Near-Infrared Light-Activated Phototherapy by Gold Nanoclusters for Dispersing Biofilms

Visual determination of heparin in serum utilizing surfen-induced aggregation emission enhancement of gold nanoclusters and heparin-induced fluorescence enhancement of surfen

We developed a ratiometric luminescence probe for heparin detection based on the interactions among surfen, glutathione-capped gold nanoclusters (GSH-AuNCs), and heparin. At neutral pH, surfen triggers aggregation-induced emission enhancement (AIEE) in GSH-AuNCs, forming dual-emission surfen-AuNC aggregates with fluorescence at 490 nm and 610 nm. Heparin competitively binds to surfen, displacing it from the aggregates, resulting in decreased fluorescence at 610 nm and increased emission at 490 nm, enabling both ratiometric and visual heparin detection. Investigations of the AIEE mechanism reveal that surfen reduces electrostatic repulsion and enhances van der Waals interactions, facilitating nanocluster aggregation. Theoretical models based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory were employed to quantify these interactions. The probe demonstrates a linear response for heparin concentrations between 0.5 and 10 μM, with a detection limit of 0.2 μM, suitable for clinical monitoring. In 10-fold diluted human plasma, the probe maintains sensitivity, allowing naked eye detection of heparin through distinct color changes. These findings highlight this ratiometric probe as a practical, sensitive, and accessible tool for heparin quantification in complex clinical samples, surpassing the limitations of single-emission probes.

An organometallic approach to sub-2 nm thiolate-protected Au nanoclusters with enhanced catalytic and therapeutic properties

Thiolate-protected gold nanoclusters (AuNCs) of sub-2 nm size have been synthesized through a novel bottom-up approach using the organometallic precursor [Au(C6F5)(tht)] (tht = tetrahydrothiophene) in a one-pot reaction under mild conditions. This protocol is simple, rapid (1 h), versatile (applicable to thiolate ligands of varying molecular sizes), and reproducible, yielding AuNCs with low size dispersion. Furthermore, the resulting nanomaterials exhibited remarkable catalytic activity, effectively reducing the pollutant 4-nitrophenol to 4-aminophenol, as well as promising photothermal and photodynamic properties upon exposure to an 808 nm laser, converting light into thermal energy and generating reactive oxygen species (ROS). Additionally, AuNCs stabilized with a nonapeptide demonstrated efficient catalase-like activity, thereby potentially enhancing the efficacy of photodynamic therapy. The cytotoxic effects against cancer (HeLa) and healthy cells (HDF) were also evaluated, showing greater selectivity for HeLa cells, with higher toxicity and increased ROS generation.

Lipoic acid assisted microwave based synthesis of Au-Ag nanoclusters with tunable fluorescence for antimicrobial and bioimaging applications

This study reports on the pioneering synthesis and application of monometallic lipoic acid (LA) stabilized gold nanoclusters (LA@AuNCs) and bimetallic gold-silver nanoclusters (LA@Au-AgNCs) fabricated via a novel microwave-assisted method. The synthesis process unveils a significant augmentation in the quantum yield of LA@AuAgNCs up to 7.9-fold compared to their monometallic counterparts (LA@Au NCs), showcasing the efficacy of the novel microwave-assisted fabrication methodology. The rapid synthesis facilitated by microwave heating not only ensures efficiency but also contributes to superior optical properties. Additionally, the strategic modulation of exogenous parameters, such as thermal conditions and ionic metal concentrations, was leveraged to meticulously engineer the nanocluster surface characteristics, facilitating the procurement of tunable photoluminescent emission spectra spanning from 650 to 800 nm. The applicability of the synthesized metallic nanoclusters has been rigorously evaluated, demonstrating their efficacy as a dual-functional therapeutic agent. Primarily, their antimicrobial properties are pronounced against both Gram-positive and Gram-negative bacterial strains, attributed to the ultrasmall dimensions of the synthesized nanoclusters. Also, these intrinsically fluorescent metallic nanoclusters were employed as advanced bioimaging probes for the precise labelling and visualization of bacterial cells.

Construction of Zwitterionic Coatings with Lubricating and Antiadhesive Properties for Invisible Aligner Applications

Invisible aligners have been widely used in orthodontic treatment but still present issues with plaque formation and oral mucosa abrasion, which can lead to complicated oral diseases. To address these issues, hydrophilic poly(sulfobetaine methacrylate) (polySBMA) coatings with lubricating, antifouling, and antiadhesive properties have been developed on the aligner materials (i.e., polyethylene terephthalate glycol, PETG) via a simple and feasible glycidyl methacrylate (GMA)-assisted coating strategy. Poly(GMA-co-SBMA) is grafted onto the aminated PETG surface via the ring-opening reaction of GMA (i.e., "grafting to" approach to obtain G-co-S coating), or a polySBMA layer is formed on the GMA-grafted PETG surface via free radical polymerization (i.e., "grafting from" approach to obtain G-g-S coating). The G-co-S and G-g-S coatings significantly reduce the friction coefficient of PETG surface. Protein adsorption, bacterial adhesion, and biofilm formation on the G-co-S- and G-g-S-coated surfaces are significantly inhibited. The performance of the coatings remains stable after storage in air or artificial saliva for 2 weeks. Both coatings demonstrate good biocompatibility in vitro and is not caused irritation to the oral mucosa of rats in vivo over 2 weeks. This study proposes a promising strategy for the development of invisible aligners with improved performance, which is beneficial for oral health treatment.

Fe3O4-Based Nanospheres with High Photothermal Conversion Efficiency for Dual-Effect and Mild Biofilm Eradication against Periodontitis

Periodontitis, a chronic inflammatory oral disease resulting from plaque biofilms, affects about 743 million individuals worldwide. However, the efficacy of current treatments is hampered by challenges in delivering antibiotics to recalcitrant oral biofilms and bacterial resistance, thereby impeding successful treatment of infectious diseases. To address the issues, an antibacterial photothermal material was designed, comprising a spherical structure of zinc oxide (ZnO) wrapped with triiron tetraoxide (Fe3O4). The outer layer of the material adsorbed epsilon-polylysine (EPL) by electrostatic action, ultimately leading to the fabrication of Fe3O4/ZnO/EPL nanoparticles (FZE NPs). The Fe3O4 core endowed the nanoparticles with efficient photothermal properties, facilitating the dispersion of dense biofilms, which dramatically promoted the adsorption and penetration of ZnO and EPL into the biofilms to effectively kill bacteria in biofilms in vitro with enhanced sterilization ability. Additionally, upon dissolution in aqueous media, EPL acts as a positively charged antimicrobial peptide that adsorbs onto the surface of negatively charged bacterial membranes, thereby effectively modulating inflammatory responses. In order to ascertain the efficacy of FZE NPs, an investigation was conducted into their antimicrobial effects against the periodontitis-associated pathogen Porphyromonas gingivalis (P. gingivalis) in vitro. Furthermore, the antiperiodontitis potential of FZE NPs was evaluated in Sprague-Dawley (SD) rats of ligamentous periodontitis. In addition, toxicity evaluations indicated that the material had an acceptable biosafety profile in vitro and in vivo. In summary, the nanospheres (FZE NPs) represent a promising therapeutic strategy for the treatment of periodontitis.

