The domains of science and technology, especially environmental protection, have brought a lot of change in nanotechnology. In the modern period, the growth of animals and plants with enough quantities is fundamentally obligatory by heavy metal ions (M+), such as Cr3+, Zn2+, Ní2+, Cu2+ and Hg2+.. However, because of their presence in both human and animal food webs, these metal ions are toxic to living things at relatively high concentrations. The ecologically friendly green approach was utilized to synthesis starch functionalized silver nanoparticles (St-Ag NPs) using water as a solvent, starch as a stabilizing agent, and glucose as a reducing agent. KOH has been used as an activator for glucose activation. The influence of diverse solutions such as AgNO3, starch, glucose, and KOH on the production of St-AgNPs was investigated. To see how these substances affect the production of St-Ag NPs, different controlled reactions were carried out in the absence of starch, glucose, and KOH. Starch, glucose, and KOH are discovered to play important roles in the synthesis of AgNPs. UV-Vis absorption spectroscopy, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM) were used for the characterization of St-Ag NPs. These starch functionalized AgNPs were used for the detection of heavy metals at 25℃. It is found during the screening process only Hg2+ showed clear changes in the color and absorption intensity of AgNPs which may be due to redox reaction that can occur between Ag0 and Hg2+. On the other hand, the color and absorption intensity of nanoparticles remain unchanged in the presence of all the other tested metals ion. The presence of other metal ions was also tested in the system. The proposed method has strong selectivity and sensitivity to Hg2+ ions. Using UV-visible spectrophotometry, the method produced had a detection limit of 1ppm. The proposed method for detecting Hg2+ in tap water samples was found to be successful..