Tailoring the polyelectrolyte coating of metal nanoparticles

Controlling the surface properties of nanoparticulate materials is necessary if they are to be exploited in applications such as colloidal crystals or biolabeling. By tailoring the polymer flexibility and the electrostatic forces involved in polyelectrolyte adsorption onto highly curved gold surfaces, through variation of the total salt concentrations suspending the chains and spheres, it is shown that irreversible polyelectrolyte wrapping of gold nanoparticles can be effected. By consecutively exposing the nanoparticles to polyelectrolyte solutions of opposite charge, polyelectrolytes can be deposited in a layer-by-layer sequence, yielding gold nanoparticles coated with uniform polyelectrolyte multilayers. Self-supporting polyelectrolyte multilayered nanocapsules are formed after dissolution of the metallic core. It has also been found that the gold nanoparticle surface charge, created by the adsorption of anions, is insufficient to overcome the ionic and hydrophobic polyanion/polycation interactions, resulting in polymer desorption from the highly curved nanoparticle surface. One successful method to immobilize the charge on the gold nanoparticle surface is to covalently attach an anionic thiol before polyelectrolyte modification.