Nanoparticles synthesis is an evergreen research field of 21st century in which the connotation of the biomediated experimental process is highly imperative. Biomediated silver nanoparticles were synthesized with the aid of an eco-friendly biomaterial, namely, aqueous Azadirachta indica extract. The effect of pH and temperature on the formation of silver nanoparticles was analyzed. Formation of the silver nanoparticles was verified by surface plasmon spectra using a UV-vis spectrophotometer. Morphology and crystalline structure of the prepared silver nanoparticles were characterized by TEM and XRD techniques, respectively. Furthermore, the biomediated silver nanoparticles without any surface modification were used for the heavy metal ion sensors in aqueous media. The prepared silver nanoparticles were successful in detecting even the minimal amount of heavy metal copper(II) ion and exhibited excellent specific metal ion selectivity.