiation of particulate pulses from background. The small, variable, amount of trace metal in each CNT makes separation from instrumental background challenging; multiple cut-offs for determining CNT number concentration were investigated to maximize the number of CNTs detected and minimize the number of false positives in the blanks. In simple solutions the number of CNT pulses detected increased linearly with concentration in the ng L−1 range. However, analysis of split samples by both spICPMS and Nanoparticle Tracking Analysis (NTA) showed the quantification of particle number concentration by spICPMS to be several orders of magnitude lower than by NTA. We postulate that this is a consequence of metal content and/or size, caused by the presence of many CNTs that do not contain enough metal to be above the instrument detection limit, resulting in undercounting CNTs by spICPMS. However, since the detection of CNTs at low ng L−1 concentrations is not possible by other techniques, spICPMS is still a more sensitive technique for detecting the presence of CNTs in environmental, materials, or biological applications. To highlight the potential of spICPMS in environmental studies the release of CNTs from polymer nanocomposites into solution was monitored, showcasing the technique's ability to detect changes in released CNT concentrations as a function of CNT loading.

One of the greatest challenges in the manufacturing and development of nanotechnologies is the requirement for robust, reliable, and accurate characterization data. Presented here are the results of an interlaboratory comparison (ILC) brought about through multiple rounds of engagement with NanoSight Malvern and ten pan-European research facilities. Following refinement of the nanoparticle tracking analysis (NTA) technique, the size and concentration characterization of nanoparticles in liquid suspension was proven to be robust and reproducible for multiple sample types in monomodal, binary, or multimodal mixtures. The limits of measurement were shown to exceed the 30–600 nm range (with all system models), with percentage coefficients of variation (% CV) being calculated as sub 5% for monodisperse samples. Particle size distributions were also improved through the incorporation of the finite track length adjustment (FTLA) algorithm, which most noticeably acts to improve the resolution of multimodal sample mixtures. The addition of a software correction to account for variations between instruments also dramatically increased the accuracy and reproducibility of concentration measurements. When combined, the advances brought about during the interlaboratory comparisons allow for the simultaneous determination of accurate and precise nanoparticle sizing and concentration data in one measurement.