UV laser induced desorption of CsI and RbI ion clusters

Experimental results of laser sputtering of cesium and rubidium iodide secondary ions are presented. A TOF mass spectrometer, operating in linear mode, continuous extraction for positive or negative ions, was used for the analysis of (CsI)_nCs⁺, (CsI)_nI⁻, (RbI)_nRb⁺ and (RbI)_nI⁻ ion emission as a function of the laser irradiance. Experimental data show that the cluster ion emission yields decrease exponentially with n, for all the laser irradiances applied. Theoretical analysis of the clusters structure was performed using density functional theory at the B3LYP/LACV3P level, for the positive and negative cluster series. A quasi-equilibrium evolution of the clusters is proposed to extract a parameter characteristic of the cluster recombination process: the effective temperature. The hypothesis of the atomic species’ recombination (during the expansion of a high density highly ionized cloud) leading to cluster formation is confirmed to some extent in a second set of experiments: the UV laser ablation of a mixed and non-mixed cesium iodide and potassium bromide targets. These experiments show that the emission yields contain contributions from both the recombination process and from the sample stoichiometry, even for high laser irradiances.     

Carbon fiber cylindrical microelectrode-based detector for the determination of antithyroid drugs

An amperometric flow-injection method for the determination of antithyroid drugs such as 6-methyl-2-thiouracil (MTU) using a carbon fiber cylindrical microelectrode-based detector is reported. A home-made flow-cell specially adapted for working with cylindrical microelectrodes ranging between 4 and 10 mm in length was used for this purpose. Methanol containing 0.05 mol l(-1) tetrabutylammonium perchlorate as the supporting electrolyte was employed, and a potential of +1.6 V was selected for the amperometric detection of MTU. No cleaning or electrode surface regeneration of the fiber was necessary during the whole working day. A limit of detection of 2.6x10(-7) mol l(-1) (37 mug MTU l(-1)) was achieved. The method was applied to the determination of MTU in spiked feed samples (peas and corn flour), at the 142 mug g(-1) level. The procedure involved the extraction of the drug in methanol, a clean-up step using Florisil cartridges and the use of the standard additions method. Recoveries of 81+/-6 and 85+/-8% were obtained for peas and corn flour, respectively.     

Determination of dinoseb by adsorptive stripping voltammetry using a mercury film electrode

An adsorptive stripping voltammetric method for the determination of the pesticide dinoseb (2-sec.-butyl-4,6-dinitrophenol) at the mercury film electrode is described. The deposition of the mercury film on a glassy carbon disk electrode was optimized. The temperature, at which the mercury film was deposited, was demonstrated to have a strong influence on the stripping peaks, the first one being much more intense than the second. A systematic study of the variables affecting the stripping response was carried out by differential pulse voltammetry. The results obtained have been compared with those at the HMDE; a significant improvement in the sensitivity of the method developed with the MFE was observed. Using a 300 s accumulation time, the limits of determination and detection were 3.6 × 10^–10 and 1.1 × 10^–10 mol L^–1, respectively. The effect of the presence of several herbicides on the dinoseb response was also tested. The method has been applied to the determination of the pesticide in spiked apple juice at two concentration levels: 12.0 and 1.2 g L^–1 of juice.     

A peroxidase-tetrathiafulvalene biosensor based on self-assembled monolayer modified Au electrodes for the flow-injection determination of hydrogen peroxide

The construction and performance under flow-injection conditions of an integrated amperometric biosensor for hydrogen peroxide is reported. The design of the bioelectrode is based on a mercaptopropionic acid (MPA) self-assembled monolayer (SAM) modified gold disk electrode on which horseradish peroxidase (HRP, 24.3 U) was immobilized by cross-linking with glutaraldehyde together with the mediator tetrathiafulvalene (TTF, 1 μmol), which was entrapped in the three-dimensional aggregate formed.

The amperometric biosensor allows the obtention of reproducible flow injection amperometric responses at an applied potential of 0.00 V in 0.05 mol L⁻¹ phosphate buffer, pH 7.0 (flow rate: 1.40 mL min⁻¹, injection volume: 150 μL), with a range of linearity for hydrogen peroxide within the 2.0 × 10⁻⁷–1.0 × 10⁻⁴ mol L⁻¹ concentration range (slope: (2.33 ± 0.02) × 10⁻² A mol⁻¹ L, r = 0.999). A detection limit of 6.9 × 10⁻⁸ mol L⁻¹ was obtained together with a R.S.D. (n = 50) of 2.7% for a hydrogen peroxide concentration level of 5.0 × 10⁻⁵ mol L⁻¹. The immobilization method showed a good reproducibility with a R.S.D. of 5.3% for five different electrodes. Moreover, the useful lifetime of one single biosensor was estimated in 13 days.

The SAM-based biosensor was applied for the determination of hydrogen peroxide in rainwater and in a hair dye. The results obtained were validated by comparison with those obtained with a spectrophotometric reference method. In addition, the recovery of hydrogen peroxide in sterilised milk was tested.     

