Synthesis of SiO2-coated CdSe/CdS/ZnS quantum dots nanohybrids
Valentina V. Goftman, SSU - UGent
Irina Yu. Goryacheva, SSU
Quantum dots (QDs) are high-luminescence photostable nanoparticles with unique optical
properties: opposite to known organic fluorescent dyes, QDs have a symmetric and narrow band
which enables emission of pure color and broad absorption spectrum. These facts allow to excite
different sized particle with a single wavelength. This makes QDs ideal labels for usage in biological
and chemical detecting [1].
Weak points of QDs, which are restricted their application as bio- and analytical labels, are
toxicity, water insolubility and absence of functional groups available for bioconjugation. To
overcome these disadvantages multiple QDs were introduced into silica nanoshells. The versatility of
silica shells in synthesis aspects as well as surface modifications offers a great advantage to the use of
the obtained material in bioanalysis [2, 3]. The other reasons of using this method are anomaly high
stability of covered particles, especially in aqueous media, easy regulation of the coating process,
chemical inertness, controlled porosity, processability, optical transparency and, last but not least,
low-cost reagents [4]. Amplification of analytical signal of the final hydrophilic hybrid QD@SiO2 can
be achieved by encapsulation a multiple QD in one silica nanobead.
The preparation of silica nanoparticles within microemulsions is a convenient route toward
monodisperse particles of controllable size. This method allows to obtain both single QDs in silica
spheres and multiple QDs in silica spheres by varying the water-to-surfactant molar ratio and time of
reaction.
Method of incorporation of multiple hydrophobic CdSe/CdS/ZnS QDs into SiO2 beads by a
two-step microemulsion process was carried out. Hydrophobic CdSe/CdS/ZnS core–shell QDs with a
peak wavelength of 615 nm and 625 nm were prepared via organic route by using oleic acid (OA) as a
capping agent, shells of CdS and ZnS were grown by SILAR technology.
1-st step of synthesis: ligand exchange of oleic acid –capped CdSe/CdS/ZnS QDs, during which
initial molecules of oleic acid removed from the QDs surface while molecules of 3mercaptopropyltrimethoxysilane (MPS) connect with it.
2-nd step of synthesis: transfer these silanized QDs into aqueous phase in the reverse micelle
solution by adding of a small amount of water and stirring for a few hours. Then these silanized QDs
assembled and subsequently encapsulated in a SiO2 shell by a reverse micelle synthesis During this
procedure the photoluminescence of QDs was not significant changed. Size of nanohybrids was
varied from 70 nm to 170 nm depending of size of initial QDs and synthesis condition (silanization
reagent, time of reaction, water-to-surfactant molar ratio).
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