Evaluation of Structure-Function Relationships of Aggregation-Induced Emission Luminogens for Simultaneous Dual Applications of Specific Discrimination and Efficient Photodynamic Killing of Gram-Positive Bacteria

Important Role of Triphenylamine in Modulating the Antibacterial Performance Relationships of Antimicrobial Peptide Mimics by Alkyl Chain Engineering

Multidrug resistance (MDR) bacteria pose a serious threat to human health, and the development of effective antimicrobial drugs is urgent. Herein, we used alkyl chain engineering to design and synthesize two series of antimicrobial peptide mimics with distinct cores: triphenylamine quaternary ammonium derivatives (TPQs) and diphenylethene quaternary ammonium derivatives (BPQs), and we investigated the effect of varying the alkyl chain lengths on antibacterial activity. We found that the introduction of a triphenylamine group significantly enhances the antibacterial activity of short-chain dimethyl quaternary ammonium derivatives while maintaining their excellent biocompatibility. Most notably, TPQ-1 exhibited negligible invasiveness toward living cells and possesses good antimicrobial activities, with good efficacy against biofilms and persisters. Moreover, TPQ-1 exhibited good antimicrobial effects in vivo and significantly accelerated the healing process of methicillin-resistant Staphylococcus aureus-infected wounds. This work promotes the practical application of antimicrobial peptide mimics and triphenylamine derivatives.

Aggregation-Induced Emission-Active Toroidal Micelles from a Conjugated Polymer: A Selective Phototheranostic Nanoplatform for Targeting Gram-Positive Bacteria

Developing advanced antimicrobial photosensitizers that target bacteria precisely is highly desirable but challenging. Traditional photosensitizers demonstrate reduced reactive oxygen species (ROS) production and quenched fluorescence upon aggregation in water, significantly affecting their phototheranostic performance. In this study, water-dispersible toroidal micelles (TPE-BT Mic) with excellent fluorescence properties and ROS generation are prepared by using aggregation-induced emission (AIE)-active conjugated polymer TPE-BT as the photosensitizer and vancomycin-decorated Pluronic F127 as both the encapsulating and targeting material. The stable toroidal micelles not only promote the aggregation of TPE-BT and induce an AIE effect but also improve its water dispersibility and biocompatibility. TPE-BT Mic with vancomycin targeting groups selectively bind to Gram-positive bacteria Staphylococcus aureus (S. aureus) via the d-alanyl-d-alanine terminus of peptidoglycan, showing strong bioimaging performance. They achieved over 97% killing efficiency for S. aureus with low white-light irradiation (20 mW/cm2). Thus, TPE-BT Mic are promising for treating Gram-positive bacterial infections and offer an innovative approach for creating effective photosensitizers to combat the menace of drug resistance.

Cationic conjugated polymers with tunable hydrophobicity for efficient treatment of multidrug-resistant wound biofilm infections

Biofilm-associated infections arising from antibiotic-resistant bacteria pose a critical challenge to global health. We report the generation of a library of cationic conjugated poly(phenylene ethynylene) (PPE) polymers featuring trimethylammonium terminated sidechains with tunable hydrophobicity. Screening of the library identified an amphiphilic polymer with a C11 hydrophobic spacer as the polymer with the highest antimicrobial efficacy against biofilms in the dark with excellent selectivity. These polymers are highly fluorescent, allowing label-free monitoring of polymer-bacteria/biofilm interactions. The amphiphilic conjugated polymer penetrated the biofilm matrix in vitro and eradicated resident bacteria through membrane disruption. This C11 polymer was likewise effective in an in vivo murine model of antibiotic-resistant wound biofilm infections, clearing >99.9 % of biofilm colonies and efficient alleviation of biofilm-associated inflammation. The results demonstrate the therapeutic potential of the fluorescent conjugated polymer platform as a multi-modal antimicrobial and imaging tool, surpassing conventional antimicrobial strategies against resilient biofilm infection.

AIE Photosensitizer with Tuned Membrane Interactions for Effective-Gram-Negative Bacteria Elimination

Photodynamic antimicrobial therapy (PDAT) for efficient bacterial infection eradication critically relies on photosensitizers (PSs) that can specifically target and disrupt bacterial membranes. However, the complex membrane architecture of Gram-negative bacteria poses a significant challenge to the efficacy of most aggregation-induced emission (AIE) PSs. Herein, we introduce TPQ, an AIE PS meticulously designed to overcome this challenge by incorporating an outer membrane disruption ability, thereby boosting PDAT efficacy against Gram-negative bacteria. TPQ demonstrated excellent microbial imaging and potent PDAT activity against both Gram-positive and Gram-negative bacteria, attributed to its inherent fluorescence, high singlet oxygen generation, and balanced electrostatic and hydrophobic interactions with bacterial membranes. Notably, TPQ achieved exceptional PDAT activity (>97% efficacy) against Gram-negative bacteria while exhibiting minimal cytotoxicity to mammalian cells. Furthermore, TPQ-mediated PDAT effectively healed Escherichia coli-infected wounds on mice models with assured biosafety. This work provides valuable insights into the rational design of AIE PSs and highlights the synergistic effect of membrane disruption for advancing PDAT applications, particularly against recalcitrant Gram-negative bacterial infections.

Modular Design of Membrane-Impermeable Versatile Probe for Specific Imaging of Cell Walls and Real-Time Detection of Cell Membrane Damage

The versatile fluorescent dyes are essential for specifically labeling plant cell walls in vivo, monitoring plasma membrane damage, and assessing cell viability. However, such dyes are rare and often discovered accidentally due to a lack of design principles. Propidium iodide, a well-known example, has limitations like low brightness, high toxicity, and poor bacterial differentiation. To address these challenges, we developed VersaDye, a modular probe designed for specific imaging of live plant cell walls and monitoring plasma membrane damage in plant cells, human cells, and certain bacteria. The design integrates impermeability principles and environment-dependent fluorophore scaffolds. VersaDye enables bright, wash-free labeling of plant cell walls and can stain various plant organs for constructing 3D tissue organization. Notably, it can selectively distinguish live Gram-positive from Gram-negative bacteria, a feature absent in other dyes. Its impermeability and targeting ability also allow it to probe membrane damage caused by physical, chemical, and biological stimuli. This study marks the first use of VersaDye in analyzing cell damage in live plants under salt stress. VersaDye offers a robust platform for wash-free, in vivo membrane damage monitoring and simultaneous cell wall labeling. Additionally, its design suggests adaptability for regulating permeability to meet specific diagnostic needs, such as identifying membrane-compromised cells in diseases or enabling high-throughput antibiotic screening targeting specific bacteria.

A dual-mechanism luminescent antibiotic for bacterial infection identification and eradication

Because of the rapid emergence of antibiotic-resistant bacteria, there is a growing need to discover antibacterial agents. Here, we design and synthesize a compound of TPA2PyBu that kills both Gram-negative and Gram-positive bacteria with an undetectably low drug resistance. Comprehensive analyses reveal that the antimicrobial activity of TPA2PyBu proceeds via a unique dual mechanism by damaging bacterial membrane integrity and inducing DNA aggregation. TPA2PyBu could provide imaging specificity that differentiates bacterial infection from inflammation and cancer. High in vivo treatment efficacy of TPA2PyBu was achieved in methicillin-resistant Staphylococcus aureus infection mouse models. This promising antimicrobial agent suggests that combining multiple mechanisms of action into a single molecule can be an effective approach to address challenging bacterial infections.

