The electrochemical behavior, antifungal and cytotoxic activities of phytofabricated MgO nanoparticles using Withania somnifera leaf extract

The antibiosis of different microbial strains, cyclic voltammetry and electrochemical impedance spectroscopy for energy storage ap- plications havent been carried out using the as-obtain[r]

Original Article

The electrochemical behavior, antifungal and cytotoxic activities of

phytofabricated MgO nanoparticles using Withania somnifera leaf

extract

H.R Raveeshaa, S Nayanaa, D.R Vasudhaa, J.P Shabaaz Begumb, S Pratibhac,

C.R Ravikumarad, N Dhananjayac,*

a Department of Botany, Bangalore University, Bengaluru, 560 056, India

b 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

a r t i c l e i n f o

Article history:

Received 19 November 2018

Received in revised form

11 January 2019

Accepted 14 January 2019

Available online 22 January 2019

Keywords:

MgO NPs

Withania somnifera

Green

Combustion

Antibiosis

Cyclic voltammetry

a b s t r a c t

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 cm
1 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/)

1 Introduction

Among various metal oxides MgO has gained keen interests due

to its non-toxic, ecofriendly nature, the availability of greater

spe-cific 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 thefields of medicine, catalytic

applications, energy storage, bio sensing as well as electrochemical

sensing applications has given a new directionality for the

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 Gram-negative 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 mem-branes probably by the creation of reactive oxygen species (ROS), such as superoxide and hydroxyl radicals As a nanoparticle ap-proaches 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 prod-ucts, water purification and also in pharmaceutical products

* Corresponding author.

E-mail address: ndhananjayas@gmail.com (N Dhananjaya).

Peer review under responsibility of Vietnam National University, Hanoi.

Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices

j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d

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

Journal of Science: Advanced Materials and Devices 4 (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

Ayur-vedic medicines The major phytochemical components present are

withanolides which are actually triterpene lactones, such as

with-aferin A, alkaloids, steroidal lactones, tropine, and cuscohygrine

The antibiosis of different microbial strains, cyclic voltammetry and

electrochemical impedance spectroscopy for energy storage

ap-plications havent been carried out using the as-obtained MgO NPs

2 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 andfinely chopped Briefly 50 g of leaf was

suspended in 500 ml of double distilled water and kept under

stirring in hot plate at 50C for 20 min The mixture was cooled to

room temperature andfiltered through Whattman paper The

fil-trates were stored in the refrigerator at 4C 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

pre-heated muffle furnace at 400 ± 10C The reaction was completed

within 5e10 min to obtain a white colored powder material The

obtained powders were subjected to calcination in a muffle furnace

at 400 C for 3 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

1 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 sub-jected to calcination at 400C for 3 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 mon-ochromatized Cu-Ka(1.5418Å) radiation The morphological fea-tures are obtained by a Carl Zeiss Ultra 55 scanning electron microscope (SEM) and a JEOL JEM 3010 transmission electron mi-croscope (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 voltam-metry (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 elec-trode (3.0 mm in diameter), a platinum wire counter elecelec-trode and

a saturated Ag/AgCl reference electrode The carbon paste electrode was prepared as follows: 70% graphite powder (particle size 50mm 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
1.6 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 Gram-positive 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 (Hi-Media, Mumbai, India) in petri plates and incubated for 24 h in aerobic conditions at 37C All glasswares used were sterilized by autoclave at 121C for 15 min before being used in the experi-ments 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 Erlenmeyerflask These flasks were then incubated at 37C at 200 rpm stirring for (24± 2) h Consequently, a bacterial suspension with an optical density of McFarland of 0.5 (1 108CFU/mL) was made separately with the isotonic solution of NaCl (0.85%) These stock solution of bacteria were diluted further ten times (1 107CFU/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 4 (2019) 57e65

2.6.3 Disc diffusion method (qualitative analysis)

In the present study, examinations of in vitro antimicrobial

ac-tivities 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 108colony forming units of each

bacterium were inoculated onto a plate Previously prepared

sam-ples impregnated on discs (6 mm) at the various concentrations

were placed aseptically on plates inoculated with bacteria and

incubated at 37C 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

syn-thesized 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

1  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

chlo-ride[10] MgO NPs stock suspension was prepared by resuspending

the nanoparticles in Type I (milli-Q) water to get afinal

concen-tration of 100mg/mL; the suspension was kept at 4C until further

use Later, the aliquot was subjected to sonication and the

sus-pensions 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 0.025mg/mL to 25mg/mL

