Influence of Surface Coating towards the Controlled Toxicity of ZnO Nanoparticles In Vitro

The uncertainties in ZnO-mediated toxicity and particle stability in a biological system remain a challenge and mitigate against deployment as next-generation nanoparticles (NPs), especially in biomedical applications. With that perspective, the present study investigates the surface chemical properties of ZnO NPs coated with three different surfactant biomolecules, namely polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB), and sodium dodecyl sulfate (SDS) to control the toxicity-induced potentials. On the testing of the surface-functionalized ZnO NPs, notable changes in the particle sizes, morphology, zeta potential, and hydrodynamic size compared to the pure ZnO NPs are observed. In addition, FTIR spectroscopy, TGA, XRD, XPS, and HRTEM analysis showed significant changes in the surface structures and surface functional groups of the three different ZnO NPs on surface functionalization. Following the physical characterization, the cell viability of rat liver BRL-3A-treated ZnO–PEG, ZnO–CTAB, and ZnO–SDS compared to pure ZnO NPs (<50%) falls between 70% and 95% in a dose-determined manner. The cells treated with the pure ZnO NPs showed a higher percentage of apoptotic cells (~61%), which is significantly higher than the 3.4%, 1.5%, and 0.6% for ZnO–PEG-, ZnO–CTAB-, and ZnO–SDS-treated cells (respectively). Furthermore, the surface functionalization was significantly observed to reduce the content of reactive oxygen species (ROS) to 13.6%, 9.7%, and 2.6% compared to the content level of ~71% from the pure ZnO-treated cells. Besides the marked impairment of mitochondrial potentials induced by the pure ZnO NPs, the surfactant–ZnO NPs were observed to slow down the induction of DNA fragmentation and retain the structural integrity of mitochondrial membranes. The toxicity effects are controlled in the order of ZnO–SDS > ZnO–CTAB > ZnO–PEG, i.e., anionic > cationic > non-ionic. Overall from the analysis, the study stresses the importance of having a suitable surface ligand for the ZnO NPs so as to use them in the biomedical sector.