Preparation of Ag nanoparticles
Ag nanoparticles were made according to the recipe described in the literature [8] and [9]. Briefly, a 100-mL aqueous solution of 1.0 × 10–3 M silver nitrate was mixed with a 300-mL aqueous solution of 2.0 × 10-3 M sodium borohydride. Triply distilled water was used for solutions, and both solutions were chilled to ice temperature before mixing. By mixing both solutions, Ag ions were reduced and clustered together to form monodispersed nanoparticles as a transparent sol in aqueous medium. The Ag solution was yellow because of the absorption at ∼390 nm. The solution was stirred repeatedly whenever some dark color appeared for approximately an hour until it became stabilized. At this point this solution of Ag nanoparticles was so stable that it did not change color for as long as several months without any stabilizing agent. Because the particle concentration of the solution is only 3.3 nM, it was concentrated 10 times using a rotary vacuum evaporator. Then, by diluting this solution, each sample of different concentration was used to investigate the concentration dependence of the antifungal effect of Ag nanoparticles.