Enhancement of a conducting polymer-based biosensor using carbon nanotube-doped polyaniline

A biosensor with improved performance was developed through the immobilization of horseradish peroxidase (HRP) onto electropolymerized polyaniline (PANI) films doped with carbon nanotubes (CNTs). The effects of electropolymerization cycle and CNT concentration on the response of the biosensor toward H₂O₂ were investigated. It was found that the application of CNTs in the biosensor system could increase the amount and stability of the immobilized enzyme, and greatly enhanced the biosensor response. Compared with the biosensor without CNTs, the proposed biosensor exhibited enhanced stability and approximately eight-fold sensitivity. A linear range from 0.2 to 19 μM for the detection of H₂O₂ was observed for the proposed biosensor, with a detection limit of 68 nM at a signal-to-noise ratio of 3 and a response time of less than 5 s.     

Recent applications of capillary electrophoresis-electrospray ionisation-mass spectrometry in drug analysis

This review considers applications in 2004-2005 of capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) to the detection and determination of small molecular mass drug molecules, taken from the Web of Knowledge database. The molecules of small molecular mass less than 1000 Da are chosen according to selected structural classes in which they give ESI signals primarily as [M + H](+) ions. These structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, other heterocyclic hypnotics, steroids, bioactive compounds containing phenolic groups, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole and time-of flight mass spectrometers. The review then gives a critical evaluation of these recent CE-ESI-MS analytical methods for the detection and determination of these small molecular mass drug molecules. Analytical information on, for example, sample concentration techniques, CE separation conditions, recoveries from biological media and limits of detection are provided.     

On the application of blind source separation for damping estimation of bridges under traffic loading

The accurate and reliable estimation of modal damping from output-only vibration measurements of structural systems is a continuing challenge in the fields of operational modal analysis (OMA) and system identification. In this paper a modified version of the blind source separation (BSS)-based Second-Order Blind Identification (SOBI) method was used to perform modal damping identification on a model bridge structure under varying loading conditions. The bridge model was created with finite elements and consisted of a series of stringer beams supported by a larger girder. The excitation was separated into two categories: ambient noise and traffic loads with noise modeled with random forcing vectors and traffic simulated with moving loads for cars and partially distributed moving masses for trains. The acceleration responses were treated as the mixed output signals for the BSS algorithm. The modified SOBI method used a windowing technique to maximize the amount of information used for blind identification from the responses. The modified SOBI method successfully found the mode shapes for both types of excitation with strong accuracy, but power spectral densities (PSDs) of the recovered modal responses showed signs of distortion for the traffic simulations. The distortion had an adverse affect on the damping ratio estimates for some of the modes but no correlation could be found between the accuracy of the damping estimates and the accuracy of the recovered mode shapes. The responses and their PSDs were compared to real-world collected data and patterns similar to distortion were observed implying that this issue likely affects real-world estimates.     

Investigation of antibacterial phytochemicals in the bark and leaves of Ficus coronata by high-performance liquid chromatography-electrospray ionization-ion trap mass spectrometry (HPLC-ESI-MS(n) ) and ESI-MS(n)

The ethyl acetate extracts of the bark and leaves of Ficus coronata were separated by column chromatography and the resulting fractions tested for their bioactivity toward methicillin-resistant-Staphylococcus aureus (MRSA) and M. luteus. The bioactive column chromatography fractions were further separated by preparative thin layer chromatography (TLC) and the resulting bands investigated by high-performance liquid chromatography-electrospray ionization-ion trap mass spectrometry (HPLC-ESI-MS(n) ) and ESI-MS(n) . The resulting retention times, molecular masses, their fragmentation patterns, and the chemnet database (www.chemnetbase.com) were then used in the dereplication process by structural elucidation of some of the compounds when compared with known structures of natural origin. Some molecular masses and the corresponding fragmentations were found that did not correlate with any known compounds thus revealing potentially novel natural products that could be investigated on a larger scale and could ultimately find application as new drugs against MRSA and other multidrug-resistant microorganisms. Structures are also proposed for known compounds that have not been previously reported for F. coronata.     

Inverse‐Opal Conducting Polymer Monoliths in Microfluidic Channels

Inverse opal monolithic flow‐through structures of conducting polymer (CP) were achieved in microfluidic channels for lab‐on‐a‐chip (LOC) applications. In order to achieve the uniformly porous monolith, polystyrene (PS) colloidal crystal (CC) templates were fabricated in microfluidic channels. Consequently, an inverse opal polyaniline (PANI) structure was achieved on‐chip, through a two‐step process involving the electrochemical growth of PANI and subsequent removal of the template. In this work the effect of CP electropolymerisation time on these structures is discussed. It was found that growth time is critical in achieving an ordered structure with well‐defined flow‐through pores. This is significant as these optimised porous structures will allow for maximising the surface area of the monolith and will also result in well‐defined flow profiles through the microchannel.     

Crystallographic report: Aquadicylcohexyltin(IV) bis(2‐picolinate) ethanol solvate

The tin atom in the title compound is in a distorted pentagonal bipyramidal geometry defined by two sets of nitrogen and oxygen donors derived from the carboxylate ligands, two carbon atoms from the cyclohexyl substituents and an oxygen atom from the coordinated water molecule; C? Sn? C 170.85(15)°. Extensive hydrogen bonding occurs in the lattice. Copyright © 2004 John Wiley & Sons, Ltd.     

Instability of an Axisymmetric Vortex in a Stably Stratified, Rotating Environment

We investigate the stability of a barotropic vorticity monopole whose stream function is a Gaussian function of the radial coordinate. The model is based on the inviscid Boussinesq equations. The vortex is assumed to exist on an $f$-plane, in an environment with constant, stable density stratification. In the unstratified, nonrotating case, we find growth rates that increase monotonically with increasing vertical wave number, the so-called “ultraviolet catastrophe” characteristic of symmetric instability. This type of instability leads to rapid turbulent collapse of the vortex, possibly accompanied by wave radiation. In the limit of strong background stratification and rotation, the vortex exhibits a scale-selective instability which leads to the formation of stable lenses. The transition between these two regimes is sharp, and coincides approximately with the centrifugal stability boundary. Received 6 December 1996 and accepted 1 November 1997     

Development of a polypyrrole-based amperometric detector for the determination of certain anions in water samples

The development of a polypyrrole-based modified electrode for use in the detection of anions in flow-injection analysis and ion chromatography is described. Chloride, nitrate, nitrite, perchlorate, bromide, carbonate, sulphate and phosphate were detected by using flow-injection analysis combined with the polypyrrole-based CME electrochemical detector. All of the anions were detected conveniently and reproducibly over a linear concentration range 1-100 mug/ml. A detection limit of 0.1 mug/ml was obtained for chloride and a limit of 1.0 mug/ml for all of the other anions. Chloride, nitrate, sulphate and phosphate, following separation using ion chromatography, were detected simultaneously by using a conductivity detector and the polypyrrole-based CME electrochemical detector in series. Both methods of detection yielded similar results with comparable sensitivity, linearity and limits of detection. This method was then applied to the analysis of fresh water samples. The electrode was stable over a 2-week period of operation with no evidence of chemical or mechanical deterioration.