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PubMed2007

Electrogenerated chemiluminescence of CdSe quantum dots dispersed in aqueous solution.

Electrogenerated chemiluminescence (ECL) of CdSe quantum dots (QDs) dispersed in aqueous solution was studied with bare electrode. The ECL emission was observed at -1.4 V vs. Ag/AgCl and the ECL spectrum peak is similar to that of the defect photoluminescence (PL) spectrum, indicating the surface defects played a critical role in the emission process. The experiment results suggested that dissolved oxygen had a great effect on the ECL intensity. Other influence factors including the electrochemical parameters and QDs concentration were investigated in detail. As an application of the CdSe QDs ECL, the pyrogallol (1, 2, 3-trihydroxybenzene) was detected in aqueous solution. Under the optimal conditions, a linear relationship between ECL intensity and pyrogallol concentration was obtained in the range from 4.0 x 10(-7) to 2.0 x 10(-5) M with a correlation coefficient of 0.9904 and the limit of detection was 6.6 x 10(-8) M (S/N = 3). A possible mechanism about ECL of QDs was also discussed.

Biosensing Techniques↗
PubMed2005

Amorphous Se: a new platform for synthesizing superparamagnetic colloids with controllable surfaces.

We have successfully incorporated iron oxide nanoparticles into monodispersed amorphous selenium (a-Se) colloids by regulating the reaction temperature during the synthesis of a-Se. The surfaces of these a-Se colloids could be coated with conformal and smooth shells made of Pt and SiO2. The Se cores could then be removed by etching with hydrazine. The spherical morphology and superparamagnetism were maintained in all these synthetic steps. The presence of Pt and SiO2 on the outer surfaces of these colloidal particles allows one to control their surface functionalities through the formation of alkanethiolate and siloxane monolayers, respectively.

Colloids↗
PubMed2004

Selenium supplementation for critically ill adults.

BACKGROUND: Selenium is a trace mineral essential to human health, which has an important role in the immune response, defence against tissue damage and thyroid function. Improving selenium status could help protect against overwhelming tissue damage and infection in critically ill adults. OBJECTIVES: This review assessed the effects of selenium supplementation including the selenium-containing compound, ebselen, on adults recovering from critical illness. SEARCH STRATEGY: We searched CENTRAL (The Cochrane Library, Issue 2, 2003), MEDLINE, (1966 to July 2003), EMBASE (1980 to Week 30 2003),CAB NAR (1973 to March 2003), BIOSIS (1985 to July 2003), CINAHL (1982 to July 2003), HEALTHSTAR (1975 to September 2002), Current Controlled Trials, and reference lists. We contacted investigators, and handsearched four journals. Date of the most recent search: December 2003. SELECTION CRITERIA: Randomized trials of selenium or ebselen supplementation by any route, in adults with critical illness (including burns, head injury, brain haemorrhage, cerebrovascular accident and surgery). DATA COLLECTION AND ANALYSIS: Two reviewers independently extracted data and assessed trial quality. We sought additional information as required from trialists. We also undertook pooling of data for outcomes and selected exploratory analyses were undertaken. MAIN RESULTS: Seven randomized trials involving813participants were included. The quality of trials, as reported, was poor, particularly for allocation concealment. The availability of outcome data was limited and trials involving selenium supplementation, were small. Thus the results must be interpreted with caution. Because of heterogeneity, results are presented for the random effects models. Four selenium trials showed no statistically significant difference in mortality (relative risk (RR) 0.52, 95% confidence interval (CI) 0.20 to 1.34). Three trials of ebselen also showed no statistically significant difference in mortality (RR 0.83, 95% CI 0.51 to 1.35). One trial of selenium found no statistically significant difference between groups for participants developing infection (RR 1.33, 95% CI 0.55 to 3.24). Three trials of ebselen provided data for participants developing infections (pyrexia, respiratory infections or meningitis), which was not statistically significant (RR 0.60, 95% CI 0.36 to 1.02). No clear evidence emerged for the benefits of selenium or ebselen supplementation for the outcomes of days on a ventilator, length of intensive care unit stay, length of hospital stay or quality of life. REVIEWERS' CONCLUSIONS: There is insufficient evidence to recommend supplementation of critically ill patients with selenium or ebselen. Trials are required which overcome the defects of the reviewed studies, particularly inadequate size and methodology. This review will be updated when four ongoing trials are completed.

Adult↗
PubMed2006

Intracellular uptake of CdSe-ZnS/polystyrene nanobeads.

