Amphiphilic star copolymer-based bimodal fluorogenic/magnetic resonance probes for concomitant bacteria detection and inhibition

Semiconducting polymer dots for multifunctional integrated nanomedicine carriers

The expansion applications of semiconducting polymer dots (Pdots) among optical nanomaterial field have long posed a challenge for researchers, promoting their intelligent application in multifunctional nano-imaging systems and integrated nanomedicine carriers for diagnosis and treatment. Despite notable progress, several inadequacies still persist in the field of Pdots, including the development of simplified near-infrared (NIR) optical nanoprobes, elucidation of their inherent biological behavior, and integration of information processing and nanotechnology into biomedical applications. This review aims to comprehensively elucidate the current status of Pdots as a classical nanophotonic material by discussing its advantages and limitations in terms of biocompatibility, adaptability to microenvironments in vivo, etc. Multifunctional integration and surface chemistry play crucial roles in realizing the intelligent application of Pdots. Information visualization based on their optical and physicochemical properties is pivotal for achieving detection, sensing, and labeling probes. Therefore, we have refined the underlying mechanisms and constructed multiple comprehensive original mechanism summaries to establish a benchmark. Additionally, we have explored the cross-linking interactions between Pdots and nanomedicine, potential yet complete biological metabolic pathways, future research directions, and innovative solutions for integrating diagnosis and treatment strategies. This review presents the possible expectations and valuable insights for advancing Pdots, specifically from chemical, medical, and photophysical practitioners' standpoints.

PEGylated Amphiphilic Gd-DOTA Backboned-Bound Branched Polymers as Magnetic Resonance Imaging Contrast Agents

MRI contrast agents with high kinetic stability and relaxivity are the key objectives in the field. We previously reported that Gd-DOTA backboned-bound branched polymers possess high kinetic stability and significantly increased T1 relaxivity than traditional branched polymer contrast agents. In this work, non-PEGylated and PEGylated amphiphilic Gd-DOTA backboned-bound branched polymers [P(GdDOTA-C6), P(GdDOTA-C10), mPEG-P(GdDOTA-C6), and mPEG-P(GdDOTA-C10)] were obtained by sequential introduction of rigid carbon chains (1,6-hexamethylenediamine or 1,10-diaminodecane) and mPEG into the structure of Gd-DOTA backboned-bound branched polymers. It is found that the introduction of both rigid carbon chains, especially the longer one, and mPEG can increase the kinetic stability and T1 relaxivity of Gd-DOTA backboned-bound branched polymers. Among them, mPEG-P(GdDOTA-C10) possesses the highest kinetic stability (significantly higher than those of linear Gd-DTPA and cyclic Gd-DOTA-butrol) and T1 relaxivity (42.9 mM-1 s-1, 1.5 T), 11 times that of Gd-DOTA and 1.4 times that of previously reported Gd-DOTA backboned-bound branched polymers. In addition, mPEG-P(GdDOTA-C10) showed excellent MRA effect in cardiovascular and hepatic vessels at a dose (0.025 or 0.05 mmol Gd/kg BW) far below the clinical range (0.1-0.3 mmol Gd/kg BW). Overall, effective branched-polymer-based contrast agents can be obtained by a strategy in which rigid carbon chains and PEG were introduced into the structure of Gd-DOTA backbone-bound branched polymers, resulting in excellent kinetic stability and enhanced T1 relaxivity.

Genetically engineered filamentous phage for bacterial detection using magnetic resonance imaging

Detecting bacterial cells with high specificity in deep tissues is challenging. Optical probes provide specificity, but are limited by the scattering and absorption of light in biological tissues. Conversely, magnetic resonance imaging (MRI) allows unfettered access to deep tissues, but lacks contrast agents for detecting specific bacterial strains. Here, we introduce a biomolecular platform that combines both capabilities by exploiting the modularity of M13 phage to target bacteria with tunable specificity and allow deep-tissue imaging using T1-weighted MRI. We engineered two types of phage probes: one for detecting the phage's natural host, viz., F-pilus expressing E. coli; and the other for detecting a different (F-negative) bacterial target, V. cholerae. We show that these phage sensors generate 3-9-fold stronger T1 relaxation upon recognizing target cells relative to non-target bacteria. We further establish a preliminary proof-of-concept for in vivo applications, by demonstrating that phage-labeled bacteria can be detected in mice using MRI. The framework developed in this study may have potential utility in a broad range of applications, from basic biomedical research to in situ diagnostics, which require methods to detect and track specific bacteria in the context of intact living systems.

One-pot preparation of Mn3O4/GSH/CdTe quantum dots complex for T1-weighted MRI/fluorescence detection of H3PO4

Magnetic resonance and fluorescence dual mode imaging with both advantages of high sensitivity and high spatial resolution, which could realize real-time, in situ, and dynamic imaging, is very suitable for detecting small molecules. And the synthesis of imaging materials with good imaging performance has become the core content. In this paper, based on biomimetic mineralization technology, GSH has been used as a material to design a one-pot method for the preparation of Mn₃O₄/GSH/CdTe quantum dots composites (MGQ in short). Furthermore, MGQ with good T₁MR and fluorescence response to the variety concentration of H₃PO₄, has been used for quantitative analysis of H₃PO₄ in serum. And the lowest limit detection could reach 0.1769 nmol/L for fluorescent detection, 0.02207 mol/L for MRI detection. MGQ would be applied as a sensor in diagnostic and clinical applications.

