Browsing by Author "Onkar Nath Srivastava"

Now showing 1 - 20 of 46

Amine functionalized graphene sheet conjugated with amphotericin B for the treatment of visceral leishmaniasis
(Advanced Engineering Solutions, 2014) Mahe Talat; Shyam M. Lal; Madhukar Rai; Shyam Sundar; Onkar Nath Srivastava
The treatment options for visceral leishmaniasis (VL), potentially caused by Leishmania donovani, are limited and unsatisfactory. Conventional AmB exhibits low solubility and instability at gastric pH and is unable to penetrate the brush border membrane of the small intestine and have have serious toxicity. Different nano vectors have been explored for the transportation of these drugs to the target. We evaluated a novel formulation of Amphotericin B (AmB) conjugated to amine-functionalized graphene (f-Gr) for safety and efficacy over conventional AmB. Graphene sheet have been synthesized by thermal exfoliation of chemically prepared graphite oxide by rapid heating at 1050°C in an Ar atmosphere. As synthesized graphene sheet was amine functionalized non-covalently with L-cysteine at room temperature. As functionalized graphene sheet was further used to conjugate AmB. The conjugate (f-Gr-AmB) was characterized by FTIR, SEM and TEM that established successful attachment of AmB to f-Gr. The f-Gr-AmB was found to exhibit lesser cytotoxity as compared to AmB also it showed significantly enhanced efficacy of f-Gr-AmB over AmB. However the results of in vivo and in vitro studies are not described here. © 2014, Advanced Engineering Solutions (AES.COM) Ottawa, Canada.
An oral formulation of amphotericin B attached to functionalized carbon nanotubes is an effective treatment for experimental visceral leishmaniasis
(2012) Vijay Kumar Prajapati; Kalpna Awasthi; Thakur Prasad Yadav; Madhukar Rai; Onkar Nath Srivastava; Shyam Sundar
Amphotericin B (AmB), is a highly effective antileishmanial agent used as first-line treatment in different formulations in visceral leishmaniasis endemic areas of Bihar, India. However, parenteral infusion, prolonged hospitalization, and toxicity are major hurdles. Our previous work demonstrated the efficacy and stability of functionalized carbon nanotubes as a delivery mechanism for AmB. In this study, using the hamster model, we have shown that this novel formulation of AmB can be administered orally, resulting in 99% inhibition of parasite growth following a 5-day course at 15 mg/kg body weight. © 2011 The Author.
Antileishmanial activity of nano-amphotericin B deoxycholate
(2008) Krishna Das Manandhar; Thakur Prasad Yadav; Vijay Kumar Prajapati; Subodh Kumar; Madhukar Rai; Anuradha Dube; Onkar Nath Srivastava; Shyam Sundar
Objectives: The aim of the present study was to compare the efficacy of a nano form of amphotericin B deoxycholate with that of conventional amphotericin B deoxycholate for the treatment of visceral leishmaniasis. Methods We have formulated nanoparticles (10-20 μM) from amphotericin B deoxycholate (1-2 nM) by applying high-pressure (150 argon) milling homogenization and have tested their efficacy in a J774A cell line and in hamsters. Parasite survival and tissue burden in spleen were evaluated for nano-amphotericin B and conventional amphotericin B. Both nano-amphotericin B and conventional amphotericin B were injected intraperitoneally at 5 mg/kg per day for 5 days. Results: The inhibition of amastigotes in the splenic tissue with nano-amphotericin B was significantly more than with conventional amphotericin B (92.18% versus 74.57%, P = 0.005). Similarly, the suppression of parasite replication in the spleen was also found to be significant (99.18% versus 97.17%, P = 0.05). In a cytotoxicity test, nano-amphotericin B against the J774A cell line had a CC50 of 12.67 mg/L in comparison with 10.61 mg/L for amphotericin B, far higher than the doses used for ED50. Conclusions: Nanoparticles of amphotericin B had significantly greater efficacy than conventional amphotericin B. This formulation may have a favourable safety profile, and if production costs are low, it may prove to be a feasible alternative to conventional amphotericin B. © The Author 2008. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.
