To prepare colloidal nanoparticles, aqueous solutions with Au3+and Pt4+ ions and additives of surfactants (SDS or PEG-MS) are irradiated with an ultrasound at 200 kHz with an input power of 4.2 W/cm2. Here the structures of nanoparticles changes with the surfactants. Au and Pt nanoparticles can be prepared individually by using SDS, and bimetallic Au/Pt alloy nanoparticles with a core–shell structure can be produced in the presence of PEG-MS. Fei Xiao and others of Wuhan University, China prepared Gold−platinum nanoparticles (AuPt NPs) on chitosan (Ch)−ionic liquid (i.e., trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide, [P(C6)3C14][Tf2N]) film by using an ultrasonic electrodeposition method. In this case Ch acted as an adsorbent for the metal ions, and [P(C6)3C14][Tf2N] played a dual role of matrix and stabilizer in the formation of the nanoparticles. Selvakannan and Murali Sastry has reported on the preparation of hollow gold and platinum nanoparticles by a transmetallation reaction in an organic solution between hydrophobized silver nanoparticles with hydrophobized chloroaurate and chloroplatinate ions in chloroform. This resulted in the formation of hollow gold and platinum shell nanoparticles respectively.