Nanostructured organic photosensitizer aggregates in disease phototheranostics

Aggregate science provides promising opportunities for the discovery of novel disease phototheranostics. Under the guidance of aggregology and the Jablonski energy level diagram, photosensitizer aggregates with tunable photophysical properties can consequently result in tailorable diagnosis and treatment modalities. This review summarizes recent advances in the formation of nanostructured organic photosensitizer aggregates, their photophysical processes (e.g., radiative emission, vibrational relaxation, and intersystem crossing), and particularly, their applications in disease phototheranostics such as fluorescence imaging and sensing, photothermal therapy, photoacoustic imaging, and photodynamic therapy. It is expected that this comprehensive summary will provide guidance for the construction of nanostructured organic photosensitizer aggregates, for establishment of aggregation-photophysical property relationships and the development of novel disease phototheranostic nanomedicines. Teaser: This article reviews the electron-delocalized π system-caused formation of nanostructured organic photosensitizer aggregates, which undergo radiative emission, vibrational relaxation, or intersystem crossing pathways to achieve fluorescence imaging and sensing, photothermal therapy, photoacoustic imaging, and photodynamic therapy.

How Exactly Do AIEgens Target Bacteria? Leveraging the Targeting Mechanism to Design Sensitive Fluorescent Immunosensors

Aggregation-induced emission luminogens (AIEgens) are promising candidates for bacterial imaging and detection because they can "Light-Up" pathogenic bacteria without complicated labeling or washing steps. However, there have been few in-depth analyses of the intrinsic mechanism underlying their utility as fluorescence probes for targeting bacteria. Therefore, using large-scale molecular dynamics simulations, we investigated the mechanism of their bacterial "Light-Up" behavior with N,N-diphenyl-4-(7-(pyridin-4-yl)benzo[c][1,2,5]thiadiazol-4-yl) aniline functionalized with 1-bromoethane (TBP-1). We propose that the triphenylamine motif of TBP-1, rather than the positively charged pyridine group, first contacts the cell membrane. After TBP-1 completely inserts into the cell membrane, the hydrophobic triphenylamine motif localizes in the hydrophobic core of the cell membrane, restricting the molecular variation of TBP-1, which induces the fluorescent "turn-on" and bacterial "Light-Up." On this basis, we established a heterogeneous lateral flow immunoassay (LFIA) for the detection of foodborne pathogens. The LFIA system showed improved sensitivity with a limit of detection as low as 10³ CFU mL^-1 and strong specificity. Our protocol opened an effective shortcut to the design of more efficient AIEgens and novel AIEgens-based immunoassays.

Recent Development of Polydopamine Anti-Bacterial Nanomaterials

Polydopamine (PDA), as a mussel-inspired material, exhibits numerous favorable performance characteristics, such as a simple preparation process, prominent photothermal transfer efficiency, excellent biocompatibility, outstanding drug binding ability, and strong adhesive properties, showing great potential in the biomedical field. The rapid development of this field in the past few years has engendered substantial progress in PDA antibacterial materials. This review presents recent advances in PDA-based antimicrobial materials, including the preparation methods and antibacterial mechanisms of free-standing PDA materials and PDA-based composite materials. Furthermore, the urgent challenges and future research opportunities for PDA antibacterial materials are discussed.

2D Molybdenum Sulfide-Based Materials for Photo-Excited Antibacterial Application

Bacterial infections have seriously threatened human health and the abuse of natural or artificial antibiotics leads to bacterial resistance, so development of a new generation of antibacterial agents and treatment methods is urgent. 2D molybdenum sulfide (MoS₂ ) has good biocompatibility, high specific surface area to facilitate surface modification and drug loading, adjustable energy bandgap, and high near-infrared photothermal conversion efficiency (PCE), so it is often used for antibacterial application through its photothermal or photodynamic effects. This review comprehensively summarizes and discusses the fabrication processes, structural characteristics, antibacterial performance, and the corresponding mechanisms of MoS₂ -based materials as well as their representative antibacterial applications. In addition, the outlooks on the remaining challenges that should be addressed in the field of MoS₂ are also proposed.

Peptide-Engineered AIE Nanofibers with Excellent and Precisely Adjustable Antibacterial Activity

Photosensitizers with aggregation-induced emission properties (AIEgens) can produce reactive oxygen species (ROS) under irradiation, showing great potential in the antibacterial field. However, due to the limited molecular skeletons, the development of AIEgens with precisely adjustable antibacterial activity is still a daunting challenge. Herein, a series of AIE nanofibers (AIE-NFs) based on the AIEgen of DTPM as the inner core and rationally designed peptides as bacterial recognition ligands (e.g., antimicrobial peptide (AMP) HHC36, ditryptophan, polyarginine, and polylysine) is developed. These AIE-NFs show precisely adjustable antibacterial behaviors simply by changing the decorated peptides, which can regulate the aggregation and inhibition of different bacteria. By mechanistic analysis, it is demonstrated that this effect can be attributed to the synergistic antibacterial activities of the ROS and the peptides. It is noteworthy that the optimized AIE-NFs, NFs-K18, can efficiently aggregate bacteria to cluster and kill four types of clinical bacteria under irradiation in vitro, inhibit the infection of methicillin-resistant Staphylococcus aureus (MRSA) and promote wound healing in vivo. To the authors' knowledge, this is the first report of AIE-NFs with precisely adjustable antibacterial activity, providing new opportunities for photodynamic therapy (PDT) treatment of infection.

