Response Of Glassy Carbon Electrode Research Articles

Effect of hydrophilic atenolol and lipophilic propranolol β-blockers on the surface and bulk aggregation of quaternary ammonium bromide surfactants: A comparative study

The variations in the surface and bulk properties of alkyltrimethylammonium bromide (ATAB) surfactants (C12 to C16) in presence of a hydrophilic β-blocker drug atenolol (ATL) and a lipophilic β-blocker drug propranolol (PPL), have been investigated using three independent techniques, viz; electrical conductivity, surface tension and cyclic voltammetry. Electrical conductivity measurement indicates that both ATL and PPL at low concentrations of 0.5 mM and 1.0 mM brings about almost equal changes to the critical micelliastion concentration of all ATAB surfactants. However, at higher concentrations (3 mM to 10 mM), PPL seems to be more effective, than ATL, in reducing the cmc and hence favouring micellization. Various interfacial parameters at the air–water interface have been determined through the measurements of surface tension of the surfactants in varying concentrations of ATL and PPL ranging from 0.5 mM to 10 mM. The thermodynamic parameters of micellization are evaluated from the temperature dependence of cmc. The variation of Gibbs energy with temperature is small while large changes in enthalpy and entropy of micellization are observed in the temperature range studied. The effect of TTAB on the electrolytic solutions of ATL and PPL on the voltametric response of glassy carbon electrode (GCE) was examined. TTAB enhanced the current signal of ATL while opposite effect was observed for PPL. The experimental results have been analysed in terms of the difference in the hydrophobicities of the two β-blocker drug molecules.

Bioinspired electro-permeable glycans on carbon: Fouling control for sensing in complex matrices

The effect of glycan adlayers on the electrochemical response of glassy carbon electrodes was studied using standard redox probes and complex aqueous matrices. Aryldiazonium cations of aryl-lactoside precursors were used to modify glassy carbon via spontaneous and electrochemically assisted covalent grafting. Contact angle and fluorescence binding using Peanut Agglutinin (PNA) as a diagnostic lectin indicate that electrografting results in adlayers with greater glycan surface density than those obtained via spontaneous reaction. X-ray photoelectron spectroscopy with a fluorinated analog confirmed that electrografting results in multilayers of cross-linked aryl-lactosides. Adsorption studies with Bovine Serum Albumin (BSA) show that aryl-lactoside adlayers minimize unspecific protein adsorption. However, no significant differences were detected between spontaneous and electrografted layers in their ability to resist protein fouling despite their differences in coverage. Voltammetry studies show that spontaneous grafting has minimal effects on the response of standard redox probes in solution, whereas electrografting results in additional charge transfer impedance arising from increased electrode passivation. Bare and lactoside-modified carbon electrodes were tested for the detection of caffeine before and after prolonged exposure to coffee solutions. Spontaneous grafting was found to result in optimal properties by imparting antifouling performance in these complex matrices while preserving fast interfacial charge transfer.

Enhanced electrochemical response of a modified glassy carbon electrode by poly(2-vinlypyridine-b-methyl methacrylate) conjugated gold nanoparticles for detection of nicotine

Poly(2-vinylpyridine-b-methylmethacrylate) coated gold nanoparticles [P(2VP-MMA)-AuNPs] were prepared and characterized by UV-Vis, FTIR, AFM, and zetasizer analysis. Investigation of the potential of the synthesized poly(2-vinylpyridine-b-methylmethacrylate) coated gold nanoparticles [P(2VP-MMA)-AuNPs] for detection of nicotine is the main focus of the current study. P(2VP-MMA)-AuNPs were coated on a glassy carbon electrode (GCE) for electrochemical detection of nicotine by cyclic voltammetry. The effect of molar mass of individual P2VP blocks and total molar mass of the block copolymer is evaluated in the context of an enhanced electrochemical response of the modified GCE for its sensing ability of nicotine in both aqueous and organic media. The electrochemical detection of nicotine is significantly enhanced by modification of the GCE with P(2VP-MMA)-AuNPs.

