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At least 811 records · Page 45Linked to original sources
PubMed2006

Shape control of II-VI semiconductor nanomaterials.

Anisotropic II-VI semiconductor nanocrystals and nanoparticles have become important building blocks for (potential) nanotechnological applications. Even though a wide variety of differently shaped nanoparticles of this class can be prepared, the underlying mechanisms are mostly not fully understood. This Review article provides a brief overview of the currently studied shape-evolution mechanisms and the most prominent synthesis methods for such particles, with an aim to provide a fundamental understanding on how different morphologies evolve, and to function as a tool to aid in the preparation of specific nanocrystals.

Anisotropy↗
PubMed2007

Synthesis of stable luminescent microspheres by a simple method.

An easy procedure for preparing microspheres containing CdSe/CdS core-shell quantum dots (QDs) was demonstrated. The luminescent properties of this microsphere were characterized by fluorescence microscopy and fluorescence spectrophotometry. Scanning electron microscopy was also used in this study. Laser confocal microscopy was carried out to describe the distribution of QDs in the microsphere. Especially, the stability of microspheres was investigated. It was found that the getting microsphere was very stable in water and showed values for physiological conditions. The inherent stability of the spheres, as well as their photostability, allows them to be used in biological applications.

Cadmium Compounds↗
PubMed2006

Rotational and translational diffusion of peptide-coated CdSe/CdS/ZnS nanorods studied by fluorescence correlation spectroscopy.

CdSe/CdS/ZnS nanorods (NRs) of three aspect ratios were coated with phytochelatin-related peptides and studied using fluorescence correlation spectroscopy (FCS). Theoretical predictions of the NRs' rotational diffusion contribution to the correlation curves were experimentally confirmed. We monitored rotational and translational diffusion of NRs and extracted hydrodynamic radii from the extracted diffusion constants. Translational and rotational diffusion constants (D(trans) and D(rot)) for NRs were in good agreement with Tirado and Garcia de la Torre's as well as with Broersma's theories when accounting for the ligand dimensions. NRs fall in the size range where rotational diffusion can be monitored with higher sensitivity than translational diffusion due to a steeper length dependence, D(rot) approximately L(-)(3) versus D(trans) approximately L(-)(1). By titrating peptide-coated NRs with bovine serum albumin, we monitored (nonspecific) binding through rotational diffusion and showed that D(rot) is an advantageous observable for monitoring binding. Monitoring rotational diffusion of bioconjugated NRs using FCS might prove to be useful for observing binding and conformational dynamics in biological systems.

Amino Acid Sequence↗
PubMed2006

Coverage-mediated suppression of blinking in solid state quantum dot conjugated organic composite nanostructures.

Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems.

Cadmium Compounds↗
PubMed2005

Surfactant-assisted synthesis of water-soluble and biocompatible semiconductor quantum dot micelles.

We report a simple, rapid approach to synthesize water-soluble and biocompatible fluorescent quantum dot (QD) micelles by encapsulation of monodisperse, hydrophobic QDs within surfactant/lipid micelles. Analyses of UV-vis and photo luminescence spectra, along with transmission electron microscopy, indicate that the water-soluble semiconductor QD micelles are monodisperse and retain the optical properties of the original hydrophobic QDs. The QD micelles were shown to be biocompatible and exhibited little or no aggregation when taken up by cultured rat hippocampal neurons.

Animals↗
PubMed2004

Semiconductor quantum dots and free radical induced DNA nicking.

There is a growing interest in the use of semiconductor quantum dots as fluorescent markers in biological applications. However, there are concerns regarding the potential environmental impact and toxic nature of these nanomaterials. In this study, we have investigated the interaction of water-soluble semiconductor quantum dots with supercoiled DNA.

Biosensing Techniques↗
PubMed2002

Modification of mercury toxicity by selenium: practical importance?

The interaction between mercury and selenium may involve a variety of toxicologically and biochemically distinct processes. In this paper, the interaction between inorganic mercury and sodium selenite, the interaction most extensively studied, as well as the interaction between methylmercury (MeHg) and selenium, the interaction perhaps most significant for non-occupational human populations, will be discussed. It has been shown that the former interaction can be understood as a modification of the kinetic behavior of inorganic mercury by selenite, but this interaction may occur only under very limited conditions. On the other hand, the mechanism of the latter interaction is largely unknown, and kinetic modification appears to play only a minor role. An interaction between MeHg and seleno-proteins or a possible interaction between the inorganic mercury, resulting from the demethylation of MeHg, and the selenium may be important. Compared to the experimental findings, little evidence of the toxicological modification of MeHg by selenium was obtained in epidemiological studies.

Animals↗
PubMed2006

Monomethylated selenium inhibits growth of LNCaP human prostate cancer xenograft accompanied by a decrease in the expression of androgen receptor and prostate-specific antigen (PSA).