The similar method was performed tofind the MIC of the positive

(tetracycline) and negative controls Tetracycline (25mg/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 20mL of the

bacterial suspension (107CFU/mL) was added to each microtitre

well and incubated at 37C 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 37C for

60 min 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

determina-tion was done by using 50mL of cultured aliquots (without INT) that

was streaked onto the Mueller-Hinton (MH) agar in a petriplate and

incubated for 24 h at 37C The lowest concentration that indicated

the complete absence of the bacterial growth on MH agar surface

was considered as the MBC

3 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

particle size of the synthesized materials was obtained using the DebyeeScherrer's formula,

where, K is constant (0.9),lis the wavelength (l¼ 1.5418A),bis full width at half maximum intensity (FWHM) and q is the half diffraction angle

Fig 1shows 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 corre-sponding 2qvalues 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 1 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,

(this is the experimental d value which depends on the 2qvalues measured experimentally) and the lattice parameter‘a’ was ob-tained by substituting the value of‘d’ in the equation,

1

d2¼h2þ k2þ l2

where, (hkl) refer to the Miller indices Since we have a cubic Per-iclase MgO system all the lattice parameters are same The small variation in d spacing and the lattice constant due to doping is tabulated inTable 1

Fig 1 XRD patterns of MgO nanoparticles synthesized using the W somnifera leaf H.R Raveesha et al / Journal of Science: Advanced Materials and Devices 4 (2019) 57e65

3.2 Scanning electron microscopy and transmission electron

microscopy studies

The SEM studies were carried out with an accelerating voltage of

20 KV to determine the morphology of the particles These

mi-crographs are as shown inFig 2 Both SEM and TEM depict the

agglomerated granular structure The diameters of the MgO NPs

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 andflaws 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 Ca2þand Eu3þ(1 mol %) we cannot observe the peaks corresponding to them in EDX patterns

3.3 Fourier transforms infra-red spectroscopy FTIR spectra are helpful in the molecular structure analysis and have been recorded in the wave number range 400 cm
1 to

4000 cm
1as shown inFig 3

The FTIR studies revealed broad peak at 3430 and a peak at

1606 cm
1which are attributed to the eOH bending and stretching

Table1

Lattice parameters.

Sample details (hkl) d-Spacing (Å) (experimental) Lattice constant (Å)

H.R Raveesha et al / Journal of Science: Advanced Materials and Devices 4 (2019) 57e65

vibrations originating from adsorbed water molecules and surface

hydroxyl groups that were strongly perturbed by the hydrogen

bonding[23] The broad peak at 419 cm
1corresponds to the MgeO

stretching vibrations[24] The broadness of the absorption band at

3600e3200 cm
1in the spectra of MgO NPs confirmed a high

de-gree 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

prop-erty of synthesized MgO NPs was examined using an UV-visible

spectrophotometer and the outcomes are shown inFig 4 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 byfitting 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]

ahy¼ A
hy
Eg

1

(4)

where“A” is an energy independent co-efficient and Egis the

op-tical band gap The absorption co-efficientais defined as

a¼2:303  103 AP

In order to determine the optical band gap, we have plotted

(ahn)2as a function of photon energy as shown in the inset ofFig 4

This plot gives us straight line as shown infigure The optical band

gap was determined by extra plotting the linear portion of the plot

(ahv)2¼ 0 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

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 mo-lecular 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 inFig 5 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 Mg0into

Mg2þwhereas the cathodic peak indicates the reduction of Mg2þ 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

1 Hz to 1 MHz with the AC amplitude of 5 mV at the steady state The Nyquist plots for the pure and the Ca and Eu doped MgO samples are shown inFig 6

The impedance of the electrodes is given by:

where, j ¼pffiffiffiffiffiffiffi
1, Zʹ and Zʹʹ are the real and imaginary parts of the impedance

Fig 3 FTIR spectra of (a) W somnifera leaf extract, (b) MgO, (c) MgO: Ca and (d) MgO:

Eu nanoparticles Fig 4 UV-Visible spectra with the insets showing Tauq's plots.