Biomolecular ligands as tools to modulate the optical and chiroptical properties of gold nanoclusters

Biomolecule-stabilized gold nanoclusters (AuNCs) have become functional nanomaterials of interest because of their unique optical properties, together with excellent biocompatibility and stability under biological conditions. In this review, we explore the recent advancements in the application of biomolecular ligands for synthesizing AuNCs. Various synthesis approaches that are employing amino acids, peptides, proteins, and DNA as biomolecular scaffolds are reviewed. Furthermore, the influence of the synthesis conditions and nature of the biomolecule on the emerging optical (absorption and photoluminescence) and chiroptical properties of AuNCs is discussed. Finally, the latest research on the applications of biomolecule-stabilized AuNCs for biosensing, bioimaging, and theranostics is presented.

Dynamics of the oral microbiome during orthodontic treatment and antimicrobial advances for orthodontic appliances

The oral microbiome plays an important role in human health, and an imbalance of the oral microbiome could lead to oral and systemic diseases. Orthodontic treatment is an effective method to correct malocclusion. However, it is associated with many adverse effects, including white spot lesions, caries, gingivitis, periodontitis, halitosis, and even some systematic diseases. Undoubtedly, increased difficulty in oral hygiene maintenance and oral microbial disturbances are the main factors in developing these adverse effects. The present article briefly illustrates the characteristics of different ecological niches (including saliva, soft tissue surfaces of the oral mucosa, and hard tissue surfaces of the teeth) inhabited by oral microorganisms. According to the investigations conducted since 2014, we comprehensively elucidate the alterations of the oral microbiome in saliva, dental plaque, and other ecological niches after the introduction of orthodontic appliances. Finally, we provide a detailed review of recent advances in the antimicrobial properties of different orthodontic appliances. This article will provide researchers with a profound understanding of the underlying mechanisms of the effects of orthodontic appliances on human health and provide direction for further research on the antimicrobial properties of orthodontic appliances.

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.

Using gold-based nanomaterials for fighting pathogenic bacteria: from detection to therapy

Owing to the unique quantum size effect and surface effect, gold-based nanomaterials (GNMs) are promising for pathogen detection and broad-spectrum antimicrobial activity. This review summarizes recent research on GNMs as sensors for detecting pathogens and as tools for their elimination. Firstly, the need for pathogen detection is briefly introduced with an overview of the physicochemical properties of gold nanomaterials. And then strategies for the application of GNMs in pathogen detection are discussed. Colorimetric, fluorescence, surface-enhanced Raman scattering (SERS) techniques, dark-field microscopy detection and electrochemical methods can enable efficient, sensitive, and specific pathogen detection. The third section describes the antimicrobial applications of GNMs. They can be used for antimicrobial agent delivery and photothermal conversion and can act synergistically with photosensitizers to achieve the precise killing of pathogens. In addition, GNMs are promising for integrated pathogen detection and treatment; for example, combinations of colorimetric or SERS detection with photothermal sterilization have been demonstrated. Finally, future outlooks for the applications of GNMs in pathogen detection and treatment are summarized.

Chitin-Assisted Synthesis of CuS Composite Sponge for Bacterial Capture and Near-Infrared-Promoted Healing of Infected Diabetic Wounds

Diabetic wounds are prone to recurrent infections, often leading to delayed healing. To address this challenge, we developed a chitin-copper sulfide (CuS@CH) composite sponge, which combines bacterial trapping with near-infrared (NIR) activated phototherapy for treating infected diabetic wounds. CuS nanoparticles were synthesized and incorporated in situ within the sponge using a chitin assisted biomineralization strategy. The positively charged chitin surface effectively adhered bacteria, while NIR irradiation of CuS generated reactive oxygen species (ROS) heat and Cu2+ to rapidly damage the trapped bacteria. This synergistic effect resulted in an exceptional antibacterial performance against E. coli (∼99.9%) and S. aureus (∼99.3%). The bactericidal mechanism involved NIR-induced glutathione oxidation, membrane lipid peroxidation, and increased membrane permeability. In diabetic mouse models, the CuS@CH sponge accelerated the wound healing of S. aureus infected wounds by facilitating collagen deposition and reducing inflammation. Furthermore, the sponge demonstrated good biocompatibility. This dual-functional platform integrating bacterial capture and NIR-triggered phototherapy shows promise as an antibacterial wound dressing to promote healing of infected diabetic wound.

Selective antibacterial and antibiofilm activity of chlorinated hemicyanine against gram-positive bacteria

Antibiotic-free therapies are highly needed due to the limited success of conventional approaches especially against biofilm related infections. In this direction, antimicrobial phototherapy, either in the form of antimicrobial photothermal therapy (aPTT) or antimicrobial photodynamic therapy (aPDT), have appeared to be highly promising candidates in recent years. These are local and promising approaches for antibiotic resistant bacterial infections and biofilms. Organic small photosensitizers (PSs) are extensively preferred in antimicrobial phototherapy applications as they offer a great opportunity to combine therapeutic action (aPTT, aPDT or both) with fluorescence imaging on a single molecule. In this study, the bactericidal effect of cationic chlorinated hemicyanine (Cl-Hem)-based type I PS, which can function as a dual aPDT/aPTT agent, was investigated on both planktonic cells and biofilms of different gram-positive (E. faecalis and S. epidermidis) and gram-negative bacteria (P. aeruginosa and K. pneumoniae) with and without 640 nm laser irradiation. Cl-Hem was shown to induce a selective phototheranostic activity against gram-positive bacteria (E. faecalis and S. epidermidis). Cl-Hem exhibited both dose and laser irradiation time dependent bactericidal effect on planktonic and biofilms of S. epidermidis. These results clearly showed that highly potent Cl-Hem can treat resistant microbial infections, while allowing fluorescence detection at the same time. High biofilm reduction observed with combined aPDT/aPTT action of Cl-Hem together with its non-cytotoxic nature points out that Cl-Hem is a promising PS for antibacterial and antibiofilm treatments.

From synthesis to applications of biomolecule-protected luminescent gold nanoclusters

Gold nanoclusters (AuNCs) are a class of novel luminescent nanomaterials that exhibit unique properties of ultra-small size, featuring strong anti-photo-bleaching ability, substantial Stokes shift, good biocompatibility, and low toxicity. Various biomolecules have been developed as templates or ligands to protect AuNCs with enhanced stability and luminescent properties for biomedical applications. In this review, the synthesis of AuNCs based on biomolecules including amino acids, peptides, proteins and DNA are summarized. Owing to the advantages of biomolecule-protected AuNCs, they have been employed extensively for diverse applications. The biological applications, particularly in bioimaging, biosensing, disease therapy and biocatalysis have been described in detail herein. Finally, current challenges and future potential prospects of bio-templated AuNCs in biological research are briefly discussed.

Antibiotic Alternatives: Multifunctional Ultra-Small Metal Nanoclusters for Bacterial Infectious Therapy Application

The prevalence of major bacterial infections has emerged as a significant menace to human health and life. Conventional treatment methods primarily rely on antibiotic therapy, but the overuse of these drugs has led to a decline in their efficacy. Moreover, bacteria have developed resistance towards antibiotics, giving rise to the emergence of superbugs. Consequently, there is an urgent need for novel antibacterial agents or alternative strategies to combat bacterial infections. Nanoantibiotics encompass a class of nano-antibacterial materials that possess inherent antimicrobial activity or can serve as carriers to enhance drug delivery efficiency and safety. In recent years, metal nanoclusters (M NCs) have gained prominence in the field of nanoantibiotics due to their ultra-small size (less than 3 nm) and distinctive electronic and optical properties, as well as their biosafety features. In this review, we discuss the recent progress of M NCs as a new generation of antibacterial agents. First, the main synthesis methods and characteristics of M NCs are presented. Then, we focus on reviewing various strategies for detecting and treating pathogenic bacterial infections using M NCs, summarizing the antibacterial effects of these nanoantibiotics on wound infections, biofilms, and oral infections. Finally, we propose a perspective on the remaining challenges and future developments of M NCs for bacterial infectious therapy.