Aggregation-Induced Emission-Active Biomacromolecules: Progress, Challenges, and Opportunities

Biomacromolecules featuring aggregation-induced-emission (AIE) characteristics generally present new properties and performances that are silent in the molecular state, providing endless possibilities for the evolution of biomedical applications. Tremendous achievements based on the research of AIE-active biomacromolecules have been made in synthetic exploration, material development, and practical applications. In this Perspective, we give a brief account in the development of AIE-active biomacromolecules. Remarkable progresses have been made in the exploration of AIE-active biomacromolecule preparation, structure-property relationships, and the relevant biomedical applications. The existing challenges and promising opportunities, as well as the future directions in AIE-active biomacromolecule research, are also discussed. It is expected that this Perspective can act as a trigger for the innovation of AIE-active biomacromolecule research and aggregate science.

Gadolinium-Coated Mesoporous Silica Nanoparticle for Magnetic Resonance Imaging

Magnetic resonance molecular imaging can provide anatomic, functional and molecular information. However, because of the intrinsically low sensitivity of magnetic resonance imaging (MRI), high-performance MRI contrast agents are required to generate powerful image information for image diagnosis. Herein, we describe a novel T₁ contrast agent with magnetic-imaging properties facilitated by the gadolinium oxide (Gd₂O₃) doping of mesoporous silica nanoparticles (MSN). The size, morphology, composition, MRI relaxivity (r₁), surface area and pore size of these nanoparticles were evaluated following their conjugation with Gd₂O₃ to produce Gd₂O₃@MSN. This unique structure led to a significant enhancement in T₁ contrast with longitudinal relaxivity (r₁) as high as 51.85 ± 1.38 mM⁻¹s⁻¹. Gd₂O₃@MSN has a larger T₁ relaxivity than commercial gadolinium diethylene triamine pentaacetate (Gd-DTPA), likely due to the geometrical confinement effect of silica nanoparticles. These results suggest that we could successfully prepare a novel high-performance T₁ contrast agent, which may be a potential candidate for in-vivo MRI.

Vancomycin-Loaded Furriness Amino Magnetic Nanospheres for Rapid Detection of Gram-Positive Water Bacterial Contamination

Bacterial pathogens pose high threat to public health worldwide. Different types of nanomaterials have been synthesized for the rapid detection and elimination of pathogens from environmental samples. However, the selectivity of these materials remains challenging, because target bacterial pathogens commonly exist in complex samples at ultralow concentrations. In this study, we fabricated novel furry amino magnetic poly-L-ornithine (PLO)/amine-poly(ethylene glycol) (PEG)-COOH/vancomycin (VCM) (AM-PPV) nanospheres with high-loading VCM for vehicle tracking and the highly efficient capture of pathogens. The magnetic core was coated with organosilica and functionalized with cilia. The core consisted of PEG/PLO loaded with VCM conjugated to Gram-positive bacterial cell membranes, forming hydrogen bonds with terminal peptides. The characterization of AM-PPV nanospheres revealed an average particle size of 56 nm. The field-emission scanning electron microscopy (FE-SEM) micrographs showed well-controlled spherical AM-PPV nanospheres with an average size of 56 nm. The nanospheres were relatively rough and contained an additional 12.4 nm hydrodynamic layer of PLO/PEG/VCM, which provided additional stability in the suspension. The furry AM-PPV nanospheres exhibited a significant capture efficiency (>90%) and a high selectivity for detecting Bacillus cereus (employed as a model for Gram-positive bacteria) within 15 min, even in the presence of other biocompatible pathogens. Moreover, AM-PPV nanospheres rapidly and accurately detected B. cereus at levels less than 10 CFU/mL. The furry nano-design can potentially satisfy the increasing demand for the rapid and sensitive detection of pathogens in clinical and environmental samples.

Antibacterial and cytotoxic properties of star-shaped quaternary ammonium-functionalized polymers with different pendant groups

The correlation between the structure and biological activity of polymers is critically important for rationally designing effective antibacterial polymers. Here, the antibacterial activity, cytotoxicity, and selectivity of structurally well-defined, star-shaped...

Recent Advances in the Development and Applications of Conjugated Polymer dots

Conjugated polymer dots or semiconducting polymer nanoparticles (Pdots) are nanoparticles prepared based on organic polymers. Pdots have the advantages of lower cost, simple preparation process, good biocompatibility, excellent stability, easy...

Aggregation-Induced Emission-Based Platforms for the Treatment of Bacteria, Fungi, and Viruses

The prevention and control of pathogenic bacteria, fungi, and viruses is a herculean task for all the countries since they greatly threaten global public health. Rapid detection and effective elimination of these pathogens is crucial for the treatment of related diseases. It is urgently demanded to develop new diagnostic and therapeutic strategies to combat bacteria, fungi, and viruses-induced infections. The emergence of aggregation-induced emission (AIE) luminogens (AIEgens) is a revolutionary breakthrough for the treatment of many diseases, including pathogenic infections. In this review, the main focus is on the applications of AIEgens for theranostic treatment of pathogenic bacteria, fungi, and viruses. Due to the AIE characteristic, AIEgens are promising fluorescent probes for the detection of bacteria, fungi, and viruses with excellent sensitivity and photostability. Moreover, AIEgen-based theranostic platforms can be fabricated by introducing bactericidal moieties or designing AIE photosensitizers and AIE photothermal agents. The current strategies and ongoing developments of AIEgens for the treatment of pathogenic bacteria, fungi, and viruses will be discussed in detail.

