Crystal–Amorphous Core–Shell Structure Synergistically Enabling TiO₂ Nanoparticles’ Remarkable SERS Sensitivity for Cancer Cell Imaging

Exploring novel surface-enhanced Raman scattering (SERS) active materials with high detection sensitivity, excellent biocompatibility, low biotoxicity, and good spectral stability is urgently required for efficacious cancer cell diagnosis. Herein, black TiO2 nanoparticles (B-TiO2 NPs) with crystal–amorphous core–shell structure are successfully developed. Remarkable SERS activity is derived from the synergistic effect of the promising crystal–amorphous core–shell structure. Abundant excitons can be generated by high-efficiency exciton transitions in the crystal core, a feature that provides sufficient charge source. Significantly, the novel crystal–amorphous heterojunction enables the efficient exciton separation at the crystal–amorphous interface, which can effectively facilitate charge transfer from the crystal core to the amorphous shell and results in exciton enrichment at the amorphous shell. Kelvin probe force microscopy (KPFM) confirms the Fermi level of the amorphous layer shifting to a relatively low position compared to that of the crystal core, allowing efficient photoinduced charge transfer (PICT) between the amorphous shell and probe molecules. The first-principles density functional theory (DFT) calculations further indicate that the amorphous shell structure possesses a narrow band gap and a relatively high electronic density of state (DOS), which can effectively promote vibration coupling with target molecules. Moreover, MCF-7 drug-resistant (MCF-7/ADR) breast cancer cells can be quickly and accurately diagnosed based on the high-sensitivity B-TiO2-based SERS bioprobe. To the best of our knowledge, this is the first time the crystal–amorphous core–shell heterojunction enhancement of the TiO2-molecule PICT process, which widens the application of semiconductor-based SERS platforms in precision diagnosis and treatment of cancer, has been investigated.