Synthesis of silver nanoparticles using Acalypha indica leaf extracts and its antibacterial activity against water borne pathogens

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Abstract

In the present study, biosynthesis of silver nanoparticles and its activity on water borne bacterial pathogens were investigated. Silver nanoparticles were rapidly synthesized using leaf extract of Acalypha indica and the formation of nanoparticles was observed within 30 min. The results recorded from UV–vis spectrum, scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) support the biosynthesis and characterization of silver nanoparticles. From high-resolution transmission electron microscopy (HRTEM) analysis, the size of the silver nanoparticles was measured 20–30 nm. Further, the antibacterial activity of synthesized silver nanoparticles showed effective inhibitory activity against water borne pathogens Viz., Escherichia coli and Vibrio cholerae. Silver nanoparticles 10 μg/ml were recorded as the minimal inhibitory concentration (MIC) against E. coli and V. cholerae. Alteration in membrane permeability and respiration of the silver nanoparticle treated bacterial cells were evident from the activity of silver nanoparticles.

Introduction

The development of reliable green process for the synthesis of silver nanoparticles is an important aspect of current nanotechnology research. Nanomaterials such as Ag, Au, Pt and Pd have been synthesized by different methods, including hard template [1], using bacteria [2], fungi [3] and plants [4]. Among these, silver nanoparticles play a significant role in the field of biology and medicine due to its attractive physiochemical properties. Klabunde et al. demonstrated that the highly reactive metal oxide nanoparticles exhibit excellent bactericidal action against Gram-positive and Gram-negative bacteria [5]. The strong toxicity of silver against wide range of microorganisms is well known and silver nanoparticles have been recently shown to be a promising antimicrobial material. Sondi et al. studied the antimicrobial activity of silver nanoparticles against Escherichia coli as a model of Gram-negative bacteria [6].

Interdisciplinary research has widened the horizons of material research, drawing new inspirations from biological systems. The towering environmental concerns had triggered the researchers to device novel methods of synthesizing the nanomaterials in biological systems such as bacteria, fungi and plants, termed as “green chemistry” approaches. Biosynthesis of silver nanoparticles using bacteria [7], [8], [9], fungi [10], [11], [12], yeast [13] and plants [14], [15], [16] were well documented. However, exploration of the plant systems as the potential nanofactories, has heightened interest in the biological synthesis of nanoparticles. Sastry et al. reported the biosynthesis of nanoparticles using plant leaf extracts and their potential application. They studied bioreduction of chloraurate ions and silver ions by extracts of geranium [17] and neem leaf [18]. Further, synthesis of gold nanotriangles and silver nanoparticles using Aloe vera plant extracts was reported [19]. Most of the above research on the synthesis of silver or gold nanoparticles utilizing plant extracts employed broths resulting from boiling fresh plant leaves. Whereas, Huang et al. exploited the synthesis of silver and gold nanoparticles using the sundried Cinnamomum camphora leaf extract [20]. Acalypha indica (Euphorbiaceae), a traditional medicinal plant of South India, has the source of bio-reductant and stabilizers. The present study was aimed to rapid synthesis of silver nanoparticles using aqueous leaves extract of A. indica and evaluates its antibacterial activity against water borne pathogens such as Escherichia coli and Vibrio cholerae. In addition, respiratory characteristics and membrane dynamics of the cells were studied to validate the antimicrobial activity of synthesized silver nanoparticles.

Section snippets

Materials

The healthy leaves of A. indica were collected from campus of University of Madras, India. AgNO3, MTT (methyl thiozolyl diphenyl-tetrazolium bromide) were purchased from Himedia Laboratories Pvt. Ltd., Mumbai, India. The bacterial cultures of E. coli (MTCC-443) and V. cholerae (MTCC-3904) were obtained from Microbial Type Culture Collection, Chandigarh, India.

Preparation of plant extract

Aqueous extract of A. indica was prepared using freshly collected leaves (10 g). They were surface cleaned with running tap water,

Results and discussion

Several approaches have been employed to obtain a better synthesis of silver nanoparticles such as chemical and biological methods. Recently, synthesis of silver nanoparticles using plant extracts getting more popular [22], [23]. Chandran et al. synthesized silver nanoparticles by using the Aloe vera extract at 24 h of incubation [19]. Similarly, in the present study silver nanoparticles were synthesized using leaves extract of A. indica. Interestingly, silver nanoparticles were synthesized

Conclusions

The biosynthesized silver nanoparticles using A.indica leaves extract proved excellent antimicrobial activity. The antimicrobial activity is well demonstrated with MIC, change in membrane permeability and respiration activity of bacterial cells treated with silver nanoparticles. Hence, the biological approach appears to be cost efficient alternative to conventional physical and chemical methods of silver nanoparticles synthesis and would be suitable for developing a biological process for

Acknowledgments

The authors convey their thanks to Director, CAS in Botany, University of Madras, for providing laboratory facilities. Thanks also due to Head of the Department of Geology, Nuclear Physics, University of Madras for providing SEM, XRD and EDS facilities. We thank SAIF, IIT-Madras, Chennai for HRTEM analysis.

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