Stable aqueous ZnO nanoparticles with green photoluminescence and biocompatibility

► Successfully prepared ZnO nanocrystals with green emission by a facile method. ► As-synthesized ZnO nanocrystals were highly stable and soluble in water. ► PL properties of the ZnO nanocrystals could be preserved for at least 30 days. ► ZnO nanocrystals have good biocompatibility. ► We think that the ZnO nanocrystals have promising applications in cell labeling.