Deploying Gold Nanomaterials in Combating Multi-Drug-Resistant Bacteria

Gold Nanoparticles Confined in Mesoporous Bioactive Glass for Periodontitis Therapy

Periodontitis is a chronic disease caused by bacterial infection and is characterized with alveolar bone resorption. Bone regeneration in periodontitis remains a critical challenge because bacterial infection induced an unfavorable microenvironment for osteogenesis. Therefore, it is necessary to design proper therapeutic platforms to control bacterial infection and promote bone regeneration. Herein, mesoporous bioactive glass (MBG) with different pore sizes (3.0, 4.3, and 12.3 nm) was used as an in situ reactor to confine the growth of gold nanoparticles (Au NPs), forming MBG@Au hybrids which combine the osteoconductivity of MBG and antibacterial properties of Au NPs. Upon near-infrared (NIR) irradiation, the MBG@Au NPs showed efficient antibacterial properties both in vitro and in vivo. Besides, the osteogenesis properties of MBG@Au also improved under NIR irradiation. Furthermore, the in vivo results demonstrated that MBG@Au can effectively promote alveolar bone regeneration and realize the healing of serious periodontitis.

Nano-Micron Combined Hydrogel Microspheres: Novel Answer for Minimal Invasive Biomedical Applications

Hydrogels, key in biomedical research for their hydrophilicity and versatility, have evolved with hydrogel microspheres (HMs) of micron-scale dimensions, enhancing their role in minimally invasive therapeutic delivery, tissue repair, and regeneration. The recent emergence of nanomaterials has ushered in a revolutionary transformation in the biomedical field, which demonstrates tremendous potential in targeted therapies, biological imaging, and disease diagnostics. Consequently, the integration of advanced nanotechnology promises to trigger a new revolution in the realm of hydrogels. HMs loaded with nanomaterials combine the advantages of both hydrogels and nanomaterials, which enables multifaceted functionalities such as efficient drug delivery, sustained release, targeted therapy, biological lubrication, biochemical detection, medical imaging, biosensing monitoring, and micro-robotics. Here, this review comprehensively expounds upon commonly used nanomaterials and their classifications. Then, it provides comprehensive insights into the raw materials and preparation methods of HMs. Besides, the common strategies employed to achieve nano-micron combinations are summarized, and the latest applications of these advanced nano-micron combined HMs in the biomedical field are elucidated. Finally, valuable insights into the future design and development of nano-micron combined HMs are provided.

Charge Effect of Mercaptobenzimidazole-Modified Ultrasmall Gold-Nanoparticles against Drug-Resistant Bacteria

The threat of bacterial infections, especially drug-resistant strains, to human health necessitates the development of high-efficient, broad-spectrum and nonantibiotic nanodisinfectant. However, the effect of interfacial charge on the antibacterial properties of nanodisinfectant remains a mystery, which greatly limits the development of highly antibacterial active nanodisinfectant. Herein, we developed three types of ultrasmall (d < 3 nm) gold-nanoparticles (AuNPs) modified with 5-carboxylic(C)/methoxy(M)amino(A)/-2-mercaptobenzimidazole (C/M/A MB) to investigate their interfacial charge on antibacterial performance. Our results showed that both the electropositive AMB-AuNPs and electronegative CMB-AuNPs exhibited no antibacterial activity against both Gram-positive (G+) and Gram-negative (G-) bacteria. However, the electroneutral MMB-AuNPs exhibited unique antibacterial performance against both G+ and G- bacteria, even against methicillin-resistant Staphylococcus aureus (MRSA). Mechanistic investigation revealed a multipathway synergistic bacteriostatic mechanism involving MMB-AuNPs inducing damage to bacterial cell membranes, disruption of membrane potential and downregulation of ATP levels, ultimately leading to bacterial demise. Furthermore, two additional electroneutral AuNPs modified with 5-methyl-2-mercaptobenzimidazole (mMB-AuNPs) and 5-ethoxy-2-mercaptobenzimidazole (EMB-AuNPs) also demonstrated commendable antibacterial efficacy against E. coli, S. aureus, and MRSA; however, their performance was comparatively inferior to that of MMB-AuNPs. This work provides valuable insights for the development of high-performance antibacterial nanomaterials.

Poly-l-lysine modified MOF nanoparticles with pH/ROS sensitive CIP release and CUR triggered photodynamic therapy against drug-resistant bacterial infection

The challenge of drug resistance in bacteria caused by the over use of biotics is increasing during the therapy process, which has attracted great attentions of the clinicians and scientists around the world. Recently, photodynamic therapy (PDT) triggered by photosensitizer (PS) has become a promising treatment method because of its high efficacy, easy operation, and low side effect. Herein, the poly-l-lysine (PLL) modified metal-organic framework (MOF) nanoparticles, ZIF/PLL-CIP/CUR, were synthesized to allow both reactive oxygen species (ROS) responsive drug release and photodynamic effect for synergistic therapy against drug resistant bacterial infections. The PLL was modified on the shell of the zeolite imidazole framework (ZIF) by the ROS-responsive thioketal linker for controllable CIP release. CUR were encapsulated in ZIF as the photosensitizer for blue light mediated photodynamic effect to produce singlet oxygen (1O2) and superoxide anion radical (O2-) for efficient inhibition towards methicillin-resistant Staphylococcus aureus (MRSA). The charge conversion from negative charge (-4.6 mV) to positive charge (2.6 mV) was observed at pH 7.4 and pH 5.5, and 70.9 % CIP was found released at pH 5.5 in the presence of H2O2, which suggests the good biosafety at physiological pH and ROS-responsive drug release of the as-prepared nanoparticle in the bacterial microenvironment. The as-prepared nanoparticles could effectively kill MRSA and disrupt bacterial biofilm by combination of chemo- and photodynamic therapy. In mice model, the as-prepared nanoparticles exhibited excellent biosafety and synergistic effect with 98.81 % healing rate in treatment of MRSA infection, which is considered as a promising candidate in combating drug resistant bacterial infection.

