A simple and “green” technique to synthesize long-term stability colloidal Ag nanoparticles: Fs laser ablation in a biocompatible aqueous medium

Abstract

A comparative study of spectral characteristics, size distribution, composition, morphology and long-term stability of colloidal Ag NPs synthesized by ultrashort pulse laser ablation of a solid target and by chemical salt reduction, both in Trisodium Citrate (TSC) aqueous solution was carried out. Several techniques were independently used to characterize optical, structural and compositional properties of the colloidal samples. Both synthesis routes yield bare core Ag and Ag@Ag2O core@shell NPs, with size distributions of roughly similar size centered at about 1.2 nm radius. Stability analysis of samples was conducted for several weeks and after one-year of fabrication, analyzing the characteristics of the plasmon resonance in the optical extinction spectra and independently by zeta potential measurements. For laser ablation colloids, plasmon peak reaches redshift saturation regime at the second week, while salt reduction colloids seem to reach saturation at times beyond one year. After one year, colloids synthesized by UPLA still show a clear single plasmon resonance in their optical spectra together with higher negative zeta potential values, compatible with very good stability characteristics and no signs of agglomeration. A suitable selection of laser pulse energy and citrate concentration may be used for tuning plasmon resonance peak position and FWHM for specific applications. The biocompatibility properties and good stability of the colloids generated by “green” UPLA may boost its use as long-term antimicrobial additive in films, antifungal paints and antibacterial composites.