In this work we investigated the process of Au-Hg alloy formation occurring on individual substrate-immobilized Au nanorods exposed to Hg(II) solutions. Dramatic transitions in the light scattered by nanorods from red to yellow or even green color and remarkable blue shifts in the corresponding scattering spectra were detected upon chemical reduction of Hg(II). Such changes occurred as a result of amalgam formation and were correlated to deposition of Hg on nanorod surfaces and subsequent reduction of the nanorods' aspect ratio towards a spherical shape. Theoretical calculations were used to support experimental findings. Time-dependent monitoring of optical changes occurring in substrate-immobilized nanorods during exposure to Hg(II) solutions and during their subsequent exposure to air was also performed. Finally a mechanism for Au-Hg amalgamation was proposed where initial fast deposition of Hg on nanorod surfaces was followed by slow diffusion of Hg into the nanorod lattices.
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