Oxygen-supplying nanotherapeutics for bacterial septic arthritis via hypoxia-relief-enhanced antimicrobial and anti-inflammatory phototherapy

Bacterial septic arthritis, an inflammatory disease caused by bacterial infections, is often accompanied by the emergence of multidrug-resistant bacteria, making therapeutic treatment a formidable challenge. With the emergence of antibiotic resistance, research on antimicrobial photodynamic therapy (aPDT) has regained attention. However, insufficient singlet oxygen production due to the hypoxia in the infection microenvironment is recognized as a key limiting the efficacy of aPDT. Hence, in this study, we designed a bacteria-targeted liposomal nanoplatform (MCPL) to alleviate hypoxia in the infectious microenvironment and enhance aPDT for bacterial septic arthritis. The nanoplatform was developed by integrating the phototherapeutic agent CyI and small-sized Pt NPs into thermosensitive liposomes, with modification of maltohexose on the liposome surface. In vitro and in vivo studies showed that MCPL could specifically target bacterial cell membranes and be thermally activated to catalytically convert endogenous hydrogen peroxide (H2O2) in the septic joint, supplementing local O2 reservoirs. This, in turn, supplies additional substrate pools for photodynamic conversion into reactive oxygen species (ROS) with bacterial toxicity. Furthermore, the antibacterial mechanism revealed that MCPL can regulate the HIF-1α and NF-κB signaling pathways in immune cells, acting as an effective modulator of antioxidant and anti-inflammatory pathways in both macrophages and neutrophils. This study demonstrates that MCPL could not induce bacterial multidrug resistance and provide as an innovative approach for treating bacterial septic arthritis.

A NIR-II emissive sonosensitized biotuner for pyroptosis-enhanced sonodynamic therapy of hypoxic tumors

Pyroptosis is considered as a new way to effectively boost the immune response of tumors and inhibit tumor growth. Effective strategies to induce pyroptosis mainly rely on chemotherapeutic drugs and phototherapy, but their potential biotoxicity and phototoxicity limit their application in biomedicine. Herein, we designed a NIR-II emitting pyroptosis biotuner, Rd-TTPA, which induced pyroptosis under ultrasound irradiation to achieve pyroptosis-enhanced sonodynamic therapy (SDT) and immunogenic cell death (ICD) for tumors. Benefiting from its A-π-D1-D2 structure enhanced donor-acceptor interaction, Rd-TTPA can induce cell pyroptosis under both normoxia (21 % O2) and hypoxia (2 % O2) conditions by rapidly generating superoxide radicals (O2-•) upon ultrasound irradiation. The sonodynamic biotuner of pyroptosis overcomes the longstanding weakness of chemical drug and photosensitizer-based pyroptosis, such as drug resistance and limited penetration depth. In-depth studies demonstrated that Rd-TTPA can selectively target tumor cell mitochondria and possess excellent in vivo NIR-II fluorescence imaging capabilities. Administrating a tumor-bearing mouse model with Rd-TPPA, satisfying antitumor efficacy via pyroptosis-augmented SDT was achieved upon the guidance of NIR-II fluorescence imaging.

Aggregation-induced emission-based phototheranostics to combat bacterial infection at wound sites: A review

The healing of chronic wounds infected by bacteria has attracted increasing global concerns. In the past decades, antibiotics have certainly brought hope to cure bacteria-infected chronic wounds. However, the misuse of antibiotics leads to the emergence of numerous multidrug-resistant bacteria, which aggravate the health threat to clinical patients. To address these increasing challenges, scientists are committed to creating novel non-antibiotic strategies to kill bacteria and promote bacteria-infected chronic wound healing. Fortunately, with the quick development of nanotechnology, the representatives of phototherapy, such as photothermal therapy (PTT) and photodynamic therapy (PDT), exhibit promising possibilities in promoting bacteria-infected wound healing. Well-known, photothermal agents and photosensitizers largely determine the effects of PTT and PDT. A common problem for these molecules is the aggregation-induced quenching effect, which highly limits their further applicability in biomedical and clinical fields. Fortunately, the occurrence of aggregation-induced emission luminogens (AIEgens) efficiently overcomes the photobleaching and exhibit advantages, such as strongly aggregated emission, superior photostability, aggregation-enhanced reactive oxygen species (ROS), and heat generation, which makes great sense to the development of PTT and PDT. This article reviews various studies conducted on novel AIEgen-based materials that can mediate potent PDT, PTT, and a combination of PDT and PTT to promote bacteria-infected chronic wound healing.

Tuning the Near-Infrared J-Aggregate of a Multicationic Photosensitizer through Molecular Coassembly for Symbiotic Photothermal Therapy and Chemotherapy

Cationic photosensitizers (PSs) offer many intriguing advantages, in addition to generating heat or reactive oxygen species for cancer phototherapy. However, the preparation of cationic PSs with enhanced near-infrared (NIR) absorption remains a significant challenge. In this work, we have synthesized a PS TPBBT, which incorporates a strong electron-withdrawing unit, benzobisthiadiazole, and four terminal pyridinium groups. It self-assembles into a mixed H/J aggregated state with a maximal absorption peak at 620 nm but coassembles with negatively charged planar small molecules to form sole J-aggregates. Following this strategy, we coassemble TPBBT with rhein, a planar, anionic traditional Chinese medicine with an anticancer activity, which allows for a near 100 nm bathochromic shift of the maximal absorption of TPBBT and improves the photothermal conversion efficiency (PCE) of TPBBT from 6.4 to 60.4% under 808 nm laser irradiation. Additionally, coassembling with TPBBT significantly enhances the cellular uptake of rhein through the photothermal effect. The coassembly of TPBBT and rhein (TPBBTein) can completely eliminate 4T1 tumors on mouse models, validating that this facile strategy not only can tune the NIR J-aggregate of cationic PS through molecular coassembly but also promotes the efficient, symbiotic combination of photothermal therapy and chemotherapy.

A Dual-Channel Fluorescent Probe for Accurate Diagnosis and Precise Photodynamic Killing of Bacterial Infections by Employing Dual-Mechanism Responses

Bacterial infections pose a huge challenge to global public health, exacerbated by the growing threat of antibiotic resistance due to overuse of antibiotics, and there is an urgent need to develop epidemiological control methods that enable accurate detection and precise treatment. In this study, we present an innovative dual-response integrated probe, Nap-CefTTPy, which is capable of dual-channel fluorescence imaging, synergizing with photodynamic therapy for the accurate diagnosis and precise treatment of bacterial infections. The probe has excellent selectivity for bacteria and can produce two independent spectral responses to bacteria through two different response mechanisms under a single laser excitation, achieving accurate diagnosis of dual-channel bacterial infections. At the same time, it can also produce reactive oxygen species for synergistic photodynamic therapy, which ensures the accuracy of diagnosis and treatment. In a mouse bacterial infection model, it largely promoted the wound healing of S. aureus-infected mice. This platform represents a significant advancement in the field, providing a novel approach for the dual-code mutual correction diagnosis and photodynamic therapy of bacterial infections.

Leading edge biosensing applications based on AIE technology

Luminescent materials provide a unique method for biological imaging. Luminescent probes can label molecules of interest and present luminescent signals. Bioluminescence bioimaging has shown great efficacy in environmental, live cell and animal studies. Light-emitting materials play a very wide role in the field of light-emitting devices and biosensing. Luminescent materials are usually used as solid films or aggregate states. However, it is difficult to monitor the selectivity and sensitivity of various ions and small molecules in living cells with ordinary luminescent materials due to the changes in various aspects of analytes. Organic luminescent materials exhibit aggregation-induced quenching (ACQ) on molecular aggregation, and the ACQ effect is very common, which greatly limits the application of luminescent materials in chemical sensing, especially in biological imaging. Academician Tang Benzhong proposed "aggregation-induced emission (AIE)" as a powerful method to solve the ACQ problem for the first time. In this paper, the working principle of AIE is reviewed, and the research on the core working mechanism of AIE technology is not only of great fundamental significance, but also can pave the way for practical innovation of AIE technology applications. In this review, we outline the current basic understanding of the working mechanism of AIE, collate the cutting-edge biosensing applications based on AIE technology, including applications based on AIE in substance detection, biological detection, and disease detection. At last, we discuss the future development of AIE research.

Molecular design strategy for microorganism discrimination based on keto-salicylaldehyde azine derivatives

The rapid and selective identification of microorganisms is of great significance for clinical therapy applications. To develop high performance probes for microbe determination, we systemically constructed series aggregation-induced emission (AIE) luminogens by modulating the structural planarity, the basicity of functional group, the length of linker moiety and the hydrophobicity based on our previous work. The detail structure-property relationship study based on experimental and theoretical observation revealed that: i) the planar skeleton is essential for probe insertion towards the cell wall via van n der Waals' force. ii) the basic function group enable the anchoring on the membrane by binding with acidic biomolecules. iii) the shortened alkyl chain is in favor of the efficient binding of basic groups with microbes and endows the desirable hydrophobicity. Based on the developed probes, the successful detection of the pathogens in clinic samples was achieved in highly sensitive and simple way. This work provides a reliable strategy for designing intelligent luminogens for microorganism discrimination and identification in efficient and sensitive way for in vitro diagnosis applications, especially point-of-care testing (POCT).

