Unravelling dual LSPR shifting effects via tip amplification from anisotropic plasmonic nanocrystal in MOFs shell

Abstract Compared to Au nanorod@ZIF-8 (Au NR@ZIF-8), Au@Ag nanorod@ZIF-8 (Au@Ag NR@ZIF-8) has a weak extra red-shift of the longitudinal LSPR band, which cannot be ascribed to external dielectric layer alteration of the plasmonic core. It is difficult to explain the phenomenon of weak extra red-shifting due to the unobservable alteration of the Au@Ag NR core accompanying the formation of the ZIF-8 shell. Hence, efforts towards exploring the inherent reason for weak extra longitudinal localized surface plasmon resonance (LSPR) red-shift of Au@Ag NR have been resorted to the amplification from three tips of Ag nanotriangle (Ag NT). The results of this investigation reveal that the weak extra LSPR red-shift of Au@Ag NR@ZIF-8 and the larger LSPR blue-shift of Ag NT@ZIF-8 may be attributed to the etching occurrence of the plasmonic core during encapsulation, common to both. Moreover, unravelling ligand etching from surfactant etching indicates that the ligand etching effect only leads to the generation of truncated Ag NT@ZIF-8, which is different from the formation of Ag nanodisk@ZIF-8 (Ag ND@ZIF-8) via the surfactant etching effect. Combined analyses of XRD, TEM, and SERS experiments are helpful for explaining the huge LSPR blue-shift of Ag NT@ZIF-8.