Journal of Science: Advanced Materials and Devices (2019) 57e65 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article The electrochemical behavior, antifungal and cytotoxic activities of phytofabricated MgO nanoparticles using Withania somnifera leaf extract H.R Raveesha a, S Nayana a, D.R Vasudha a, J.P Shabaaz Begum b, S Pratibha c, C.R Ravikumara d, N Dhananjaya c, * a Department of Botany, Bangalore University, Bengaluru, 560 056, India Molecular Diagnostics and Nanobiotechnology Laboratories, Department of Microbiology and Biotechnology, Bangalore University, Bangalore, 560056, India c Centre for Advanced Materials Research Lab, Department of Physics, BMS Institute of Technology and Management, Bengaluru, 560 064, India d Research Center, Department of Science, East West Institute of Technology, Bangalore, 560091, India b a r t i c l e i n f o a b s t r a c t Article history: Received 19 November 2018 Received in revised form 11 January 2019 Accepted 14 January 2019 Available online 22 January 2019 Magnesium oxide nanoparticles (MgO NPs) without and with Ca, Eu dopant were synthesized by using the W somnifera leaf extract through the low temperature green combustion method The detailed analytical characterizations such as Powder X-Ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM), Fourier Transform-infrared Spectra (FTIR), etc have been carried out for the obtained NPs The PXRD patterns confirmed the formation of the Periclase structure with the cubic phase whereas the SEM and TEM results revealed the agglomerated roughly spherical granular structures of about 50e70 nm in size FTIR spectra confirmed the formation of the metaleoxygen stretching vibration (Mg-O) bond at 419 cmÀ1 Multifunctional studies were performed over the MgO NPs for their electrochemical impedance, cyclic voltammetry and antibacterial activities © 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: MgO NPs Withania somnifera Green Combustion Antibiosis Cyclic voltammetry Introduction Among various metal oxides MgO has gained keen interests due to its non-toxic, ecofriendly nature, the availability of greater specific area, the biocompatibility and the easy convenience of its sources Henceforth it has been implemented in designing the magnesium batteries, biosensors, antimicrobial drugs and catalysts for the waste water treatment A new era of nano dimensional metals along with metal oxides emerged in material chemistry area attracting great researcher's attention due to their diverse multipurpose applications The importance of these materials in the fields of medicine, catalytic applications, energy storage, bio sensing as well as electrochemical sensing applications has given a new directionality for the * Corresponding author E-mail address: ndhananjayas@gmail.com (N Dhananjaya) Peer review under responsibility of Vietnam National University, Hanoi upcoming inventions in the synthesis of such novel materials through different synthesis routes In recent years, much attention is paid to MgO NPs due to their potential applications in industries, electronics, health care applications [1] MgO NPs have a broad spectrum of activities against microorganisms, including Gramnegative and positive-bacteria and are of particular importance for multiple drug resistant pathogenic bacterial strains [2e4] The MgO NPs suspension exhibited considerable antibacterial activity against Gram-negative and Gram-positive bacteria suggestively due to the fact that MgO NPs can easily enter the bacterial cell and deliver an amazing surface area for interactions that hinders the growth mechanism of the bacteria [5] The large number of studies suggest that nanoparticles cause the disruption of bacterial membranes probably by the creation of reactive oxygen species (ROS), such as superoxide and hydroxyl radicals As a nanoparticle approaches near the membrane, a potential called zeta potential is created [2,6e8] The crucial advantages of using MgO NPs are its low cost and non-toxicity that enables its use in consumer products, water purification and also in pharmaceutical products https://doi.org/10.1016/j.jsamd.2019.01.003 2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 58 H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 [4,9e12] Various methods have been utilized in synthesizing the MgO NPs, such as solidestate reaction, solegel prepicitation, vapor phase oxidation and pulsed laser deposition [13e15], etc Amongst these, solution combustion method stands unique for its simple, less time consuming and economical nature [16] Also the fuel plays an