Oxygen-driven, high-efficiency production of nitrogen-doped carbon dots from alkanolamines and their application for two-photon cellular imaging

A novel oxygen-driven method has been developed for low-cost, large-scale, and high-efficiency production of nitrogen-doped carbon dots (N-C-dots) by bubbling pure oxygen into monoethanolamine (MEA) under heating conditions. We find that the addition of pure oxygen significantly increases the reaction rate, and makes feasible one-pot gram scale fabrication (3.36 g) of highly photoluminescent N-C-dots in a couple of hours (2.0 h). With an instantaneous nucleation and gradual growth mechanism, precise control over the particle size of the N-C-dots from 2.0 to 16.1 nm is achieved by simply prolonging the heating time from 0.5 to 4.0 h. The as-prepared N-C-dots contain aromatic CN heterocycles in the core and have plentiful hydrophilic groups on the surface. Practically, the oxygen-driven method can be used to synthesize fluorescent N-C-dots from other alkanolamines such as diethanolamine (DEA) and triethanolamine (TEA), which shows general universality. Due to the strong up-conversion photoluminescence, good aqueous dispersibility, high photostability, excellent biocompatibility, and low cytotoxicity, the N-C-dots are demonstrated to be promising two-photon probes for high contrast bioimaging applications.