Cooperative and Reversible Anisotropic Assembly of Gold Nanoparticles by Modulation of Noncovalent Interparticle Interactions

Controlled and reversible anisotropic self-assembly of gold nanoparticles (GNPs) is achieved by ligand exchange with concentrations of ligand below that needed for their complete capping, that is, using substoichiometric ligand coverages. A thoughtful rationale of the ligand chemical structure and control over exchange conditions have been pursued to foster a reversible process grounded on the cooperative balance between attractive, and repulsive interactions. The gradual replacement of the electrostatic and steric repulsions between the GNPs with attractive dipolar interactions and enhanced steric repulsions is accomplished by ligand exchange with an oligo (ethylene glycol) alkanethiol. The modulation of interparticle interactions is driven by the extent of ligand substitution and allows the reversible assembly of nanoparticles and tuning of their optical properties.