Synthesis, characterisation and dispersion of zinc oxide nanorods for biomedical applications

Nanoparticles are increasingly being recognised for their potential utility in biomedicine. Here, the authors present a low-temperature, solvothermal method to synthesise zinc oxide (ZnO) nanorods using ZnO nanoparticles as precursors, with the addition of low-density polyethylenimine (PEI). This surfactant, which is in regular use in biology, has a double advantage: (i) it catalyses the synthesis owing to the amino groups on its polymeric chain and (ii) it wraps around ZnO nanorods as the crystal grows. The synthesis is followed by scanning electron microscopy, energy-dispersive spectroscopy and spectrophotometric analysis. The length of nanorods was dependent on the reaction time: around 300 nm, 1 μm and 5 μm, respectively, for 3, 6 and 12 h of reaction time. Toxicology studies showed that cellular response is both dose and size-dependent. Sub-1 μm ZnO nanorods were found to be internalised by cells and strongly affect cell viability with a process mediated by reactive oxygen species (ROS) production. The internalisation rate of bigger nanostructures is significantly lower, resulting in a moderate cytotoxicity with no detectable ROS production.