Gold nanoclusters cure implant infections by targeting biofilm

The biofilm-mediated implant infections pose a huge threat to human health. It is urgent to explore strategies to reverse this situation. Herein, we design 3-amino-1,2,4-triazole-5-thiol (ATT)-modified gold nanoclusters (AGNCs) to realize biofilm-targeting and near-infrared (NIR)-II light-responsive antibiofilm therapy. The AGNCs can interact with the bacterial extracellular DNA through the formation of hydrogen bonds between the amine groups on the ATT and the hydroxyl groups on the DNA. The AGNCs show photothermal properties even at a low power density (0.5 W/cm2) for a short-time (5 min) irradiation, making them highly effective in eradicating the biofilm with a dispersion rate up to 90 %. In vivo infected catheter implantation model demonstrates an exceptional high ability of the AGNCs to eradicate approximately 90 % of the bacteria encased within the biofilms. Moreover, the AGNCs show no detectable toxicity or systemic effects in mice. Our study suggests the great potential of the AGNCs for long-term prevention and elimination of the biofilm-mediated infections.

Application of biofilm dispersion-based nanoparticles in cutting off reinfection

Bacterial biofilms commonly cause chronic and persistent infections in humans. Bacterial biofilms consist of an inner layer of bacteria and an autocrine extracellular polymeric substance (EPS). Biofilm dispersants (abbreviated as dispersants) have proven effective in removing the bacterial physical protection barrier EPS. Dispersants are generally weak or have no bactericidal effect. Bacteria dispersed from within biofilms (abbreviated as dispersed bacteria) may be more invasive, adhesive, and motile than planktonic bacteria, characteristics that increase the probability that dispersed bacteria will recolonize and cause reinfection. The dispersants should be combined with antimicrobials to avoid the risk of severe reinfection. Dispersant-based nanoparticles have the advantage of specific release and intense penetration, providing the prerequisite for further antibacterial agent efficacy and achieving the eradication of biofilms. Dispersant-based nanoparticles delivered antimicrobial agents for the treatment of diseases associated with bacterial biofilm infections are expected to be an effective measure to prevent reinfection caused by dispersed bacteria. KEY POINTS: • Dispersed bacteria harm and the dispersant's dispersion mechanisms are discussed. • The advantages of dispersant-based nanoparticles in bacteria biofilms are discussed. • Dispersant-based nanoparticles for cutting off reinfection in vivo are highlighted.

Functional nanomaterials as photosensitizers or delivery systems for antibacterial photodynamic therapy

Bacterial infection is a global health problem that closely related to various diseases threatening human life. Although antibiotic therapy has been the mainstream treatment method for various bacterial infectious diseases for decades, the increasing emergence of bacterial drug resistance has brought enormous challenges to the application of antibiotics. Therefore, developing novel antibacterial strategies is of great importance. By producing reactive oxygen species (ROS) with photosensitizers (PSs) under light irradiation, antibacterial photodynamic therapy (aPDT) has emerged as a non-invasive and promising approach for treating bacterial infections without causing drug resistance. However, the insufficient therapeutic penetration, poor hydrophilicity, and poor biocompatibility of traditional PSs greatly limit the efficacy of aPDT. Recently, studies have found that nanomaterials with characteristics of favorable photocatalytic activity, surface plasmonic resonance, easy modification, and high drug loading capacity can improve the therapeutic efficacy of aPDT. In this review, we aim to provide a comprehensive understanding of the mechanism of nanomaterials-mediated aPDT and summarize the representative nanomaterials in aPDT, either as PSs or carriers for PSs. In addition, the combination of advanced nanomaterials-mediated aPDT with other therapies, including targeted therapy, gas therapy, and multidrug resistance (MDR) therapy, is reviewed. Also, the concerns and possible solutions of nanomaterials-based aPDT are discussed. Overall, this review may provide theoretical basis and inspiration for the development of nanomaterials-based aPDT.

Drug-loaded lipid nanoparticles improve the removal rates of the Staphylococcus aureus biofilm

Biofilms of the foodborne pathogen Staphylococcus aureus show improved resistance to antibiotics and are difficult to eliminate. To enhance antibacteria and biofilm dispersion via extracellular matrix diffusion, a new lipid nanoparticle was prepared, which employed a mixture of phospholipids and a 0.8% surfactin shell. In the lipid nanoparticle, 31.56 μg mL-1 of erythromycin was encapsulated. The lipid nanoparticle size was approximately 52 nm and the zeta-potential was -67 mV, which was measured using a Marvin laser particle size analyzer. In addition, lipid nanoparticles significantly dispersed the biofilms of S. aureus W1, CICC22942, and CICC 10788 on the surface of stainless steel, reducing the total viable count of bacteria in the biofilms by 103 CFU mL-1 . In addition, the lipid nanoparticle can remove polysaccharides and protein components from the biofilm matrix. The results of laser confocal microscopy showed that the lipid nanoparticles effectively killed residual bacteria in the biofilms. Thus, to thoroughly eliminate biofilms on material surfaces in food factories to avoid repeated contamination, drug-lipid nanoparticles present a suitable method to achieve this.

Promoting the Near-Infrared-II Fluorescence of Diketopyrrolopyrrole-Based Dye for In Vivo Imaging via Donor Engineering

Small-molecule dyes for fluorescence imaging in the second near-infrared region (NIR-II, 900-1880 nm) hold great promise in clinical applications. Constructing donor-acceptor-donor (D-A-D) architectures has been recognized to be a feasible strategy to achieve NIR-II fluorescence. However, the development of NIR-II dyes via such a scheme is hampered by the lack of high-performance electron acceptors and donors. Diketopyrrolopyrrole (DPP), as a classic organic optoelectronic material, enjoys strong light absorption, high fluorescence quantum yield (QY), and facile derivatization. Nevertheless, its application in the NIR-II imaging field has been hindered by its limited electron-withdrawing ability and the aggregation-caused quenching (ACQ) effect resulting from the planar structure of DPP. Herein, with DPP as an electron acceptor and through donor engineering, we have successfully designed and synthesized a DPP-based dye named T-27, in which the strong D-A interaction confers excellent NIR absorption and high-brightness NIR-II fluorescence tail emission. By strategically introducing long alkyl chains on the donor unit to increase intermolecular spacing and reduce the influence of solvent molecules, T-27 exhibits an improved anti-ACQ effect in aqueous solutions. After being encapsulated into DSPE-PEG2000, T-27 nanoparticles (NPs) show a relative NIR-II fluorescence QY of 3.4% in water, representing the highest value among the DPP-based NIR-II dyes reported to date. The outstanding photophysical properties of T-27 NPs enable multimode NIR-IIa bioimaging under 808 nm excitation. As such, the T-27 NPs can distinguish mouse femoral vein and artery and achieve cerebral vascular microscopic imaging with a penetrating depth of 800 μm, demonstrating the capability for high-resolution deep-tissue imaging. This work holds significant potential in the field of bioimaging and provides a new strategy for developing bright NIR-II dyes.