Phototherapy and optical waveguides for the treatment of infection

With rapid emergence of multi-drug resistant microbes, it is imperative to seek alternative means for infection control. Optical waveguides are an auspicious delivery method for precise administration of phototherapy. Studies have shown that phototherapy is promising in fighting against a myriad of infectious pathogens (i.e. viruses, bacteria, fungi, and protozoa) including biofilm-forming species and drug-resistant strains while evading treatment resistance. When administered via optical waveguides, phototherapy can treat both superficial and deep-tissue infections while minimizing off-site effects that afflict conventional phototherapy and pharmacotherapy. Despite great therapeutic potential, exact mechanisms, materials, and fabrication designs to optimize this promising treatment option are underexplored. This review outlines principles and applications of phototherapy and optical waveguides for infection control. Research advances, challenges, and outlook regarding this delivery system are rigorously discussed in a hope to inspire future developments of optical waveguide-mediated phototherapy for the management of infection and beyond.

AIE active polymers for biological applications

The discovery of aggregation-induced emission (AIE) phenomenon, significantly altered the understanding of the scientific world about the luminophore aggregation. Polymers with AIE features have recently emerged as promising materials with wide range of applications in optoelectronics devices, chemosensors, bioimaging, cancer theranostics and drug delivery. By introducing the AIE active molecule into the polymer structure, novel materials encompassing the characteristics properties of both the functional materials such as excellent brightness, versatile structure modification, high biocompatibility, exceptional stability and facile processability are achieved. This chapter presents the advances in synthetic design as well as potential biological applications of AIE active polymers, beginning with a brief introduction to the AIE phenomenon. The versatile synthetic route, easier functionalization, and light up feature of the AIE active polymers offer direct visualization of the physiological processes within or outside the living organisms. This chapter also precisely describes the photodynamic therapy/photothermal therapy (PDT/PTT) with up-to-date advancement of AIE active polymer and their emerging applications in biomedical field. The AIE active Photosensitizers (PSs) are much more efficient in singlet oxygen (¹O₂) production than their small molecule AIE active PSs due to their enhanced inter system crossing (ISC) process and improved light-harvesting ability. Additionally, the present chapter aims to focus on all recent AIE active polymers for drug screening and drug delivery. The AIE active polymer often shows decent drug loading capacity, high stability and good biocompatibility comprising image guided drug monitoring features. Lastly, the concluding discussion reveals the future prospective of the AIE active polymers.

Advances in aggregation induced emission (AIE) materials in biosensing and imaging of bacteria

With their ubiquitous nature, bacteria have had a significant impact on human health and evolution. Though as commensals residing in/on our bodies several bacterial communities support our health in many ways, bacteria remain one of the major causes of infectious diseases that plague the human world. Adding to this, emergence of antibiotic resistant strains limited the use of available antibiotics. The current available techniques to prevent and control such infections remain insufficient. This has been proven during one of greatest pandemic of our generation, COVID-19. It has been observed that bacterial coinfections were predominantly observed in COVID-19 patients, despite antibiotic treatment. Such higher rates of coinfections in critical patients even after antibiotic treatment is a matter of concern. Owing to many reasons across the world drug resistance in bacteria is posing a major problem i. According to Center for Disease control (CDC) antibiotic report threats (AR), 2019 more than 2.8 million antibiotic resistant cases were reported, and more than 35,000 were dead among them in USA alone. In both normal and pandemic conditions, failure of identifying infectious agent has played a major role. This strongly prompts the need to improve upon the existing techniques to not just effective identification of an unknown bacterium, but also to discriminate normal Vs drug resistant strains. New techniques based on Aggregation Induced Emission (AIE) are not only simple and rapid but also have high accuracy to visualize infection and differentiate many strains of bacteria based on biomolecular variations which has been discussed in this chapter.

Fast Broad-Spectrum Staining and Photodynamic Inhibition of Pathogenic Microorganisms by a Water-Soluble Aggregation-Induced Emission Photosensitizer

Pathogenic microorganisms pose great challenges to public health, which is constantly urgent to develop extra strategies for the fast staining and efficient treatments. In addition, once bacteria form stubborn biofilm, extracellular polymeric substance (EPS) within biofilm can act as protective barriers to prevent external damage and inward diffusion of traditional antibiotics, which makes it frequently develop drug-resistant ones and even hard to treat. Therefore, it is imperative to develop more efficient methods for the imaging/detection and efficient inhibition of pathogenic microorganisms. Here, a water-soluble aggregation-induced emission (AIE)-active photosensitizer TPA-PyOH was employed for fast imaging and photodynamic treatment of several typical pathogens, such as S. aureus, methicillin-resistant Staphylococcus aureus, L. monocytogenes, C. albicans, and E. coli. TPA-PyOH was non-fluorescent in water, upon incubation with pathogen, positively charged TPA-PyOH rapidly adhered to pathogenic membrane, thus the molecular motion of TPA-PyOH was restricted to exhibit AIE-active fluorescence for turn-on imaging with minimal background. Upon further white light irradiation, efficient reactive oxygen species (ROS) was in-situ generated to damage the membrane and inhibit the pathogen eventually. Furthermore, S. aureus biofilm could be suppressed in vitro. Thus, water-soluble TPA-PyOH was a potent AIE-active photosensitizer for fast fluorescent imaging with minimal background and photodynamic inhibition of pathogenic microorganisms.

