Conjugated Polymers with Aggregation-Induced Emission Characteristics for Fluorescence Imaging and Photodynamic Therapy

Conjugated Polymer-Photosensitizers for Cancer Photodynamic Therapy and Their Multimodal Treatment Strategies

Conjugated polymers (CPs) have emerged as promising candidates for photodynamic therapy (PDT) in cancer treatment due to their high fluorescence quantum yield, excellent photostability, and remarkable reactive oxygen species (ROS) generation capability. This review systematically summarizes molecular design strategies to augment CP photosensitivity efficiency, including: (1) constructing donor-acceptor (D-A) alternating structures, (2) incorporating aggregation-induced emission (AIE) moieties, (3) employing heavy-atom effects, and (4) designing hyperbranched architectures. In addition, considering the limitations of monotherapy like tumor heterogeneity, we will further discuss the synergistic treatment strategies of CP-mediated PDT in combination with other therapeutic modalities, including photothermal therapy (PTT)-PDT, immunotherapy-PDT, chemotherapy-PDT, Chemiluminescence (CL)-PDT, diagnostic technology-PDT, and chemodynamic therapy (CDT)-PDT. These multimodal approaches leverage complementary mechanisms to achieve enhanced tumor eradication efficacy.

New NIR-Activated Organic Molecule-Based Nanocomposite as an Efficient Sensitizer for Photothermal and Photodynamic Therapy of Cancer

Acceptor-donor-acceptor (A-D-A)-configured molecules with coplanar dithieno[2,3-d:2',3'-d']thieno[3,2-b:3',2'-b']dipyrrole (DTPT) as the core are promising organic semiconductor materials utilized in organic photovoltaic devices owing to their efficient charge transportation capabilities. In addition to optoelectronic applications, they are potential in photothermal and photodynamic applications due to their light-absorption properties. This study evaluates the utilization of DTPT-based fused-ring-conjugated small molecules with strong near-infrared (NIR) absorption as stable organic photosensitizers for phototherapy by forming nanoparticles (NPs) with D-α-tocopherol polyethylene glycol 1000 succinate (TPGS). Among them, NPs prepared from the 2-(3-cyano-4,5,5-trimethylfuran-2(5H)-ylidene)malononitrile (TCF) end-capping DTPT-centered molecule, DTPTTCF, exhibit low cytotoxicity, enhance photothermal conversion efficiency and superior photodynamic activity. In vitro and in vivo experiments demonstrate the remarkable anticancer efficacy of DTPTTCF@TPGS NPs that can effectively suppress cancer cell proliferation under 808 nm laser treatment. Additionally, soft X-ray tomography (SXT) is employed as a high-resolution tool to observe intracellular variations that reveal distinct vacuolization in the NPs + Laser treated group. These observations highlight that the DTPTTCF@TPGS NPs cause significant damage to cancer cells under NIR irradiation. Furthermore, in vivo, experiments demonstrate the apoptosis of cancer cells within tumor tissues and the effective elimination of tumors upon NIR irradiation of DTPTTCF@TPGS NPs treated mice. This work manifests the potential application of the DTPT-cored A-D-A-type molecule as an advanced agent for tumor phototherapy with enhanced efficacy and selectivity.

Proton Tunneling Allows a Proton-Coupled Electron Transfer Process in the Cancer Cell

Proton-coupled electron transfer (PCET) is a fundamental redox process and has clear advantages in selectively activating challenging C-H bonds in many biological processes. Intrigued by this activation process, we aimed to develop a facile PCET process in cancer cells by modulating proton tunneling. This approach should lead to the design of an alternative photodynamic therapy (PDT) that depletes the mitochondrial electron transport chain (ETC), the key redox regulator in cancer cells under hypoxia. To observe this depletion process in the cancer cell, we monitored the oxidative-stress-induced depolarization of mitochondrial inner membrane potential (MMP) using fluorescence lifetime imaging microscopy (FLIM). Typically, increasing metabolic stress of cancer cells is reflected in a nontrivial change in the fluorophore's fluorescence lifetime. After 30 min of irradiation, we observed a shift in the mean lifetime value and a drastic drop in overall fluorescence signal. In addition, our PCET strategy resulted in drastic reorganization of mitochondrial morphology from tubular to vesicle-like and causing an overall depletion of intact mitochondria in the hypodermis of C. elegans. These observations confirmed that PCET promoted ROS-induced oxidative stress. Finally, we gained a clear understanding of the proton tunneling effect in the PCET process through photoluminescence experiments and DFT calculations.