A comparative study of electrochemical performances of carbon nanomaterial-modified electrodes for DNA detection. Nanotubes or graphene?

A comparative study about the electrochemical response of glassy carbon electrode modified with four different carbon nanomaterial (CNM) against dsDNA is reported. The CNM used were oxidized and nonoxidized multiwalled carbon nanotubes (MWNT-OX and MWNT, respectively), graphene oxide (GO) and chemically reduced graphene oxide (RGO) and dispersed in 3:1 chitosan/water mixture. The electrodes were characterized by cyclic voltammetry, scanning electrochemical microscopy, and contact angle measurements. The results showed that the type and degree of oxidation have a strong effect on the electroactivity of the modified electrode. GCE/RGO clearly exhibited the most electroactive surface among the CNMs, demonstrating that the graphitic structure is highly important. A more sensitive electrochemical response against dsDNA was obtained when GCE/RGO electrode was used. Therefore, RGO is the CNM recommended for further consideration in the development of DNA biosensors.

Effect of the Dispersing Agent on the Electrochemical Response of Glassy Carbon Electrodes Modified with Dispersions of Carbon Nanotubes

AbstractThe electrochemical response of a glassy carbon electrode modified with carbon nanotubes (CNT) dispersed in two solvents, water and DMF, and two polymers, chitosan and Nafion is reported. The films were homogeneous when the dispersing agent was water or DMF. In the case of polymers, the surfaces present areas with different density of CNTs. A more sensitive electrochemical response was obtained when CNTs are dispersed in the solvents. In the case of CNT dispersed with polymers, the nature of the polymer demonstrated to be a critical parameter not only for dispersing the nanotubes but also for the electrochemical activity of the resulting electrodes.

Effect of surfactants on the voltammetric response and determination of an antihypertensive drug

The effect of adding surface-active agents to electrolytes containing terazosin, an antihypertensive drug, on the voltammetric response of glassy carbon electrode was studied. The current signal due to the oxidation process was a function of the amount of terazosin, pH of the medium, type of surfactant, and accumulation time at the electrode surface. Two surfactants were used, an anionic type, sodium dodecyl sulfate (SDS) and a cationic type, cetyl trimethyl ammonium bromide (CTAB). Addition of SDS to the terazosin-containing electrolyte was found to enhance the oxidation current signal while CTAB showed an opposite effect. Beside the interfacial interaction of the surfactant with the electrode surface in reference to the bias applied potential and the charge of surfactant, terazosin-surfactant interaction in the electrolytic solution was found to be critical to the magnitude of current signal. Addition of SDS to terazosin-containing buffer solution resulted in a decrease in the drug absorption spectrum both in the ultra-violet and visible (UV–vis) regions. Moreover, NMR measurements showed considerable chemical shifts for the aromatic protons of the quinazolinyl moiety of the terazosin in presence of SDS. The affected aromatic protons are positioned next to the interacting protonated amino-group of the terazosin with the charged sulfonate-group of SDS. On the other hand, addition of CTAB did not cause noticeable changes both to the UV–vis and NMR spectra of the drug. The use of SDS in the electrochemical determination of terazosin using linear sweep voltammetry and differential pulse voltammetry at solid glassy carbon electrode enhanced the detection limit from 6.00 × 10 −7 mol L −1 in absence of surfactant to 4.58 × 10 −9 mol L −1 when present. The validity of using this method in the determination of drug active ingredient in urine samples and tablet formulations was also demonstrated.

