Synthesis of silver nanocatalyst in presence of poly(ethylene glycol) and its application for electrocatalytic reduction of hydrogen peroxide

The synthesis of powdered Ag nanoparticles in presence of poly(ethylene glycol) as reducing agent and stabilizer in aqueous medium is reported. The structure and properties of the Ag nanoparticles have been characterised by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray data. XRD study shows that the particles are crystalline in nature with face centered cubic geometry. Formation of stable silver nanoparticles gives mostly spherical particles with diameter in the range of 12–30 nm. The catalytic activity of the nanocrystalline AgNPs, for the reduction of hydrogen peroxide has been studied at the surface of glassy carbon electrode modified with Ag nanoparticles and poly(methyl methacrylate) (AgNPs-PMMA/GCE) prepared by casting of the AgNPs-PMMA solution on GCE. The sensor responds to H2O2 with high selectivity, good reproducibility and stability, over a linear range of 22–1700 µM with a detection limit of 4.8 µM using amperometry.

<b>Voltammetric determination of L-cysteic acid on a 1-[4-(ferrocenyl-ethynyl)phenyl]-1-ethanone modified carbon paste electrode</b>

The electrochemical behaviour of L-cysteic acid was studied at the surface of 1-[4-(ferrocenyl-ethynyl)phenyl]-1-ethanone modified carbon paste electrode (4FEPEMCPE) in aqueous media using cyclic voltammetry and double step potential chronoamperometry. It has been found, that under optimum condition (pH 7.00) in cyclic voltammetry, the oxidation of L-cysteic acid at the surface of 4FEPEMCPE is occurred at a potential about 220 mV less positive than that an unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α, and catalytic reaction rate constant, K/h, were also determined using electrochemical approaches. The electrocatalytic oxidation peak current of L-cysteic acid showed a linear dependent on the L-cysteic acid concentration and linear calibration curves were obtained in the ranges of 9 × 10-5 - 6.2 × 10-3 M and 2.0 × 10-7 - 1.17 × 10-5 M of L-cysteic acid concentration with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, respectively. The detection limits (3σ) were determined equal to 2.3 × 10-5 M and 8.7 × 10-8 M by CV and DPV methods. This method was also examined as a selective, simple and precise new method for voltammetric determination of L-cysteic acid in serum of patient's blood with migraine disease

Direct Electrochemistry of Polyphenol Oxidase

The electrochemistry of banana tissues on a carbon paste electrode modified with multi-walled carbon nanotubes (MWCNTs) is presented. Cyclic voltammetry is applied to investigate the direct electrochemistry of banana tissues i.e. a source of polyphenol oxidase (PPO). A redox couple with an anodic and counterpart cathodic peak is obtained. The influence of various parameters such as pH, scan rate of potential and heating on the electrochemical properties of polyphenol oxidase in banana tissues were examined. For apple tissues, a same signal is observed on a carbon paste electrode (CPE) modified with multi-walled carbon nanotubes. It was found that presence of carbon nanotubes (CNTs) is essential to observe the electrochemical activity of polyphenol oxidase in banana and apple tissues. In this paper, the electrochemistry of fruits was described. We have shown that multi-walled carbon nanotubes can enhance the direct electron transfer between the electroactive center of polyphenol oxidase in banana tissues and the underlying electrode

Synthesis of silver nanocatalyst in presence of poly(ethylene glycol) and its application for electrocatalytic reduction of hydrogen peroxide

843-847The synthesis of powdered Ag nanoparticles in presence of poly(ethylene glycol) as reducing agent and stabilizer in aqueous medium is reported. The structure and properties of the Ag nanoparticles have been characterised by X-ray diffraction, transmission electron microscopy and energy dispersive X-ray data. XRD study shows that the particles are crystalline in nature with face centered cubic geometry. Formation of stable silver nanoparticles gives mostly spherical particles with diameter in the range of 12–30 nm. The catalytic activity of the nanocrystalline AgNPs, for the reduction of hydrogen peroxide has been studied at the surface of glassy carbon electrode modified with Ag nanoparticles and poly(methyl methacrylate) (AgNPs-PMMA/GCE) prepared by casting of the AgNPs-PMMA solution on GCE. The sensor responds to H2O2 with high selectivity, good reproducibility and stability, over a linear range of 22–1700 µM with a detection limit of 4.8 µM using amperometry

Keggin-type polyoxometalate embedded polyvinylidene fluoride for thin film microextraction of organophosphorus pesticides

