Colorimetric optical chemosensor of toxic metal ion (Hg2+) and biological activity using green synthesized AgNPs.

In this paper, we have reported the green synthesis of silver nanoparticles (AgNPs) using silver nitrate and Ficus carica (fig) stem extract at room temperature. We have also explored the effect of volume of extract (1-3 ml) on the formation of AgNPs using various analytical techniques such as Fourier-transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM), and energy-dispersive X-ray analyzer (EDX). The formations of AgNPs were monitored by ultraviolet-visible spectrophotometer as well as from color change through the naked eye. The absorption peaks appear between 442 and 455 nm, confirming to surface plasmon resonance (SPR) of AgNPs. It is clear from the FTIR results that the biologically active compounds present in the extract act as capping and reducing agents for AgNPs creation. Electron microscopy results show that by increasing the concentration of extract, the morphology and size of AgNPs changed due to the presence of more phenolic group. The green synthesized AgNPs have been sequentially employed for the selective and sensitive detection of toxic metal ion (Hg2+) in aqueous medium and antimicrobial activity against all tested microbes including five gram negative and two gram positive. Furthermore, the brown color of green synthesized AgNPs turned into colorless with Hg2+ ion by naked eye response and the limit of detection was 1.06 µM. Figure (A) represents the UV-visible spectra of AgNPs with different concentrations of Hg2+ (0.1-10 µM) in aqueous solution and inset shows the variation of the absorbance of AgNPs solution as a function of Hg2+ ion concentration. Figure (B) represents the images of color variations of AgNPs with different concentrations of Hg2+ (10−1-10−7 M) in aqueous solution. [ABSTRACT FROM AUTHOR]