ABSTRACT
Light scattering from metal nanoparticles and fluorescence from quantum dots offer distinct advantages over traditional fluorophores when it comes to detection of single molecules in living cells.
Subject(s)
Biochemistry , Molecular Biology , Nanotechnology , Biochemical Phenomena , Quantum DotsABSTRACT
When water is heated and pressurized above the critical point, it becomes a suitable solvent to employ organic capping ligands to control and stabilize the synthesis of nanocrystals. Without alkanethiol ligands, Cu(NO(3))(2) hydrolyzes to form polydisperse copper(II) oxide particles with diameters from 10 to 35 nm. However, in the presence of 1-hexanethiol, X-ray photoelectron spectroscopy, selected area electron diffraction, and transmission electron microscopy reveal the formation of copper nanocrystals approximately 7 nm in diameter. The use of a different precursor, Cu(CH(3)COO)(2), leads to particles with significantly different morphologies. A mechanism is proposed for sterically stabilized nanocrystal growth in supercritical water that describes competing pathways of hydrolysis to large oxidized copper particles versus ligand exchange and arrested growth by thiols to produce small monodisperse Cu nanoparticles.
ABSTRACT
A new synthetic method was developed to produce robust, highly crystalline, organic-monolayer passivated silicon (Si) nanocrystals in a supercritical fluid. By thermally degrading the Si precursor, diphenylsilane, in the presence of octanol at 500 degrees C and 345 bar, relatively size-monodisperse sterically stabilized Si nanocrystals ranging from 15 to 40 A in diameter could be obtained in significant quantities. Octanol binds to the Si nanocrystal surface through an alkoxide linkage and provides steric stabilization through the hydrocarbon chain. The absorbance and photoluminescence excitation (PLE) spectra of the nanocrystals exhibit a significant blue shift in optical properties from the bulk band gap energy of 1.2 eV due to quantum confinement effects. The stable Si clusters show efficient blue (15 A) or green (25-40 A) band-edge photoemission with luminescence quantum yields up to 23% at room temperature, and electronic structure characteristic of a predominantly indirect transition, despite the extremely small particle size. The smallest nanocrystals, 15 A in diameter, exhibit discrete optical transitions, characteristic of quantum confinement effects for crystalline nanocrystals with a narrow size distribution.
ABSTRACT
BACKGROUND: Septic patients are often intolerant of enteral feedings due to a combination of motility disturbances and impaired absorptive function. Our laboratory has previously demonstrated that endotoxemia results in rapid intestinal transit and decreased jejunal absorption of water, electrolytes, and glucose. We hypothesized that the changes in jejunal transit and absorption during endotoxemia may be dependent on the dose of endotoxin. MATERIALS AND METHODS: Under general anesthesia, rats underwent placement of an internal jugular line, a femoral arterial line, and a 20-cm jejunal Thiry-Vella loop. The jejunal segment was perfused with an isotonic solution containing polyethylene glycol. For 90 min, baseline measurements of blood pressure, heart rate, jejunal absorption of water, electrolytes, and glucose, and jejunal transit were made. Following this baseline period I, rats were given 0.9% NaCl (1 ml/kg) or one of three doses of Escherichia coli lipopolysaccharide (0.5, 1.0, or 5.0 mg/kg). Studies were then repeated for an additional 90 min. RESULTS: Changes in blood pressure and heart rate were similar among the four groups of animals. Endotoxin decreased water and glucose flux, increased potassium flux, and quickened intestinal transit in a dose-dependent fashion. CONCLUSIONS: We conclude that endotoxemia causes dose-dependent changes in jejunal transit and absorption. The effects of increasing doses of endotoxin on jejunal absorptive and motor function do not appear to be mediated by changes in blood pressure or heart rate.
