A Green Method for Silver Nanoparticle Synthesis Using H. isora

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The development of methods for the large-scale production of nanoparticles has become of intense interest to researchers in recent years.
In the quickly developing field of nanomedicine, metals such as silver, gold and platinum are used to synthesize metal nanoparticles that show good potential for applications in pharmacology and medicine. Silver nanoparticles, with their potent antimicrobial activity are of particular interest.
Various methods exist for the synthesis of nanoparticles, but these techniques involve the use of toxic chemicals, presenting a problem in terms of hazardous by-products and environmental pollution.
As an alternative, researchers have been using “green” methods to synthesize the particles, using plant extracts. Many of the plants so far used have demonstrated several medicinal properties and some have shown in vitro antioxidant and antibacterial activities.
One of the plant extracts that has recently been reported on in the journal Applied Nanoscience is Helicteres isora, a fruit which has previously been shown to exhibit anticancer, antihyperglycemic, insulin-sensitizing and hypolipidemic activities.

Researchers from Bharathidasan University and Rajah Serfoji Government College have managed to synthesize silver nanoparticles using aqueous H. isora root extract.
S. Bhakya and team washed and dried the roots before turning them into powder using pestle and mortar. The nanoparticles were made by mixing aqueous silver nitrate solution with the root extracts and incubating at room temperature for six hours. The particles were then collected by centrifugation.

Figure 1. UV–Vis spectra of synthesized AgNPs using root extract: a extract; b color changed after adding AgNO3; c different incubation times

UV-visible spectroscopy confirmed the synthesis of silver nanoparticles and Fourier transform infrared spectroscopy showed that the extract served as both a reducing and stabilizing agent. Transmission electron microscopy and X-ray diffraction analyses revealed that the nanoparticles were crystalline in nature and were an average size of 30 to 40 nm.
On testing for antioxidant activity, a DPPH scavenging assay showed that the nanoparticles had effective inhibition activity, compared to the standard antioxidant, butylated hydroxytoluene (BHT).
Using ascorbic acid as a standard, the hydrogen peroxide scavenging activity of the nanoparticles was tested, which showed the concentrations at 100 µg/mL inhibition were 93.31% for the AgNPs compared with 85.35% for ascorbic acid.
The nanoparticles showed a concentration-dependent activity in nitric oxide scavenging activity, with the greatest activity being 80.46%, at a concentration of 100 µg/mL, although this was less than the activity observed for BHT, which was 81.35%.
Using the disc diffusion method, the team showed that the nanoparticles displayed high antibacterial activity against both Gram-negative and Gram-positive bacteria. This activity was higher against S.typhi and P.aeruginosa than against M. luteus and B. subtilis, possibly owing to the difference in cell wall structure between Gram-positive and Gram-negative bacteria.

Figure 2. Antibacterial effects of green synthesized AgNPs from H. isora

The authors say this green synthesis of silver nanoparticles using H.isora root extract represents an effective alternative to chemical and physical synthesis methods.
“H. isora root extract can be used efficiently in the production of potential antioxidant and antibacterial AgNPs for commercial application,” they conclude.
You can read the entire article here.

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