The ideal optical properties of quantum dots (QDs) offer the possibility of using them as fluorescent probes in biological staining and diagnostics. Some techniques have been developed to incorporate QDs into polymer beads, to solve the problems relating to QDs' surface chemistry, such as water solubility, biocompatibility, chemical stability in physiological media, and so on, or to pack different combinations of QDs and produce QD encoded polymer beads. However, the QD encoded polymer beads that have been reported so far are above 100 nm; therefore they are very useful for multiplexed bioassays, but not suitable for staining or labeling of subcellular components or intracellular measurements because of the relatively big size of the beads. There is great need for QD encoded polymer beads smaller than 100 nm. In this work, luminescent CdSe-ZnS QDs were incorporated into polystyrene (PS) beads grafted with carboxyl groups with the use of an emulsion polymerization method, and separation of nanoscale QD encoded PS beads (30 nm) was performed through centrifugation at high speed in viscous solution. The nanobeads were further surface modified with folic acid and their intracellular delivery into NIH-3T3 and HT-29 cell lines was investigated with the use of confocal microscope. The longevity of QDs allows the intracellular delivery of the nanobeads to be tracked over a certain time period.

Animals↗
PubMed1988

Digital image processing of crystalline specimens examined by electron microscopy.

Crystalline specimens imaged in the electron microscope are analysed using digital processing. Some principles of structural analysis using the method of Fourier decomposition are discussed. Complementary techniques, such as enhancement by gradient and Laplacian operators, have been found useful in analysing electron micrographs. The application of these techniques to some problems in Materials Science and Biology are reviewed. By selecting and phase-correcting spots in the computed diffraction pattern, it was possible to localize atoms, molecules, and their defective arrangement in evaporated gold, sputter-deposited tungsten films, and single crystals of cadmium selenide. Digital processing based on the theory of helical diffraction was used to explore the three-dimensional arrangement of molecules in cellular components of alveolar soft part sarcoma, Hirano bodies, and neurofibrillar tangles in the human brain.

Actins↗
PubMed1993

Cell growth on immobilized cell growth factor. 7. Protein-free cell culture by using growth-factor-immobilized polymer membrane.

A protein-free culture of anchorage-dependent cells, mouse fibroblast cells, STO and 3T3-L1 and fibroic sarcoma cells, Swiss albino HSDM1C1, grown on a cell-growth protein, insulin, and/or a cell-adhesion protein, collagen, which are immobilized or coimmobilized on surface-hydrolyzed poly(methyl methacrylate) membrane, was investigated. By adding metal ions and lipids to the culture medium, a protein-free culture medium was composed, which was potent in promoting cell proliferation similarly to serum-containing culture medium. In particular, with insulin/collagen-coimmobilized membrane, a protein-free culture was established without detachment of growing cells over a long period. These protein-immobilized membranes could be used repeatedly.

Amino Acid Sequence↗
PubMed2003

Multicolor luminescence patterning by photoactivation of semiconductor nanoparticle films.

Indiscriminate adsorption of nanoparticles (NPs) significantly complicates the preparation of mesoscale NP patterns considered as enabling technology for many devices and processes. Instead of selected chemical functionalization of the substrate surface prior to the assembly of nanocolloids, the required optical properties - in our case, high quantum yield luminescence - are imparted to the layer-by-layer assembled films by spatially selected photoactivation. The films are made by sequential adsorption of a positively charged polyelectrolyte and a negatively charged CdSe/CdS aqueous dispersion with an initial quantum yield of 0.5-2%. The photoactivation process takes place in the presence of oxygen and may be accompanied by photoetching. A 50-500-fold increase in the luminescence intensity of CdSe/CdS citrate-stabilized particles (quantum yield 25-45%) after visible light illumination provides excellent pattern contrast. Micron scale luminescence patterns were produced from NPs of various CdSe core diameters with red, yellow, and green emission. It was also demonstrated that different emission colors such as orange and green can be combined in one image by taking advantage of spatially selective photoetching. The presented optical patterning technique significantly simplifies the preparation of luminescence patterns as compared to conventional methods. The high signal-to-noise ratio associated with it is essential for optical devices, information processing, and biophotonics. The most immediate use of this approach is expected in cryptography and cell monitoring.

Cadmium Compounds↗
PubMed2005

A modular nanoparticle-based system for reagentless small molecule biosensing.

Metalloprotein tethered CdSe nanoparticles have been generated to provide selective and reagentless maltose biosensing. As opposed to cell or protein detection by semiconducting nanoparticle bioconjugates, a modular method for small-molecule detection using semiconducting nanoparticle bioconjugates has been difficult. Here we report a method for reagentless protein-based semiconducting nanoparticle biosensors. This method uses Ru(II) complex-CdSe nanoparticle interactions and the maltose-induced conformation changes of maltose binding protein to alter the CdSe nanoparticle fluorescence emission intensity. In this proof-of-principle system, the maltose-induced protein conformation changes alter the Ru(II) complex-CdSe nanoparticle interaction, which increases the CdSe emission intensity. Altered CdSe emission intensity effects are best described as electron transfer from the Ru(II) complex to the CdSe excited state forming the nonfluorescent CdSe anion. Four surface-cysteine, Ru(II) complex-attached maltose-binding proteins have been studied for maltose dependent alteration of CdSe emission intensities. With 3.0-3.5 nm diameter CdSe nanoparticles, all ruthenated maltose-binding proteins display similar maltose-dependent increases (1.4-fold) in CdSe emission intensity and maltose binding affinities (KA = 3 x 106 M-1). For these four systems, the only difference was the sample-to-sample variation in maltose-dependent responses. Thus, very few surface cysteine mutations need to be examined to find a successful biosensor, as opposed to analogous systems using organic fluorophores. This strategy generates a unimolecular, or reagentless, semiconducting nanoparticle biosensor for maltose, which could be applied to other proteins with ligand-dependent conformation changes.

