Fabrication and biological imaging of hydrazine hydrate cross-linked AIE-active fluorescent polymeric nanoparticles.

Amphiphilic copolymers play a paramount role in the fabrication of fluorescent polymeric nanoparticles (FPNs) through the self-assembly procedure. In this work, novel hydrazine hydrate cross-linked amphiphilic poly(PEG‑co‑FHMA) copolymers were constructed via reversible addition-fragmentation chain transfer (RAFT) polymerization, containing an aggregation-induced emission (AIE) active hydrophobic moiety and a hydrophilic poly(ethylene glycol) (PEG) group. Different characterization techniques have been employed to confirm their successful synthesis. Due to their amphiphilic property, the resulting poly(PEG‑co‑FHMA) copolymers can self-assemble into FPNs in aqueous solution and form poly(PEG‑co‑FHMA) FPNs with size ranging from 100 to 200 nm. The investigation of photophysical properties demonstrated poly(PEG‑co‑FHMA) FPNs possess strong fluorescence, large Stokes shift, excellent AIE characteristic, low critical micelle concentration and remarkable photostability. Biological assay results suggested that these cross-linked AIE-active FPNs are of low toxicity and excellent cell dyeing performances. All of these features make them promising candidates for biomedical applications. As compared with typical AIE-active FPNs based on the synthetic AIE-active compounds, the novel cross-linked AIE-active FPNs based on the Schiff base is rather simple, good designable and universal. More importantly, this strategy could also be adopted for preparation of a large number of AIE-active FPNs because of the well designability of copolymers and salicylaldehyde derivatives. Thus this work will provide a novel route for preparation of multifunctional AIE-active FPNs in a rather facile manner.