The electronic and optical properties of semiconductor and gold nanoparticles was synthesized through tailoring size and shape. The reduction of HAuCl 4 was carried out in an attempt to follow a more controlled procedure, using DMF in the presence of small gold seeds with uniform size distribution. Though the presence of the seeds was expected to assist gold reduction, with the gold surface acting as a catalyst, the thermal reduction at reflux produced a lower yield of decahedra, with a noticeable polydispersity and presence of other less-defined geometries in all samples. The use of ultrasound was a key step to the controlled and reproducible synthesis of monodisperse decahedra with high yield. A model for the resolution of Maxwell's equations for bicones described extremely well the optical properties of the bipyramids, so that a good correlation between particle size and optical response can be established.