Fluorescent silicon nanomaterials have initiated great interest for their potential biological applications. In this paper,
we report the synthesis of water-soluble, luminescent silicon nanoparticles with high quantum yield. The surfaces of
the Si nanoparticles were capped by hydrophobic or hydrophilic organic molecules that passivate and protect the silicon
particles from oxidation. The as-synthesized silicon nanoparticles displayed strong photoluminescence in the blue
region of the visible spectrum. The attached organic molecules conveyed both water solubility and high stability, and
coating had little adverse effect on the optical properties of nanoparticles. These results have major implications
towards using colloidal silicon nanoparticles effectively in biological fluorescence imaging.
We report the phase transfer of hydrophobic CdSe/Zn1-xMnxS quantum dots (QDs) into water by encapsulation with octylamine-modified poly(acrylic acid) (PAA).
CdSe/Zn1-xMnxS 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/Zn1-xMnxS QDs to make them water soluble. We investigated the optical properties and the solubility of the
CdSe/Zn1-xMnxS QDs in water. It was found that the PAA with a modification percentage of ~ 45% resulted in soluble CdSe/Zn1-xMnxS QDs with the highest quantum yield (QY) in water of approximately 20%. The QY of
CdSe/Zn1-xMnxS 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/Zn1-xMnxS 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.
We report the synthesis of high quality ZnS nanoparticles using sulfur and zinc acetate as the S and Zn source, respectively. It was found that sulfur and zinc acetate could be easily dissolved in the mixture of trioctylphosphine oxide (TOPO) and hexadecylamine (HDA) at a temperature of about 65°C and ZnS nanoparticles were generated at temperatures above 150°C. These reactive species of sulfur and zinc were also used for an epitaxial growth of ZnS shell around a CdSe core. The formation of ZnS nanoparticles was confirmed by powder X-ray diffraction (XRD). Particle size and size distribution were studied by transmission electron microscopy (TEM). Optical properties were characterized by a combination of UV-vis and photoluminescence (PL) spectroscopy. The PL quantum yield of the CdSe/ZnS nanoparticles reached about 66% compared with the dye, Rhodamine 6G (R6G). The present synthetic strategy is a "greener" and simpler synthetic scheme due to the use of air-stable and environmentally benign reagents of sulfur and zinc acetate instead of air-sensitive ones such as dimethylzinc and bis(trimethylsilyl) sulfide.
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