Reactivity Toward Ag⁺: A General Strategy to Generate a New Emissive Center from NIR-Emitting Gold Nanoparticles

We report a facile strategy for the transformation of single NIR-emitting AuNPs to dual-NIR-emitting bimetallic Ag@AuNPs based on the robust reactivity toward Ag(I) ions under mild conditions. The reactivities toward Ag(I) ions were found to be significantly different between visible- and NIR-emitting glutathione (GSH)-coated AuNPs: the high GSH surface coverage on the 610 nm-emitting AuNPs resulted in a reversible interaction due to enough surface steric hindrance to resist Ag(I) ions from interaction with the Au(0) core, whereas the low GSH surface coverage on the 810 nm-emitting AuNPs led to both antigalvanic reaction and Ag(I)-carboxylate shell formation on the surface of the AuNPs, which were responsible for the formation of a new emissive center at 705 nm. This strategy was also demonstrated to exhibit excellent generalization toward various NIR-emitting AuNPs with surface chemistries containing carboxyl groups, opening a new pathway of tailoring the optical properties of metallic NPs through surface reactivity.