The relationship between pH and zeta potential of ∼ 30 nm metal oxide nanoparticle suspensions relevant to in vitro toxicological evaluations

Abstract

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.

Keywords::

• Metal oxide nanoparticles
• zeta potential
• agglomeration
• pH
• cellular viability

Acknowledgments

The authors thank Dr Bing Guo of the Department of Mechanical Engineering at Texas A&M University for supplying the Fe₂O₃ nanoparticle samples. We also thank the Department of Veterinary Physiology and Pharmacology for supporting this work.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.