On-site fuel electroanalysis: Determination of lead,copper and mercury in fuel bioethanol by anodic stripping voltammetry using screen-printed gold electrodes

The potential application of commercial screen-printed gold electrodes (SPGEs) for the trace determination of lead, copper, and mercury in fuel bioethanol is demonstrated. Samples were simply diluted in 0.067 mol L⁻¹ HCl solution prior to square-wave anodic stripping voltammetry (SWASV) measurements recorded with a portable potentiostat. The proposed method presented a low detection limit (<2 μg L⁻¹) for a 240 s deposition time, linear range between 5 and 300 μg L⁻¹, and adequate recovery values (96–104%) for spiked samples. This analytical method shows great promise for on-site trace metal determination in fuel bioethanol once there is no requirement for sample treatment or electrode modification.     

A novel hybrid mode of sample injection to enhance CZE sensitivity for simultaneous determination of a pyridine-triphenylborane anti-fouling agent and its degradation products

We developed a novel hybrid sample injection mode (HSIM) that presents the combination of electrokinetic injection and vacuum injection to enhance detection sensitivity in CZE. Samples were introduced using both vacuum and electrokinetic injections simultaneously, with a water plug injected into the capillary prior to sample introduction (i.e. similarly to field-amplified sample injection, FASI). Using a sample mixture containing an anti-fouling agent applied to ship hulls, pyridine-triphenylborane and its degradation products (diphenylborinic acid, phenylboronic acid, and phenol) dissolved in ACN, the length of water plug, time, and voltage for sample introduction were optimized. The signal intensity (peak height) was found to be up to a 30-fold increased using HSIM by applying 4 kV for 4 s at the inlet end of the capillary as the cathode with supplementary vacuum in comparison with only vacuum injection for 4 s. The LODs (at a S/N of 3) for pyridine-triphenylborane, diphenylborinic acid, phenylboronic acid, and phenol were 0.88, 1.0, 21, and 23 μg/L, respectively. At the level of 0.04 mg/L, the RSDs (n=4, intra-day) for the above analytes were in the ranges of 1.9-11, 4.3-9.2, and 0.34-0.66% for peak area, peak height, and migration time, respectively. The HSIM is a simple and promising procedure useful for enhancing the sensitivity for both low-and high-mobility ions in CZE.     

Different strategies for the preconcentration and separation of parabens by capillary electrophoresis

Several strategies, namely, large volume sample stacking (LVSS), field‐amplified sample injection (FASI), sweeping, and in‐line SPE‐CE, were investigated for the simultaneous separation and preconcentration of a group of parabens. A BGE consisting of 20 mM sodium dihydrogenphosphate (pH 2.28) and 150 mM SDS with 15% ACN was used for the separation and preconcentration of the compounds by sweeping, and a BGE consisting of 30 mM sodium borate (pH 9.5) was used for the separation and preconcentration of the compounds by LVSS, FASI, and in‐line SPE‐CE. Several factors affecting the preconcentration process were investigated in order to obtain the maximum enhancement of sensitivity. The LODs obtained for parabens were in the range of 18–27, 3–4, 2, and 0.01–0.02 ng/mL, and the sensitivity evaluated in terms of LODs was improved up to 29‐, 77‐, 120‐, and 18 400‐fold for sweeping, LVSS, FASI, and in‐line SPE‐CE, respectively. These preconcentration techniques showed potential as good strategies for focusing parabens. The four methods were validated with standard samples to show the potential of these techniques for future applications in real samples, such as biological and environmental samples.     

Improvement in the sensitivity of microfluidic ELISA through field amplified stacking of the enzyme reaction product

In this article, we demonstrate a novel approach to enhancing the sensitivity of enzyme-linked immunosorbent assays (ELISA) through pre-concentration of the enzyme reaction product (resorufin/4-methylumbelliferone) in free solution. The reported pre-concentration was accomplished by transporting the resorufin/4-methylumbelliferone molecules produced in the ELISA process towards a high ionic-strength buffer stream in a microfluidic channel while applying a voltage drop across this merging region. A sharp change in the electric field around the junction of the two liquid streams was observed to abruptly slow down the negatively charged resorufin/4-methylumbelliferone species leading to the reported pre-concentration effect based on the field amplified stacking (FAS) technique. It has been shown that the resulting enhancement in the detectability of the enzyme reaction product significantly improves the signal-to-noise ratio in the system thereby reducing the smallest detectable analyte concentration in the ELISA method. Applying the above-described approach, we were able to detect mouse anti-BSA and human TNF-α at concentrations nearly 60-fold smaller than that possible on commercial microwell plates. For the human TNF-α sample, this improvement in assay sensitivity corresponded to a limit of detection (LOD) of 0.102 pg mL⁻¹ using the FAS based microfluidic ELISA method as compared to 7.03 pg mL⁻¹ obtained with the traditional microwell plate based approach. Moreover, because our ELISAs were performed in micrometer sized channels, they required sample volumes about two orders of magnitude smaller than that consumed in the latter case (1 μL versus 100 μL).     