"All in one" nanoprobe Au-TTF-1 for target FL/CT bioimaging, machine learning technology and imaging-guided photothermal therapy against lung adenocarcinoma

The accurate preoperative diagnosis and tracking of lung adenocarcinoma is hindered by non-targeting and diffusion of dyes used for marking tumors. Hence, there is an urgent need to develop a practical nanoprobe for tracing lung adenocarcinoma precisely even treating them noninvasively. Herein, Gold nanoclusters (AuNCs) conjugate with thyroid transcription factor-1 (TTF-1) antibody, then multifunctional nanoprobe Au-TTF-1 is designed and synthesized, which underscores the paramount importance of advancing the machine learning diagnosis and bioimaging-guided treatment of lung adenocarcinoma. Bright fluorescence (FL) and strong CT signal of Au-TTF-1 set the stage for tracking. Furthermore, the high specificity of TTF-1 antibody facilitates selective targeting of lung adenocarcinoma cells as compared to common lung epithelial cells, so machine learning software Lung adenocarcinoma auxiliary detection system was designed, which combined with Au-TTF-1 to assist the intelligent recognition of lung adenocarcinoma jointly. Besides, Au-TTF-1 not only contributes to intuitive and targeted visualization, but also guides the following noninvasive photothermal treatment. The boundaries of tumor are light up by Au-TTF-1 for navigation, it penetrates into tumor and implements noninvasive photothermal treatment, resulting in ablating tumors in vivo locally. Above all, Au-TTF-1 serves as a key platform for target bio-imaging navigation, machine learning diagnosis and synergistic PTT as a single nanoprobe, which demonstrates attractive performance on lung adenocarcinoma.

Imaging-Guided Antibacterial Based on Gold Nanocrystals and Assemblies

Bacterial infection becomes a severe threat to human life and health worldwide. Antibiotics with the ability to resist pathogenic bacteria are therefore widely used, but the misuse or abuse of antibiotics can generate multidrug-resistant bacteria or resistant biofilms. Advanced antibacterial technologies are needed to counter the rapid emergence of drug-resistant bacteria. With the excellent optical properties, engineerable surface chemistry, neglectable biotoxicity, gold nanocrystals are particularly attractive in biomedicine for cancer therapy and antibacterial therapy, as well as nanoprobes for bioimaging and disease diagnosis. In this perspective, gold nanocrystal-based antibacterial performance and deep-tissue imaging are summarized, including near-infrared-light excited photoacoustic imaging and fluorescence imaging through deep tissue infections. On the basis of integrating "imaging-therapy-targeting" in single nanotheranostic, the current challenges of imaging-guided antibacterial and therapy based on gold nanocrystals are discussed, and some insights are provided into the gold nanocrystal-based nanoplatform that integrates antibacterial activity and therapy. This perspective is expected to provide comprehensive guidance for diagnosing and combating bacterial infections based on gold nanostructures.

Size and charge effects of metal nanoclusters on antibacterial mechanisms

Nanomaterials, specifically metal nanoclusters (NCs), are gaining attention as a promising class of antibacterial agents. Metal NCs exhibit antibacterial properties due to their ultrasmall size, extensive surface area, and well-controlled surface ligands. The antibacterial mechanisms of metal NCs are influenced by two primary factors: size and surface charge. In this review, we summarize the impacts of size and surface charge of metal NCs on the antibacterial mechanisms, their interactions with bacteria, and the factors that influence their antibacterial effects against both gram-negative and gram-positive bacteria. Additionally, we highlight the mechanisms that occur when NCs are negatively or positively charged, and provide examples of their applications as antibacterial agents. A better understanding of relationships between antibacterial activity and the properties of metal NCs will aid in the design and synthesis of nanomaterials for the development of effective antibacterial agents against bacterial infections. Based on the remarkable achievements in the design of metal NCs, this review also presents conclusions on current challenges and future perspectives of metal NCs for both fundamental investigations and practical antibacterial applications.

An injectable and thermosensitive hydrogel with nano-aided NIR-II phototherapeutic and chemical effects for periodontal antibacteria and bone regeneration

Periodontitis is a common public health problem worldwide and an inflammatory disease with irregular defect of alveolar bone caused by periodontal pathogens. Both antibacterial therapy and bone regeneration are of great importance in the treatment of periodontitis. In this study, injectable and thermosensitive hydrogels with 3D networks were used as carriers for controlled release of osteo-inductive agent (BMP-2) and Near Infrared Region-II (NIR-II) phototherapy agents (T8IC nano-particles). T8IC nano-particles were prepared by reprecipitation and acted as photosensitizer under 808 nm laser irradiation. Besides, we promoted photodynamic therapy (PDT) through adding H2O2 to facilitate the antibacterial effect instead of increasing the temperature of photothermal therapy (PTT). Hydrogel + T8IC + Laser + BMP-2 + H2O2 incorporated with mild PTT (45 °C), enhanced PDT and sustained release of BMP-2. It was present with excellent bactericidal effect, osteogenic induction and biosafety both in vitro and in vivo. Besides, immunohistochemistry staining and micro-CT analyses had confirmed that PTT and PDT could promote bone regeneration through alleviating inflammation state. Altogether, this novel approach with synergistic antibacterial effect, anti-inflammation and bone regeneration has a great potential for the treatment of periodontitis in the future.

Recent Advances in Nanozyme-Mediated Strategies for Pathogen Detection and Control

Pathogen detection and control have long presented formidable challenges in the domains of medicine and public health. This review paper underscores the potential of nanozymes as emerging bio-mimetic enzymes that hold promise in effectively tackling these challenges. The key features and advantages of nanozymes are introduced, encompassing their comparable catalytic activity to natural enzymes, enhanced stability and reliability, cost effectiveness, and straightforward preparation methods. Subsequently, the paper delves into the detailed utilization of nanozymes for pathogen detection. This includes their application as biosensors, facilitating rapid and sensitive identification of diverse pathogens, including bacteria, viruses, and plasmodium. Furthermore, the paper explores strategies employing nanozymes for pathogen control, such as the regulation of reactive oxygen species (ROS), HOBr/Cl regulation, and clearance of extracellular DNA to impede pathogen growth and transmission. The review underscores the vast potential of nanozymes in pathogen detection and control through numerous specific examples and case studies. The authors highlight the efficiency, rapidity, and specificity of pathogen detection achieved with nanozymes, employing various strategies. They also demonstrate the feasibility of nanozymes in hindering pathogen growth and transmission. These innovative approaches employing nanozymes are projected to provide novel options for early disease diagnoses, treatment, and prevention. Through a comprehensive discourse on the characteristics and advantages of nanozymes, as well as diverse application approaches, this paper serves as a crucial reference and guide for further research and development in nanozyme technology. The expectation is that such advancements will significantly contribute to enhancing disease control measures and improving public health outcomes.

Photothermal/Photoacoustic Therapy Combined with Metal-Based Nanomaterials for the Treatment of Microbial Infections

The increased spread and persistence of bacterial drug-resistant phenotypes remains a public health concern and has contributed significantly to the challenge of combating antibiotic resistance. Nanotechnology is considered an encouraging strategy in the fight against antibiotic-resistant bacterial infections; this new strategy should improve therapeutic efficacy and minimize side effects. Evidence has shown that various nanomaterials with antibacterial performance, such as metal-based nanoparticles (i.e., silver, gold, copper, and zinc oxide) have intrinsic antibacterial properties. These antibacterial agents, such as those made of metal oxides, carbon nanomaterials, and polymers, have been used not only to improve antibacterial efficacy but also to reduce bacterial drug resistance due to their interaction with bacteria and their photophysical properties. These nanostructures have been used as effective agents for photothermal therapy (PTT) and photodynamic therapy (PDT) to kill bacteria locally by heating or the controlled production of reactive oxygen species. Additionally, PTT or PDT therapies have also been combined with photoacoustic (PA) imaging to simultaneously improve treatment efficacy, safety, and accuracy. In this present review, we present, on the one hand, a summary of research highlighting the use of PTT-sensitive metallic nanomaterials for the treatment of bacterial and fungal infections, and, on the other hand, an overview of studies showing the PA-mediated theranostic functionality of metal-based nanomaterials.

