Laser Ablation: An Easy Route To Obtain Gold And Silver Nanomaterials

Gold and silver nanoparticles (AuNP and AgNP) have a very important role in nanotechnolgy and nanoscience, due to their physical, chemical and biochemical properties. We produced colloidal solution of Au and Ag nanoparticles in a fast and inexpensive way by laser ablation of the bulk metals in a liquid buffer using the 1064 nm line of a Q -switched Nd – YAG laser. On one hand these solutions are stable without any external chemical reagent, so nanoparticles can be obtained free in solution. On the other hand we succesfully performed the laser ablation synthesis (LAS) in water and in organic solvents, so it is possible to functionalize these particles during as well as after the LAS, simply solubilizing the ligands in the appropriate solvent.[1,2] Furthermore we found that in toluene, LAS of AuNP produces a graphite – gold nanocomposite. The graphitic matrix determined the quenching of the characteristic surface plasmon absorption (SPA) of the AuNP, that can be restored by the matrix removal.[3] The characterization of AuNP and AgNP solutions is easily achieved by UV – vis spectroscopy using the Mie Theory to fit the SPA. For free particles in solution we conveniently fitted the SPA with the Mie Model for compact spheres and the Gans model for spheroids. We verified that one can account for the isolated nanoparticles fraction using the Mie model for simple spheres and for the aggregated nanoparticles fraction using the Gans model for spheroids.[2] In the case of the graphite – AuNP composite we reproduced the SPA quenching using the Mie model extension for core@shell particles.[3] HRTEM images confirmed the results obtained with the UV-vis spectroscopy. Finally we were able to obtain a certain control on the average size and aggregation of nanoparticles by laser treatment at 532 nm of AuNP solution. [1] V. Amendola, G. Mattei, C. Cusan, M. Prato and M. Meneghetti; Synthetic Metals 2005; 155; 283–286 [2] Vincenzo Amendola, Stefano Polizzi and Moreno Meneghetti; J Phys Chem B 2006; 110; 7232-7237 [3] Vincenzo Amendola, Gian Andrea Rizzi, Stefano Polizzi and Moreno Meneghetti; J Phys Chem B 2005; 109; 23125-23128