Eradication of Antibiotic-Resistant Gram-Positive Bacteria and Biofilms by Rationally Designed AIE-Active Iridium(III) Complexes Derived from Cyclometalating 2-Phenylquinoline and Ancillary Bipyridyl Ligands

Antibiotic resistance caused by Gram-positive bacteria is a growing global human health threat. Selective discrimination and eradication of Gram-positive bacteria and their biofilms is challenging. Therapeutic strategies with multiple modes of action are urgently needed to address the increase in Gram-positive bacteria-resistant nosocomial infections. In this work, we have presented rationally designed aggregation-induced emission (AIE)-active cationic cyclometalated iridium(III) complexes derived from 2-phenylquinoline and 2,2'-bipyridine ligands for Gram-positive antibacterial studies. The AIE properties of these complexes were exploited for selective discrimination between Gram-positive and Gram-negative bacteria. These complexes displayed good antimicrobial activity against critical Gram-positive ESKAPE pathogens with minimum inhibitory concentrations in the low micromolar range but were inactive against Gram-negative pathogens. Importantly, the complexes can inhibit biofilm formation and eradicate bacteria from mature biofilms, which are major causes of persistent infections and antibiotic resistance and are more difficult to eliminate. In addition, these complexes showed low hemolytic activity against mammalian cells and a high therapeutic index, indicating good selectivity. Interestingly, the complexes kill bacteria through a variety of modes of mechanism, including ROS generation, cell membrane disruption, and depolarization and the loss of bacterial membrane integrity. These findings offer opportunities for designing metal AIEgens to treat Gram-positive bacterial infections effectively.

Photo-Amplified Plasma Membrane Rupture by Membrane-Anchoring NIR-II Small Molecule Design for Improved Cancer Photoimmunotherapy

Immunotherapy is a promising cancer treatment method for eradicating tumor cells by enhancing the immune response. However, there are several major obstacles to conventional phototherapy-mediated immune responses, including inadequate immunogenicity and immunosuppressive environment. Here, we present a novel photoimmunotherapy modality-the development of membrane-anchoring small molecule inducing plasma membrane rupture (PMR) by NIR-II photo-stimulation, thus evoking cell necrotic death and enhancing antitumor immunotherapy. Our top-performing membrane-anchoring small molecule (CBT-3) exhibits temperature-tunable PMR efficiency, allowing rapid necrotic death in cancer cells at 50 μM dose by using exogenous NIR-II light-mediated mild photothermal effect (1064 nm, 0.6 W cm-2). Further evidence indicated that this gentle therapeutic approach activated inflammatory signaling pathways in cells, enhanced immunogenic cell death, and reshaped the immunosuppressive tumor microenvironment, ultimately promoting systemic antitumor immune responses in vivo. This study represents the first instance of utilizing NIR-II photo-amplified PMR effect based on membrane-anchoring small molecule, providing a novel avenue for advancing cancer photoimmunotherapy.

Aggregation-Induced Emission Luminogens for Plant Photodynamic Seed Sterilization

Pathogen-carrying seeds can significantly impact plant growth and development and may lead to serious public health incidents. Modern agriculture heavily relies on synthetic chemical microbicides and physical methods to eradicate pathogens transmitted by plant seeds. To counteract the misuse of microbicides, a class of cationic amphiphilic aggregate-induced emission luminogens (AIEgens) are developed as photodynamic seed sterilization agents. AIEgens function as antimicrobial agents in seed treatment. These materials are engineered to specifically bind to pathogenic microorganisms on seed surfaces. Furthermore, when combined with photodynamic therapy, AIEgens can be activated to produce reactive oxygen species that selectively destroy pathogens. Sterilization experiments with tomato seeds carrying Pseudomonas syringae and mung bean seeds carrying Pseudomonas aeruginosa demonstrate that AIEgens can effectively eliminate both plant and animal pathogens carried by seeds. Therefore, AIEgens offer a promising solution for preventing the spread of seed-borne pathogens.

AIE-Active Antibacterial Photosensitizer Disrupting Bacterial Structure: Multicenter Validation against Drug-Resistant Pathogens

Antimicrobial resistance (AMR) has emerged as a global challenge in treating bacterial infections, creating an urgent need for broad-spectrum antimicrobial agents that can effectively combat multidrug-resistant (MDR) bacteria. Despite advancements in novel antimicrobial agents, many fail to comprehensively cover common resistant bacterial strains or undergo rigorous multi-center validation. Herein, a cationic AIE-active photosensitizers are developed, ITPM, derived from a triphenylamine-pyridine backbone to address the MDR challenge. Rigorous validation demonstrates that ITPM possesses superior fluorescence imaging capabilities and exceptional antibacterial efficacy. And its broad-spectrum activity is verified through a multi-center study involving six clinically relevant MDR strains. Additionally, resistance development studies and comparisons with advanced clinical antibiotics reveal that ITPM exhibits potent, broad-spectrum antimicrobial activity with minimal resistance development. This efficacy is attributed to its unique antibacterial mechanism involving disrupting bacterial internal structures. These findings establish ITPM as a promising candidate for broad-spectrum antimicrobial therapy, offering a potential solution to the growing crisis of AMR in clinical settings.

AIE-based ruthenium complexes as photosensitizers for specifically photo-inactivate gram-positive bacteria

The emergence of multidrug-resistant bacterial have caused severe burden for public health. Particularly, Staphylococcus aureus as one of ESKAPE pathogens have induced various infectious diseases and resulted in increasing deaths. Developing new antibacterial agents is still urgent and challenging. Fortunately, in this study, based on aggregation-induced emission (AIE) ruthenium complexes were designed and synthesized, which realized the high efficiency of reactive oxygen species generation and remarkably killed S. aureus unlike conventional antibiotics action. Significantly, owing to good singlet oxygen production ability, Ru1 at only 4 μg/mL of concentration displayed good antibacterial photodynamic therapy effect upon white light irradiation and could deplete essential coenzyme NADH to disrupt intracellular redox balance. Also, the electrostatic interaction between Ru1 and bacteria enhanced the possibility of antibacterial. Under light irradiation, Ru1 could efficiently inhibit the biofilm growth and avoid the development of drug-resistant. Furthermore, Ru1 possessed excellent biocompatibility and displayed remarkable therapy effect in treating mice-wound infections in vivo. These findings indicated that AIE-based ruthenium complexes as new antibacterial agent had great potential in photodynamic therapy of bacteria and addressing the drug-resistance crisis.

Evaluation of the alkyl chain length and photocatalytic antibacterial performance of cation g-C3N4

Several cation graphite carbon nitrides (g-C3N4-(CH2)n-ImI+) were synthesized by chemically attaching imidazolium appended alkane chains with different lengths (n = 2, 4, 8, 12 and 16) to g-C3N4. The introduction of a cation segment potentially improved the interaction between the carbon material and Gram negative (MDR-A. baumannii) and Gram positive (S. aureus) bacteria as characterized by ζ potential measurement. Short alkane chain (carbon numbers of 2, 4 and 8) carbon materials displayed relatively stronger bacterial interactions compared to long alkane chain bearing ones (n = 12 and 16). In addition, short chain carbon materials (g-C3N4-(CH2)4-ImI+) displayed relatively higher photocatalytic reactive oxygen species (1O2, ˙O2- and ˙OH) production efficiency. Bacterial interaction and ROS production efficiency synergistically contribute to photocatalytic antibacterial performance. The current data revealed that g-C3N4 with short flexible cations attached exhibited bacterial interaction and ROS production. Among these synthesized materials, g-C3N4-(CH2)4-ImI+ exhibited the most pronounced photocatalytic antibacterial efficiency (>99%).