AIE-Based & Organic Luminescent Materials: Nanoarchitectonics and Advanced Applications

Organic luminescence materials makes the molecule more enthusiastic in wide variety of applications. The luminescent organic materials are in a attraction of the researchers, and the Aggregation-Induced Emission (AIE) is attributed to the occurrence that particular chromophores (typically fluorophores) display very low or nearly no emission in the monomolecular soluble state but become highly emissive when forming aggregates in solution or in solid state. This phenomenon is relatively abnormal when compared with many other traditional fluorophores. AIE research suppresses aggregation-caused quenching (ACQ). Nevertheless, the carbon dots (CDs) and quantum dots have shown to have tyical florescence properties, therefore, recent years many researchers have also attracted for their developments. The CDs, luminescent, and AIE materials are not only used in biomedical applications and organic light-emitting diodes but also in sensing, self-assembly, and other areas. One should introduce promising material to a designed framework that exhibits AIE characteristics to ensure moral results in AIE. Amongest, AIE-active tetraphenylethylene (TPE) is attractive fluorophores due to its easy synthesis strategy. This review article discusses the synthesis properties of TPE, CDs, and luminescent materials with a broad range of applications. We have outlined linear, branched-shaped supramolecular, and hybrid macromolecules due to its potential in the future.

Progress of NIR-II fluorescence imaging technology applied to disease diagnosis and treatment

Near-infrared two-region (NIR-II, 1000-1700 nm) fluorescence imaging has received widespread attention because of its high in vivo penetration depth, high imaging resolution, fast imaging speed and high efficiency, dynamic imaging, and high clinical translatability. This paper reviews the application of NIR-II imaging technology in disease diagnosis and treatment. The paper highlights the latest research progress of commonly used NIR-II imaging materials and the latest progress of multifunctional diagnostic platforms based on NIR-II imaging technology, and discusses the challenges and directions for the development and utilization of novel NIR-II imaging probes.

Molecular Engineering Design of Enhanced Donor-Acceptor Therapeutic Reagent for Efficient Image-Guided Photodynamic Therapy

The greatest barrier to the further development and clinical application of tumor image-guided photodynamic therapy (PDT), is the inconsistency between the fluorescence intensity and singlet oxygen generation yield of the photosensitizer under light excitation. Herein, a novel donor-acceptor (D-A) system is designed from the point of molecular selection by wrapping a classical porphyrin molecule (5,10,15,20-tetraphenylphorphyrin, H2 TPP) as an acceptor into conjugated polymer (Poly[N,N'-bis(4-butylpheny)-N,N'-bis(phenyl)benzidine], ADS254BE) as a donor through fluorescence resonance energy transfer (FRET) mechanism, which exhibits bright red emission centered at 650 nm (quantum yield, 0.12), relatively large Stoke shift of 276 nm, enhanced singlet oxygen generation rate of 0.73, and excellent photostability. The investigations on distribution and killing effect of nanomaterials in cancer cells reveal that ADS254BE/H2 TPP NPs can accumulate in the cytoplasm for imaging while simultaneously producing a large amount of singlet oxygen to remarkably kill cancer cells, which can be used for real-time image-guided PDT. In the xenograft tumor model, real-time imaging and long-term tracing in tumor tissue with ADS254BE/H2 TPP NPs disclose that the growth of lung cancer in mice can be effectively inhibited during in situ imaging. From the standpoint of molecular engineering design, this work provides a feasible strategy for novel D-A systems to improve the development of image-guided PDT.

Water soluble AIEgen-based thermosensitive and antibacterial hydroxypropyl chitin hydrogels for non-invasive visualization and wound healing

Antimicrobial hydrogels containing antibacterial agents have been extensively studied for postoperative infections, wound repair and tissue engineering. However, the abuse of antibiotics has led to the enhancement of bacterial resistance and traditional antibacterial agents are losing their effect. Therefore, fabricating novel and efficient antibacterial hydrogels with enhanced photodynamic antimicrobial activity, good biocompatibility, biodegradability and injectability are highly desirable for clinical application. Herein, a fluorescent and sunlight-triggered synergetic antibacterial thermosensitive hydrogel (red fluorescent hydroxypropyl chitin, redFHPCH) is constructed based on a new water-soluble AIEgen (aggregation-induced emission fluorogen) covalently introduced in hydroxypropyl chitin for non-invasive visualization and wound healing. The thermosensitive redFHPCH solution showing good injectability with fluidity at low temperature was completely transformed into hydrogel under body temperature. The in vitro and in vivo visualization and reactive oxygen species (ROS) generation of the redFHPCH hydrogel are demonstrated clearly because of its excellent AIE fluorescence imaging quality in the red/near-infrared region and superefficient ROS production by sunlight. Moreover, the redFHPCH hydrogel with positively charged quaternary ammonium groups displays a strong synergistic antibacterial effect for healing of infected wound under sunlight irradiation. We believe that this novel strategy can open a new door to explore diversified and multifunctional hydrogels for clinical application.