Applied potential dependent growth of SnO 2 nanostructures by anodic oxidation of tin
(2012) Dinesh Pratap Singh; Onkar Nath Srivastava
Nanothread, nanotetrapod and nanocube like structures of SnO 2 have been synthesized by anodic oxidation through a simple electrolysis process utilizing tin as a sacrificial electrode. The synthesized nanostructures were dependent to applied potential between the electrodes. The method is based on anodization pursuant to the simple electrolysis of plain water (with ionic conductivity 6-10 μS/m and pH ~ 6.5) at different voltages. The platinum and tin were utilized as cathode and anode respectively. The applied potential was varied 2 V, 4 V, 6 V and 8 V to see it's effect on the growth of nanostructures. The synthesized materials were delaminated in the electrolyte. TEM characterization of the material as synthesized and settled down at the bottom of the electrolytic cell after electrolysis revealed the nanothread like structures at 2 V, nanotetrapod like structures at 4 and 6 V and nanocube like structures at 8 V. A tentative explanation for the formation and growth of SnO 2nanostructures has also been given. © 2012 American Scientific Publishers. All rights reserved.
Characterization and evaluation of amine-modified graphene amphotericin B for the treatment of visceral leishmaniasis: In vivo and in vitro studies
(Dove Medical Press Ltd., 2014) Shyam Lal Mudavath; Mahe Talat; Madhukar Rai; Onkar Nath Srivastava; Shyam Sundar
Amphotericin B (AmB) has been the first-line treatment for visceral leishmaniasis (VL), a neglected protozoan disease, especially in regions like Bihar, India, where resistance to antimonials is widespread. However, adverse drug reactions are a major limiting factor. We evaluated a novel formulation of AmB conjugated to amine-modified graphene (f-Gr) for safety and efficacy over conventional AmB. The f-Gr was prepared in a gentle one-step process of noncovalent (amine) functionalization with the help of amino acid L-cysteine. This f-Gr was further conjugated to AmB by peptide bond. The conjugate (f-Gr-AmB) was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. f-Gr-AmB was found to exhibit lesser cytotoxicity toward J774A.1 cells than AmB, and did not induce any hepatic or renal toxicity in Swiss albino mice. In vitro antileishmanial assay in J774A.1 cells showed significantly enhanced efficacy of f-Gr-AmB over AmB. Furthermore, percentage inhibition of amastigote replication in a hamster model of VL was significantly higher in the f-Gr-AmB treated group (87.8%) compared to the AmB group (70.4%). These results suggest that f-Gr-AmB could be a safe and effective alternative to conventional AmB in the treatment of VL. © 2014 Mudavath et al.
Cicer a-galactosidase immobilization onto functionalized graphene nanosheets using response surface method and its applications
(Elsevier Ltd, 2014) Neelesh Singh; Garima Srivastava; Mahe Talat; Himanshu Raghubanshi; Onkar Nath Srivastava; Arvind M. Kayastha
Cicer a-galactosidase was immobilized onto functionalized graphene with immobilization efficiency of 84% using response surface methodology (Box-Behnken design). The immobilized enzyme had higher thermal stability than the soluble one, attractive for industrial applications. Immobilization of the enzyme lowered the Km to 1/3rd compared to the soluble enzyme. Raffinose family oligosaccharides (RFOs) are mainly responsible for flatulence by taking soybean derived food products. The immobilized enzyme can be used effectively for the hydrolysis of RFOs. After ten successive runs, the immobilized enzyme still retained approximately 60% activity, with soybean RFOs. The easy availability of enzyme source, ease of its immobilization on matrices, non-toxicity, increased stability of immobilized enzyme and effective hydrolysis of RFOs increase the Cicer a-galactosidase application in food processing industries. © 2013 Elsevier Ltd.
Curious structural characteristics from the carbon deposits on the graphitic electrodes subjected to arc evaporation
(Japan Society of Applied Physics, 1997) Radha Kamalakaran; Ajay Kumar Singh; Onkar Nath Srivastava
We report the transmission electron microscopic investigations made on the tips of the graphite electrodes used for production of C60-buckminsterfullerene. This was achieved by triggering an electrical arc (150 A, 20V, ac) in helium (100 Torr) atmosphere between the graphite electrodes and then scraping the tip of the electrode to prepare sample for electron microscopy. The scraped material was investigated in the CM-12 Philips transmission electron microscope both in diffraction and imaging modes. An abundance of tubules were found and the diffraction patterns from them exhibited sharp diffraction spots arranged along elliptical rings. On tilting the specimen the major axis of the ellipse varied in definite was depending on the relative orientations of electron beam, tubule axis and tilt axis. A detailed geometrical exemplification has been proposed which explains the observed features in the diffraction patterns. The occurrence of possibly a new form of carbon corresponding to primitive cubic with a = 2.14 Å and nucleation of diamond on ac electrical arc treated graphite electrode are also mentioned.
