Studies of sol-gel ceramic film incorporating methylene blue on glassy carbon: an electrocatalytic system for the simultaneous determination of ascorbic and uric acids

Pseudocapacitive-dye-molecule-based high-performance flexible supercapacitors

Currently, the development of novel, cheap and high-performance electrode materials for flexible energy-storage devices is being intensively pursued. Organic dyes are regarded as one of the most common water pollution sources, and their discharge not only damages the ecological balance but also wastes a lot of valuable chemical raw materials. With intrinsic redox functional groups, two types of widely used dyes including anthraquinone derivatives and phenothiazine dyes can be effectively removed from their effluent by a facile galvanostatic polymerization method, and resource utilized as electrochemical energy-storage materials. Based on this, a new kind of flexible supercapacitor based on dye molecules has been successfully fabricated, and exhibits excellent electrochemical performance, demonstrating a wise strategy for simultaneous wastewater treatment and preparation of functional devices.

Rapid Detection of Ascorbic Acid Based on a Dual-Electrode Sensor System Using a Powder Microelectrode Embedded with Carboxyl Multi-Walled Carbon Nanotubes

In this paper, carboxyl groups were introduced by liquid oxidation methods onto multi-walled carbon nanotubes (MWCNTs) to improve the MWCNTs' electrocatalytic properties. A platinum wire microelectrode (ME) was corroded using aqua regia and subsequently embedded with MWCNTs to achieve more active sites, producing a so-called powder microelectrode (PME). Compared with conventional MEs, the PME has a larger specific surface area and more active sites. When PME was used to detect ascorbic acid (AA), the AA oxidation potential shifted negatively and current peak was visibly increased. The calibration curve obtained for AA was in a range of 5.00 × 10-6~9.50 × 10-4 mol·L-1: Ipa(μA) = 3.259 × 10-2+ 1.801 × 10² C (mol·L-1) under the optimum testing conditions. Moreover, the detection and quantitation limits were confirmed at 4.89 × 10-7 mol·L-1 and 1.63 × 10-7 mol·L-1, respectively. When the fabricated PME was practically applied to detect AA, it was shown a recovery rate of 94~107% with relative standard deviation (RSD) <5%. The proposed strategy thus offers a promising, rapid, selective and low-cost approach to effective analysis of AA.

A novel voltammetric sensor for nevirapine, based on modified graphite electrode by MWCNs/poly(methylene blue)/gold nanoparticle

In the present study, a graphite electrode (GE) modified by conductive film (containing functionalized multi-walled carbon nanotubes (f-MWCNTs), poly methylene blue p(MB) and gold nanoparticles (AuNPs)) was introduced for determination of nevirapine (NVP) as an anti-HIV drug by applying the differential pulse anodic stripping voltammetry (DPASV) technique. Modification of the electrode was investigated by scanning electron microscopy (SEM) and impedance electrochemical spectroscopy (EIS). All electrochemical effective parameters on detection of NVP were optimized and the oxidation peak current of drug was used for its monitoring. The obtained results confirmed that the oxidation peak currents increased linearly by increasing in NVP concentrations in the range of 0.1-50 μM and a detection limit of 53 nM was achieved. The proposed sensor (AuNPs/p(MB)/f-MWCNTs/GE) was successfully applied for the determination of NVP in blood serum and pharmaceutical samples. It revealed the excellent stability, repeatability and reproducibility as well.

Economical, facile synthesis of network-like carbon nanosheets and their use as an enhanced electrode material for sensitive detection of ascorbic acid

A highly sensitive electrochemical sensor for the detection of ascorbic acid (AA) was first fabricated using network-like carbon nanosheets (NCN) as an enhanced electrode modifier.

Methylene blue incorporated mesoporous silica microsphere based sensing scaffold for the selective voltammetric determination of riboflavin

Methylene blue incorporated sulfonic acid functionalized mesoporous silica microspheres is synthesized and utilized as effective sensing scaffold for electrochemical determination of nanomolar levels of riboflavin.

Controlled synthesis of graphene–Gd(OH)3 nanocomposites and their application for detection of ascorbic acid

Graphene–Gd(OH)₃ nanocomposites have been synthesized by hydrothermal method, which show superior activity towards ascorbic acid detection.

DNA-based nanocomposite as electrochemical chiral sensing platform for the enantioselective interaction with quinine and quinidine

A DNA-based nanocomposite was prepared to develop a simple strategy for electrochemical chiral analysis.

Direct electrochemistry and electrocatalysis of myoglobin immobilized on L-cysteine self-assembled gold electrode

Myoglobin (Mb) has been successfully immobilized on a self-assembled monolayer (SAM) of L-cysteine (Cys) on a gold electrode, Au/Cys. The presence of a pair of well-defined and nearly reversible waves centered at ca. 0.086 V vs Ag/AgCl (pH 6.5) suggests that the native character of Mb heme Fe(III/II) redox couple has been obtained. The formal potential of Mb on Cys SAM exhibited pH-dependent variation in the pH range of 5-9 with a slope of 55 mV/pH, indicating that the electron transfer is accompanied by a single proton exchange. Thermodynamic and kinetic aspects of Mb adsorption processes on Au/Cys were studied by using voltammetric and quartz-crystal microbalance methods. The Au/Cys electrode with immobilized Mb exhibited electrocatalytic activity toward ascorbic acid (AA) oxidation with an overpotential decrease of over 400 mV and a linear dependence of current on the AA concentration from 0.5 to 5.0 mmol L(-1).

Simultaneous determination of tryptophan, uric acid and ascorbic acid at iron(III) doped zeolite modified carbon paste electrode

A new chemically modified electrode is constructed based on iron(III) doped zeolite modified carbon paste electrode (Fe(3+)Y/ZCME). The electrode was evaluated as a sensor for sub-micromolar determination of tryptophan (Trp), uric acid (UA) and ascorbic acid (AA) in aqueous solutions. The measurements were carried out by application of the differential pulse voltammetry (DPV) method in phosphate buffer solution with pH 3.5. Iron(III) loaded in zeolite can increase anodic peak currents by adsorption of Trp, UA and AA on electrode surface The analytical performance was evaluated with respect to the carbon paste composition, pH of solution, accumulation time and accumulation potential. The prepared electrode shows voltammetric responses with high sensitivity and selectivity for Trp, UA and AA in optimal conditions, which makes it very suitable for simultaneous determination of these compounds. The linear calibration range for AA in the presence of 50 microM UA and 50 microMTrp was 0.6 microM to 100 microM, with a correlation coefficient of 0.9992, and a detection limit of 0.21 microM (S/N=3). A linear relationship was found for UA in the range of 0.3-700 microM containing 10 microM AA and 50 microM Trp, with a correlation coefficient of 0.9990 and a detection limit of 0.08 microM. The linear calibration range for Trp in the presence of 10 microM AA and 50 microM UA was 0.2-150 microM, with a correlation coefficient of 0.9996, and a detection limit of 0.06 microM. The proposed method was successfully applied for determination Trp, UA and AA in biological systems and pharmaceutical samples.