Slow-Photon-Amplified Charge-Transfer SERS in MOF Photonic Crystals for Plasmon-Free Ultrasensitive Molecular Barcoding

Metal–organic frameworks (MOFs) offer unique chemical selectivity for surface-enhanced Raman scattering (SERS), yet their intrinsically weak light–matter coupling fundamentally limits sensitivity and has long hindered their practical deployment as plasmon-free SERS substrates. Here, we report a photonic-crystal strategy that fundamentally amplifies charge-transfer (CT)-mediated SERS in MOFs by exploiting slow photons at the photonic stop-band edge. Using UiO-66(Zr) nanocrystals as the model MOF, the assembled ordered MOF photonic crystals (PhCs) with tunable Bragg reflection are precisely aligned to the excitation wavelength. The resulting slow-light effect dramatically increases photon residence time and local electromagnetic field within the MOF pore domains. This slow-photon confinement synergistically couples with CT processes between MOFs and analyte molecules, resulting in a tenfold enhancement in SERS intensity compared with disordered MOF assemblies and an enhancement factor up to 5.15 × 10 8 without any plasmonic components. By leveraging the intrinsic band-structure tunability of MOFs, selective CT-SERS is further demonstrated across different molecular systems and environments. The optimized MOF-PhCs substrate enables ppb-level detection and multicomponent discrimination of lung-cancer-associated volatile organic compounds, which are digitally encoded into machine-readable Raman barcodes. This work establishes slow-photon-regulated MOF photonic crystals as a versatile platform for plasmon-free, chemically programmable, and functionally integrated SERS sensing.