Metal–Organic-Frameworks-Isolated Au Nanobipyramids as Synergetic Surface-Enhanced-Raman-Scattering Substrates

Recently, mushrooming efforts in surface-enhanced Raman scattering (SERS) have been devoted to applying semiconductor-like metal–organic frameworks (MOFs) as a charge-transfer center rather than only a porous filter or stabilizing layer in a metal@MOF core–shell substrate. However, the influence of an enhanced electric field on the charge-transfer process of MOFs has not been quantitatively explored, leading to an elusive understanding of the synergetic effect of metal@MOF core–shell substrates. Here we reveal a synergetic effect through SERS measurements of gold nanobipyramid (Au NBP) @zeolitic-imidazolate-framework (ZIF) core–shell nanostructures with varied thickness and composition of the shell. The synergetic effect was confirmed by the stronger enhancement factors of some NBP@ZIFs than that of pure NBP-785 with methyl orange (MO) and rhodamine 6G as the probe. Moreover, a reorientation phenomenon of MO discovered in the ZIF shell probably also accounted for the higher intensity, given that the probe orientation could impact the SERS intensity. Besides elucidating the charge transfer and synergy effect of the metal@MOF core–shell SERS substrates, this work could also provide new ideas to enrich the family of the shell-isolated nanoparticle-enhanced Raman spectroscopy substrates by employing porous materials as the shell.