Silicon nanowires as field-effect transducers for biosensor development: A review

The unique electronic properties and miniaturized dimensions of silicon nanowires (SiNWs) are attractive for label-free, real-time and sensitive detection of biomolecules. Sensors based on SiNWs operate as field effect transistors (FETs) and can be fabricated either by top–down or bottom–up approaches. Advances in fabrication methods have allowed for the control of physicochemical and electronic properties of SiNWs, providing opportunity for interfacing of SiNW-FET probes with intracellular environments. The Debye screening length is an important consideration that determines the performance and detection limits of SiNW-FET sensors, especially at physiologically relevant conditions of ionic strength (>100 mM). In this review, we discuss the construction and application of SiNW-FET sensors for detection of ions, nucleic acids and protein markers. Advantages and disadvantages of the top–down and bottom–up approaches for synthesis of SiNWs are discussed. An overview of various methods for surface functionalization of SiNWs for immobilization of selective chemistry is provided in the context of impact on the analytical performance of SiNW-FET sensors. In addition to in vitro examples, an overview of the progress of use of SiNW-FET sensors for ex vivo studies is also presented. This review concludes with a discussion of the future prospects of SiNW-FET sensors.     

Enhancement of Field Emission Characteristics for Multi-Walled Carbon Nanotubes Treated with a Mixed Solution of Chromic Trioxide and Nitric Acid

A simple acid treatment method was applied to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (CNTs) grown on silicon substrates using a mixed solution of chromic trioxide (CrO₃) and nitric acid (HNO₃). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy dispersive spectrometer (EDS) were employed to investigate the mechanism causing the modified field emission (FE) properties of the CNT films. After 20 min of CrO₃+HNO₃ treatment, the emitted currents were enhanced by more than one order of magnitude compared with those of the untreated CNTs. This large increase in emitted current can be attributed to the favorable surface morphologies, open-ended structures, and highly curved CNT surfaces in the CNT films. These factors altogether caused an increase in the field enhancement factors of CNTs. We also demonstrated that using a mixed solution of CrO₃+HNO₃ post-treatment exhibited a higher emission current and a lower turn-on electric field than in the CNTs treated with HNO₃. The method provides a simple, economical, and effective way to enhance the CNT field emission properties.     

Al/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage (I-V) characteristics of Al/Ti/4H-SiC Schottky barrier diodes (SBDs) in the temperature range of 77 K-500 K,which shows that Al/Ti/4H-SiC SBDs have good rectifying behaviour.An abnormal behaviour,in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature (T),has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the Al/Ti/4H-SiC interface.The effective Richardson constant A =154 A/cm 2 · K 2 is determined by means of a modified Richardson plot ln(I 0 /T 2)-(qσ) 2 /2(kT) 2 versus q/kT,which is very close to the theoretical value 146 A/cm 2 · K 2.     

Solutions of Euler-Lagrange equations for self-interacting field of linear frames on product manifold of group space

We investigate a model of self-interacting field of linear frames on the product manifold M × G, where G is a semisimple Lie group acting freely and transitively on a manifold M. We find two families of solutions of the Euler-Lagrange equations for the field of frames.     

X射线在介质中的剂量分布计算

研究了放射治疗中X射线在介质中的输运过程, 编程实现了基于蒙特卡罗方法的剂量计算. 并在便于图形处理的软件Matlab中对光子输运结果进行了可视化处理. 对X射线在均匀介质和非均匀介质中的蒙特卡罗模拟结果与实测结果、其他蒙特卡罗软件模拟结果进行了比较, 结果符合较好. 实验结果表明该方法既可以获得很快的仿真速度, 又能得到精确直观的剂量计算结果, 为提高放射治疗水平具有重要的指导意义和应用价值.