Studies on the reversible aggregation of cysteine-capped colloidal silver particles interconnected via hydrogen bonds

The surface modification of aqueous silver colloidal particles with the ami no acid cysteine and the cross-linking of the colloidal particles in soluti on is described. Capping of the silver particles with cysteine is accomplis hed by a thiolate bond between the amino acid and the nanoparticle surface. The silver colloidal particles are stabilized electrostatically by ionizin g the carboxylic acid groups of cysteine. Aging of the cysteine-capped coll oidal solution leads to aggregation of the particles via hydrogen bond form ation between amino acid molecules located on neighboring silver particles. The aggregation is reversible upon heating the solution above 60 degreesC. The rate of cross-linking of the silver particles via hydrogen bond format ion may be accelerated by screening the repulsive electrostatic interaction s between the particles using salt. The process of aggregation and heat-ind uced dispersion of the particles has been studied by UV-vis spectroscopy, l aser light scattering, and transmission electron microscopy measurements.