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.