The present research is the first report on the application of Keggin-type phosphotungstic acid/polyvinylidene fluoride membrane. This compound as a simple, cost-effective and novel sorbent was used for the extraction and pre-concentration of two organophosphorus pesticides in real samples in the thin film solid-phase microextraction (TFME) method. TFME as one of the sub-branches of solid phase microextraction resolves the problems of SPME methods, including their limited absorption capacity. These extraction methods have a high surface-to-volume ratio, which improves their sensitivity compared to other geometries. Under optimal conditions, the limit of detections (LODs), the limit of quantifications (LOQs), and relative standard deviation (RSD) of this method varied in the ranges of 0.29–0.31 μg L−1, 0.96–1.0 μg L−1, and 3.9%–6.2%, respectively. This method showed a linear dynamic range (LDR) of 1.0–500 μg L−1 with a coefficient of determination (r2) above 0.9978. This promising method was used to analyze malathion and diazinon

Direct electrochemistry and bioelectrocatalysis of a class II non-symbiotic plant haemoglobin immobilised on screen-printed carbon electrodes.

In this study, direct electron transfer (ET) has been achieved between an immobilised non-symbiotic plant haemoglobin class II from Beta vulgaris (nsBvHb2) and three different screen-printed carbon electrodes based on graphite (SPCE), multi-walled carbon nanotubes (MWCNT-SPCE), and single-walled carbon nanotubes (SWCNT-SPCE) without the aid of any electron mediator. The nsBvHb2 modified electrodes were studied with cyclic voltammetry (CV) and also when placed in a wall-jet flow through cell for their electrocatalytic properties for reduction of H(2)O(2). The immobilised nsBvHb2 displayed a couple of stable and well-defined redox peaks with a formal potential (E degrees ') of -33.5 mV (vs. Ag|AgCl|3 M KCl) at pH 7.4. The ET rate constant of nsBvHb2, k (s), was also determined at the surface of the three types of electrodes in phosphate buffer solution pH 7.4, and was found to be 0.50 s(-1) on SPCE, 2.78 s(-1) on MWCNT-SPCE and 4.06 s(-1) on SWCNT-SPCE, respectively. The average surface coverage of electrochemically active nsBvHb2 immobilised on the SPCEs, MWCNT-SPCEs and SWCNT-SPCEs obtained was 2.85 x 10(-10) mol cm(-2), 4.13 x 10(-10) mol cm(-2) and 5.20 x 10(-10) mol cm(-2). During the experiments the immobilised nsBvHb2 was stable and kept its electrochemical and catalytic activities. The nsBvHb2 modified electrodes also displayed an excellent response to the reduction of hydrogen peroxide (H(2)O(2)) with a linear detection range from 1 muM to 1000 muM on the surface of SPCEs, from 0.5 muM to 1000 muM on MWCNT-SPCEs, and from 0.1 muM to 1000 muM on SWCNT-SPCEs. The lower limit of detection was 0.8 muM, 0.4 muM and 0.1 muM at 3sigma at the SPCEs, the MWCNT-SPCEs, and the SWCNT-SPCEs, respectively, and the apparent Michaelis-Menten constant, [Formula: see text], for the H(2)O(2) sensors was estimated to be 0.32 mM , 0.29 mM and 0.27 mM, respectively

Diazonium-based impedimetric aptasensor for the rapid label-free detection of Salmonella typhimurium in food sample

Fast and accurate detection of microorganisms is of key importance in clinical analysis and in food and water quality monitoring. Salmonella typhimurium is responsible for about a third of all cases of food borne diseases and consequently, its fast detection is of great importance for ensuring the safety of foodstuffs. We report the development of a label-free impedimetric aptamer-based biosensor for S. typhimurium detection. The aptamer biosensor was fabricated by grafting a diazonium-supporting layer onto screen printed carbon electrodes (SPEs), via electrochemical or chemical approaches, followed by chemical immobilisation of aminated-aptamer. FTIR-ATR, contact angle and electrochemical measurements were used to monitor the fabrication process. Results showed that electrochemical immobilisation of the diazonium-grafting layer allowed the formation of a denser aptamer layer, which resulted in higher sensitivity. The developed aptamer-biosensor responded linearly, on a logarithm scale, over the concentration range 1 x 10(1) to 1 x 10(8) CFU mL(-1), with a limit of quantification (LOQ) of 1 x 10(1) CFU mL(-1) and a limit of detection (LOD) of 6 CFU mL(-1). Selectivity studies showed that the aptamer biosensor could discriminate S. typhimurium from 6 other model bacteria strains. Finally, recovery studies demonstrated its suitability for the detection of S. typhimurium in spiked (1 x 10(2), 1 x 10(4) and 1 x 10(6) CFU mL(-1)) apple juice samples. (C) 2016 Elsevier B.V. All rights reserved.Funding Agencies|Vetenskapsradet (Pathoscreen project; Swedish Research Link) [D0675001]; Ministry of Science Research and Technology of Iran</p