Browsing by Author "Rajiv Prakash"

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A chitosan-based polyaniline-Au nanocomposite biosensor for determination of cholesterol
(2014) Monika Srivastava; S.K. Srivastava; N.R. Nirala; Rajiv Prakash
A polyaniline-gold (PAni-Au) nanocomposite is chemically synthesized and impregnated in a chitosan matrix for immobilization of cholesterol oxidase on an indium tin oxide-coated glass plate for development of cholesterol biosensors. The PAni-Au nanocomposite is characterized for structural and thermal properties. Further the PAni-Au nanocomposite is used for cholesterol oxidase immobilization and linkage is examined by FTIR. The nanocomposite is used to form a modified bioelectrode by immobilizing cholesterol oxidase in the chitosan matrix and examined under an optical microscope for uniformity and morphological studies. A modified bioelectrode (ChOx/PAni-Au-CH/ITO) is used to detect cholesterol by using a voltammetric technique with a redox mediator. The sensor exhibits linearity in a wide range of 50-500 mg dL-1 with a detection limit of 37.89 mg dL-1, a sensitivity of 0.86 μA mg dL-1 and a shelf life of more than 3 weeks when stored at 4 °C. Voltammetric studies have also been carried out with common possible interferents. Responses are recorded to get enzyme-substrate kinetics for the biosensor and found as Km = 10.84 mg dL-1. The low value of Km indicates that the prepared nanocomposite facilitates the enzymatic reaction and enzymatic activity. Excellent immobilization and enzyme-substrate reactions show a distinct advantage of this matrix over other matrixes used for cholesterol biosensors. The novelty of the prepared electrode lies in its reusability, higher sensitivity, better shelf life, and accuracy. © 2014 The Royal Society of Chemistry.
A comparative Study of Aptasensor Vs Immunosensor for Label-Free PSA Cancer Detection on GQDs-AuNRs Modified Screen-Printed Electrodes
(Nature Publishing Group, 2018) Monika Srivastava; Narsingh R. Nirala; S.K. Srivastava; Rajiv Prakash
Label-free and sensitive detection of PSA (Prostate Specific Antigen) is still a big challenge in the arena of prostate cancer diagnosis in males. We present a comparative study for label-free PSA aptasensor and PSA immunosensor for the PSA-specific monoclonal antibody, based on graphene quantum dots-gold nanorods (GQDs-AuNRs) modified screen-printed electrodes. GQDs-AuNRs composite has been synthesized and used as an electro-active material, which shows fast electron transfer and catalytic property. Aptamer or anti-PSA has immobilized onto the surface of modified screen printed electrodes. Three techniques are used simultaneously, viz. cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedence spectroscopy (EIS) to investigate the analytical performance of both PSA aptasensor and PSA immunosensor with its corresponding PSA antigen. Under optimum conditions, both sensors show comparable results with an almost same limit of detection (LOD) of 0.14 ng mL-1. The results developed with aptasensor and anti-PSA is also checked through the detection of PSA in real samples with acceptable results. Our study suggests some advantages of aptasensor in terms of better stability, simplicity and cost effectiveness. Further our present work shows enormous potential of our developed sensors for real application using voltammetric and EIS techniques simultaneous to get reliable detection of the disease. © 2018 The Author(s).
A comparative study of polyanthranilic acid (pANA)/metal and polycarbazole (Pcz)/metal contacts for electronic and optoelectronic applications
(2008) A.D.D. Dwivedi; Arun Kumar Singh; Rajiv Prakash; P. Chakrabarti
We report fabrication and characterization of an organic photodetector (OPD) in the form of ITO coated glass / Polycarbazole (PCz) /Al Schottky contact for application in visible region and Al/PANA/ITO, Ti/PANA/ITO Schottky contacts of application in U. v: region. The current voltage (I-V) characteristics of the devices were measured by using microprobe arrangement. The performance parameters of ITO / Polycarbazole (PCz)/Al Schottky contact have been compared and contrasted with those of ITO/PANA/Al and ITO/PANA/Ti Schottky contacts. UV-Vis spectroscopic measurement revealed strong absorption spectra of the two types of devices in the visible and U.V. region respectively.
