Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles.

UV-Vis Spectroscopic Characterization of Nanomaterials in Aqueous Media

The physicochemical characterization of nanomaterials (NMs) is often an analytical challenge, due to their small size (at least one dimension in the nanoscale, i.e. 1-100 nm), dynamic nature, and diverse properties. At the same time, reliable and repeatable characterization is paramount to ensure safety and quality in the manufacturing of NM-bearing products. There are several methods available to monitor and achieve reliable measurement of nanoscale-related properties, one example of which is Ultraviolet-Visible Spectroscopy (UV-Vis). This is a well-established, simple, and inexpensive technique that provides non-invasive and fast real-time screening evaluation of NM size, concentration, and aggregation state. Such features make UV-Vis an ideal methodology to assess the proficiency testing schemes (PTS) of a validated standard operating procedure (SOP) intended to evaluate the performance and reproducibility of a characterization method. In this paper, the PTS of six partner laboratories from the H2020 project ACEnano were assessed through an interlaboratory comparison (ILC). Standard gold (Au) colloid suspensions of different sizes (ranging 5-100 nm) were characterized by UV-Vis at the different institutions to develop an implementable and robust protocol for NM size characterization.

Protein Corona Modulates Uptake and Toxicity of Nanoceria via Clathrin-Mediated Endocytosis

Particles present in diesel exhaust have been proposed as a significant contributor to the development of acute and chronic lung diseases, including respiratory infection and allergic asthma. Nanoceria (CeO2 nanoparticles) are used to increase fuel efficiency in internal combustion engines, are present in exhaust fumes, and could affect cells of the airway. Components from the environment such as biologically derived proteins, carbohydrates, and lipids can form a dynamic layer, commonly referred to as the "protein corona" which alters cellular nanoparticle interactions and internalization. Using confocal reflectance microscopy, we quantified nanoceria uptake by lung-derived cells in the presence and absence of a serum-derived protein corona. Employing mass spectrometry, we identified components of the protein corona, and demonstrated that the interaction between transferrin in the protein corona and the transferrin receptor is involved in mediating the cellular entry of nanoceria via clathrin-mediated endocytosis. Furthermore, under these conditions nanoceria does not affect cell growth, viability, or metabolism, even at high concentration. Alternatively, despite the antioxidant capacity of nanoceria, in serum-free conditions these nanoparticles induce plasma membrane disruption and cause changes in cellular metabolism. Thus, our results identify a specific receptor-mediated mechanism for nanoceria entry, and provide significant insight into the potential for nanoparticle-dependent toxicity.