Silver nanoparticles stabilised with cationic single-chain surfactants. Structure-physical properties-biological activity relationship study

Increasing number of biological applications of silver nanoparticles requires a detailed determination of the relationship between nanoparticle structure and its physical and biological properties. In this paper, synthesis, measurements of nanoparticle size and zeta potential and some biological activities of silver nanoparticles stabilised with single-chain cationic surfactants are provided. The main goal of the study is the investigation of the relationship between molecular structure of stabilising agent, physicochemical properties and biological activity of cationic surfactant-stabilised silver nanoparticles. Two structural features, heterocyclic character of hydrophilic part of surfactant molecule and hydrophobicity change of its substituents, were correlated with synthesis, stability and biological activity of silver nanoparticles. Substituted ammonium, pyridinium and piperidinium surfactants were selected as stabilisers of silver nanoparticles. It was found that nanoparticle stabilising effect is improved by increasing the length of hydrophobic substituents on the ammonium polar head which results in the formation of nanoparticles small in size and with sufficiently positive zeta potential. Application of dibutylsubstituted ammonium surfactant molecules resulted in the formation of small silver nanoparticles in the size range 25-30 nm and a zeta potential of +60 mV. Aromatic pyridinium surfactant molecules provide slightly better stabilisation than saturated piperidinium surfactants. Surfactant-stabilised silver nanoparticles were antimicrobially efficient against Gram-positive pathogens and yeast. The highest cytotoxic activity was determined for silver nanoparticles stabilised with dibutyl-substituted ammonium surfactant and pyridinium surfactant which corresponds with small and charged nanoparticles formed by using these surfactants. Maximum cytotoxic activity was found in the surfactant concentration range 16-25 mu M. (C) 2018 Published by Elsevier B.V.