A fluorescent Ce-EDTA probe for the sensing of ascorbic acid and lysine in real samples
(Royal Society of Chemistry, 2022) None Rajpal; Ashish Kumar; Subhajit Jana; Priya Singh; Rajiv Prakash
In the present work, a fluorescent probe based on an aqueous dispersion of coordination complex Ce-EDTA is utilized for sensing carboxyl compounds. Ce-EDTA is synthesized herein by a hydrothermal method with the help of stoichiometric ratios of cerium (Ce) (+iii) salts and green ligand ethylenediamine N,N,N,N tetra-acetic acid (EDTA). In Ce-EDTA, the Ce ion is surrounded by hexadentate EDTA and three labile aqua ligands, evidenced by FT-IR, XPS, and UV-visible spectroscopy. It exists in the form of polygonal microplates, as apparent by SEM. The sensing mechanism is proposed by choosing carboxyl groups as a part of the ring and open chain. Under the optimized situations, the fluorescence intensities of Ce-EDTA are monitored towards various concentrations of l-lysine (Lys) and ascorbic acid (AA) in these regards. They exhibit a linear response from 20.29 μM to 251.74 μM and 5.62 μM to 60.87 μM with a linear correlation coefficient (R2) of 0.98 and 0.99, respectively. The lower limit of detection is observed as 3.6 μM in the case of Lys and 2.04 μM in the case of AA. The as-prepared probe exhibits suitability for selectivity of AA and Lys in the presence of various interfering agents as well as in real samples for the detection of AA in orange and Lys in soybean seed. © 2022 RSC.
A graphene oxide assisted surface plasmon resonance sensor for chloroquine phosphate detection: A theoretical and experimental study
(Elsevier Ltd, 2025) Anil V.S. kumar; Awadhesh Kumar; Monika Srivastava; Rajiv Prakash; Sanjay Kumar Srivastava
The present work deals with a surface plasmon resonance (SPR) sensor that gives real-time and label-free detection of chloroquine phosphate (CQ) with graphene oxide (GO) in water as well as real samples. In this work, theoretical and experimental analysis are performed for present SPR biosensor for the detection of CQ. Furthermore, a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) is utilized for the attachment of GO over the gold layer, which works as a good probe for the detection of CQ. The present biosensor detects micromolar concentrations of CQ in water and real samples (blood serum) with a limit of detection (LOD) value of 0.21 μM and 0.34 μM, respectively. Furthermore, other biomolecules like urea, L-cysteine, D-glucose and glycine are also tested and it shows maximum sensitivity towards CQ. © 2025 Elsevier Ltd
A sensitive SPR biosensor for glucose detection using MoS2 quantum dots
(Elsevier Inc., 2025) Awadhesh Kumar; A. Sameer Ruban Kumar; Pinky Sagar; Monika Srivastava; Amritanshu Pandey; Rajiv Prakash; Sanjay Kumar Srivastava
Diabetes patients require continuous blood glucose monitoring throughout the year. In this study, we present a highly sensitive surface plasmon resonance (SPR) biosensor for glucose detection, utilizing molybdenum disulfide quantum dots (MoS2 QDs). The proposed biosensor is based on the Kretschmann configuration, consisting of sequentially deposited layers of chromium (Cr), gold (Au), L-cysteine (Cys), and MoS2 QDs on a BK-7 glass substrate through a coating technique. A self-assembled monolayer (SAMs) of Cys is employed to covalently bond the amine groups to the Au surface, ensuring strong adhesion. The sensor demonstrates a linear detection range of 0.5–10 mM for glucose, with a limit of detection (LOD) of 0.31 mM. The experimental results align well with theoretical predictions calculated using the transfer matrix method, indicating strong agreement between the two. Additionally, the biosensor exhibits excellent selectivity in the presence of other biomolecules, specifically showing a high affinity for glucose. The proposed SPR biosensor is highly promising for blood D-glucose detection in diabetic patients due to its miniaturization, high sensitivity, and stability. This work highlights its potential for application in real-time glucose monitoring devices. © 2025 Elsevier B.V.
