We evaluated the cytotoxicity of various morphological classes of TiO(2) nanostructures (including 0-D nanoparticles, 1-D nanorods, and 3-D assemblies) toward living cells. These TiO(2) nanostructures were modified with fluorescent dye molecules, mediated via a dopamine linkage, in order to facilitate a confocal study of their internalization. Specifically, we noted that both TiO(2) 1-D nanorods and 0-D nanoparticles could internalize into cells after 24 h of incubation time. However, only incubation with TiO(2) 1-D nanorods and 3-D micrometer-scale sea urchin-like assemblies at concentrations of up to 125 microg/mL yielded data suggestive of cell viabilities of close to 100%. Moreover, upon irradiation with UV light for periods of a few minutes at energy densities of up to 1 J/cm(2), we observed up to 60% mortality rates, indicative of the cytotoxic potential of photoirradiated TiO(2) nanostructures due to the generation of reactive oxygen species.