Boosting antibacterial activity with mesoporous silica nanoparticles supported silver nanoclusters

Antibacterial activity of a silver-incorporated vancomycin-modified mesoporous silica against methicillin-resistant Staphylococcus aureus

Since conventional antibiotics are almost ineffective on methicillin-resistant Staphylococcus aureus (MRSA) strains, designing their antibacterial alternatives is necessary. Besides, the use of vancomycin is applied for specific detection of the bacteria. Silver-incorporated vancomycin-modified mesoporous silica nanoparticles (MSNs@Van@Ag NPs) were designed for detection and treatment of MRSA bacteria. Mesoporous silica nanoparticles (MSNs) were synthesized through the template method, modified with vancomycin, and finally incorporated with silver nanoparticles (Ag NPs). The MSNs@Van@Ag NPs with a homogenously spherical shape, average size of 50-100 nm, surface area of 955.8 m2/g, and thermal stability up to 200°C were successfully characterized. The amount of Ag incorporated into the MSNs@Van@Ag was calculated at 3.9 ppm and the release amount of Ag was received at 2.92 ppm (75%) after 100 h. The in vitro antibacterial susceptibility test showed the MIC of 100 μg mL-1 for MSNs@Van and 50 μg mL-1 for MSNs@Van@Ag, showing in vitro enhanced effect of Ag and vancomycin in the bactericidal process. An in vivo acute pneumonia model was performed and biochemical assays and pathological studies confirmed the nanomedicine's short-term safety for in vivo application. Cytokine assay using ELISA showed that MSN@Van@Ag causes a reduction of pro-inflammatory cytokines and bacterial proliferation leading to alleviation of inflammatory response.

Bacterial-responsive biodegradable silver nanoclusters composite hydrogel for infected wound therapy

Skin wounds are susceptible to bacterial infections, which hinder healing and extend recovery. Herein, we designed a silver nanoclusters (Ag NCs) composite hydrogel for infected wound treatment via bacterial enzymatic degradation and Ag release. Using biocompatible gelatine and polyethylene glycol as the main components, DNA-templated Ag NCs were covalently linked to a polymer network to obtain the final nanocomposite hydrogel. This hydrogel exhibited good compressive and tensile stiffness, bioadhesion and water absorption. The overexpressed bacterial enzymes protease and DNase in the infected wound were hydrolysed by the gel matrix, subsequently releasing antibacterial Ag ions. In vitro experimental results proved that the hydrogel demonstrated excellent bactericidal effect on Staphylococcus aureus and Escherichia coli, which are commonly implicated in clinical wound infections. Animal experiments revealed that the hydrogel considerably promoted cell proliferation and wound healing with less inflammatory responses. Thus, these results demonstrate strategies for bacterial enzyme-responsive Ag release for infected wound healing, facilitating further development of intelligent bandages.

Acetate Ions Facilitated Immobilization of Highly Dispersed Transition Metal Oxide Nanoclusters in Mesoporous Silica

The immobilization of tiny active species within inert mesoporous silica imparts a range of functions, enhancing their applicability. A significant obstacle is the spontaneous migration and aggregation of these species within the mesopores, which threaten their uniform distribution. To address this, we propose a postmodification method that involves grafting transition metal oxide nanoclusters into silica mesopores via interfacial condensation, catalyzed by acetate ions. Specifically, CuO nanoclusters, in the form of oligomeric [O1-x-Cu2-(OH) 2x]n2+, have a strong interaction with the silica framework. This interaction inhibits their growth and prevents mesopore blockage. Theoretical calculation results reveal that the acetate ion promotes proton transfer among various hydroxy species, lowering the free energy and thereby facilitating the formation of Cu-O-Si bonds. This technique has also been successfully applied to the encapsulation of four other types of transition metal oxide nanoclusters. Our encapsulation strategy effectively addresses the challenge of dispersing transition metal oxides in mesoporous silica, offering a straightforward and widely applicable method for enhancing the functionality of mesoporous materials.