A smartphone-enabled colorimetric sensor based on Au-CuO nanozyme for visual and quantitative detection of antihypertensive drug hydralazine
(Elsevier Ltd, 2023) Ravi Prakash Ojha; S.K. Srivastava; Monika Srivastava; Rajiv Prakash
In the present study, we have unfolded a smartphone-assisted colorimetric approach for the visual detection of the antihypertensive drug, Hydralazine (Hyz) in the buffer and pharmaceutical samples. The method stands on the oxidase mimetic property of gold-decorated copper oxide (Au-CuO), which is synthesized using a facile one-step chemical reduction process. The synthesis of Au-CuO was successfully concluded using several characterization techniques. Au-CuO showed amplified oxidase mimicking behavior towards 3,3′,5,5′-tetramethylbenzidine (TMB) which was used as a colorimetric substrate in the subsistence of oxygen dissolved in the reaction medium. Employing the competitive inhibition property of Hyz to TMB, a colorimetric method has been designed for the quantification of Hyz. The method manifested good accuracy and reproducibility in 1 μM–75 μM concentration range with a significant detection limit of 600 nM. Further, the technique was extended for smartphone-based digital image colorimetry (DIC) sensing of Hyz by capturing images of developed color corresponding to different Hyz concentrations with as developed RGB software and their analysis. The work opens a simple approach to medical diagnosis for the visual detection of high blood pressure patients in remote areas. © 2023 Elsevier B.V.
A strategy to achieve efficient dual-mode luminescence in lanthanide-based magnetic hybrid nanostructure and its demonstration for the detection of latent fingerprints
(Academic Press Inc., 2017) Praveen K. Shahi; Priyam Singh; Akhilesh K. Singh; Sunil K. Singh; Shyam B. Rai; Rajiv Prakash
We have synthesized a novel inorganic-organic hybrid nanostructure (IOHN) composed of fluoride nanophosphor (NaGd0.78Er0.02Yb0.2F4) and β-diketones complex (Eu(DBM)3Phen). The Le Bail fitting of X-ray diffraction data suggests that the nanophoshor crystallizes in a hexagonal structure (P63/m space group). The TEM studies reveal that the nanophosphor and the IOHN both have average particle size of 6–8 nm. The Eu(DBM)3Phen and NaGd0.78Er0.02Yb0.2F4 show characteristic down-shifting (DS) and up-conversion (UC) emission, under UV and NIR excitation, respectively. The IOHN comprises an excellent dual-mode optical features (DS and UC) of both the phases. Energy transfer from Er3+ (doped in inorganic phase) to Eu3+ (coordinated in organic phase) clearly demonstrates for a viable coupling between both the phases. IOHN material was found to be unique for the visualization of latent fingermarks. Because of ultrafine particle size the surface to volume ratio is relatively higher which improves the attachment of particles with the fingermarks. On the other hand, the strong paramagnetic property helps to remove excess material with magnetic wand easily. These properties provide an opportunity to probe even very weak fingermarks. Notwithstanding this, the dual-mode emission is useful for the visualization of latent fingermarks on multi-color surfaces as well. © 2016 Elsevier Inc.
