Facile preparation of fluorescent nanodiamond-based polymer composites through a metal-free photo-initiated RAFT process and their cellular imaging

Nanodiamond (ND)-based fluorescent probes have been extensively researched in cell imaging applications. Several outstanding properties of fluorescent NDs (FNDs), such as their excellent biocompatibility, intensive fluorescence and chemical stability in organisms, have made them the most promising carbon materials in biomedicine. However, the production of FNDs with nitrogen-vacancy defect centers was rather complicated and costly, which limited their wide application in the biomedical field. Moreover, the particle size of these types of FNDs was much larger than that of NDs produced by the detonation method; thus, it is difficult for them to penetrate the cell membrane. In this present work, a facile and ultrafast photo-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization was introduced for the fabrication of FND-based polymer composites. The photo-initiated RAFT polymerization is time saving, environmentally friendly and highly efficient. To prepare these FNDs, fluorescein was converted into diacryloyl fluorescein (AcFl), which was used not only as the photocatalyst but also a fluorescent comonomer. The functional monomer 2-methacryloyloxyethyl phosphorylcholine (MPC) was introduced to improve the water dispersibility of the FNDs. The successful fabrication of FNDs-polyMPC composites was proven by a series of characterization methods. These FNDs-polyMPC composites show high water dispersibility, strong fluorescence and low toxicity. The cell uptake behavior suggested that FNDs-polyMPC composites can be facilely internalized by cells. Taken together, FNDs-polyMPC composites can be fabricated by a photo-initiated RAFT polymerization. These FNDs-polyMPC composites possess excellent physicochemical and biological properties and are promising candidates for cell imaging applications.