Selective amperometric sensing of hydrogen peroxide with Nafion/copper particulates chemically modified electrode

940-945Nafion/copper particulates chemically modified glassy carbon electrode has been prepared by in situ electrochemical deposition. The electrode is found to to be successful for selective amperometric sensing of hydrogen peroxide at -0.2 V vs Ag/AgCl at physiological pH without interference from uric acid, ascorbic acid, catechol, cysteine, nitrite and nitrate. Two linear regions, 20-200 µM and 220-400 µM, for H2O2 detection with the slope and regression coefficient values of 33.2 nA/µM and 25.61 nA/µM and 0.9975 and 0.9999 respectively are obtained with 1.63 µM detection limit (S/N = 3). Application to real samples analysis is demonstrated for milk, urine and tea samples with appreciable recovery values

A new highly conducting carbon black (CL-08) modified electrode functionalized with syringic acid for sensitive and selective L-cysteine electrocatalysis at low potential

Highly selective, sensitive and low potential detection of biological analytes by simple and rapid electrochemical technique using low cost nanocarbons is a demanding research since last decade. Herein, we report a low cost, new, nanocarbon, the carbon black (CL-08) functionalized with syringic acid (SA) modified glassy carbon electrode (GCE) for selective L-cysteine (L-CySH) electrocatalysis at 0.04 V vs Ag/AgCl. The new matrix is competitive in the low potential L-CySH detection compared to the multiwalled carbon nanotube, graphite powder, carbon mesoporous and graphitized mesoporous carbon. The possible in situ generated redox products namely 2,6-dimethoxy benzoquinone and 3,4-dihydroxy-5-methoxy benzoic acid were proposed to form on the GCE/SA@CL-08 with two electron transfer and nernstian behaviours. FTIR and UV–vis analyses collectively revealed the presence of quinone species. The GCE/SA@CL-08 showed L-CySH electrocatalysis with good selectivity, 0.42 nA.μM−1 and 5.4 nA.μM−1 sensitivity in the detection range of 20–100 μM and 100–1000 μM respectively with 639 nM limit of detection, in chronoamperometry. A successful demonstration of L-CySH detection from the simulated blood serum and processed chicken samples with substantial recovery values using the GCE/SA@CL-08 were presented in this study

Tetracycline Immobilization as Hydroquinone Derivative at Dissolved Oxygen Reduction Potential on Multiwalled Carbon Nanotube

Upon continuous potential cycling of multiwalled carbon nanotube modified electrode (GCE/MWCNT) with Tetracycline antibiotic (Tet) at −0.5 to 0.4 V vs Ag/AgCl in pH 7 phosphate buffer solution, the Tet drug gets selectively immobilized as Tet-hydroquinone derivative (Tet-HQ) on the GCE/MWCNT (GCE/Tet-HQ@MWCNT) and showed a specific surface confined redox peak at E1/2 =−0.24 ± 0.02 V vs Ag/AgCl. Control potential cycling experiment with o-cresol resulted to similar electrochemical characteristic too. But with p-cresol, no such surface confined redox peak was noticed. Dissolved oxygen reduction to hydrogen peroxide (as an intermediate species) at −0.45 V vs Ag/AgCl and its chemical oxidation of the surface bound Tet@MWCNT to Tet-HQ@MWCNT is proposed as a plausible mechanism. Separate ring-disk screen-printed carbon electrode assembly, where MWCNT and a H2O2 detection catalyst (nano-MnO2) modified on the ring and disk respectively, coupled with flow injection analysis showed specific current signals for oxygen reduction reaction at −0.45 V vs Ag/AgCl on the disk and subsequent H2O2 oxidation on ring at 0.8 V vs Ag/AgCl. The surface confined redox system showed highly selective electrocatalytic reduction signal to hydrogen peroxide at ∼0.22 V vs Ag/AgCl without any interference from the ascorbic acid, uric acid, cysteine and nitrite

A new electro-generated o-dianisidine derivative stabilized MWCNT-modified GCE for low potential gallic acid

