Integration of TADF Photosensitizer as “Electron Pump” and BSA as “Electron Reservoir” for Boosting Type I Photodynamic Therapy

Type I photosensitization provides an effective solution to the problem of unsatisfactory photodynamic therapeutic (PDT) effects caused by the tumor hypoxia. The challenge in the development of Type I mode is to boost the photosensitizer's own electron transfer capacity. Herein, we found that the use of bovine serum albumin (BSA) to encapsulate a thermally activated delayed fluorescence (TADF) photosensitizer PS can significantly promote the Type I PDT process to generate a mass of superoxide anions (O₂^•-). This Type I photosensitization opened a new strategy by employing BSA as "electron reservoir" and TADF photosensitizer as "electron pump". We integrated these roles of BSA and PS in one system by preparing nanophotosensitizer PS@BSA. The Type I PDT performance was demonstrated with tumor cells under hypoxic conditions. Furthermore, PS@BSA took full advantage of the tumor-targeting role of BSA and achieved efficient PDT for tumor-bearing mice in the in vivo experiments. This work provides an effective route to improve the PDT efficiency of hypoxic tumors.

Improving Photodynamic Therapy Anticancer Activity of a Mitochondria-Targeted Coumarin Photosensitizer Using a Polyurethane-Polyurea Hybrid Nanocarrier

Integration of photosensitizers (PSs) within nanoscale delivery systems offers great potential for overcoming some of the "Achiles' heels" of photodynamic therapy (PDT). Herein, we have encapsulated a mitochondria-targeted coumarin PS into amphoteric polyurethane-polyurea hybrid nanocapsules (NCs) with the aim of developing novel nanoPDT agents. The synthesis of coumarin-loaded NCs involved the nanoemulsification of a suitable prepolymer in the presence of a PS without needing external surfactants, and the resulting small nanoparticles showed improved photostability compared with the free compound. Nanoencapsulation reduced dark cytotoxicity of the coumarin PS and significantly improved in vitro photoactivity with red light toward cancer cells, which resulted in higher phototherapeutic indexes compared to free PS. Importantly, this nanoformulation impaired tumoral growth of clinically relevant three-dimensional multicellular tumor spheroids. Mitochondrial photodamage along with reactive oxygen species (ROS) photogeneration was found to trigger autophagy and apoptotic cell death of cancer cells.

Donor manipulation for constructing a pH sensing thermally activated delayed fluorescent probe to detect alkaliphiles

pH homeostasis is essential for alkaliphiles, given their widespread use in biotechnological applications. However, quantitative monitoring of alkaline pH in alkaliphiles remains challenging. Here, we synthesized for the first time, a thermally activated delayed fluorescent (TADF) pH probe: NI-D-OH. Our probe exhibits a good linear relationship between fluorescence intensity and pH in the neutral to alkaline range (pH 7.0-8.6), as well as long-lived TADF emission. We further show that NI-D-OH can be used to monitor intracellular pH in living organisms, and evaluate the effect of Na⁺ on the pH homeostasis, demonstrating the potential for alkaline pH monitoring and time-resolved fluorescence imaging.

Thermally Activated Delayed Fluorescence Material: An Emerging Class of Metal-Free Luminophores for Biomedical Applications

The development of simple, efficient, and biocompatible organic luminescent molecules is of great significance to the clinical transformation of biomaterials. In recent years, purely organic thermally activated delayed fluorescence (TADF) materials with an extremely small single-triplet energy gap (ΔEST ) have been considered as the most promising new-generation electroluminescence emitters, which is an enormous breakthrough in organic optoelectronics. By merits of the unique photophysical properties, high structure flexibility, and reduced health risks, such metal-free TADF luminophores have attracted tremendous attention in biomedical fields, including conventional fluorescence imaging, time-resolved imaging and sensing, and photodynamic therapy. However, there is currently no systematic summary of the TADF materials for biomedical applications, which is presented in this review. Besides a brief introduction of the major developments of TADF material, the typical TADF mechanisms and fundamental principles on design strategies of TADF molecules and nanomaterials are subsequently described. Importantly, a specific emphasis is placed on the discussion of TADF materials for various biomedical applications. Finally, the authors make a forecast of the remaining challenges and future developments. This review provides insightful perspectives and clear prospects towards the rapid development of TADF materials in biomedicine, which will be highly valuable to exploit new luminescent materials.

