Photoluminescence of carbon dots prepared by ball milling and their application in Hela cell imaging

Carbon dots are small carbon nanoparticles with various surface passivation schemes. The deliberate functionalization of carbon nanoparticles and carbonization of organic or carbon-rich species are two main synthesis routes for carbon dots. However, these two synthesis routes suffer from drawbacks such as critical reaction conditions and uncontrollable structure and performance. In our present work, a hybrid approach combining the advantageous characteristics of these two synthesis routes was applied to prepare carbon dots. The spherical and hydrophilic carbon dots were prepared by high-energy ball milling of active carbon and potassium carbonate. The carbon dots prepared are disperse and fine with an average size of 3.5 nm and a size distribution of 1.6–6.0 nm. They exhibit a nearly excitation-independent and high photostable blue photoluminescence behavior with the maximal emission wavelength at 430 nm. They also show an excellent photostability under high NaCl concentrations or long UV exposure time and a stable photoluminescence behavior in a wide pH range from 3 to 11. They are nearly not cytotoxic to Hela cells, can be taken up by Hela cells, and applied to Hela cell imaging. Our hybrid approach did not use any strong basic and can be scaled up for large-scale preparation of carbon dots.