Detection and imaging of bacterial biofilms with glutathione-stabilized gold nanoclusters

Bacterial biofilms colonize chronic wounds and surfaces of medical devices, thus making the development of reliable methods for imaging and detection of biofilms crucial. Although fluorescent identification of bacteria is sensitive and non-destructive, the lack of biofilm-specific fluorescent dyes limits the application of this technique to biofilm detection. Here, we demonstrate, for the first time, that fluorescent glutathione-stabilized gold nanoclusters (GSH-AuNCs) without targeting ligands can specifically interact with extracellular matrix components of Gram-negative and Gram-positive bacterial biofilms resulting in fluorescent staining of bacterial biofilms. By contrast, fluorescent bovine serum albumin-stabilized gold nanoclusters and 11-mercaptoundecanoic acid - stabilized gold nanoclusters do not stain the extracellular matrix of biofilms. According to molecular docking studies, GSH-AuNCs show affinity to several targets in extracellular matrix, including amyloid-anchoring proteins, matrix proteins and polysaccharides. Some experimental evidence was obtained for the interaction of GSH-AuNCs with the lipopolysaccharide (LPS) that was isolated from the matrix of Azospirillum baldaniorum biofilms. Based on GSH-AuNCs properties, we propose a new fluorescent method for the measurement of biofilm biomass with a limit of detection 1.7 × 10⁵ CFU/mL. The sensitivity of the method is 10-fold higher than the standard biofilm quantification with the crystal violet assay. There is a good linear relationship between the fluorescence intensity from the biofilms and the number of CFU from the biofilms in the range from 2.6 × 10⁵ to 6.7 × 10⁷ CFU/mL. The developed nanocluster-mediated method of biofilm staining was successfully applied for quantitative detection of biofilm formation on urinary catheter surface. The presented data suggest that fluorescent GSH-AuNCs can be used to diagnose medical device-associated infections.

Green Synthesis of Liquid Metal-Doped Carbon Dots for Treating Multidrug-Resistant Gram-Negative Bacteria

Global emergence of multidrug-resistant (MDR) gram-negative bacteria triggers severe infections that result in an epidemic. It is urgent to discover novel classes of antibacterial agents. Here, a green route for synthesizing polyethylene glycol-based carbon dots (PEG-CDs) doped with liquid metal (LM-Cdots) via a solvent-free system is presented. LM-Cdots synthesized via ultrasound exhibit great antibacterial activity against gram-negative bacteria (E. coli, P. aeruginosa, K. pneumoniae, and A. baumannii) and their multidrug-resistant (MDR) clinical isolates. In the in vitro antibacterial test with MDR K. pneumoniae, LM-Cdots show an extremely low minimum inhibition concentration (MIC) of 0.63 µg mL-1 . Compared to naked PEG-CDs, the MIC is improved by 1000 times. In vivo results reveal that LM-Cdots can accelerate wound healing with low biotoxicity and inflammation.

Ultrasmall Coinage Metal Nanoclusters as Promising Theranostic Probes for Biomedical Applications

Ultrasmall coinage metal nanoclusters (NCs, <3 nm) have emerged as a novel class of theranostic probes due to their atomically precise size and engineered physicochemical properties. The rapid advances in the design and applications of metal NC-based theranostic probes are made possible by the atomic-level engineering of metal NCs. This Perspective article examines (i) how the functions of metal NCs are engineered for theranostic applications, (ii) how a metal NC-based theranostic probe is designed and how its physicochemical properties affect the theranostic performance, and (iii) how metal NCs are used to diagnose and treat various diseases. We first summarize the tailored properties of metal NCs for theranostic applications in terms of biocompatibility and tumor targeting. We focus our discussion on the theranostic applications of metal NCs in bioimaging-directed disease diagnosis, photoinduced disease therapy, nanomedicine, drug delivery, and optical urinalysis. Lastly, an outlook on the challenges and opportunities in the future development of metal NCs for theranostic applications is provided.

Promoting the healing of methicillin-resistant Staphylococcus aureus-infected wound by a multi-target antimicrobial AIEgen of 6-Aza-2-thiothymine-decorated gold nanoclusters

The use of conventional antibiotic therapies is in question owing to the emergence of drug-resistant pathogenic bacteria. Therefore, novel, highly efficient antibacterial agents to effectively overcome resistant bacteria are urgently needed. Accordingly, in this work, we described a novel class luminogen of 6-Aza-2-thiothymine-decorated gold nanoclusters (ATT-AuNCs) with aggregation-induced emission property that possessed potent antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA). Scanning electron microscopy was performed to investigate the interactions between ATT-AuNCs and MRSA. In addition, ATT-AuNCs exhibited excellent ROS generation efficiency and could effectively ablate MRSA via their internalization to the cells. Finally, tandem mass tag-labeling proteome analysis was carried out to investigate the differential expression proteins in MRSA strains. The results suggested that ATT-AuNCs killed MRSA cells through altering the expression of multiple target proteins involved in DNA replication, aminoacyl-tRNA synthesis, peptidoglycan and arginine biosynthesis metabolism. Parallel reaction monitoring technique was further used for the validation of these proteome results. ATT-AuNCs could also be served as a wound-healing agent and accelerate the healing process. Overall, we proposed ATT-AuNCs could serve as a robust antimicrobial aggregation-induced emission luminogen (AIEgen) that shows the ability to alter the activities of multiple targets for the elimination of drug-resistant bacteria.

Multi-Targeted Peptide-Modified Gold Nanoclusters for Treating Solid Tumors in the Liver

Apoptosis and autophagy determine the fate of cancer cells. However, simply promoting apoptosis of tumor cells is limited in the treatment of unresectable solid liver tumors. Generally, autophagy is considered the anti-apoptotic "guardian". But the pro-apoptotic effects of autophagy can be activated by excessive endoplasmic reticulum (ER) stress. Here, amphiphilic peptide-modified glutathione (GSH)-gold nanocluster aggregates (AP₁ P₂ -PEG NCs) were designed with the enrichment of solid liver tumors and the prolonged stress in the ER, which can achieve the mutual promotion of autophagy and apoptosis in liver tumor cells. In this study, orthotopic and subcutaneous liver tumor models show the anti-tumor effectiveness of AP₁ P₂ -PEG NCs, with a better antitumor effect than sorafenib, biosafety (Lethal Dose, 50% (LD₅₀ ) of 827.3 mg kg^-1 ), wide therapeutic window (non-toxic in 20 times of therapeutic concentration) and high stability (blood half-life of 4 h). These findings identify an effective strategy to develop peptide-modified gold nanocluster aggregates with low toxicity, high potency, and selectivity for solid liver tumors treatment.

Identification of Antibiotic Resistance in ESKAPE Pathogens through Plasmonic Nanosensors and Machine Learning

Antibiotic-resistant ESKAPE pathogens cause nosocomial infections that lead to huge morbidity and mortality worldwide. Rapid identification of antibiotic resistance is vital for the prevention and control of nosocomial infections. However, current techniques like genotype identification and antibiotic susceptibility testing are generally time-consuming and require large-scale equipment. Herein, we develop a rapid, facile, and sensitive technique to determine the antibiotic resistance phenotype among ESKAPE pathogens through plasmonic nanosensors and machine learning. Key to this technique is the plasmonic sensor array that contains gold nanoparticles functionalized with peptides differing in hydrophobicity and surface charge. The plasmonic nanosensors can interact with pathogens to generate bacterial fingerprints that alter the surface plasmon resonance (SPR) spectra of nanoparticles. In combination with machine learning, it enables the identification of antibiotic resistance among 12 ESKAPE pathogens in less than 20 min with an overall accuracy of 89.74%. This machine-learning-based approach allows for the identification of antibiotic-resistant pathogens from patients and holds great promise as a clinical tool for biomedical diagnosis.