A Dual-Nanozyme-Catalyzed Cascade Reactor for Enhanced Photodynamic Oncotherapy against Tumor Hypoxia

Tumor hypoxia is a typical characteristic of tumor microenvironment (TME), which seriously compromises the therapeutic effect of photodynamic therapy (PDT). The development of nanozymes with oxygen-generation ability is a promising strategy to overcome the oxygen-dependent of PDT but remained a great challenge. Herein, a dual-nanozymes based cascade reactor HAMF is proposed to alleviate tumor hypoxia for enhanced PDT. The hollow mesoporous silica nanoparticles (HMSNs) are constructed as an excellent nanocarrier to load ultra-small gold nanoparticles (Au NPs) and manganese dioxide (MnO₂ ) shell via in situ reduction method, and further coordination with an efficient photosensitizer 4-DCF-MPYM (4-FM), a thermally activated delayed fluorescence (TADF) fluorescein derivative. With the response to TME, MnO₂ can catalyze endogenous H₂ O₂ into O₂ and subsequently accelerating glucose oxidation by Au NPs to produce additional H₂ O₂ , which is reversely used as the substrate for MnO₂ -catalyzed reaction, thereby constantly producing singlet oxygen (¹ O₂ ) for enhanced PDT upon light irradiation. This work proposed a cascade reactor based on dual-nanozyme to relieve tumor hypoxia for effective tumor suppression, which may enrich the application of multi-nanozymes in biomedicine.

Highly Efficient Aggregation-Induced Red-Emissive Organic Thermally Activated Delayed Fluorescence Materials with Prolonged Fluorescence Lifetime for Time-Resolved Luminescence Bioimaging

Organic thermally activated delayed fluorescence (TADF) materials are emerging as potential candidates for time-resolved fluorescence imaging in biological systems. However, the development of purely organic TADF materials with bright aggregated-state emissions in the red/near-infrared (NIR) region remains challenging. Here, we report three donor-acceptor-type TADF molecules as promising candidates for time-resolved fluorescence imaging, which are engineered by direct connection of electron-donating moieties (phenoxazine or phenothiazine) and an electron-acceptor 1,8-naphthalimide (NI). Theoretically and experimentally, we elucidate that three TADF materials possessed remarkably small ΔE_ST to promote the occurrence of reverse intersystem crossing (RISC). Moreover, they all exhibit aggregation-induced red emissions and long delayed fluorescence lifetimes without the influence of molecular oxygen. More importantly, these long-lived and biocompatible TADF materials, especially the phenoxazine-substituted NI fluorophores, show great potential for high-contrast fluorescence lifetime imaging in living cells. This study provides further a molecular design strategy for purely organic TADF materials and expands the versatile biological application of long-lived fluorescence research in time-resolved luminescence imaging.

Enhancing Intersystem Crossing to Achieve Thermally Activated Delayed Fluorescence in a Water-Soluble Fluorescein Derivative with a Flexible Propenyl Group

It is a challenge to rationally design an organic molecule with thermally activated delayed fluorescence (TADF) due to the intrinsically spin-forbidden transition. Meanwhile, those reported TADF organic molecules have difficulty to be directly applied in the field of biological and medical imaging because they usually have no water solubility. Here, a water-soluble TADF organic molecule DCF-BXJ was developed by introducing a flexible propenyl group into the commercial traditional fluorophore DCF (2,7-dichlorofluorescein). The flexible group provides nonradiative rotational motion, which causes an efficient energy level cross between the S₁ state and the T₂ state of DCF-BXJ. Results of transient absorption spectra and theoretical calculations supported that nonradiative rotational motion of the flexible group can enhance intersystem crossing (ISC) and bring out TADF. This work provides a new mechanism explanation for TADF existing in organic molecules.

A single component self-assembled thermally activated delayed fluorescence nanoprobe

A novel versatile thermally activated delayed fluorescence (TADF) nanoprobe, AI-Cz-NP, was constructed by self-assembly of a single-component amphiphilic monomer for potential applications in confocal imaging and time-resolved fluorescence imaging.