Ultralow Loading Copper-Intercalated MoO3 Nanobelts with High Activity against Antibiotic-Resistant Bacteria

In recent years, the infection rate of antibiotic resistance has been increasing year by year, and the prevalence of super bacteria has posed a great threat to human health. Therefore, there is an urgent need to find new antibiotic alternatives with long-term inhibitory activity against a broad spectrum of bacteria and microorganisms in order to avoid the proliferation of more multidrug-resistant (MDR) bacteria. The presence of natural van der Waals (vdW) gaps in layered materials allows them to be easily inserted by different guest species, providing an attractive strategy for optimizing their physicochemical properties and applications. Here, we have successfully constructed a copper-intercalated α-MoO3 nanobelt based on nanoenzymes, which is antibacterial through the synergistic effect of multiple enzymes. Compared with α-MoO3, MoO3-x/Cu nanobelts with a copper loading capacity of 2.11% possess enhanced peroxidase (POD) catalytic activity and glutathione (GSH) depletion, indicating that copper intercalation significantly improves the catalytic performance of the nanoenzymes. The MoO3-x/Cu nanobelts are effective in inducing POD and oxidase (OXD) and catalase (CAT) activities in the presence of H2O2 and O2, which resulted in the generation of large amounts of reactive oxygen species (ROS), which were effective in bacterial killing. Interestingly, MoO3-x/Cu nanobelts can serve as glutathione oxidase (GSHOx)-like nanoenzymes, which can deplete GSH in bacteria and thus significantly improve the bactericidal effect. The multienzyme-catalyzed synergistic antimicrobial strategy shows excellent antimicrobial efficiency against β-lactamase-producing Escherichia coli (ESBL-E. coli) and methicillin-resistant Staphylococcus aureus (MRSA). MoO3-x/Cu exhibits excellent spectral bactericidal properties at very low concentrations (20 μg mL-1). Our work highlights the wide range of antibacterial and anti-infective biological applications of copper-intercalated MoO3-x/Cu nanobelt catalysts.

ZnO nanoparticles induced biofilm formation in Klebsiella pneumoniae and Staphylococcus aureus at sub-inhibitory concentrations

Biofilm formation by the pathogenic bacteria generates a serious threat to the public health as it can increase the virulence potential, resistance to drugs, and escape from the host immune response mechanisms. Among the environmental factors that influence the biofilm formation, there are only limited reports available on the role of antimicrobial agents. During the antimicrobial drug administration or application for any purpose, the microbial population can expect to get exposed to the sub-minimum inhibitory concentration (sub-MIC) of the drug which will have an unprecedented impact on microbial responses. Hence, the study has been conducted to investigate the effects of sub-MIC levels of zinc oxide nanoparticles (ZnO NPs) on the biofilm formation of Klebsiella pneumoniae and Staphylococcus aureus. Here, the selected bacteria were primarily screened for the biofilm formation by using the Congo red agar method, and their susceptibility to ZnO NPs was also evaluated. Quantitative difference in biofilm formation by the selected organisms in the presence of ZnO NPs at the sub-MIC level was further carried out by using the microtiter plate-crystal violet assay. Further, the samples were subjected to atomic force microscopy (AFM) analysis to evaluate the properties and pattern of the biofilm modulated under the experimental conditions used. From these, the organisms treated with sub-MIC levels of ZnO NPs were found to have enhanced biofilm formation when compared with the untreated sample. Also, no microbial growth could be observed for the samples treated with the minimum inhibitory concentration (MIC) of ZnO NPs. The results observed in the study provide key insights into the impact of nanomaterials on clinically important microorganisms which demands critical thinking on the antimicrobial use of nanomaterials.

Near-infrared light responsive gold nanoparticles coating endows polyetheretherketone with enhanced osseointegration and antibacterial properties

Polyetheretherketone (PEEK) is considered as a promising dental implant material owing to its excellent physicochemical and mechanical properties. However, its wide range of applications is limited by its biologically inert nature. In this study, a near-infrared (NIR) light responsive bioactive coating with gold nanoparticles (AuNPs) and metronidazole adhered to the PEEK surface via dopamine polymerization. Compared to pure PEEK, the hydrophilicity of the treated PEEK surface was significantly improved. In addition, under NIR light, the surface coating exhibited photothermal conversion effect, and gold nanoparticles and the antibiotic can be released from the coating. This improved the antibacterial properties of PEEK materials. Moreover, the coating was more conducive to the early adhesion of bone mesenchymal stem cells. The results of in vitro and in vivo osteogenic activity studies showed that the developed coating promoted osseointegration of PEEK implants, and NIR light irradiation further improved the antibacterial ability and osteogenic activity of PEEK implants. Through RNA sequencing, the potential underlying mechanism of promoting bone formation of the AuNPs coating combined metronidazole was interpreted. In summary, the developed coating is a potential surface treatment strategy that endows PEEK with enhanced osseointegration and antibacterial properties.

[18F]-Radiolabelled Nanoplatforms: A Critical Review of Their Intrinsic Characteristics, Radiolabelling Methods, and Purification Techniques

A wide range of nano-objects is found in many applications of our everyday life. Recognition of their peculiar properties and ease of functionalization has prompted their engineering into multifunctional platforms that are supposed to afford efficient tools for the development of biomedical applications. However, bridging the gap between bench to bedside cannot be expected without a good knowledge of their behaviour in vivo, which can be obtained through non-invasive imaging techniques, such as positron emission tomography (PET). Their radiolabelling with [18F]-fluorine, a technique already well established and widely used routinely for PET imaging, with [18F]-FDG for example, and in preclinical investigation using [18F]-radiolabelled biological macromolecules, has, therefore, been developed. In this context, this review highlights the various nano-objects studied so far, the reasons behind their radiolabelling, and main in vitro and/or in vivo results obtained thereof. Then, the methods developed to introduce the radioelement are presented. Detailed indications on the chemical steps involved are provided, and the stability of the radiolabelling is discussed. Emphasis is then made on the techniques used to purify and analyse the radiolabelled nano-objects, a point that is rarely discussed despite its technical relevance and importance for accurate imaging. The pros and cons of the different methods developed are finally discussed from which future work can develop.

