Amorphous carbon dots with high two-photon fluorescence for cellular imaging passivated by hyperbranched poly(amino amine)

Amorphous carbon dots (C-Dots) with high two-photon fluorescence were prepared by using citric acid (CA) as the carbon source and hyperbranched poly(amino amine) (HPAA) as the surface passivation agent through a facile hydrothermal approach. The C-Dots with an average diameter about 10 nm were readily dispersed in water. They exhibited excellent fluorescence properties and excitation-dependent fluorescence behavior with the corresponding quantum yield (QY) of 17.1% in aqueous solution. Interestingly, the C-Dots emitted bright fluorescence even in the solid state with a QY of 16.3%, which is the highest value obtained for carbon-based nanomaterials. Using the MTT assay, the C-Dots showed low cytotoxicity against L929 normal cells. Furthermore, they were easily internalized by HeLa cells and presented high quality one- and two-photon cellular imaging, suggesting significant potential for application in biological imaging.