Fluorescent Heterotelechelic Single-Chain Polymer Nanoparticles: Synthesis, Spectroscopy, and Cellular Imaging

The folding and collapse of individual polymer chains into single-chain polymer nanoparticles (SCPNs) is a versatile and emerging platform for biological applications such as diagnostics, imaging, and therapy, where components for two or more of these functions can be combined onto a single polymer carrier. Here, we prepare heterotelechelic polymers with three sets of separately addressable chemical handles at their α-terminus and ω-terminus, and along their backbone. As a model system, the α- and ω-termini are conjugated with a targeting ligand (folic acid or biotin) and therapeutic drug cargo (camptothecin), respectively, and the backbone is grafted with pendant fluorescent dye molecules, poly(ethylene glycol) oligomers, and benzene-1,3,5-tricarboxamide. These polymers fold in water to give fluorescent SCPNs, which are characterized with respect to their physical and photophysical properties. The latter reveals a relationship between polymer folding, quantum yield, and resistance to photobleaching. The SCPNs are then shown to be useful for immunolabeling of SK-BR-3 breast cancer cells and exhibit little or no acute cytotoxicity. This work demonstrates that SCPNs can be used as a viable platform for bioconjugation and cell labeling, helps establish a set of design criteria for optimizing future biological applications, and opens the door to the development of SCPNs for a broader range of theranostic applications.