Development and Demonstration of Air Stable rGO-EC@AB5 Type Hydrogenated Intermetallic Hybrid for Hydrogen Fuelled Devices
(Wiley-VCH Verlag, 2017) Ashish Bhatnagar; Bipin Kumar Gupta; Prashant Tripathi; Ayfer Veziroglu; Michael Sterlin Leo Hudson; Mohammad Abu Shaz; Onkar Nath Srivastava
Hydrogen is a promising alternative energy vector, but its use at an appropriate site requires storage, which is a crucial aspect. Hydrogen storage (HS) in the form of metal hydrides represents an attractive possibility, and is being investigated worldwide. La(Ni0.95Fe0.05)5 (LNF) has achieved significant attention as a HS media due to its suitable thermodynamics. However, its use as an effective storage material is hindered due to burning of hydrogenated LNF (LNFH) on exposure to air. The pristine LNFH catches fire rapidly on exposure to atmosphere. Here, a breakthrough strategy is demonstrated for design of hydrogenated air-stabilized hybrid material by encapsulating LNF inside reduced graphene oxide-ethyl cellulose. This novel hybrid material does not ignite upon exposure to air. This proposed hybrid material could be the ultimate choice for air-stable and safe storage for fuel cell/internal combustion engine-based vehicles. Further, the effectiveness of this hydrogen storage material is demonstrated for fuel cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effective removal of fluoride from water by coconut husk activated carbon in fixed bed column: Experimental and breakthrough curves analysis
(Elsevier B.V., 2018) Mahe Talat; Sweta Mohan; Viney Dixit; Devendra Kumar Singh; Syed Hadi Hasan; Onkar Nath Srivastava
The bio-waste coconut husk was converted into activated carbon through merely treating with KOH and thus obtained activated carbon was characterized by XRD, TGA, SEM and TEM analysis. The prepared activated carbon having very high surface area (1448 m2/g) was utilized as an adsorbent for the removal of fluoride (F-) from water. Fluoride adsorption experiments were performed on the laboratory-scale column at different bed height, flow rates, and F- concentrations to explore the potential of prepared adsorbent and it was found to be very efficient adsorbent as it showed high adsorption capacity 6.5 mg/g at pH 5, F- concentration 10 mg/L and adsorbent dose 1.4 g/L. Various breakthrough models i.e. Bed Depth Service Time (BDST), Thomas and Yoon–Nelson were applied on breakthrough data to analyze the breakthrough curves. The high R2 values obtained for the BDST model revealed its validity for this adsorption system. Breakthrough curves were successfully analyzed and described by both Thomas and Yoon–Nelson models. The exhausted adsorbent was efficiently regenerated with the 10% NaOH solution and regenerated adsorbent showed remarkable uptake capacity with a slight reduction in adsorption performance up to the 3 cycles. Life factor calculation indicated that adsorbent bed would have sufficient bed capacity up to 8.3 cycles to avoid breakthrough at time t = 0 and the bed would be completely exhausted after 9.0 cycles. © 2018
Envisioning the innovations in nanomedicine to combat visceral leishmaniasis: For future theranostic application
(Future Medicine Ltd., 2019) Om Prakash Singh; Mallikarjuna Rao Gedda; Shyam Lal Mudavath; Onkar Nath Srivastava; Shyam Sundar
Visceral leishmaniasis (VL) is a life-threatening parasitic disease affecting impoverished people of the developing world; and much effort has been spent on the early case detection and treatment. However, current diagnostics and treatment options are not sufficient for appropriate surveillance in VL elimination setting. Hence, there is a dire need to develop highly sensitive diagnostics and less toxic effective treatments for proper management of cases and to achieve the sustained disease elimination. Although, promising results have been observed with nanomedicines in leishmaniasis; there are great challenges ahead especially in translating this to clinical setting. This review provides updated progress of nanomedicines in VL, and discussed how these innovations and future directions play vital role in achieving VL elimination. © 2019 Future Medicine Ltd.
