Modulating the Energy-Band of Metal Oxide@Metal-Organic Framework Core-Shell Nanoparticles for Enhanced Raman Sensing

Surface-enhanced Raman scattering spectroscopy (SERS) can provide molecular fingerprint peaks of the vibration information with great specificity and sensitivity. It is widely used in biomedical and chemical fields. Semiconductor-based substrates represent a hot spot in the field of SERS beyond conventional noble metals, and metal-organic frameworks are rarely realized for SER detection. Here, we modulate the energy-band structures of metal-organic frameworks (MOFs) further by metal oxides (MOs) to match the energy band of a target analyte. We construct MOF-encapsulated metal oxide core-shell nanoparticles (MO@MOFs) as substrates for Raman enhancement. Attributed to the high structural tailorability of both core and shell, a series of energy-band structures have been created. We perform SERS detection of rhodamine b (RhB) on MO@MOF and find that the enhanced factor of Fe3O4@MOF(Co) and TiO2@MOF(Ni) reach as high as 10(8) and 10(6), respectively, with low detection limits of 10(-8) M, much lower than that using the corresponding MOFs. The SERS enhancement is based on mechanisms including charge transfer, interband and molecule resonances, and ground-state charge-transfer interactions. This work will promote the application of semiconductor-based nanomaterials with special modularity for surface-enhanced Raman scattering substrates.