UV-assisted synthesis of ultra-small GO-Austar for efficient PTT therapeutic architectonic construction

Conventional Au nanomaterial synthesis typically necessitates the involvement of extensive surfactants and reducing agents, leading to a certain amount of chemical waste and biological toxicity. In this study, we innovatively employed ultra-small graphene oxide as a reducing agent and surfactant for the in situ generation of small Au nanoparticles under ultraviolet irradiation (UV) at ambient conditions. After ultra-small GO-Au seeds were successfully synthesized, we fabricated small star-like Au nanoparticles on the surface of GO, in which GO effectively prevented Austar from aggregation. To further use GO-Austar for cancer PTT therapy, through the modification of reduced human serum albumin-folic acid conjugate (rHSA-FA) and loading IR780, the final probe GO-Austar@rHSA-FA@IR780 was prepared. The prepared probe showed excellent biocompatibility and superb phototoxicity towards MGC-803 cells in vitro. In vivo, the final probe dramatically increased tumor temperature up to 58.6 °C after 5 minutes of irradiation by an 808 nm laser, significantly inhibiting tumor growth and nearly eradicating subcutaneous tumors in mice. This research provides a novel and simple method for the synthesis of GO-Au nanocomposites, showcasing significant potential in biological applications.

Nanoclay Hydrogel Microspheres with a Sandwich-Like Structure for Complex Tissue Infection Treatment

Addressing complex tissue infections remains a challenging task because of the lack of effective means, and the limitations of traditional bioantimicrobial materials in single-application scenarios hinder their utility for complex infection sites. Hence, the development of a bioantimicrobial material with broad applicability and potent bactericidal activity is necessary to treat such infections. In this study, a layered lithium magnesium silicate nanoclay (LMS) is used to construct a nanobactericidal platform. This platform exhibits a sandwich-like structure, which is achieved through copper ion modification using a dopamine-mediated metallophenolic network. Moreover, the nanoclay is encapsulated within gelatin methacryloyl (GelMA) hydrogel microspheres for the treatment of complex tissue infections. The results demonstrate that the sandwich-like micro- and nanobactericidal hydrogel microspheres effectively eradicated Staphylococcus aureus (S. aureus) while exhibiting excellent biocompatibility with bone marrow-derived mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs). Furthermore, the hydrogel microspheres upregulated the expression levels of osteogenic differentiation and angiogenesis-related genes in these cells. In vivo experiments validated the efficacy of sandwich-like micro- and nanobactericidal hydrogel microspheres when injected into deep infected tissues, effectively eliminating bacteria and promoting robust vascular regeneration and tissue repair. Therefore, these innovative sandwich-like micro- and nanobacteriostatic hydrogel microspheres show great potential for treating complex tissue infections.

Hydrogels Containing Chitosan-Modified Gold Nanoparticles Show Significant Efficacy in Healing Diabetic Wounds Infected with Antibiotic-Resistant Bacteria

Purpose

Persistent Infections and inflammation are associated with impaired wound healing in diabetic patients. There is a pressing demand for innovative antimicrobial strategies to address infections arising from antibiotic-resistant bacteria. Polymer-modified gold nanoparticles (AuNPs) show broad-spectrum antibacterial properties and significant biocompatibility. This study investigated the antibacterial and wound healing efficacy of hydrogel dressings conjugated with chitosan-AuNPs in diabetic model rats.

Methods

Chitosan (CS)-functionalized gold nanoparticles (CS-AuNPs) were incorporated into hydrogel dressings (Gel/CS-AuNPs), which were formulated through the chemical cross-linking of gelatin with sodium alginate (SA). The basic characteristics of Gel/CS-AuNPs were analyzed by TEM, SEM, XRD, and UV-visible spectra. Rheological, swelling, degradation, and adhesive properties of Gel/CS-AuNPs were also determined. In vitro anti-bactericidal effects of the Gel/CS-AuNPs were analyzed with E. coli, S. aureus, and MRSA. In vitro biocompatibility of the Gel/CS-AuNPs was evaluated using NIH3T3 cells. The in vivo antibacterial and wound healing efficacy of the Gel/CS-AuNPs was analyzed in the diabetic wound model rats. Histological and immunofluorescence staining were performed to determine the status of angiogenesis, epithelization, inflammation response, and collagen deposition.

Results

Gel/CS-AuNPs demonstrated significant high biodegradability, water absorption bactericidal, and biocompatibility, and slight adhesiveness. Gel/CS-AuNPs exhibited pronounced antibacterial efficacy against gram-negative, gram-positive, and MRSA in a CS-AuNPs-dose-dependent manner. In the diabetic wound model rats, Gel/CS-AuNPs effectively killed MRSA, reduced inflammation, and promoted angiogenesis and collagen deposition and remodeling at the wound site. As a result, Gel/CS-AuNPs expedited the recovery process for infected diabetic wounds. Among the hydrogels with different CS-AuNPs concentrations, Gel/CS-Au25 with 25% CS-AuNPs showed the best bactericidal and wound healing performance.

Conclusion

Gel/CS-AuNPs significantly improve the healing of MRSA-infected diabetic wounds in the rat model. Therefore, Gel/CS-AuNPs show great promise for the treatment of diabetic infection wound healing.

Recent advances in electrochemical aptasensors and genosensors for the detection of pathogens

In recent years, pathogenic microorganisms have caused significant mortality rates and antibiotic resistance and triggered exorbitant healthcare costs. These pathogens often have high transmission rates within human populations. Rapid diagnosis is crucial in controlling and reducing the spread of pathogenic infections. The diagnostic methods currently used against individuals infected with these pathogens include relying on outward symptoms, immunological-based and, some biomolecular ones, which mainly have limitations such as diagnostic errors, time-consuming processes, and high-cost platforms. Electrochemical aptasensors and genosensors have emerged as promising diagnostic tools for rapid, accurate, and cost-effective pathogen detection. These bio-electrochemical platforms have been optimized for diagnostic purposes by incorporating advanced materials (mainly nanomaterials), biomolecular technologies, and innovative designs. This review classifies electrochemical aptasensors and genosensors developed between 2021 and 2023 based on their use of different nanomaterials, such as gold-based, carbon-based, and others that employed other innovative assemblies without the use of nanomaterials. Inspecting the diagnostic features of various sensing platforms against pathogenic analytes can identify research gaps and open new avenues for exploration.

In situ peptide assemblies for bacterial infection imaging and treatment

Bacterial infections, especially antibiotic-resistant ones, remain a major threat to human health. Advances in nanotechnology have led to the development of numerous antimicrobial nanomaterials. Among them, in situ peptide assemblies, formed by biomarker-triggered self-assembly of peptide-based building blocks, have received increasing attention due to their unique merits of good spatiotemporal controllability and excellent disease accumulation and retention. In recent years, a variety of "turn on" imaging probes and activatable antibacterial agents based on in situ peptide assemblies have been developed, providing promising alternatives for the treatment and diagnosis of bacterial infections. In this review, we introduce representative design strategies for in situ peptide assemblies and highlight the bacterial infection imaging and treatment applications of these supramolecular materials. Besides, current challenges in this field are proposed.

