Influence of Chloride and Fluoride Ions on the Interaction of Amino Acids with Silver Nanoparticles

Due to their optical and antimicrobial properties, silver nanoparticles are being used in an increasing number of commercial and medical applications. Since their effect on the environment and living organisms is only partially known, probing their behavior in various solution conditions is important. The goal of our work is to study the interaction of amino acids with the nanoparticles and examine the effect of salts on this interaction. Initially, we have investigated the kinetics of the aggregation of citrate-capped silver nanoparticles upon the addition of different sodium halides. The principle issue we address is whether all sodium halides behave in a similar manner or if there is a specific ion effect. We monitored the aggregation rate using UV-Visible spectroscopy. We also characterized the size distribution of the silver nanoparticles using transmission electron microscopy. To analyze our data, we use the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory. Although this theory does not distinguish between the type of halide, we find that the chloride and fluoride ions have very different onsets of aggregation. By comparing DLVO simulations to our measured aggregation rate constants, we find that the different effects of the two halide ions are likely due to their effect on the nanoparticle surface charge; the chloride ion apparently replaces the citrate initially present on the nanoparticles while the fluoride ion does not. Using this information, we plan to apply our results to the study of the interaction of amino acids with the silver nanoparticles.