Trimetallic Ag@AuPt Neapolitan nanoparticles.

Trimetallic Ag@AuPt Neapolitan nanoparticles were prepared by two sequential galvanic exchange reactions of 1-hexanethiolate-capped silver nanoparticles (AgC6, 5.70 ± 0.82 nm in diameter) with gold(I)-thiomalic acid (Au(I)TMA) and platinum(II)-hexanethiolate (Pt(II)C6) complexes. The first reaction was carried out at the air-water interface by the Langmuir method where the AgC6 nanoparticles formed a compact monolayer and water-soluble Au(I)TMA was injected into the water subphase; the nanoparticles were then deposited onto a substrate surface in the up-stroke fashion and immersed into an acetone solution of Pt(II)C6. As both reactions were confined to an interface, the Au and Pt elements were situated on two opposite poles of the original Ag nanoparticles. The tripatchy structure was clearly manifested in elemental mapping of the nanoparticles, and consistent with the damping and red-shift of the nanoparticle surface plasmon resonance. Further characterizations by X-ray photoelectron spectroscopy showed that the reactions were mostly confined to the top layers of the Ag metal cores, and contact angle and infrared spectroscopic measurements confirmed the incorporation and segregated distribution of the organic capping ligands on the nanoparticle surface.