Green synthesis of Ag nanoparticles using Tamarind fruit extract for the antibacterial studies

Highlights

• Highly stabilized colloidal silver nanoparticles (AgNPs) are produced.

• Tamarindus indica (Tamarind) fruit extract is first time used to synthesize AgNPs.

• Microwave oven is used for faster heating to synthesize AgNPs.

• A detailed study of antibacterial activities is discussed.

Abstract

In the present study, first time we report the microwave-assisted green synthesis of silver nanoparticles (AgNPs) using Tamarindus indica natural fruit extract. The plant extract plays a dual role of reducing and capping agent for the synthesis of AgNPs. The formation of spherical shape AgNPs is confirmed by XRD, HR-SEM, and HR-TEM. The presence of face-centered cubic (FCC) silver is confirmed by XRD studies and the average crystallite size of AgNPs is calculated to be around 6–8 nm. The average particle diameter is found to be around 10 nm, which is identified from HR-TEM images. The purity of AgNPs is confirmed by EDX analysis. The presence of sigmoid curve in UV–Visible absorption spectra suggests that the reaction has complicated kinetic features. To investigate the functional groups of the extract and their involvement in the reduction of AgNO₃ to form AgNPs, FT-IR studies are carried out. The redox peaks are observed in cyclic voltammetry in the potential range of − 1.2 to + 1.2 V, due to the redox active components of the T. indica fruit extract. In photoluminescence spectroscopy, the excited and emission peaks were obtained at 432 nm and 487 nm, respectively. The as-prepared AgNPs showed good results towards antibacterial activities. Hence, the present approach is a facile, cost- effective, reproducible, eco-friendly, and green method.

Introduction

Recently, nanomaterials have attracted researchers among the scientific world, because of their most important and peculiar properties which are different when compared with their bulk materials. Among them, noble metal nanoparticles, such as Ag, Au, Pt, and Pd nanoparticles are used in physical, chemical and biological applications [1], [2]. AgNPs represents a good candidate to carry out the nanostructured part of antibacterial and anticancer applications [3], [4], [5], [6], [7]. The properties of the nanomaterials are controlled by their shape, size and nature. AgNPs are highly in demand, because of its various applications in medicine, water treatment and catalysis. In general, colloidal dispersions lead to the formation of AgNPs and their morphology differ, based on the methods adopted for the synthesis [8], [9], [10]. The size and shape of AgNPs can be controlled by different synthesis methods, for example, are discharge, lazer CVD, physical adsorption and emulsion polymerization are used as common methods to prepare AgNPs. But, because of the usage of the toxic chemicals or solvents or non-biodegradable agents, these methods should be avoided. Without using the above said toxic chemicals as reducing or stabilizing agents, AgNPs cannot be prepared. Since, these methods are potential threats to the environment and biological systems; there is a need for a green synthesis to prepare eco-friendly AgNPs. The use of capping agents is also important. Since, as per thermodynamics, oxidation of AgNPs is not a favorable one, because of its higher positive reduction potential, which will lead to a stable condition in both aqueous and alcoholic medium.

Recently, green synthesis has gained importance over other physical and chemical methods, since, it offers environmental friendly, cheap, biocompatible, shape, and size controlled nanoparticles. The key aspect of nanotechnology is primarily aimed at the development of suitable and reliable synthesis routes, which in turn governs the size and shape, chemical composition and large scale production with better monodispersion for the synthesis of nanomaterials. Various synthesis methods are available in literature including green routes based on using plants, bacteria, and fungi, and they are given importance because of their non-toxic, economical and eco-friendly method of preparation and bio-compatible nature. Also, AgNPs prepared by using the above mentioned methods donot/less use of toxic chemicals, which makes them to be used in medical and pharmaceutical applications [11], [12], [13]. Also, AgNPs based antimicrobial packaging is a promising form of active food packaging, which plays an important role in extending shelf-life of foods and reduce the risk of pathogens. Also, the use of AgNPs as antimicrobial agents in food packaging is a mature technology, which concerns on the risks associated with the potential ingestion of the Ag ions migrated into food and drinks. This leads to a prudent attitude of food safety authorities [14]. There are reports available on the formation of AgNPs using plant extracts like Murraya koenigii leaf [15], Mangosteen leaf [16], Mangifera indica leaf [17], Jatropha curcas [18], Cinnamomum zeylanicum leaf [19], Camellia sinensis [20], Aloe vera [21], mushroom [22], and honey [23]. There are few reports on the preparation of AgNPs using fruit extract, such as papaya [24], tansy [25], pear [26], lemon [27] and goose berry [28]. The advantage of using plant and fruit extract includes the formation of stable nanoparticles without molecular aggregation even if they are stored for a longer time.

In our study, we have synthesized AgNPs using T. indica fruit, which is commonly known as Tamarind fruit. In general, Tamarind is sweet and sour in taste and has tartaric acid, sugar and vitamins. In traditional medicine and food, it is used as the main ingredient in general. Hence we have explained the synthesis of AgNPs using T. indica fruit extract without the addition of any external surfactant, capping agent or template. Thus, we have attempted a simple, non-toxic, eco-friendly and economically viable green synthesis of AgNPs, which stands stable for more than six months in the liquid form.