Atomically precise Au nanocluster-embedded carrageenan for single near-infrared light-triggered photothermal and photodynamic antibacterial therapy

In this study, we report atomically precise gold nanoclusters-embedded natural polysaccharide carrageenan as a novel hydrogel platform for single near-infrared light-triggered photothermal (PTT) and photodynamic (PDT) antibacterial therapy. Briefly, atomically precise captopril-capped Au nanoclusters (Au₂₅Capt₁₈) prepared by an alkaline NaBH₄ reduction method and then embedded them into the biosafe carrageenan to achieve superior PTT and PDT dual-mode antibacterial effect. In this platform, the embedded Au₂₅Capt₁₈, as simple-component phototherapeutic agents, exhibit superior thermal effects and singlet oxygen generation under a single near-infrared (NIR, 808 nm) light irradiation, which enables rapid elimination of bacteria. Carrageenan endows the hydrogel platform with superior gelation characteristics and wound microenvironmental regulation. The Au₂₅Capt₁₈-embedded hydrogels exhibited good water retention, hemostasis, and breathability, providing a favorable niche environment for promoting wound healing. In vitro experiments confirmed the excellent antibacterial activity of the Au₂₅Capt₁₈ hydrogels against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. The antibacterial effect and promoting wound healing function were further validated in a S. aureus-infected wound model. Biosafety evaluation showed that the Au₂₅Capt₁₈ hydrogel has excellent biocompatibility. This PTT/PDT dual-mode therapy offers an alternative strategy for battling bacterial infections without antibiotics. More importantly, this hydrogel is facile to prepare which is helpful for expanding applications.

Recent Nanotechnologies to Overcome the Bacterial Biofilm Matrix Barriers

Bacterial biofilm-related infectious diseases severely influence human health. Under typical situations, pathogens can colonize inert or biological surfaces and form biofilms. Biofilms are functional aggregates that coat bacteria with extracellular polymeric substances (EPS). The main reason for the failure of biofilm infection treatment is the low permeability and enrichment of therapeutic agents within the biofilm, which results from the particular features of biofilm matrix barriers such as negatively charged biofilm components and highly viscous compact EPS structures. Hence, developing novel therapeutic strategies with enhanced biofilm penetrability is crucial. Herein, the current progress of nanotechnology methods to improve therapeutic agents' penetrability against biofilm matrix, such as regulating material morphology and surface properties, utilizing the physical penetration of nano/micromotors or microneedle patches, and equipping nanoparticles with EPS degradation enzymes or signal molecules, is first summarized. Finally, the challenges, perspectives, and future implementations of engineered delivery systems to manage biofilm infections are presented in detail.

Phages and Nanotechnology: New Insights against Multidrug-Resistant Bacteria

Bacterial infections are a major threat to the human healthcare system worldwide, as antibiotics are becoming less effective due to the emergence of multidrug-resistant strains. Therefore, there is a need to explore nontraditional antimicrobial alternatives to support rapid interventions and combat the spread of pathogenic bacteria. New nonantibiotic approaches are being developed, many of them at the interface of physics, nanotechnology, and microbiology. While physical factors (e.g., pressure, temperature, and ultraviolet light) are typically used in the sterilization process, nanoparticles and phages (bacterial viruses) are also applied to combat pathogenic bacteria. Particularly, phage-based therapies are rising due to the unparalleled specificity and high bactericidal activity of phages. Despite the success of phages mostly as compassionate use in clinical cases, some drawbacks need to be addressed, mainly related to their stability, bioavailability, and systemic administration. Combining phages with nanoparticles can improve their performance in vivo. Thus, the combination of nanotechnology and phages might provide tools for the rapid and accurate detection of bacteria in biological samples (diagnosis and typing), and the development of antimicrobials that combine the selectivity of phages with the efficacy of targeted therapy, such as photothermal ablation or photodynamic therapies. In this review, we aim to provide an overview of how phage-based nanotechnology represents a step forward in the fight against multidrug-resistant bacteria.

Mechanical nanolattices printed using nanocluster-based photoresists

Natural materials exhibit emergent mechanical properties as a result of their nanoarchitected, nanocomposite structures with optimized hierarchy, anisotropy, and nanoporosity. Fabrication of such complex systems is currently challenging because high-quality three-dimensional (3D) nanoprinting is mostly limited to simple, homogeneous materials. We report a strategy for the rapid nanoprinting of complex structural nanocomposites using metal nanoclusters. These ultrasmall, quantum-confined nanoclusters function as highly sensitive two-photon activators and simultaneously serve as precursors for mechanical reinforcements and nanoscale porogens. Nanocomposites with complex 3D architectures are printed, as well as structures with tunable, hierarchical, and anisotropic nanoporosity. Nanocluster-polymer nanolattices exhibit high specific strength, energy absorption, deformability, and recoverability. This framework provides a generalizable, versatile approach for the use of photoactive nanomaterials in additive manufacturing of complex systems with emergent mechanical properties.

Enhanced antibacterial activity with increasing P doping ratio in CQDs

It is an urgent challenge to develop efficient antibacterial agents against resistant bacteria in the treatment of infectious diseases. Carbon quantum dots (CQDs) have attracted much attention owing to their good stability, low toxicity and excellent biocompatibility. In this work, CQDs doped with different contents of the element phosphorus (P) were prepared by a simple hydrothermal method using valine as a carbon source, triethylamine as a nitrogen source and different volumes of phosphoric acid as a phosphorus source. The average diameter and the surface charge could be regulated from 2.89 nm to 1.56 nm and +2.58 mV to +5.47 mV by increasing the content of the element P in these CQDs. Importantly, these CQDs showed effective bacterial inhibition against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The minimal inhibitory concentration (MIC) decreased from 0.71, to 0.51 to 0.18 mg mL-1 on E. coli and S. aureus with the increase of P element content. Furthermore, the morphologies of E. coli cells and S. aureus were damaged and became irregular upon treatment with these CQDs. The results of singlet oxygen (1O2) detection demonstrated that intracellular 1O2 was generated during the antibacterial process. We speculated that bacterial inhibition induced by these CQDs was accompanied by disruption of permeability and structural integrity, owing to strong electrostatic interactions between negatively charged bacteria and positively charged CQDs and production of singlet oxygen of CQDs. Together, this study indicates that the CQDs can be a candidate to treat resistant bacterial infections and may improve the understanding of killing pathogens by antibacterial CQD drugs.

