Facile fabrication of highly soluble, extremely small-sized drug carriers using globular poly(ethylene glycol)

We report extremely small-sized drug-carrying globular poly(ethylene glycol) particles. These particles were prepared using fullerene (C ₆₀ ) as a backbone structure and poly(ethylene glycol) as a hydrophilic shell. All π–π carbon bonds in C ₆₀ were combined with poly(ethylene glycol), which form a “globular nano-cage” with a hollow core (originating from the soccer-ball-shaped truncated icosahedron of C ₆₀ ) and the poly(ethylene glycol) shell. Subsequently, we constructed chlorin e6-conjugated globular poly(ethylene glycol). The obtained globular poly(ethylene glycol)–chlorin e6 (average 3.6 nm in diameter) was soluble in aqueous solution and enabled improved singlet oxygen generation. The preferential cellular uptake of globular poly(ethylene glycol)–chlorin e6 resulted in significant enhancement of in vitro or in vivo photodynamic tumor cell ablation under light illumination. Our approach offers a versatile strategy to create extremely small-sized drug carriers using a biocompatible polymer for various biomedical applications.