Restricting Bond Rotations by Ring Fusion: A Novel Molecular Design Strategy to Improve Photodynamic Antibacterial Efficacy of AIE Photosensitizers

Membrane-Anchored Aggregation-Induced Emission Luminogens: Accurate Labeling and Efficient Photodynamic Inactivation of Streptococcus mutans in Anticaries Therapy

Dental caries is a widespread bacterial infectious disease that imposes a significant public health burden globally. The primary culprits in caries development are cariogenic bacteria, notably Streptococcus mutans (S. mutans), due to their robust biofilm-forming capabilities. To address this issue, a series of cationic pyridinium-substituted photosensitizers with aggregation-induced emission have been designed. All of these aggregation-induced emission luminogens (AIEgens) exhibit outstanding microbial visualization and photodynamic killing of S. mutans, thanks to their luminous fluorescence and efficient singlet oxygen generation ability. Notably, one of the membrane-anchored AIEgens (TDTPY) can inactivate planktic S. mutans and its biofilm without causing significant cytotoxicity. Importantly, application of TDTPY-mediated photodynamic treatment on in vivo rodent models has yielded commendable imaging results and effectively slowed down caries progression with assured biosafety. Unlike traditional single-mode anticaries materials, AIEgens integrate the dual functions of detecting and removing S. mutans and are expected to build a new caries management diagnosis and treatment platform. To the best of our knowledge, this is also the first report on the use of AIEgens for anticaries studies both in vitro and in vivo.

Near-infrared AIEgens with high singlet-oxygen yields for mitochondria-specific imaging and antitumor photodynamic therapy

AIE-active photosensitizers (PSs) are promising for antitumor therapy due to their advantages of aggregation-promoted photosensitizing properties and outstanding imaging ability. High singlet-oxygen (¹O₂) yield, near-infrared (NIR) emission, and organelle specificity are vital parameters to PSs for biomedical applications. Herein, three AIE-active PSs with D-π-A structures are rationally designed to realize efficient ¹O₂ generation, by reducing the electron-hole distribution overlap, enlarging the difference on the electron-cloud distribution at the HOMO and LUMO, and decreasing the ΔE_ST. The design principle has been expounded with the aid of time-dependent density functional theory (TD-DFT) calculations and the analysis of electron-hole distributions. The ¹O₂ quantum yields of AIE-PSs developed here can be up to 6.8 times that of the commercial photosensitizer Rose Bengal under white-light irradiation, thus among the ones with the highest ¹O₂ quantum yields reported so far. Moreover, the NIR AIE-PSs show mitochondria-targeting capability, low dark cytotoxicity but superb photo-cytotoxicity, and satisfactory biocompatibility. The in vivo experimental results demonstrate good antitumor efficacy for the mouse tumour model. Therefore, the present work will shed light on the development of more high-performance AIE-PSs with high PDT efficiency.

In Situ Imaging and Anti-inflammation of 3D Printed Scaffolds Enabled by AIEgen

Three-dimensional (3D) printed bioactive scaffolds have been widely used in the field of bone tissue engineering. However, its in vivo visualization and bacterial inflammation are intractable issues during the surgery and treatment. Herein, we first synthesized an aggregation-induced emission-active luminogen (AIEgen) named 4BC with efficient reactive oxygen species (ROS) generation. Then, a series of 3D bioactive scaffolds loaded with 4BC were fabricated by a precipitation adsorption method, namely 4BC@scaffolds, which showed good in situ imaging performance for the implanted scaffolds by using simple UV light irradiation. Among them, the 4BC@TMP scaffold composed of trimagnesium phosphate (TMP) had excellent bactericidal ability for Escherichia coli and Staphylococcus aureus in vitro and resisted bacterial inflammation in vivo through photodynamic action. H&E and immunofluorescence staining were performed to further evaluate the inhibitory effect of bacterial inflammation in vivo. This work verified that AIEgen-based 3D scaffolds are promising bioactive frameworks for bioimaging and antibacterial applications.

Molecular engineering to red-shift the absorption band of AIE photosensitizers and improve their ROS generation ability

Increasing the number of acceptors and extending their π-conjugation will red-shift the absorption-emission band, increase the maximum molar extinction coefficient, and improve the ROS generation ability of AIE-photosensitizers.

