Nitrogen-Bearing Carbon Nanoparticles by Pyrolytic Decomposition of Piperazine Citrate Macromolecules for Cellular Imaging.

In this work, highly photoluminescent carbon nanoparticles (CNPs) are fabricated by pyrolytic decomposition of piperazine citrate at high pressure and high temperature. Piperazine serves as a hydrolytic, surface-passivating, and N-doping agent, facilitating the formation of a photopolymer. The as-synthesized CNPs, without any surface protection/passivation, exhibit excellent photolumi-nescence and a maximum quantum yield of 84%. The average particle size of the N-doped CNPs is 0.89±0.05 nm. In addition, the N-doped CNPs exhibit uniform diameters and nearly spherical shapes. The X-ray photoelectron spectroscopy results reveal that the CNPs are composed of carbon (64.4 wt%), oxygen (18.5 wt%), and nitrogen (17.1 wt%), indicating the presence of nitrogen-doped and carbon-rich moieties in the CNPs. Notably, the CNPs purified by the procedure developed in this work exhibit more stable luminescence properties than those purified with the conventional dialysis membrane. In addition, the potential application of the CNPs as fluorescent bioimaging probes, which offer a broad dosing window and exhibit multicolor emission, is investigated by directly cultur-ing A549 cells with the CNPs. The results reveal that the CNPs exhibit not only exceptional optical stability, but also outstanding biocompatibility and cell labeling capability. After incubating the A549 cells with CNPs, the CNPs are confined in perinuclear vacuole-similar shapes with a granulated form in cytoplasm preserving the nucleus. Notably, no significant morphological deterioration such as nuclear contraction is detected.