Pankaj Gupta

Polymelamine modified edge plane pyrolytic graphite sensor for the electrochemical assay of serotonin

A sensitive and novel electrochemical method has been developed for the determination of an important neurotransmitter, serotonin, using a polymelamine modified edge plane pyrolytic graphite sensor (EPPGS). Melamine was used for the modification of sensor by electropolymerizing it at the surface of EPPGS in acidic medium to form a layer of conducting polymer. Field emission scanning electron microscopy (FE-SEM) and electrochemical impedance spectroscopy (EIS) were used for the characterization of the surface of polymer modified sensor. The electrochemical measurements were carried out using square wave voltammetry and cyclic voltammetry. The polymelamine modified sensor exhibited excellent electrocatalytic activity towards the electrochemical oxidation of serotonin, exhibiting a larger peak current and shift of peak potential to less positive potentials as compared to the unmodified sensor. The dynamic range for the serotonin determination was found between 1-100 µm and 0.1-100 µm with detection limit of 492 nM and 30 nM for unmodified and polymer modified sensors, respectively. The determination of serotonin in human blood serum and urine has been carried out. The common metabolites such as ascorbic acid, dopamine, xanthine and hypoxanthine do not interfere in the determination up to 10-fold concentration, revealing good selectivity of the proposed sensor.

Graphene and Co-polymer composite based molecularly imprinted sensor for ultratrace determination of melatonin in human biological fluids

A novel molecularly imprinted polymer (MIP) sensor based on a composite of graphene (GR) and a co-polymer of 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) and melamine (MM) has been fabricated for detecting melatonin. The MIP film was fabricated by the deposition of a graphene layer on a glassy carbon electrode (GCE) surface followed by electropolymerizing AHNSA and MM in the presence of melatonin. The morphology of the sensor was characterized by using Field Emission-Scanning Electron Microscopy (FE-SEM) and Electrochemical Impedance Spectroscopy (EIS). The electrochemical performance of the imprinted sensor was investigated by using cyclic voltammetry and square wave voltammetry. The electropolymerization conditions, method of template removal, effect of template to monomer ratio and incubation time were optimized. Electrochemical results showed that the oxidation peak current increased linearly with the concentration of melatonin in the range 0.05 to 100 μM L−1. The detection limit of the imprinted electrochemical sensor towards the melatonin determination is calculated to be 60 × 10−10 mol L−1. The suitability of the GR/MIP based sensor has been demonstrated in detecting melatonin in biological samples.

Developments on electrochemical discharge machining: A review of experimental investigations on tool electrode process parameters

The electrochemical discharge machining is a combination of electrochemical machining and electrical discharge machining. The machining is achieved by chemical etching effect and melting of workpiece material due to electrical discharges. This process is used for a variety of nonconductive materials (glass, quartz, ceramic, Pyrex and so on) for the purpose of micromachining and specially for micro electro mechanical system applications. This article presents a comprehensive review of recent developments on tool electrode process parameters, which have resulted in enhanced efficiency and accuracy of the machining process. The tool electrode process parameters are shape, size, roughness, insulation and motion of tool and so on. These process parameters affect the process performance in terms of material removal rate, surface quality and dimensional accuracy of micromachined products. For example, spherical tool geometry provides five times higher material removal rate as compared to cylindrical tool geometry. The impact of electrochemical discharge machining process parameters associated with tool electrode is also discussed. A summary of review and proposed research directions is presented in this article.

Effect of Pulse Duration on Quality Characteristics of Blind Hole Drilled in Glass by ECDM

Electrochemical discharge machining (ECDM) has proven its usefulness for micro-machining of hard, brittle, and nonconductive materials. Pulse duration is one of the most important process parameters in ECDM. The present article investigates the effect of pulse duration on aspect ratio of glass material machined by ECDM. An effective range of pulse duration was identified experimentally to achieve better control on the quality characteristics. The quality characteristics measured were machining depth, surface damage, aspect ratio, and tool wear. Results reveal that a limited range of pulse duration affects the quality characteristics leading to high aspect ratio. Further, values of process parameters for high aspect ratio of holes were identified. Effect of applied voltage on tool wear was also investigated.

Graphene modified glassy carbon sensor for the determination of aspirin metabolites in human biological samples

A graphene modified glassy carbon (GR/GCE) sensor has been developed for the determination of aspirin metabolites 2,3- and 2,5-dihydroxybenzoic acids (2,3- and 2,5-DHB). The modified sensor was characterized by Field Emission Scanning Electron Microscopy and Electrochemical Impedance Spectroscopy. The electrochemical behavior of 2,3- and 2,5-DHB was investigated by cyclic and square wave voltammetry. The modified sensor exhibited excellent electrocatalytic activity for the oxidation of 2,3- and 2,5-DHB, leading to a remarkable enhancement in the peak current as compared to the bare sensor. The results were attributed to the enhanced surface area and high conductivity of GR. The anodic peak currents of 2,3- and 2,5-DHB were found to be linear in the concentration range of 1-150 µM and 1-200 µM with the detection limits of 47 nM and 51 nM, respectively. The sensor was capable to determine 2,5-DHB effectively without any interference from the uric acid and other metabolites present in the urine samples. The practical utility of GR/GCE has been successfully demonstrated for the determination of 2,5-DHB in the urine samples of persons undergoing treatment with aspirin.

