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At least 613 records · Page 34Linked to original sources
PubMed2004

Hierarchical nanoparticle assemblies formed by decorating breath figures.

The combination of two self-assembly processes on different length scales leads to the formation of hierarchically structured nanoparticle arrays. Here, the formation of spherical cavities, or 'breath figures'-made by the condensation of micrometre-sized water droplets on the surface of a polymer solution-that self-assemble into a well-ordered hexagonal array, is combined with the self-assembly of CdSe nanoparticles at the polymer solution-water droplet interface. Complete evaporation of the solvent and water confines the particle assembly to an array of spherical cavities and allows for ex situ investigation. Fluorescence confocal, transmission electron and scanning electron microscope images show the preferential segregation of the CdSe nanoparticles to the polymer solution-water interface where they form a 5-7-nm-thick layer, thus functionalizing the walls of the holes. This process opens a new route to fabricating highly functionalized ordered microarrays of nanoparticles, potentially useful in sensory, separation membrane or catalytic applications.

Cadmium Compounds↗
PubMed2005

Study of colloidal quantum-dot surfaces using an innovative thin-film positron 2D-ACAR method.

Nanosized inorganic particles are of great interest because their electronic properties can be easily tailored, providing a tremendous potential for applications in optoelectronic devices, light-emitting diodes, solar cells and hydrogen storage. Confinement of electrons and holes to dimensions comparable to their wavelength leads to quantum-well states with modified wavefunctions and density of states. Surface phenomena are crucial in determining nanoparticle properties in view of their large surface-to-volume ratio. Despite a wealth of information, many fundamental questions about the nature of the surface and its relationship with the electronic structure remain unsolved. Ab initio calculations on CdSe nanocrystals suggest that passivating the ligands does not produce the ideal wurtzite structure and that Se atoms relax outwards irrespective of passivation. Here we show that implanted positrons are trapped at the surface of CdSe nanocrystals. They annihilate mostly with the Se electrons, monitor changes in composition and structure of the surface while hardly sensing the ligand molecules, and we thus unambiguously confirm the predicted strong surface relaxation.

Cadmium Compounds↗
PubMed2003

Controlled growth of tetrapod-branched inorganic nanocrystals.

Nanoscale materials are currently being exploited as active components in a wide range of technological applications in various fields, such as composite materials, chemical sensing, biomedicine, optoelectronics and nanoelectronics. Colloidal nanocrystals are promising candidates in these fields, due to their ease of fabrication and processibility. Even more applications and new functional materials might emerge if nanocrystals could be synthesized in shapes of higher complexity than the ones produced by current methods (spheres, rods, discs). Here, we demonstrate that polytypism, or the existence of two or more crystal structures in different domains of the same crystal, coupled with the manipulation of surface energy at the nanoscale, can be exploited to produce branched inorganic nanostructures controllably. For the case of CdTe, we designed a high yield, reproducible synthesis of soluble, tetrapod-shaped nanocrystals through which we can independently control the width and length of the four arms.

Cadmium Compounds↗
PubMed2003

Mortalin imaging in normal and cancer cells with quantum dot immuno-conjugates.

Quantum dots are the nanoparticles that are recently emerging as an alternative to organic fluorescence probes in cell biology and biomedicine, and have several predictive advantages. These include their i) broad absorption spectra allowing visualization with single light source, ii) exceptional photo-stability allowing long term studies and iii) narrow and symmetrical emission spectrum that is controlled by their size and material composition. These unique properties allow simultaneous excitation of different size of quantum dots with a single excitation light source, their simultaneous resolution and visualization as different colors. At present there are only a few studies that have tested quantum dots in cellular imaging. We describe here the use of quantum dots in mortalin imaging of normal and cancer cells. Mortalin staining pattern with quantum dots in both normal and cancer cells mimicked those obtained with organic florescence probes and were considerably stable.

Antibodies, Monoclonal↗
PubMed1997

Intracerebral recombinant HSV-1 vector does not reactivate latent HSV-1.

Herpes simplex virus type-1 (HSV-1) has been used for gene delivery in the nervous system for the treatment of brain tumors and other neurological diseases. In most protocols, recombinant viruses containing the gene of interest are directly injected into the brain. Since many people harbor latent wild-type HSV-1 virus in sensory ganglia and other regions of the nervous system, there is a potential risk that the injected recombinant virus may reactivate the latent wild-type virus to cause severe encephalitis. The present study used two rat latent infection models to evaluate this risk. Adult rats were infected with wild-type kos by cornea scarification or by intracerebral injection, and after the establishment of latency, the ICP6(-) strain hrR3 was injected intracerebrally. In the control group, the latent virus was reactivated by treatment of cadmium sulfate. Viral shedding from tears was detected by incubation with Vero cells, and the trigeminal ganglia, cortical tissue and the eyes were collected to detect reactivated wild-type virus by RT-PCR. Our results showed that while the reactivated wild-type virus was readily detectable in the cadmium-sulfate-treated animals, intracerebrally infected hrR3 did not reactivate the latent virus in either the corneal model or the cerebral model. These results indicate that intracranial injection of partially defective recombinant virus may bear little risk of reactivating latent wild-type virus harbored in the sensory ganglia or the brain in our animal model.