Air-Stable Highly Sensitive Self-Assembled P3HT/GQD Nanocomposite-Based Organic Thin-Film Transistor for Multiparametric H2S Real-Time Detection at Room Temperature
(Institute of Electrical and Electronics Engineers Inc., 2023) Ankit Verma; V.N. Mishra; Rajiv Prakash
This article demonstrates the highly selective and responsive room temperature (RT = 25 °C) operated hydrogen sulfide (text{H}_{{2}}text{S} ) gas sensor based on poly(3-hexylthiophene-2,5-diyl) (P3HT)/graphene quantum dot (GQD) nanocomposite as a sensing surface. The GQD has an average size of 2 nm that is randomly distributed over the P3HT film and enhances the charge transfer mechanism and the surface area/volume ({S}/{V} ) ratio of the sensing surface, which incorporates quick and highly responsive text{H}_{{2}}text{S} sensing. The sensing film has been developed on a SiO2-coated text{p}{++} Si substrate by solution-processed floating-film transfer (FTM) method, and the multiparameters of the fabricated sensor have been investigated with varying text{H}_{{2}}text{S} gas concentrations in the range of 0-25 ppm. To investigate the effect of the GQD in the polymer matrix, the sensing performance of the pristine P3HT-based organic thin-film transistor (OTFT) has been compared to P3HT/GQD nanocomposite-based OTFT. The P3HT/GQD-based OTFT has better sensing responses of 91% at 25 ppm over pristine P3HT-based OTFT 30% at 25 ppm. The enhanced sensing performance of the nanocomposite matrix (P3HT/GQD) is attributed to an improved charge carrier transfer mechanism due to GQD over the pristine P3HT-based OTFT. © 2001-2012 IEEE.
An anthraquinone moiety/cysteamine functionalized-gold nanoparticle/chitosan based nanostructured composite for the electroanalytical detection of dissolved oxygen within aqueous media
(Royal Society of Chemistry, 2014) Ida Tiwari; Mandakini Gupta; Rajiv Prakash; Craig E. Banks
This work reports a nanostructured composite electrode comprising gold nanoparticles, anthraquinone derivatives and chitosan electrically wired via immobilisation upon a glassy carbon macroelectrode. The as-prepared nanostructured composite was morphologically characterised using transmission electron microscopy with surface characterization performed with atomic force microscopy while other physical characterization was undertaken by infra-red, UV-Vis, and energy dispersive X-ray spectroscopy. Electrochemical investigations and stability measurements of the composite electrode were performed by cyclic voltammetry. Electrocatalytic activity of the composite electrode was investigated for the oxygen reduction reaction in 0.1 M phosphate buffer solution of pH 6.5. Furthermore, the response characteristics show that this fabricated electrode has a shelf-life of between 3 and 4 months and has improved electrochemical and electrical properties and firm adhesion of the material with homogeneous dispersion at the electrode surface. The linear range and detection limit for the electrochemical detection of dissolved oxygen under the optimum conditions using the nanostructured composite was found to be over the accessible range of 0.2 to 5.8 mg L-1 and 0.03 mg L-1 respectively. This journal is © the Partner Organisations 2014.
An assembly and interaction of upconversion and plasmonic nanoparticles on organometallic nanofibers: Enhanced multicolor upconversion, downshifting emission and the plasmonic effect
(Institute of Physics Publishing, 2017) Priyam Singh; Praveen Kumar Shahi; Rajiv Prakash; Shyam Bahadur Rai
We present novel inorganic-organic hybrid nanoparticles (HNPs) constituting inorganic NPs, NaY0.78Er0.02Yb0.2F4, and organometallic nanofiber, Tb(ASA)3Phen (TAP). X-ray diffraction, Fourier transform infrared absorption and transmission electron microscopy analyses reveal that prepared ultrafine upconversion NPs (UCNPs (5-8 nm)) are dispersed on the surface of the TAP nanofibers. We observe that the addition of TAP in UCNPs effectively limits the surface quenching to boost the upconversion (UC) intensity and enables tuning of UC emission from the green to the red region by controlling the phonon frequency around the Er3+ ion. On the other hand, TAP is an excellent source of green emission under ultraviolet exposure. Therefore prepared HNPs not only give enhanced and tunable UC but also emit a strong green color in the downshifting (DS) process. To further enhance the dual-mode emission of HNPs, silver NPs (AgNPs) are introduced. The emission intensity of UC as well as DS emission is found to be strongly modulated in the presence of AgNPs. It is found that AgNPs enhance red UC emission. The possible mechanism involved in enhanced emission intensity and color output is investigated in detail. The important optical properties of these nano-hybrid materials provide a great opportunity in the fields of biological imaging, drug delivery and energy devices. © 2017 IOP Publishing Ltd.
