Novel silver nano-wedges for killing microorganisms

doi:10.1016/j.materresbull.2011.07.040

Materials Research Bulletin

Volume 46, Issue 11, November 2011, Pages 1860-1865

https://doi.org/10.1016/j.materresbull.2011.07.040 Get rights and content

Abstract

In the current study, for the first time, photochemical facile green synthesis of salep capped silver nano-wedges was reported via the wet chemical synthesis procedure. Sunlight-UV as an available reducing agent caused mild reduction of silver ions to the silver nano-wedges. Salep as an effective capping/shaping polysaccharide bioresource material was used in the reaction medium and caused creation of flower-like self-assembled structures of the silver nano-wedges. The formation of silver nano-wedges and their flower-like self-assembled structures was confirmed by SEM technique. Further investigations were carried out using UV–vis, FTIR, GPC and XRD data. The prepared silver nano-wedges showed potent biocidal activity against three classes of microorganisms (Escherichia coli Gram-negative bacteria, Staphylococcus aureus Gram-positive bacteria and Candida albicans fungus). The silver nano-wedges prepared with this method can be introduced as real poniards because of their unique shape and antibacterial/antifungal activity and would be promising nominees for a wide range of biomedical applications.

Graphical abstract

Highlights

► For the first time, green synthesis of salep capped Ag nano-wedges was reported via the wet chemical synthesis method. ► Salep, a capping/shaping polysaccharide composite, resulted in synthesis of the Ag nano-wedges. ► Biomedical activity of the Ag nano-wedges introduces these poniard-like materials as a forceful biocide.

Introduction

During the fast growth of nanoscience in the recent decade, bionanotechnology as a leading science plays important role in the development of biosynthetic and eco-friendly approaches for the synthesis of nanostructures. Silver nanoparticles (Ag-NPs) are promising agents in the bionanotechnology, because of their unique activity against unfavorable processes in bioscience. The Ag-NPs have been widely used in wound dressing; wound healing, water treatment filters, inks, sensors, catalysts, cosmetics, orthopaedics, surgical instruments and vascular prosthesis. Ever-increasing applications of these real silver bullets [1] in biomedical field are due to the anti-bacterial [2], anti-fungal [3], anti-viral [4], anti-platelet [5], anti-proliferative [6], anti-inflammatory (apoptosis detection) [7] and anti-angiogenesis properties (cancer therapy) [8].

Green synthesis of Ag-NPs possesses three main steps, which were evaluated by green chemistry perspectives, including selection of solvent medium, environmentally benign reducing agent and nontoxic capping agent [9]. For the biological green synthesis of Ag-NPs, many bacteria, fungi and plants are found as arsenals of Ag-NP synthesizer [10]. In wet chemical synthesis, various bioresource materials such as starch [11], dextran [12], sodium alginate [13], chitosan [14], gum acacia [15], gum arabic [16], carboxymethyl cellulose [17], carboxymethyl curdlan and carboxymethyl fucoidan [18] were used as capping agents for the green synthesis of Ag-NPs. In the category of proteins and their derivatives, wool keratin [19], gelatin [20], gelatin-g-poly (methyl methacrylate) white emulsion [21], bovine serum albumin (BSA) and poly-l-lysine (PLL) [22], and oligonucleotide based on DNA [23] were utilized for stabilization of Ag-NPs in solution or synthesis of hybrid nanomaterial Ag-NP conjugates.

Salep [24] is a multi-component polysaccharide (Supplementary information, p. 1) which can be obtained from dried tubers of certain natural terrestrial orchids and has been used as curative matter for many years because of its nutritive and demulcent properties. In the recent years, several unique soft materials based on salep [25], [26] have been synthesized and their applications as carrier matrix for colonic delivery of tetracycline hydrochloride [27] and nanoreactor for preparation of hematite nanoparticles [28] have been developed. There are two kinds of salep growing in Iran. The first one has branched or palmate and another one has rounded or unbranched tubers. Palmate-tuber salep (PTS) contains more glucomannan (∼58%) [29], hence was chosen for the present study. Glucomannans are natural, neutral and water-soluble fibers, which can assist to normalize blood sugar, relieve stress on the pancreas, preventing of chronic diseases and discourage blood sugar abnormalities such as hypoglycemia.

In the current study, silver nano-wedges (Ag-NWs) were synthesized in aqueous solutions at room temperature based on the main principles of the green synthesis, using sunlight-UV as facile nontoxic reducing agent. Salep, a fully biocompatible capping/shaping polysaccharide, brought about stabilization of the Ag-NWs in solution and caused formation of flower-like self-assembled structures. So far, there are not any data in the literature claiming Ag-NW synthesis and this is the first report on preparation of ones. Biomedical activity of these Ag-NWs including bactericidal (against Escherichia coli and Staphylococcus aureus) and fungicidal (against Candida albicans) assays introduces these poniard-like materials as a forceful biocide for killing of microorganisms.

Section snippets

Materials

The palmate-tuber salep (PTS) was purchased from a supplier in Kordestan, Iran (M_n = 1.17 × 10⁶ g/mol, M_w = 1.64 × 10⁶ g/mol (high M_w), PDI = 1.39, eluent = water, flow rate = 1 mL/min, acquisition interval = 0.43 s from GPC results). Silver nitrate (AgNO₃) was purchased from Merck (Germany) and all solutions were prepared using double distilled-deionized water.

Preparation of Ag-NPs

In the current work, Ag-NWs were synthesized via a facile reagent-free green method. For its preparation, 100 mg salep was poured into 10 mL tepid water at

Reaction mechanism

It is well known that ultrasonic waves, prolonged reflux, UV-irradiation, γ-rays and reducing agents can reduce the silver cations (Ag⁺) to the Ag-NPs in the presence of a capping agent. In this study, Ag-NWs have been prepared by the sunlight UV-irradiation. The sunlight-UV as a gratis source of reducing agent was applied and caused facile and inexpensive preparation of the Ag-NWs without any surplus material. Salep, as a multi-advantage (biocompatible, biodegradable and non-toxic effective

Conclusions

In summary, for the first time, we have developed a highly facile and inexpensive approach to prepare salep capped silver nano-wedges, which are stable in the aqueous solutions. It is predicted that this green synthesis procedure can be easily extended to other similar systems, which is valuable for the utilization of other bioresource materials. These Ag-NW poniard-like materials exhibited strong antimicrobial activity against E. coli and S. aureus bacteria and potent antifungal activity

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Novel silver nano-wedges for killing microorganisms

Abstract

Graphical abstract

Highlights

Introduction

Section snippets

Materials

Preparation of Ag-NPs

Reaction mechanism

Conclusions

Med. Chem. Commun.

Biotechnol. Adv.

Biometals

J. Nanobiotechnol.

ACS Nano

BMC Cell Biol.

Nanomed. Nanotechnol.

Biomaterials

Adv. Colloid Interface

Biotechnol. Adv.

Radiat. Phys. Chem.

Anal. Biochem.

Radiat. Phys. Chem.

Carbohydr. Res.

Radiat. Phys. Chem.

Colloid Surf. B

Mater. Chem. Phys.

Mater. Chem. Phys.

Bioresource Technol.

J. Appl. Polym. Sci.

Adv. Mater.

Nano Lett.

J. Food Eng.

Starch-Starke

J. Appl. Polym. Sci.

J. Photochem. Photobiol. B