H.R Raveesha et al / Journal of Science: Advanced Materials and Devices 4 (2019) 57e65

Also, Z0¼ R and Z00¼c¼ 1

uC[29] R is the resistance andcis 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

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, tofit the data into an equivalent circuit, a model containing a constant phase element (Q1) should be used The impedance of Q1is described[29]as

Fig 5 Cyclic voltammetric studies of pure MgO sample and Ca and Eu doped MgO samples.

Fig 6 Nyquist plot for the pure MgO sample and the Ca and Eu doped MgO samples.

Fig 7 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 4 (2019) 57e65

whereuis the angular frequency in rad∙s
1, Y and n are adjustable

parameters of the constant phase element (Q1) The value of n¼ 1

corresponds to the double layer capacitance, n¼ 0 corresponds to

the resistance and n¼ 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 inFig 7 In the

given circuits, the solution resistance corresponding to Rsis 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

elec-trodes are represented by W[29] During the transition from the

high-frequency semicircle to the mid-high-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)

quan-titatively 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

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 intercala-tion/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 diam-eter 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 2lists the EISfitted circuit parameters of RCtand Cdlrelated

to the prepared MgO electrodes and these parameters were obtained

byfitting the experimental data according to the equivalent circuit The decrease in RCtand the increase in Cdlindicate that the electro-chemical 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 Cdlvalue and causes the decrease in the RCtvalue [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 inTable 3

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,

Table2

EIS fitted circuit parameters of R Ct and C dl values.

Name of the electrode R Ct (U) C dl (F)

Table 3

Comparison of CV characteristics of MgO NPs.

4 Hydrothermal method MgCl 2 200 nm wide and 30 nm thick platelets 20mA [33]

5 W somnifera extract Mg(NO 3 ) 2 50-70 Granular spherical NPs 0.3e1 mA This work

Table 4

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)

E coli 5.01 ± 0.21 10.90 ± 0.19 15.56 ± 0.43 3.53 ± 0.71 8.45 ± 0.55 12.26 ± 0.48 4.56 ± 0.60 9.52 ± 0.48 11.82 ± 0.19

P aeruginosa 6.09 ± 0.14 11.23 ± 0.12 17.09 ± 0.33 7.42 ± 0.62 9.05 ± 0.31 13.98 ± 0.70 3.39 ± 0.53 7.91 ± 0.72 12.01 ± 0.65

B cereus 5.09 ± 0.14 9.09 ± 0.42 12.90 ± 0.15 4.74 ± 0.15 7.90 ± 0.56 12.63 ± 0.21 2.48 ± 0.78 5.56 ± 0.10 14.21 ± 0.81

S aureus 4.09 ± 0.14 7.08 ± 0.33 11.13 ± 0.76 3.20 ± 0.26 6.90 ± 0.72 10.56 ± 0.21 6.61 ± 0.89 9.02 ± 0.19 13.39 ± 0.43

Table 5

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 asmg/mL).

Samples Antimicrobial activity Escherichia coli Pseudomonas aeruginosa Bacillus cereus Staphylococcus aureus

H.R Raveesha et al / Journal of Science: Advanced Materials and Devices 4 (2019) 57e65

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

syn-thesized NPs The relative antibacterial activity of the MgO

suspen-sions against the Gram-positive and the Gram-negative pathogens

was studied qualitatively through the disk diffusion and

quantita-tively in terms of the MIC and the MBC The microbicidal values of the

biosynthesized MgO-NPs suspensions are given inTable 4below with

the concentration range being 25e100mg/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

con-centration 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

sub-culturing to the agar media without the antibiotics or any

antimi-crobials The MIC and MBC values of all synthesized MgO NPs

materials against bacteria are shown inTable 5 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 mannerFig 8(b) MICs detected was 2.5mg/mL

and MBC values was 25mg/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

suscep-tibility to the MgO NPs at 25mg/mL with nanoparticles prepared

with plant extract (60 ml of W somnifera extract)

4 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 UV-Visible adsorption studies is to be about 5 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 Eu3þdoped MgO NPs have shown the enhancement of the positive electrode performance and hence improved the electrochemical behavior of the MgO NPs In addi-tion, MgO NPs have shown the considerable antibiosis against various pathogenic microorganisms

Conflict of interest

No conflict of Interest

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