Increasing the Selectivity of Light-Active Antimicrobial Agents - Or How To Get a Photosensitizer to the Desired Target

Photosensitizers combine the inherent reactivity of reactive oxygen species with the sophisticated reaction control of light. Through selective targeting, these light-active molecules have the potential to overcome certain limitations in drug discovery. Ongoing advances in the synthesis and evaluation of photosensitizer conjugates with biomolecules such as antibodies, peptides, or small-molecule drugs are leading to increasingly powerful agents for the eradication of a growing number of microbial species. This review article, therefore, summarizes challenges and opportunities in the development of selective photosensitizers and their conjugates described in recent literature. This provides adequate insight for newcomers and those interested in this field.

Multifunctional nanotheranostics for near infrared optical imaging-guided treatment of brain tumors

Malignant brain tumors, a heterogeneous group of primary and metastatic neoplasms in the central nervous system (CNS), are notorious for their highly invasive and devastating characteristics, dismal prognosis and low survival rate. Recently, near-infrared (NIR) optical imaging modalities including fluorescence imaging (FLI) and photoacoustic imaging (PAI) have displayed bright prospect in innovation of brain tumor diagnoses, due to their merits, like noninvasiveness, high spatiotemporal resolution, good sensitivity and large penetration depth. Importantly, these imaging techniques have been widely used to vividly guide diverse brain tumor therapies in a real-time manner with high accuracy and efficiency. Herein, we provide a systematic summary of the state-of-the-art NIR contrast agents (CAs) for brain tumors single-modal imaging (e.g., FLI and PAI), dual-modal imaging (e.g., FLI/PAI, FLI/magnetic resonance imaging (MRI) and PAI/MRI) and triple-modal imaging (e.g., MRI/FLI/PAI and MRI/PAI/computed tomography (CT) imaging). In addition, we update the most recent progress on the NIR optical imaging-guided therapies, like single-modal (e.g., photothermal therapy (PTT), chemotherapy, surgery, photodynamic therapy (PDT), gene therapy and gas therapy), dual-modal (e.g., PTT/chemotherapy, PTT/surgery, PTT/PDT, PDT/chemotherapy, PTT/chemodynamic therapy (CDT) and PTT/gene therapy) and triple-modal (e.g., PTT/PDT/chemotherapy, PTT/PDT/surgery, PTT/PDT/gene therapy and PTT/gene/chemotherapy). Finally, we discuss the opportunities and challenges of the CAs and nanotheranostics for future clinic translation.

Vision Defense: Efficient Antibacterial AIEgens Induced Early Immune Response for Bacterial Endophthalmitis

Bacterial endophthalmitis (BE) is an acute eye infection and potentially irreversible blinding ocular disease. The empirical intravitreous injection of antibiotic is the primary treatment once diagnosed as BE. However, the overuse of antibiotic contributes to the drug resistance of pathogens and the retinal toxicity of antibiotic limits its application in clinic. Herein, a cationic aggregation-induced emission luminogens named with triphenylamine thiophen pyridinium (TTPy) is reported for photodynamic treatment of BE. TTPy can selectively discriminate and kill bacteria efficiently over normal ocular cells. More importantly, TTPy shows excellent antibacterial ability in BE rat models infected by Staphylococcus aureus. Meanwhile, the bacterial killing behavior triggered by TTPy induces innate immune response at an early stage of infection, limiting subsequent robust inflammation and protecting retina from bacterial toxins and inflammation-induced bystander damage. In addition, TTPy performs better antibacterial ability than commercially used Rose Bengal, suggesting its excellent capability of vision salvage in acute BE. This study exhibits an efficient photodynamic antibacterial treatment to BE, which induces an early intraocular immune response and saves useful vision, endowing TTPy a promising potential for clinical application of ocular infections.