Multifaceted Assessment of Porous Silica Nanocomposites: Unraveling Physical, Structural, and Biological Transformations Induced by Microwave Field Modification

In response to the persistent challenge of heavy and noble metal environmental contamination, our research explores a new idea to capture silver through porous spherical silica nanostructures. The aim was realized using microwave radiation at varying power (P = 150 or 800 W) and exposure times (t = 60 or 150 s). It led to the development of a silica surface with enhanced metal-capture capacity. The microwave-assisted silica surface modification influences the notable changes within the carrier but also enforces the crystallization process of silver nanoparticles with different morphology, structure, and chemical composition. Microwave treatment can also stimulate the formation of core-shell bioactive Ag/Ag2CO3 heterojunctions. Due to the silver nanoparticles' sphericity and silver carbonate's presence, the modified nanocomposites exhibited heightened toxicity against common microorganisms, such as E. coli and S. epidermidis. Toxicological assessments, including minimum inhibitory concentration (MIC) and half-maximal inhibitory concentration (IC50) determinations, underscored the efficacy of the nanocomposites. This research represents a significant stride in addressing pollution challenges. It shows the potential of microwave-modified silicas in the fight against environmental contamination. Microwave engineering underscores a sophisticated approach to pollution remediation and emphasizes the pivotal role of nanotechnology in shaping sustainable solutions for environmental stewardship.

Antimicrobial protection of two controlled release silver nanoparticles on simulated silk cultural relic

HYPOTHESIS

Silver nanoparticles coated with organic-inorganic hybrid silica or inorganic silica have antimicrobial ability, and the coating can also effectively improve the dispersion and stability of the particles. The slow release of silver ions (Ag+) can improve the antimicrobial activity of silver nanoparticles. The synthesized nanoparticles are light yellow, which does not affect the look and feel of the silk cultural relics and meets the requirements of the principle of minimum interference.

EXPERIMENTS

Two kinds of silver-based nanoparticles were synthesized: silver core-shell nanoparticle (Ag@mSiO2) and silver yolk-shell nanoparticle (Ag@YSiO2). The morphology, surface properties and Ag+ release efficiency of two nanoparticles were characterized. The antimicrobial effects of two nanoparticles on Aspergillus niger (A. niger) and Penicillium citrinum (P. citrinum) were compared.

FINDINGS

Both of Ag@mSiO2 and Ag@YSiO2 had uniform size and good stability. Two nanoparticles had pore structure and silver nanocore, which provided the basis for the dissolution and exchange of Ag+. Because more silver ions were released, Ag@mSiO2 had higher antimicrobial activity than Ag@YSiO2 for A. niger and P. citrinum. For various silk samples, Ag@mSiO2 exhibited excellent antimicrobial properties. Meanwhile, there was little change in the color and tearing strength of Ag@mSiO2 coated silk.

Porous Polymersomes as Carriers for Silver Nanoparticles and Nanoclusters: Advantages of Compartmentalization for Antimicrobial Usage

The global threat to public health posed by antibiotic-resistant bacterial infections requires the exploration of innovative approaches. Nanomaterials, particularly silver nanoparticles (AgNPs) and nanoclusters (AgNCs), have emerged as potential solutions to address the pressing issue of a bacterial healthcare crisis. However, the high cytotoxicity levels and low stability associated with AgNPs and AgNCs limit their applicability. To overcome these challenges, AgNCs and AgNPs were synthesized in the presence of porous polymersomes, resulting in a compartmentalized system that enhances stability, reduces cytotoxicity, and maintains high antimicrobial activity. The encapsulated particles exhibit a distribution of silver components on both the surface and the core, which is confirmed through the analysis of surface charge and center of mass. Moreover, our investigation demonstrates improved stability of the nanoparticles and nanoclusters upon entrapment in the porous system, as evidenced by the ion release assay. The antimicrobial effectiveness of porous polymersomes containing AgNPs and AgNCs was demonstrated by visualizing the biofilms and quantifying the penetration depth. Furthermore, cytotoxicity studies showed that compartmentalization increases cell compatibility for AgNC-based systems, showcasing the many advantages this system holds.

Silica nanoparticles: A review of their safety and current strategies to overcome biological barriers

Silica nanoparticles (SNP) have gained tremendous attention in the recent decades. They have been used in many different biomedical fields including diagnosis, biosensing and drug delivery. Medical uses of SNP for anti-cancer, anti-microbial and theranostic applications are especially prominent due to their exceptional performance to deliver many different small molecules and recently biologics (mRNA, siRNA, antigens, antibodies, proteins, and peptides) at targeted sites. The physical and chemical properties of SNP such as large specific surface area, tuneable particle size and porosity, excellent biodegradability and biocompatibility make them an ideal drug delivery and diagnostic platform. Based on the available data and the pre-clinical performance of SNP, recent interest has driven these innovative materials towards clinical application with many of the formulations already in Phase I and Phase II trials. Herein, the progress of SNP in biomedical field is reviewed, and their safety aspects are analysed. Importantly, we critically evaluate the key structural characteristics of SNP to overcome different biological barriers including the blood-brain barrier (BBB), skin, tumour barrier and mucosal barrier. Future directions, potential pathways, and target areas towards rapid clinical translation of SNP are also recommended.

