Quasi-BIC metasurfaces enable rapid, localized singlet-oxygen generation

Bound states in the continuum (BIC) provide a photonic route to concentrate and store electromagnetic energy with minimal radiative leakage. Here, we report Au-TiO₂ metasurfaces that couple q-BIC optical resonance to interfacial charge transfer, enabling hot-carrier-mediated generation of ¹O₂ within subwavelength optical paths. Photonic engineering acts through two cooperative effects: (i) increased optical absorption that boosts hot-carrier generation at the Au/TiO₂ interface; and (ii) ultralow noble-metal loading that suppresses electron-hole recombination at metal/semiconductor junctions, thereby prolonging carrier lifetimes. These effects jointly yield a synergistic enhancement of ¹O₂ production beyond either pathway alone. Under continuous-wave excitation, the metasurfaces reach a local molar-level concentration of ¹O₂ within seconds, corresponding to an approximately six-order-of-magnitude increase in local ¹O₂ concentration compared with conventional approaches. Tuning structural asymmetry and excitation wavelength enables wavelength- and position-selective cytotoxicity without additional molecular sensitizers. By decoupling strong absorption from nobel-metal usage while extending hot-carrier persistence in a single platform, BIC-engineered metasurfaces offer a general way to achieve efficient photon-to-chemical conversion at solid-liquid interfaces. This approach is of significant value to rapid-acting photodynamic therapy, selective oxidation, and flow microreactors where low dose and geometric precision are critical.