Study of stability and antimicrobial activity of colloidal Ag/SiO2 nanocomposites

Ag/SiO2 colloidal nanocomposites (NCs) were synthesised by the chemical reduction of silver ions on a silica surface; NaBH4 was used as a reducing agent, while chitosan served as a stabiliser. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) results of Ag/SiO2 showed a high-density distribution of silver nanoparticles on the silica surface. The influence of pH, ionic concentrations on the stability of Ag/SiO2 colloidal NCs was investigated. Ag/SiO2 colloidal NCs were stable in a wide range of pH values (3-10) and the presence of cations (Mg2+ 25 mM, Ca2+ 15 mM, Fe2+ 1 mM, Fe3+ 0.8 mM). Furthermore, the antimicrobial activity of Ag/SiO2 colloidal NCs against Ralstonia solanacearum 15 (R. solanacearum 15), Bipolaris oryzae (B. oryzae) was evaluated. The minimum inhibitory concentration (MIC) of Ag/SiO2 colloidal NCs for R. solanacearum 15 was 10 ppm, two times lower than that of silver nanoparticles (AgNPs) at 20 ppm, which were prepared by the same route. The inhibitory rate of Ag/SiO2 colloidal NCs against B. oryzae was 99.3% higher than the inhibitory rate of AgNPs 80.4% at the same Ag concentration of 32 ppm. Therefore, Ag/SiO2 colloidal NCs with high antimicrobial activity and stability in wide range pH and ionic strength are a promising pesticide in agriculture.