Organically Modified Mesoporous Silica Nanoparticles against Bacterial Resistance

Bacterial antimicrobial resistance is posed to become a major hazard to global health in the 21st century. An aggravating issue is the stalled antibiotic research pipeline, which requires the development of new therapeutic strategies to combat antibiotic-resistant infections. Nanotechnology has entered into this scenario bringing up the opportunity to use nanocarriers capable of transporting and delivering antimicrobials to the target site, overcoming bacterial resistant barriers. Among them, mesoporous silica nanoparticles (MSNs) are receiving growing attention due to their unique features, including large drug loading capacity, biocompatibility, tunable pore sizes and volumes, and functionalizable silanol-rich surface. This perspective article outlines the recent research advances in the design and development of organically modified MSNs to fight bacterial infections. First, a brief introduction to the different mechanisms of bacterial resistance is presented. Then, we review the recent scientific approaches to engineer multifunctional MSNs conceived as an assembly of inorganic and organic building blocks, against bacterial resistance. These elements include specific ligands to target planktonic bacteria, intracellular bacteria, or bacterial biofilm; stimuli-responsive entities to prevent antimicrobial cargo release before arriving at the target; imaging agents for diagnosis; additional constituents for synergistic combination antimicrobial therapies; and aims to improve the therapeutic outcomes. Finally, this manuscript addresses the current challenges and future perspectives on this hot research area.

Novel Antibacterial Materials and Coatings-A Perspective by the Editors

The fight between humans and bacteria has escalated to a new level.

Antibacterial Properties of Mesoporous Silica Nanoparticles Modified with Fluoroquinolones and Copper or Silver Species

Antibiotic resistance is a global problem and bacterial biofilms contribute to its development. In this context, this study aimed to perform the synthesis and characterization of seven materials based on silica mesoporous nanoparticles functionalized with three types of fluoroquinolones, along with Cu2+ or Ag+ species to evaluate the antibacterial properties against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, including clinical and multi-drug-resistant strains of S. aureus and P. aeruginosa. In addition, in order to obtain an effective material to promote wound healing, a well-known proliferative agent, phenytoin sodium, was adsorbed onto one of the silver-functionalized materials. Furthermore, biofilm studies and the generation of reactive oxygen species (ROS) were also carried out to determine the antibacterial potential of the synthesized materials. In this sense, the Cu2+ materials showed antibacterial activity against S. aureus and E. coli, potentially due to increased ROS generation (up to 3 times), whereas the Ag+ materials exhibited a broader spectrum of activity, even inhibiting clinical strains of MRSA and P. aeruginosa. In particular, the Ag+ material with phenytoin sodium showed the ability to reduce biofilm development by up to 55% and inhibit bacterial growth in a "wound-like medium" by up to 89.33%.

Enhanced Antibacterial Activity of Novel Fluorescent Glutathione-Capped Ag Nanoclusters

Ag nanomaterials are promising candidates for the discovery of next-generation antibiotics with a high antibacterial effect against multi-drug resistant strains. This paper reports a simple synthesis of novel water-soluble glutathione-capped silver nanoclusters (GSH-Ag NCs) with an enhanced antibacterial activity. According to thin layer chromatography (TLC), the synthesized GSH-Ag NCs are an individual fraction of the same composition without any impurities. According to matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and energy dispersive X-ray (EDX) analyses, the silver core of the GSH-Ag NCs contains approximately 35 silver atoms, and the molecular weight of these nanoclusters is about 11 kDa. The fabricated silver nanoclusters have a reddish fluorescence (λex/λem = 509/645 nm), with a large Stokes shift (>130 nm), and ultra-small size (less than 2 nm) according to transmission electron microscopy (TEM) data and dynamic light scattering (DLS) analysis. The antibacterial activity and minimal inhibitory concentrations of the silver nanoclusters towards Escherichia coli, Staphylococcus aureus, Bacillus cereus and Enterobacter cloacae were evaluated using the agar well-diffusion method and resazurin metabolism assay. The antibacterial activity of chelated silver in the nanoclusters was found to be significantly higher compared to the activity of free silver ions. To explain the possible mechanisms underlying the antibacterial actions of the GSH-Ag nanoclusters, molecular docking was performed, and prospective bacterial targets were identified using AutoDock.

