Non-conjugated polyethylenimine copolymer-based unorthodox nanoprobe for bioimaging and related mechanisms exploration
Unconventional non-conjugated photoluminescent polymers have attracted increasing attention in bioimaging application, however their nonclassical photoluminescent mechanisms remain largely unclear. Herein, an amphiphilic copolymer polyethyleneimine-poly(D,L-lactide) (PEI-PDLLA) was synthesized and the obtained PEI-PDLLA copolymer exhibited intrinsic visible blue luminescence in the solid and concentrated solution states under 365 nm UV light irradiation. Using a computational assay approach, we investigated the unconventional photoluminescent mechanism of PEI-PDLLA. The results revealed that such photoluminescence should be related to the “clustered heteroatoms chromophores” formed by through-space electronic interactions of N-heteroatom in PEI. The copolymers can function as a fluorescent nanoprobe (PEI-PDLLA NPs) via a facile nanoprecipitation method and the self-assembly mechanism of PEI-PDLLA NPs was also in-depth investigated by molecular dynamics simulation. Intriguingly, the PEI-PDLLA NPs exhibited a remarkable excitation-dependent multi-wavelength emission characteristic, which was promising in acquiring high precision imaging effect. Moreover, in contrast with conventional organic dyes with aggregation-caused quenching (ACQ), the fluorescence intensity of the PEI-PDLLA NPs was enhanced with increasing solution concentration. Furthermore, their applications in bioimaging indicated that PEI-PDLLA NPs could be utilized as a lysosome-specific and tumor-targeted nanoprobe with excellent photostability and good biocompatibility.