In this paper, we present a greener synthesis of silver and gold nanoparticles using an aqueous extract of Ficus benjamina leaves. The metal nanoparticles were synthesized via conventional heating and microwave-assisted methods using the aqueous extract as reducing and capping agent. It was observed that the use of a Ficus benjamina leaf aqueous extract via microwave-assisted heating represent a faster, greener and easier method than a conventional heating procedure for the synthesis of silver and gold nanospheres, also leading to narrower nanoparticle size. The sensing characteristics of the microwave-assisted silver nanoparticles were evaluated for the specific determination and semiquantification of Zn(II) ions. The colorimetric semiquantification of Zn(II) ions was achieved by UV vis spectroscopy, using an empirical model in a concentration range between 0.2 and 2.0 mM, reaching total precipitation at concentrations higher than 2.0 mM.