Non-DLVO Aggregation of Gold Nanoparticles Modified with Amino Acids

We investigated the aggregation behavior of gold nano particles modified with amino acids by changing the electrolyte concentration and charge state of the amino acids. Electrolyte promoting DLVO-type aggregation was observed when the protonation ratio of amino acids was below 50%, whereas it switched to non-DLVO-type aggregation when the protonation ratio was 90%. The observed non-DLVO aggregation is discussed in terms of zwitterionic binding between amino acids on adjacent nanoparticles, where the electrolyte acts as an aggregation inhibitor.