Femtosecond Laser Synthesis of AuAg Nanoalloys: Photoinduced Oxidation and Ions Release

A femtosecond laser irradiation approach has been developed for the production of homogeneous AuAg nanoalloys of various compositions. The mean size was controlled by the dextran-nanoparticle affinity and resulted in the production of 5-7 nm nanoalloys for all nanoparticle compositions. Strong improvement of the oxidation resistance resulted from the increase of the atomic gold fraction in the nanoparticles. At gold fractions above 0.4, most of the nanoparticle oxidation was quenched, inhibiting the release of toxic silver ions in solution. The oxidation of the produced nanoparticles was mainly attributed to the generation of free radicals (O-center dot, H-center dot, (OH)-O-center dot) and of molecular reactive oxygen species (O-2, H-2, H2O2) formed by the decomposition of the water molecules through femtosecond laser-induced optical breakdown. For some biological applications, like surface-enhanced Raman spectroscopy (SERS), it is anticipated that AuAg nanoalloys would be the best compromise in terms of chemical stability and plasmonic response, as they possess much better resistance to oxidation in comparison to pure silver and a much stronger and narrower plasmon peak in comparison to pure gold.