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A Voltammetric Sensor Based on NiO Nanoparticle-Modified Carbon-Paste Electrode for Determination of Cysteamine in the Presence of High Concentration of Tryptophan  [PDF]
Hassan Karimi-Maleh,Maryam Salimi-Amiri,Fatemeh Karimi,Mohammad A. Khalilzadeh,Mehdi Baghayeri
Journal of Chemistry , 2013, DOI: 10.1155/2013/946230
Abstract: A carbon-paste electrode modified with ferrocenecarboxaldehyde and NiO nanoparticle (NiO/NPs) was used for the sensitive and selective voltammetric determination of cysteamine in the presence of tryptophan. The oxidation of cysteamine at the modified electrode was investigated by cyclic voltammetry (CV), chronoamperometry, and square-wave voltammetry (SWV). The values of the catalytic rate constant ( ) and diffusion coefficient ( ) for cysteamine were calculated. The modified electrode exhibits an efficient electron-mediating behavior together with well-separated oxidation peaks for cysteamine and tryptophan. At the optimum pH of 7.0 in a 0.1?M phosphate buffer solution, the SWV anodic peak currents showed a linear relationship versus cysteamine concentrations in the range of 0.09–300.0?μM and a detection limit of 0.06?μM. Finally, the proposed method was also examined as a selective, simple, and precise electrochemical sensor for the determination of cysteamine in real samples such as urine and capsule. 1. Introduction Cysteamine is a significant thiol drug for the treatment of cystinosis [1]. Since cysteamine therapy has become available for patients with nephropathic cystinosis (MIM219800) in the early 1980s, quality of life for these patients has greatly improved [2, 3]. The most frequent and most severe form, infantile cystinosis, is characterized by the development of renal Fanconi syndrome in the first year of life and leads to end-stage renal disease in the first decade of life when untreated [4]. Mutations in the CTNS gene, encoding for lysosomal cystine transporter cystinosin, are the causes of cystinosis [5]. Lysosomal accumulation of cystine, which is the hallmark of this autosomal recessive disorder, can be depleted by the aminothiol cysteamine [6]. Although treatment with cysteamine substantially decreases intracellular cystine accumulation, renal Fanconi syndrome is not cured, but end-stage renal disease can be postponed in the majority of the patients. Numerous chemical and instrumental techniques for detection of cysteamine have been reported [7–11]. Tryptophan (Trp), a vital constituent of proteins and a precursor for biologically important molecules such as the neurotransmitter serotonin and the neurohormone melatonin, is an amino acid essential to humans and animals due to its physiological roles [12]. It is also indispensable in human nutrition for establishing and maintaining a positive nitrogen balance [2]. In previous reports, spectroscopy [13], chemiluminescence [14], capillary electrophoresis [15], high-performance liquid
Electrocatalytic determination of cysteamine using multiwall carbon nanotube paste electrode in the presence of 3,4-dihydroxycinnamic acid as a homogeneous mediator
Keyvanfard, Mohsen;Sami, Samad;Karimi-Maleh, Hassan;Alizad, Khadijeh;
Journal of the Brazilian Chemical Society , 2013, DOI: 10.1590/S0103-50532013000100006
Abstract: the electrooxidation of cysteamine (ca) was studied by modified carbon nanotubes paste electrode in the presence of 3,4-dihydroxycinnamic acid (3,4-dhca) using cyclic voltammetry, chronoamperometry and linear sweep voltammetry. using the modified electrode, the kinetics of ca electrooxidation was considerably enhanced by lowering the anodic over-potential through a catalytic fashion. the mechanism of ca electrochemical behavior at the modified electrode surface was analyzed by various electrochemical methods in the presence of mediator. the prepared modified electrode showed voltammetric responses with high sensitivity for ca, making it very suitable for the detection of ca at trace levels. a linear dynamic range of 0.25-400 μmol l-1 for ca was obtained in buffered solutions with ph 7.0. the limit of detection was 0.09 μmol l-1.