Evaluation of Safety and Antileishmanial Efficacy of Amine Functionalized Carbon-Based Composite Nanoparticle Appended With Amphotericin B: An in vitro and Preclinical Study
(Frontiers Media S.A., 2020) Mallikarjuna Rao Gedda; Prasoon Madhukar; Alok Kumar Vishwakarma; Vimal Verma; Anurag Kumar Kushwaha; Ganesh Yadagiri; Shyam Lal Mudavath; Om Prakash Singh; Onkar Nath Srivastava; Shyam Sundar
Visceral leishmaniasis (VL) has been a major health concern in the developing world, primarily affecting impoverished people. It is caused by a protozoan parasite Leishmania donovani and is characterized by immune dysfunction that can lead to deadly secondary infections. Several adverse side effects limit the existing treatment options; hence, the need of the hour is some drug option with high efficacy and no toxicity. To make targeted delivery of Amphotericin B (AmB), we have used amine-functionalized versions of carbon nanostructures, namely f-CNT and f-Graphene (f-Grap). The results with f-Grap-AmB, because of a much larger surface area, were expected to be better. However, the results obtained by us showed only marginal improvement (IC50 f-Grap-AmB; 0.0038 ± 0.00119 μg/mL). This is, in all likelihood, due to the agglomeration effect of f-Grap-AmB, which is invariably obtained with graphene. To resolve this issue, we have synthesized a graphene-CNT composite (graphene 70% and CNT 30% by weight). Because CNT is dispersed in between graphene sheets, the agglomeration effect is avoided, and our study suggests that the f-Composite-AmB (f-Comp-AmB) showed no toxicity against the murine J774A.1 macrophage cell line and did not induce any hepatic or renal toxicity in Swiss albino mice. The f-Comp-AmB also showed a remarkable elevation in the in vitro and in vivo antileishmanial efficacy in comparison to AmB and f-CNT-AmB or f-Grap-AmB in J774A.1 and Golden Syrian hamsters, respectively. Additionally, we have also observed that the percentage suppression of parasite replication in the spleen of the hamster was significantly higher in the f-Comp-AmB (97.79 ± 0.2375) treated group in comparison with the AmB (85.66 ± 1.164) treated group of hamsters. To conclude, f-Comp-AmB could be a safe and reliable therapeutic option over the other carbon-based nanoparticles (NPs), i.e., f-CNT-AmB, f-Grap-AmB, and conventional AmB. © Copyright © 2020 Gedda, Madhukar, Vishwakarma, Verma, Kushwaha, Yadagiri, Mudavath, Singh, Srivastava and Sundar.
Evolution and structural transition of quasicrystalline phases in Al-Fe-Cu-Cr and Al-Fe-Cu-Mn alloys during high energy ball milling
(Institute of Physics Publishing, 2010) Thakur Prasad Yadav; Nilay Krishna Mukhopadhyay; Radhey Shyam Tiwari; Onkar Nath Srivastava
The main objective of the current work was to investigate the transformation mechanism in quasicrystals during mechanical alloying/milling. The quasicrystalline phases have been synthesized by melting the individual elements as well as by mechanical alloying of the concerned elements using high energy ball milling. The transformation of icosahedral and decagonal quasicrystalline phases to various disordered states in Al-Fe-Cu-Cr and Al-Fe-Cu-Mn alloys during milling of the pre-alloyed material. The milling of a quasicrystalline alloy was carried out using a high energy ball mill by varying milling times up to 40h under liquid hexane medium and at various milling intensity. X-ray diffraction was carried out for evaluating the lattice strain, lattice parameters and crystallite sizes of the mechanically milled samples. The evolution of nano icosahedral and nano decagonal phases as well as crystalline phases was found to occur. The subsequent thermal treatment led to the structural ordering in the concerned phases. The implication of the evolution of various phases, their structural correlations and their relative stability will be discussed. © 2010 IOP Publishing Ltd.
