Synthesis, characterization and energy transfer studies of fluorescent dye-labeled metal-chelating polymers anchoring pendant thiol groups for surface modification of quantum dots and investigation on their application for pH-responsive controlled release of doxorubicin.

We describe the synthesis of an end-functionalized fluorescent dye-labeled poly(N-(2-thiolethyl methacrylamide) as a metal chelating polymer with a very narrow size distribution and controllable molecular weights by reversible addition-fragmentation chain transfer polymerization. In following, we apply this water-soluble metal-chelating polymer for surface modification of cadmium telluride quantum dots (CdTe QDs) by ligand exchange method. The obtained poly(N-(2-thiolethyl methacrylamide)/CdTe QDs hybrid was fully characterized using Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analysis (TG) and transmission electron microscopy (TEM). The size of the prepared hybrid was estimated around 3.2 nm by TEM. Furthermore, we used this hybrid for improving the release performance of doxorubicin hydrochloride as a chemotherapeutic model drug. The in vitro release of doxorubicin was studied in pH 5.4 and 7.4, which release curves were nicely fitted by the Korsemeyer-Peppas equation and the release followed by non-Fickian diffusion or anomalous diffusion in pH 5.4. The synthesized fluorescent dye-labeled hybrid can be used as a donor-acceptor pair for fluorescence resonance energy transfer (FRET) experiments, so the energy transfer behavior between fluorescent dye as a donor and CdTe QDs as an acceptor were interrogated using Förster/fluorescence resonance energy transfer model, which the distance was found to be 3.95 nm. This present work has potential for both diagnostic and therapeutic aspects for cancer patients.