Review of Advances in Coating and Functionalization of Gold Nanoparticles: From Theory to Biomedical Application

Nanoparticles, especially gold nanoparticles (Au NPs) have gained increasing interest in biomedical applications. Used for disease prevention, diagnosis and therapies, its significant advantages in therapeutic efficacy and safety have been the main target of interest. Its application in immune system prevention, stability in physiological environments and cell membranes, low toxicity and optimal bioperformances are critical to the success of engineered nanomaterials. Its unique optical properties are great attractors. Recently, several physical and chemical methods for coating these NPs have been widely used. Biomolecules such as DNA, RNA, peptides, antibodies, proteins, carbohydrates and biopolymers, among others, have been widely used in coatings of Au NPs for various biomedical applications, thus increasing their biocompatibility while maintaining their biological functions. This review mainly presents a general and representative view of the different types of coatings and Au NP functionalization using various biomolecules, strategies and functionalization mechanisms.

pH-responsive on-demand release of eugenol from metal-organic frameworks for synergistic bacterial killing

Bacterial infections are a big challenge in clinical treatment, making it urgent to develop innovative antibacterial systems and therapies to combat bacterial infections. In this study, we developed a novel MOF-based synergistic antibacterial system (Eu@B-UiO-66/Zn) by loading a natural antibacterial substance (eugenol) with hierarchically porous MOF B-UiO-66 as a carrier and further complexing it with divalent zinc ions. Results indicate that the system achieved a controlled release of eugenol under pH responsive stimulation, with the complexation ability of eugenol and Zn2+ ions as a switch. Due to the destruction of a coordination bond between eugenol and Zn2+ ions by an acidic medium, the release of eugenol loaded in Eu@B-UiO-66/Zn reached 80% at pH 5.8, which was significantly higher than that under pH 8.0 (51%). Moreover, the inhibitory effect of Eu@B-UiO-66/Zn against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) after 24 h was 96.4% and 99.7%, respectively, owing to the synergistic antibacterial effect of eugenol and Zn2+ ions, which was significantly stronger than free eugenol and Eu@B-UiO-66. We hope that this strategy for constructing responsive MOF-based antibacterial carriers could have potential possibilities for the application of MOF materials in antibacterial fields.

Carbon dots@noble metal nanoparticle composites: research progress report

Carbon dots@noble metal nanoparticle composites are formed by combining carbon dots and metal nanoparticles using various strategies. Carbon dots exhibit a reducing ability and function as stabilisers; consequently, metal-ion solutions can be directly reduced by them to synthesise gold, silver, and gold-silver alloy particles. Carbon dots@gold/silver/gold-silver particle composites have demonstrated the potential for several practical applications owing to their superior properties and simple preparation process. Until now, several review articles have been published to summarise fluorescent carbon dots or noble metal nanomaterials. Compared with metal-free carbon dots, carbon dots@noble metal nanoparticles have a unique morphology and structure, resulting in new physicochemical properties, which allow for sensing, bioimaging, and bacteriostasis applications. Therefore, to promote the effective development of carbon dots@noble metal nanoparticle composites, this paper primarily reviews carbon dots@gold/silver/gold-silver alloy nanoparticle composites for the first time in terms of the following aspects. (1) The synthesis strategies of carbon dots@noble metal nanoparticle composites are outlined. The principle and function of carbon dots in the synthesis strategies are examined. The advantages and disadvantages of these methods and composites are analysed. (2) The characteristics and properties of such composites are described. (3) The applications of these composite materials are summarised. Finally, the potentials and limitations of carbon dots@noble metal nanoparticle composites are discussed, thus laying the foundation for their further development.

CO2-Responsive Rosin-Based Supramolecular Hydrogels: Diverse Chiral Nanostructures and Their Application in In Situ Synthesis of Chiral Gold Nanoparticles

Natural small molecules have demonstrated tremendous potential for the construction of supramolecular chiral nanostructures owing to their unique molecular structures and chirality. In this study, novel CO2-responsive supramolecular hydrogels were constructed using a series of rosin-based surfactants (CnMPAN, n = 10, 12, and 14). The macroscopic properties, rheological properties, nanostructures, and intermolecular interactions of the hydrogels were investigated using differential scanning calorimetry, rotational rheometry, cryogenic transmission electron microscopy, and Fourier transform infrared spectroscopy. Interestingly, diverse nanostructures containing helical nanofibers, interwoven nanofibers, and twisted nanoribbons were formed in the hydrogels, which were rarely observed in reported supramolecular hydrogels, and the strength of the hydrogels was significantly enhanced by increasing the CnMPAN concentration and the alkyl chain length. The obtained hydrogels exhibited excellent CO2-responsiveness, with no obvious variation in the nanostructures and rheological properties after response to CO2/N2 for five cycles. Taking advantage of the chiral nanostructures of hydrogels, gold nanoparticles (GNPs) were further prepared. The average particle sizes of the resulting GNPs were as low as 2.5 nm, and the GNPs also had a chiral structure. It is worth noting that no additional reductants and UV-light irradiation were used during the reduction process of GNPs. This study emphasizes that the unique molecular structure and chirality of rosin are critical for the preparation of hydrogels with chiral nanostructures. In addition, this study enriches the applications of forest resources.

In the View of Electrons Transfer and Energy Conversion: The Antimicrobial Activity and Cytotoxicity of Metal-Based Nanomaterials and Their Applications

The global pandemic and excessive use of antibiotics have raised concerns about environmental health, and efforts are being made to develop alternative bactericidal agents for disinfection. Metal-based nanomaterials and their derivatives have emerged as promising candidates for antibacterial agents due to their broad-spectrum antibacterial activity, environmental friendliness, and excellent biocompatibility. However, the reported antibacterial mechanisms of these materials are complex and lack a comprehensive understanding from a coherent perspective. To address this issue, a new perspective is proposed in this review to demonstrate the toxic mechanisms and antibacterial activities of metal-based nanomaterials in terms of energy conversion and electron transfer. First, the antimicrobial mechanisms of different metal-based nanomaterials are discussed, and advanced research progresses are summarized. Then, the biological intelligence applications of these materials, such as biomedical implants, stimuli-responsive electronic devices, and biological monitoring, are concluded based on trappable electrical signals from electron transfer. Finally, current improvement strategies, future challenges, and possible resolutions are outlined to provide new insights into understanding the antimicrobial behaviors of metal-based materials and offer valuable inspiration and instructional suggestions for building future intelligent environmental health.

