A capacitive immunosensor for detection of cholera toxin

Contamination of food with biological toxins as well as their potential use as weapons of mass destruction has created an urge for rapid and cost effective analytical techniques capable of detecting trace amounts of these toxins. This paper describes the development of a sensitive method for detection of cholera toxin (CT) using a flow-injection capacitive immunosensor based on self-assembled monolayers. The sensing surface consists of monoclonal antibodies against the B subunit of CT (anti-CT), immobilized on a gold transducer. Experimental results show that the immunosensor responded linearly to CT concentrations in the range from 1.0 × 10⁻¹³ to 1.0 × 10⁻¹⁰ M under optimized conditions. The limit of detection (LOD) was 1.0 × 10⁻¹⁴ M. Two more analytical methods were employed for detection of CT using the same antibody namely, sandwich ELISA and surface plasmon resonance (SPR)-based immunosensor. The former had an LOD of 1.2 × 10⁻¹² M and a working range from 3.7 × 10⁻¹¹ to 2.9 × 10⁻¹⁰ M whereas, the later had an LOD of 1.0 × 10⁻¹¹ M and a linearity ranging from 1.0 × 10⁻⁹ to 1.0 × 10⁻⁶ M. These results demonstrate that the developed capacitive immunosensor system has a higher sensitivity than the other two techniques. The binding affinity of CT to the immobilized anti-CT was determined using the SPR-based immunosensor and an association constant (K_A) of 1.4 × 10⁹ M⁻¹ was estimated.     

Pd‐PEPPSI‐IPent: An Active,Sterically Demanding Cross‐Coupling Catalyst and Its Application in the Synthesis of Tetra‐Ortho‐Substituted Biaryls

Incredible Bulk : A series of N‐heterocyclic carbene catalysts (see picture) were prepared and evaluated in the Suzuki–Miyaura reaction. A variety of sterically encumbered tetra‐ortho‐substituted biaryl products were formed from unreactive aryl chlorides using the isopentyl‐substituted catalyst at temperatures ranging from 65 °C to room temperature. The cyclopentyl‐substituted catalyst was virtually inactive, demonstrating that “flexible bulk” is essential to promote these transformations.

     

Disterolphospholipids: Nonexchangeable Lipids and Their Application to Liposomal Drug Delivery

Extreme makeover of cholesterol : Cholesterol exchange is a major reason for the instability of liposomes in blood. The formation of a covalent hybrid between cholesterol and glycerophosphocholine preserves the bilayer‐stabilizing effect of free cholesterol but prevents its transfer from the bilayer. Thus, disterolphospholipids (e.g. 1 ) are valuable new components for liposome formulation.

     

Genetic individualization of <Emphasis Type="Italic">Cannabis sativa</Emphasis> by a short tandem repeat multiplex system

Cannabis sativa is the most frequently used of all illicit drugs in the USA. Cannabis has been used throughout history for its stems in the production of hemp fiber, seed for oil and food, and buds and leaves as a psychoactive drug. Short tandem repeats (STRs) were chosen as molecular markers owing to their distinct advantages over other genetic methods. STRs are codominant, can be standardized such that reproducibility between laboratories can be easily achieved, have a high discrimination power, and can be multiplexed. In this study, six STR markers previously described for C. sativa were multiplexed into one reaction. The multiplex reaction was able to individualize 98 cannabis samples (14 hemp and 84 marijuana, authenticated as originating from 33 of the 50 states of the USA) and detect 29 alleles averaging 4.8 alleles per loci. The data did not relate the samples from the same state to each other. This is the first study to report a single-reaction sixplex and apply it to the analysis of almost 100 cannabis samples of known geographic origin. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Delay-dependent dissipativity of singular time-delay systems

Email: msmahmoud{at}kfupm.edu.sa Received on September 21, 2007; Revision received March 10, 2008. Accepted on April 30, 2008 In this paper, new results are established for the delay-dependentproblems of dissipative analysis and state-feedback synthesisof singular time-delay (STD) systems with polytopic uncertainties.The developed results for the nominal singular system encompassavailable results on approach, passivity and positive realnessfor STD systems as special cases. All the sufficient stabilityconditions are cast as linear matrix inequality-based feasibilitytests. Robust dissipativity results are also derived. Numericalexamples are provided.     

Multichip vertical-external-cavity surface-emitting lasers: a coherent power scaling scheme

We propose an efficient coherent power scaling scheme, the multichip vertical-external-cavity surface-emitting laser (VECSEL), in which the waste heat generated in the active region is distributed on multi-VECSEL chips such that the pump level at the thermal rollover is significantly increased. The advantages of this laser are discussed, and the development and demonstration of a two-chip VECSEL operating around 970 nm with over 19 W of output power is presented.     

