Browsing by Author "V.S. Tripathi"

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A novel amperometric hydrogen peroxide biosensor based on horseradish peroxidase incorporated in organically modified sol-gel glass matrix/graphite paste with multiwalled carbon nanotubes
(2010) Ida Tiwari; K.P. Singh; Manorma Singh; B.C. Upadhyay; V.S. Tripathi
We herein report an electrochemical hydrogen peroxide sensor based on horseradish peroxidase immobilized in organically modified sol-gel glass (ormosil) with mediator ferricyanide along with multiwalled carbon nanotubes (mwcnts). The ormosil material is converted to fine powder followed by incorporation within graphite paste electrode. The electrochemistry of redox materials encapsulated within ormosil has been studied. The requirement of mwcnts is examined. The ormosil prepared with optimum concentration of mwcnts shows better redox electrochemistry as compared to that made without mwcnts. The biosensor has been characterized by cyclic voltammetry and chroanoamperometry. The performance, stability, and reproducibility of a new peroxide biosensor are reported. © Taylor & Francis Group, LLC.
A novel ferrocene encapsulated palladium-linked ormosil-based electrocatalytic dopamine biosensor
(2001) P.C. Pandey; S. Upadhyay; Ida Tiwari; G. Singh; V.S. Tripathi
A novel finding on the development of electrocatalytic biosensor for dopamine is reported. The new electrocatalytic dopamine biosensor is developed using ferrocene encapsulated palladium (Pd)-linked organically-modified sol-gel glass (ormosil). The alkoxy precursors used for the preparation of new ormosil-based electrocatalytic biosensor are palladium-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. The optimum concentrations of these precursors are added in aqueous solution of ferrocene monocarboxylic acid and HCl followed by gelation for 30 h at 25°C to form ormosil. The ferrocene encapsulated ormosil is characterized based on cyclic voltammetric measurements. The CV results shows peak separation of 57-59 mV and a linear relation between peak current and square root of scan rate suggesting well behaved reversible electrochemistry of ormosil encapsulated ferrocene. The CV results and the detection of ferrocene in working medium shows that ferrocene is not leached out of ormosil matrix. The tyrosinase is immobilized within polyvinyl alcohol over the ferrocene encapsulated new ormosil and finally mounted using nucleopore membrane. The electrocatalytic response of immobilized tyrosinase over new ormosil is observed and the results are reported. The performance, stability, and reproducibility of new ormosil-based dopamine biosensor are reported. © 2001 Elsevier Science B.V.
A novel ormosil based electrocatalytic biosensor for glucose/ethanol based on dehydrogenase modified electrode
(Wiley-VCH Verlag, 2001) P.C. Pandey; S. Upadhyay; Ida Tiwari; V.S. Tripathi
A novel ormosil material for designing electrocatalytic biosensors for glucose and ethanol based on dehydrogenase catalyzed reactions is reported. The electrode material is prepared using palladium-linked glycidoxypropyltrimethoxysilane, ferrocene monocarboxylic acid, trimethoxysilane and HCl. The ormosil prepared from these ingredients shows reversible electrochemistry of ormosil encapsulated ferrocene. The electrocatalytic oxidation of NADPH/NADH and subsequently novel dehydrogenase based biosensors for glucose and ethanol are developed. The results based on cyclic voltammetry and amperometry are reported. The enzyme sensors are developed based on the modification of electrode material by dehydrogenase enzymes. The modification of electrode material is made by two approaches of enzyme immobilization: immobilization of dehydrogenase within polyvinyl alcohol and sandwiching the dehydrogenase within two layers of ormosils among which the first layer being the electrode material itself and the second layer of ormosil prepared without palladium linkage precursor and ferrocene. The biosensor made by the second approach shows high stability and much better reproducibility of enzyme electrode performance. The results on glucose and alcohol sensing based on electrochemical measurements are reported.
