Controllable nanostructured surface modification on quantum dot for biomedical application in aqueous medium

To develop biocompatible polymer modification method on a quantum dot (QD) surface, we have studied poly(2-methacryloyloxyethyl phosphoryicholine) (poly(MPC)) grafting on trioctylphosphine oxide (TOPO)-coated QD (CdSe/ZnS) surface using new strategy with a double functional reversible addition-fragmentation chain transfer (RAFT) agent. Sodium 2- dodecylsulfanylthiocarbonylsulfanyl- 2-methyl propionate (DMP-Na) was focused and prepared as the double functional RAFT agent. As the first function, the DMP-Na possessed surface activity that forms micelle in aqueous solution and solubilize the TOPO-coated QD into the solution. The DMP-Na indicated critical micelle concentration (CMC) from surface tension measurement in an aqueous medium. Over CMC, the QD was able to be solubilized into DMP-Na micelle and showed multicolor fluorescence spectra with narrow full-width at half maximum (FWHM) corresponding to diameter of the QD. Additionally, as the second function, the DMP-Na possessed chain transfer agent ability that synthesizes a poly(MPC)grafted QD in an aqueous medium. In this strategy, fluorescence properties with narrow FWHM and peak top did not change before and after solubilization into the DMP-Na micelle aqueous solution and even after polymerization of the MPC initiated from the DMP-Na. The poly(MPC)-modified QD showed good biocompatibility based on the poly(MPC) properties, and was able to suppress uptake by HeLa cells despite diameter of the poly(MPC)-modified QD was approximately 12 nm.