Near-infrared-emissive Polymersomes: Self-assembled Soft Matter for in Vivo Optical Imaging

We demonstrate that synthetic soft materials can extend the utility of natural vesicles, from predominantly hydrophilic reservoirs to functional colloidal carriers that facilitate the biomedical application of large aqueous-insoluble compounds. Near-infrared (NIR)-emissive polymersomes (50-nm- to 50-microm-diameter polymer vesicles) were generated through cooperative self assembly of amphiphilic diblock copolymers and conjugated multi(porphyrin)-based NIR fluorophores (NIRFs). When compared with natural vesicles comprised of phospholipids, polymersomes were uniquely capable of incorporating and uniformly distributing numerous large hydrophobic NIRFs exclusively in their lamellar membranes. Within these sequestered compartments, long polymer chains regulate the mean fluorophore-fluorophore interspatial separation as well as the fluorophore-localized electronic environment. Porphyrin-based NIRFs manifest photophysical properties within the polymersomal matrix akin to those established for these high-emission dipole strength fluorophores in organic solvents, thereby yielding uniquely emissive vesicles. Furthermore, the total fluorescence emanating from the assemblies gives rise to a localized optical signal of sufficient intensity to penetrate through the dense tumor tissue of a live animal. Robust NIR-emissive polymersomes thus define a soft matter platform with exceptional potential to facilitate deep-tissue fluorescence-based imaging for in vivo diagnostic and drug-delivery applications.