important role in the formation of nanoparticles which involves the mixing of the precursors in the molecular level The green combustion method is one such way which involves the plant related extracts to prepare the non-toxic porous nanoparticles of high purity and with high specific surface area [17] According to the literature survey, many researches have been undertaken using the various chemical reagents as well as biological fuels (as reducing agents) for preparing MgO NPs For instance, Rao et al [18] have used the orange peel, Jiahaibai et al [19] have used the starch as reducing agent, Sushma et al [20] Clitoria ternatea extract, Sudheer Kumar et al [21] E tirukalli plant latex extract and Reddy Yadav et al [12] have used water melon juice for synthesizing MgO NPs In the present paper, we report the phytofabrication of MgO NPs using W somnifera leaf extract for electrochemical sensing and their antifungal as well as cytotoxic activity We have chosen the W somnifera, known commonly as ashwagandha, which is a plant belonging to Solanaceae family as reducing agent (fuel) in the preparation of MgO NPs It has been widely used in Indian Ayurvedic medicines The major phytochemical components present are withanolides which are actually triterpene lactones, such as withaferin A, alkaloids, steroidal lactones, tropine, and cuscohygrine The antibiosis of different microbial strains, cyclic voltammetry and electrochemical impedance spectroscopy for energy storage applications havent been carried out using the as-obtained MgO NPs Experimental 2.1 Materials used Magnesium nitrate, Calcium nitrate and Europium oxide were purchased from SD Fine Chemicals and Sigma Aldrich Europium nitrate was obtained by dissolving Europium oxide in nitrating mixture and keeping on the sand bath The chemicals were used without any further purification 2.2 Preparation of leaf extracts The healthy plants of W somnifera were collected from Dibbur village, Chickballapur taluk and Chickballapur district in the month of January 2017 Fresh leaves of W somnifera were washed in running tap water, dried and finely chopped Briefly 50 g of leaf was suspended in 500 ml of double distilled water and kept under stirring in hot plate at 50 C for 20 The mixture was cooled to room temperature and filtered through Whattman paper The filtrates were stored in the refrigerator at C for further studies 2.3 Green synthesis of nanoparticles The nanoparticles were prepared by the green combustion method Briefly, the reaction mixture was prepared by adding different concentrations (20, 40, 60 and 80 ml) of the leaf extract (fuel) and Magnesium nitrate hexahydrate (Mg(NO3)2.6H2O) (4.64 g) as a source of magnesium The mixture was kept in a preheated muffle furnace at 400 ± 10 C The reaction was completed within 5e10 to obtain a white colored powder material The obtained powders were subjected to calcination in a muffle furnace at 400 C for h The nanoparticles were stored in airtight container until further use The synthesis of the magnesium oxide doped with calcium and europium was done by taking the aqueous mixture containing stoichiometric amounts of Magnesium nitrate hexahydrate with mol% of calcium nitrate and europium nitrate in an optimized volume of leaf extract (60 ml), respectively The mixture was kept for combustion in a pre-heated muffle furnace at (400 ± 10) C to obtain a white colored material These powders were further subjected to calcination at 400 C for h 2.4 Characterization of nanoparticles The PXRD patterns of the calcined MgO NPs were obtained by the Philip X'pert PRO x-ray diffractometer with the graphite monochromatized Cu-Ka (1.5418 Å) radiation The morphological features are obtained by a Carl Zeiss Ultra 55 scanning electron microscope (SEM) and a JEOL JEM 3010 transmission electron microscope (TEM) operating at 300 kV The FTIR spectra were taken using the Perkin Elmer Spectrophotometer with KBr as reference The energy band gap was estimated using Tauq's the plot from the absorption data obtained by the Shimadzu UV-1800 UV-Visible spectrophotometer in the range 200e900 nm The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed on a potentiostat of the Model CHI608E 2.5 Procedure for electrochemical sensing and electrode preparation Experiments were carried out in a conventional electrochemical cell The electrode system contained a carbon paste working electrode (3.0 mm in diameter), a platinum wire counter electrode and a saturated Ag/AgCl reference electrode The carbon paste electrode was prepared as follows: 70% graphite powder (particle size 