Mercury contamination emanating from anthropogenic activities has been a global problem. Thus, the development of cheap and efficient techniques for sensing mercury in aqueous solutions is of significance for the protection of humans and other organisms. The sensing of mercury using silver nanoparticles fabricated using phytochemicals extracted from Synadeum roots (SYR) is reported. The synthesis of silver nanoparticles (SYR-AgNPs) was confirmed by a strong plasmon resonance in the UV-Vis spectrum at 420 nm due to oscillations of electrons in the silver nanoparticles. The fabricated silver nanoparticles were used in the sensing of mercury ions from aqueous solutions. The addition of mercury changed SYR-AgNPs color to colorless, and the change was proportional to mercury concentration. The prepared silver nanoparticles displayed a high selectivity for the detection of mercury against other divalent metal ions (Hg²⁺, Ba²⁺, Mg²⁺, Zn²⁺, Cu²⁺, Ni²⁺, Co²⁺ and Fe²⁺). Similarly, the sensing of mercury was insignificantly affected in the presence of the metallic ions. The application of silver nanoparticles in the sensing of mercury displayed a detection limit of 11.3 M. The method was successfully used to detect mercury in tap water samples. Therefore, the findings in the current study indicate that the prepared SYR-AgNPs can serve as a potential cheap and readily available method for sensing mercury ions in environmental samples.