Water Dispersible Red Fluorescent Carbon Nanoparticle via Carbonization of Resorcinol

Although fluorescent carbon nanoparticles have enormous biomedical application potential, the synthesis of high quality red fluorescent carbon nanoparticles is challenging. Here we report water dispersible, red fluorescent carbon nanoparticles of 10–25 nm hydrodynamic size with the fluorescence quantum yield of 25%. The approach involves controlled carbonization of resorcinol in ethylene glycol–Na3PO4 at 190 °C under air exposure. At this condition resorcinol undergoes oxidative phenol coupling associated with dehydration that leads to the nucleation of a π-conjugated 2D graphitic sheet followed by growth into a condensed graphitic core. The method is used to prepare 50–60 mg of particles in one batch and can be easily adapted for gram scale synthesis. The nanoparticles maintain good colloidal stability and fluorescence stability under physiological conditions, display concentration dependent and reversible transition between red to green fluorescence, and can be conjugated with primary amine terminated m...