Melting heat transfer effects on stagnation point flow of micropolar fluid saturated in porous medium with internal heat generation （absorption）

The effect of melting heat transfer on the two dimensional boundary layer flow of a micropolar fluid near a stagnation point embedded in a porous medium in the presence of internal heat generation/absorption is investigated. The governing non-linear partial differential equations describing the problem are reduced to a system of non-linear ordinary differential equations using similarity transformations solved numerically using the Chebyshev spectral method. Numerical results for velocity, angular velocity and temperature profiles are shown graphically and discussed for different values of the inverse Darcy number, the heat generation/absorption parameter, and the melting parameter. The effects of the pertinent parameters on the local skin-friction coefficient, the wall couple stress, and the local Nusselt number are tabulated and discussed. The results show that the inverse Darcy number has the effect of enhancing both velocity and temperature and suppressing angular velocity. It is also found that the local skin-friction coefficient decreases, while the local Nusselt number increases as the melting parameter increases.     

Effect of the rotation,magnetic field and initial stress on peristaltic motion of micropolar fluid

In this work, the effect of magnetic field, rotation and initial stress on peristaltic motion of micropolar fluid in a circular cylindrical flexible tube with viscoelastic or elastic wall properties has been considered. Runge–Kutta technique are used. Runge–Kutta method is developed to solve the governing equations of motion resulting from a perturbation technique for small values of amplitude ratio. The time mean axial velocity profiles are presented for the case of free pumping and analyzed to observe the influence of wall properties, magnetic field, rotation and initial stress for various values of micropolar fluid parameters. In the case of viscoelastic wall, the effect of viscous damping on mean flow reversal at the boundary is seen. The numerical results of the time mean velocity profile are discussed in detail for homogeneous fluid under the effect of wall properties, magnetic field, initial stress and rotation for different cases by figures. The results indicate that the effect of wall properties, rotation, initial stress and magnetic field are very pronounced. Numerical results are given and illustrated graphically.     

Influence of rotation and generalized magneto-thermoelastic on Rayleigh waves in a granular medium under effect of initial stress and gravity field

Influence of rotation, relaxation times, magnetic field, initial stress and gravity field on attenuation coefficient (Imaginary part of frequency equation root) and Rayleigh waves velocity (the real part of frequency equation root) in an elastic half-space of granular medium is studied. The analytical solution is obtained by using Lame’s potential techniques. The numerical calculations are carried out for the frequency equation of Rayleigh waves velocity. The results are displayed graphically. Some results of previous investigations are deduced as special cases from this study.     

Coreflooding Studies to Investigate the Potential of Carbonated Water Injection as an Injection Strategy for Improved Oil Recovery and CO<Subscript>2</Subscript> Storage

Carbonated water injection (CWI) is a CO₂-augmented water injection strategy that leads to increased oil recovery with added advantage of safe storage of CO₂ in oil reservoirs. In CWI, CO₂ is used efficiently (compared to conventional CO₂ injection) and hence it is particularly attractive for reservoirs with limited access to large quantities of CO₂, e.g. offshore reservoirs or reservoirs far from large sources of CO₂. We present the results of a series of CWI coreflood experiments using water-wet and mixed-wet Clashach sandstone cores and a reservoir core with light oil (n-decane), refined viscous oil and a stock-tank crude oil. The experiments were carried out to assess the performance of CWI and to quantify the level of additional oil recovery and CO₂ storage under various experimental conditions. We show that the ultimate oil recovery by CWI is higher than the conventional water flooding in both secondary and tertiary recovery methods. Oil swelling as a result of CO₂ diffusion into the oil and the subsequent oil viscosity reduction and coalescence of the isolated oil ganglia are amongst the main mechanisms of oil recovery by CWI that were observed through the visualisation experiments in high-pressure glass micromodels. There was also evidence of a change in the rock wettability that could also influence the oil recovery. The coreflood test results also reveal that the CWI performance is influenced by oil viscosity, core wettability and the brine salinity. Higher oil recovery was obtained with the mixed-wet core than the water-wet core, with light oil than with the viscous oil and low salinity carbonated brine than high-salinity carbonated brine. At the end of the flooding period, an encouraging amount of the injected CO₂ was stored in the brine and the remaining oil in the form of stable dissolved CO₂. The experimental results clearly demonstrate the potential of CWI for improving oil recovery as compared with the conventional water flooding (secondary recovery) or as a water-based EOR (enhanced oil recovery) method for watered out reservoirs.