Characterization and Stability of Silver Nanoparticles in Starch Solution Obtained by Femtosecond Laser Ablation and Salt Reduction

Silver nanoparticles(Ag NPs) colloids obtained by femtosecond laser ablation in soluble starch (st) solution and silver salt reduction methods were characterized using optical extinction spectroscopy, micro-Raman spectroscopy, transmission electron microscopy, and zeta potential. Type, number density, and relative percentage of species were determined for the first time based on OES and Raman analysis. Both synthesis methods yield bare Ag and core shell Ag@ Ag2O spherical NPs with log-normal size distributions centered in the range 1-3 nm. Pulsed laser ablation produced also hollow Ag species. The presence of an Ag2O shell is fundamental for the antibacterial properties of Ag NPs through the production of Ag+ ions. Stability studies based on the evolution of OES and zeta potential show that laser ablation method produces colloids that stabilize much faster than those synthesized by salt reduction method for a given st concentration. It was found that an increase in soluble st concentration produces a redshift of the Ag plasmon peak with respect to neat water, which is steeper for high pulse energy. Particularly, low energy pulses seem to produce more stable colloids than high energy pulses. Knowledge of these facts may be useful in synthesis of silver colloids for specific applications in biomedicine and food industry.