In a groundbreaking advancement poised to revolutionize photodynamic therapy, researchers at Tsinghua University, China, have unveiled a novel approach to rapidly produce singlet oxygen with unprecedented efficiency and precision. This achievement stems from integrating the principles of bound states in the continuum (BIC) into meticulously engineered metasurfaces, marking a significant leap beyond the limitations that have hampered traditional molecular photosensitizers for decades.
Singlet oxygen, the excited state of molecular oxygen with formidable cytotoxic capabilities, has long been a cornerstone in targeting tumor cells via photodynamic therapy. Conventional production methods rely heavily on molecular photosensitizers, which suffer from inherent drawbacks such as photobleaching, limited wavelength selectivity, and biocompatibility issues. Metallic and semiconductor nanostructures emerged as alternatives due to their photostability; however, their quantum yields for singlet-oxygen generation remained too low to enable rapid, localized therapeutic outcomes under clinically viable low-dose illumination.
The breakthrough by Prof. Xing Fu and Prof. Qiang Liu’s team transcends these constraints by leveraging quasi-bound states in the continuum within an innovative Au–TiO₂ metasurface design. This architecture comprises elliptical TiO₂ nanopillars capped with an ultrathin 7 nm gold layer, engineered with subtle symmetry breaking that transforms a theoretically non-radiative BIC into a radiative quasi-BIC resonance. This purposeful symmetry perturbation dramatically enhances visible-light absorption at 532 nm, achieving an impressive 45% absorption within an optical path mere hundreds of nanometers thick. Such efficiency in light capture is vital to triggering the subsequent photochemical processes.
Under continuous-wave laser excitation, the metasurface’s enhanced near-field intensities lead to a marked elevation of the electronic temperature in the gold layer. This phenomenon facilitates the generation of energetic “hot carriers,” electrons that possess sufficient energy to inject into the conduction band of TiO₂. These injected electrons then catalyze interfacial redox reactions with the surrounding oxygen molecules, converting the triplet ground state into the highly reactive singlet oxygen species. The geometric design ensures that this reaction zone is tightly confined adjacent to the metasurface, enabling a concentrated and narrowly localized reactive oxygen environment.
Critically, the researchers have circumvented a prevailing issue in photocatalysis: the trade-off between metal loading and carrier lifetime. Typically, increasing metallic content amplifies light absorption but simultaneously accelerates carrier recombination, thus hindering catalytic efficiency. By maintaining an ultra-thin gold layer and leveraging the quasi-BIC resonance, the team achieved robust absorption with minimal metal volume, preserving extended carrier lifetimes and promoting efficient charge transfer.
One of the most remarkable outcomes of this advancement is the striking enhancement in singlet-oxygen quantum yield—surpassing conventional methods by an astonishing six orders of magnitude. This rapid, molar-level production occurs within mere seconds of illumination at continuous-wave operation, signifying a quantum leap in both speed and scale of reactive oxygen species generation suitable for therapeutic and chemical applications.
Beyond sheer efficiency, the metasurface’s resonant properties offer programmable selectivity. By geometrically scaling the nanopillar array, the resonance wavelength can be precisely tuned, enabling selective activation at desired illumination wavelengths. This spectral addressability facilitates spatially resolved cytotoxic effects, with demonstrated pixel-wise control over tumor-cell apoptosis guided by patterned illumination. Notably, this approach obviates the need for molecular photosensitizers, thereby sidestepping associated stability and compatibility issues.
The interplay of plasmonic and dielectric components within the metasurface underpins these photochemical innovations. While gold nanoparticles have historically served as hot-carrier generators in photocatalytic systems, coupling with TiO₂ elliptical nanopillars tuned near their BIC transitions magnifies the near-field enhancement and modulates charge dynamics. This synergy represents a paradigm shift in designing photocatalytic interfaces tailored for high-efficiency photon-to-chemical conversions.
Moreover, the localized generation of singlet oxygen holds significant promise for clinical applications beyond photodynamic cancer therapy. The capacity for rapid, spatially precise reactive species generation could impact selective oxidation reactions in chemical synthesis, environmental remediation, and microfluidic reactor technologies. The ability to deploy low doses of light while achieving targeted chemical effects is a profound advantage in reducing collateral damage and enhancing process efficiency.
The concept of engineering quasi-BIC states in metasurfaces to facilitate photocatalysis exemplifies the convergence of photonics and catalysis, leveraging wave-matter interactions for chemical control at the nanoscale. By translating this fundamental physics insight into a practical device architecture, the Tsinghua team has established a versatile platform that could be extended to diverse catalytic and sensing applications demanding high spatiotemporal precision.
In sum, the research showcases a compelling instance where advanced materials design, nanophotonics, and surface chemistry intersect to address longstanding challenges in reactive oxygen species generation. The quasi-BIC metasurface paradigm not only provides a robust solution for the rapid generation of singlet oxygen at therapeutic scales but also introduces a new dimension of control and efficiency that could redefine the capabilities of photodynamic therapy and beyond.
The publication in Light: Science & Applications stands as a testament to these interdisciplinary achievements. As the authors highlight, “BIC-engineered metasurfaces offer a generalizable route for efficient photon-to-chemical conversion at solid–liquid interfaces, unlocking immediate opportunities in photodynamic therapy, selective oxidation, and microreactor technologies where both low light dose and geometric precision are paramount.”
This pioneering work opens the door to further exploration of BIC and quasi-BIC states in nanophotonic structures tailored for catalytic applications, signaling a shift towards engineered nanoscale systems that harness light with exquisite control for biomedical and chemical innovations.
Subject of Research: Nanoscale photonics, photocatalysis, and photodynamic therapy.
Article Title: Quasi-BIC metasurfaces enable rapid, localized singlet-oxygen generation
News Publication Date: 2026 (exact date not specified)
Web References: DOI 10.1038/s41377-026-02267-9
Image Credits: Xing Fu et al.