Photo-Enhanced Antimicrobial Activity of Polymers Containing an Embedded Photosensitiser

This work presents the synthesis of a novel photosensitive acrylate monomer for use as both a self-catalyst in the photoinduced electron/energy transfer-reversible addition fragmentation chain transfer (PET-RAFT) polymerisation process and a photosensitiser (PS) for antibacterial applications. Hydrophilic, cationic, and antimicrobial formulations are explored to compare the antibacterial effects between charged and non-charged polymers. Covalent attachment of the catalyst to well-defined linear polymer chains has no effect on polymerisation control or singlet oxygen generation. The addition of the PS to polymers provides activity against S. aureus for all polymer formulations, resulting in up to a 99.99999 % killing efficacy in 30 min. Antimicrobial peptide mimetic polymers previously active against P. aeruginosa, but not S. aureus, gain significant bactericidal activity against S. aureus through the inclusion of PS groups, with 99.998 % killing efficiency after 30 min incubation with light. Thus, a broader spectrum of antimicrobial activity is achieved using two distinct mechanisms of bactericidal activity via the incorporation of a photosensitiser monomer into an antimicrobial polymer.

Orchestrating Nitric Oxide and Carbon Monoxide Signaling Molecules for Synergistic Treatment of MRSA Infections

The local delivery of gaseous signaling molecules (GSMs) has shown promising therapeutic potential. However, although GSMs have a subtle interplay in physiological and pathological conditions, the co-delivery of different GSMs for therapeutic purposes remains unexplored. Herein, we covalently graft a nitric oxide (NO)-releasing N-nitrosamine moiety onto the carbon monoxide (CO)-releasing 3-hydroxyflavone (3-HF) antenna, resulting in the first NO/CO-releasing donor. Under visible light irradiation, photo-mediated co-release of NO and CO reveals a superior antimicrobial effect toward Gram-positive bacteria with a combination index of 0.053. The synergy of NO and CO hyperpolarizes and permeabilizes bacterial membranes, which, however, shows negligible hemolysis and no evident toxicity toward normal mammalian cells. Moreover, the co-release of NO and CO can efficiently treat MRSA infection in a murine skin wound model, showing a better therapeutic capacity than vancomycin.

Membrane-disruptive peptides/peptidomimetics-based therapeutics: Promising systems to combat bacteria and cancer in the drug-resistant era

Membrane-disruptive peptides/peptidomimetics (MDPs) are antimicrobials or anticarcinogens that present a general killing mechanism through the physical disruption of cell membranes, in contrast to conventional chemotherapeutic drugs, which act on precise targets such as DNA or specific enzymes. Owing to their rapid action, broad-spectrum activity, and mechanisms of action that potentially hinder the development of resistance, MDPs have been increasingly considered as future therapeutics in the drug-resistant era. Recently, growing experimental evidence has demonstrated that MDPs can also be utilized as adjuvants to enhance the therapeutic effects of other agents. In this review, we evaluate the literature around the broad-spectrum antimicrobial properties and anticancer activity of MDPs, and summarize the current development and mechanisms of MDPs alone or in combination with other agents. Notably, this review highlights recent advances in the design of various MDP-based drug delivery systems that can improve the therapeutic effect of MDPs, minimize side effects, and promote the co-delivery of multiple chemotherapeutics, for more efficient antimicrobial and anticancer therapy.

Theranostic platforms for specific discrimination and selective killing of bacteria

Bacterial infections are serious threats to public health due to lack of advanced techniques to rapidly and accurately diagnose these infections in clinics. Although bacterial infections can be treated with broad-spectrum antibiotics based on empirical judgment, the emergence of antimicrobial resistance has attracted global attention due to long-term misuse and abuse of antibiotics by humans in recent decades. Therefore, it is imperative to selectively discriminate and precisely eliminate pathogenic bacteria. Herein, in addition to the conventional methods for bacterial identification, we comprehensively reviewed the recently developed theranostic platforms for specific discrimination and selective killing of bacteria according to their different interactions with the target bacteria, such as electrostatic and hydrophobic interactions, molecular recognition, microenvironment response, metabolic labeling, bacteriophage targeting, and others. These theranostic agents not only benefit from improved therapeutic efficiency but also present limited susceptibility to induce bacterial resistance. The strategies summarized in this review will open up new avenues in developing effective antimicrobial materials to accurately diagnose and treat bacterial infections in the post-antibiotic era. STATEMENT OF SIGNIFICANCE: Bacterial infections are difficult to be rapidly and accurately diagnosed, and are generally treated with broad-spectrum antibiotics, which leads to the development of drug resistance. By integrating imaging modalities and therapeutic methods in a single treatment, various theranostic agents have been developed to address the abovementioned issues. Therefore, the emerging theranostic platforms for selective identification and elimination of bacteria based on the distinct interactions of the theranostic agents with the target bacteria are summarized in this review. We believe that the information provided in this review will guide researchers in designing advanced antibacterial theranostics for practical applications in the post-antibiotic era.

Imaging, Identification and Inhibition of Microorganisms Using AIEgens

Microorganisms, including bacteria, viruses and fungi, are ubiquitous in nature. Some are extremely beneficial to life on Earth, whereas some cause diseases and disrupt normal human physiology. Pathogenic microorganisms can also undergo mutations and develop resistance to antimicrobial agents, which complicates diagnostic and therapeutic regimens. This calls for continuing efforts to develop new strategies and tools that can provide fast, sensitive and accurate diagnosis, as well as effective treatment of ever-evolving infectious diseases. Aggregation-induced emission luminogens (AIEgens) have shown promise in imaging, identification and inhibition of various microbial species. Compared to conventional organic fluorophores, AIEgens can offer improved photostability, and have found utilities in imaging microorganisms. AIEgens have been shown to detect microbial viability and differentiate among different microbial strains. Theranostic AIEgens that integrate imaging and killing of microbes have also been developed. This review highlights examples in the literature where AIEgens have been employed as molecular probes in the imaging, discrimination and killing of bacteria, viruses and fungi.