Influence of the linkage between long alkyl tails and cationic groups on membrane activity of nano-sized hyperbranched polyquaterniums

The recurrent emergence of serious pathogens necessitates novel insights and highly efficient antibacterial agents. However, the innate inability of metal ions and reactive oxygen species (ROS) to differentiate between bacteria and mammalian cells presents a challenge, limiting the selectivity crucial for an ideal antimicrobial solution. Herein, we present a systematic exploration involving two variants of nano-sized hyperbranched polyquaterniums (NHBPQs) - one featuring a lengthy alkyl tail linked to the ammonium unit at the N-atom center (NHBPQ-A), and the other in a segregated configuration (NHBPQ-B). The exterior alkyl chain chains act as a barrier to the cationic group's non-specific adsorption due to spatial site resistance, causing NHBPQ-A in broad-spectrum cytotoxicity. Conversely, the distinct molecular configuration of NHBPQ-B in the segregated state affords greater flexibility, allowing the cationic groups to be released and interact non-specifically, finally resulting in selective bactericidal activity. Leveraging this selectivity, the optimized NHBPQ-B exhibits robust anti-infectious performance in a model of methicillin-resistant Staphylococcus aureus (MRSA)-infected wounds. This work establishes a promising avenue for biocompatible NHBPQs, holding significant potential in addressing MRSA infections and ameliorating both genetically encoded and phenotypic antibiotic resistance mechanisms.

Multiscale Bioresponses of Metal Nanoclusters

Metal nanoclusters (NCs) are well-recognized novel nano-agents that hold great promise for applications in nanomedicine because of their ultrafine size, low toxicity, and high renal clearance. As foreign substances, however, an in-depth understanding of the bioresponses to metal NCs is necessary but is still far from being realized. Herein, this review is deployed to summarize the biofates of metal NCs at various biological levels, emphasizing their multiscale bioresponses at the molecular, cellular, and organismal levels. In the parts-to-whole schema, the interactions between biomolecules and metal NCs are discussed, presenting typical protein-dictated nano-bio interfaces, hierarchical structures, and in vivo trajectories. Then, the accumulation, internalization, and metabolic evolution of metal NCs in the cellular environment and as-imparted theranostic functionalization are demonstrated. The organismal metabolism and transportation processes of the metal NCs are subsequently distilled. Finally, this review ends with the conclusions and perspectives on the outstanding issues of metal NC-mediated bioresponses in the near future. This review is expected to provide inspiration for tailoring the customization of metal NC-based nano-agents to meet practical requirements in different sectors of nanomedicine.

Heterogeneity of dispersed species in nickel-loaded carbon-based catalysts for near-infrared photoresponsive synergistic antimicrobial therapy

The development of novel efficient, safe antimicrobial strategies is an urgent need, as the misuse of antibiotics has become a significant threat to human health. Therefore, we have loaded metal Ni with environmentally friendly carbon black as a substrate, with species varying from single atoms to nanoclusters and nanoparticles. The results obtained from the antimicrobial systems and the role of different types of metal species in the photosensitized antimicrobial reactions were compared to better understand the catalytic behavior of different metal entities (single atoms, nanoclusters, and nanoparticles). Furthermore, the antimicrobial mechanisms of these materials were described by physical and chemical characterization, biological experiments, and theoretical calculations. Such systematic studies provide new ideas and prospects for developing more efficient and environmentally friendly antimicrobial materials.

Photopolymerized keratin-PGLa hydrogels for antibiotic resistance reversal and enhancement of infectious wound healing

Infectious wounds have become serious challenges for both treatment and management in clinical practice, so development of new antibiotics has been considered an increasingly difficult task. Here, we report the design and synthesis of keratin 31 (K31)-peptide glycine-leucine-amide (PGLa) photopolymerized hydrogels to rescue the antibiotic activity of antibiotics for infectious wound healing promotion. K31-PGLa displayed an outstanding synergistic effect with commercial antibiotics against drug-resistant bacteria by down-regulating the synthesis genes of efflux pump. Furthermore, the photopolymerized K31-PGLa/PEGDA hydrogels effectively suppressed drug-resistant bacteria growth and enhanced skin wound closure in murine. This study provided a promising alternative strategy for infectious wound treatment.

Peptide-Mimicking Poly(2-oxazoline)s Possessing Potent Antifungal Activity and BBB Penetrating Property to Treat Invasive Infections and Meningitis

Invasive fungal infections, including meningitis, cause a high mortality rate due to few available antifungal drugs and frequently associated side effects and quick emergence of drug-resistant fungi. The restrictive permeability of the blood-brain barrier (BBB) further limits the efficacy of antifungal agents substantially in treating meningitis. Hereby, we design and synthesize guanidinium-functionalized poly(2-oxazoline)s by mimicking cell-penetrating peptides. The optimal polymer, PGMeOx10 bearing a methylene spacer arm, displays potent activities against the drug-resistant fungi and biofilm, negligible toxicity, and insusceptibility to antimicrobial resistance. Moreover, PGMeOx10 can break BBB retractions to exert promising antifungal functions in the brain. PGMeOx10 demonstrates potent in vivo antifungal therapeutic efficacy in mouse models including skin infection, systemic infections, and meningitis. PGMeOx10 effectively rescues infected mice and reduces fungal burden and inflammation in the brain. These results and the excellent biosafety of poly(2-oxazoline)s indicate the effectiveness and potential of our strategy to design promising antifungal agents in treating systemic infections and meningitis.

