Laser-induced photochemical reduction for the production of gold and silver nanoparticles on gold nanostructures

This research explores two methods for the photo-chemical reduction of gold and silver ions, utilizing either a continuous-wave (CW) laser or a femtosecond laser, in conjunction with plasmon-assisted hot electrons. The study focuses on the photoreduction of chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) solutions containing gold nanostructures under irradiation from either CW or femtosecond laser. Specifically, we employed a 445 nm CW laser to irradiate gold nanowires, formed through the photo-driven self-assembly of gold nanorods, in HAuCl₄ solution. Through this photoreduction process, we observed the newly formed gold nanoparticles on the surface of gold nanowires. In addition, we also used 445 nm to irradiate gold triangular nanoplates in AgNO₃ solution with ascorbic acid as a reducing agent. We observed that silver nanoparticles clearly formed and attached to the edges of a gold triangular nanoplate. In another approach, an 800 nm femtosecond laser was used to irradiate gold nanorods, gold triangular/hexagonal nanoplates and a gold nanofilm in AgNO₃ solution with a reducing agent under inverted microscopy. For instance, silver nanoparticles were observed to attach to the edges of the gold triangular and hexagonal nanoplates, facilitating the growth of the nanoplates. The formation of photochemically reduced nanoparticles was confirmed using energy-dispersive X-ray spectroscopy. Notably, 3D silver dendritic structures were synthesized with the femtosecond laser and deposited onto the gold nanofilm, a process attributed to two-photon absorption effect. The high sensitivity of these immobilized dendrites for surface-enhanced Raman scattering applications was also demonstrated.