Exploring biomaterials/molecules as a reducing/capping agent for the synthesis of metal nanoparticles has set a new trend in green nanotechnology with improved environmental safety. Herein, a facile, one-pot, and green synthesis of silver nanoparticles (AgNPs) was achieved using Panax ginseng root extract that was obtained from the root powder as a cost-effective and environmentfriendly biomaterial. Optical, functional, and morphological characteristics of the synthesized AgNPs were determined using ultraviolet–visible (UV–vis), Fourier transform infrared (FTIR) spectrophotometers, transmission electron microscopy (TEM), and atomic force microscopy (AFM). The synthesized AgNPs were used for the detection of Hg2+ by obtaining the absorption spectrum of the compound as a function of Hg2+concentration, which resulted in a decrease in absorption peak intensity with a slight blue shift. The AgNP solution decolored upon dissolution due to the formation of an Ag–Hg amalgam. The sensing characteristics were found to be linear when tested from 10 μM to 1 mM Hg2+ concentration and the detection limit was estimated as 5 μM. To check the selectivity of the sensor towards Hg2+, the sensor response was measured for different heavy metals such as K+, Na+, Cu2+, Ni2+, Ca2+, Zn2+, Mg2+, and Mn2+, at 10 mM concentrations.