Evolution of a nanocrystalline (Co,Ni)Al2O4 spinel phase from quasicrystalline precursor
(2008) Thakur Prasad Yadav; Radhey Shyam Tiwari; Onkar Nath Srivastava; Nilay Krishna Mukhopadhyay
This work reports on the synthesis of a spinel phase from a thermodynamically stable decagonal quasicrystalline Al70 Co15Ni15 alloy. The Al70Co15 Ni15 alloy, synthesized through slow cooling of the molten alloy, was subjected to milling in an attritor ball mill at 400 rpm for 5, 10, 20, 30, and 40 h with a ball to powder ratio of 20:1 in the hexane medium. The differential thermal analysis, X-ray diffraction, scanning, and transmission electron microscopy techniques have been used for characterization of milled as well as annealed powders. The Voigt function analysis has been used for calculation of the effective crystallite size and relative strain of ball-milled samples. The crystallite size has been found to be ∼ 14 nm after 40 h of milling along with a lattice strain of 8.1%. The annealing experiments have been carried out under two different conditions: (i) in vacuum and (ii) in air. The results of the present investigation clearly revealed that the nano-decagonal phase was stable in vacuum while annealing at 600°C for 40h. However, during annealing under a similar condition in air, the formation of a nanospinel of (Ni,Co)Al2O4 of size ∼ 60 nm was identified. The possible structural evolution of the spinel from the quasicrystalline phase has been discussed. © 2008 American Ceramic Society.
Facile synthesis of large surface area graphene and its applications
(Springer Verlag, 2017) Mahe Talat; Prashant Tripathi; Onkar Nath Srivastava
In 2008, one of the most costly materials on earth was graphene which was obtained by exfoliation method, having a model area of a human hair cross section costing more than $1000 as of April 2008 [2]. Since then, hunger for searching low-cost, non-hazardous alternative methods for scalable production of graphene continued. Graphene’s flexible chemistry with an atomic thickness makes it superlatives in material science, an ideal candidate for countless applications. Incredibly light weight and flexible, yet 200 times stronger than steel. Highly conductive but at the same time transparent, first 2D material existing but is one million times smaller than the diameter of a single human hair. Having all these amazing properties, graphene is creating an impact in wide range of industries including in fields of electronics, EMI shielding, composites, sensing devices as well as in energy storage, biomedical devices, and many more. Application of this wonder material is restricted to our imagination only. These engineering applications necessitate accessibility of graphene on the large scale, and methods used to synthesize this are facile, cost-effective, simple, quick, and single-step process, and thus appropriate processes are essential for synthesizing it down to a single-sheet level. The quality and quantity of graphene also plays an essential role, as the occurrence of defects, structural disorders, impurities, multiple domains, grain boundaries, and wrinkles in the graphene sheet can leave an unwanted effect on its electronic and optical properties. The present chapter will be aimed at the preparation of high quality few-layer graphene on a bulk scale from graphite in an affordable, nontoxic, and easy method. The methods which will be discussed in this chapter will be mostly on microwave-assisted synthesis of graphene and electrochemical exfoliation method used in our lab as well as reported by other workers, and how these methods are advantageous over conventional exfoliation methods. Last segment of this chapter will deal with applications of graphene particularly in EMI shielding. © 2017, Springer Nature Singapore Pte Ltd.
Functionalized graphene sheets as immobilization matrix for fenugreek β-Amylase: Enzyme kinetics and stability studies
(Public Library of Science, 2014) Garima Srivastava; Kritika Singh; Mahe Talat; Onkar Nath Srivastava; Arvind M. Kayastha
β-Amylase finds application in food and pharmaceutical industries. Functionalized graphene sheets were customised as a matrix for covalent immobilization of Fenugreek β-amylase using glutaraldehyde as a cross-linker. The factors affecting the process were optimized using Response Surface Methodology based Box-Behnken design of experiment which resulted in 84% immobilization efficiency. Scanning and Transmission Electron Microscopy (SEM, TEM) and Fourier Tansform Infrared (FTIR) spectroscopy were employed for the purpose of characterization of attachment of enzyme on the graphene. The enzyme kinetic studies were carried out for obtaining best catalytic performance and enhanced reusability. Optimum temperature remained unchanged, whereas optimum pH showed shift towards acidic range for immobilized enzyme. Increase in thermal stability of immobilized enzyme and non-toxic nature of functionalized graphene can be exploited for production of maltose in food and pharmaceutical industries. © 2014 Srivastava et al.
