pH-dependent adsorption of α-amino acids, lysine, glutamic acid, serine and glycine, on TiO2 nanoparticle surfaces.

TiO2 nanoparticles (NPs) are widely used in different applications, and potential exposure to these NPs raises concerns about their impact on human health. In contact with biological fluids, proteins adsorb onto NPs to create a protein corona. Protein adsorption is highly dependent on the affinity between exterior amino acid residues and the NP surface. Thus, studying amino acids adsorption onto NPs can provide insight into protein corona formation. Herein, the pH-dependent adsorption of α-amino acids onto TiO2 NPs in buffered solutions is described. Methods include attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy to analyze molecular interactions and dynamic light scattering (DLS) to measure changes in size and zeta-potential upon adsorption. Depending on the predominant speciation and TiO2 NP surface charge, adsorption involves a combination of carboxylate and amine group interactions. Gly and Lys reveal a similar trend of higher adsorption with increasing pH. In contrast, Glu adsorption decreases with increasing pH. Ser adsorption onto TiO2 NPs surfaces is the highest around pHIEP. These differences are attributed to the different speciation of the functional groups within the amino acids and the TiO2 surface charge at each pH. Under our experimental conditions, multiple surface species coexist at different pH values. Protonated surface species are present for all amino acids at pH 2. At pH 9, Lys and Glu adsorbate spectra have new peaks at 1740 cm-1 and 1744 cm-1, respectively. This is a possible result of surface-induced deprotonation of the amine group and proton transfer to the carboxylate. Analyzing the pH-dependent adsorption of amino acids can provide a better understanding of biomolecule-surface interactions in in vivo and different biological milieu.

Size, composition, morphology, and health implications of airborne incidental metal-containing nanoparticles.

There is great concern regarding the adverse health implications of engineered nanoparticles. However, there are many circumstances where the production of incidental nanoparticles, i.e., nanoparticles unintentionally generated as a side product of some anthropogenic process, is of even greater concern. In this study, metal-based incidental nanoparticles were measured in two occupational settings: a machining center and a foundry. On-site characterization of substrate-deposited incidental nanoparticles using a field-portable X-ray fluorescence provided some insights into the chemical characteristics of these metal-containing particles. The same substrates were then used to carry out further off-site analysis including single-particle analysis using scanning electron microscopy and energy-dispersive X-ray spectroscopy. Between the two sites, there were similarities in the size and composition of the incidental nanoparticles as well as in the agglomeration and coagulation behavior of nanoparticles. In particular, incidental nanoparticles were identified in two forms: submicrometer fractal-like agglomerates from activities such as welding and supermicrometer particles with incidental nanoparticles coagulated to their surface, herein referenced as nanoparticle collectors. These agglomerates will affect deposition and transport inside the respiratory system of the respirable incidental nanoparticles and the corresponding health implications. The studies of incidental nanoparticles generated in occupational settings lay the groundwork on which occupational health and safety protocols should be built.