This chapter mostly discusses the silver (Ag) and gold (Au) nanostructures because of their resistance to corrosion. Metal nanoparticles are used in applications involving electronics, photonics, photography, catalysis, information storage, biological labeling, optoelectronics, and imaging. Leaf extracts from Eucalyptus macrocarpa were used to synthesize, at room temperature, silver nanocubes. The leaf extracts represented both the stabilizing and the reducing agent. They obtained both spherical and cubic silver nanoparticles, as showed in their TEM analysis. The coupling of distinct metals physicochemical properties made bimetallic nanoparticles an important area of interest for numerous applications. The nitrophenol reduction was probably controlled by the Au surface properties and by the Au alloy nanoparticles. The production of nanoscale gaps between metallic surfaces by the assembly of plasmonic nanoparticles is an inexpensive method of generating hotspots when illuminated (intense electric field strength in small volumes).