Graphene decorated with Fe nanoclusters for improving the hydrogen sorption kinetics of MgH 2 - Experimental and theoretical evidence
(Royal Society of Chemistry, 2016) M. Sterlin Leo Hudson; Keisuke Takahashi; A. Ramesh; Seema Awasthi; Ashish Kumar Ghosh; Ponniah Ravindran; Onkar Nath Srivastava
Graphene decorated with Fe clusters is proposed to be a possible alternative catalyst for the hydrogenation and dehydrogenation reactions of MgH 2 . In particular, graphene decorated with Fe clusters is effective for both hydrogenation and dehydrogenation processes of MgH 2 . The change in enthalpy and entropy values of hydrogen absorption determined for MgH 2 with 5 wt% graphene decorated with Fe clusters is -50.4 ± 2.9 kJ per mole of H 2 and 99.8 ± 5.2 J K -1 per mole of H 2 , respectively. This is significantly lower than those for well-established metal catalysts and nano-interfacial confined MgH 2 . Moreover, the graphene decorated with Fe clusters facilitates the fast rehydrogenation kinetics of MgH 2 , which reabsorbed 90% of the total reabsorption capacity in less than 4 minutes at 300 °C and 20 atm. In addition, TEM analysis reveals that MgH 2 particles are covered by graphene with Fe clusters, resulting in the reduction of grain growth. Density functional theory shows that the defects in graphene act as the active sites for the dehydrogenation of MgH 2 , while the Fe clusters reduce the adsorption of dissociated H atoms, resulting in low-temperature dehydrogenation. Thus, graphene decorated with metal clusters could open up a new way of designing a new type of catalyst which could replace transition metal catalysts. © The Royal Society of Chemistry 2016.
Graphene nanosheets assisted carbon hollow cylinder for high-performance field emission applications
(Institute of Physics Publishing, 2019) Prashant Tripathi; Bipin Kumar Gupta; Prashant K Bankar; Mahendra A More; Dattatray J Late; Onkar Nath Srivastava
Electron sources are critical constituents for myriad many electronic applications including electron imaging, mass spectroscopy etc. Here, we report the realization of high-performance field emission from graphene assisted carbon hollow cylinders (Gr-CHCs) composed of multi-stacked radially aligned CNTs. These CHCs have built-in synthesis related Fe nanoparticles (NPs). This engineered nano-structure exhibits excellent field emission properties such as one of the ultra-low turn-on field (0.64 V μm-1 at 10 μA cm-2), low threshold field (0.74 V μm-1 at 100 μA cm-2), very high current density (15.49 mA cm-2 at 1.32 V μm-1) which is nearly double the current density obtained in our previous study. High field enhancement factor (0.72 × 104) with highly stable emission current at 100 μA was observed for more than 3 hrs at the base pressure of ∼1 × 10-8 mbar. This study suggests an approach to enhance the current density using the proposed innovative nanostructure and forms the basic theme of this communication. Highly efficient and stable field emissions observed are attributed to the geometry of cylinder and the production of the high density of sharp protrusions within the graphene sheets which enhance the local electric field and dramatically enhance field emission. This innovative cylindrical geometry associated with graphene assisted on Fe bearing aligned CNTs along with the periphery of the bulk cylinder provides an easy injection of electrons from the conduction band of CHCs into the vacuum in the presence of an external electric field. The tunability of field emission properties of these CHCs can be easily achieved by tailoring their diameter (10 and 20 mm) and different concentrations of the precursor. This new approach of the graphene assisted cylindrical geometry-based field emitter source provides enormous prospects and demand for next-generation high resolutions display devices. © 2019 IOP Publishing Ltd.
