Phosphonium surfactant stabilised silver nanoparticles. Correlation of surfactant structure with physical properties and biological activity of silver nanoparticles

Abstract

Silver nanoparticles were prepared by chemical reduction method and stabilised with cationic single-chain phosphonium surfactants of variable alkyl chain length and a different number of methyl and phenyl substituents in the hydrophilic headgroup part of surfactant molecule. Physical properties of silver nanoparticles were studied utilizing several experimental methods, such as visible spectroscopy, dynamic light scattering and scanning electron microscopy for the nanoparticle size determination and zeta potential measurements for the characterization of the charge of nanoparticles. As the physical measurements indicate, zeta potential of phosphonium surfactant stabilised silver nanodispersions was found to be in the range +27 mV to +50 mV depending on the alkyl chain length of the stabilising surfactant. Hydrodynamic diameter values of phosphonium surfactant stabilised silver nanoparticles were found to be between 40 nm and 109 nm with the smallest diameter values being around 40 nm for the nanoparticles stabilised with hydrophobic triphenyl-substituted phosphonium surfactants. Investigations of biological activity of both silver nanodispersions and silver-free aqueous solutions of surfactants are represented by the determination of antimicrobial activity against Gram-negative, Gram-positive bacterial strains and against yeast. Cytotoxicity of the systems mentioned above was determined on human carcinoma HepG2 cell line. Based on the obtained results, the relationship between phosphonium surfactant structure and physical and biological properties of nanoparticles is analysed. The results indicate that the increasing number of phenyl substituents in the surfactant headgroup and the increasing alkyl chain length play a dominant role in the improvement of biological activity of phosphonium surfactant stabilised silver nanoparticles as well as result in the formation of stable silver nanodispersions with small hydrodynamic diameter and a highly positive zeta potential.