Assessment of contamination of soil due to heavy metals around coal fired thermal power plants at Singrauli region of India
(2010) Prashant Agrawal; Anugya Mittal; Rajiv Prakash; Manoj Kumar; T.B. Singh; S.K. Tripathi
In the present study, an attempt was made to measure contamination of soil around four large coal-based Thermal Power Plants. The concentration of Cadmium, Lead, Arsenic and Nickel was estimated in all four directions from Thermal Power Plants. The soil in the study area was found to be contaminated to varying degrees from coal combustion byproducts. The soil drawn from various selected sites in each direction was largely contaminated by metals, predominantly higher within 2-4 km distance from Thermal Power Plant. Within 2-4 km, the mean maximum concentration of Cadmium, Lead, Arsenic and Nickel was 0.69, 13.69, 17.76, and 3.51 mg/kg, respectively. It was also observed that concentration was maximum in the prevalent wind direction. The concentration of Cadmium, Lead, Arsenic and Nickel was highest 0.69, 13.23, 17.29 and 3.56 mg/kg, respectively in west direction where wind was prevalent. © 2010 Springer Science+Business Media, LLC.
Biphasic electropolymerization of polyaniline-multiwalled carbon nanotube nanocomposite
(Nova Science Publishers, Inc., 2013) Monika Srivastava; Ashish Kumar; Bhavana Gupta; Sanjay K. Srivastava; Rajiv Prakash
Despite the tremendous research on conjugated polymers to date, polyaniline, PAni and its derivatives are the most interesting conjugated polymers due to their unique electrochemical properties, easy polymerization, low cost and wide range of application. In the recent years polymer composites formation with various nanofillers are explored to enhance the various properties of the polymers. Multi-walled carbon nanotube, MWNT is one of the well-known nanofillers for its excellent electrical, mechanical and thermal properties. Besides all properties, the processability, stability and solubility hinder its commercial utilization and fabrication of devices. To overcome these limitations, coating of PAni over MWNTs is one of the possible ways to obtain the high performance of the resulted nanocomposite towards device applications. Although various strategies have been developed to produce such nanocomposites (i.e. polymer supported by conducting templates) but still the homogeneity/uniformity of nanocomposite and stability are the major challenges. Though the electrochemical polymerization technique suffers from various limitations, it is still a good approach for the uniform and thin film formation. However, formation of composites is rather difficult as the fillers may not be electroactive and also may not form homogeneous suspension (or colloidal state) in the electrolytes in which monomers are dissolved. Therefore, the distribution of fillers in the polymer matrixes is difficult to control using conventional electrochemical methods. We proposed a biphasic electropolymerization method as an efficient approach for polymerization of monomers with nanofillers to get uniform and homogeneous polymercomposites. This technique not only provides a better selection of solvents for monomers and fillers but also better control of diffusion and kinetics. In this chapter, electrochemical techniques used for synthesis with the latest development in the electrochemical synthesis of PAni nanocomposite is described with our novel biphasic electropolymerization technique for multi-walled carbon nanotubepolyaniline (MWNT-PAni) nanocomposite. MWNT-PAni nanocomposite formation, based on the biphasic electropolymerization technique, provides a general method for the formation of uniform nanocomposites for other polymers and fillers. © 2013 by Nova Science Publishers, Inc. All rights reserved.
Contamination of drinking water due to coal-based thermal power plants in India
(Bellwether Publishing, Ltd., 2011) Prashant Agrawal; Anugya Mittal; Rajiv Prakash; Manoj Kumar; S.K. Tripathi
This study assessed the impact of an Anpara and Renusgar coal-based thermal power plants on drinking water sources. In this work, the concentration of trace metals such as Pb, Cd, Ni, and As in groundwater samples obtained from hand pumps located near these power plants were measured. The concentration levels of all the studied heavy metals in groundwater were found to be higher than the maximum acceptable limits of World Health Organization for drinking water. © Taylor & Francis Group, LLC.