OBJECTIVES: Epidemiological studies and prevention trials suggest selenium is a promising preventive agent for prostate cancer. Selenium-containing compounds inhibited the growth of prostate cancer cell lines including androgen sensitive LNCaP and androgen insensitive DU145 and PC3 cells in vitro. Previous study revealed a novel mechanism of selenium action in which selenium (methylseleninic acid (MSA)) markedly reduced androgen receptor (AR) signaling in prostate cancer cells, suggesting that selenium might act as an antiandrogen, which could serve as a therapeutic agent for prostate cancer. In this study, we tested whether selenium (methylselenocysteine (MSC)) affects tumor growth of human prostate cancer cells by targeting AR signaling in vivo. METHODS: Prostate tumor xenografts were established in nude mice by co-inoculating LNCaP cells with Matrigel. The mice-bearing tumors were treated with or without MSC (100 microg/mouse/day) via intraperitoneal injection for 2 weeks. The effect of MSC on tumor growth, AR, and prostate-specific antigen (PSA) expression was examined. RESULTS: Methylselenocysteine (MSC) significantly inhibited LNCaP tumor growth (P < 0.05). AR expression in tumor tissues and serum PSA levels were considerably decreased in MSC-treated mice compared to the vehicle controls. CONCLUSIONS: Pharmacological dose of MSC inhibits the growth of LNCaP human prostate cancer in vivo accompanied by a decrease in the expression of AR and PSA. These findings suggest that selenium (MSC) can serve as a therapeutic agent aimed at disruption of AR signaling for prostate cancer.

Animals↗
PubMed2001

Intramolecular homolytic substitution at selenium: synthesis of novel selenium-containing vitamin E analogues.

Treatment of 1-(benzylselenenyl)-5-butyl-5-nonanol (10) with oxalyl chloride followed by the sodium salt of N-hydroxypyridine-2-thione afforded the corresponding pyridine-2-thione-N-oxycarbonyl (PTOC) oxalate ester which was not isolated but immediately heated to provide 2,2-dibutylselenane (7). This transformation presumably involves a tertiary alkyl radical that undergoes intramolecular homolytic substitution at selenium with loss of the benzyl radical to provide the selenium-containing ring system (7). A similar protocol, when applied to 1-(2-benzylselenenyl-5-methoxyphenyl)-3-methyl-3-heptanol (18) and 1-(2-benzylselenenyl-5-methoxyphenyl)-3,7,11,15-tetramethyl-3-hexadecanol (19), followed by deprotection, afforded the selenium-containing alpha-tocopherol analogues 4 and 1f, respectively, in moderate yields. To the best of our knowledge, these transformations represent the first examples of tertiary radicals involved in homolytic substitution chemistry at selenium.

Heterocyclic Compounds↗
PubMed2005

The inhibition of osteogenesis with human bone marrow mesenchymal stem cells by CdSe/ZnS quantum dot labels.

CdSe/ZnS quantum dots (QDs) have recently been used as cell tracers for long term imaging of live cells. A number of studies indicate that introduction of quantum dots to cells have no apparent deleterious effects on the morphology or growth of cells. In the present study, the human bone marrow mesenchymal stem cells (hBMSCs) were used as a model to examine the effects of QDs on the growth and osteogenic differentiation of the cells. The CdSe/ZnS QDs were delivered into hBMSCs by liposome-mediated transfection with high efficiency; analysis by transmission electron microscopy revealed that the internalized QDs could be located in the endosome-like vesicles. Uptake of QDs into hBMSCs did not affect the proliferation and cell cycle distribution of the cells. When induced to differentiate along the osteogenic lineage, the QD-containing-hBMSCs were shown to have mineral deposition on the extracellular matrix. However, the cells displayed lower alkaline phosphatase activity as compared to those without QDs. Analysis by reverse transcriptase polymerase chain reaction further demonstrated that the expression of two osteogenic markers, osteopontin and osteocalcin, was significantly inhibited. Together our results show that the presence of QDs in hBMSCs prevents the full response of the cells to induced osteogenic differentiation.

Bone Marrow Cells↗
PubMed2005

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles.

The effect of additives on the photostability of semiconductor nanoparticles was studied using CdSe, CdSe/ZnSe and CdSe/ZnS particles of various sizes and composition. The additives included phosphine oxides, amines, and antioxidants. Strong initial enhancement of band edge emission by hexadecylamine was observed for the uncoated particles but stability over a week period in light and air was shown to be poor. Inorganic coatings rendered the nanoparticles initially insensitive to additive but provided little extra stability in terms of photoluminescence. Antioxidant was shown to be effective at reducing the rate of photooxidative degradation for all particles in chloroform but not in toluene.

Adsorption↗
PubMed2002

Development of new analytical methods for selenium speciation in selenium-enriched yeast material.

A sequential extraction allowing the discrimination of water-soluble and non-soluble selenium fractions has been developed to evaluate the availability of selenium (Se) in an Se-enriched yeast candidate reference material. The fractionation of selenium-containing compounds in the extracts was achieved on preparative grade 200 Superdex 75 and columns. It showed that water-soluble selenium is present in several fractions with a large mass distribution. Low-molecular- (< or = 10,000) and high-molecular-mass selenocompounds (range 10,000-100,000) were considered separately for further experiments. The analytical approach for low-molecular-mass selenocompounds was based onanion-exchange HPLC with on-line inductively coupled plasma (ICP) MS for quantitative analysis. Selenocystine, selenomethionine, selenite and selenate were quantified in the fractions isolated in preparative chromatography. The study revealed the existence of various unidentified Se species in yeast material. The Se-containing proteins in the yeast material have been further separated and selenium quantified by the combination of gel electrophoresis and electrothermal vaporization-ICP-MS. This new approach allows the separation of the proteins with high resolution by sodium dodecylsulfate-polyacrylamide gel electrophoresis and the sensitive determination of selenium in the protein bands.

Calibration↗