Ablação via laser para síntese de nanopartículas de liga híbrida Au-Ag para aplicações em nanobiofotônica

Abstract

The synthesis of hybrid metallic nanoparticles remains a major challenge in nanoscience due to the need for reproducible, fast, and environmentally friendly methods. In this work, we investigated the production of gold-silver (Au-Ag) nanoparticles through laser ablation in liquid (LASiS), aiming at the formation of a homogeneous alloy for nanobiophotonic applications. The process was carried out in two steps: (i) initial synthesis of Au and Ag colloids using a 1064 nm fiber laser, and (ii) re-irradiation of the mixed colloids with a 532 nm Nd:YAG laser. The samples were characterized by UV-Vis spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). UV-Vis results indicated the transition from bimodal plasmon peaks to a single peak centered at 495 nm after 25 minutes of irradiation, confirming alloy formation. Importantly, the experiments demonstrated the possibility of plasmon tuning, enabling control of the resonance peak from 400 nm (silver) to 525 nm (gold), with intermediate values depending on the relative Au:Ag ratio. SAED analyses corroborated a face-centered cubic (FCC) structure with d-spacing values intermediate between pure Au and Ag. SERS experiments with urea as probe molecules revealed significant Raman signal enhancement due to plasmonic hotspot formation. We conclude that the two-step LASiS approach is effective for obtaining pure and stable Au-Ag hybrid nanoparticles with tunable optical properties, showing strong potential for biosensors and photonic devices, while offering a sustainable alternative to conventional chemical methods.