Characterization of green synthesized nano-formulation (ZnO–A. vera) and their antibacterial activity against pathogens

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Highlights

  • ZnO–A. vera nano-formulation has good biocompatible structure and optical properties.

  • ZnO–A. vera nano-formulation has enriched antibacterial activities to pathogens.

  • Antibacterial activities are possibly relevant to structure and optical properties.

  • This nano-formulation could be a significant antibacterial agent for pathogens.

Abstract

The application of nanotechnology in medicine has recently been a breakthrough in therapeutic drugs formulation. This paper presents the structural and optical characterization of a new green nano-formulation (ZnO–Aloe vera) with considerable antibacterial activity against pathogenic bacteria. Its particle structure, size and morphology were characterized by XRD, TEM and SEM. And optical absorption spectra and photoluminescence were measured synchronously. Their antibacterial activity against Escherichia coli and Staphylococcus aureus was also investigated using thermokinetic profiling and agar well diffusion method. The nano-formulation is spherical shape and hexagonal with a particle size ranging from 25 to 65 nm as well as an increased crystallite size of 49 nm. For antibacterial activity, the maximum inhibition zones of ZnO and ZnO + A. vera are 18.33 and 26.45 mm for E. coli, 22.11 and 28.12 mm for S. aureus (p < 0.05). Considering Pmax, Qt and k, ZnO + A. vera nano-formulation has a significant (p < 0.05) antibacterial effect against S. aureus almost at all concentration and against E. coli at 15 and 25 mg/L. ZnO + A. vera nano-formulation is much more toxic against S. aureus than E. coli, with an IC50 of 13.12 mg/L and 21.31 mg/L, respectively. The overall results reveal that the ZnO–A. vera nano-formulation has good surface energy, crystallinity, transmission, and enriched antibacterial activities. Their antibacterial properties are possibly relevant to particle size, microstructural ionization, the crystal formation and the Gram property of pathogens. This ZnO–A. vera nano-formulation could be utilized effectively as a spectral and significant antibacterial agent for pathogens in future medical and environmental concerns.

Introduction

Antibiotic resistance by bacteria is an increasing global public health concern (Ferro et al., 2003), and tremendous efforts have invested to developing novel antibacterial strategies against pathogenic bacteria. Recent advances in nanotechnology, particularly the ability to prepare highly ordered nanoparticles of any size and shape, have led to the development of new biocidal agents (Pasquet et al., 2014). Presently, nanotechnology has received considerable attention in the formulation of therapeutic drugs in medicine (Yang et al., 2009). There have been several reports of nanotechnology being used in the food and agriculture field, but the applications in drug delivery and pharmaceuticals remain relatively recent and limited (Pinto Reis et al., 2006). Nano-formulations are used as effective drug delivery systems due to their extremely small droplet sizes, high kinetic stability, low viscosity and optical transparency, which has made them very attractive in the pharmaceutical industry (Wang et al., 2007).

Metal nanoparticles have been studied extensively because of their exclusive catalytic, optical, electronic, magnetic and antimicrobial (Duran et al., 2005) and anti-inflammatory properties (Taylor et al., 2005). Among the metal oxide nanoparticles, ZnO has aroused high interest in pharmaceutical industry due to its good antibacterial activities against a broad spectrum of bacteria, low toxicity, and easy clearance (Pasquet et al., 2014, Sun et al., 2014). In relatively short period of time, several physical and chemical procedures have been used for the synthesis of large quantities of metal nanoparticles. Chemical methods lead to the presence of some toxic chemicals adsorbed on the surface that may have adverse effects in medical application (Jain et al., 2009, Gunalan et al., 2012). Therefore, development of clean, biocompatible, nontoxic and eco-friendly methods for nanoparticles synthesis deserves merit.

Currently, plant-mediated biological synthesis of nanoparticles is gaining importance due to its simplicity, eco-friendliness and extensive antimicrobial activity (Gunalan et al., 2012). Moreover, researchers are focused on the development of efficient eco-friendly methods for the synthesis of nano-formulations loaded with a variety of natural anti-bacterial agents with Aloe vera as a popular choice. A new method has been reported to produce In2O3 NPs with particle size of 5–50 nm using indium acetylacetonate and A. vera extract solution (Maensiri et al., 2008). This simple process using cheap precursors of A. vera extract provides high-yield nano-sized materials with well-defined crystalline structures and appropriate optical properties (Obonyo et al., 2012). This study therefore seeks to explore the formulation of phyto-nano blend as an effective anti-bacterial agent in an era of increasing resistance to antibiotics in respect of green medication.

Accordingly, this study is aimed to characterize the structural and optical properties of a biocompatible and environmentally friendly ZnO nano-formulation and assess its bactericidal performance impregnated with A. vera extract. This work further evaluates the antibacterial activity of the resulting nano-formulation against two pathogenic bacteria, Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, using agar well diffusion method and thermodynamic assay. Finally, the antibacterial mechanism of ZnO-doped A. vera nanoformulation is deduced.

Section snippets

Biosynthesis of ZnO–A. vera nanoformulations

ZnO nanomaterial was purchased from Sigma–Aldrich (St. Louis, MO, USA). The A. vera powder (purity >90%)was obtained from A. vera leaf extract solution using a freeze dryer by rapidly freezing the peel and then eliminating the water by sublimation according to the previous method (Asma et al., 2011). To obtain the ZnO–A. vera nanoformulation, 1 g each of the dried ZnO powder and A. vera was separately dissolved in 1.5 mL of deionized water (DW). Equal volume ratio of these two solutions were

Surface morphologies and structural properties

The SEM and TEM monographs in Fig. 1, Fig. 2 clearly show the distribution of ZnO nanoparticles prepared with or without A. vera extract. The images show the spherical shape and hexagonal nanoparticles as previous studies (Jalal et al., 2010, Sangeetha et al., 2011). The obtained nanoparticles were homogeneous and agglomerated with a particle size ranging from 25 to 65 nm with some deviations. The peculiar structures were analyzed in further details using high-resolution TEM analysis. Fig. 3(a)

Conclusion

This present work was preliminarily concerned about the structural and optical characterization of a new A. vera nano-formulation biosynthesized with ZnO nanoparticles, as well as its antibacterial activity against two morphologically variant pathogenic bacteria E. coli and S. aureus. The results indicated that ZnO + A. vera nano-formulation have good surface energy, absorption capacity, crystallinity, transmission, and enriched antibacterial activities. It could possibly be utilized as spectral

Conflict of interest

The authors declare that there are no conflicts of interest.

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Acknowledgments

This work is supported in parts by grants from the International Joint Key Project from National Natural Science Foundation of China (40920134003), the National Natural Science Foundation of China (41273092) and the National Outstanding Youth Research Foundation of China (40925010).

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