Microwave assisted synthesis of gold nanoparticles and their antibacterial activity against <i>Escherichia coli</i> (<i>E. coli</i>)

Arshi, Nishat,Ahmed, Faheem,Kumar, Shalendra,Anwar, M.S.,Lu, Junqing,Koo, Bon Heun,Lee, Chan Gyu Elsevier 2011 Current Applied Physics Vol.11 No.1

<P><B>Abstract</B></P><P>We report a simple one step microwave irradiation method for the synthesis of gold nanoparticles using citric acid as reducing agent and cetyl trimethyl ammonium bromide (CTAB) as binding agent. The reaction was completed under two different microwave irradiation times (40 s and 70 s) for the production of two types of gold nanoparticles. The synthesized nanoparticles were characterized using UV–Vis absorption spectroscopy and transmission electron microscopy (TEM) measurements. UV–Vis study revealed the formation of gold nanoparticles with surface plasmon absorption maxima at 590 and 560 nm for 40 and 70 s irradiation time respectively. From TEM analysis, it is observed that the gold nanoparticles have spherical shape with particle size distribution in the range 1–10 nm and 1–2 nm for 40 s and 70 s irradiation time respectively. Antibacterial activity of gold nanoparticles as a function of particle concentration against gram-negative bacterium <I>Escherichia coli</I> (<I>E. coli</I>) was carried out in solid growth media. The two types of gold nanoparticles show high antibacterial activity with zone of inhibition of about 22 mm against <I>E. coli</I> (ATCC 25922 strain). Very small difference in the antibacterial activity for the two types of gold nanoparticles were observed. Though nanoparticles synthesized for 70 s irradiation time show slightly better antibacterial activity.</P> <P><B>Highlights</B></P><P>► Gold nanoparticles have been successfully synthesized using microwave irradiation technique. ► The mean diameter was ∼ 4.05 nm for 40 s and ∼1.05 nm for 70 s. ► Characteristic absorption peak was found to be 590 nm for 40 s and 560 nm for 70 s. ► The zone of inhibition for the two types of nanoparticles was almost similar (22 mm). ► Smaller size nanoparticles synthesized for 70s showed a slightly better antibacterial action.</P>

Effect of illumination on hydrogenated amorphous silicon thin films doped with chalcogens

Sharma, S.K.,Kumar, K.N.P.,Kang, K.J.,Mehra, R.M. North-Holland 2009 Journal of non-crystalline solids Vol.355 No.31

Hydrogenated amorphous silicon thin films doped with chalcogens (Se or S) were prepared by the decomposition of silane (SiH<SUB>4</SUB>) and H<SUB>2</SUB>Se/H<SUB>2</SUB>S gas mixtures in an RF plasma glow discharge on 7059 corning glass at a substrate temperature 230<SUP>o</SUP>C. The illumination measurements were performed on these samples as a function of doping concentration, temperature and optical density. The activation energy varied with doping concentration and is higher in Se-doped than S-doped a-Si:H thin films due to a low defect density. From intensity versus photoconductivity data, it is observed that the addition of Se and S changes the recombination mechanism from monomolecular at low doping concentration films to bimolecular at higher doping levels. The photosensitivity (σ<SUB>ph</SUB>/σ<SUB>d</SUB>) of a-Si,Se:H thin films decreases as the gas ratio H<SUB>2</SUB>Se/SiH<SUB>4</SUB> increased from 10<SUP>-4</SUP> to 10<SUP>-1</SUP>, while the photosensitivity of a-Si,S:H thin films increases as the gas ratio H<SUB>2</SUB>S/SiH<SUB>4</SUB> increased from 6.8x10<SUP>-7</SUP> to 1.0x10<SUP>-4</SUP>.

A hybrid method for fundamental heart sound segmentation using group-sparsity denoising and variational mode decomposition

V. G. Sujadevi,Neethu Mohan,S. Sachin Kumar,S. Akshay,K. P. Soman 대한의용생체공학회 2019 Biomedical Engineering Letters (BMEL) Vol.9 No.4

Segmentation of fundamental heart sounds–S1 and S2 is important for automated monitoring of cardiac activity includingdiagnosis of the heart diseases. This pa-per proposes a novel hybrid method for S1 and S2 heart sound segmentation usinggroup sparsity denoising and variation mode decomposition (VMD) technique. In the proposed method, the measured phonocardiogram(PCG) signals are denoised using group sparsity algorithm by exploiting the group sparse (GS) property ofPCG signals. The denoised GS-PCG signals are then decomposed into subsequent modes with specifi c spectral characteristicsusing VMD algorithm. The appropriate mode for further processing is selected based on mode central frequencies and modeenergy. It is then followed by the extraction of Hilbert envelope (HEnv) and a thresholding on the selected mode to segmentS1 and S2 heart sounds. The performance advantage of the proposed method is verifi ed using PCG signals from benchmarkdatabases namely eGeneralMedical, Littmann, Washington, and Michigan. The proposed hybrid algorithm has achieved asensitivity of 100%, positive predictivity of 98%, accuracy of 98% and detection error rate of 1.5%. The promising resultsobtained suggest that proposed approach can be considered for automated heart sound segmentation.

