The route from plants to silver nanoparticles. Elsevier 2020Plant extracts offer an easy, environmentally friendly way to make silver nanoparticles for possible medical, cosmetic and industrial applications.
Silver nanoparticles have antibacterial and medicinal applications, but existing methods for making them generate toxic residues and are time-consuming and expensive. In the journal Results in Materials researchers in India report a natural, non-toxic, easier and cheaper procedure, that uses the biosynthetic powers of plants to make the nanoparticles.
“The region of India where I live contains many plants whose medicinal properties have not been explored,” says research group member Amol Nande of Guru Nanak College of Science, explaining his interest in plant chemistry. This interest in local plants led Nande and his colleagues to also investigate the possibility of using plants for making metallic nanoparticles.
The researchers prepared extract of leaves from jackfruit (Artocarpus heterophylus) and neem or Indian lilac tree (Azadirachta indica) simply by boiling chopped leaves in water and collecting the soluble extract by filtration. When the extracts were mixed with silver nitrate solution and mildly heated at 50oC, silver atoms aggregated into nanoparticles that could be collected by centrifugation. The chemicals in the plant leaf extracts were acting as ‘reducing agents’ converting the silver ions (Ag+) in silver nitrate into silver atoms (Ag).
Electron microscopy indicated that the nanoparticles had a crystalline structure of between 20 and 45 nanometres diameter. The size seemed to depend on the precise conditions under which the coagulation into particle form occured. X-ray diffraction studies suggested that some of the silver became oxidised into silver oxide in the presence of air. The researchers also used Fourier-transform infrared spectroscopy to explore the ‘functionalisation’ of the particles: the process by which they bond with various chemical groups (‘functional groups’) in ways that can be expected to influence their properties. They found that some chemical functional groups could be used to limit the oxidation of the silver atoms back into silver ions.
Nande emphasizes that with no toxic chemicals required to prepare the nanoparticles, and no toxic residues produced, they are ready for direct use in medical and cosmetic applications. “Any residues that are present are likely to be biocompatible,” he says.
Silver nanoparticles are already used in medicine, as antimicrobial agents, drug delivery systems and in anti-cancer treatments. They are also used in shampoos, soaps, cosmetics and toothpastes. Having found their improved method for making them, the researchers next plan to explore the specific biological activities of their own nanoparticles, including antibacterial, anti-inflammatory, anti-diabetic and anti-cancer effects.
“Besides the potential biological applications it will be interesting to investigate the electrical, optical and other physical properties,” Nande adds. The wider opportunities in physical science applications might include the development of new catalysts and opto-electronic materials.
The team also plan to widen the scope of their biosynthetic method by exploring making iron nanoparticles from iron-rich spinach leaves. There is potentially a rich harvest of different nanoparticles to be gathered from the natural chemistry of plants.
Article details:
“Green synthesis of silver nanoparticles using plant leaf extraction of Artocarpus heterophylus and Azadirachta indica,” Results in Materials (2020)