Two-equivalent electrochemical reduction of a cyano-complex [Tl III(CN) 2] + and the novel di-nuclear compound [(CN) 5Pt II−Tl III] 0

Extending our recent insights in two-electron transfer microscopic mechanisms for a Tl III/Tl I redox system [D.E. Khoshtariya, et al., Inorg. Chem. 41 (2002) 1728], the electrochemical response of glassy carbon electrode in acidified solutions of Tl III (ClO 4) 3 containing different concentrations of sodium cyanide has been extensively studied for the first time by use of cyclic voltammetry and the CVSIM curve simulation PC program. The complex [Tl III(CN) 2] + has been thoroughly identified electrochemically and shown to display a single well-defined reduction wave (which has no anodic counterpart), ascribed to the two-equivalent process yielding [Tl I(aq)] +. This behavior is similar to that of [Tl III(aq)] 3+ ion in the absence of sodium cyanide, disclosed in the previous work, and is compatible with the quasi-simultaneous yet sequential two-electron transfer pattern (with two reduction waves merged in one), implying the rate-determining first electron transfer step (resulting in the formation of a covalently interacting di-thallium complex as a metastable intermediate), and the fast second electron transfer step. Some preliminary studies of the two-equivalent reduction of directly metal–metal bonded stable compound [(CN) 5Pt II–Tl III] 0 has been also performed displaying two reduction waves compatible with a true sequential pattern.

Study of the Potentiometric Response of Glassy Carbon Electrodes Coated with the Polycationic Ionomer Tosflex

The perfluorinated polycationic polymer Tosflex was used to modify glassy carbon electrodes in order to study the potentiometric response towards anions. The electrodes exhibited a reversible response towards all the tested analytes in the range 10−4–10−1 M, but the resulting slope was sub-Nernstian and the selectivity was very poor. If the glassy carbon surface was submitted to oxidative electrochemical pretreatment, before being coated with the Tosflex membrane, the behavior changed dramatically, since the electrode displayed a response only towards oxidizable anions, such as iodide, thiosulfate, sulfite. The electrode response was attributed to a redox process between the analytes and the oxidized sites of the graphitic oxide film produced by electrochemical anodization. The response characteristics of the activated GC/Tosflex electrode were investigated pointing out the very high selectivity towards sulfite.

Potentiometric Response of Glassy Carbon Electrodes Coated with Crown Ether LB Film

Potentiometric Response of Glassy Carbon Electrodes Coated with Crown Ether LB Film

Photo-switchable ion and enzyme sensors. Photoinduced potentiometric response of glassy carbon electrode coated with polymer or polymer/enzyme dual membrane.

Photo-switchable ion and enzyme sensors were fabricated by the use of glassy carbon electrode coated with nonactindoped or enzyme modified poly(vinyl chloride) (PVC) membranes. The ion sensor with nonactin-doped PVC membrane, which contained spirobenzopyran as the photosensitive dye, exhibited a potentiometric photoresponse to NH4+ ion in the solution. The dynamic range of the NH4+ ion sensor was 10(-7)--10(-3) M. Urea, adenosine, and asparagine sensors were prepared by coating the surface of the NH4+-ion sensor with urease, adenosine deaminase, and asparaginase membranes, respectively. These enzyme sensors could be used for determining the substrates at the micro mole level. The performance characteristics of these sensors were compared with those previously prepared membrane electrode sensors.

Ion Chromatography Using an Electrochemical Detector: Response to Non-Electroactive Anions

Abstract The effect of non electroactive anions on the response of glassy carbon electrode used as an electrochemical detector in an ionic chromatographic system with dual column has been investigated and a method to eliminate this anomalous behaviour has been proposed. The results showed that the response of the electrode observed for non electroactive anions is related to the drop in pH of the eluent during the elution of anions.

Effect of pH on the response of glassy carbon electrodes

The use of glassy carbon as an electrode material engenders a number of practical problems owing to the presence of C—O functionalities on its surface. One such problem is the susceptibility of the electrode to pH changes. Highly surface-active glassy carbon electrodes having a high proportion of irreversible C—O groups are particularly prone to variations in pH compared with ones having mainly quinoidal species. This is reflected in the performance of glassy carbon in the cyclic voltammetry of hydroquinone.