A new method for producing highly concentrated non-aqueous dispersions of silver nanoparticles and the evaluation of their bactericidal activity

Different preparation methods of silver nanoparticles (AgNP) are well described in the literature, most of them in aqueous medium. Aqueous dispersions of AgNP normally have a limited capacity to tolerate high nanosilver concentrations. However, AgNP production in non-aqueous medium is still scarce although its exploitation for example, as coating for hydrophobic surfaces, would be of a huge importance in many technological applications. In this work, we report the chemical preparation of highly concentrated non-aqueous AgNP dispersions obtained by reduction of silver cation, from two distinct salt sources (AgNO₃ and AgBF₄), by 1-butanol in the presence of a biocompatible poly(ether-block-amide) copolymer, named PEBA. The highest concentration reached was around 5 mM, when it used AgBF₄ as silver source and 4 % (w/w) of a PEBA solution in 1-butanol. This AgNP concentration is notably higher than the values reported in aqueous medium. The AgNP formation was attested by UV–Vis spectroscopic analysis, which showed the characteristic strong plasmon band at 420 nm. The X-ray diffraction patterns confirmed the formation of a crystalline fcc silver metallic phase with particle diameters ranging from 5 to 10 nm accordingly to transmission electron microscopy examination. It was also observed that the AgNP dimensions are dependent on the PEBA and silver salt concentrations. The AgNP dispersions presented a very high antimicrobial activity against E. coli and S. aureus microorganisms, even in low concentration, attested by the Kirby-Bauer method.