Highly Efficient AIE-Active palmatine photosensitizer for photodynamic inactivation of Listeria monocytogenes in apple juice preservation

Photodynamic sterilization is a promising alternative to conventional antibacterial approaches with merits of high efficiency and safety. The exploration of aggregation-induced emission (AIE)-type photosensitizers from natural sources is highly valued by researchers and food industry. Herein, the use of palmatine (PA), an aggregation-induced emission-active natural product from traditional Chinese medicine, as photosensitizers for photodynamic inactivation of a tenacious foodborne pathogen of Listeria monocytogenes is investigated. Antibacterial and antibiofilm activity against L. monocytogenes of PA-mediated photodynamic process were first assessed. The results showed that PA-mediated photodynamic process could inhibit the growth of L. monocytogenes, and the minimum bactericidal concentration was determined as 80 μM. At this PA dosing level, well-established biofilms of L. monocytogenes can be effectively destroyed under light irritation. Afterward, cell- and gene-level investigations were conducted to explore the antibacterial mechanism. It is concluded that the exceptional photodynamic antibacterial activity of PA against L. monocytogenes is attributed to the disruption of the cell wall and membrane, increased cell permeability, leakage of functional proteins, and damage to DNA structure. Subsequently, PA-mediated photodynamic process was applied to reduce bacterial activity in apple juice while preserving its quality. Overall, this work highlights the significant potential of PA-mediated photodynamic strategy for controlling foodborne pathogens in food systems.

A General Strategy for Enhanced Photodynamic Antimicrobial Therapy with Perylenequinonoid Photosensitizers Using a Macrocyclic Supramolecular Carrier

Perylenequinonoid natural products are a class of photosensitizers (PSs) that exhibit high reactive oxygen species (ROS) generation and excellent activity for Type I/Type II dual photodynamic therapy. However, their limited activity against gram-negative bacteria and poor water solubility significantly restrict their potential in broad-spectrum photodynamic antimicrobial therapy (PDAT). Herein, a general approach to overcome the limitations of perylenequinonoid photosensitizers (PQPSs) in PDAT by utilizing a macrocyclic supramolecular carrier is presented. Specifically, AnBox·4Cl, a water-soluble cationic cyclophane, is identified as a universal macrocyclic host for PQPSs such as elsinochrome C, hypocrellin A, hypocrellin B, and hypericin, forming 1:1 host-guest complexes with high binding constants (≈107 m -1) in aqueous solutions. Each AnBox·4Cl molecule carries four positive charges that promote strong binding with the membrane of gram-negative bacteria. As a result, the AnBox·4Cl-PQPS complexes can effectively anchor on the surfaces of gram-negative bacteria, while the PQPSs alone cannot. In vitro and in vivo experiments demonstrate that these supramolecular PSs have excellent water solubility and high ROS generation, with broad-spectrum PDAT effect against both gram-negative and gram-positive bacteria. This work paves a new path to enhance PDAT by showcasing an efficient approach to improve PQPSs' water solubility and killing efficacy for gram-negative bacteria.

Intelligent Carbon Dots with Switchable Photo-Activated Oxidase-Mimicking Activity and pH Responsive Antioxidant Activity Adaptive to the Wound Microenvironment for Selective Antibacterial Therapy

Intelligent antibacterial agent with controllable activities adaptive to the wound microenvironment is appealing to reduce drug resistance and enhance antibacterial efficiency. In this study, celery is chosen as the carbon source to construct celery-based carbon dots (CECDs) with double activities, i.e., reactive oxygen species (ROS)-production and ROS-clearance activities. The ROS-production capability of CECDs is dependent on the oxidase (OXD)-mimicking activity, which is only photo-activated and thus artificially controlled by light to avoid the production of excess ROS. Meanwhile, the optimal OXD-mimicking activity occurrs at the pH of 5, close to microenvironmental pH at the bacterial infection site, which will enhance the antibacterial efficacy. On the other hand, CECDs exhibit the antioxidant activity at the neutral or weak alkaline pH, which will assist the healing of the wound. Thus, the conversion of ROS-production and ROS-clearance ability of CECDs can be dynamically and intelligently switched automatically with microenvironmental pH at different stages of treatment (from acid to neutral/weak basic). The proposed CECDs exert adorable selective antibacterial activity against Gram-positive bacteria and satisfactory therapeutic effect on bacteria infected mice. This study paves a new avenue to design the intelligent antibacterial nanoagent sensitive to the infected microenvironmental condition, reducing drug resistance and assisting precise medicine.

Enhancing antibacterial photodynamic therapy with NIR‐activated gold nanoclusters: Atomic‐precision size effect on reducing bacterial biofilm formation and virulence

Persistent biofilm infections pose a critical health threat with their relentless presence and amplified antibiotic resistance. Traditional antibacterial photodynamic therapy can inhibit bacteria extracellularly but struggles to control biofilm formation and virulence. Thus, there is an urgent need to develop photosensitizers, such as ultra‐small gold nanoclusters (AuNCs), that can penetrate biofilms and internalize into bacteria. However, AuNCs still face the challenge of insufficient reactive oxygen species (ROS) production and limited near‐infrared light absorption. This study develops a model of indocyanine green (ICG)‐sensitized AuNCs with atomic‐precision size effect. This approach achieved near‐infrared light absorption while inhibiting radiation transitions, thereby regulating the generation of ROS. Notably, different‐sized AuNCs (Au10NCs, Au15NCs, Au25NCs) yielded varied ROS types, resulting from different energy level distributions and electron transfer rates. ICG‐Au15NCs achieved a treatment efficacy of 99.94% against Staphylococcus aureus infections in vitro and significantly accelerated wound healing in vivo. Moreover, this study highlights the unique role of ICG‐AuNCs in suppressing quorum sensing, virulence, and ABC transporters compared to their larger counterparts. This strategy demonstrates that atomic‐precision size effect of AuNCs paves the way for innovative approaches in antibacterial photodynamic therapy for infection control.

Carbon-Dots-Mediated Improvement of Antimicrobial Activity of Natural Products

The development of new microbicidal compounds has become a top priority due to the emergence and spread of drug-resistant pathogenic microbes. In this study, blue-emitting and positively charged carbon dots (CDs), called Du-CDs, were fabricated for the first time utilizing the natural product extract of endophyte Diaporthe unshiuensis YSP3 as raw material through a one-step solvothermal method, which possessed varied functional groups including amino, carboxyl, hydroxyl, and sulfite groups. Interestingly, Du-CDs exhibited notably enhanced antimicrobial activities toward both bacteria and fungi as compared to the natural product extract of YSP3, with low minimum inhibitory concentrations. Moreover, Du-CDs significantly inhibited the formation of biofilms. Du-CDs bound with the microbial cell surface via electronic interaction or hydrophobic interaction entered the microbial cells and were distributed fully inside the cells. Du-CDs caused cell membrane damage and/or cell division cycle interruption, resulting in microbial cell death. Moreover, Du-CDs exhibited an improved antimicrobial effect and accelerated wound healing ability with good biocompatibility in the mouse model. Overall, we demonstrate that the formation of CDs from fungal natural products presents a promising and potential means to develop novel antimicrobial agents with great fluorescence, improved microbiocidal effect and wound healing capacity, and good biosafety for combating microbial infections.

Expanding Our Horizons: AIE Materials in Bacterial Research

Bacteria share a longstanding and complex relationship with humans, playing a role in protecting gut health and sustaining the ecosystem to cause infectious diseases and antibiotic resistance. Luminogenic materials that share aggregation-induced emission (AIE) characteristics have emerged as a versatile toolbox for bacterial studies through fluorescence visualization. Numerous research efforts highlight the superiority of AIE materials in this field. Recent advances in AIE materials in bacterial studies are categorized into four areas: understanding bacterial interactions, antibacterial strategies, diverse applications, and synergistic applications with bacteria. Initial research focuses on visualizing the unseen bacteria and progresses into developing strategies involving electrostatic interactions, amphiphilic AIE luminogens (AIEgens), and various AIE materials to enhance bacterial affinity. Recent progress in antibacterial strategies includes using photodynamic and photothermal therapies, bacterial toxicity studies, and combined therapies. Diverse applications from environmental disinfection to disease treatment, utilizing AIE materials in antibacterial coatings, bacterial sensors, wound healing materials, etc., are also provided. Finally, synergistic applications combining AIE materials with bacteria to achieve enhanced outcomes are explored. This review summarizes the developmental trend of AIE materials in bacterial studies and is expected to provide future research directions in advancing bacterial methodologies.