Copper(II) ion sensor based on electropolymerized undoped conducting polymers
(2002) Rajiv Prakash; R.C. Srivastava; P.C. Pandey
A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu2+ ions with a detection limit of 10-5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying -0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu2+ ions with little selectivity for Pb2+ and negligible response towards Ag+, Hg2+, Cu+, Ni2+, Co2+, Fe2+, Fe3+ or Zn2+. Potentiometric responses for Cu2+ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu2+ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks.
Cu-Fe Prussian blue analog nanocube with intrinsic oxidase mimetic behaviour for the non-invasive colorimetric detection of Isoniazid in human urine
(Elsevier Inc., 2021) Ravi Prakash Ojha; Shweta Pal; Rajiv Prakash
Isoniazid (INH) is a crucial antibiotic widely applicable in the chemotherapy of Tuberculosis. Any discrepancy of INH in the blood may be life-threatening and causes neurotoxicity and other health issues. In this work, we present a colorimetric technique for the easy quantification of the INH in human urine. We have synthesized Cu-Fe Prussian blue analogue nanocube (CuFe-PBA-NC) using a simple precipitation method. The synthesized nanocube has been successfully characterized by Fourier transfer infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The synthesized CuFe-PBA-NC act as an excellent oxidase mimic, having a very high affinity for TMB (3,3′,5,5′-tetramethylbenzidine) furnishing a blue color compound with a characteristic absorbance peak at λmax = 652 nm. Further, we have exploited the oxidase property of CuFe-PBA-NC for the colorimetric detection of the INH in human urine. The developed sensor shows very high sensitivity in the range of 1 to 100 μM with a detection limit of 0.44 μM. Furthermore, a portable kit was developed for the onsite detection of the INH concentrations in the test samples. The method is easy and cost-effective with sensitive detection of INH. © 2021
Development of inorganic-organic hybrid nanostructured material for H2O2 sensing application
(Institute of Physics Publishing, 2020) Arvind Kumar; Praveen Kumar Shahi; Amresh Bahadur; Sunil Kumar Singh; Rajiv Prakash; Ram Anjore Yadav; Shyam Bahadur Rai
An organic-inorganic hybrid nanoparticle (HNPs) composed of Sm(TTA)3Phen, a coordination compound, and NaY0.78Er0.02Yb0.20F4, an upconversion nanoparticles (UCNPs), has been developed and used for H2O2 sensing application. Herein, Sm(TTA)3Phen absorbs ultraviolet (UV) light and gives fluorescence in yellow-red-near infrared (NIR) region. Whereas, the UCNPs absorb NIR radiations (980 nm) and consequently emit in green-red region through photon upconversion process. Two important optical phenomena are observed when HNPs are simultaneously excited with UV (266 nm) and NIR (980 nm) laser radiation- (i) an energy transfer from Sm3+ to Er3+ ions, and (ii) color tunable emission from red to green, if the power of 980 nm laser is varied. Further, the material is highly competent to sense H2O2 through fluorescence quenching of Sm3+ emission in presence of H2O2. The nature of quenching is conspicuously different for different concentration/volume range of H2O2. For lower volume range, the rate of decrease of emission/excitation intensity is linear, while for higher volume range the decay in intensity is exponential. The attained minimum detection limit for H2O2 is 2 μl, which is significant for sensing applications. © 2020 The Author(s). Published by IOP Publishing Ltd.
