High concentration silver nanoparticles stably dispersed in water without chemical reagent

New laser ablation method to drastically improve nanoparticle yield was developed. In this method, laser was irradiated from the bottom of a piriform flask to the precipitated powder target. Nanoparticle yield became much higher than that obtained by the conventional method. Silver nanoparticle colloid with high concentration was prepared in a single step and the colloid has been stable for more than 6 months without any chemical reagents. The shape of nanoparticles was estimated to be four-sided pyramid or octahedral by scanning transmission electron microscopy (STEM) observation. In addition, STEM image showed narrow size distribution. A typical bacteria, Bacillus coli, became extinct within 24 h in silver nanocolloid with the concentration of 20 mg/L.