Exciting Bacteria to a Hypersensitive State for Enhanced Aminoglycoside Therapy by a Rationally Constructed AIE Luminogen

The diminishing effectiveness of existing aminoglycoside antibiotics (AGs) compels scientists to seek new approaches to enhance the sensitivity of current AGs. Despite ongoing efforts, currently available approaches remain restricted. Herein, a novel strategy involving the rational construction of an aggregation-induced-emission luminogen (AIEgen) is introduced to significantly enhance Gram-positive bacteria's susceptibility to AGs. The application of this approach involves the simple addition of AIEgens to bacteria followed by a 5 min light irradiation. Under light exposure, AIEgens efficiently generate reactive oxygen species (ROS), elevating intrabacterial ROS levels to a nonlethal threshold. Post treatment, the bacteria swiftly enter a hypersensitive state, resulting in a 21.9-fold, 15.5-fold, or 7.2-fold increase in susceptibility to three AGs: kanamycin, gentamycin, and neomycin, respectively. Remarkably, this approach is specific to AGs, and the induced hypersensitivity displays unparalleled longevity and heritability. Further in vivo studies confirm a 7.0-fold enhanced bactericidal ability of AGs against Gram-positive bacteria through this novel approach. This research not only broadens the potential applications of AIEgens but also introduces a novel avenue to bolster the effectiveness of AGs in combating bacterial infections.

Coupling Nanoscale Precision with Multiscale Imaging: A Multifunctional Near-Infrared Dye for the Brain

Live imaging of primary neural cells is crucial for monitoring neuronal activity, especially multiscale and multifunctional imaging that offers excellent biocompatibility. Multiscale imaging can provide insights into cellular structure and function from the nanoscale to the millimeter scale. Multifunctional imaging can monitor different activities in the brain. However, this remains a challenge because of the lack of dyes with a high signal-to-background ratio, water solubility, and multiscale and multifunctional imaging capabilities. In this study, we present a neural dye with near-infrared (NIR) emissions (>700 nm) that enables ultrafast staining (in less than 1 min) for the imaging of primary neurons. This dye not only enables multiscale neural live-cell imaging from vesicles in neurites, neural membranes, and single neurons to the whole brain but also facilitates multifunctional imaging, such as the monitoring and quantifying of synaptic vesicles and the changes in membrane potential. We also explore the potential of this NIR neural dye for staining brain slices and live brains. The NIR neural dye exhibits superior binding with neural membranes compared to commercial dyes, thereby achieving multiscale and multifunctional brain neuroimaging. In conclusion, our findings introduce a significant breakthrough in neuroimaging dyes by developing a category of small molecular dyes.

A Near-Infrared-II Excitable Pyridinium Probe with 1000-Fold ON/OFF Ratio for γ-Glutamyltranspeptidase and Cancer Detection

Activity-based detection of γ-Glutamyltranspeptidase (GGT) using near-infrared (NIR) fluorescent probes is a promising strategy for early cancer diagnosis. Although NIR pyridinium probes show high performance in biochemical analysis, the aggregation of both the probes and parental fluorochromes in biological environments is prone to result in a low signal-to-noise ratio (SBR), thus affecting their clinical applications. Here, we develop a GGT-activatable aggregate probe called OTBP-G for two-photon fluorescence imaging in various biological environments under 1040 nm excitation. By rationally tunning the hydrophilicity and donor-acceptor strength, we enable a synergistic effect between twisted intramolecular charge transfer and intersystem crossing processes and realize a perfect dark state for OTBP-G before activation. After the enzymatic reaction, the parental fluorochrome exhibits bright aggregation-induced emission peaking at 670 nm. The fluorochrome-to-probe transformation can induce 1000-fold fluorescence ON/OFF ratio, realizing in vitro GGT detection with an SBR > 900. Activation of OTBP-G occurs within 1 min in vivo, showing an SBR > 400 in mouse ear blood vessels. OTBP-G can further enable the early detection of pulmonary metastasis in breast cancer by topically spraying, outperforming the clinical standard hematoxylin and eosin staining. We anticipate that the in-depth study of OTBP-G can prompt the development of early cancer diagnosis and tumor-related physiological research. Moreover, this work highlights the crucial role of hydrophilicity and donor-acceptor strength in maximizing the ON/OFF ratio of the TICT probes and showcases the potential of OTBP as a versatile platform for activity-based sensing.

Membrane Disruption-Enhanced Photodynamic Therapy against Gram-Negative Bacteria by a Peptide-Photosensitizer Conjugate

Photodynamic therapy (PDT) emerges as a promising strategy for combating bacteria with minimal drug resistance. However, a significant hurdle lies in the ineffectiveness of most photosensitizers against Gram-negative bacteria, primarily attributable to their characteristic impermeable outer membrane (OM) barrier. To tackle this obstacle, we herein report an amphipathic peptide-photosensitizer conjugate (PPC) with intrinsic outer membrane disruption capability to enhance PDT efficiency against Gram-negative bacteria. PPC is constructed by conjugating a hydrophilic ultrashort cationic peptide to a hydrophobic photosensitizer. PPC could efficiently bind to the OM of Gram-negative bacteria through electrostatic adsorption, and subsequently disrupt the structural integrity of the OM. Mechanistic investigations revealed that PPC triggers membrane disruption by binding to both lipopolysaccharide (LPS) and phospholipid leaflet in the OM, enabling effective penetration of PPC into the Gram-negative bacteria interior. Upon light irradiation, PPC inside bacteria generates singlet oxygen not only to effectively decrease the survival of Gram-negative bacteria P. aeruginosa and E. coli to nearly zero in vitro, but also successfully cure the full-thickness skin infection and bacterial keratitis (BK) induced by P. aeruginosa in animal models. Thus, this study provides a broad-spectrum antibacterial phototherapeutic design strategy by the synergistic action of membrane disruption and PDT to combat Gram-negative bacteria.

Aggregation-Induced Emission Photosensitizer with Ag(I)-π Interaction-Enhanced Reactive Oxygen Species for Eliminating Multidrug Resistant Bacteria

Multidrug-resistant (MDR) bacteria pose serious threats to public health due to the lack of effective and biocompatible drugs to kill MDR bacteria. Photodynamic antibacterial therapy has been widely studied due to its low induction of resistance. However, photosensitizers that can efficiently generate reactive oxygen species (ROS) through both type I and type II mechanisms and that have the capability of multiple modes of action are rarely reported. Addressing this issue, we developed a near-infrared-emitting triphenylamine indole iodoethane (TTII) and its silver(I) self-assembled (TTIIS) aggregation-induced emission (AIE) photosensitizer for multimode bacterial infection therapy. TTII can efficiently produce both Type I ROS •OH and Type II ROS 1O2. Interestingly, the Ag(I)-π interaction contributed in TTIIS efficiency promotion of the generation of 1O2. Moreover, by releasing Ag+, TTIIS enabled photodynamic-Ag(I) dual-mode sterilization. As a result, TTIIS achieved an effective enhancement of antibacterial activity, with a 1-2-fold boost against multidrug-resistant Escherichia coli (MDR E. coli). Both TTII and TTIIS at a concentration as low as 0.55 μg mL-1 can kill more than 98% of methicillin resistant Staphylococcus aureus (MRSA) on MRSA-infected full-thickness defect wounds of a mouse, and both TTII and TTIIS were effective in eliminating the bacteria and promoting wound healing.