AIE-Active Photosensitizers: Manipulation of Reactive Oxygen Species Generation and Applications in Photodynamic Therapy

Photodynamic therapy (PDT) is a non-invasive approach for tumor elimination that is attracting more and more attention due to the advantages of minimal side effects and high precision. In typical PDT, reactive oxygen species (ROS) generated from photosensitizers play the pivotal role, determining the efficiency of PDT. However, applications of traditional PDT were usually limited by the aggregation-caused quenching (ACQ) effect of the photosensitizers employed. Fortunately, photosensitizers with aggregation-induced emission (AIE-active photosensitizers) have been developed with biocompatibility, effective ROS generation, and superior absorption, bringing about great interest for applications in oncotherapy. In this review, we review the development of AIE-active photosensitizers and describe molecule and aggregation strategies for manipulating photosensitization. For the molecule strategy, we describe the approaches utilized for tuning ROS generation by attaching heavy atoms, constructing a donor-acceptor effect, introducing ionization, and modifying with activatable moieties. The aggregation strategy to boost ROS generation is reviewed for the first time, including consideration of the aggregation of photosensitizers, polymerization, and aggregation microenvironment manipulation. Moreover, based on AIE-active photosensitizers, the cutting-edge applications of PDT with NIR irradiated therapy, activatable therapy, hypoxic therapy, and synergistic treatment are also outlined.

Emerging Single-Atom Catalysts/Nanozymes for Catalytic Biomedical Applications

Single-atom catalysts (SACs) are a type of atomically dispersed nanozymes with the highest atom utilization, which employ low-coordinated single atoms as the catalytically active sites. SACs not only inherit the merits of traditional nanozymes, but also hold high catalytic activity and superb catalytic selectivity, which ensure their tremendous application potential in environmental remediation, energy storage and conversion, chemical industry, nanomedicine, etc. Nevertheless, undesired aggregation effect of single atoms during preactivation and reaction processes is significantly enhanced owing to the high surface free energy of single atoms. In this case, appropriate substrates are requisite to prevent the aggregation event through the powerful interactions between the single atoms and the substrates, thereby stabilizing the high catalytic activity of the catalysts. In this review, the synthetic methods and characterization approaches of SACs are first described. Then the application cases of SACs in nanomedicine are summarized. Finally, the current challenges and future opportunities of the SACs in nanomedicine are outlined. It is hoped that this review may have implications for furthering the development of new SACs with improved biophysicochemical properties and broadened biomedical applications.

Recent Advances in AIEgen-Based Photodynamic Therapy and Immunotherapy

Cancer, one of the leading causes of death, has seriously threatened public health. However, there is still a lack of effective treatments. Nowadays, photodynamic therapy (PDT), relying on photosensitizers to trigger the generation of reactive oxygen species (ROS) for killing cancer cells, has been emerging as a noninvasive anti-cancer strategy. To enhance the overall anti-cancer efficacy of PDT, various approaches including molecular design and combination with other therapeutic techniques have been proposed and implemented. Especially, photodynamic immunotherapy that can effectively evoke the body's immune response has attracted much attention. Recently, a class of photosensitizers with aggregation-induced emission (AIE) character have shown unique promises, taking advantage of their profound fluorescence and ROS-generating ability in the aggregation state. Despite the promising results demonstrated by several groups, the associated studies are few and the mechanism of such AIEgen-based photodynamic immunotherapy has not been fully understood. This review discusses the recent advances in the AIEgen-based enhanced PDT with a special focus on the AIE photosensitizers for photodynamic immunotherapy, aiming to inspire more opportunities for in-depth investigation of the working principles in this emerging anti-cancer approach.

Vision redemption: Self-reporting AIEgens for combined treatment of bacterial keratitis

Bacterial keratitis (BK) is one of the most commonly leading causes of visual impairment and blindness worldwide, and suffers the risk of drug-resistant infections due to the abuse of antibiotics. Herein, we report a cationic diphenyl luminogen with aggregation-induced emission called IQ-Cm containing isoquinolinium and coumarin units for theranostic study of BK. IQ-Cm has no obvious cytotoxicity to mammalian cells below a certain concentration, and could preferentially bind to bacteria over mammalian cells. IQ-Cm can be used as a sensitive self-reporting probe to rapidly discriminate live and dead bacteria by the visual emission colors. The intrinsic dark toxicity to bacteria and generation of reactive oxygen species under light irradiation endow IQ-Cm with excellent antibacterial activity in vitro and in BK rabbit models infected with S. aureus. The present study provides a sensitive and efficient theranostic strategy for rapid discrimination of various bacterial states and the combined treatment of BK based on the intrinsic dark antibacterial activity and photodynamic therapy effect.