Chlorine‐Enhanced Surface Mobility of Au(100)

Motivated by experimental studies of two‐dimensional Ostwald ripening on Au(100) electrodes in chlorine‐containing electrolytes, we have studied diffusion processes using density functional theory. We find that chlorine has a propensity to temporary form AuCl complexes, which diffuse significantly faster than gold adatoms. With and without chlorine, the lowest activation energy is found for the exchange mechanism. Chlorine furthermore reduces the activation energy for the detachment from kink sites. Kinetic Monte Carlo simulations were performed on the basis of extensive density functional theory calculations. The island‐decay rate obtained from these Monte Carlo simulations, as well as the decay rate obtained from the theoretical activation energies and frequency factors when inserted into analytical solutions for Ostwald ripening, are in agreement with experimental island‐decay rates in chlorine‐containing electrolytes.     

Disposable amperometric magnetoimmunosensor for the sensitive detection of the cardiac biomarker amino-terminal pro-B-type natriuretic peptide in human serum

A novel amperometric magnetoimmunosensor using an indirect competitive format is developed for the sensitive detection of the amino-terminal pro-B-type natriuretic peptide (NT-proBNP). The immunosensor design involves the covalent immobilization of the antigen onto carboxylic-modified magnetic beads (HOOC-MBs) activated with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS), and further incubation in a mixture solution containing variable concentrations of the antigen and a fixed concentration of an HRP-labeled detection antibody. Accordingly, the target NT-proBNP in the sample and that immobilized on the MBs compete for binding to a fixed amount of the specific HRP-labeled secondary antibody. The immunoconjugate-bearing MBs are captured by a magnet placed under the surface of a disposable gold screen-printed electrode (Au/SPE). The amperometric responses measured at –0.10 V (vs. a Ag pseudo-reference electrode), upon addition of 3,3′,5,5′-tetramethylbenzidine (TMB) as electron transfer mediator and H₂O₂ as the enzyme substrate, are used to monitor the affinity reaction. The developed magnetoimmunosensor provides attractive analytical characteristics in 10-times diluted human serum samples, exhibiting a linear range of clinical usefulness (0.12–42.9 ng mL⁻¹) and a detection limit of 0.02 ng mL⁻¹, which can be used in clinical diagnosis of chronic heart failure in the elderly and for classifying patients at risk of death after heart transplantation. The magnetoimmunosensor was successfully applied to the analysis of spiked human serum samples.     

Multiplexed Determination of Amino‐Terminal Pro‐B‐Type Natriuretic Peptide and C‐Reactive Protein Cardiac Biomarkers in Human Serum at a Disposable Electrochemical Magnetoimmunosensor

A rapid magnetoimmunosensor for the simultaneous determination of two cardiac biomarkers, amino‐terminal pro‐B‐type natriuretic peptide (NT‐proBNP) and C‐reactive protein (CRP), in human serum is described. Specific capture antibodies were covalently immobilized onto carboxylic acid‐modified magnetic beads. The quantification of NT‐proBNP and CRP was performed by using indirect competitive and sandwich configurations, respectively, and horseradish peroxidase‐labeled tracers. The use of dual screen‐printed carbon electrodes allowed the achievement of simultaneous independent amperometric readout for each cardiac biomarker. The developed methodology showed very low limits of detection (0.47 ng mL^?1). An international standard for CRP serum spiked with NT‐proBNP was analyzed to evaluate the usefulness of the magnetoimmunosensor.     

Dual Amperometric Immunosensor for Improving Cancer Metastasis Detection by the Simultaneous Determination of Extracellular and Soluble Circulating Fraction of Emerging Metastatic Biomarkers

This paper reports the development of a dual immunosensor using magnetic microcarriers (MBs) and amperometric transduction at dual screen‐printed carbon electrodes (SPdCEs) for the simultaneous determination of two biomarkers: interleukin‐13 receptor α2 (IL‐13Rα2) and E‐cadherin (E‐CDH), with both extracellular and soluble fraction; oncogenic and tumor suppressor markers, respectively, of great relevance in metastatic processes. The implemented methodology involved the formation of sandwich‐type immunocomplexes using specific capture antibodies immobilized onto carboxylic acid magnetic microbeads (HOOC‐MBs), and biotinylated detector antibodies labeled with streptavidin?horseradish peroxidase conjugates (Strep‐HRP). The amperometric detection was performed by addition of hydrogen peroxide in the presence of hydroquinone (HQ) as the redox mediator. The dual immunosensing platform provided linear calibration ranges suitable for the determination of both biomarkers in liquid and solid clinical specimens as well as excellent selectivity against other cancer biomarkers. This simple handling dual bioplatform was applied to the determination of the soluble and extracellular fraction of the target biomarkers in serum and paraffined‐embedded tissues from colorectal cancer (CRC) patients diagnosed at different tumor grade. The obtained results reveal great potential of this configuration to improve the reliability in diagnosing metastatic CRC.     

Tooth-root stress calculation of high transverse contact ratio spur and helical gears

In this paper, a non-uniform model of load distribution along the line of contact of spur and helical gears, obtained from the minimum elastic potential criterion, has been used, combined with the equations of the linear elasticity, to evaluate the tooth-root stress of high transverse contact ratio gears. The values of both critical stress and load conditions have been obtained and a complete analysis of the tooth bending strength has been carried out. As the load per unit of length at any point of the line of contact and any position of the meshing cycle has been described by a very simple equation, a complete study of the location and the value of the tooth-root stress has been carried out. From this study, a recommendation for the calculation of the bending load capacity of high transverse contact ratio spur and helical gears is proposed.