Heme-Mimetic Photosensitizer with Iron-Targeting and Internalizing Properties for Enhancing PDT Activity and Promoting Infected Diabetic Wound Healing

The management of multibacterial infections remains clinically challenging in the care and treatment of chronic diabetic wounds. Photodynamic therapy (PDT) offers a promising approach to addressing bacterial infections. However, the limited target specificity and internalization properties of traditional photosensitizers (PSs) toward Gram-negative bacteria pose significant challenges to their antibacterial efficacy. In this study, we designed an iron heme-mimetic PS (MnO2@Fe-TCPP(Zn)) based on the iron dependence of bacteria that can be assimilated by bacteria and retained in different bacteria strains (Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus) and which shows high PDT antibacterial efficacy. For accelerated wound healing after antibacterial treatment, MnO2@Fe-TCPP(Zn) was loaded into a zwitterionic hydrogel with biocompatibility and antifouling properties to form a nanocomposite antibacterial hydrogel (PSB-MnO2@Fe-TCPP(Zn)). In the multibacterial infectious diabetic mouse wound model, the PSB-MnO2@Fe-TCPP(Zn) hydrogel dressing rapidly promoted skin regeneration by effectively inhibiting bacterial infections, eliminating inflammation, and promoting angiogenesis. This study provides an avenue for developing broad-spectrum antibacterial nanomaterials for combating the antibiotic resistance crisis and promoting the healing of complex bacterially infected wounds.

Aggregation-induced emission of TTCPy-3: A novel approach for eradicating Nocardia seriolae infections in aquatic fishes

Aquatic fishes are threatened by the strong pathogenic bacterium Nocardia seriolae, which challenges the current prevention and treatment approaches. This study introduces luminogens with aggregation-induced emission (AIE) as an innovative and non-antibiotic therapy for N. seriolae. Specifically, the AIE photosensitizer, TTCPy-3 is employed against N. seriolae. We evaluated the antibacterial activity of TTCPy-3 and investigated the killing mechanism against N. seriolae, emphasizing its ability to aggregate within the bacterium and produce reactive oxygen species (ROS). TTCPy-3 could effectively aggregate in N. seriolae, generate ROS, and perform real-time imaging of the bacteria. A bactericidal efficiency of 100% was observed while concentrations exceeding 4 μM in the presence of white light irradiation for 10 min. In vivo, evaluation on zebrafish (Danio rerio) confirmed the superior therapeutic efficacy induced by TTCPy-3 to fight against N. seriolae infections. TTCPy-3 offers a promising strategy for treating nocardiosis of fish, paving the way for alternative treatments beyond traditional antibiotics and potentially addressing antibiotic resistance.

Antibacterial Antimicrobial Peptide Grafted HA/SF/Alg Wound Dressing Containing AIEgens for Infected Wound Treating

Chronic wounds are characterized with excessive biofluid and persistent infection. Therefore, there is an urgent desire to develop a multifunctional wound dressing that can meet the extreme requirements including effective antibacterial and powerful wound microenvironment regulation and protection function to promote wounds heal quickly. In this study, a multifunctional composite dressing (HA-AMP/SF/Alg/Rb-BG-AIEgens) was synthesized by combining a mesoporous bioactive glass framework loaded with AIEgens (Rb-BG-AIEgens) with cross-linked antimicrobial peptide grafted hyaluronic acid (HA-AMP), sodium alginate (Alg), and silk fibroin (SF). It is important to note that the Rb-BG-AIEgens can achieve real-time and sensitive bacterial detection. HA-AMP can achieve broad spectrum antibacterial and avoid the residue of drug-resistant bacteria. The HA-AMP/SF/Alg/Rb-BG-AIEgens dressing can up-regulate related proliferative proteins, thereby promoting regeneration of tissue and the rapid healing of chronic wounds. With good biocompatibility and antibacterial ability, HA-AMP/SF/Alg/Rb-BG-AIEgens dressing has great potential to become a next generation wound dressing for clinical biological fluid management and chronic bacterial infection treatment.

Photodynamic therapy alone or in combination to counteract bacterial infections

INTRODUCTION

Antibacterial photodynamic therapy presents a promising alternative to antibiotics, with potential against multidrug-resistant bacteria, offering broad-spectrum action, reduced resistance risk, and improved tissue selectivity.

AREAS COVERED

This manuscript reviews patent literature in the field of antibacterial photodynamic therapy through the period of 2019-2023. All data are from the US and European patent databases and SciFinder.

EXPERT OPINION

Antibacterial photodynamic therapy (PDT) is an appealing approach for treating bacterial infections, especially biofilm-related ones, by releasing reactive oxygen species (ROS) upon light activation. Its success is driven by a growing variety of photosensitizers (PSs) with tailored properties, like water solubility, controllable surface charge, and ROS generation efficiency. Among them, Aggregation Induced Emission (AIE)-type PSs are promising, demonstrating enhanced efficacy when aggregated in biological environments. However, the penetration of pristine PSs into bacterial biofilms within deep tissues or complex anatomical regions is limited, reducing their antibacterial effectiveness. To address this, nanotechnology has been integrated into antibacterial PDT to synthesize various nano-PSs. This adaptability allows seamless integration with other antimicrobial treatments, offering a comprehensive approach to combat localized infections, especially in dentistry and dermatology. By combining PSs with complementary therapies, antibacterial PDT offers a multifaceted strategy for effective microbial control and management.

D-Glucose-Mediated Gold Nanoparticle Fabrication for Colorimetric Detection of Foodborne Pathogens

Gold nanoparticle (AuNP) fabrication via the oxidation of D-glucose is applied for detecting two foodborne pathogens, Enterococcus faecium (E. faecium) and Staphylococcus aureus (S. aureus). D-glucose is used as a reducing agent due to its oxidation to gluconic acid by sodium hydroxide (NaOH), resulting in the formation of AuNPs. Based on this mechanism, we develop AuNP-based colorimetric detection in conjunction with loop-mediated isothermal amplification (LAMP) for accurately identifying the infectious bacteria. Here, Au+ ions bind to the base of double-stranded DNA. In the presence of D-glucose and NaOH, the LAMP amplicon-Au+ complex maintains its bound state at 65 °C for 10 min while it is reduced to AuNPs in a dispersed form, exhibiting a red color. We aimed to pre-mix D-glucose with LAMP reagents before amplification and induce successful colorimetry without inhibiting amplification to simplify the experimental process and decrease the reaction time. Therefore, the entire process, including LAMP and colorimetric detection, is accomplished in approximately 1 h. The limit of detection of E. faecium and S. aureus is confirmed using the introduced method as 101 CFU/mL and 100 fg/μL, respectively. We expect that colorimetric detection using D-glucose-mediated AuNP synthesis offers an application for simple and immediate molecular diagnosis.

Mesophilic Argonaute-Based Single Polystyrene Sphere Aptamer Fluorescence Platform for the Multiplexed and Ultrasensitive Detection of Non-Nucleic Acid Targets

The rapid, simultaneous, and accurate identification of multiple non-nucleic acid targets in clinical or food samples at room temperature is essential for public health. Argonautes (Agos) are guided, programmable, target-activated, next-generation nucleic acid endonucleases that could realize one-pot and multiplexed detection using a single enzyme, which cannot be achieved with CRISPR/Cas. However, currently reported thermophilic Ago-based multi-detection sensors are mainly employed in the detection of nucleic acids. Herein, this work proposes a Mesophilic Argonaute Report-based single millimeter Polystyrene Sphere (MARPS) multiplex detection platform for the simultaneous analysis of non-nucleic acid targets. The aptamer is utilized as the recognition element, and a single millimeter-sized polystyrene sphere (PSmm) with a large concentration of guide DNA on the surface served as the microreactor. These are combined with precise Clostridium butyricum Ago (CbAgo) cleavage and exonuclease I (Exo I) signal amplification to achieve the efficient and sensitive recognition of non-nucleic acid targets, such as mycotoxins (<60 pg mL-1) and pathogenic bacteria (<102 cfu mL-1). The novel MARPS platform is the first to use mesophilic Agos for the multiplex detection of non-nucleic acid targets, overcoming the limitations of CRISPR/Cas in this regard and representing a major advancement in non-nucleic acid target detection using a gene-editing-based system.

