关键词: 三重态-三重态湮灭上转换, 光氧化还原, 纳米颗粒, 生物合成, 纳米生物技术

Abstract:

The low excitation intensity, high upconversion quantum efficiency, and tunable absorption/emission wavelengths of triplet-triplet annihilation upconversion (TTA-UC)-based materials, which are novel photon upconversion materials, make them a promising candidate for biomedical applications. These materials facilitate the conversion of low-energy photons to high-energy emission through a bimolecular absorption process. This process is regulated by the triplet-triplet energy transfer (TTET) of photosensitizers and the triplet-triplet annihilation (TTA) of annihilators. TTA-UC's cutting-edge applications, including deep-tissue imaging, targeted photodynamic therapy (PDT), and precise optogenetic, are made extremely suitable by their nonlinear optical properties, which enable them to surpass the penetration depth constraints of conventional fluorescent materials. In contrast, molecular oxygen (³O₂) induces non-radiative decay pathways, resulting in severe quenching effects that significantly reduce upconversion quantum efficiency, particularly in physiological environments. In the past decade, researchers worldwide have effectively proposed a variety of innovative strategies to mitigate the oxygen-quenching effect to address this technical bottleneck. This review provides a comprehensive overview of the current scientific approaches for the development of high-performance and oxygen-resistant TTA-UC materials, with an emphasis on the elucidation of their underlying working mechanisms. (1) The stabilization of TTA-UC pairs through synergistic electron-deficient group modifications and molecular conformation engineering to improve photostability; (2) Oxygen-resistant TTA-UC nanoparticles can be achieved through reductive oil-droplet as soft core; (3) The kinetics of intermolecular triplet energy transfer can be optimized for oxygen tolerance through microstructural regulation. These approaches are critically assessed with respect to their advantages and disadvantages. Additionally, this review evaluates the primary obstacles that TTA-UC nanoparticles face, such as the improvement of TTA-UC efficacy in the near-infrared region and the development of novel TTA-UC nanoparticle preparation strategies and surface bioconjugate chemistry. It is suggested that TTA-UC be integrated with synthetic biology to facilitate the development of biosynthesized upconversion proteins, favor the establishment of upconversion luminescence as a fundamental tool in life sciences, and facilitate its practical implementation across multiple biomedical fields in the near future.

Key words: triplet-triplet annihilation upconversion, photoredox, nanoparticles, biosynthesis, nanobiotechnology