An amperometric sensor for nanomolar detection of hydrogen peroxide based on encapsulation of horseradish peroxidase in thymol blue-ormosil composite
(2011) Ida Tiwari; Manorama Singh; V.S. Tripathi; G. Lakshminarayana; Masayuki Nogami
An amperometric biosensor based on horseradish peroxidase and thymol blue-organically modified sol-gel glass composite has been fabricated for the determination of H 2O 2. We are for the first time reporting electrochemistry of thymol blue encapsulated within organically modified sol-gel glass. The biosensor has been characterized by electrochemical and amperometric measurements. The biosensor shows fast response with minimum interference. Under the optimized experimental conditions, H 2O 2 could be determined in a linear calibration range from 1.0×10 -8 M to 1.2×10 -3 M with a correlation coefficient of 0.998, sensitivity of 23.74 μA/mM and a detection limit of 1 nM at S/N ratio = 3. Copyright © 2011 American Scientific Publishers All rights reserved.
An organically modified silicate-based ethanol biosensor
(Academic Press Inc., 2001) P.C. Pandey; S. Upadhyay; Ida Tiwari; V.S. Tripathi
A novel electrocatalytic ethanol biosensor using ferrocene-encapsulated palladium (Pd)-linked organically modified sol-gel glass (ormosil) is reported. The alkoxy precursors used to prepare the new ormosil-based electrocatalytic biosensor are Pd-linked glycidoxypropyltrimethoxysilane and trimethoxysilane. Pd-glycidoxypropyltrimethoxysilane (black solution) is made by mixing aqueous solutions of palladium chloride and glycidoxypropyltrimethoxysilane. The new ormosil is made using a Pd-linked silane precursor, trimethoxysilane, an aqueous solution of ferrocene monocarboxylic acid, and HCl. Alcohol dehydrogenase (ADH) is assembled over the ferrocene-ormosil layer using polyvinyl alcohol and then protecting the immobilized enzyme layer using Millipore filter membranes (pore size 1 μm). The electrocatalytic response of immobilized ADH, soluble nicotinamide adenine dinucleotide, and Pd-linked ormosil-encapsulated ferrocene is then observed. The electrocatalytic oxidation of NADH and the subsequent ADH-catalyzed formation of NADH are monitored electrochemically. Typical results recorded after the addition of varying concentrations of ethanol are reported; however, the sensor is sensitive to other alcohol and known ADHsensitive substrates. The stability and reproducibility of the new ethanol biosensor are reported. © 2001 Academic Press.
Ormosil-based peroxide biosensor - a comparative study on direct electron transport from horseradish peroxidase
(Elsevier Sequoia SA, 2001) P.C. Pandey; S. Upadhyay; Ida Tiwari; V.S. Tripathi
An ormosil-based peroxide biosensor, based on direct electron transfer from horseradish peroxidase (HRP) encapsulated within ormosil in the presence of peroxide is reported. The HRP is immobilized within two different matrixes: (1) graphite paste electrode and (2) a new organically modified sol-gel glass (ormosil) electrode. The direct electron transfer from these two matrixes has been studied based on cyclic voltammetry and amperometric measurement. In both cases, direct electron transfer takes place between 0.1 and -0.2 V versus Ag/AgCl, however, the direct bioelectrochemical response of HRP is influenced by direct reduction of peroxide even in the absence of HRP at -0.2 V versus Ag/AgCl, whereas, direct bioelectrochemical response of biosensor at 0.05 V versus Ag/AgCl is only the function of enzymatic reaction. The mass transfer kinetics within these two matrixes have been analyzed using the data on cyclic voltammograms of soluble ferrocene at the surface of paste and ormosil modified electrodes. The data on peak current versus square root of scan rate shows linear relation and passes through origin while using HRP modified paste electrode, whereas, the same has positive intercept while using ormosil modified peroxide biosensor suggesting well-behaved diffusion limited conditions within paste matrix and poor diffusion kinetics of mass-transport within ormosil matrix. The ormosil-based peroxide biosensor is developed using a bilayer of ormosil within which HRP is sandwiched between two layers. The new ormosil matrix with and without encapsulated HRP is analyzed by scanning electron microscopy (SEM). The HRP encapsulated ormosil electrode shows greater than 90% reproducible response for more than 3 months when stored in dry condition at 4 °C. The typical calibration curves on the subsequent additions of peroxide of ormosil-based biosensor at 0.05 V versus Ag/AgCl and at -0.2 V versus Ag/AgCl are reported. The various parameters such as inhibition of peroxidase at higher peroxide concentrations, direct reduction of peroxide near -0.2 V versus Ag/AgCl, the kinetics of electron transfer due to direct oxidation of peroxide at 0.7 V versus Ag/AgCl on bare glassy carbon electrode, and direct electron transfer from enzymatically oxidized peroxidase are discussed.
