Rate equation modelling of erbium luminescence dynamics in erbium-doped silicon-rich-silicon-oxide

Erbium doped silicon-rich silica offers broad band and very efficient excitation of erbium photoluminescence (PL) due to a sensitization effect attributed to silicon nanocrystals (Si-nc), which grow during thermal treatment. PL decay lifetime measurements of sensitised Er³⁺ ions are usually reported to be stretched or multi exponential, very different to those that are directly excited, which usually show a single exponential decay component.In this paper, we report on SiO₂ thin films doped with Si-nc's and erbium. Time resolved PL measurements reveal two distinct 1.54 μm Er decay components; a fast microsecond component, and a relatively long lifetime component (10 ms). We also study the structural properties of these samples through TEM measurements, and reveal the formation of Er clusters. We propose that these Er clusters are responsible for the fast μs decay component, and we develop rate equation models that reproduce the experimental transient observations, and can explain some of the reported transient behaviour in previously published literature.     

Micro Solid‐Contact Ion‐Selective Electrode Using a Carbon Nanotube Tower as Ion‐to‐Electron Transducer and Conductive Substrate

Solid contact (SC) ion‐selective electrodes (ISEs) have been recognized as the next generation of ISEs. In this work, the electrical conductivity and mechanical strength of a carbon nanotube (CNT) tower enable it to play the dual roles of transducer and substrate for micro SC‐ISEs. The electrode had a close to Nernstian slope of 35 mV/decade a_Ca2+, a linear range of four orders of magnitude of calcium ion activity (10^?5.6 to 10^?1.8 M), and a detection limit of 1.6×10^?6 M. The simplified fabrication by a one‐step drop casting makes miniaturizing SC‐ISEs and fabricating sensor arrays easier to achieve.     

Far-infrared absorption studies of Be acceptors in δ-doped GaAs/AlAs multiple quantum wells

We report a far-infrared absorption study of internal transitions of shallow Be acceptors in both bulk GaAs and a series of δ-doped GaAs/AlAs multiple quantum well samples with well thicknesses of 20, 15 and 10 nm. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of Beacceptor states from the ground state to the first three odd-parity excited states, respectively. Using a variational principle, the 2p-1s transition energies of quantum confined Be acceptors are calculated as a function of the well width. It is found that the theoretical calculation of the 2p_z → 1s transitions is in good agreement with the D-like line experimental data.     

High pressure Raman spectroscopy of single-walled carbon nanotubes: Effect of chemical environment on individual nanotubes and the nanotube bundle

The pressure-induced tangential mode Raman peak shifts for single-walled carbon nanotubes (SWNTs) have been studied using a variety of different solvents as hydrostatic pressure-transmitting media. The variation in the nanotube response to hydrostatic pressure with different pressure transmitting media is evidence that the common solvents used are able to penetrate the interstitial spaces in the nanotube bundle. With hexane, we find the surprising result that the individual nanotubes appear unaffected by hydrostatic pressures (i.e. a flat Raman response) up to 0.7 GPa. Qualitatively similar results have been obtained with butanol. Following the approach of Amer et al. [J. Chem. Phys. 121 (2004) 2752], we speculate that this is due to the inability of SWNTs to adsorb some solvents onto their surface at lower pressures. We also find that the role of cohesive energy density in the solvent-nanotube interaction is more complex than previously thought.     

Isolation of clobazam-orosomucoid complexes from patients' sera.

Orosomucoid, a member of the lipocalin family, may function in the in vivo transport of lipophilic compounds such as basic and neutral drugs. We describe the identification of 7-chloro-1-methyl-1,5-benzodiazepine-2,4-dione (clobazam) bound to the serum orosomucoid from individuals actively taking this tranquillizer. This suggests not only that other endogenous factors limit access to the benzodiazepine binding site on human serum albumin, but also that the differential binding of benzodiazepines and their metabolites by orosomucoid should be considered in determining therapeutic doses, particularly in the acute phase response.     

The distribution and behaviour of artificial radionuclides in sediments of the north Wales coast,U.K.

The distribution of¹³⁴Cs,¹³⁷Cs and²¹⁴Am in surface and core sediments from areas in north Wales has been investigated. Coastal sites show a predominance of Sellafield-derived material for all three radionuclides whereas estuarine sites show an increased proportion of Chemobyl-derived caesium present. By the use of the¹³⁴Cs/¹³⁷Cs ratio, a mean proportion of Chemobyl-derived¹³⁷Cs in surface sediments collected in 1991 fell from 34% at an estuarine site to 11% at a coastal site. In deeper sections of cores representing sedimentation dates near the Chemobyl accident, up to 90% of¹³⁷Cs at the estuarine site and 26% at the coastal site can be attributed to Chemobyl. By using the position of the Chemobyl¹³⁴Cs and¹³⁷Cs peak in the cores, sedimentation rates of 0.7 mm·a^–1 were calculated.     

Electrochemical immunoassay: an ultrasensitive method.

Hydrodynamic electrochemical techniques such as liquid chromatography and flow injection analysis with electrochemical detection are very effective for the rapid determination of the enzyme-generated product in enzyme immunoassays. The authors have used this detection method in various assay formats using both alkaline phosphatase and glucose-6-phosphate dehydrogenase as labels. Assays for digoxin will be used illustratively. Recently, the authors have used 70 mL microcapillary hematocrit tubes as the immunoassay reaction vessel and alkaline phosphatase as the labeling enzyme. The assay, complete in 30 min, had a detection limit of 5,6 x 10 -20 moles of IgG in serum. The linear range was four orders of magnitude. This low detection limit is due to a combination of the favorable geometry of the reaction vessel and the suppression of nonspecific adsorption by the addition of ion-pairing blocking agents. Even lower detectable amounts should be achievable with smaller reaction vessels. The capability for detecting such small amounts of analyte is potentially useful for the analysis of extremely small samples such as single cells and blood samples from premature infants.     

Amperometric homogeneous competitive immunoassay in a perfluorocarbon emulsion oxygen therapeutic (PEOT)

The effect of a perfluorocarbon emulsion oxygen therapeutic (PEOT) on the detection of the drugs theophylline and phenytoin was explored using a commercial enzyme multiplied immunoassay technique (EMIT®). The EMIT technique is based on the enzymatic production of NADH, which is typically detected in serum samples spectrophotometrically. Here, amperometry using the rotating disk electrode on a single drop of solution is demonstrated to detect theophylline and phenytoin in the presence of PEOT. In the study, 2,6-dichloroindophenol (DCIP) added to the immunoassay mixture is reduced by the NADH to DCIPH₂. Oxidation of DCIPH₂ is monitored electrochemically at +200 mV using a glassy carbon rotating disk electrode. Slopes of amperograms are proportional to the concentration of drug in the immunoassay sample. This technique yields excellent quantitative data in the therapeutic range for both drugs in 2–20 % PEOT.     

Effect of some physico-chemical conditions on an immunoassay for viable Escherichia coli

Viable Escherichia coli can be detected by an immunoassay in which live bacteria captured on antibody-coated paramagnetic beads are induced to synthesize the enzyme β-galactosidase, which catalyzes the hydrolysis of the slightly fluorescent substrate 4-methyl umbelliferyl-β-d-galactoside to the highly fluorescent product 7-hydroxy-4-methylcoumarin for detection. The effects of bacterial strain, presence of dead bacteria, and some environmental stresses on assay performance were evaluated.