			Home About us Contact

Short Response Time (short + response_time)

Distribution by Scientific Domains

Chemistry	80%

Selected Abstracts

Comparative Studies of Tridentate Sulfur and Nitrogen-Containing Ligands as Ionophores for Construction of Cadmium Ion-Selective Membrane Sensors

ELECTROANALYSIS, Issue 11 2007
Ashok, Kumar Singh
Abstract New polymeric membrane cadmium-ion selective sensors have been prepared by incorporating nitrogen and sulfur containing tridentate ligands as the ionophores into the plasticized PVC membranes. Poly(vinyl chloride) (PVC) based membranes of potassium hydrotris[N -(2,6-xylyl)thioimdazolyl) borate] (KTt2,6-xylyl) and potassium hydrotris(3-phenyl-5-methylpyrazolyl) borate (KTpPh,Me) with sodium tetraphenyl borate (NaTPB) as an anionic excluder and dibutylphthalate (DBP), tributylphthalate (TBP), dioctylsebacate (DOS), and o -nitrophenyloctyl ether (o -NPOE) as plasticizing solvent mediators were investigated in different compositions. KTt2,6-xylyl was found to be a selective and sensitive ion carrier for Cd(II) membrane sensor. A membrane composed of KTt2,6-xylyl:NaTPB:PVC:DBP with the % mole ratio 2.3,:,1.1,:,34.8,:,61.8 (w/w) works well over a very wide concentration range (7.8×10,8,1.0×10,2,M) with a Nernstian slope of 29.4±0.2,mV/decades of activity between pH values of 3.5 to 9.0 with a detection limit of 4.37×10,8,M. The sensor displays very good discrimination toward Cd(II) ions with regard to most common cations. The proposed sensor shows a short response time for whole concentration range (ca. 8,s). The effects of the cationic (tetrabutylammonium chloride, TBC), anionic (sodium dodecyl sulfate, SDS) and nonionic (Triton X-100) surfactants were investigated on the potentiometric properties of proposed cadmium-selective sensor. The proposed sensor based on KTt2,6-xylyl ionophore has also been used for the direct determination of cadmium ions in different water samples and human urine samples. [source]

Biosensor Based on Self-Assembling Glucose Oxidase and Dendrimer-Encapsulated Pt Nanoparticles on Carbon Nanotubes for Glucose Detection

ELECTROANALYSIS, Issue 6 2007
Lihuan Xu
Abstract A novel amperometric glucose biosensor based on layer-by-layer (LbL) electrostatic adsorption of glucose oxidase (GOx) and dendrimer-encapsulated Pt nanoparticles (Pt-DENs) on multiwalled carbon nanotubes (CNTs) was described. Anionic GOx was immobilized on the negatively charged CNTs surface by alternatively assembling a cationic Pt-DENs layer and an anionic GOx layer. Transmission electron microscopy images and ,-potentials proved the formation of layer-by-layer nanostructures on carboxyl-functionalized CNTs. LbL technique provided a favorable microenvironment to keep the bioactivity of GOx and prevent enzyme molecule leakage. The excellent electrocatalytic activity of CNTs and Pt-DENs toward H2O2 and special three-dimensional structure of the enzyme electrode resulted in good characteristics such as a low detection limit of 2.5,,M, a wide linear range of 5,,M,0.65,mM, a short response time (within 5,s), and high sensitivity (30.64,,A mM,1,cm,2) and stability (80% remains after 30 days). [source]

Chitosan-Glutamate Oxidase Gels: Synthesis, Characterization, and Glutamate Determination

ELECTROANALYSIS, Issue 23 2005
Maogen Zhang
Abstract The biopolymer chitosan (CHIT) was chemically modified with glutaric dialdehyde (GDI) and used for the covalent immobilization of enzyme glutamate oxidase (GmOx). The relationships between the loaded, retained, and active units of GmOx in the CHIT-GDI-GmOx gels were determined by electrochemical assays. The latter indicated that on average ca. 95% of the GmOx was retained in the CHIT-GDI matrix that was loaded with 0.10,3.0 units of the enzyme. The maximum activity of the GmOx immobilized in the gels corresponded to ca. 5% of the activity of the free enzyme. Platinum electrodes coated with CHIT-GDI-GmOx gels (films) were used as amperometric biosensors for glutamate. Such biosensors displayed good operational and long-term stability (at least 11,h and 100 days, respectively) in conjunction with low detection limit of 0.10,,M glutamate (S/N=3), linear range up to 0.5,mM (R2=0.991), sensitivity of 100 mA M,1 cm,2, and short response time (t90%=2,s). This demonstrated an efficient signal transduction in the Pt/CHIT-GDI-GmOx+glutamate system. The CHIT-GDI-GmOx gels constitute a new biosensing element for the development of glutamate biosensors. [source]

Novel Structural Modulation in Ceramic Sensors Via Redox Processing in Gas Buffers

INTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2006
Abdul-Majeed Azad
High selectivity, enhanced sensitivity, short response time, and long shelf-life are some of the key features sought in the solid-state ceramic-based chemical sensors. As the sensing mechanism and catalytic activity are predominantly surface-dominated, benign surface features in terms of small grain size, large surface area, high aspect ratio and, open and connected porosity, are required to realize a successful material. In order to incorporate these morphological features, a technique based on rigorous thermodynamic consideration of the metal/metal oxide coexistence is described. By modulating the oxygen partial pressure across the equilibrium M/MO proximity line, formation and growth of new oxide surface on an atomic/submolecular level under conditions of "oxygen deprivation," with exotic morphological features, has been achieved in potential sensor materials. This paper describes the methodology and discusses the results obtained in the case of potential semiconducting ceramic oxide-based carbon monoxide and hydrogen sensors with enhanced characteristics. [source]

The Use of Optical Fiber Bundles Combined with Electrochemistry for Chemical Imaging

CHEMPHYSCHEM, Issue 2 2003
Sabine Szunerits Dr.
Abstract The present Review describes the progress made in using imaging optical fiber bundles for fluorescence and electrochemical-initiated chemiluminescence imaging. A novel optoelectrochemical micro-ring array has been fabricated and demonstrated for concurrent electrochemical and optical measurements. The device comprises optical fibers coated with gold via electroless gold deposition and assembled in a random array format. The design yielded an array of approximately 200 micro-ring electrodes, where interdiffusional problems were minimized. The inner diameter of the ring electrode is fixed by the diameter of the individual optical fibers (25 ,m), while the outer radius is determined by the thickness of the deposited gold. While all the fibers are optically addressable, they are not all electrochemically addressable. The resolution of this device is in the tens of micrometers range, determined by the diameter of the optical fiber (25 ,m) and by the spacing between each electrically connected fiber. For the purpose of having well-behaved microelectrode characteristics, this spacing was designed to be larger than 60 ,m. The array was characterized using ferrocyanide in aqueous solution as a model electroactive species to demonstrate that this microelectrode array format exhibits steady-state currents at short response times. This device has potential application to be used as an optoelectronic sensor, especially for the electrolytic generation and transmission of electrochemiluminescence, and was used to demonstrate that electrochemically generated luminescent products can be detected with the fiber assembly. [source]