Recent advances in nanoantibiotics against multidrug-resistant bacteria

Multidrug-resistant (MDR) bacteria-caused infections have been a major threat to human health. The abuse of conventional antibiotics accelerates the generation of MDR bacteria and makes the situation worse. The emergence of nanomaterials holds great promise for solving this tricky problem due to their multiple antibacterial mechanisms, tunable antibacterial spectra, and low probabilities of inducing drug resistance. In this review, we summarize the mechanism of the generation of drug resistance, and introduce the recently developed nanomaterials for dealing with MDR bacteria via various antibacterial mechanisms. Considering that biosafety and mass production are the major bottlenecks hurdling the commercialization of nanoantibiotics, we introduce the related development in these two aspects. We discuss urgent challenges in this field and future perspectives to promote the development and translation of nanoantibiotics as alternatives against MDR pathogens to traditional antibiotics-based approaches.

pH Switchable Nanozyme Platform for Healing Skin Tumor Wound Infected with Drug-Resistant Bacteria

Nanozymes capable of generating reactive oxygen species have recently emerged as promising treatments for wounds infected with drug-resistant bacteria, possessing a reduced possibility of inducing resistance. However, the therapeutic effect is limited by a shortage of endogenous oxy-substrates and undesirable off-target biotoxicity. Herein, a ferrocenyl coordination polymer (FeCP) nanozyme, featuring pH switchable peroxidase (POD)- and catalase (CAT)-like activity is incorporated with indocyanine green (ICG) and calcium peroxide (CaO2 ) to fabricate an H2 O2 /O2 self-supplying system (FeCP/ICG@CaO2 ) for precise treatment of bacterial infections. At the wound site, CaO2 reacts with water to generate H2 O2 and O2 . Acting as a POD mimic under an acidic bacterial microenvironment, FeCP catalyzes H2 O2 into hydroxyl radicals to prevent infection. However, FeCP switches to CAT-like activity in neutral tissue, decomposing H2 O2 into H2 O and O2 to prevent oxidative damage and facilitate wound healing. Additionally, FeCP/ICG@CaO2 shows photothermal therapy capability, as ICG can emit heat under near-infrared laser irradiation. This heat assists FeCP in fully exerting its enzyme-like activity. Thus, this system achieves an antibacterial efficiency of 99.8% in vitro for drug-resistant bacteria, and effectively overcomes the main limitations of nanozyme-based treatment assays, resulting in satisfactory therapeutic effects in repairing normal and special skin tumor wounds infected with drug-resistant bacteria.

Phenylboronic Acid-Modified Gold Nanoclusters as a Nanoantibiotic to Treat Vancomycin-Resistant Enterococcus faecalis-Caused Infections

Vancomycin is one of the last lines of defense against certain drug-resistant bacteria-caused infections. However, the high susceptibility to drug resistance and high toxicity seriously limit the application of vancomycin. Nanoantibiotics provide opportunities to solve these problems. Herein, we present mercaptophenylboronic acid (MBA)-modified gold nanoclusters with well-defined molecular formulas and structure (Au44(MBA)18) and excellent antibacterial activities against various drug-resistant bacteria such as vancomycin-resistant Enterococcus faecalis (VRE). Au44(MBA)18 interacts with bacteria by first attaching to teichoic-acid and destroying the cell wall and subsequently binding to the bacterial DNA. Au44(MBA)18 could be administered via multiple routes and has a high biosafety (500 mg/kg, no ototoxicity), overcoming the two major shortcomings of vancomycin (sole administration route and high ototoxicity). Our study is insightful for curing infections caused by multidrug-resistant bacteria using nanoantibiotics with high biosafety.

Tailoring the Surface and Composition of Nanozymes for Enhanced Bacterial Binding and Antibacterial Activity

With the advantages of diverse structures, tunable enzymatic activity, and high stability, nanozymes are widely used in medicine, chemistry, food, environment, and other fields. As an alternative to traditional antibiotics, nanozymes attract more and more attention from the scientific researchers in recent years. Developing nanozymes-based antibacterial materials opens up a new avenue for the bacterial disinfection and sterilization. In this review, the classification of nanozymes and their antibacterial mechanisms are discussed. The surface and composition of nanozymes are critical for the antibacterial efficacy, which can be tailored to enhance both the bacterial binding and the antibacterial activity. On the one hand, the surface modification of nanozymes enables binding and targeting of bacteria that improves the antibacterial performance of nanozymes including the biochemical recognition, the surface charge, and the surface topography. On the other hand, the composition of nanozymes can be modulated to achieve enhanced antibacterial performance including the single nanozyme-mediated synergistic and multiple nanozymes-mediated cascade catalytic antibacterial applications. In addition, the current challenges and future prospects of tailoring nanozymes for antibacterial applications are discussed. This review can provide insights into the design of future nanozymes-based materials for the antibacterial treatments.

Enhancing Surgical Outcomes: A Critical Review of Antibiotic Prophylaxis in Orthopedic Surgery

The postoperative burden remains significant due to the possibility of prolonged hospitalization, escalated healthcare costs, and patient distress caused by postorthopedic surgical site infections (SSIs). Orthopedic surgery is likewise faced with a significant challenge posed by these conditions. A positive association has been observed between the presence of postorthopedic SSIs and heightened susceptibility to adverse health outcomes, along with elevated rates of morbidity and mortality. Systemic antibiotic prophylaxis (SAP) reduces the risk of acquiring an SSI. Closed fractures, open fractures, arthroplasty, and percutaneous fixation each possess distinct attributes that impact the data and antimicrobial therapy. When implementing SAP, it is crucial to strike a delicate equilibrium between maintaining effective antibiotic stewardship protocols and preventing the occurrence of SSIs. This practice effectively prevents both the incidence of negative consequences and the emergence of antibiotic resistance. The objective of this study was to examine the existing literature on the use of surgical antibiotic prophylaxis in orthopedic surgery and explore the potential consequences associated with the inappropriate administration of antibiotics.

Bismuth-based two-dimensional nanomaterials for cancer diagnosis and treatment

The intrinsic high X-ray attenuation and insignificant biological toxicity of Bi-based nanomaterials make them a category of advanced materials in oncology. Bi-based two-dimensional nanomaterials have gained rapid development in cancer diagnosis and treatment owing to their adjustable bandgap structure, high specific surface area and strong NIR absorption. In addition to the single functional cancer diagnosis and treatment modalities, Bi-based two-dimensional nanomaterials have been certified for accomplishing multi-imaging guided multifunctional synergistic cancer therapies. In this review, we summarize the recent progress including controllable synthesis, defect engineering and surface modifications of Bi-based two-dimensional nanomaterials for cancer diagnosis and treatment in the past ten years. Their medical applications in cancer imaging and therapies are also presented. Finally, we discuss the potential challenges and future research priorities of Bi-based two-dimensional nanomaterials.

