Synthesis and properties of biocompatible water-soluble silica-coated CdSe/ZnS semiconductor quantum dots (original) (raw)
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Synthesis of water-soluble and bio-taggable CdSe@ZnS quantum dots
RSC, 2018
Many synthesized semiconductor QDs materials are formed using trioctylphosphine oxide (TOPO) but it requires high temperature, is very expensive and is also hydrophobic. Our study deals with selective syntheses of CdSe and core–shell CdSe/ZnS quantum dots (QDs) in aqueous solution by a simple heating and refluxing method. It is more hydrophilic, needs less temperature, is economically viable and is eco-friendly. Bio-ligands, such as thioacetamide, itaconic acid and glutathione, were used as stabilizers for the biosynthesis of QDs. A simplified aqueous route was used to improve the quality of the colloidal nanocrystals. As a result, highly monodisperse, photoluminescent and biocompatible nanoparticles were obtained. The synthesized QDs were characterized by XRD, FTIR, confocal microscopy, ultraviolet (UV) absorption and photoluminescence (PL). The size of synthesized QDs was observed as 5.74 nm and the core–shell shape was confirmed by using XRD and confocal microscopy respectively. The QD nanoparticles showed antibacterial activity against pathogenic bacteria.
Biocompatible CdSe−ZnS Core−Shell Quantum Dots Coated with Hydrophilic Polythiols
Langmuir, 2009
We designed four polymeric ligands for semiconductor quantum dots and synthesized these macromolecular constructs in four steps, starting from commercial precursors. These ligands have a poly(methacrylate) backbone with pendant thiol groups and poly(ethylene glycol) chains. The thiol groups anchor these ligands on the surface of preformed CdSe-ZnS core-shell quantum dots, and the poly(ethylene glycol) chains impose hydrophilic character on the resulting assemblies. Indeed, three of the four sets of quantum dots are soluble in aqueous environments and are stable under these conditions for days over a wide pH range (5.0-9.0). Furthermore, the polymeric coatings wrapped around the inorganic nanoparticles preserve the photophysical properties of the CdSe core and ensure relatively compact dimensions. Specifically, the luminescence quantum yield is ca. 0.4 and the hydrodynamic diameter ranges from 15 to 29 nm with the nature of the polymeric ligand. Model studies with human umbilical vein endothelial cells demonstrated that these hydrophilic quantum dots cross the cell membrane and localize either in the cytosol or in the nucleus. The length of the poly(ethylene glycol) chains appears to guide the intracellular localization of these luminescent probes. In addition, these studies indicated that these particular nanoparticles are not cytotoxic. In fact, their cellular internalization has essentially no influence on cell growth. In summary, we developed novel polymeric ligands able to impose hydrophilic character and biocompatibility on CdSe-ZnS core-shell nanoparticles. Thus, our results can lead to a new family of valuable luminescent probes for cellular imaging, based on the unique photophysical properties of semiconductor quantum dots.
The influence of surface coating on the properties of water-soluble CdSe and CdSe/ZnS quantum dots
Journal of Nanoparticle Research, 2013
It is well-known that ligands coating the surface of luminescent semiconductor nanocrystals (quantum dots [QDs]) play an important role in the preparation, stability and physical properties of the colloidal QDs in both organic and aqueous media. Here we report on the synthesis and characterization of core (CdSe QDs) and core-shell structured QDs (CdSe/ZnS QDs), both of them stabilized in aqueous medium through different mechanisms of modification of their surface chemistry. The approaches evaluated for QDs transfer to aqueous media were ligand exchange and polymer coating. Experiments were performed using two typical thioalkyl acids as ligands, namely mercaptoacetic acid (QDs-MAA) and 2-mercaptoethanesulphonic acid (QDs-MES), and an amphiphilic polymer (PQDs) based on poly(maleic anhydride) functional groups. The effects of pH (buffer solution), illumination and the presence of ions in the QD environment on the spectroscopic properties of the different synthesized QDs are reported. The stability of the prepared QDs has been comparatively evaluated aimed to elucidate which surface chemistry provides the suitable properties to be employed as fluorescence labels in distinct types of applications. The experimental results and conclusions will be useful for the development of sensitive sensors or assays adopting QDs as fluorescence labels.
Synthesis and Properties of Water-Soluble Core–Shell–Shell Silica–CdSe/CdS–Silica Nanoparticles
Journal of Nanoscience and Nanotechnology, 2006
This paper describes the synthesis of highly water-soluble and fluorescent core-shell-shell silica-CdSe/CdS-silica nanoparticles (CSS silica-QDs-silica NPs). We used cadmium nitrate and 1,1-dimethyl-2-selenourea precursors to synthesize CdSe quantum dots (QDs) in aqueous solution under simultaneous illumination with a diode-pumped solid state green laser and a Xe-Hg lamp. After passivation of the CdSe QDs with CdS, the CdSe/CdS QDs were then conjugated covalently to (3-mercaptopropyl)trimethoxysilane (MPS); we call these nanoparticles "MPS-QDs". We mixed the MPS-QDs with tetraethoxysilane (TEOS), ethanol, and NH 3 . By controlling the concentrations of the reagents, the stirring speed, and the reaction time, we synthesized CSS silica-QDs-silica NPs having sizes ranging from 75 to 190 nm. The incubation time for preparing the MPS-QDs and their concentrations are important parameters in determining the morphologies of the CSS silica-QDssilica NPs. When we mixed 50 nM MPS-QDs, 1.1 mM TEOS, and 78 mM NH 3 and reacted them at a stirring speed of 750 rpm, we obtained 85-nm-diameter CSS silica-QDs-silica NPs having a QD shell thickness of ca. 20 nm. The CSS silica-QDs-silica NPs provide a strong photoluminescence intensity (quantum yield 88%) and exhibit enhanced stability both photochemically and in high-conductivity media (e.g., 1.0 M NaCl).
