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At least 19 recordsLinked to original sources
PubMed2004

ZnS/CdS/ZnS quantum dot quantum well produced in inverted micelles.

A ZnS/CdS/ZnS quantum dot quantum well was prepared in AOT micelles successfully and was characterized by absorption spectroscopy and fluorescence spectroscopy. Luminescence in the region of 350-600 nm was observed. The complete ZnS shell might reduce the number of defects on the surface of the CdS well, which were assumed to act as centers for radiationless recombination, resulting in the luminescence enhancement.

Journal Article↗
PubMed2005

Effect of layer thickness on the luminescence properties of ZnS/CdS/ZnS quantum dot quantum well.

ZnS/CdS/ZnS quantum dot quantum well was prepared. The optical properties of ZnS/CdS/ZnS QDQW with different thickness of CdS well and ZnS shell were studied. Absorption spectra, emission spectra, and luminescence lifetimes were measured. The observed luminescence was assigned to the bulk donor-acceptor pair recombination of CdS and can be enhanced by increasing the thickness of the CdS well or coating an appropriate thickness of ZnS shell on the surface of the CdS well. The luminescence enhancement was caused by the relative reduce in the surface effect. The luminescence lifetimes were influenced strongly by the surface state.

Journal Article↗
PubMed2004

Photoluminescence of tetrahedral quantum-dot quantum wells.

Taking into account the tetrahedral shape of a quantum-dot quantum well (QDQW) when describing excitonic states, phonon modes, and the exciton-phonon interaction in the structure, we obtain within a nonadiabatic approach a quantitative interpretation of the photoluminescence spectrum of a single CdS/HgS/CdS QDQW. We find that the exciton ground state in a tetrahedral QDQW is bright, in contrast to the dark ground state for a spherical QDQW. The position of the phonon peaks in the photoluminescence spectrum is attributed to interface optical phonons. We also show that the experimental value of the Huang-Rhys parameter can be obtained only within the nonadiabatic theory of phonon-assisted transitions.

Journal Article↗
PubMed2003

Molecular profiling of single cells and tissue specimens with quantum dots.

Quantum dots are tiny light-emitting particles on the nanometer scale. They are emerging as a new class of biological label with properties and applications that are not available with traditional organic dyes and fluorescent proteins. Recent advances, as reported in Science and Nature Biotechnology, have led to quantum dot bioconjugates that are highly luminescent and stable. These bioconjugates raise new possibilities for studying genes, proteins and drug targets in single cells, tissue specimens and even in living animals.

Animals↗
PubMed2004

On the cyto-toxicity caused by quantum dots.

Quantum dots (QDs) such as CdSe QDs have been introduced as new fluorophores. The QDs conjugated with antibody are starting to be widely used for immunostaining. However there is still not sufficient analysis of the toxicity of QDs in the literature. Therefore we evaluated the cell damage caused by the quantum dots for biological applications. We performed cell viability assay to determine the difference in cell damage depending on the sizes and colors of mercapto-undecanoic acid (MUA) QDs and the cell types. The results showed that the cell viability decreased with increasing concentration of MUA-QDs. But in the case of Vero cell (African green monkey's kidney cell) with red fluorescence QD (QD640), the cell damage was less than for the others. Furthermore through the flow cytometry assay we found that this cell damage caused by MUA-QD turned out to be cell death after 4-6-hr incubation. From the two assays described above, we found that there is a range of concentration of MUA-QDs where the cell viability decreased without cell death occurring and thus we conclude that attention should be given when MUAQDs are applied to living organisms even in low concentrations.

Animals↗
PubMed2004

Chemical analysis and cellular imaging with quantum dots.

Quantum dots are tiny light-emitting particles on the nanometer scale. They are emerging as a new class of biological labels with properties and applications that are not available with traditional organic dyes and fluorescent proteins. Their novel properties such as improved brightness, resistance against photobleaching, and multicolor light emission, have opened new possibilities for ultrasensitive chemical analysis and cellular imaging. In this Research Highlight article , we discuss the unique optical properties of semiconductor quantum dots, surface chemistry and bioconjugation, current applications in bioanalytical chemistry and cell biology, and future research directions.

Animals↗
PubMed2005

Silica-coated nanocomposites of magnetic nanoparticles and quantum dots.

Quantum dots (QDs) and magnetic nanoparticles (MPs) are of interest for biological imaging, drug targeting, and bioconjugation because of their unique optoelectronic and magnetic properties, respectively. To provide for water solubility and biocompatibility, QDs and MPs were encapsulated within a silica shell using a reverse microemulsion synthesis. The resulting SiO2/MP-QD nanocomposite particles present a unique combination of magnetic and optical properties. Their nonporous silica shell allows them to be surface modified for bioconjugation in various biomedical applications.

