Bright Fluorescent Nanodiamonds: No Photobleaching and Low Cytotoxicity

Abstract

Diamond nanocrystals emit bright fluorescence at 600−800 nm after irradiation by a 3 MeV proton beam (5 × 10¹⁵ ions/cm²) and annealing at 800 °C (2 h) in vacuum. The irradiation/annealing process yields high concentrations of nitrogen-vacancy defect centers (∼10⁷ centers/μm³), making possible visualization of the individual 100 nm diamond crystallites using a fluorescence microscope. The fluorescent nanodiamonds (FND) show no sign of photobleaching and can be taken up by mammalian cells with minimal cytotoxicity. The nanomaterial can have far-reaching biological applications.