50 mm and density 20 mg/100 ml), 15% prepared sample and 15% silicone oil were mixed by hand to produce a homogeneous carbon paste electrode The carbon paste was then packed into the cavity of a customized carbon paste electrode and smoothened on a weighing paper The electrolyte being a 1M KOH solution and the potential range was À1.6 V to 0.6 V (vs Ag/AgCl electrode) and the scanning rate was 10, 20, 30, 40 and 50 mV/s 2.6 Antibacterial activity of phyto-nanofabricated MgO NPs 2.6.1 Pathogenic bacterial strains The investigation was designed involving the exposure of four pathogenic bacterial strains to MgO NPs These bacterial strains include two Gram-negative bacteria Escherichia coli (ATCC 8739) and Pseudomonas aeruginosa (ATCC 9027) and, two strains of Grampositive Bacillus cereus (ATCC 11778) and Staphylococcus aureus (ATCC 6538) 2.6.2 Preparation of MgO nanoparticles stock solutions and media All the bacteria were cultured on the Mueller-Hinton agar (HiMedia, Mumbai, India) in petri plates and incubated for 24 h in aerobic conditions at 37 C All glasswares used were sterilized by autoclave at 121 C for 15 before being used in the experiments Fresh 24 h cultures were used for preparing the bacterial suspensions by means of a single colony selected from the stock bacterial culture The loop full of inoculum was inoculated to 20 ml of sterile nutrient broth in a 100 ml Erlenmeyer flask These flasks were then incubated at 37 C at 200 rpm stirring for (24 ± 2) h Consequently, a bacterial suspension with an optical density of McFarland of 0.5 (1  108 CFU/mL) was made separately with the isotonic solution of NaCl (0.85%) These stock solution of bacteria were diluted further ten times (1  107 CFU/mL) and used straight away for the analysis as inoculum in the testing as described below H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 2.6.3 Disc diffusion method (qualitative analysis) In the present study, examinations of in vitro antimicrobial activities of biosynthesized MgO-NPs towards Gram positive and Gram negative pathogens were carried out by using a disc diffusion method [22] Briefly, the bacteria were grown overnight in a nutrient broth The bacterial inoculum was standardized to 0.5 MF units, meaning that approximately 108 colony forming units of each bacterium were inoculated onto a plate Previously prepared samples impregnated on discs (6 mm) at the various concentrations were placed aseptically on plates inoculated with bacteria and incubated at 37 C for 24 h All tests were carried out in the dark condition After incubation, the zone of whole inhibition was measured All tests were replicated three times 2.6.4 Evaluation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of MgO nanoparticles by microdilution technique (quantitative analysis) The MIC's are measured as the gold-standard for defining the susceptibility of the microorganism to the antimicrobial compound Henceforth, this is used to judge the performance of all other techniques of susceptibility testing The MIC and MBC of the synthesized MgO NPs obtained under different reaction conditions were determined by the broth microdilution method The MIC was determined according to the Clinical and Laboratory Standards Institute [22] with some slight modifications using a 96-well microdilution plate where the bacterial strains concentration was  107 CFU/mL The viability of the bacterial pathogens when exposed to different concentrations of biosynthesized MgO NPs was analyzed in a 96-well plate using iodonitrotetrazolium chloride [10] MgO NPs stock suspension was prepared by resuspending the nanoparticles in Type I (milli-Q) water to get a final concentration of 100 mg/mL; the suspension was kept at C until further use Later, the aliquot was subjected to sonication and the suspensions were mixed with Mueller-Hinton broth for use in the subsequent experiments To identify the MgO NPs with potential inhibitory effect on bacterial pathogens, all the four bacterial strains were exposed to MgO NPs ranging from 0.025 mg/mL to 25 mg/mL The similar method was performed to find the MIC of the positive (tetracycline) and negative controls Tetracycline (25 mg/mL) was effective against the pathogenic bacterial strains considered as the positive control Aseptic Mueller-Hinton broth with 0.85% NaCl was used as the negative control The MIC was defined as the lowest concentration of agent that restricted the bacterial growth to a level lower than 0.05 at 600 nm (no visible growth) The 20 mL of the bacterial suspension (107 CFU/mL) was added to each microtitre well and