Construction of a matchstick-shaped Au@ZnO@SiO2-ICG Janus nanomotor for light-triggered synergistic antibacterial therapy

The drug-resistance of bacteria poses a serious threat to public health, so the exploration of new antibacterial materials has attracted extensive attention. Here, we report Au@ZnO@SiO₂-ICG nanomotors as an antibacterial candidate. Firstly, we prepared the Janus structure Au@ZnO loaded with indocyanine green (ICG) and constructed a synergistic antibacterial platform with photothermal and photodynamic properties triggered by dual light sources. Specifically, the metal/semiconductor heterostructure of Au@ZnO has a synergistic effect under ultraviolet (UV) irradiation, which can adjust the transfer of interface electrons, so as to greatly improve the generation of cytotoxic ROS for photodynamic sterilization. The loaded ICG is an effective photosensitizer, and can induce a stronger photothermal effect in collaboration with Au under near-infrared light (NIR). In addition, the asymmetric structures of nanomotors have autonomous movement with the help of generated temperature gradient when exposed to NIR light, conducive to breaking through the bacterial membrane and improving the membrane insertion ability of antibacterial therapeutic agents. The results indicate that the prepared Au@ZnO@SiO₂-ICG nanomotors show excellent light responses and synergistic sterilization ability to Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus). This study will provide a new idea for the application of metal-semiconductor nanocomposites in the treatment of bacterial infection.

Engineering efficient artificial nanozyme based on chitosan grafted Fe-doped-carbon dots for bacteria biofilm eradication

Bacterial biofilms have evoked worldwide attention owing to their serious threats to public health, but how to effectively eliminate bacterial biofilms still remains great challenges. Here, we rationally designed a novel and vigorous chitosan grafted Fe-doped-carbon dots (CS@Fe/CDs) as an efficient artificial nanozyme to combat rigid bacterial biofilms through the selective activation of Fenton-like reaction-triggered peroxidase-like catalytic activity and the synergistic antibacterial activity of CS. On the one hand, the peroxidase-like catalytic activity made CS@Fe/CDs catalyze H₂O₂ for producing hydroxyl radicals (•OH), resulting in efficient cleavage of extracellular DNA (eDNA). On the other hand, CS was capable of binding with the negatively charged cell membrane through electrostatic interaction, changing the cell membrane permeability and causing cell death within bacterial biofilms. Based on their synergistic effects, the fragments of bacterial biofilm and exposed bacteria were persistently eradicated. Remarkably, CS@Fe/CDs-based nanozyme not only enabled the effective destroying of gram-positive Staphylococcus aureus (S. aureus) biofilms, but also completely eliminated gram-negative Pseudomonas aeruginosa (P. aeruginosa) biofilms, showing great potential as a promising anti-biofilm agent against bacteria biofilms. This proposed synergistic strategy for bacterial biofilm eradication might offer a powerful modality to manage of bacterial biofilm fouling in food safety and environmental protection.

Deploying Gold Nanomaterials in Combating Multi-Drug-Resistant Bacteria

Antibiotic resistance has become a serious threat to human health due to the overuse of antibiotics. Different antibiotics are being developed to treat resistant bacteria, but the development cycle of antibiotics is hard to keep up with the high incidence of antibiotic resistance. Recent advances in antimicrobial nanomaterials have made nanotechnology a powerful solution to this dilemma. Among these nanomaterials, gold nanomaterials have excellent antibacterial efficacy and biosafety, making them alternatives to antibiotics. This review presents strategies that use gold nanomaterials to combat drug-resistant bacteria. We focus on the influence of physicochemical factors such as surface chemistry, size, and shape of gold nanomaterials on their antimicrobial properties and describe the antimicrobial applications of gold nanomaterials in medical devices. Finally, the existing challenges and future directions are discussed.

Antibacterial metal nanoclusters

Combating bacterial infections is one of the most important applications of nanomedicine. In the past two decades, significant efforts have been committed to tune physicochemical properties of nanomaterials for the development of various novel nanoantibiotics. Among which, metal nanoclusters (NCs) with well-defined ultrasmall size and adjustable surface chemistry are emerging as the next-generation high performance nanoantibiotics. Metal NCs can penetrate bacterial cell envelope more easily than conventional nanomaterials due to their ultrasmall size. Meanwhile, the abundant active sites of the metal NCs help to catalyze the bacterial intracellular biochemical processes, resulting in enhanced antibacterial properties. In this review, we discuss the recent developments in metal NCs as a new generation of antimicrobial agents. Based on a brief introduction to the characteristics of metal NCs, we highlight the general working mechanisms by which metal NCs combating the bacterial infections. We also emphasize central roles of core size, element composition, oxidation state, and surface chemistry of metal NCs in their antimicrobial efficacy. Finally, we present a perspective on the remaining challenges and future developments of metal NCs for antibacterial therapeutics.

Heterostructured Metal-Organic Frameworks/Polydopamine Coating Endows Polyetheretherketone Implants with Multimodal Osteogenicity and Photoswitchable Disinfection

Clinically, bacteria-induced contagion and insufficient osseointegrative property inevitably elicit the failure of orthopedic implants. Herein, a heterostructured coating consisting of simvastatin (SIM)-laden metal-organic frameworks and polydopamine nanolayers is created on a porous bioinert polyetheretherketone implant. The heterostructured coating significantly promotes cytocompatibility and osteogenic differentiation through multimodal osteogenicity mechanisms of zinc ion (Zn²⁺ ) therapy, SIM drug therapy, and surface micro-/nano-topological stimulation. Under the illumination of near-infrared (NIR) light, singlet oxygen (¹ O₂ ) and local hyperthermia are produced; besides, NIR light dramatically accelerates the release of Zn²⁺ ions from heterostructured coatings. Gram-positive and -negative bacteria are effectively eradicated by the synergy of photothermal/photodynamic effects and photo-induced accelerated delivery of Zn²⁺ ions. The superior osteogenicity and osseointegration, as well as photoswitchable disinfection controlled by NIR light are corroborated via in vivo results. This work highlights the great potential of photoresponsive heterostructured orthopedic implants in treatment of the noninvasive bone reconstruction of bacteria-associated infectious tissues through multimodal phototherapy and photoswitchable ion-therapy.

Composite of gold nanoclusters and basified human serum albumin significantly boosts the inhibition of Alzheimer's β-amyloid by photo-oxygenation

Photo-oxygenation has become an effective way to inhibit Alzheimer's β-amyloid protein (Aβ) fibrillogenesis, which involves oxidative modification of Aβ by photo-oxidants. However, limitations of the current photo-oxidants, such as low biocompatibility and low affinity for Aβ, hinder the progression of the photo-oxygenation strategy. Herein, using human serum albumins (HSA) with binding affinity for Aβ as a platform, we have fabricated HSA-stabilized gold nanoclusters (AuNCs@HSA) and further modified the AuNCs@HSA with ethylenediamine to create basified HSA (HSA-B)-stabilized AuNCs. The basified composite, AuNCs@HSA-B, showed significantly higher potency on the inhibition of β-amyloid formation and capability of reactive oxidative species generation than AuNCs@HSA. In addition to the inhibition effect, under near-infrared (NIR) laser irradiation, AuNCs@HSA-B generated singlet oxygen to oxygenate Aβ monomers, distinctly alleviating Aβ-mediated neurotoxicity at a low concentration. In vivo studies demonstrated that NIR-activated AuNCs@HSA-B promoted the lifespan extension of transgenic C. elegans strain CL2006 by decreasing the Aβ burden. This well-designed AuNCs@HSA-B integrates inhibition, Aβ targeting, and photo-oxygenation, providing new insights into the development of protein-based photo-oxidant against Alzheimer's β-amyloid. STATEMENT OF SIGNIFICANCE: Alzheimer's disease (AD) has been threatening human health for more than 100 years. Recently, researchers have focused on inhibiting β-amyloid protein (Aβ) aggregation by exploring photo-excited biomaterials, which enable modulation of Aβ fibrillization with high spatiotemporal controllability. The present work demonstrates the fabrication of basified human serum albumins (HSA-B)-stabilized gold nanoclusters (AuNCs@HSA-B), and shows the potential of this near-infrared (NIR) laser-activated AuNCs@HSA-B as a photo-oxidant against Aβ aggregation by photo-oxygenation. Our work should open a new horizon in the design of protein-based photo-oxidant for treating AD in the future.