Coated Materials, Biocompatible↗
PubMed2005

In vivo molecular and cellular imaging with quantum dots.

Quantum dots (QDs), tiny light-emitting particles on the nanometer scale, are emerging as a new class of fluorescent probe for in vivo biomolecular and cellular imaging. In comparison with organic dyes and fluorescent proteins, QDs have unique optical and electronic properties: size-tunable light emission, improved signal brightness, resistance against photobleaching, and simultaneous excitation of multiple fluorescence colors. Recent advances have led to the development of multifunctional nanoparticle probes that are very bright and stable under complex in vivo conditions. A new structural design involves encapsulating luminescent QDs with amphiphilic block copolymers and linking the polymer coating to tumor-targeting ligands and drug delivery functionalities. Polymer-encapsulated QDs are essentially nontoxic to cells and animals, but their long-term in vivo toxicity and degradation need more careful study. Bioconjugated QDs have raised new possibilities for ultrasensitive and multiplexed imaging of molecular targets in living cells, animal models and possibly in humans.

Animals↗
PubMed2005

Differences in subcellular distribution and toxicity of green and red emitting CdTe quantum dots.

Quantum dots (QDs) are emerging as alternative or complementary tools to the organic fluorescent dyes currently used in bioimaging. QDs hold several advantages over conventional fluorescent dyes including greater photostability and a wider range of excitation/emission wavelengths. However, recent work suggests that QDs exert deleterious effects on cellular processes. This study examined the subcellular localization and toxicity of cadmium telluride (CdTe) QDs and pharmacological means of preventing QD-induced cell death. The localization of CdTe QDs was found to depend upon QD size. CdTe QDs exhibited marked cytotoxicity in PC12 and N9 cells at concentrations as low as 10 microg/ml in chronic treatment paradigms. QD-induced cell death was characterized by chromatin condensation and membrane blebbing and was more pronounced with small (2r=2.2+/-0.1 nm), green emitting positively charged QDs than large (2r=5.2+/-0.1 nm), equally charged red emitting QDs. Pretreatment of cells with the antioxidant N-acetylcysteine and with bovine serum albumin, but not Trolox, significantly reduced the QD-induced cell death. These findings suggest that the size of QDs contributes to their subcellular distribution and that drugs can alter QD-induced cytotoxicity.

Acetylcysteine↗
PubMed2002

Quantum Monte Carlo calculations of nanostructure optical gaps: application to silicon quantum dots.

Quantum Monte Carlo (QMC) calculations of the optical gaps of silicon quantum dots ranging in size from 0 to 1.5 nm are presented. These QMC results are used to examine the accuracy of density functional (DFT) and empirical pseudopotential based calculations. The GW approximation combined with a solution of the Bethe-Salpeter equation performs well but is limited by its scaling with system size. Optical gaps predicted by DFT vary by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalism are found to be minimal in these systems.

Journal Article↗
PubMed2001

Semiconductor quantum dot: a quantum light source of multicolor photons with tunable statistics.

We investigate the intensity correlation properties of single photons emitted from an optically excited single semiconductor quantum dot. The second order temporal coherence function of the photons emitted at various wavelengths is measured as a function of the excitation power. We show experimentally and theoretically that a quantum dot is not only a source of nonclassically correlated monochromatic photons but is also a source of multicolor photons with tunable correlation properties. We found that the emitted photon statistics can be varied by the excitation rate from a sub-Poissonian one, where the photons are temporally antibunched, to super-Poissonian, where they are temporally bunched.

Journal Article↗
PubMed2004

Quantum-dot quantum-interference infrared design proposal photodetector: and modeling of performance characteristics.

A novel design of an IR photodetector operating at wavelengths around 10 microm is presented. It is based on a three-level quantum coherence effect in semiconductor quantum dots as measured in balanced-homodyne detection in a Mach-Zehnder interferometer. The advantage of this design is the combination of room-temperature operation and fast response time, whereas the major drawback is the high noise-equivalent power.

Computer Simulation↗
PubMed2001

Glancing-angle diffraction anomalous fine structure of InAs quantum dots and quantum wires.

We have performed Diffraction Anomalous Fine Structure measurements at the As K-edge of self-growth InAs/InP(001) Quantum Wires and InAs/GaAs(001) Quantum Dots. The samples have been grown by Molecular Beam Epitaxy and their equivalent thickness is of 2.5 monolayers. We have measured the (440) and (420) Bragg reflections in glancing-angle scattering geometry, at incidence angles close to the substrate critical angle. We demonstrate the feasibility of the experiment reporting, for the first time. Diffraction Anomalous Fine Structure spectra of such low coverage epitaxial layers, and we show that the analysis of the Diffraction Anomalous Fine Structure lineshape together with the analysis of oscillatory part of the signal, can provide information about composition and strain of the nanostructures.

Journal Article↗