incubated at 37 C for 24 h in an incubator The tests were repeated few times in triplicates Accordingly, the MIC values of the test materials were revealed by adding 25 mL of indicator dye, iodonitrotetrazolium chloride (INT at 0.5 mg/mL) in each well after 24 h The microtitre plates were additionally incubated at 37 C for 60 The MICs of each compounds were determined as the lowest concentration of the nanoparticles or drug that stopped the colour change from yellow to red (Fig 8(a)) The MBC determination was done by using 50 mL of cultured aliquots (without INT) that was streaked onto the Mueller-Hinton (MH) agar in a petriplate and incubated for 24 h at 37 C The lowest concentration that indicated the complete absence of the bacterial growth on MH agar surface was considered as the MBC 59 particle size of the synthesized materials was obtained using the DebyeeScherrer's formula, D¼ Kl b cos q (1) where, K is constant (0.9), l is the wavelength (l ¼ 1.5418A), b is full width at half maximum intensity (FWHM) and q is the half diffraction angle Fig shows the XRD patterns of MgO, MgO:Ca and MgO:Eu NPs synthezised using the leaf extract of the W somnifera plant The diffraction peaks were well indexed to the cubic crystal system of Periclase (JCPDS card No 43e1022) with space group Fm-3m (No 225) having the lattice parameter 4.215 Å The PXRD peaks appearing at 37.02, 42.88, 62.33,7.76 and 78.57 of the corresponding 2q values were identified to the reflexions from the (111), (200), (220), (311) and (222) planes of cubic MgO [12] The average crystallite size as calculated using Scherrer's formula was found to be in the range 50e70 nm This variation is probably due to the dopants added to the host lattice Since mol% of Ca and Eu are inserted into MgO crystal, the lattice parameter gets changed and it can be investigated by XRD by calculating inter planar spacing‘d’, using the equation, d¼ l 2sinq (2) (this is the experimental d value which depends on the 2q values measured experimentally) and the lattice parameter ‘a’ was obtained by substituting the value ofd in the equation, h2 ỵ k2 ỵ l2 ẳ d a2 (3) where, (hkl) refer to the Miller indices Since we have a cubic Periclase MgO system all the lattice parameters are same The small variation in d spacing and the lattice constant due to doping is tabulated in Table Results and discussion 3.1 X-ray diffraction analysis The crystallite phase formation and the size of particles were determined by using X-ray diffraction measurements The average Fig XRD patterns of MgO nanoparticles synthesized using the W somnifera leaf extract 60 H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 Table1 Lattice parameters Sample details (hkl) d-Spacing (Å) (experimental) Lattice constant (Å) MgO (200) (220) (200) (220) (200) (220) 2.108 1.490 2.108 1.491 2.110 1.491 4.2161 4.2164 4.2161 4.2176 4.2218 4.2188 MgO:Ca MgO:Eu were found to be around 50e70 nm The combustion reactions mainly involve the metaleligand formation which will be either flaming or non-flaming type depending on the fuel nature The pores and flaws as seen in the micrographs may be due to the release of voluminous gases out of the reaction mixture during combustion EDX is an analytical technique used for the elemental analysis of a sample which utilizes X-rays that are emitted from the specimen when bombarded by the electron beam Since we have doped only minute quantity of both Ca2ỵ and Eu3ỵ (1 mol %) we cannot observe the peaks corresponding to them in EDX patterns 3.2 Scanning electron microscopy and transmission electron microscopy studies 3.3 Fourier transforms infra-red spectroscopy The SEM studies were carried out with an accelerating voltage of 20 KV to determine the morphology of the particles These micrographs are as shown in Fig Both SEM and TEM depict the agglomerated granular structure The diameters of the MgO NPs FTIR spectra are helpful in the molecular structure analysis and have been recorded in the wave number range 400 cmÀ1 to 4000 cmÀ1 as shown in Fig The FTIR studies revealed broad peak at 3430 and a peak at 1606 cmÀ1 which are attributed to the eOH bending and stretching Fig SEM and TEM images of (a,b) MgO, (c, d) MgO: Ca and (e, f) MgO: Eu nanoparticles H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 Fig FTIR spectra of (a) W somnifera leaf extract, (b) MgO, (c) MgO: Ca and (d) MgO: Eu nanoparticles vibrations originating from adsorbed water molecules and surface hydroxyl groups that were strongly perturbed by the hydrogen bonding [23] The broad peak at 419 cmÀ1 corresponds to the MgeO stretching vibrations [24] The broadness of the absorption band at 3600e3200 cmÀ1 in the spectra of MgO NPs confirmed a high degree of hydrogen bonding of water molecules among themselves and with the crystallite surface [21] 3.4 UVevisible spectroscopy The UVeVisible spectral analysis of biosynthesized MgO NPs was concducted at a resolution of 200e900 nm The optical property of synthesized MgO NPs was examined using an UV-visible spectrophotometer and the outcomes are shown in Fig It shows a broad absorption peak at ~230 nm which is in good agreement with the reported literature The energy band gap of MgO NPs was determined by fitting the absorption data to the direct transition equation In this method the absorption data following a power law behavior of the WoodeTauc relation is given below [25] À ahy ¼ A hy À Eg Á1 (4) where “A” is an energy independent co-efficient and Eg is the optical band gap The absorption co-efficient a is defined as a¼ 2:303  103  AP LC (5) In order to determine the optical band gap, we have plotted (ahn) as a function of photon energy as shown in the inset of Fig This plot gives us straight line as shown in figure The optical band gap was determined by extra plotting the linear portion of the plot (ahv) ¼ The energy band gap values of MgO, MgO: Ca and MgO: Eu as obtained by drawing the tangential intercept on the x-axis were found to be 5.37, 5.24, and 5.47eV, respectively 61 Fig UV-Visible spectra with the insets showing Tauq's plots 3.5 Cyclic voltammetry and electrochemical impedance spectroscopy Cyclic voltammetry (CV) is the most commonly employed tool to determine the oxidation-reduction process of the inorganic molecular species The efficiency of charge, discharge of the electrodes and the reversibility of the reaction between the electrodes can be quantized and is carried out using CV Results of the cyclic voltammetric studies of the pure and the Ca and Eu doped MgO samples are respectively shown in Fig The characteristics of the observed capacitance was different from that of the electrical double layer capacitor as indicated by the shape of the CV curve, which was usually close to an ideal rectangular shape However, it was observed that the increase in the scan rates doesn't affect the mass transportation and electron conduction within the material [26] The anodic peak was formed due to the oxidation of Mg0 into Mg2ỵ whereas the cathodic peak indicates the reduction of Mg2ỵ into Mg0 The quasi-reversible electron transfer process is shown by the CV curves which indicating that the basis of the measured capacitance is the redox mechanism [27] Conversely, the shape of the curve indicates that the determined characteristic capacitance is distinct from that of the electrical double layer capacitor, which might turn out to represent a CV curve that may sometimes be close to a perfect rectangle [28] The electrochemical impedance measurements of the different MgO samples vs Ag/AgCl were conducted in the frequency range of Hz to MHz with the AC amplitude of mV at the steady state The Nyquist plots for the pure and the Ca and Eu doped MgO samples are shown in Fig The impedance of the electrodes is given by: Zuị ẳ Z þ jZ 00 ¼ Zreal þ jZimaginary ¼ R þ jX (6) pffiffiffiffiffiffiffi where, j ¼ À1, Zʹ and Zʹʹ are the real and imaginary parts of the impedance 62 H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 Fig Cyclic voltammetric studies of pure MgO sample and Ca and Eu doped MgO samples As seen in the EIS spectrum the depressed semicircles with a centre below the real axis are the plots at high frequencies in the complex plane Therefore, to fit the data into an equivalent circuit, a model containing a constant phase element (Q1) should be used The impedance of Q1 is described [29] as ZCPE ẳ Yjuịn (7) Fig Nyquist plot for the pure MgO sample and the Ca and Eu doped MgO samples Also, Z ¼ R and Z 00 ¼ c ¼ u1C [29] R is the resistance and c is the reactive capacitance From the impedance spectra it was noticed that the impedance of the electrode A was larger and on the other hand, the impedance of the electrode C was found to be smaller and thus, this leads to higher discharge rates Fig Equivalent circuit of the Nyquist plots of an impedance measurement of different MgO electrodes H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 increase in the capacitance because the imaginary line moves towards the Y-axis The capacity of this MgO electrode is attributed to the synergistic effect of the electric double-layer capacitance on the high surface area of the AC and the pseudo capacitance via the