Facet-selective deposition of Au and Pt on Ag nanocubes for the fabrication of bifunctional Ag@Au–Pt nanocubes and trimetallic nanoboxes

We report a facile route to the synthesis of Ag@Au-Pt trimetallic nanocubes in which the Ag, Au, and Pt atoms are exposed at the corners, side faces, and edges, respectively. Our success relies on the use of Ag@Au nanocubes, with Ag2O patches at the corners and Au on the side faces and edges, as seeds for the site-selective deposition of Pt on the edges only in a reaction system containing ascorbic acid (H2Asc) and poly(vinylpyrrolidone). At an initial pH of 3.2, H2Asc can dissolve the Ag2O patches, exposing the Ag atoms at the corners of a nanocube. Upon the injection of the H2PtCl6 precursor, the Pt atoms derived from the reduction by both H2Asc and Ag are preferentially deposited on the edges, leading to the formation of Ag@Au-Pt trimetallic nanocubes. We demonstrate the use of 2,6-dimethylphenyl isocyanide as a molecular probe to confirm and monitor the deposition of Pt atoms on the edges of nanocubes through surface-enhanced Raman scattering (SERS). We further explore the use of these bifunctional trimetallic nanoparticles with integrated plasmonic and catalytic properties for in situ SERS monitoring the reduction of 4-nitrothiophenol by NaBH4. Upon the removal of Ag via H2O2 etching, the Ag@Au-Pt nanocubes evolve into trimetallic nanoboxes with a wall thickness of about 2 nm and well-defined openings at the corners. The trimetallic nanoboxes embrace plasmon resonance peaks in the near-infrared region with potential in biomedical applications.