Biosensing Techniques↗
PubMed2006

Effects of temperature on the alignment and electrooptical responses of a nematic nanoscale liquid crystalline film.

The surface-induced alignment and electrooptical (EO) dynamics of a 50-nm-thick liquid crystalline (4-n-pentyl-4'-cyanobiphenyl; 5CB) film were studied at three temperatures: 25 and 33 degrees C (near the crystalline-nematic and nematic-isotropic transition temperatures, respectively) and 29 degrees C (a median temperature in the stability region of the nematic phase). The ZnSe surfaces that entrap the liquid crystal (LC) film have been polished unidirectionally to produce a grooved surface presenting nanometer-scale corrugations, a structure that induces a planar and homogeneous orientation in the nematic phase. The present work attempts to understand the influences of temperature on the surface-induced alignment and corresponding EO dynamics of the material. Step-scan time-resolved spectroscopy measurements were made to determine the rate constants for the electric-field-induced orientation and thermal relaxation of the 5CB film. The field-driven orientation rates vary sensitively with temperature across a range that spans the stability limits of the nematic phase; the relaxation rates, however, vary very little across this same temperature range. We propose that these differences in LC behavior arise as consequence of the interplay of the temperature dependence of the elastic constants, viscosity, and degree of orientational order of the LC medium. A simple theoretical model provides some understanding of these behaviors.

Biphenyl Compounds↗
PubMed2006

Colloidal CdSe quantum wires by oriented attachment.

We report here a relatively low temperature (100-180 degrees C) synthetic route to high-quality and single-crystalline CdSe nanowires using air-stable and generic chemicals. The diameter of nanowires was controlled and varied in an exceptionally small size regime, between 1.5 and 6 nm. This was achieved by using alkylamines, a single type or a mixture of two different types of amines, with different chain lengths and varying the reaction temperature. The experimental results suggest the coexistence of two types of fragments in the prewire aggregates, known as "pearl-necklace" or "string-of-pearls" in the literature, which are loosely associated and chemically fused sections.

Anisotropy↗
PubMed2005

Size and ligand effects on the electrochemical and spectroelectrochemical responses of CdSe nanocrystals.

The electrochemical properties of CdSe quantum dots with electrochemically inactive surface ligands (TOPO) have been investigated in comparison with the analogous nanocrystals containing electrochemically active oligoaniline ligands. The TOPO-capped nanocrystals have been studied in a wide size range (from 3 to 6.5 nm) with the goal to amplify the influence of the quantum confinement effect on the electrochemical response. The determined HOMO and LUMO levels have been found in good agreement with the ones obtained from photoluminescence studies and those predicted theoretically. Ligand exchange with aniline tetramer significantly influences the voltammetric peaks associated with the HOMO oxidation and the LUMO reduction of the quantum dots, which are shifted to higher and lower potentials, respectively. These shifts are interpreted in terms of the positive ligand charging which precedes the oxidation of the nanocrystals and the insulating nature of the ligand in the case of the nanocrystal reduction. The ligand-nanocrystal interactions have also been studied by UV-Vis-NIR and Raman spectroelectrochemistry in comparison with a specially prepared model compound which, apart from the anchoring function is identical to the grafted oligoaniline ligand. Both spectroelectrochemical techniques clearly indicate the same nature of the oxidation/reduction pathway for both the model compound and the grafted ligand. The influence of the grafting is manifested by a shift in the onset of the ligand oxidation as compared to the case of the "free" model compound. Since both components (ligands and nanocrystals) mutually influence their electrochemical and spectroelectrochemical properties, the newly developed system can be considered as a true molecular hybrid. Such hybrids are of interest because the potential zone of the ligand electroactivity is well separated from that of the nanocrystals and, as a result, the organic part can be electrochemically switched between the semiconducting and the conducting states with no change in the oxidation state of the nanocrystal. The newly developed system offers therefore the possibility of an electrical addressing of individual nanocrystals via the conducting ligands.

Aniline Compounds↗
PubMed2006

Self-organized CdSSe quantum dots thin films.

Self-organized and strained CdSSe quantum dot (Q-dot) thin films have been grown on ITO-coated glass substrates by novel wet chemical route. The Q-dots are (002) oriented faceted pyramids with average particle size of 7.5 nm. The X-ray diffraction results reveal the formation of a solid solution of CdSSe. Atomic force microscopy is used to investigate the morphology of the nanocrystalline thin films. The energy dispersive X-ray analysis spectrum confirms the presence of Cd, S, and Se in the films. Optical absorption and photoluminescence spectra show the blue shift for quantum dot thin films.

Cadmium Compounds↗