Photoluminescence measurements of quantum-dot-containing semiconductor microdisk resonators using optical fiber taper waveguides  [PDF]
Kartik Srinivasan,Andreas Stintz,Sanjay Krishna,Oskar Painter
Physics , 2005, DOI: 10.1103/PhysRevB.72.205318
Abstract: Fiber taper waveguides are used to improve the efficiency of room temperature photoluminescence measurements of AlGaAs microdisk resonant cavities with embedded self-assembled InAs quantum dots. As a near-field collection optic, the fiber taper improves the collection efficiency from microdisk lasers by a factor of ~ 15-100 times in comparison to conventional normal incidence free-space collection techniques. In addition, the fiber taper can serve as a efficient means for pumping these devices, and initial measurements employing fiber pumping and collection are presented. Implications of this work towards chip-based cavity quantum electrodynamics experiments are discussed.
Study on the Electrode Materials of Electrochemical Capacitor  [cached]
Xiaolai Liu,Jin Li
International Journal of Chemistry , 2011, DOI: 10.5539/ijc.v3n2p198
Abstract: Super capacitor is a kind of new energy-storage component developed in recent years, with many advantages such as large energy-storage capacity, light quality, pollution free, multiple charging and discharging. Starting from the principle, development, and application of capacitor, the electrode materials including activated carbon fiber, carbon nano tube (CNT), ordered mesoporous carbon, and graphene used for the super capacitor are introduced in this article.
Optical fiber taper coupling and high-resolution wavelength tuning of microdisk resonators at cryogenic temperatures  [PDF]
Kartik Srinivasan,Oskar Painter
Physics , 2006, DOI: 10.1063/1.2431719
Abstract: A system for studying microcavity resonators at cryogenic temperatures (~10 K) through evanescent coupling via optical fiber taper waveguides is reported, and efficient fiber coupling to AlGaAs microdisk cavities with embedded quantum dots is demonstrated. As an immediate application of this tool, we study high-resolution tuning of microdisk cavities through nitrogen gas adsorption, as first discussed by Mosor, et al. By proper regulation of the nitrogen gas flow and delivery of the gas to the sample surface, continuous tuning can be achieved with modest gas flows, and overall wavelength shifts as large as 4 nm are achieved.
Electrochemical Reduction of Uniformly Dispersed Pt and Ag Nanodots on Carbon Fiber Electrodes  [PDF]
Yi-Hao Pai,Gong-Ru Lin
Journal of Nanomaterials , 2009, DOI: 10.1155/2009/384601
Abstract: Electrochemical characterization of the uniformly dispersed Pt and Ag nanodots synthesized after in situ scalable electron-beam reduction on copper grid and carbon-fiber electrode is demonstrated. By employing plasma pretreatment to produce functional organosilicon micronetworks-based reaction sites on copper grid, the size and standard deviation of the electrochemically reduced metallic nanodots can be strictly confined. When detuning the accelerating voltage of electron-beam from 3 to 120 kV, the reshaped nanodot diameter enlarges from 12.7±0.8 to 18.3±3.6 nm due to the gradual self-aggregation. In comparison with sputtering method, the electroactivity of Pt nanodot covered carbon fiber electrode obtained after electron-beam reduction exhibits a larger electroactive surface (Spt) of 16.56 cm2/mg. The electron-beam reduction provides a better dispersion of the reduced Pt nanodots based catalysts on carbon-fiber electrode, promoting the utilization efficiency of these nanoscale catalyst (defined as the ratio of electroactive to geometric area) from 2.5% to 7%.
