Zeta potential measurements are common in nanotoxicology. This research probes the effects of pH and time on nanoparticle zeta potential, agglomerate size, and cellular viability. The nanoparticles TiO2, Fe2O3, Al2O3, ZnO, and CeO2, were titrated from pH 12.0–2.0. The isoelectric points (IEP) of the nanoparticles were near neutral with the exception of TiO2 (IEP = 5.19) and Fe2O3 (IEP = 4.24). Nanoparticle agglomerates were largest at the IEP. TiO2 and Fe2O3 increased in zeta potential and agglomerate size over time; while Al2O3 and ZnO displayed little change. CeO2 increased in zeta potential; however, the net charge remained negative. Cytotoxicity studies revealed that TiO2 and Fe2O3 caused decreasing cellular viability over 48 h. Al2O3, ZnO, and CeO2 cellular viability remained similar to control. Results indicate that alterations in the pH have a large effect on zeta potential and agglomerate size which may be used as a predictive measure of nanotoxicity.
The relationship between pH and zeta potential of ~30 nm metal oxide nanoparticle suspensions relevant to in vitro toxicological evaluations