Montmorillonite nanosheets with enhanced photodynamic performance for synergistic bacterial ablation

Montmorillonite (MMT), as a naturally sourced and FDA-approved biomaterial, has attracted considerable attention due to its extensive application in biomedical areas, such as intestinal ailments, drug delivery, and additive manufacturing. In this work, two-dimensional montmorillonite (2D-MMT) ultrathin nanosheets were successfully prepared from sodium montmorillonite (Na-MMT) by utilizing a freeze-drying assisted method. Possessing a large specific surface area and increased number of exposed hydroxyl groups, 2D-MMT nanosheets exhibited better antibacterial ability than the original Na-MMT. More strikingly, we found that both 2D-MMT nanosheets and Na-MMT could generate reactive oxygen species (ROS) upon visible light illumination, which could promote their antibacterial efficiency. As a result, 2D-MMT nanosheets showed efficient antibacterial performance in the presence of light towards Escherichia coli with a simultaneous enhancement of surface adsorption and photodynamic ablation. What's more, a possible mechanism for ROS generation by MMT upon light illumination was first proposed in this work. The combination of the increased physical adsorption capacity and ROS generation ability of 2D-MMT nanosheets would help inspire the development of MMT as a promising antimicrobial candidate in the future.

Aggregation-induced emission active metal complexes: a promising strategy to tackle bacterial infections

This Feature Article discusses the recent development of metal-based aggregation-induced emission luminogens for detection, discrimination and decimation of bacterial pathogens to tackle antimicrobial resistance.

Poly-tetrahydropyrimidine Antibacterial Hydrogel with Injectability and Self-Healing Ability for Curing the Purulent Subcutaneous Infection

Infections caused by pathogenic microorganisms have always been the Achilles heel in the clinic. In this work, to overcome this conundrum, we proposed an injectable multifunctional hydrogel material with outstanding antibacterial properties and self-healing properties and no adverse effects on health. The cross-linked hydrogel with three-dimensional (3D) networks was quickly formed via the dynamic Schiff base between amino-modified poly-tetrahydropyrimidine (PTHP-NH₂) and multiple vanillin polymer P(DMA-VA) in 30 s. This hydrogel composite presents effective defense against both Gram-positive and Gram-negative bacteria, especially for the pyogenic Staphylococcus aureus. Moreover, the hydrogel showed almost no hemolysis and cytotoxicity. In vivo investigations indicated that hydrogels effectively killed S. aureus and protected against deterioration of inflammation. Besides, bioimaging of mice demonstrated that the hydrogel could be completely metabolized within 16 h. In a nutshell, given its outstanding antibacterial property and biocompatibility, the novel hydrogel could be an ideal candidate for the subcutaneous infection application.

Insight into the structure-antibacterial activity of amino cation-based and acetate anion-based ionic liquids from computational interactions with the POPC phospholipid bilayer

Investigations relevant to ionic liquids (ILs) as antibacterial agents have drawn considerable attention. However, the high cost and potential toxicity of ILs have severely limited their extensive applications, which has motivated researchers to design inexpensive and health-benign ILs. In this work, the interactions between the hydrated zwitterionic phospholipid (POPC) bilayer and a series of hypothetical amino cation-based and acetate anion-based ILs with different counterparts were investigated using molecular dynamics (MD) simulations to predict their antibacterial abilities. The cations of the ILs were found to insert into the lipid bilayer spontaneously, especially amino cations. Reorientation of the inserted imidazolium-based cations was observed, while the inserted amino cations showed no obvious reorientation phenomena, probably because of the strong charge interactions between the positive NH₃ groups of the amino cation and the negative PO₄ groups of the lipid bilayer. Due to their strong affinity with water, acetate-based anions disperse better in water solution, which weakens the insertion of the cations into the lipid bilayer to some extent. The structure and dynamic properties of the lipid bilayer, such as electrostatic potential, local ordering, area per lipid, volume per lipid, bilayer thickness, and lateral diffusion, are significantly influenced by the insertion of the cations, which results in disorder of the lipid bilayer and further disruption of the activity of the cell membrane. The insights into the relationship between the structures of ILs and their antibacterial activity in this work will provide a good reference for the screening and design of less expensive, safer, and greener IL candidates as antibacterial agents.

