Ag/SiO₂ nanoparticles stabilization with lignin derived from rice husk for antifungal and antibacterial activities

Antibacterial materials have been developed for a long time but bacteria adapt very quickly and become resistant to these materials. This study focuses on the synthesis of a hybrid material system from lignin and silver/silica nanoparticles (Lig@Ag/SiO₂ NPs) which were used against bacteria including Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and inhibited the growth of the fungal Aspergillus flavus (A. flavus). The results showed that the spherical diameter of Lig@Ag/SiO₂ NPs has narrow Gaussian distribution with a range from 15 nm to 40 nm in diameter. Moreover, there was no growth of E. coli in samples containing Lig@Ag/SiO₂ NPs during 72-h incubation while colonies of S. aureus were only observed at high concentrations (10⁶ CFU/mL) although both species of bacteria were able to thrive even at low bacterial concentration when they were exposed to Ag/SiO₂ or lignin. For fungal resistance results, Lig@Ag/SiO₂ NPs not only reduced mycelial growth but also inhibited sporulation in A. flavus, leading to decreasing the spreading of spores into the environment. This result represents a highly effective fungal growth inhibition of Lig@Ag/SiO₂ NPs compared to lignin or Ag/SiO₂, which could not inhibit the growth of sporulation.