Fluorescent polymeric micelles containing fluorene derivatives for monitoring drug encapsulation and release

In this study, we demonstrate a new series of fluorescent polymeric micelles self-assembled from two amphiphilic block copolymers, poly(ethylene glycol)-block-poly[styrene-co-[4-tri(9,9-dihexylfluoren-2,7-yl)styrene]] [PEG-b-P(S-co-TFS), P1] and poly(ethylene glycol)-block-poly[styrene-co-[4-(2-(4-benzo-[2,1,3]-thiadiazole)-9,9-dihexylfluoren-7-yl)styrene]] [PEG-b-P(S-co-BTFS), P2], with fluorescent moieties based on two different fluorene derivatives. The weight fraction and the chemical structure of these two fluorene derivatives could be correlated to the nanostructures and photophysical properties of the corresponding polymeric micelles. In particular, facile adjustment on the emission color of micelles enables the delicate design of drug carriers for the drug with specific photophysical properties. Two fluorescent drugs, curcumin (CUM) and doxorubicin (DOX), are chosen as model drugs for P1 and P2 micelles. Due to the spectral overlap between fluorescent micelles and drugs and their close proximity in the core of micelles, Förster resonance energy transfer (FRET) from micelles to drugs is observed for both the CUR-loaded P1-1 micelles and DOX-loaded P2-1 micelles, which could serve as an indication of successful encapsulation of drug in these micelles. Furthermore, the subsequent decrement of FRET resulting from the increasing distance between fluorene moieties and drugs could be used as an optical approach for monitoring the drug release from the drug carriers.