Effect of surfactants and polymers on stability and antibacterial activity of silver nanoparticles (NPs)

In this first systematic study, we describe the influence of various surfactants and polymers on aggregation stability and antibacterial activity of silver nanoparticles (NPs) prepared by a modified Tollens process. The surfactant/polymer stabilizing effect was monitored using the newly established method based on a titration of the aqueous dispersion of the silver NPs by aqueous solution of poly(diallyldimethylammonium) chloride (PDDA). The aggregation process was evaluated by the dynamic light scattering (DLS) and UV/vis spectra measurements and finally confirmed by TEM. Among all of the investigated modifiers, two surfactants (sodium dodecyl sulfate-SDS and polyoxyethylenesorbitane monooleate-Tween 80) and one polymer (polyvinylpyr-rolidone-PVP 360) exhibit superior stabilization of the silver NP dispersions against the process of aggregation. The differences in the stabilization ability of various tested substances are discussed with respect to their structure and possible mechanism of the surface interaction with the NPs. The antibacterial activity of the modified silver NPs was significantly enhanced especially when modified by SDS where the minimum inhibition concentration (MIC) decreased under the "magical value" of 1 mu g(.)mL(-1). A correlation was found between the aggregation stability and enhanced antibacterial activity in the system of the silver NPs modified by SDS, Tween 80, and high molecular polymer PVP 360.