Green Synthesized Silver and Gold Nanoparticles for Colorimetric Detection of Hg²⁺, Pb²⁺, and Mn²⁺ in Aqueous Medium

In this study, we report a simple and green method for the synthesis of l-tyrosine-stabilized silver (AgNPs) and gold nanoparticles (AuNPs) in aqueous medium under ambient sunlight irradiation. The nanoparticles (NPs) are characterized by UV–visible spectroscopy, high-resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), and dynamic light scattering (DLS) techniques. The size and shape of the metal NPs could be controlled by changing the concentration of the substrate, metal precursors, and pH of the medium. The synthesized AgNPs are found to be highly sensitive to Hg²⁺ and Mn²⁺ ions with the detection limit for both ions as low as 16 nM under optimized conditions. However AuNPs are found to be sensitive to Hg²⁺ and Pb²⁺ ions with a detection limit as low as 53 and 16 nM, respectively. The proposed method was found to be useful for colorimetric detection of heavy metal ions in aqueous medium