Biodegradable Polymer Theranostic Fluorescent Nanoprobe for Direct Visualization and Quantitative Determination of Antimicrobial Activity

We report a biodegradable fluorescent theranostic nanoprobe design strategy for simultaneous visualization and quantitative determination of antibacterial activity for the treatment of bacterial infections. Cationic-charged polycaprolactone (PCL) was tailor-made through ring-opening polymerization methodology, and it was self-assembled into well-defined tiny 5.0 ± 0.1 nm aqueous nanoparticles (NPs) having a zeta potential of +45 mV. Excellent bactericidal activity at 10.0 ng/mL concentration was accomplished in Gram-negative bacterium Escherichia coli (E. coli) while maintaining their nonhemolytic nature in mice red blood cells (RBC) and their nontoxic trend in wild-type mouse embryonic fibroblast cells with a selectivity index of >10⁴. Electron microscopic studies are evident of the E. coli membrane disruption mechanism by the cationic NP with respect to their high selectivity for antibacterial activity. Anionic biomarker 8-hydroxy-pyrene-1,3,6-trisulfonic acid (HPTS) was loaded in the cationic PCL NP via electrostatic interaction to yield a new fluorescent theranostic nanoprobe to accomplish both therapeutics and diagnostics together in a single nanosystem. The theranostic NP was readily degradable by a bacteria-secreted lipase enzyme as well as by lysosomal esterase enzymes at the intracellular compartments in <12 h and support their suitability for biomedical application. In the absence of bactericidal activity, the theranostic nanoprobe functions exclusively as a biomarker to exhibit strong green-fluorescent signals in live E. coli. Once it became active, the theranostic probe induces membrane disruption on E. coli, which enabled the costaining of nuclei by red fluorescent propidium iodide. As a result, live and dead bacteria could be visualized via green and orange signals (merging of red+green), respectively, during the course of the antibacterial activity by the theranostic probe. This has enabled the development of a new image-based fluorescence assay to directly visualize and quantitatively estimate the real-time antibacterial activity. Time-dependent bactericidal activity was coupled with selective photoexcitation in a confocal microscope to demonstrate the proof-of-concept of the working principle of a theranostic probe in E. coli. This new theranostic nanoprobe creates a new platform for the simultaneous probing and treating of bacterial infections in a single nanodesign, which is very useful for a long-term impact in healthcare applications.

In vivo photothermal inhibition of methicillin-resistant Staphylococcus aureus infection by in situ templated formulation of pathogen-targeting phototheranostics

Bacterial infection has caused a serious threat to human public health. Methicillin-resistant Staphylococcus aureus (MRSA) is a representative drug-resistant bacterium, which is difficult to eradicate completely, resulting in high infection probability with severe mortality. Herein, pathogen-targeting phototheranostic nanoparticles, Van-OA@PPy, are developed for efficient elimination of MRSA infection. Van-OA@PPy nanoparticles are fabricated from the in situ templated formation of polypyrrole (PPy) in the presence of ferric ions (Fe³⁺) and a polymer template, hydrophilic poly(2-hydroxyethyl methacrylate-co-N,N-dimethyl acrylamide), P(HEMA-co-DMA). PPy nanoparticles are further coated with vancomycin conjugated oleic acid (Van-OA) to afford the resultant pathogen-targeting Van-OA@PPy. A high photothermal conversion efficiency of ∼49.4% is achieved. MRSA can be efficiently killed due to sufficient nanoparticle adhesion and fusion with MRSA, followed by photothermal therapy upon irradiation with an 808 nm laser. Remarkable membrane damage of MRSA is observed, which contributes greatly to the inhibition of MRSA infection. Furthermore, the nanoparticles have high stability and good biocompatibility without causing any detectable side effects. On the other hand, residual Fe³⁺ and PPy moieties in Van-OA@PPy endow the nanoparticles with magnetic resonance (MR) imaging and photoacoustic (PA) imaging potency, respectively. The current strategy has the potential to inspire further advances in precise diagnosis and efficient elimination of MRSA infection in biomedicine.

Polyanionic Composite Membranes Based on Bacterial Cellulose and Amino Acid for Antimicrobial Application

Ideal wound dressing materials should be active components in the healing process. Bacterial cellulose (BC) has attracted a great deal of attention as novel wound dressing materials; however, it has no intrinsic antimicrobial activity. To explore the practical application values of BC and develop novel wound dressing materials, a series of composite membranes based on BC and polymeric ionic liquids (BC/PILs, composed of BC, and PILs formed by choline and different amino acids) with antimicrobial activity were synthesized by an ex situ method. The physicochemical and antimicrobial properties and biocompatibility of these membranes were systematically investigated. The results indicated that BC/PIL membranes with excellent properties could be obtained by adjusting the concentration and type of PILs. Several kinds of BC/PIL membranes exhibited good biocompatibility and high antimicrobial activity against Gram-positive and Gram-negative bacteria and fungus. The anionic PILs played important roles in the antimicrobial activity of BC/PIL membranes. The obtained membranes provided a novel promising candidate for wound dressing materials.

Detection of Bacterial Alkaline Phosphatase Activity by Enzymatic In Situ Self-Assembly of the AIEgen-Peptide Conjugate

Abnormal levels of alkaline phosphatase (ALP) activity are associated with various diseases, and many ALP probes have been developed to date. However, the development of ALP-sensitive probes for living cells, especially for the detection of bacterial ALP, remains challenging because of the complex and dynamic context. In this study, we constructed the first fluorescent probe (TPEPy-pY) for sensing bacterial ALP activity. TPEPy-pY is an AIEgen-peptide conjugate with property of aggregation-induced emission (AIE) and could turn on its fluorescence by ALP-catalyzed in situ self-assembly of the probe. The probe shows excellent selectivity and sensitivity for ALP activity, with a detection limit of 6.6 × 10^-3 U mL^-1. TPEPy-pY performs well in detection and in situ imaging of bacterial ALP activity against E. coli. Also, the detection does not require tedious washing steps and takes approximately 1 h, which is advantageous over commercial ALP kits. Therefore, the proposed strategy paved a new avenue for bacterial ALP detection, and we envision that more self-assembling fluorescent probes will be designed with higher sensitivity in the near future.

