Plant biomolecule-functionalized ultrasensitive silver nanoparticles for immediate sensing of mercury in wastewater

This study explores a time-effective, cost-effective, one-pot eco-friendly synthesis method for plant biomolecule-functionalized silver nanoparticles (AgNPs) using aqueous leaf extract of<i>Averrhoa carambola</i>L. The polyphenolic compounds naturally present in the leaves act as reducing agents for Ag ions. This environmentally friendly approach eliminates the need of toxic chemicals, external reducing or stabilizing agents, complex instrumentation and specialized technical expertise for a safe, cost-effective and sustainable method for AgNP synthesis in 15 min. The as-synthesized nanoparticles were characterized by transmission electron microscopy, field-emission scanning electron microscopy, x-ray diffraction, and UV-Vis, Fourier transform infrared and Raman spectroscopy. It was observed that the nanoparticles are spherical in shape with an average diameter of 20 nm and have a highly stable zeta potential value of -28.3 mV. The phytochemicals present in the leaf extract were identified by gas chromatography coupled with mass spectrometry. The yellow colloidal AgNP solution with a surface plasmon resonance peak at 416 nm immediately turns to colorless after adding Hg²⁺salt solution over other metal ions. Additionally, the effect of Hg²⁺concentration on AgNP absorption intensity was observed and the limit of detection of mercury was found to be 2.6<i>µ</i>M. Therefore, the proposed green route for biomolecule-functionalized AgNPs can be used for rapid detection of hazardous Hg²⁺even at trace concentration in wastewater.