intercalation/extraction of the Eu ions in the MgO lattice The Nyquist plot of the pure MgO electrode reveals that in the higher frequency range, the impedance spectrum consists of an elevated arc with a bigger diameter and also the imaginary line moves towards the X-axis indicating that the electrode reaction is under the charge-transfer control The charge transfer resistance of this electrode has a high and a low capacitance of the double layer [32,33] Table lists the EIS fitted circuit parameters of RCt and Cdl related to the prepared MgO electrodes and these parameters were obtained by fitting the experimental data according to the equivalent circuit The decrease in RCt and the increase in Cdl indicate that the electrochemical activity of the electrode increases From the available data, it is very clearly evident that the electrochemical activity of the MgO electrode with Eu dopant is higher and it is due to the dopant effect which enhances the Cdl value and causes the decrease in the RCt value [34,35] The performance of the positive electrode is thus enhanced by reducing the resistance within the MgO electrode with the Eu dopant compared to the Ca dopant as indicated by the EIS results The comparison of the electrochemical behavior of MgO NPs in the context with previous works is tabulated in Table Table2 EIS fitted circuit parameters of RCt and Cdl values Name of the electrode RCt (U) Cdl (F) MgO (L) MgO eCa (L) MgO eEu (L) 68.67 63.65 47.64 0.0001827 0.0002754 0.002665 63 where u is the angular frequency in rad∙sÀ1, Y and n are adjustable parameters of the constant phase element (Q1) The value of n ¼ corresponds to the double layer capacitance, n ¼ corresponds to the resistance and n ¼ 0.5 corresponds to the Warburg diffusion The equivalent circuit for the Nyquist plots of the impedance measurements of the different MgO samples is shown in Fig In the given circuits, the solution resistance corresponding to Rs is in the high-frequency region intercepting the semicircle on the real axis of the Nyquist spectrum by providing the resistance at the electrodeeelectrolyte interface These semicircles are attributed to an interfacial charge transfer resistance (Rct) or a ypolarization resistance (Rp) and the double-layer capacitance (C) connected to each other in a parallel circuit Further, the Warburg element W is shown by a straight line in the low-frequency region in the Nyquist spectrum [30] The diffusion of zinc ions from the electrolyte as well as the electrons from the working electrode into the pores on the surface of the MgO electrodes are represented by W [29] During the transition from the highfrequency semicircle to the mid-frequency point, the electrolytic diffusion of ions takes place Q represents the constant phase element which is parallelly connected to the charge-transfer resistance (Rct) and is also parallel to the leakage resistance (Rl) [31] The charge transfer resistance (Rct) and the double layer capacitance (Cdl) quantitatively determine the semicircle at high frequencies as evidenced from the Nyquist plots From these plots, it is clear that the charge transfer resistance decreases in the electrode B, followed by an 3.6 Antibacterial activity of phytonanofabricated magnesium oxide nanoparticles The present study focuses on the pathogenic bacteria that are typically nominated, cataloged and standardized strains with the significant medical significance These pathogenic microorganisms are accountable for numerous diseases, cases of hospital infection, Table Comparison of CV characteristics of MgO NPs Sl no Method and fuel used Precursor Morphology Current in CV Reference Neem extract Orange peel extract Chemical method Hydrothermal method W somnifera extract Mg(NO3)2 Mg(NO3)2 Mg(NO3)2 MgCl2 Mg(NO3)2 90 nm spherical NPs 90 spherical NPs 80 spherical NPs 200 nm wide and 30 nm thick platelets 50-70 Granular spherical NPs 25 mA 65 mA 75 mA 20 mA 0.3e1 mA [28] [28] [28] [33] This work Table Inhibition zone of phytonanofabricated MgO nanoparticles from W somnifera extracts on selected human pathogens (Inhibition zone measured in mm) Pathogens Concentration of Mgo NPs (mg/mL) MgO MgO: Ca 25 E coli P aeruginosa B cereus S aureus 5.01 6.09 5.09 4.09 ± ± ± ± 0.21 0.14 0.14 0.14 50 100 10.90 ± 0.19 11.23 ± 0.12 9.09 ± 0.42 7.08 ± 0.33 15.56 17.09 12.90 11.13 MgO: Eu 25 ± ± ± ± 0.43 0.33 0.15 0.76 3.53 7.42 4.74 3.20 50 ± ± ± ± 0.71 0.62 0.15 0.26 8.45 9.05 7.90 6.90 100 ± ± ± ± 0.55 0.31 0.56 0.72 12.26 13.98 12.63 10.56 25 ± ± ± ± 0.48 0.70 0.21 0.21 4.56 3.39 2.48 6.61 50 ± ± ± ± 0.60 0.53 0.78 0.89 9.52 7.91 5.56 9.02 