Interaction of silica nanoparticles with tau proteins and PC12 cells: Colloidal stability, thermodynamic, docking, and cellular studies.

Study on the side effects of the nanoparticles (NPs) can provide useful information regarding their biological and medical applications. Herein, the colloidal stability of the silicon dioxide NPs (SiO NPs) in the absence and presence of tau was investigated by TEM and DLS techniques. Afterwards, the thermodynamic parameters of interaction between SiO NPs and tau were determined by fluorescence spectroscopy and docking studies. Finally, the cytotoxic effects of SiO NPs on the viability of PC12 cells were investigated by MTT, AO/EB staining and flow cytometry assays. TEM, DLS, and zeta potential investigations revealed that tau can reduce the colloidal stability of SiO NPs. Fluorescence spectroscopy study indicated that SiO NPs bound to the tau with high affinity through hydrogen bonds and van der Waals interactions. Docking study also determined that Ser, Thr and Tyr residues provide a polar microenvironment for SiO NPs/tau interaction. Cellular studies demonstrated that SiO NPs can induce cell mortality through both apoptosis and necrosis mechanisms. Therefore, it may be concluded that the biological systems such as nervous system proteins can affect the colloidal stability of NPs and vice versa NPs in the biological systems can bind to proteins and cell membranes non-specifically and may induce toxicity.