ZIF-Mediated Gold Nanorod Assembly for Surface-Enhanced Raman Scattering Detection of 4‑Nitrobenzenethiol

Nanoparticle assemblies exhibit unique properties compared to single entities due to interactions between their building blocks. Although the development of large-area assemblies has been extensively studied, finite nanoparticle assemblies with tens of building blocks have not been adequately explored. Here, we prepared a finite assembly of anisotropic gold nanorods through encapsulation by a zeolitic imidazolate framework-8 (ZIF). The three-dimensional reconstruction of the ZIF-encapsulated nanorod assembly indicated that the assembled nanorods are separate bundles aligned side-by-side, each of which serves as a nucleation center for a cube-shaped ZIF domain. Further experiments showed that the assembly pattern and the shell dimension can be controlled by the cysteamine and surfactant concentrations. Moreover, the ZIF-encapsulated nanorod assembly had twice the surface-enhanced Raman scattering signal of a single nanorod and showed higher selectivity for 4-nitrobenzenethiol versus rhodamine 6G. Our model system will significantly contribute to the development of finite anisotropic nanoparticle assemblies with microporous metal–organic framework shells and extend their applicability.