Bioconjugate Chemistry, 2008
Chemical modification of the surface of CdSe/ZnS quantum dots (QDs) with small molecules or functional ligands often alters the characteristics of these particles. For instance, dopamine conjugation quenches the fluorescence of the QDs, which is a property that can be exploited for sensing applications if the conjugates are taken up into living cells. However, different sizes and/or preparations of mercaptocarboxylic acid solubilized QDs show very different properties when incubated with cells. It is unknown what physical parameters determine a QDs ability to interact with a cell surface, be endocytosed, escape from endosomes, and/or enter the nucleus. In this study, we examine the surface chemistry of QD-dopamine conjugates and present an optimized method for tracking the attachment of small biomolecules to the surface. It is found that the fluorescence intensity, surface charge, colloidal stability, and biological interactions of the QDs vary as a function of the density of dopamine on the surface. Successful targeting of QD-dopamine to dopamine receptor positive PC12 cells correlates with greater homogeneity of particle thiol layer, and a minimum number of ligands required for specific association can be estimated. These results will enable users to develop methods for screening QD conjugates for biological activity before proceeding to experiments with cell lines and animals.
Journal of Nanoparticle Research, 2016
A silanization process was employed to transfer hydrophobic quantum dots (QDs) prepared via an organic route at high temperature into water phase. The QDs were further coated with a thin organic SiO 2 shell to form QDs@SiO 2 composite nanoparticles by ligand exchange or remaining initial organic ligands on the surface. In this study, QDs with different ligands, either trioctylphosphine oxide (TOPO) or oleic acid (OA), were employed to investigate the effects of ligands on the reverse micelles in preparing QDs@SiO 2 nanoparticles. In the preparing process, hydrophobic QDs were silanized by partially hydrolyzed tetraethyl orthosilicate (TEOS). For TOPO-capped CdSe QDs, surface TOPO ligands were completely replaced by partially hydrolyzed TEOS. As for OA-capped CdSe/Cd x Zn 1-x S QDs, surface OA ligands were partially replaced. It was found that the ligand exchange drastically reduced the photoluminescence (PL) efficiency of CdSe QDs. Furthermore, the cytotoxicity studies of QDs@SiO 2 have been carried out in detail. The results indicate that CdSe/Cd x Zn 1-x S QDs@SiO 2 composite nanoparticles exhibit lower cytotoxicity compared with CdSe QDs@SiO 2 , because the SiO 2 shell and remained OA ligand layer can effectively prevent the leakage of toxic Cd 2? ions. Meanwhile, it was found that these CdSe/Cd x Zn 1-x S QDs@SiO 2 nanocomposites could keep excellent PL properties even for 24 h incubating with Siha cells, which indicating that our prepared composite nanoparticles are potentially applicable for cell imaging in biological systems.
Capping of CdSe–ZnS quantum dots with DHLA and subsequent conjugation with proteins
Nature Protocols, 2006
We provide a detailed protocol for designing water-soluble CdSe–ZnS quantum dots (QDs) based on cap exchange of the native hydrophobic shell with dihydrolipoic acid (DHLA) ligands, and the preparation of functional QD bioconjugates for use in immunoassays. Our conjugation strategy is based on non-covalent self-assembly between DHLA-capped QDs and protein appended with either an electrostatic attachment domain (namely, the basic
Synthesis and Characterization of Aqueous Carboxyl-Capped CdS Quantum Dots for Bioapplications
Industrial & Engineering Chemistry Research, 2007
A direct and environmentally friendly synthesis method was developed to produce aqueous CdS quantum dots (QDs) at room temperature. The transmission electron microscopy (TEM) and X-ray diffraction (XRD) results showed the small size and the cubic zinc blende structure of the nanocrystals. The quantum yield was comparable to that of the commercial core-shell QDs. With 3-mercaptopropionic acid (MPA) as the capping molecule, the feasibility of using the aqueous CdS QDs as imaging tool was demonstrated with Salmonella typhimurium cells. The photoluminescence (PL) properties of the present aqueous CdS QDs can be optimized by adjusting various processing parameters. The emission was due to trap states and was related to the dispersion condition. In particular, with higher pH and MPA/Cd ratio of 2, the QDs exhibited stronger emission. The temperature-and concentration-dependent properties of QDs resulted from the intrinsic interactions between nanoparticles. The aqueous CdS QDs displayed long lifetime of 12 h under UV light and excellent stability in DI water, PBS, and cytosol for more than 26 days. The ease of processing and good PL properties of the aqueous CdS QDs provide a practical and economical approach for single-target imaging application.
Biochemical and Biophysical Research Communications, 2012
CdSe-core, ZnS-capped semiconductor quantum dots (QDs) are of great potential for biomedical applications. However, applications in the gastrointestinal tract for in vivo imaging and therapeutic purposes are hampered by their sensitivity to acidic environments and potential toxicity. Here we report the use of coatings with a combination of polythiol ligands and silica shell (QDs PolyT-APS) to stabilize QDs fluorescence under acidic conditions. We demonstrated the stability of water-soluble QDs PolyT-APS both in vitro, in strong acidic solutions, and in vivo. The biodistribution, stability and photoluminescence properties of QDs in the gastrointestinal tract of mice after per os administration were assessed. We demonstrated that QDs coated with current traditional materials -mercapto compounds (QDs MPA) and pendant thiol group (QDs PolyT) -are not capable of protecting QDs from chemically induced degradation and surface modification. Polythiol ligands and silica shell quantum dots (QDs PolyT-APS) are suitable for biological and biomedical applications in the gastrointestinal tract.