Microneedle System with Biomarker-Activatable Chromophore as Both Optical Imaging Probe and Anti-bacterial Agent for Combination Therapy of Bacterial-Infected Wounds and Outcome Monitoring

Wounds infected with bacteria, if left untreated, have the potential to escalate into life-threatening conditions, such as sepsis, which is characterized by widespread inflammation and organ damage. A comprehensive approach to treating bacterial-infected wounds, encompassing the control of bacterial infection, biofilm eradication, and inflammation regulation, holds significant importance. Herein, a microneedle (MN) patch (FM@ST MN) has been developed, with silk fibroin (SF) and tannic acid-based hydrogel serving as the matrix. Encapsulated within the MNs are the AIEgen-based activatable probe (FQ-H2O2) and the NLRP3 inhibitor MCC950, serving as the optical reporter/antibacterial agent and the inflammation regulator, respectively. When applied onto bacterial-infected wounds, the MNs in FM@ST MN penetrate bacterial biofilms and gradually degrade, releasing FQ-H2O2 and MCC950. The released FQ-H2O2 responds to endogenously overexpressed reactive oxygen species (H2O2) at the wound site, generating a chromophore FQ-OH which emits noticeable NIR-II fluorescence and optoacoustic signals, enabling real-time imaging for outcome monitoring; and this chromophore also exhibits potent antibacterial capability due to its dual positive charges and shows negligible antibacterial resistance. However, the NLRP3 inhibitor MCC950, upon release, suppresses the activation of NLRP3 inflammasomes, thereby mitigating the inflammation triggered by bacterial infections and facilitating wound healing. Furthermore, SF in FM@ST MN aids in tissue repair and regeneration by promoting the proliferation of epidermal cells and fibroblasts and collagen synthesis. This MN system, free from antibiotics, holds promise as a solution for treating and monitoring bacterially infected wounds without the associated risk of antimicrobial resistance.

Interdisciplinary-Inspired Smart Antibacterial Materials and Their Biomedical Applications

The discovery of antibiotics has saved millions of lives, but the emergence of antibiotic-resistant bacteria has become another problem in modern medicine. To avoid or reduce the overuse of antibiotics in antibacterial treatments, stimuli-responsive materials, pathogen-targeting nanoparticles, immunogenic nano-toxoids, and biomimetic materials are being developed to make sterilization better and smarter than conventional therapies. The common goal of smart antibacterial materials (SAMs) is to increase the antibiotic efficacy or function via an antibacterial mechanism different from that of antibiotics in order to increase the antibacterial and biological properties while reducing the risk of drug resistance. The research and development of SAMs are increasingly interdisciplinary because new designs require the knowledge of different fields and input/collaboration from scientists in different fields. A good understanding of energy conversion in materials, physiological characteristics in cells and bacteria, and bactericidal structures and components in nature are expected to promote the development of SAMs. In this review, the importance of multidisciplinary insights for SAMs is emphasized, and the latest advances in SAMs are categorized and discussed according to the pertinent disciplines including materials science, physiology, and biomimicry.

Recent advances of aggregation‐induced emission in body surface organs

The surface organs mainly comprise the superficial layers of various parts of the mammalian body, including the skin, eyes, and ears, which provide solid protection against various threats to the entire body. Damage to surface organs could lead to many serious diseases or even death. Currently, despite significant advancements in this field, there remain numerous enigmas that necessitate expeditious resolution, particularly pertaining to diagnostic and therapeutic objectives. The advancements in nanomedicine have provided a significant impetus for the development of novel approaches in the diagnosis, bioimaging, and therapy of superficial organs. The aggregation‐induced emission (AIE) phenomenon, initially observed by Prof. Ben Zhong Tang, stands out due to its contrasting behavior to the aggregation‐caused quenching effect. This discovery has significantly revolutionized the field of nanomedicine for surface organs owing to its remarkable advantages. In this review of literature, we aim to provide a comprehensive summary of recent advances of AIE lumenogen (AIEgen)‐based nanoplatforms in the fields of detection, diagnosis, imaging, and therapeutics of surface organ‐related diseases and discuss their prospects in the domain. It is hoped that this review will help attract researchers’ attention toward the utilization of this field for the exploration of a wider range of biomedical and clinical applications.

Precise molecular engineering for the preparation of pyridinium photosensitizers with efficient ROS generation and photothermal conversion

Organic photosensitizers (PSs) with aggregation-induced emission properties have great development potential in the integrated application of multi-mode diagnosis and treatment of photodynamic therapy (PDT) and photothermal therapy (PTT). However, preparing high-quality PSs with both optical and biological properties, high reactive oxygen species (ROS) and photothermal conversion ability are undoubtedly a great challenge. In this work, a series of pyridinium AIE PSs modified with benzophenone have been synthesized. A wide wavelength range of fluorescent materials was obtained by changing the conjugation and donor-acceptor strength. TPAPs5 has a significant advantage over similar compounds, and we have also identified the causes of high ROS generation and high photothermal conversion in terms of natural transition orbitals, excited state energy levels, ground-excited state configuration differences and recombination energy. Interestingly, migration of target sites was also found in biological imaging experiments, which also provided ideas for the design of double-targeted fluorescent probes. Therefore, the present work proposed an effective molecular design strategy for synergistic PDT and PTT therapy.

Pyridinium-Derived Mesoionic N-Heterocyclic Olefins (py-mNHOs)

Mesoionic polarization allows access to electron-rich olefins that have found application as organocatalysts, ligands, or nucleophiles. Herein, we report the synthesis and characterization of a series of 3-methylpyridinium-derived mesoionic olefins (py-mNHOs). We used a DFT-supported design concept, which showed that the introduction of aryl groups in the 1-, 2-, 4-, and 6-positions of the heterocyclic core allowed the kinetic stabilization of the novel mesoionic compounds. Tolman electronic parameters indicate that py-mNHOs are remarkably strong σ-donor ligands toward transition metals and main group Lewis acids. Additionally, they are among the strongest nucleophiles on the Mayr reactivity scale. In reactions of py-mNHOs with electron-poor π-systems, a gradual transition from the formation of zwitterionic adducts via stepwise to concerted 1,3-dipolar cycloadditions was observed experimentally and analyzed by quantum-chemical calculations.

One-Stop Integrated Nanoagent for Bacterial Biofilm Eradication and Wound Disinfection

To meet the requirements of biomedical applications in the antibacterial realm, it is of great importance to explore nano-antibiotics for wound disinfection that can prevent the development of drug resistance and possess outstanding biocompatibility. Therefore, we attempted to synthesize an atomically dispersed ion (Fe) on phenolic carbon quantum dots (CQDs) combined with an organic photothermal agent (PTA) (Fe@SAC CQDs/PTA) via a hydrothermal/ultrasound method. Fe@SAC CQDs adequately exerted peroxidase-like activity while the PTA presented excellent photothermal conversion capability, which provided enormous potential in antibacterial applications. Based on our work, Fe@SAC CQDs/PTA exhibited excellent eradication of Escherichia coli (>99% inactivation efficiency) and Staphylococcus aureus (>99% inactivation efficiency) based on synergistic chemodynamic therapy (CDT) and photothermal therapy (PTT). Moreover, in vitro experiments demonstrated that Fe@SAC CQDs/PTA could inhibit microbial growth and promote bacterial biofilm destruction. In vivo experiments suggested that Fe@SAC CQDs/PTA-mediated synergistic CDT and PTT exhibited great promotion to wound disinfection and recovery effects. This work indicated that Fe@SAC CQDs/PTA could serve as a broad-spectrum antimicrobial nano-antibiotic, which was simultaneously beneficial for bacterial biofilm eradication, wound disinfection, and wound healing.

Recyclable and Environmentally Friendly Magnetic Nanoparticles with Aggregation-Induced Emission Photosensitizer for Sustainable Bacterial Inactivation in Water

Bacterial photodynamic inactivation based on the combined actions of photosensitizers, light, and oxygen presents a promising alternative for eliminating bacteria compared to conventional water disinfection methods. However, a significant challenge in this approach is the inability to retrieve photosensitizers after phototreatment, posing potential adverse environmental impacts. Additionally, conventional photosensitizers often exhibit limited photostability and photodynamic efficiency. This study addresses these challenges by employing an aggregation-induced emission (AIE) photosensitizer, iron oxide magnetic nanoparticles (Fe3O4 MNPs), and Pluronic F127 to fabricate AIE magnetic nanoparticles (AIE MNPs). AIE MNPs not only exhibit fluorescence imaging capabilities and superior photosensitizing ability but also demonstrate broad-spectrum bactericidal activities against both Gram-positive and Gram-negative bacteria. The controlled release of TPA-Py-PhMe and magnetic characteristics of the AIE MNPs facilitate reuse and recycling for multiple cycles of bacterial inactivation in water. Our findings contribute valuable insights into developing environmentally friendly disinfectants, emphasizing the full potential of AIE photosensitizers in photodynamic inactivation beyond biomedical applications.

