The production of pH-sensitive photoluminescent carbon nanoparticles by the carbonization of polyethylenimine and their use for bioimaging

A cationic branched polyelectrolyte of large molecular weight, i.e., polyethylenimine (PEI) of 25,000 Da, was used as both a carbon source and a passivating agent to prepare photoluminescent carbon nanoparticles (CNPs) in one step. In contrast to the previously reported pH-insensitive CNPs, these CNPs have a distinct pH-sensitive feature that gives them the potential to serve as a proton sensor in monitoring cell metabolization process with proton release. When incubated with HeLa cells, the CNPs could readily penetrate the cell membrane and exhibit low cytotoxicity and favorable biocompatibility. The CNPs have been used for HeLa cell imaging.