"One body and two wings" novel nanozyme combined with photothermal therapy for Combat Drug-Resistant Bacteria

Bacterial resistance caused by antibiotic therapy is a serious problem. Therefore, there is an urgent need to find alternative methods to overcome bacterial resistance. Herein, we synthesized a new type of iridium oxide (IrOx) as an alternative to antibiotics. Iridium oxide not only has good catalytic properties, but also has photothermal properties, and then realizes the "one body and two wings" strategy to enhance the antibacterial effect. Research results show that near-infrared light can enhance the peroxidase catalytic activity of IrOx and generate highly toxic hydroxyl radicals (·OH) by catalyzing hydrogen peroxide (H₂O₂). Hydroxyl radicals have a high redox potential, which can overcome the drug resistance of gram-positive and negative bacteria. Importantly, IrOx has no obvious cellular and in vivo toxicity. Accordingly, the novel photothermal nanozyme is expected to be applied to bacterial infectious diseases, such as wound healing, sepsis, and implant-related infections.

Biofilm Formation by Pathogenic Bacteria: Applying a Staphylococcus aureus Model to Appraise Potential Targets for Therapeutic Intervention

Carried in the nasal passages by up to 30% of humans, Staphylococcus aureus is recognized to be a successful opportunistic pathogen. It is a frequent cause of infections of the upper respiratory tract, including sinusitis, and of the skin, typically abscesses, as well as of food poisoning and medical device contamination. The antimicrobial resistance of such, often chronic, health conditions is underpinned by the unique structure of bacterial biofilm, which is the focus of increasing research to try to overcome this serious public health challenge. Due to the protective barrier of an exopolysaccharide matrix, bacteria that are embedded within biofilm are highly resistant both to an infected individual’s immune response and to any treating antibiotics. An in-depth appraisal of the stepwise progression of biofilm formation by S. aureus, used as a model infection for all cases of bacterial antibiotic resistance, has enhanced understanding of this complicated microscopic structure and served to highlight possible intervention targets for both patient cure and community infection control. While antibiotic therapy offers a practical means of treatment and prevention, the most favorable results are achieved in combination with other methods. This review provides an overview of S. aureus biofilm development, outlines the current range of anti-biofilm agents that are used against each stage and summarizes their relative merits.

Tumor microenvironment pH-responsive pentagonal gold prism-based nanoplatform for multimodal imaging and combined therapy of castration-resistant prostate cancer

Given that there is lack of effective therapies for castration-resistant prostate cancer (CRPC), the combination of photothermal (PTT), photodynamic (PDT), and chemical therapy (CT) has emerged as a prominent strategy. Tumor-targeted delivery and controlled release of antitumor drug are key-elements of any combined therapy. Considering these important elements, we designed and constructed tumor microenvironment (TME)-activated nanoprobes (PGP/CaCO₃@IR820/DTX-HA). The CaCO₃ shell could efficiently entrap the photosensitizer IR820 and the chemotherapeutic docetaxel (DTX) on the surface of pentagonal gold prisms (PGPs) to prevent elimination from the circulation, and it could act as a TME-trigger to achieve TME-responsive drug release. After modification with hyaluronic acid, PGP/CaCO₃@IR820/DTX-HA was capable of synergistic TME-triggered PTT/PDT/CT and tumor-targeted delivery. Our in vitro and in vivo studies demonstrate that PGP/CaCO₃@IR820/DTX-HA could achieve synergistic antitumor effects following near-infrared (NIR)-light irradiation. In addition, using the NIR fluorescence signal from IR820 and the photoacoustic (PA) signal from PGPs, i.e., through multimodal fluorescence/photoacoustic imaging, we could monitor the in vivo distribution and excretion of PGP/CaCO₃@IR820/DTX-HA. Therefore, it can be concluded that PGP/CaCO₃@IR820/DTX-HA shows promising clinical translational potential as a treatment for CRPC. STATEMENT OF SIGNIFICANCE: Utilizing pentagonal gold prisms (PGPs), we constructed a multifunctional nanoplatform (PGP/CaCO₃@IR820/DTX-HA) for effectively delivering agents into the tumor microenvironment (TME) for the diagnosis and therapy of castration-resistant prostate cancer (CRPC). The synthetic nanoplatform can satisfy TME-activated synergistic photothermal therapy (PTT)/photodynamic therapy (PDT)/chemical therapy (CT) and NIR fluorescence imaging/photoacoustic (PA) imaging. Hyaluronic acid (HA) on the surface of nanoplatform allowed the specific tumor-targeting capacity and biocompatibility. In conclusion, PGP/CaCO₃@IR820/DTX-HA could be a promising integrated nanoplatform for CRPC diagnosis and treatment.

Single Probe-Based Chemical-Tongue Sensor Array for Multiple Bacterial Identification and Photothermal Sterilization in Real Time

Simple and efficient identification of multiple bacteria and sterilization in real time is of considerable significance for clinical diagnostics and quality control in food. Herein, a novel chemical-tongue sensor array with 3,3',5,5'-tetramethylbenzidine (TMB) as a single probe was developed for bacterial identification and photothermal elimination. The synthesized bimetallic palladium/platinum nanoparticles (Pd/Pt_NPs) present excellent catalytic capability that can catalyze TMB into oxidized TMB (oxTMB) with four feature absorption peaks. Bacteria have different ability on inhibiting the reaction between TMB and Pd/Pt_NPs. With the absorbance intensity of oxTMB at the four feature peaks as readout, nine kinds of bacteria including two drug-resistant bacteria can be successfully distinguished via linear discriminant analysis. Remarkably, oxTMB exhibits excellent photothermal properties and can effectively kill bacteria in real time under near-infrared laser irradiation. The strategy of selecting TMB as a single probe simplifies the experimental operation and reduces the time cost. Furthermore, the developed sensing system was used to promote the wound healing process of MRSA-infected mice in vivo. The investigation provides a promising simple and efficient strategy for bacterial identification and sterilization with a universal platform, which has great potential application in clinical diagnosis and therapy.

Fabrication of a Lignin-Copper Sulfide-Incorporated PVA Hydrogel with Near-Infrared-Activated Photothermal/Photodynamic/Peroxidase-like Performance for Combating Bacteria and Biofilms

Antibiotic-resistant bacteria and biofilms are among the most difficult challenges in infection treatment. Herein, lignin-copper sulfide (LS-CuS) nanocomposites were incorporated into a poly(vinyl alcohol) (PVA) hydrogel to fabricate a LS-CuS@PVA composite hydrogel with near-infrared-activated photothermal, photodynamic, and peroxidase-like performance. The antibacterial tests of LS-CuS@PVA exhibited the highest antibacterial rate that caused 3.8-log and 4.8-log reductions of colony forming units (CFUs) against Escherichia coli and Staphylococcus aureus in the presence of H₂O₂ under near-infrared (NIR) light irradiation for 10 min. The significantly improved bactericidal performance could be attributed to the synergistic effects of hyperthermia and reactive oxygen species (ROS). Furthermore, the LS-CuS@PVA hydrogel could eradicate the already formed biofilm and inhibit biofilm formation. Considering the highly effective antibacterial and antibiofilm activity of the LS-CuS@PVA hydrogel, this work could provide new insights for the design of poly(vinyl alcohol)-based composite hydrogels for wound healing and wound dressing.