Transient Water Flow and Nitrate Movement Simulation in Partially Saturated Zone

AbstractWater flow through vadose zone is important for soil ecology and for groundwater development. A thorough knowledge of water flow and solute transport through unsaturated zone is also needed...

Electrochemical investigations of 8-hydroxydeoxyguanosine and its determination at an edge plane pyrolytic graphite electrode

The electrochemical oxidation of 8-hydroxydeoxyguanosine (8-OHdG) has been studied at the edge plane surface of a pyrolytic graphite electrode (EPPGE) by cyclic sweep, square wave voltammetry, spectral studies, controlled potential electrolysis and related techniques. The oxidation of 8-OHdG occurred in a single well-defined peak over the entire pH range. The effect of pH revealed that the oxidation of 8-OHdG involved an equal number of electrons and protons. The 8-OHdG exhibited a linear calibration curve over a concentration range of 0.5–100 μM and the detection limit and sensitivity are found to be 28 × 10−9 M and 1.068 μA μM−1 respectively. The kinetics of the decay of the UV-absorbing intermediate generated during oxidation has been studied and the decay has been found to follow first order kinetics having a rate constant (k) in the range ∼2.5 × 10−3 s−1. The products of electrochemical oxidation have been characterized by using GC-MS studies. A tentative mechanism for the oxidation of 8-OHdG has also been suggested.

Impact of Hydrocarbon Pollutants on Partially Saturated Soil Media in Batch System: Morphological Analysis Using SEM Techniques

Soil surface morphology is an important functional parameter in fate and transport of pollutants in subsurface. Therefore, the aim of present study is to investigate the soil morphological changes using batch experiments having different concentration of a hydrocarbon pollutant, toluene. A series of six batch sets containing 20 g of oven-dried sand with particle size of 0.5–1.0 mm and 40% porosity were prepared at room temperature under partially saturated condition. Various concentrations of dissolved toluene varying from 5 to 100 ppm were considered in the designed batches. After 24 h of the incubation, when the soil water concentration reached to equilibrium, the temporary slides of respective soil samples were prepared. To capture the high magnification at pore scale, scanning electron microscopy (SEM) analysis was conducted at magnification of 10×, 20×, 30× and 40×. The results showed that the level of soil surface losses and the number of cavities on soil surface were increased with increasing hydrocarbon concentration. Furthermore, attenuation in the brightness of the sand particles was observed with increment in hydrocarbon concentration indicating the more adsorption capacity of toluene at high concentration levels. Results of this study are helpful in investigating the geochemical stability of soil, remediation strategy and for upscaling of fate and transport of pollutants in subsurface environment.

A carbon ion beam irradiated MWCNT/AuNPs composite sensor for a sensitive assay of purine-nucleosides of DNA

Multi-walled carbon nanotube (MWCNT) and gold nanoparticle (AuNPs) composite modified glassy carbon (MWCNT/AuNPs/GC) was irradiated with a high energy carbon ion beam and the surface morphology of the irradiated sensor was analysed using Raman spectroscopy, FE-SEM and Electrochemical Impedance Spectroscopy (EIS). The irradiated MWCNT/AuNPs/GC sensor has been applied for the electrochemical investigation of deoxyguanosine (dGuo) and deoxyadenosine (dAdo) by using square wave voltammetry and cyclic voltammetry. The irradiated sensor has been found to exhibit an excellent electrocatalytic activity, leading to an enhancement in the peak currents of dGuo and dAdo. The peak potentials also shifted to less positive potentials as compared to the unirradiated MWCNT/AuNPs/GC (pristine). The peak current of dGuo and dAdo was found to be linear in the range of 1–500 μM and detection limits of 126 and 109 nM, respectively, were observed. The practical utility of the irradiated sensor has been demonstrated by the determination of dGuo and dAdo in the DNA samples extracted from herring sperm and a MCF7 cell line (human breast cancer cells). Further, the carbon beam irradiated sensor displayed high sensitivity and reproducibility and has been found to be suitable in clinical diagnosis.

Effect of Electrolytes on Quality Characteristics of Glass during ECDM

Electrochemical discharge machining (ECDM) is an ideal process for machining of nonconductive materials in micro-domain. The material removal takes place due to combined action of localised sparks and electrolysis in an electrolytic chamber. The electrolyte is most important process parameter for ECDM as it governs spark action as well as electrolysis. This article presents a comparison of three preferred electrolytes used in ECDM viz. NaCl, KOH and NaOH on drilling of glass workpiece material. The quality characteristics measured are material removal rate (MRR) and hole overcut. Results reveal that NaOH provides 9.7 and 3.8 times higher MRR than NaCl and KOH respectively. MRR and hole overcut are found significantly affected by spark characteristics.