100 ± ± ± ± 0.48 0.72 0.10 0.19 11.82 12.01 14.21 13.39 ± ± ± ± 0.19 0.65 0.81 0.43 Table Antibacterial effect of phytonanofabricated MgO nanoparticles from W somnifera extracts on selected pathogenic bacterial strains- Gram-negative: Escherichia coli and Pseudomonas aeruginosa; Gram-positive: Bacillus cereus and Staphylococcus aureus (Concentration expressed as mg/mL) Samples Antimicrobial activity Escherichia coli Pseudomonas aeruginosa Bacillus cereus Staphylococcus aureus MgO MIC MBC MIC MBC MIC MBC 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 2.5 25 MgO: Ca MgO: Eu 64 H.R Raveesha et al / Journal of Science: Advanced Materials and Devices (2019) 57e65 Fig Antibacterial sensitivity test by MIC and MBC using the microdilution technique (a) on selected pathogenic bacteria (b)-Escherichia coli (Ec); Pseudomonas aeruginosa(Pa); Bacillus cereus (Bc) and Staphylococcus aureus(Sa) The first well was first 25 mg/ml and then diluted 10 times in each further well sequentially up to the 8th (0.0000025 mg/ml) PCPositive control, NC-Negative control colonization of medical devices, and also testified for the ability to acquire resistance [36,37] Additionally, they are the bacterial strains commonly used in studies of the antibacterial activity of green synthesized NPs The relative antibacterial activity of the MgO suspensions against the Gram-positive and the Gram-negative pathogens was studied qualitatively through the disk diffusion and quantitatively in terms of the MIC and the MBC The microbicidal values of the biosynthesized MgO-NPs suspensions are given in Table below with the concentration range being 25e100 mg/mL Furthermore, MgO nanoparticles are effective against the Gram-Negative with 3e17 mm and against the Gram-positive bacteria 5e14 mm, respectively of the inhibition zone These results are in agreement with the qualitative antimicrobial assessment of MgO-NPs The growth inhibition was measured to assess the antibacterial activities of the MgO NPs against the Gram-negative and the Gram-positive pathogens The MIC of an antibacterial compound for a given bacteria is the lowermost concentration necessary to prevent the bacterial growth in a standard test MBC is the minimal concentration of drug that is lethal to the inoculum and can be determined from the MIC broth tests by subculturing to the agar media without the antibiotics or any antimicrobials The MIC and MBC values of all synthesized MgO NPs materials against bacteria are shown in Table MgO NPs shows a significant inhibition against E coli, P aeruginosa, B cereus and S aureus with discrete differences in the susceptibility to the MgO NPs in a dose-dependent manner Fig 8(b) MICs detected was 2.5 mg/mL and MBC values was 25 mg/mL for all the four bacterial pathogens tested The MICs observed for the Gram-positive bacteria (B cereus and Staphylococcus) and for the Gram-negative bacteria (E coli and P aeruginosa) with nanoparticles prepared with W somnifera plant extract (60 ml), also reveal a higher potency compared to all other conditions (Table 5) However, the doping of MgO NPs with Ca and Eu did not show any significant difference in the antibacterial effect both on Gram-positive and Gram-negative bacterial pathogens [38] In relation to the MBC test, all four bacterial pathogens viz., E coli, P aeruginosa, B cereus and S aureus show a higher susceptibility to the MgO NPs at 25 mg/mL with nanoparticles prepared with plant extract (60 ml of W somnifera extract) Conclusion The phytonanofabrication of the MgO NPs is successfully done through the green solution combustion method using the W Somnifera leaf extract The Periclase natured the cubic MgO NPs constituted of the strong Mg-O stretching vibrations as confirmed by FTIR spectrum The energy band gap has been found using UVVisible adsorption studies is to be about eV EIS studies show that there exist contributions from both the grain as well as the grain boundaries to the impedance of the prepared MgO NPs which was verified by the Nyquist plot Eu3ỵ doped MgO NPs have shown the enhancement of the positive electrode performance and hence improved the electrochemical behavior of the MgO NPs In addition, MgO NPs have shown the considerable antibiosis against various pathogenic microorganisms Conflict of interest No conflict of Interest References [1] G Karunakaran, M Jagathambal, V Manickam, S.K Govindan, E Kolesnikov, A Dmitry, D Kuznetsov, Hydrangea paniculata flower extract-mediated green synthesis of Mg NPs and Ag NPs for health care applications, Powder 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