Thiol-Induced Assembly of Au Nanoparticles into Chainlike Structures and Their Fixing by Encapsulation in Silica Shells or Gelatin Microspheres

This article describes a simple method for controlling the assembly of gold nanoparticles (Au NPs) into chainlike structures with tunable lengths and interparticle separations. The chainlike assemblies were induced to form by adding HS(CH2)nCOOH (n = 2, 10, and 15) into a suspension of Au NPs in a mixture of ethanol and water (98:2 by volume). The number of Au NPs in the chainlike assemblies could be altered by varying the concentration of the thiol while the interparticle distance between Au NPs in the chain could be adjusted by using thiols of different chain lengths. The chainlike assemblies of Au NPs were structurally unstable during storage and purification. We solved this problem by fixing the chainlike assemblies with silica coating via the Stöber method or by encapsulating them inside gelatin microspheres with the use of a fluidic device. After fixing, the chainlike assemblies of Au NPs could be preserved for a long period of time, during which their characteristic optical properties remained unchanged.