Angiopep2-Conjugated Star-Shaped Polyprodrug Amphiphiles for Simultaneous Glioma-Targeting Therapy and MR Imaging

The development of valuable theranostic agents for overcoming the blood-brain barrier (BBB) to achieve efficient imaging-guided glioma-targeting delivery of therapeutics remains a great challenge for personalized glioma therapy. We herein developed a novel functional star-shaped polyprodrug amphiphile (denoted as CPP-2) via a combination of successive reversible addition-fragmentation chain transfer (RAFT) polymerization and click functionalization. In a diluted solution, the star amphiphile existed as structurally stable unimolecular micelles, containing hydrophobic cores conjugated with reduction-responsive camptothecin prodrugs Camptothecin (CPT) prodrug monomer (CPTM) and a tertiary amine monomer (2-(diethylamine) ethyl methacrylate, DEA) and hydrophilic oligo-(ethylene glycol) monomethyl ether methacrylat (OEGMA) outer coronas covalently decorated with dual-targeting moieties Angiopep2 (ANG) and small magnetic resonance imaging (MRI) contrast agents DOTA-Gd. In vitro and in vivo data in this study demonstrated that the ANG-modified micelles were capable of efficiently penetrating the BBB and delivering loaded cargoes such as CPT and Gd³⁺ contrast agents to glioma cells, leading to a considerably enhanced t₁ relaxivity as well as antiglioma efficacy. Simultaneously, the targeted antiglioma efficacy and noninvasive MR imaging for a visualized therapy were realized. These collective findings augured well for the star polyprodrug amphiphiles to be utilized as a novel theranostic platform for clinical application in glioma therapy.

Janus micromotors for motion-capture-lighting of bacteria

The rapid and sensitive identification of bacteria has long been a major challenge in quality control, environmental monitoring and food safety. In the current study, the "motion-capture-lighting" strategy is proposed via integration of motion-enhanced capture of bacteria and capture-induced fluorescence turn-on of micromotors. Compared with the commonly used microtubes and microparticles, micromotors of flexible fiber rods could offer multiple interactions with the bacterial surface with less steric hindrance. Janus fiber rods (JFRs) are prepared by cryocutting of aligned fibers prepared by side-by-side electrospinning. Catalase is grafted on one side of JFRs to produce oxygen bubbles for propulsion of Janus micromotors (JMs), and mannose is conjugated on the other side for specific recognition of FimH proteins from fimbriae on the bacterial surface. The biphasic Janus structure of JFRs and the separate grafting of catalase and mannose on the opposite sides of JMs are confirmed after fluorescent labelling. JMs with aspect ratios of 0.5, 1, 2 and 4 are fabricated, and the aspect ratios of JMs show significant effects on the tracking trajectories and motion speed. JMs with the aspect ratio of 2 exhibit significantly higher magnitudes of mean square displacement (MSD) with a directional motion trajectory, leading to higher bacterial capture and larger fluorescence intensity changes. The bacteria capture leads to lighting up of JMs due to the aggregation-induced emission (AIE) effect of tetraphenylethene (TPE) derivatives. Under an ultraviolet lamp, the fluorescence color of JM suspensions turns from blue to bluish-green and to green after incubation with E. coli of 102 and 105 CFU mL-1, respectively. The fluorescence intensities of JM suspensions could be fitted to an equation versus bacterial concentrations, and the limit of detection (LOD) was around 45 CFU mL-1 within 1 min. Thus, this study demonstrates a motion-capture-lighting strategy for visual, rapid and real-time detection of bacteria without complicated sample pretreatment, expensive apparatus, and trained operators.

Targeting intracellular, multi-drug resistant Staphylococcus aureus with guanidinium polymers by elucidating the structure-activity relationship

Intracellular persistence of bacteria represents a clinical challenge as bacteria can thrive in an environment protected from antibiotics and immune responses. Novel targeting strategies are critical in tackling antibiotic resistant infections. Synthetic antimicrobial peptides (SAMPs) are interesting candidates as they exhibit a very high antimicrobial activity. We first compared the activity of a library of ammonium and guanidinium polymers with different sequences (statistical, tetrablock and diblock) synthesized by RAFT polymerization against methicillin-resistant S. aureus (MRSA) and methicillin-sensitive strains (MSSA). As the guanidinium SAMPs were the most potent, they were used to treat intracellular S. aureus in keratinocytes. The diblock structure was the most active, reducing the amount of intracellular MSSA and MRSA by two-fold. We present here a potential treatment for intracellular, multi-drug resistant bacteria, using a simple and scalable strategy.

AIE-based theranostic systems for detection and killing of pathogens

Pathogenic bacteria, fungi and viruses pose serious threats to the human health under appropriate conditions. There are many rapid and sensitive approaches have been developed for identification and quantification of specific pathogens, but many challenges still exist. Culture/colony counting and polymerase chain reaction are the classical methods used for pathogen detection, but their operations are time-consuming and laborious. On the other hand, the emergence and rapid spread of multidrug-resistant pathogens is another global threat. It is thus of utmost urgency to develop new therapeutic agents or strategies. Luminogens with aggregation-induced emission (AIEgens) and their derived supramolecular systems with unique optical properties have been developed as fluorescent probes for turn-on sensing of pathogens with high sensitivity and specificity. In addition, AIE-based supramolecular nanostructures exhibit excellent photodynamic inactivation (PDI) activity in aggregate, offering great potential for not only light-up diagnosis of pathogen, but also image-guided PDI therapy for pathogenic infection.