Research Highlight

Recipe for green antibiotic

doi:10.1038/nindia.2011.152 Published online 29 October 2011

New research has shown that guava leaf extract can be used to synthesize silver nanoparticles with better antibacterial activities than those synthesized through chemical processes. Using guava leaf extract is also an eco-friendly way of producing such nanoparticles.

Silver nanoparticles have drawn much attention because of their electrical and biological applications. Silver nanoparticles are also coveted nanomaterials for their antibacterial properties. To avoid the use of harmful chemicals when synthesizing such nanoparticles, researchers have used biological molecules such as vitamin C and microorganisms such as fungi.

Although these processes can be used to develop novel agents for synthesizing nanoparticles, none are capable of enhancing the quality of synthesis or the antibacterial activities of the resulting nanoparticles. To devise a better synthesis process, the researchers reduced silver ions to 'greener silver nanoparticles' (Gr-Ag-NPs) using guava (Psidium guajava) leaf extract. They then compared the antibacterial activities of Gr-Ag-NPs with chemically synthesized nanoparticles (Ch-Ag-NPs) for fighting samples of Escherichia coli over a period of 12 hours.

The Gr-Ag-NPs demonstrated better antibacterial activities than Ch-Ag-NPs. After five hours, the Gr-Ag-NPs were anchored onto the surface of bacterial cells, whereas the Ch-Ag-NPs were not. After eight hours, the Gr-Ag-NPs had ruptured the bacterial cell walls. By 12 hours, the Gr-Ag-NPs had entered the bacterial cells and stopped the replication of bacterial DNA, thus ushering in bacterial cell death.

The GR-Ag-NPs owe their better antibacterial activity to organic molecules such as tannins, eugenol and flavonoids present in guava leaf extract. These organic molecules remained attached to the surface of Gr-Ag-NPs, thereby enhancing their ability to anchor to and disintegrate bacterial cells. "Our study serves as a milestone for the development of novel antibacterial drugs based on silver nanoparticles," says lead researcher Anchal Srivastava.

The authors of this work are from: Department of Physics, Department of Zoology and Department of Microbiology, Banaras Hindu University, Varanasi, and Centre of Material Sciences, University of Allahabad, Allahabad, India, Department of Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, USA, and Department of Materials Science and Engineering, Norwegian University of Science and Technology, Trondheim, Norway.


  1. Parashar, U. K. et al. Study of mechanism of enhanced antibacterial activity by green synthesis of silver nanoparticles. Nanotechnology. 22, 415104 (2011) | Article | PubMed |