Synergistic Antibacterial Effects of Amoxicillin and Gold Nanoparticles: A Therapeutic Option to Combat Antibiotic Resistance

Compacted Au@16-mph-16/DNA-AMOX (NSi) nanosystems were prepared from amoxicillin (AMOX) and precursor Au@16-mph-16 gold nanoparticles (Ni) using a Deoxyribonucleic acid (DNA) biopolymer as a glue. The synthesized nanocarrier was tested on different bacterial strains of Escherichia coli, Staphylococcus aureus, and Streptococcus pneumoniae to evaluate its effectiveness as an antibiotic as well as its internalization. Synthesis of the nanosystems required previous structural and thermodynamic studies using circular dichroism (CD) and UV-visible techniques to guarantee optimal complex formation and maximal DNA compaction, characteristics which facilitate the correct uptake of the nanocarrier. Two nanocomplexes with different compositions and structures, denoted NS1 and NS2, were prepared, the first involving external Au@16-mph-16 binding and the second partial intercalation. The Ni and NSi nanosystems obtained were characterized via transmission electron microscopy (TEM), zeta potential, and dynamic light scattering (DLS) techniques to measure their charge, aggregation state and hydrodynamic size, and to verify their presence inside the bacteria. From these studies, it was concluded that the zeta potential values for gold nanoparticles, NS1, and NS2 nanosystems were 67.8, -36.7, and -45.1 mV. Moreover, the particle size distribution of the Au@16-mph-16 gold nanoparticles and NS2 nanoformulation was found to be 2.6 nm and 69.0 nm, respectively. However, for NS1 nanoformulation, a bimodal size distribution of 44 nm (95.5%) and 205 nm (4.5%) was found. Minimal inhibitory concentration (MIC) values were determined for the bacteria studied using a microdilution plates assay. The effect on Escherichia coli bacteria was notable, with MIC values of 17 µM for both the NS1 and NS2 nanosystems. The Staphylococcus aureus chart shows a greater inhibition effect of NS2 and NP2 in non-diluted wells, and clearly reveals a great effect on Streptococcus pneumoniae, reaching MIC values of 0.53 µM in more diluted wells. These results are in good agreement with TEM internalization studies of bacteria that reveal significant internalization and damage in Streptococcus pneumoniae. In all the treatments carried out, the antibiotic capacity of gold nanosystems as enhancers of amoxicillin was demonstrated, causing both the precursors and the nanosystems to act very quickly, and thus favoring microbial death with a small amount of antibiotic. Therefore, these gold nanosystems may constitute an effective therapy to combat resistance to antibiotics, in addition to avoiding the secondary effects derived from the administration of high doses of antibiotics.

Eradication of Bacterial Persister Cells By Leveraging Their Low Metabolic Activity Using Adenosine Triphosphate Coated Gold Nanoclusters

Bacteria first develop tolerance after antibiotic exposure; later genetic resistance emerges through the population of tolerant bacteria. Bacterial persister cells are the multidrug-tolerant subpopulation within an isogenic bacteria culture that maintains genetic susceptibility to antibiotics. Because of this link between antibiotic tolerance and resistance and the rise of antibiotic resistance, there is a pressing need to develop treatments to eradicate persister cells. Current anti persister cell strategies are based on the paradigm of "awakening" them from their low metabolic state before attempting eradication with traditional antibiotics. Herein, we demonstrate that the low metabolic activity of persister cells can be exploited for eradication over their metabolically active counterparts. We engineered gold nanoclusters coated with adenosine triphosphate (AuNC@ATP) as a benchmark nanocluster that kills persister cells over exponential growth bacterial cells and prove the feasibility of this new concept. Finally, using AuNC@ATP as a new research tool, we demonstrated that it is possible to prevent the emergence of antibiotic-resistant superbugs with an anti-persister compound. Eradicating persister cells with AuNC@ATP in an isogenic culture of bacteria stops the emergence of superbug bacteria mediated by the sub-lethal dose of conventional antibiotics. Our findings lay the groundwork for developing novel nano-antibiotics targeting persister cells, which promise to prevent the emergence of superbugs and prolong the lifespan of currently available antibiotics.

Near-Infrared Copper Sulfide Hollow Nanostructures with Enhanced Photothermal and Photocatalytic Performance for Effective Bacterial Sterilization

The development of nonantibiotic strategies to combat bacterial infection is highly needed, owing to the widespread infectious disease and bacterial resistance becoming a significant health threat to the world's population. In recent years, photoactivated antibacterial therapies including photocatalytic and photothermal therapies have attracted increasing attention due to their high efficiency and low side effect. Herein, we introduce a copper sulfide (Cu_2-xS) hollow nanostructure-based near-infrared antibacterial platform with synergy photothermal and photocatalytic properties for effective bacterial sterilization. Compared to traditional Cu_2-xS nanoparticles, this unique hollow Cu_2-xS nanostructure can generate multiple scattered light, which is conducive to light collection. Moreover, its thin shell can shorten the transmission distance of carrier, thus reducing the charge recombination that usually causes the greatest energy loss. As a result, such a Cu_2-xS hollow nanostructure enables enhanced photothermal and photocatalytic bacterial killing activities against both Escherichia coli and Staphylococcus aureus, showing promise for antibiotic-free infection treatment and other bacterial sterilization applications.

Promoting photothermal antibacterial activity through an excited-state intramolecular proton transfer process

The construction of an efficient photothermal antibacterial platform is a promising strategy for the treatment of drug-resistant bacterial infections. Herein, through the introduction of excited-state intramolecular proton transfer to promote the photothermal effect, N-(2,4-dihydroxybenzylidene)-4-aminophenol (DOA)-polyvinyl alcohol (PVA) systems (DPVA) can reach 55 °C within 10 s under irradiation. They show superior antibacterial behavior against drug-resistant bacteria and a therapeutic effect on infected skin wounds with only 100 s of irradiation, much faster than those of reported photothermal materials (5-10 min). This work provides a convenient approach to fabricate broad-spectrum antibacterial wound dressings for treating bacteria-infected wounds, greatly contributing to the design and applications of photothermal antibacterial platforms.