Antimicrobial Activity and Crystallization Features in Bio-Based Composites of PLLA and MCM-41 Particles Either Pristine or Functionalized with Confined Ag Nanowires

Composites based on an L-rich poly(lactic acid) (PLLA) and MCM-41, either neat or modified with a silver (MCM-41@Ag), are achieved by solvent casting, being next processed by compression molding. Ag is mainly embedded as nanowires within the hybrid MCM-41@Ag particles, enabling its antimicrobial character. In these composites, the PLLA thermal stability, nucleation efficiency, and mechanical response are dependent on the MCM-41 nature and, to a lesser extent, on its content. Thus, differences in transitions of the PLLA matrix are noticed during cooling at 10 °C/min and in the subsequent heating when composites with neat or modified MCM-41 are compared. A very remarkable nucleation effect is played by pristine MCM-41, being inferior when MCM-41@Ag is incorporated into the PLLA. Wide angle X-ray scattering (WAXS) measurements using synchrotron radiation and performed under variable-temperature conditions in the composites containing MCM-41@Ag indicate that during cold crystallization, the disordered α' polymorph is initially formed, but it rapidly transforms into ordered α crystals. A long spacing peak, clearly seen in pure PLLA, appears as a small shoulder in PLLAMCM@Ag4 and is undetectable in PLLAMCM@Ag9 and PLLAMCM@Ag20. Furthermore, an increase in MH with the silica content is found in the two sets of composites, the higher MH values being observed in the family of PLLA and MCM-41@Ag. Finally, remarkable antimicrobial features are noticeable in the composites with MCM-41@Ag since this modified silica transfers its biocidal characteristics into the PLLA composites.

Photocatalytic Ag/AgBr-MBG for Rapid Antibacterial and Wound Repair

In daily life and during surgery, the skin, as the outermost organ of the human body, is easily damaged to form wounds. If the wound was infected by the bacteria, especially the drug-resistant bacteria such as methicillin-resistant staphylococcus aureus (MRSA), it was difficult to recover. Therefore, it was important to develop the safe antimicrobial strategy to inhibit bacterial growth in the wound site, in particular, to overcome the problem of bacterial drug resistance. Here, the Ag/AgBr-loaded mesoporous bioactive glass (Ag/AgBr-MBG) was prepared, which had excellent photocatalytic properties under simulated daylight for rapid antibacterial activity within 15 min by generating reactive oxygen species (ROS). Meanwhile, the killing rate of Ag/AgBr-MBG against MRSA was 99.19% within 15 min, which further reduced the generation of drug-resistant bacteria. In addition, Ag/AgBr-MBG particles could disrupt bacterial cell membranes, showing the broad-spectrum antibacterial properties and promoting tissue regeneration and infected wound healing. Ag/AgBr-MBG particles might have potential applications as a light-driven antimicrobial agent in the field of biomaterials.

Utilizing Imine Bonds to Create a Self-Gated Mesoporous Silica Material with Controlled Release and Antimicrobial Properties

In recent years, silica nanomaterials have been widely studied as carriers in the field of antibacterial activity in food. Therefore, it is a promising but challenging proposition to construct responsive antibacterial materials with food safety and controllable release capabilities using silica nanomaterials. In this paper, a pH-responsive self-gated antibacterial material is reported, which uses mesoporous silica nanomaterials as a carrier and achieves self-gating of the antibacterial agent through pH-sensitive imine bonds. This is the first study in the field of food antibacterial materials to achieve self-gating through the chemical bond of the antibacterial material itself. The prepared antibacterial material can effectively sense changes in pH values caused by the growth of foodborne pathogens and choose whether to release antibacterial substances and at what rate. The development of this antibacterial material does not introduce other components, ensuring food safety. In addition, carrying mesoporous silica nanomaterials can also effectively enhance the inhibitory ability of the active substance.

