Naked micelles: well-defined polymer nanoparticles from photo-cleavable block copolymer micelles

Ultra-small nanoparticles (NPs) with accessible surface functionalities in the range of 3-50 nm are of great interest due to their defined size and surface properties, which could bridge the gap between natural and synthetic materials. Although NPs available in nature present more sophisticated functions as compared to synthetic materials, the physicochemical and colloidal behaviour is primarily dominated by geometry and surface charge; synthetic counterparts could mimic aggregation and interaction behaviour based on similar size, shape and surface structure. Inorganic ultra-small NPs exist in a large variety; however polymeric counterparts present major problems when trying to produce them in a controlled manner in the sub-50 nm range. Here, we present the synthesis and self-assembly of a photolabile diblock copolymers into spheres, worms and vesicles followed by photocleaving of the corona leaving the core unaltered, which is then surrounded by negative charge. The polymer features a water-soluble polyethylene oxide (PEO) corona block and a hydrophobic polystyrene (PS) core block. The two blocks are covalently linked by an o -nitrobenzyl moiety (ONB), which upon exposure to UV light ( λ = 365 nm) opens up, leaving a carboxylic acid functionality on the PS core for electrostatic stabilization. The negatively charged core then interacts with cationic species, e.g. , cationic gold NPs (AuNPs), which will decorate the PS surface. We report that photo-cleaving the corona of block copolymer micelles provides well-defined nanoparticles with surface charges accessible for electrostatic modification.