AIE-Active Antibiotic Photosensitizer with Enhanced Fluorescence in Bacteria Infected Cells and Better Therapy Effect toward Drug-Resistant Bacteria

It is well-known that bacterial infections will induce a variety of diseases in the clinic. In particular, the emergence of drug-resistant bacteria has increased the threat to human health. The development of multiple modes of therapy will effectively fight against drug-resistant bacterial infections. In this work, we covalently attached an AIE photosensitizer to the antibiotic of moxifloxacin hydrochloride (MXF-HCl) and synthesized an antibiotic derivative, MXF-R, with pharmacological activity and photodynamic activation. In infected cells, MXF-R showed enhanced fluorescence after it specifically binds to bacteria; thus, in situ visualization of the bacteria was realized. Notably, through chemo- and photodynamic therapy, MXF-R exhibited better antibacterial activity than its parent antibiotic in rapid sterilization, and it achieved effective killing for moxifloxacin resistant bacteria. In addition, MXF-R shows a broad-spectrum antibacterial effect and could be used in the recovery therapy of infected wounds in mice, demonstrative of a significant therapeutic effect and good biological safety. Thus, as a promising multifunctional antibacterial agent, MXF-R will have tremendous potential in in situ visualization study and killing of drug-resistant bacteria. This work provides an innovative strategy for solving critical disease through the combination of materials and biomedical sciences.

Aggregation-induced emission photosensitizer-based photodynamic therapy in cancer: from chemical to clinical

Cancer remains a serious threat to human health owing to the lack of effective treatments. Photodynamic therapy (PDT) has emerged as a promising non-invasive cancer treatment that consists of three main elements: photosensitizers (PSs), light and oxygen. However, some traditional PSs are prone to aggregation-caused quenching (ACQ), leading to reduced reactive oxygen species (ROS) generation capacity. Aggregation-induced emission (AIE)-PSs, due to their distorted structure, suppress the strong molecular interactions, making them more photosensitive in the aggregated state instead. Activated by light, they can efficiently produce ROS and induce cell death. PS is one of the core factors of efficient PDT, so proceeding from the design and preparation of AIE-PSs, including how to manipulate the electron donor (D) and receptor (A) in the PSs configuration, introduce heavy atoms or metal complexes, design of Type I AIE-PSs, polymerization-enhanced photosensitization and nano-engineering approaches. Then, the preclinical experiments of AIE-PSs in treating different types of tumors, such as ovarian cancer, cervical cancer, lung cancer, breast cancer, and its great potential clinical applications are discussed. In addition, some perspectives on the further development of AIE-PSs are presented. This review hopes to stimulate the interest of researchers in different fields such as chemistry, materials science, biology, and medicine, and promote the clinical translation of AIE-PSs.

An AIE photosensitizer with unquenched fluorescence based on nitrobenzoic acid for tumor-targeting and image-guided photodynamic therapy

Fluorescence quenching occurs in most nitroaromatic compounds due to photoinduced electron transfer (PET) effects, limiting their use as image-guided photosensitizers for anticancer photodynamic therapy (PDT) or as probes for nitroreductase in hypoxic cells. Herein, we developed a tumor-targeting aggregation-induced emission photosensitizer (AIE-PS), Biotin-TTVBA, by binding TTVBA (a nitrobenzoic acid-based AIE-PS with a free carboxylic acid group) to biotin. Biotin-TTVBA has near-infrared emission characteristics in DMSO containing 99% toluene, a large Stoke's shift (210 nm), high photostability, wash-free cell staining ability and type I/II photosensitivity. Compared with TTVBA, Biotin-TTVBA significantly increased cellular uptake (a 60-fold increase) and selective uptake of tumor cells (a 250% increase in the ratio of tumor cells to normal cells), resulting in enhanced antitumor activity against tumor cells (HeLa and MCF-7) and a decreased IC₅₀ value (from >40 μM to 2.5 μM). Taken together, the results of this study call attention to AIE-PSs based on nitroaromatic groups because of their strong fluorescence and ROS generation ability, which can be used in image-guided photodynamic therapy and provide a new approach for tumor-targeting design of AIE-PSs.