Electrochemical behavior of dopamine in presence of Ascorbic Acid by using an electrochemical modified gold electrode and an electrochemical and chemical modified gold electrode with a thiol
Menolasina,Sabino; Contreras,Ricardo R; Aguilar,Anfrelis; Contreras,Olga; Rodríguez,Alexis;
Revista Técnica de la Facultad de Ingeniería Universidad del Zulia , 2007,
Abstract: this paper presents the results about the detection and quantification of dopamine (da) in presence of ascorbic acid (aa) by using an electrochemical modified gold electrode and an electrochemical and chemical modified gold electrode with a self assembled monolayer of a novel compound, the n-methyl-1-cyclopenten-2-dithiocarboxylic acid. the cyclic voltammetry (cv) and square wave voltammetry (swv) techniques were using for these experiments
Adjunction of Avidin to a Cysteamine Self-Assembled Monolayer for Impedimetric Immunosensor  [PDF]
Oussama Ouerghi, M. Fethi Diouani, A. Belkacem, A. Elsanousi, Nicole Jaffrezic-Renault
Journal of Biomaterials and Nanobiotechnology (JBNB) , 2016, DOI: 10.4236/jbnb.2016.71001
Abstract: In this work an impedimetric immunosensor based on affinity immobilization method of a biotin labelled anti-human IgG antibody, used as a model system, was reported. The experimental procedure involves the growth of a self-assembled monolayer of a thiol (cysteamine) carrying terminal amine groups on gold electrodes. Glutarardehyde, a homobifunctional cross-linker, was used as a coupling reagent for the covalent linking of avidin to the amine groups of cysteamine. The attachment of the biotin labeled antibodies (anti-Human IgG) to the subsequent modified gold electrode was achieved by affinity interactions tacking advantage of the strong avidin-biotin bridge. The stepwise assembly process of the electrode was interrogated by means of cyclic voltammetry, electrochemical impedance spectroscopy and contact angle measurements. The response of the antibody modified electrode to their target antigens was investigated in the presence of BSA (bovin serum albumin) in order to alleviate non-specific adsorption problems. A proposed electrical model was used to analyse the experimental data. The resulting immunosensor has a linear dynamic range of 100 - 900 ng?ml1 of antigen and a detection limit of 100 ng?ml1.
Mode Coupling and Cavity-Quantum-Dot Interactions in a Fiber-Coupled Microdisk Cavity  [PDF]
Kartik Srinivasan,Oskar Painter
Physics , 2006, DOI: 10.1103/PhysRevA.75.023814
Abstract: A quantum master equation model for the interaction between a two-level system and whispering-gallery modes (WGMs) of a microdisk cavity is presented, with specific attention paid to current experiments involving a semiconductor quantum dot (QD) embedded in a fiber-coupled, AlGaAs microdisk cavity. In standard single mode cavity QED, three important rates characterize the system: the QD-cavity coupling rate g, the cavity decay rate kappa, and the QD dephasing rate gamma_perpendicular. A more accurate model of the microdisk cavity includes two additional features. The first is a second cavity mode that can couple to the QD, which for an ideal microdisk corresponds to a traveling wave WGM propagating counter to the first WGM. The second feature is a coupling between these two traveling wave WGMs, at a rate beta, due to backscattering caused by surface roughness that is present in fabricated devices. We consider the transmitted and reflected signals from the cavity for different parameter regimes of {g,beta,kappa,gamma_perpendicular}. A result of this analysis is that even in the presence of negligible roughness induced backscattering, a strongly coupled QD mediates coupling between the traveling wave WGMs, resulting in an enhanced effective coherent coupling rate g = sqrt(2)*g0 corresponding to that of a standing wave WGM with an electric field maximum at the position of the QD. In addition, analysis of the second-order correlation function of the reflected signal from the cavity indicates that regions of strong photon antibunching or bunching may be present depending upon the strength of coupling of the QD to each of the cavity modes. Such intensity correlation information will likely be valuable in interpreting experimental measurements of a strongly-coupled QD to a bi-modal WGM cavity.
Three electrode electrochemical microfluidic cell: construction and characterization
Silva, Rodrigo A. B. da;Almeida, Edimar G. N. de;Rabelo, Adriano C.;Silva, Abílio T. C. da;Ferreira, Lucas F.;Richter, Eduardo M.;
Journal of the Brazilian Chemical Society , 2009, DOI: 10.1590/S0103-50532009000700006
Abstract: this work describes the construction and characterization of an electrochemical flow-through microcell with the three electrodes (working, pseudo-reference, and auxiliary) inserted in microchannels with thickness smaller than 20 μm. these microchannels were constructed between two stacked polycarbonate slides using one or more overlapped toner masks as spacer. this strategy allows the construction of microcells with a variable internal volume on the working electrode (0.6 to 2.4 μl). three different materials were optimized as electrodes: gold film or graphite-epoxy composite as working electrode, silver-epoxy composite as pseudo-reference electrode and, graphite-epoxy composite as auxiliary electrode. the performance of the microfluidic cell was characterized by cyclic voltammetry, potentiometric stripping analysis at constant current, and square wave anodic stripping voltammetry using ferrocyanide and heavy metals (cu2+, hg2+, pb2+, and cd2+) as model analytes.
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