The reactivity study of peptide A3-capped gold and silver nanoparticles with heavy metal ions

• Apparent color change upon the addition of Hg2+ or As3+ ions into A3-AuNPs solution.
• Distinct color change of A3-AgNPs solution only in the presence of Hg2+ ions.
• The Hg2+ concentration limit of A3-AgNPs about 40 times lower than A3-AuNPs.
• Based on the DLS, TEM and XPS results, two reaction mechanisms have been proposed.

Peptide A3-capped gold and silver nanoparticles were prepared by chemical reduction of metal salt precursors. The nanoparticles exhibited apparent but distinctly different color changes upon the addition of selected heavy metal ions. For gold nanoparticles, the solution color was found to change from red to blue in the presence of Hg2+ or As3+ ions, accompanied with broadening and a red-shift of the surface plasmon resonance peak. In contrast, silver nanoparticles showed an apparent color change from yellow to colorless only in the presence of Hg2+, along with a blue-shift and diminishment of the surface plasmon resonance peak. The Hg2+ reaction concentration limit of silver nanoparticle was about 40 times lower than that of gold nanoparticle. Based on the dynamic light scattering, transmission electron microscopy and X-ray photoelectron spectroscopic results, the reaction mechanism has been proposed. Such a sensitive variation of the nanoparticle optical properties to selective ions might be exploited for ion detection for potential applications.

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