Singlet oxygen: Properties, generation, detection, and environmental applications

Singlet oxygen (1O2) is molecular oxygen in the excited state with high energy and electrophilic properties. It is widely found in nature, and its important role is gradually extending from chemical syntheses and medical techniques to environmental remediation. However, there exist ambiguities and controversies regarding detection methods, generation pathways, and reaction mechanisms which have hindered the understanding and applications of 1O2. For example, the inaccurate detection of 1O2 has led to an overestimation of its role in pollutant degradation. The difficulty in detecting multiple intermediate species obscures the mechanism of 1O2 production. The applications of 1O2 in environmental remediation have also not been comprehensively commented on. To fill these knowledge gaps, this paper systematically discussed the properties and generation of 1O2, reviewed the state-of-the-art detection methods for 1O2 and long-standing controversies in the catalytic systems. Future opportunities and challenges were also discussed regarding the applications of 1O2 in the degradation of pollutants dissolved in water and volatilized in the atmosphere, the disinfection of drinking water, the gas/solid sterilization, and the self-cleaning of filter membranes. This review is expected to provide a better understanding of 1O2-based advanced oxidation processes and practical applications in the environmental protection of 1O2.

Supramolecular pyrrole radical cations for bacterial theranostics

Bacterial infections with emerging resistance to antibiotics require urgent development of antibacterial agents with new core skeletons. Recently, a series of antibacterial agents have been reported based on positively charged organic groups, such as ammonium, guanidine, and phosphonium groups, which can selectively bind and destroy negatively charged bacterial membranes. To achieve imaging-guided precise antibacterial therapy, these positively charged organic groups usually require further decoration with imaging modalities, such as fluorescence. However, most fluorophores with electron-closed shell structures usually suffer from tedious synthetic procedures for preparation. We herein prepare a series of positively charged and deep-red fluorescent supramolecular pyrrole radical cations (P˙+-CB[7]) based on the simple mixing of pyrroles and CB[7] in water under air. The readily available deep-red fluorescent P˙+-CB[7] can not only be used for selective imaging and killing of live Gram-positive bacteria with excellent biocompatibility, but also for imaging of dead Gram-negative bacteria killed by drugs and in vivo monitoring of phagocytosis of bacteria by innate immune cells in zebrafish. It is believed that the deep-red fluorescent pyrrole radical cations as a new core skeleton are promising in bacterial theranostics.

Host-Guest Photosensitizer of a Cationic BODIPY Derivative and Cucurbit[7]uril for High-Efficiency Visible Light-Induced Photooxidation Reactions

In recent years, there has been a notable surge of interest in the fields of organic and pharmaceutical research about photocatalysts (PCs) and photosensitizers (PSs). In this study, a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) molecule adorned with quaternary ammonium (TMB) functionality was meticulously designed and synthesized. This compound has remarkable characteristics such as exceptional water solubility, great optical qualities, and commendable photostability. It can form a 1:1 complex (TMB-CB[7]) with cucurbit[7]uril (CB[7]) through host-guest interactions in the aqueous solution and shows obvious fluorescence enhancement. The reactive oxygen species (ROS) including superoxide anion radical (O2·-) and singlet oxygen (1O2) generation ability of TMB-CB[7] were promoted compared with that of TMB in the aqueous solution. More interestingly, the ROS generated from TMB-CB[7] can be used as PCs for aerobic cross dehydrogenation coupling reactions and photooxidation reactions in water with high yields of 89 and 95%, respectively. Therefore, the utilization of a host-guest PS presents a novel and environmentally friendly approach for conducting photocatalyzed organic processes under ambient conditions using visible light.

An AIE Metal Iridium Complex: Photophysical Properties and Singlet Oxygen Generation Capacity

Photodynamic therapy (PDT) has garnered significant attention in the fields of cancer treatment and drug-resistant bacteria eradication due to its non-invasive nature and spatiotemporal controllability. Iridium complexes have captivated researchers owing to their tunable structure, exceptional optical properties, and substantial Stokes displacement. However, most of these complexes suffer from aggregation-induced quenching, leading to diminished luminous efficiency. In contrast to conventional photosensitizers, photosensitizers exhibiting aggregation-induced luminescence (AIE) properties retain the ability to generate a large number of reactive oxygen species when aggregated. To overcome these limitations, we designed and synthesized a novel iridium complex named Ir-TPA in this study. It incorporates quinoline triphenylamine cyclomethylated ligands that confer AIE characteristics for Ir-TPA. We systematically investigated the photophysical properties, AIE behavior, spectral features, and reactive oxygen generation capacity of Ir-TPA. The results demonstrate that Ir-TPA exhibits excellent optical properties with pronounced AIE phenomenon and robust capability for producing singlet oxygen species. This work not only introduces a new class of metal iridium complex photosensitizer with AIE attributes but also holds promise for achieving remarkable photodynamic therapeutic effects in future cellular experiments and biological studies.

Multifunctional nucleoside-AIEgens bearing quaternary ammonium cationic for reversible response, bioimaging, and antibacterial

A multifunctional nucleoside-based AIEgens sensor (TPEPy-dU) was constructed for visual screening of Hg2+, determine to the reversible response of Fe3+ and biothiols, and applied for cell imaging, and drug-free bacterial killing. The TPEPy-dU displayed 10-folds fluorescence enhancement at 540 nm of emission in response to trace Hg2+ ions with 10 nM of LOD, which can be immediately quenched by adding Fe3+ or GSH/Cys-containing sulfhydryl groups. Moreover, their bacterial staining efficiency closely correlates with their antibacterial efficacy as they demonstrated comparatively higher antibacterial activity against Gram-positive bacteria than Gram-negative bacteria. The drug-free antibacterial results involved the stating prominent surface damages at the sites of interactions between bacterial cells and TPEPy-dU that were further verified by CLSM and SEM images. It can be applied as a potential fluorescent agent to explore the related antibacterial mechanisms for treating and monitoring bacterial infections in vivo due to their nontoxic nature. Compared with conventional sensors and antibacterial therapies, these findings elevated the synthetic strategies of fluorescent probes and represented an advanced antibacterial agent wearing quaternary ammonium cationic with low resistance in clinical diagnosis.

Tumor Microenvironment-Responsive One-for-All Molecular-Engineered Nanoplatform Enables NIR-II Fluorescence Imaging-Guided Combinational Cancer Therapy

The activable NIR-based phototheranostic nanoplatform (NP) is considered an efficient and reliable tumor treatment due to its strong targeting ability, flexible controllability, minimal side effects, and ideal therapeutic effect. This work describes the rational design of a second near-infrared (NIR-II) fluorescence imaging-guided organic phototheranostic NP (FTEP-TBFc NP). The molecular-engineered phototheranostic NP has a sensitive response to glutathione (GSH), generating hydrogen sulfide (H2S) gas, and delivering ferrocene molecules in the tumor microenvironment (TME). Under 808 nm irradiation, FTEP-TBFc could not only simultaneously generate fluorescence, heat, and singlet oxygen but also greatly enhance the generation of reactive oxygen species to improve chemodynamic therapy (CDT) and photodynamic therapy (PDT) at a biosafe laser power of 0.33 W/cm2. H2S inhibits the activity of catalase and cytochrome c oxidase (COX IV) to cause the enhancement of CDT and hypothermal photothermal therapy (HPTT). Moreover, the decreased intracellular GSH concentration further increases CDT's efficacy and downregulates glutathione peroxidase 4 (GPX4) for the accumulation of lipid hydroperoxides, thus causing the ferroptosis process. Collectively, FTEP-TBFc NPs show great potential as a versatile and efficient NP for specific tumor imaging-guided multimodal cancer therapy. This unique strategy provides new perspectives and methods for designing and applying activable biomedical phototheranostics.