Studies on glucose biosensors based on nonmediated and mediated electrochemical oxidation of reduced glucose oxidase encapsulated within organically modified sol-gel glasses
(Wiley-VCH Verlag, 1999) P.C. Pandey; S. Upadhyay; H.C. Pathak; Ida Tiwari; V.S. Tripathi
A new, organically modified sol-gel glass electrode is reported using 3-aminopropyltriethoxy silane and 2-(3,4-epoxycyclohexyl)-ethyltrimethoxy silane as sol-gel precursors for the construction of electrochemical biosensors. Four different systems of new sol-gel glass modified glucose electrodes are made in acidic medium having common sol-gel precursors and: 1) glucose oxidase, 2) glucose oxidase along with polyethylene glycol, 3) glucose oxidase and graphite powder, and 4) glucose oxidase along with polyethylene glycol and graphite powder. Both nonmediated and mediated electrochemical regeneration of immobilized glucose oxidase within sol-gel glasses are studied in these four systems. The nonmediated regeneration is achieved in the presence of oxygen as electron donor whereas mediated regeneration involves soluble ferrocene monocarboxylic acid as electron donor in each system. The electrochemical performance of sol-gel glass based biosensors is compared on the basis of cyclic voltammetry and amperometry. This leads to the observations: i) all four systems reach a diffusion limited condition associated with the transport of soluble ferrocene monocarboxylic acid as well as for dissolved oxygen within the sol-gel matrix, ii) the relative rate of diffusion of these analytes increases from system 1 to system 4, iii) both nonmediated and mediated amperometric responses at suitable potentials are based on the oxidation of H2O2 and enzymatically reduced soluble ferrocene with relatively amplified electrochemical signal of system 4. Data on the reduction of oxygen at conventional graphite disk electrode and at typical sol-gel glass modified electrode are reported.
Studies on new ormosils derived from reactive alkoxysilane precursors as a function of hydrophobicity/hydrophilicity
(2005) P.C. Pandey; S. Upadhyay; B.C. Upadhyay; V.S. Tripathi
We report here on the development of nine different ormosil systems derived from the reaction of two reactive ormosil precursors (3-glycidoxypropyltrimethoxysilane and 2-(34-epoxycyclohexyl)ethyltrimethoxysilane) with 3-aminopropyltrimethoxysilane phenyltrimethoxysilane and/or trimethoxysilane to control hydrophobicity and hydrophilicity in the resulting gels. The immobilization of redox relays such as potassium ferricyanide and ferrocene monocarboxylic acid/potassium ferricyanide mixtures in selected ormosils was demonstrated. The physical and electrochemical properties of the resulting gels were investigated using UV-vis spectroscopy transmission electron microscopy and cyclic voltammetry and the effect of sol-gel precursor chemistry on these properties will be discussed. © 2005 Springer Science + Business Media Inc.
Studies on polycarbazole-modified electrode and its applications in the development of solid-state potassium and copper(II) ion sensors
(John Wiley & Sons Inc, 2000) P.C. Pandey; R. Prakash; G. Singh; I. Tiwari; V.S. Tripathi
The electrochemical synthesis of polycarbazole, having better stability and electrochromic activity, in dichloromethane containing 0.1 M tetrabutyl ammonium perchlorate (TBAP), is studied. The polycarbazole matrix obtained by the potentiostatic and potentiodynamic modes of electropolymerization is characterized based on scanning electron microscopy, differential calorimetry, and infrared spectroscopy. De-doping of the polymer by electrochemical reduction in TBAP-free dichloromethane followed by incubation of the polymer film in 1 M aqueous KCl solution for 24 h is studied.