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Additional file 1. Additional material that includes complementary figures of material characterization (Figs. S1â S6: XRD, TEM, DLS, XPS, and FTIR for ZnO and SnO2 NPs), changes in relative macroscopic conductance of lysenin channels in the presence of ZnO NPs and EDTA (Fig. S7), and conductance inhibition at high ionic strength (Fig. S8).

The prospect of nanotechnology is exciting not only for its promise to miniaturize complex devices, but perhaps even more so because of the unconventional characteristics exhibited by many nano-sized materials. Zinc oxide (ZnO) nanoparticles are being explored for applications ranging from sunscreens, to advanced textiles, to self-charging electronic devices. As their industrial production accelerates, attention must be given to their potential to interact with organisms and ecosystems in unexpected ways. The goal of this work was to assess the interaction of ZnO nanoparticles with immune cell cultures consisting of various cell types to identify the mechanisms underlying ZnO nanotoxicity. Using immunofluorescent staining and flow cytometry, the effect of ZnO nanoparticles on various murine immune cell types was studied. After preliminary viability testing using AnnexinV and Live/Dead staining, ZnO were shown to be significantly more toxic than titanium dioxide nanoparticles and gold nanoparticles, and they began inducing apoptosis within eight hours in culture at 50 μg/ml. To evaluate the role of particle uptake into cells and explore surface modification techniques applicable to ZnO nanoparticles, a coating of polyethylene glycol (PEG) was conjugated to the nanoparticle surface through hydrogen-bonding, but it did not attenuate nanotoxicity. Upon further characterization, the PEGylated ZnO surface was found to have adsorbed serum proteins, possibly due to the non-uniform molecular architecture of PEG. Protein adsorption may have therefore been responsible for permitting nanoparticle internalization. As an alternative, ZnO nanoparticle-treated cells were treated with extracellular inhibitors of suspected ROS and cation mechanisms, and the antioxidant enzyme catalase was found to significantly reduce ZnO nanotoxicity, implicating a role of extracellular H2O2. Using an intracellular reactive oxygen detection dye, 2',7'-di-chlorofluorescein diacetate, ZnOnanoparticles were shown to induce an "oxidative burst" within the cell, which was not reduced by catalase. Taken together, catalase inhibition studies reveal that ZnO nanotoxicity within splenocyte cultures may act largely through apoptotic signaling between cell types. Future strategies to engineer safe nano ZnO may therefore include catalase-mimicking components, such as nano platinum.