The exploration of functional group interactions and electro-generated species stabilization on chemically modified electrodes for efficient electro-analytical application is a continuing research area in electrochemistry. In addition, the electrochemical behaviours of the intermediate species, which are generated from the aromatic organic redox mediator and possess both methoxy and amine functional groups, have been rarely studied for electro-analytical applications. For the first time, we report the stabilization of an electro-generated enone derivative of the o-dianisidine (EDo-D) dimer formed as one of the intermediate species during o-dianisidine immobilization. The electro-generated o-dianisidine derivative (o-DD)-stabilized multi-walled carbon nanotube (MWCNT)-modified glassy carbon electrode (GCE/o-DD@MWCNT) exhibited two highly reproducible and, well-defined surface-confined redox couples in a pH 7 phosphate buffer solution (PBS). FTIR analyses indicated the presence of an amine group linkage and an azo product in the o-DD@MWCNT hybrid. UV-Vis and GC-MS analyses confirmed the presence of o-dianisidine in its azo dimer form within the MWCNT. In addition, the enone derivative of the o-dianisidine dimer present on the GCE/o-DD@MWCNT successfully sensed gallic acid (GA) at 0.16 V vs. Ag/AgCl in pH 7 PBS. Highly selective GA detection was achieved with a sensitivity of 0.4580 µA µM-1, a detection range of 100-1300 µM and a detection limit of 144 nM using chronoamperometry. GCE/o-DD@MWCNT also demonstrated effective GA detection in simulated real grape juice and water samples

Evaluation of radical scavenging capacity of polyphenols found in natural malaysian honeys by voltammetric techniques

As minor constituents present in natural honey, polyphenols have the capacity as antioxidant by donating electron to halt detrimental actions of free radicals. The present work aims to analyze the electrochemical behaviour of polyphenols identified in Malaysian Apis and Trigona honey samples, determine and compare their reducing strengths as well as qualitatively evaluate the radical scavenging capacity of these phenolics in Malaysian honey samples. Six flavonoids, eight phenolic acids, and tannin pentagalloyl glucose (PGG) dissolved in 0.1 M PBS pH 7 were studied by cyclic voltammetry (CV). Seventeen Malaysian honey samples were analyzed using differential pulse voltammetry (DPV). Cyclic voltammograms revealed that polyphenols with catechol moiety in their structure exhibited Ep1a at low potentials, ranging between +0.173 V and +0.404 V. PGG and quercetin may have equal tendency to donate electron (same Ep1a) but higher peak current was observed for the former indicates its higher reducing strength, suggesting PGG as the strongest antioxidant among studied polyphenols. From DP voltammograms, oxidation of honey phenolics occurred in all honey samples with predominant catechol-bearing peak P1 observed in nanas N1, kelulut K3 and tualang T1 honeys. The varied peak current intensities observed for P1-P3 in all analyzed Malaysian honey samples suggested that these honey samples can act against free radicals at varying degree and thus are good sources of natural antioxidants

New real-time force monitoring device with enhanced accuracy for evaluation of applied force during the joint mobilization technique

BACKGROUND: Force Monitoring Devices (FMDs) reported in the literature to monitor applied force during Joint Mobilization Technique (JMT) possess complex design/bulky which alters the execution of treatment, has poor accuracy and is unable to feel the resistance provided by soft tissues limits its usage in the clinical settings. OBJECTIVES: This study aims to develop a highly accurate, portable FMD and to demonstrate real-time monitoring of force applied by health professionals during JMT without altering its execution. METHODS: The FMD was constructed using the FlexiForce sensor, potential divider, ATmega 328 microcontroller, custom-written software, and liquid crystal display. The calibration, accuracy, and cyclic repeatability of the FMD were tested from 0 to 90 N applied load with a gold standard universal testing machine. For practical demonstration, the FMD was tested for monitoring applied force by a physiotherapist while performing Maitland's grade I to IV over the 6th cervical vertebra among 30 healthy subjects. RESULTS: The obtained Bland-Altman plot limits agreement for accuracy, and cyclic repeatability was -1.57 N to 1.22 N, and -1.26 N to 1.26 N, respectively with standard deviation and standard error of the mean values of 3.77% and 0.73% and 2.15% and 0.23%, respectively. The test-retest reliability of the FMD tested by the same researcher at an interval of one week showed an excellent intra-class correlation coefficient of r= 1.00. The obtained force readings for grade I to IV among 30 subjects ranged from 10.33 N to 45.24 N. CONCLUSIONS: Appreciable performance of the developed FMD suggested that it may be useful to monitor force applied by clinicians during JMT among neck pain subjects and is a useful educational tool for academicians to teach mobilization skills