Aggregation of glutathione-functionalized Au nanoparticles induced by Ni2+ ions

Aggregation of glutathione (GSH)-functionalized Au nanoparticles induced by Ni2+ ions were found to be related to pH of the solutions. At pH lower than 9.0, introduction of Ni2+ ions was less effective to induce aggregation of the Au nanoparticles. At pH around 9.8, the Au nanoparticles experienced extensive aggregation upon the addition of Ni2+ ions. When pH was higher than 10.5, Ni2+ ion-induced aggregation of the Au nanoparticles was suppressed gradually with increasing pH. It was identified that such pH-mediated aggregation behaviors are attributed to the different coordination fashions of GSH on the Au nanoparticle surface with Ni2+ ions. At pH lower than 9.0, addition of Ni2+ ions was less effective to induce aggregation of the Au nanoparticles when only the carboxyl group of the glutamyl residue was available for the metal ions. The Au nanoparticles underwent extensive aggregation at pH around 9.8 when both the carboxyl and deprotonated amine groups of the glutamyl residue in GSH could coordinate with the metal ions. At pH higher than 10.5, the coordination was gradually suppressed by the hydroxyl groups in solutions, addition of Ni2+ ions is less effective to cross-link the Au nanoparticles. Such a work is helpful for understanding the sensitivity and selectivity of GSH-functionalized Au nanoparticles to metal ions.