Over the past two decades, nanoparticles have been applied in a variety of industries, including energy, electronics, food, agriculture, cosmetics, bioremediation, and many more. In a new study, researchers have synthesized silver nanoparticles using a sustainable and environmentally safe method through the use of fruit waste. This study is available as pre-test in Materials Today: Proceedings.
Study: Sustainable synthesis of silver nanoparticles using fruit residues and their antibacterial activity. Image credit: Candle photo / Shutterstock.com
Various methods for nanoparticle synthesis
Previous studies describe hydrothermal, physical, biological, chemical, and sol-gel methods for synthesizing different types of nanoparticles. These studies have highlighted some of the limitations of available chemical and physical methods, including the high cost of production and use of harmful chemicals, which affect the environment and humans in the event of direct contact.
A biological process, also known as green nanoparticle synthesis, is an ecological process that does not require harmful chemicals. In addition, this method does not require external energy, is inexpensive, and is faster for large-scale nanoparticle development.
In green nanoparticle synthesis, scientists use natural reducing and stabilizing agents (capping). Interestingly, several metallic nanoparticles have been successfully developed, for example, gold, silver, and transition metals. In this process, plant extracts from the root, bark, leaf, stem, buds, flowers, fruits or latex can be used as a reducing agent to synthesize metal nanoparticles.
Typically, metal compounds are reduced by a reducing agent to produce nanoparticles. Some of the phytoconstituents of plant extracts, such as ketones, terpenoids, phenols, flavones, quinones, and a carboxylic acid, are associated with the conversion of metal compounds into their corresponding nanoparticles. Among the phytoconstituents, the researchers observed that flavones and quinones are water-soluble and have the highest reducing properties.
One of the drawbacks associated with green nanoparticle synthesis is the difficulty in controlling the monodisperse morphology of the nanoparticles produced. This is due to the varied function of various bioactive compounds present in the plant extract. The concentration of specific phytoconstants present in the plant extract has a significant effect on the production of nanoparticles.
Among various metal nanoparticles, silver nanoparticles have been widely applied in biomedical research due to their outstanding antimicrobial properties, high sensitivity, and catalytic properties. Several studies have shown that silver nanoparticles can inhibit many harmful pathogens. These studies have also shown that silver nanoparticles are highly effective against kanamycin, ampicillin, amphotericin, and amoxicillin.
Development of silver nanoparticles using fruit residues: a new study
In this study, researchers used the extracts of fruit residues from Artocarpus heterophyllus (jackfruit) and Punica granatum (pomegranate) as reducing agents for the synthesis of silver nanoparticles at room temperature. Some of the benefits of using fruit waste extract include easy availability, a low cost process, and non-toxicity.
The scientists first analyzed the production of silver nanoparticles by observing the color change of the reaction solution. The silver nanoparticles were produced five to six hours after the fruit residue extract was added to the silver ion solution. Recently synthesized silver nanoparticles were characterized by UV-Vis spectroscopy.
The researchers reported that the maximum absorbance peak occurred between 420 and 450 nm for both types of fruit residue extracts, which is the characteristic peak of silver nanoparticles. The average size of the nanoparticles determined by transmission electron microscopy (TEM) was consistent with dynamic light scattering (DLS) analysis reports. This finding implies that the silver nanoparticles produced were well dispersed in the solution.
The current study reported that the average size of silver nanoparticles synthesized using Punica granatum was 25 nm and Artocarpus heterophyllus was 15 nm. Interestingly, the researchers observed that the silver nanoparticles remained stable in solution even after fourteen days of their synthesis. This report was further confirmed by Zeta potential analysis, which showed a robust peak at 12.8 mV and 24.4 mV for nanoparticles produced with Punica Granatum and Artocarpus heterophyllus, respectively.
The electron diffraction pattern of the selected area (SAED) provided structural information of the synthesized nanoparticles. In this study, the scientists reported the presence of crystalline planes and therefore concluded that the newly synthesized silver nanoparticles contain a face-centered cubic structure.
Importantly, this study has shown that silver nanoparticles produced with Punica Granatum and Artocarpus heterophyllus showed strong antibacterial activity against E-coli, a Gram-positive bacterium that causes foodborne illness. Scientists observed that antibacterial efficacy improved with the improvement of the concentration of silver nanoparticles.
Concluding remarks
In this study, the researchers synthesized silver nanoparticles using extracts of fruit residues from Punica Granatum and Artocarpus heterophyllus. These extracts acted as reducing and stabilizing agents. The scientists claimed that this sustainable, environmentally friendly method could be used for large-scale synthesis of silver nanoparticles. It is important to note that this nanoparticle could be used effectively in biomedical applications, as it showed a strong antibacterial effect.
Reference
Rajput, H. et al. (2022) Sustainable synthesis of silver nanoparticles using fruit residues and their antibacterial activity. Materials Today: Proceedings. https://www.sciencedirect.com/science/article/pii/S2214785322034605
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