Reply to ''Comment on ''Facile chemical bath deposition of CuS nano peas like structure as a high efficient counter electrode for quantum-dot-sensitized solar cells'' by H.-J. Kim, J.-H. Kim, CH. S. S. Pavan Kumar, D. Punnoose, S.-K. Kim, C. V. V. M. Gop

Kim, H.J.,Kim, J.H.,Pavan Kumar, C.H.S.S.,Punnoose, D.,Kim, S.K.,Gopi, C.V.V.M.,Rao, S.S. Elsevier Sequoia 2015 Journal of Electroanalytical Chemistry Vol.756 No.-

Synthesis of Tetrazolo[1,5-a]quinoxaline based Azetidinones & Thiazolidinones as Potent Antibacterial & Antifungal Agents

Kumar, Shiv,Khan, S.A.,Alam, Ozair,Azim, Rizwan,Khurana, Atul,Shaquiquzzaman, M.,Siddiqui, Nadeem,Ahsan, Waquar Korean Chemical Society 2011 Bulletin of the Korean Chemical Society Vol.32 No.7

4-Chlorotetrazolo[1,5-a]quinoxaline (III) was synthesized by azide (2+3) cycloaddition of 2,3-dichloroquinoxaline (II). Compound (III) on further refluxing with hydrazine hydrate furnished 4-hydrazinotetrazolo[1,5-a]quinoxaline (IV). Further refluxing of (IV) with different aromatic aldehydes in methanol yielded corresponding Schiff's bases V(a-j). Various 4-aminotetrazolo[1,5-a]quinoxaline based azetidinones VII(a-j) were synthesized by stirring the compounds V(a-j), at low temperature, with equimolar mixture of chloroacetylchloride & triethylamine in dry benzene, while 4-aminotetrazolo[1,5-a]quinoxaline based thiazolidinones VIII(a-j) were synthesized by refluxing Schiff's bases V(a-j) with thioglycolic acid in oil-bath. The structures of all the compounds were confirmed on the basis of $^1H$-NMR & FT-IR spectral data. All the newly synthesized compounds were screened for in-vitro antimicrobial activity against E. coli, S. aureus, K. pneumoniae & P. aeruginosa & antifungal activity against C. albicans. Few of them have exhibited the promising activity.

Enhanced protective potential of novel citronella essential oil microsponge hydrogel against Anopheles stephensi mosquito

Kumar Nitish,Kumar Sunil,Singh S.P.,Rao Rekha 한국응용곤충학회 2021 Journal of Asia-Pacific Entomology Vol.24 No.1

Citronella oil has been frequently used as an insect repellant and antibacterial agent for management of vector borne diseases. In this study, the fabrication of citronella oil microsponge loaded hydrogel (HG-COMS) was conceptualized in order to provide future insight for developing delayed release formulation. The hydrogel was characterized for drug content, drug interaction studies, spreadability, texture analysis and in vitro occlusive behaviour and results were found satisfactory. Further, in vitro antimicrobial studies were carried out to compare the antimicrobial inhibitory potential of the HG-COMS against citronella oil loaded hydrogel (HG-CO). HG-COMS formulation showed better antimicrobial efficacy than HG-CO (zone of inhibition of E. coli, P. aeruginosa and S. aureus; with P value less than 0.01, 0.001 and 0.05, respectively). In addition, the safety (irritation potential) of the oil loaded hydrogel formulation was assessed by Hen’s Egg Test Chorioallantoic Membrane (HAT-CAM) method. Mosquito repellent activity against Anopheles stephensi (malaria vector mosquito) was also performed in a net cage having blood starved female mosquitoes. The repellent potential of prepared HG-COMS (34% repellency for 6 h) was found dependent on release of CO from the microsponges as well as from the gel matrix. HET-CAM test revealed that HG-COMS (irritation score: 6.43 ± 0.77) was found very promising in comparison to HG-CO (irritation score: 12.77 ± 0.36), and was thus, considered safer for dermal use. HG-COMS showed reduced frequency of application, no skin irritation and potential for controlling A. stephensi for longer time periods. Hence, HG-COMS is found as a promising eco-friendly protective option, to minimize the burden of mosquito-transmitted diseases, especially malaria in future.

Studies on the Biology and Predatory Behaviour of Eocanthecona furcellata (Wolff.) Predating on Spilarctia obliqua (Walk.) in Mulberry Plantation

Kumar, Vineet,Morrison, M.N.,Rajadurai, S.,Babu, A.M.,Thiagarajan, V.,Datta, R.K. Korean Society of Sericultural Science 2001 International Journal of Industrial Entomology Vol.2 No.2