Facile One-Step Electrospinning Process to Prepare AgNPs-Loaded PLA and PLA/PEO Mats with Antibacterial Activity

Nanofibers can play an important role in developing new kinds of medical applications. Poly(lactic acid) (PLA) and PLA/poly(ethylene oxide) (PEO) antibacterial mats containing silver nanoparticles (AgNPs) were prepared by a simple one-step electrospinning method that allows AgNPs to be synthesized simultaneously with the preparation of the electrospinning solution. The electrospun nanofibers were characterized by scanning electron microscopy, transmission electron microscopy and thermogravimetry, while silver release over time was monitored by inductively coupled plasma/optical emission spectroscopy. The antibacterial activity was tested against Staphylococcus epidermidis and Escherichia coli by colony forming unit (CFU) count on agar after 15, 24 and 48 h of incubation. AgNPs were found to be mainly concentrated in the PLA nanofiber core, and the mats showed steady but slow Ag release in the short term; in contrast, AgNPs were uniformly distributed in the PLA/PEO nanofibers, which released up to 20% of their initial silver content in 12 h. A significant (p < 0.05) antimicrobial effect towards both tested bacteria, highlighted by a reduction in the CFU/mL counts, was observed for the nanofibers of PLA and PLA/PEO embedded with AgNPs, with a stronger effect exerted by the latter, confirming the more efficient silver release from these samples. The prepared electrospun mats may have good potential for use in the biomedical field, particularly in wound dressing applications, where a targeted delivery of the antimicrobial agent is highly desirable to avoid infections.

Highly biocompatible Ag nanocluster-reinforced wound dressing with long-term and synergistic bactericidal activity

Clinical application of antibiotic-free agents like silver nanoparticle-derived materials remains a critical challenge due to their limited long-term antibacterial activity and potential system toxicity. Herein, a highly biocompatible Ag nanocluster-reinforced hydrogel with enhanced synergistic antibacterial ability has been developed. Specifically, bioactive curcumin was incorporated into lysozyme-protected ultrasmall Ag nanoclusters (LC-AgNCs) and further integrated with sodium alginate (Sa) hydrogel (LC-AgNCs@Sa) through multiple interaction forces. Due to the synergistic antibacterial activity, LC-AgNCs could effectively kill both S. aureus and E. coli bacteria with a concentration down to 2.5 μg mL^-1. In-depth mechanism investigations revealed that the bactericidal effect of LC-AgNCs lies in their bacterial membrane destruction, reactive oxygen species (ROS) production, glutathione depletion and prooxidant-antioxidant system disruption ability. Curcumin can mediate the intracellular ROS balance to protect NIH 3T3 cells from oxidative stress and improve the biocompatibility of LC-AgNCs@Sa. LC-AgNCs@Sa with long-term antibacterial ability can effectively protect the wound from bacterial invasion in vivo, and significantly accelerate the wound healing process due to their distinctive functions of inhibiting inflammatory factor (TNF-α) production, promoting collagen deposit and facilitating re-epithelization. This study provides a new, versatile strategy for the design of high-performance antibacterial dressing for broad infectious disease therapy.

Potent intrinsic bactericidal activity of novel copper telluride nano-grape clusters with facile preparation

Bactericidal nanomedicines often suffer from a complicated design and insufficient intrinsic inhibitory efficacy. Herein, novel anti-bacterial copper telluride (CuTe) nano-clusters are reported, featuring superior bactericidal efficiency, facile preparation, and unique mechanism. These nanoparticles, well dispersable in water, resembled grape clusters with rough surfaces. The CuTe nano-grape clusters exhibited ultra-high sterilization efficacy at ultra-low concentration, particularly for Gram-negative bacteria, and were more potent than conventional anti-microbial nanoparticles. Also, the grape clusters effectively inhibited the bacterial biofilm development. Further investigation revealed the synergized mechanisms of reactive oxygen species (ROS) generation and glutathione (GSH) depletion. Interestingly, electron microscopy revealed that the grape clusters served as bacterial hunters by tightly adhering to bacterial surfaces. The bacteria subsequently suffered from the leakage of various intracellular components including nucleic acid, proteins, and potassium. Most encouragingly, CuTe drastically reduced bacterial number in a mouse model with lethal intraperitoneal infection and increased the mouse survival rate to 90%. This finding could inspire the development of highly potent bactericidal inorganic formulations with simplified structure, multiple antibacterial mechanisms, and promising application potential.

