Synthesis and properties of water-soluble CdSe/Zn_(1-x)Mn_xS Semiconductor quantum dots using an amphiphilic polymer

摘要

We report the phase transfer of hydrophobic CdSe/Zn_(1-x)Mn_xS quantum dots (QDs) into water by encapsulation with octylamine-modified poly(acrylic acid) (PAA). CdSe/Zn_(1-x)Mn_xS QDs are of interest as multimodality biological probes where the photoluminescence and magnetic relaxivity can be tuned independently. Different percentages of the carboxyl groups in PAA were grafted with octylamine molecules and the modified PAA was used for capping CdSe/Zn_(1-x)Mn_xS QDs to make them water soluble. We investigated the optical properties and the solubility of the CdSe/Zn_(1-x)Mn_xS QDs in water. It was found that the PAA with a modification percentage of ~ 45% resulted in soluble CdSe/Zn_(1-x)Mn_xS QDs with the highest quantum yield (QY) in water of approximately 20%. The QY of CdSe/Zn_(1-x)Mn_xS QDs in water was lower than the initial measurement in chloroform and dropped in the initial stages of phase transfer, stabilizing at 20%. Hydrodynamic size of the polymer encapsulated CdSe/Zn_(1-x)Mn_xS QDs in water was evaluated by dynamic light scattering (DLS). The smallest average hydrodynamic diameter of ～ 30 nm was achieved when the molecular ratio of QDs to PAA for capping was 1 nanomole of QDs to 24 micromole of monomer unit.