Facile green synthesis of gold nanoparticles using leaf extract of antidiabetic potent Cassia auriculata

Abstract

A simple biological method for the synthesis of gold nanoparticles (AuNPs) using Cassia auriculata aqueous leaf extract has been carried out in the present study. The reduction of auric chloride led to the formation of AuNPs within 10 min at room temperature (28 °C), suggesting a higher reaction rate than chemical methods involved in the synthesis. The size, shape and elemental analysis were carried out using X-ray diffraction, TEM, SEM-EDAX, FT-IR and visible absorption spectroscopy. Stable, triangular and spherical crystalline AuNPs with well-defined dimensions of average size of 15–25 nm were synthesized using C. auriculata. Effect of pH was also studied to check the stability of AuNPs. The main aim of the investigation is to synthesize AuNPs using antidiabetic potent medicinal plant. The stabilizing and reducing molecules of nanoparticles may promote anti-hyperglycemic if tested further.

Introduction

Gold nanoparticles (AuNPs) are very important nanoscale materials that have been studied extensively as they exhibit completely new and improved properties when compared to the bulk metals. Novel methods involved in the preparation of nanoparticles of noble metals like gold has gained importance due to its remarkable size-dependant optical and electronic properties. Gold nanoparticles are unique due to their tunable Surface Plasmon Resonance (SPR); hence they are used in bio-labeling [1], biosensors devices for the detection of viruses and bacteria [2], biomedical science including drug delivery [3], tissue/tumor imaging, photo thermal therapy and immuno-chromatographic identification of pathogens in clinical specimens [4]. Due to the recent awareness of green chemistry, it has been concluded that gold nanoparticles are biocompatible, inert [5], bind readily to a large range of biomolecules such as proteins/enzymes [6], [7], DNA [8], amino acids [9], [10] and expose large surface area for the immobilization ion of such biomolecules and environmentally friendly chemicals. Biosynthesis of metal nanoparticles using natural products is an emerging area of nanoscience research. Natural environment is a rich source of crude untreated extracts of plants, marine organisms and microorganisms and it is crucial to investigate their properties. Based on the capping agents, environmentally benign AuNPs using biological components will have excellent effect in biomedical applications.

There are several reports on the use of natural material sources like plants [11], [12] and algae [13], [14] in the synthesis of gold nanoparticles. The microorganisms such as bacteria [15], fungi [16], [17] and yeast [18] have been exploited for toxic metals recovery via reduction of the metal ions. The integration of green chemistry principles to nanotechnology is one of the key issues in nanoscience research. In continuation of the efforts for synthesizing gold nanoparticles by green route, a facile, rapid and single-pot aqueous biosynthesis of gold nanoparticles using the leaf extract of Cassia auriculata (Tanners cassia) has been reported here. C. auriculata, a sacred shrub of India, is well-known for its medicinal use which is used for the treatment of diabetes, urinary disorders, ulcers, skin diseases and chronic fever [19]; its anti-hyperglycemic and anti-hyperlipidemic properties are also well-known [20]. The important ingredients of the extract are flavoniods, tannins, steroids, carbohydrates and amino acids. Functionalized AuNPs have applications in various fields such as biomedical, catalysis and DNA detection [21], [22], [23]. Application of AuNPs in these fields is dependent on the functionalization to synthesize nanoparticles with desired shape, size and monodispersity. Functionalized nanoparticles should be stable without undergoing degradation or partial oxidation. There are several physical and chemical methods for the synthesis of metallic nanoparticles that are followed by the material scientists currently [24] but the importance of the stabilizing biomolecules in the green synthesis and its stability has not been studied intensively. In the present investigation, the synthesis of gold nanoparticles emphasizes the potentiality of C. auriculata in reducing and stabilizing gold nanoparticles. The gold nanoparticles synthesized were characterized using UV–vis spectroscopy, FT-IR, XRD, SEM-EDAX and TEM analysis. The synthesis was carried out at room temperature (28 °C) and the nanoparticles formed were around 15–25 nm in size.