Metal–Organic Framework/Au Core/Shell Nanocubes for Spatially Aligned Molecular Analysis and Molecular-Fingerprint Sensing with Surface-Enhanced Raman Scattering

The spatial configuration of molecules on metal surfaces is a key parameter in reliably modulating the surface-enhanced Raman scattering (SERS) signals quantitatively, but the methods and platforms for controlling this configuration are not well established. Here, we utilized metal–organic frameworks (MOFs) to periodically and spatially arrange molecules in synthesizing zeolite imidazole framework-8 (ZIF-8)/Au core/shell nanocubes (ZACS NCs) for quantitative SERS. The uniform plasmonic Au nanoshell deposition onto ZIF-8 NCs was accomplished by the (100) facets of ZIF-8 and the use of cetyltrimethylammonium chloride (CTAC). In ZACS NCs, an interfacial Au/Zn alloy layer is between the AuNC core and ZIF-8 shell, which can modulate the plasmonic properties of the ZACS NCs. Single-particle Raman analysis suggests that characteristic vibrational Raman moieties of 2-methylimidazole (2-mIM) ligands have a clear laser polarization angle dependence. Importantly, the micro-Raman analysis results from all of the eight different vibrational moieties of ZIF-8 display highly linear relationships between particle concentration and SERS intensity, verifying that the spatially aligned configuration and periodicity of these moieties within ZIF-8 generate quantitative SERS signals. Finally, it was shown that the characteristic Raman peaks of 2-mIM ligands from the ZACS NCs can be used to detect and differentiate various targets of interest. This opens a new paradigm for versatile plasmonic porous materials.