Antibacterial Nanomaterials: Mechanisms, Impacts on Antimicrobial Resistance and Design Principles

Antimicrobial resistance (AMR) is one of the biggest threats to the environment and health. AMR rapidly invalidates conventional antibiotics, and antimicrobial nanomaterials have been increasingly explored as alternatives. Interestingly, several antimicrobial nanomaterials show AMR-independent antimicrobial effects without detectable new resistance and have therefore been suggested to prevent AMR evolution. In contrast, some are found to trigger the evolution of AMR. Given these seemingly conflicting findings, a timely discussion of the two faces of antimicrobial nanomaterials is urgently needed. This review systematically compares the killing mechanisms and structure-activity relationships of antibiotics and antimicrobial nanomaterials. We then focus on nano-microbe interactions to elucidate the impacts of molecular initiating events on AMR evolution. Finally, we provide an outlook on future antimicrobial nanomaterials and propose design principles for the prevention of AMR evolution.

Nanocarriers for the delivery of antibiotics into cells against intracellular bacterial infection

The barrier function of host cells enables intracellular bacteria to evade the lethality of the host immune system and antibiotics, thereby causing chronic and recurrent infections that seriously threaten human health. Currently, the main clinical strategy for the treatment of intracellular bacterial infections involves the use of long-term and high-dose antibiotics. However, insufficient intracellular delivery of antibiotics along with various resistance mechanisms not only weakens the efficacy of current therapies but also causes serious adverse drug reactions, further increasing the disease and economic burden. Improving the delivery efficiency, intracellular accumulation, and action time of antibiotics remains the most economical and effective way to treat intracellular bacterial infections. The rapid development of nanotechnology provides a strategy to efficiently deliver antibiotics against intracellular bacterial infections into cells. In this review, we summarize the types of common intracellular pathogens, the difficulties faced by antibiotics in the treatment of intracellular bacterial infections, and the research progress of several types of representative nanocarriers for the delivery of antibiotics against intracellular bacterial infections that have emerged in recent years. This review is expected to provide a reference for further elucidating the intracellular transport mechanism of nanocarrier-drug complexes, designing safer and more effective nanocarriers and establishing new strategies against intracellular bacterial infection.

Stimuli-Activable Metal-Bearing Nanomaterials and Precise On-Demand Antibacterial Strategies

Bacterial infections remain the leading cause of death worldwide today. The emergence of antibiotic resistance has urged the development of alternative antibacterial technologies to complement or replace traditional antibiotic treatments. In this regard, metal nanomaterials have attracted great attention for their controllable antibacterial functions that are less prone to resistance. This review discusses a particular family of stimuli-activable metal-bearing nanomaterials (denoted as SAMNs) and the associated on-demand antibacterial strategies. The various SAMN-enabled antibacterial strategies stem from basic light and magnet activation, with the addition of bacterial microenvironment responsiveness and/or bacteria-targeting selectivity and therefore offer higher spatiotemporal controllability. The discussion focuses on nanomaterial design principles, antibacterial mechanisms, and antibacterial performance, as well as emerging applications that desire on-demand and selective activation (i.e., medical antibacterial treatments, surface anti-biofilm, water disinfection, and wearable antibacterial materials). The review concludes with the authors' perspectives on the challenges and future directions for developing industrial translatable next-generation antibacterial strategies.

Recent Advances in Colorimetric Sensors Based on Gold Nanoparticles for Pathogen Detection

Infectious pathogens cause severe threats to public health due to their frightening infectivity and lethal capacity. Rapid and accurate detection of pathogens is of great significance for preventing their infection. Gold nanoparticles have drawn considerable attention in colorimetric biosensing during the past decades due to their unique physicochemical properties. Colorimetric diagnosis platforms based on functionalized AuNPs are emerging as a promising pathogen-analysis technique with the merits of high sensitivity, low-cost, and easy operation. This review summarizes the recent development in this field. We first introduce the significance of detecting pathogens and the characteristics of gold nanoparticles. Four types of colorimetric strategies, including the application of indirect target-mediated aggregation, chromogenic substrate-mediated catalytic activity, point-of-care testing (POCT) devices, and machine learning-assisted colorimetric sensor arrays, are systematically introduced. In particular, three biomolecule-functionalized AuNP-based colorimetric sensors are described in detail. Finally, we conclude by presenting our subjective views on the present challenges and some appropriate suggestions for future research directions of colorimetric sensors.

Antibacterial Properties of Gold Nanoparticles in the Modification of Medical Implants: A Systematic Review

The widespread occurrence of bacterial infections and their increased resistance to antibiotics has led to the development of antimicrobial coatings for multiple medical implants. Owing to their desirable properties, gold nanoparticles (AuNPs) have been developed as antibacterial agents. This systematic investigation sought to analyze the antibacterial effects of implant material surfaces modified with AuNPs. The data from 27 relevant studies were summed up. The included articles were collected from September 2011 to September 2021. According to the retrieved literature, we found that medical implants modified by AuNPs have good antibacterial effects against gram-positive and gram-negative bacteria, and the antibacterial effects would be improved by near-infrared (NIR) radiation.

Synthesis of ZnO/Au Nanocomposite for Antibacterial Applications

Annually, antimicrobial-resistant infections-related mortality worldwide accelerates due to the increased use of antibiotics during the coronavirus pandemic and the antimicrobial resistance, which grows exponentially, and disproportionately to the current rate of development of new antibiotics. Nanoparticles can be an alternative to the current therapeutic approach against multi-drug resistance microorganisms caused infections. The motivation behind this work was to find a superior antibacterial nanomaterial, which can be efficient, biocompatible, and stable in time. This study evaluated the antibacterial activity of ZnO-based nanomaterials with different morphologies, synthesized through the solvothermal method and further modified with Au nanoparticles through wet chemical reduction. The structure, crystallinity, and morphology of ZnO and ZnO/Au nanomaterials have been investigated with XRD, SEM, TEM, DLS, and FTIR spectroscopy. The antibacterial effect of unmodified ZnO and ZnO/Au nanomaterials against Escherichia coli and Staphylococcus aureus was investigated through disc diffusion and tetrazolium/formazan (TTC) assays. The results showed that the proposed nanomaterials exhibited significant antibacterial effects on the Gram-positive and Gram-negative bacteria. Furthermore, ZnO nanorods with diameters smaller than 50 nm showed better antibacterial activity than ZnO nanorods with larger dimensions. The antibacterial efficiency against Escherichia coli and Staphylococcus aureus improved considerably by adding 0.2% (w/w) Au to ZnO nanorods. The results indicated the new materials' potential for antibacterial applications.