One-Step Green Synthesis of Gold Nanoparticles Using Black Cardamom and Effect of pH on Its Synthesis

Singh and Srivastava Nanoscale Research Letters (2015) 10:353 DOI 10.1186/s11671-015-1055-4 NANO COMMENTARY Open Access One-Step Green Synthesis of Gold Nanoparticles Using Black Cardamom and Effect of pH on Its Synthesis Ashwani Kumar Singh* and O. N. Srivastava Abstract In the present article, an effective, one-step, and environmentally benign protocol for the synthesis of gold nanoparticles has been discussed. The black cardamom extract is used as a reducing agent for HAuCl4.3H2O. In order to synthesize gold nanoparticles, an aqueous solution of HAuCl4.3H2O was mixed with an optimized concentration of black cardamom extract where 1,8-cineole is the dominant component. Choosing black cardamom extract as a reducing agent can be justified under the light of the fact that it has a very fast reducing ability. Gold nanoparticles with different shapes and sizes were synthesized by varying the ratio of AuCl4 ions to black cardamom extract. Kinetics of reactions has been evaluated through monitoring of surface plasmon behavior of gold nanoparticles as a function of time. Based on Fourier transform infrared spectroscopy (FTIR) studies, a tentative mechanism of reduction of Au nanoparticles has also been proposed which includes oxidation of 1,8-cineole to 2-oxo-1,8-cineole. Further, a comprehensive study to investigate the effect of pH on the synthesis of Au nanoparticles has been carried out. Keywords: Green synthesis; Gold nanoparticles; Natural precursor; pH effect Background Attaining of unique properties by tailoring the materials at atomic level can be achieved by the process of nanotechnology [1]. There have been impressive developments in the field of nanotechnology in the recent past years, with numerous methodologies formulated to synthesize nanoparticles of particular size and also of shape depending on specific requirement. Recently, a resurgence of interest in metal nanoparticles has resulted due to their potential applications in the emerging field of plasmonics [2–4]. Plasmonics uses the unique optical properties of metallic nanomaterials to manipulate the transfer of light on the nanoscale and is a promising technology for integrating the large datacarrying capacity of optical interconnects with nanoscale electronic devices. Metal nanoparticles are known to display tremendous potential for biological and chemical sensing [5–10] and cancer therapy [11]. They can serve as a model system to experimentally probe the effects of quantum * Correspondence: DST Unit on Nanoscience and Technology, Department of Physics, Banaras Hindu University, Varanasi 221005, India confinement on electronic, magnetic, and other fated properties [12–14]. They have also been widely exploited for use in photography [15], catalysis [16, 17], photonics [18], optoelectronics [19], information storage [20], surface-enhanced Raman scattering (SERS) [21–23], and formulation of magnetic ferrofluids [24]. Among various methods available for the synthesis of metal nanoparticles, laser evaporation and chemical reduction are the major ones [25]. However, each method has certain limitations. For example, the use of costly and sophisticated instruments and the problems associated with their handling in case of laser evaporation and also the yields of nanoparticles are quite low. Similarly, chemical reduction method may end up with the adsorption of some toxic chemical species on the surface even though gold nanoparticles are considered biocompatible which needs an additional step of removal of these toxic species. This may have some adverse effects in medical applications. Therefore, there is an urgent need to develop an environmentally benign nanoparticle synthesis protocol. This tempts the researchers in the field of nanoparticle synthesis and assembly to utilize some eco-compatible natural compounds for the © 2015 Singh and Srivastava. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Singh and Srivastava Nanoscale Research Letters (2015) 10:353 reduction of Ag- and Au-containing salts for the synthesis of Ag and Au nanoparticles [26, 27]. Recently, microorganisms mediated nanoparticle synthesis and gained much importance because of biocompatibility and facile assembly of nanoparticles [28–33]. Sastri et al. opened an avenue to the synthesis of metal nanoparticles by eukaryotic organisms [34, 35]. Later, they carried out extracellular synthesis of Ag and Au nanoparticles, using fungi [36–38]. They demonstrated that the shift from bacteria to fungi as a means of developing ‘natural nanofactories’ has the added advantage for the processing and handling of the biomass. Further, plant extracts have received considerable attention as an effective reducing agent for Ag- and Aucontaining salts to synthesize the Ag and Au nanoparticles. Jose-Yacaman et al. have reported the first living plant-mediated synthesis of silver and gold nanoparticles [39]. Similar biosynthesis of nanoparticles was achieved by Sastri et al. by using plant leaf extracts, and they explored further potential applications [40]. They studied bio reduction of silver ions and chloroaurate ions by the broth of geranium leaf [41] or neem leaf [42]. They also demonstrated the synthesis of gold nanotriangles from tamarind leaf extract and studied their potential application in vapor sensing [43]. Recently, some scientist synthesized the gold nanotriangles and silver nanoparticles, using aloe vera plant extract [44]. With this literature background, we herein report a novel, eco-compatible, and green synthesis of gold Fig. 1 XRD pattern of as-synthesized gold nanoparticles Page 2 of 12 nanoparticles from AuIII salts by using extract of black cardamom as a natural reducing agent. Black cardamom is widely used extensively in India, in foods, beverages, mouth fresheners, and native medicine. Black cardamom has been used as reducing agent in our synthesis protocols. Synthesis of gold nanoparticles by employing Black cardamom as a reducing agent and the effect of pH on synthesis have been discussed and described in this article. Experimental Details Materials and Methods HAuCl4.3H2O, procured from Sigma Aldrich and dried black cardamom easily available in commercial market, have been adopted as staring materials. These materials have been used without any further purification. Preparation of Black Cardamom Extract In the synthesis protocol adopted here, black cardamom has been used as a reducing agent, prepared by simply dipping 5 gm of it for 24 h into 100 mL of double-distilled water. The solid content was filtered out, leaving the residual extract of dark brownish color. This e (...truncated)