Growth of different nanostructures of Cu2O (nanothreads, nanowires, and nanocubes) by simple electrolysis based oxidation of copper
(2007) Dinesh Pratap Singh; Nageswara Rao Neti; A.S.K. Sinha; Onkar Nath Srivastava
Cuprous oxide (Cu2O) nanostructures have been synthesized by anodic oxidation of copper through a simple electrolysis process employing plain water (with ionic conductivity ∼6 μS/m) as an electrolyte. No special electrolytes, chemicals, and surfactants are needed. The method is based on anodization pursuant to the simple electrolysis of water at different voltages. Platinum was taken as cathode and copper as anode. The applied voltage was varied from 2 to 10 V. The optimum anodization time of about 1 h was employed for each case. Two different types of Cu2O nanostructures have been found. One type was delaminated from copper anode and collected from the bottom of the electrochemical cell and the other was located on the copper anode itself. The nanostructures collected from the bottom of the cell are either nanothreads embodying beads of different lengths and diameter ∼10-40 nm or nanowires (length ∼600-1000 nm and diameter ∼10-25 nm). Those present on the copper anode were nanoblocks with a preponderance of nanocubes (nanocube edge ∼400 nm). The copper electrode served as a sacrificial anode for the synthesis of different nanostructures. A tentative mechanism for the formation of Cu2O nanostructures has been suggested. The present work represents the first such attempt where Cu2O nanostructures were formed under the oxidation induced by as simple a process as electrolysis of plain water. Both anodization potential and time influence the morphology of nanostructures of Cu2O. Thus, nanothreads are formed at 6 V during 15-30 min, whereas nanowires result when anodization time is extended to 45-60 min. Also two different types of Cu2O nanostructures, one which is present in the solution (nanothreads and nanowires) and the other which is located on the copper anode (nanocubes), are synthesized in the same electrolysis run. The optical band gap as calculated from the UV-visible absorption spectra of the nanothreads and nanowires corresponds to 2.61 and 2.69 eV, respectively, which is larger than the known band gap (2.17 eV) of bulk Cu2O. © 2007 American Chemical Society.
Immobilization of β-galactosidase onto functionalized graphene nano-sheets using response surface methodology and its analytical applications
(2012) Devesh Kishore; Mahe Talat; Onkar Nath Srivastava; Arvind M. Kayastha
Background: β-Galactosidase is a vital enzyme with diverse application in molecular biology and industries. It was covalently attached onto functionalized graphene nano-sheets for various analytical applications based on lactose reduction. Methodology/Principal Findings: Response surface methodology based on Box-Behnken design of experiment was used for determination of optimal immobilization conditions, which resulted in 84.2% immobilization efficiency. Native and immobilized functionalized graphene was characterized with the help of transmission and scanning electron microscopy, followed by Fourier transform infrared (FTIR) spectroscopy. Functionalized graphene sheets decorated with islands of immobilized enzyme were evidently visualized under both transmission and scanning electron microscopy after immobilization. FTIR spectra provided insight on various chemical interactions and bonding, involved during and after immobilization. Optimum temperature and energy of activation (Ea) remains unchanged whereas optimum pH and Km were changed after immobilization. Increased thermal stability of enzyme was observed after conjugating the enzyme with functionalized graphene. Significance: Immobilized β-galactosidase showed excellent reusability with a retention of more than 92% enzymatic activity after 10 reuses and an ideal performance at broad ranges of industrial environment. © 2012 Kishore et al.
Lactose nano-probe optimized using response surface methodology
(2009) Alka Dwevedi; Ashwani Kumar Singh; Dinesh Pratap Singh; Onkar Nath Srivastava; Arvind M. Kayastha
A lactose nano-probe has been developed by immobilization of PsBGAL onto gold nanoparticles (AuNps). It is helpful for severe lactose intolerants for quality check of lactose hydrolyzed milk and estimation of hidden lactose present in variety of food products. Optimization of PsBGAL immobilization onto AuNps using spacer arm (cysteamine-glutaraldehyde) was carried out by response surface methodology (Box-Behnken design). The process has led to immobilization of enzyme onto AuNps with an efficiency of 140.81%. AuNp-PsBGAL was characterized using transmission electron microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Immobilized enzyme showed broad temperature and pH optima and a significant enhancement in catalytic efficiency (Vmax/Km) with respect to soluble PsBGAL. AuNp-PsBGAL was stable under dried conditions than wet conditions for 6 months with loss of 10.2% and 87.53%, respectively. It has reusability of over five batchwise uses, with almost no loss in activity. Hill's coefficient was found to be 1.71 corresponding to lactose concentration ranging from 0.1% to 2.0%. © 2009 Elsevier B.V. All rights reserved.