Donor-π-Acceptor-Type Configured, Dimethylamino-Based Organic Push-Pull Chromophores for Effective Reduction of Mild Steel Corrosion Loss in 1 M HCl
(American Chemical Society, 2018) Madhu Tiwari; Vinod Kumar Gupta; Ram Adhar Singh; Gopal Ji; Rajiv Prakash
In this work, donor-π-acceptor-type four crystalline compounds have been tested for the first time to restrict the corrosion of mild steel in 1 M HCl. The details of the compounds are: C1, 4-N,N-dimethylamino-β-nitrostyrene; C2, 2-(4-(dimethylamino) benzylidene)malononitrile; C3, ethyl 2-cyano-3-(4-(dimethylamino) phenyl)acrylate; and C4, methyl 2-cyano-3-(4-(dimethylamino)phenyl)acrylate. The corrosion inhibition potentials of the compounds have been primarily investigated by electrochemical techniques, such as linear polarization resistance, Tafel polarization curves, and electrochemical impedance spectroscopy. The secondary investigation is performed by scanning electron microscopy, fluorescence surface imaging, spectroscopic techniques (UV-visible and Fourier transform infrared spectroscopy), and X-ray diffraction patterns. The results disclosed that 50 mg L-1 of the compounds (1-4) in 1 M HCl provided the maximum inhibition efficiency as 93% (1), 88% (2), 82% (3), and 86% (4). The function of the compounds as corrosion inhibitors is explained with equilibrium corrosion potential, adsorption isotherms, and the frontier molecular orbital energies of the compounds (EHOMO and ELUMO) estimated by cyclic voltammetry curves and UV-visible spectra. © 2018 American Chemical Society.
Effect of organic solvents on peroxidases from rice and horseradish: Prospects for enzyme based applications
(Elsevier B.V., 2012) Priyanka Singh; Rajiv Prakash; Kavita Shah
A feasibility test for rice peroxidase (RP) enzyme as a substitute for horseradish peroxidase (HRP) was carried out. The activity of HRP was maximum at 30 °C with pH 6.0-7.0. The purified rice peroxidase showed optimum activity at 30 °C with pH 7-8 and was thermostable till 68 °C, which is higher than the temperature reported for HRP. RP obeyed Michaelis-Menten kinetics. With increasing substrate concentrations, RP and HRP had Vmax as 8.23 μM min-1 and 4.21 μM min-1 and Km as 5.585 and 3.662 mM, respectively. In 10% 1,4-dioxane and ethanol, RP exhibited 2 and 1.3 times higher activity, respectively than HRP. Shelf life studies show RP to be significantly stable till 60 h in 20% 1,4-dioxane and till 12 h in ethanol. The activity of RP/HRP increased gradually with 0%-40% ethanol or 0%-30% 1,4-dioxane till 20 h with a sharp decline thereafter. The stability of HRP and RP reduced with increasing storage period. Enzyme efficiencies compared as Vm/Km showed water miscible organic solvents, viz.1,4-dioxane and ethanol, to exhibit a regular decrease in V m/Km with increase in organic solvent concentration whereas, a reverse trend was observed with water-immiscible solvent like chloroform. The relative activity of RP and HRP enzymes upon immobilization on poly-5-carboxy-indole shows increasing enzyme activity with time and with guaiacol/dopamine hydrochloride as substrates. Immobilized RP had a better relative activity with dopamine as substrate than immobilized HRP, whereas with guaiacol both RP and HRP had a comparable activity upon immobilization. Results suggest rice peroxidase to be a cheaper and convenient enzyme system for immobilization using organic solvents. The high thermal stability, more stability in organic solvents and longer shelf life of RP over the immobilizing matrix suggest conducting polyindole having carboxyl functional groups to be a suitable matrix for the covalent entrapment of rice peroxidase through amide linkage. Good sensitivity and fast response to dopamine makes RP a suitable enzyme system for monitoring dopamine levels in aqueous medium. © 2012 Elsevier B.V. All rights reserved.
Effect of post annealing on structural properties of ZnO thin films deposited by thermal evaporation technique
(2008) C. Periasamy; P. Chakrabarti; Rajiv Prakash
The thermal evaporation deposition technique was used to produce zinc oxide thin film onto p-type silicon substrate at room temperature. The prepared film was post annealed at different temperature from 400 to 800°C in O 2 ambient atmosphere for 20 minutes. The effect of post annealing temperature on the structural properties and surface morphological of ZnO thin films have been studied by XRD and AFM respectively. XRD analysis reveals that the prepared films were polycrystalline in nature with c-axis orientation. The optical band gap and resistivity of ZnO thin film were estimated using UV-Visible and four probe measurements respectively.