Animals↗
PubMed2002

Application of functionalized CdS nanoparticles as fluorescence probe in the determination of nucleic acids.

Nanometer-sized fluorescent particles were successfully synthesized. The nanoparticles have a narrow, tunable, symmetric emission spectrum and a broad, continuous excitation spectrum. They are also photochemically stable. A synchronous fluorescence method was developed for the rapid determination of DNA with functionalized CdS as a fluorescence probe, based on the synchronous fluorescence quenching of functionalized CdS in the presence of DNA. Maximum fluorescence is produced at pH 7.0, with maximum excitation and emission wavelengths of 360 and 620 nm, respectively. The maximum emission wavelength of synchronous fluorescence is 354 nm when delta lambda = 260 nm. Under optimum conditions, the calibration graphs are linear over the range 0-3.5 microg mL(-1) for calf thymus DNA (CT-DNA) and 0.2-3.0 microg mL(-1) for fish sperm DNA. The corresponding detection limit is 0.01 microg mL(-1) for CT-DNA and 0.02 microg mL(-1) for fish sperm DNA. The relative standard deviation of seven replicate measurements is 2.2% for 1 microg mL(-1) calf thymus DNA and 2.4% for 1 microg mL(-1) fish sperm DNA. The method is simple, rapid and sensitive. The recovery and relative standard deviation are very satisfactory.

Animals↗
PubMed2003

Cadmium sulfide nanocluster-based electrochemical stripping detection of DNA hybridization.

A novel, sensitive electrochemical DNA hybridization detection assay, using cadmium sulfide (CdS) nanoclusters as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the CdS nanocluster oligonucleotide DNA probe, followed by the dissolution of the CdS nanoclusters anchored on the hybrids and the indirect determination of the dissolved cadmium ions by sensitive anodic stripping voltammetry (ASV) at a mercury-coated glassy carbon electrode (GCE). The results showed that only a complementary sequence could form a double-stranded dsDNA-CdS with the DNA probe and give an obvious electrochemical response. A three-base mismatch sequence and non-complementary sequence had negligible response. The combination of the large number of cadmium ions released from each dsDNA hybrid with the remarkable sensitivity of the electrochemical stripping analysis for cadmium at mercury-film GCE allows detection at levels as low as 0.2 pmol L(-1) of the complementary sequence of DNA.

Animals↗
PubMed2004

Multi-step synthesis of nanoparticles performed on millisecond time scale in a microfluidic droplet-based system.

This paper reports a plug-based, microfluidic method for performing multi-step chemical reactions with millisecond time-control. It builds upon a previously reported method where aqueous reagents were injected into a flow of immiscible fluid (fluorocarbons)(H. Song et al., Angew. Chem. Int. Ed., 2003, 42, 768). The aqueous reagents formed plugs--droplets surrounded and transported by the immiscible fluid. Winding channels rapidly mixed the reagents in droplets. This paper shows that further stages of the reaction could be initiated by flowing additional reagent streams directly into the droplets of initial reaction mixture. The conditions necessary for an aqueous stream to merge with aqueous droplets were characterized. The Capillary number could be used to predict the behavior of the two-phase flow at the merging junction. By transporting solid reaction products in droplets, the products were kept from aggregating on the walls of the microchannels. To demonstrate the utility of this microfluidic method it was used to synthesize colloidal CdS and CdS/CdSe core-shell nanoparticles.

Cadmium Compounds↗
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↗
PubMed2005

Biomolecule detection via target mediated nanoparticle aggregation and dielectrophoretic impedance measurement.

A new biosensing system is described that is based on the aggregation of nanoparticles by a target biological molecule and dielectrophoretic impedance measurement of these aggregates. The aggregation process was verified within a microchannel via fluorescence microscopy, demonstrating that this process can be used in a real time sensor application. Positive dielectrophoresis is employed to capture the nanoparticle aggregates at the edge of thin film electrodes, where their presence is detected either by optical imaging via fluorescence microscopy or by measuring the change in electrical impedance between adjacent electrodes. The electrical detection mechanism demonstrates the potential for this method as a micro total analysis system (microTAS).

Avidin↗