The stink bug, Eocanthecona furcellata (Wolff.) is a natural and potential biocontrol agent of Spilarctia obliqua (Walk.). The present investigation reveals the biology, predatory efficiency and reproductive parameters of the predator which feeds on S. obliqua caterpillars in mulberry plantation. In order to find out the role of prey sine on the biology of the predators the predatory insects were separately fed with small and large caterpillars of S. obliqua. The incubation period of the eggs of E. furcellata was 8.37${\pm}$0.44 days, while the nymphal duration varied as per the prey sine. The predator when supplied with small larvae of prey, consumed 61.1 larvae and completed nymphal stage in 19.9 days; while those fed with larger prey, consumed 36.1 larvae and completed their nymphal stage in 21.55 days. The prey size also influences the reproductive parameters of the predator, The adult female predator is more voracious feeder than the adult male and consumed 41.9${\pm}$0.64 small larvae and 42.2${\pm}$0.87 large larvae during their life span. The longevity of male and female was observed as 20.7 and 29.4 days respectively. Visualization of the predator as well as the movement of the prey increases the predatory efficiency. Scanning electron microscopic studies on the feeding part explain its support in effective predation. Field observations indicated a drastic fall in the incidence of the mulberry pest, S. obliqua with the increased population E. furcellata in mulberry plantation.

Ultra-fast Detection and Differentiation of Mycoplasma haemofelis and Candidatus M. Haemominutum in Korean Feral Cats by Microchip Electrophoresis with Programmed Field Strength Gradients

Kumar, Kailasa S.,Lee, Hee-Gu,Yoo, Dong-Jin,Kang, Seong-Ho Korean Chemical Society 2008 Bulletin of the Korean Chemical Society Vol.29 No.1

A microchip-based capillary gel electrophoresis (MCGE) technique was developed for the ultra-fast detection and differentiation of Candidatus Mycoplasma haemominutum (Candidatus M. haemominutum, California strain) and Mycoplasma haemofelis (M. haemofelis, Ohio strain) in Korean feral cats through the application of programmed field strength gradients (PFSG) in a conventional glass double-T microchip. The effects of the poly (ethyleneoxide) (PEO) concentration and electric field strength on the separation of DNA fragments were investigated. The PCR-amplified products of Candidatus M. haemominutum (202-bp) and M. haemofelis (273-bp) were analyzed by MCGE within 75 s under a constant applied electric field of 117.6 V/cm and a sieving matrix of 0.3% PEO (Mr 8 000 000). When the PFSG was applied, MCGE analysis generated results 6.8-times faster without any loss of resolution or reproducibility. The MCGE-PFSG technique was also applied to eleven samples selected randomly from 33 positive samples. The samples were detected and differentiated within 11 s. The analysis time of the MCGE-PFSG technique was approximately 980-times faster than that using conventional slab gel electrophoresis.

Ultrahigh electrically and thermally conductive self-aligned graphene/polymer composites using large-area reduced graphene oxides

Kumar, P.,Yu, S.,Shahzad, F.,Hong, S.M.,Kim, Y.H.,Koo, C.M. Pergamon Press ; Elsevier Science Ltd 2016 Carbon Vol.101 No.-

<P>In this work, for the first time we fabricated highly self-aligned large-area reduced graphene oxide/poly (vinylidene fluoride-co-hexafluoropropylene) (rLGO/PVDF-HFP) composite films through simple solution casting followed by low temperature chemical reduction process. The resulting free-standing rLGO/PVDF-HFP composite thin film revealed excellent electrical conductivity of similar to 3000 S/m and ultrahigh inplane thermal conductivity of similar to 19.5 W/mK at rLGO content of 27.2 wt %. This ultrahigh electrical and thermal conductivity were attributed to the good interfacial interaction, effective chemical reduction, high aspect ratio, and preferential orientation of graphene sheets along the film direction. We believe that our new fabrication procedure can be effectively used for large-scale production and commercialization of conductive composite materials for many thermal and electrical conduction applications. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Oxide Scale Characterization and Study of Oxidation Kinetics in T91 Steel Exposed to Dry Air at High Temperatures (873–1073 K)

S. Das,S. Sanyal,P. Halder,A. Varma,Y. Ravi Kumar,S. Mandal 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.8

In this study, the oxidation response of a T91 steel in dry air environment has been investigated by performing cyclic oxidationtests at 873, 973 and 1073 K for a total duration of 1000 h with intermediate intervals. The temperature range for thisstudy is chosen to be higher than the operating temperature range of the alloy to accelerate the oxidation kinetics. Developinga comprehensive understanding of the mechanisms and kinetics involved at such accelerated oxidation environmentswould help to formulate better strategies for countering oxidation related failure events. The results of this study showedthat the oxidation rate is greatly influenced by temperature as well as exposure time, and follows a near-parabolic rate law. Characterization of the oxide scales revealed formation of dual oxide layers where the inner layer is primarily rich in Feand Cr, and the outer layer in Fe only. At 1073 K, formation of cracks can be observed in the oxide scales after 24 h, whichbecame more severe after 1000 h. The oxidation kinetics, when fitted to an Arrhenius type equation, can be associated withactivation energy (Q) and parabolic rate constant (kp) values. The Q values lie within 104–109 kJ/mol, whereas the kp valuesincrease with temperature due to increase in the reaction rate. The kinetic equation developed based on the Q and kp valuescan be used to predict the thickness (inner, outer and overall) of the oxide scales in T91 steel at any temperature and timewithin the studied ranges.