CONICET | Buscador de Institutos y Recursos Humanos

Among the different types of nanoparticles (NPs), Ag compounds have been used as antimicrobial agents since many years. Silver ions or NPs have a broad bactericide, spectrum as well as showing effectiveness against viruses and fungi. Ag NPs in solution show remarkable physical and chemical properties that depend on their size and shape. As long as optical properties are concerned, the refractive index of the surrounding medium and the presence of an oxide shell around the NP have to be taken into account to determine the characteristics of the plasmon resonance. Ag NPs colloids in soluble starch (st) solution were synthesized by two methods: femtosecond (fs) laser ablation of a solid target on one hand and a chemical reduction method on the other. An ultrafast pulse Ti:Sa laser of 120 fs duration and a central wavelength at 800 nm, focused on a solid silver target immersed in an aqueous solution of starch at different fluences, was used for ablation manufacture. The chemical synthesis of the Ag NPs was performed by adding dropwise a freshly prepared NaBH4 solution over a solution containing AgNO3 and starch. The mixture was kept under magnetic stirring in an ice / water bath for 2 hours. In this work we study size distribution, structure, species and configuration of the obtained colloidal Ag NPs were determined using optical extinction spectroscopy, micro-Raman spectroscopy and TEM techniques. Stability analysis based on the time evolution of plasmon peak position and FWHM of the colloidal suspensions fabricated by both methods was carried out. Fitting of the experimental spectra with Mie theory allowed determining size distribution, structure and composition. Z-potential measurements were also performed on the same samples yielding results which agree with stability by optical method. Results of characterization and stability studies may be applied in future prospects to study the antimicrobial capacity and application as active packaging in the food industry.