Synthesis and properties of biocompatible water-soluble silica-coated CdSe/ZnS semiconductor quantum dots Page: 4 of 35
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diffusion of heavy atoms into the solution. In order to slow such a process, and to mask
the toxicity of the nanocrystals for bioorganisms, a complete and robust encapsulation of
the inorganic fluorophores is mandatory.14,19,20
Guided by these considerations, we reported an alternative approach in which the
core/shell nanoparticles are embedded in a polymerized silica shell.14 In this article we
describe this synthesis in more detail. The procedure yields nanocrystals encapsulated in
a silica shell of about 2-5 nm, functionalized with thiols and/or amines on the surface.
The silanized (or silica coated) nanocrystals are soluble in buffer solutions over a wide
range of pH even at high salt concentrations (up to 200 mM), and, they retain the optical
properties of the original core/shell particles. We emphasize that silica-coated
nanocrystals have a greater stability in biological buffers compared to nanoparticles
primed with thiolated molecules such as mercaptopropionic acid, and this stability can
justify the amount of effort spent producing them.
This article is organized as follows: in a first part, we describe the synthesis of silica
coated and mercaptopropionic acid coated nanocrystals in detail. Next, we focus on the
influence of the silica shell on the optical properties of the nanocrystals. Finally, we
compare the size distribution and the chemical surface properties of both silica-coated
and mercaptopropionic acid coated CdSe/ZnS nanocrystals.
Experimental section
A. Chemicals and materials
Tri-octyl phosphine oxide (TOPO, #346187), mercapto-propyltrimethyloxsilane (MPS,
#175617), amino-propyltrimethyloxsilane (APS, #281778), tetramethyl ammonium4
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Gerion, Daniele; Pinaud, Fabien; Williams, Shara C.; Parak, Wolfgang J.; Zanchet, Daniela; Weiss, Shimon et al. Synthesis and properties of biocompatible water-soluble silica-coated CdSe/ZnS semiconductor quantum dots, article, February 12, 2001; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc725600/m1/4/: accessed March 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.