Mesoporous silica nanoparticles as carrier to overcome bacterial drug resistant barriers

Antibiotic resistance has become a global threat to health due to abuse of antibiotics. Lots of existing antibiotics have lost their effect on drug resistant bacteria. Moreover, the discovery of novel antibiotics becomes more and more difficult. It is necessary to develop new strategies to fight against antibiotic resistance. Nano-drug delivery systems endow old antibiotics with new vitality to defeat the antibiotic resistant barrier by protecting antibiotics against hydrolysis, increasing uptake and circumventing efflux pump. Among them, mesoporous silica nanoparticles (MSNs) are one of the most extensively investigated as carrier of antibiotics due to large drug loading capability, tunable physicochemical characteristics, and biocompatibility. MSNs can improve the delivery of antibiotics to bacteria greatly by reducing size, modifying surface, and regulating shapes. Furthermore, MSNs hybridized metal ions or metal nanoparticles exert stronger antibacterial effect by controlling the release of metal ions or increasing active oxygen species. In addition, metal capped MSNs are also able to load antibiotics to exert synergistic antibacterial effect. This paper firstly reviewed the current application of various nanomaterials as antibacterial agents, and then focused on the MSNs including the introduction of MSNs and various approaches for improving antibacterial effect of MSNs.

Bacterial infection microenvironment-responsive porous microspheres by microfluidics for promoting anti-infective therapy

The overuse of antibiotics for treating bacterial infection has caused severe bacterial resistance and become a public health threat worldwide. It is desired to develop novel antibiotic delivery systems as efficient antibacterial strategies for promoting anti-infective therapy. Herein, the AgNPs-loaded N-[(2-hydroxy-3-trimethyl ammonium) propyl] chitosan (HTCC)/hyaluronic acid (HA) porous microspheres (HHPMs) by microfluidics have been developed as novel bacterial infection microenvironment (IME)-responsive antibiotic delivery systems for promoting antimicrobial therapy. The release of AgNPs can respond explicitly to the IME with acidic pH values and relatively high hyaluronidase concentration. The unique porous structures of HHPMs can effectively facilitate the capture and enrichment of bacteria, thus exerting synergistic antibacterial effects, which can be more efficient in instant bacteria inhibiting and killing. The excellent biocompatibility of HHPMs is revealed by investigating their hemolytic activity and cytotoxicity. In vivo assays demonstrate that the fabricated AgNPs-loaded HHPMs can effectively resist bacterial infection and promote wound healing and tissue regeneration at infected wound sites by inhibition of the bacterial survival. This work indicates that fabricated HHPMs are ideal bacterial infection microenvironment-responsive materials for antibiotic delivery and show great promises for promoting anti-infective therapy in clinics.

Silver Nanoparticles Functionalized Nanosilica Grown over Graphene Oxide for Enhancing Antibacterial Effect

The continuous growth of multidrug-resistant bacteria due to the overuse of antibiotics and antibacterial agents poses a threat to human health. Silver nanoparticles, silica-based materials, and graphene-based materials have become potential antibacterial candidates. In this study, we developed an effective method of enhancing the antibacterial property of graphene oxide (GO) by growing nanosilica (NS) of approximately 50 nm on the graphene oxide (GO) surface. The structures and compositions of the materials were characterized through powdered X-ray diffraction (P-XRD), transmission electron microscopy (TEM), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), ultraviolet-visible spectroscopy (UV-VIS), dynamic light scattering (DLS), Raman spectroscopy (RM), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmet-Teller (BET) surface area, and pore size determination. The silver nanoparticles (AgNPs) with an average diameter of 26 nm were functionalized on the nanosilica (NS) surface. The composite contained approximately 3% of silver nanoparticles. The silver nanoparticles on nanosilica supported over graphene oxide (GO/NS/AgNPs) exhibited a 7-log reduction of Escherichia coli and a 5.2-log reduction of Bacillus subtilis within one hour of exposure. Both GO/NS and GO/NS/AgNPs exhibited substantial antimicrobial effects against E. coli and B. subtilis.

Hybrid Nanosystems Based on Nicotinate-Functionalized Mesoporous Silica and Silver Chloride Nanoparticles Loaded with Phenytoin for Preventing Pseudomonas aeruginosa Biofilm Development

Pseudomonas aeruginosa (PA) is one of the most common bacteria isolated from chronic wounds and burns. Its treatment is a challenge due to antimicrobial drug resistance and biofilm formation. In this context, this study aimed to perform the synthesis and full characterization of hybrid nanosystems based on mesoporous silica nanoparticles (MSNs) functionalized with a nicotinic ligand and silver chloride nanoparticles, both phenytoin sodium (Ph)-loaded and unloaded, to evaluate the antibacterial properties against three different strains of PA (including two clinical strains) in a planktonic state and as biofilms. Ph is a well-known proliferative agent, which was incorporated into the hybrid nanomaterials to obtain an effective material for tissue healing and prevention of infection caused by PA. The Ph-loaded materials promoted a quasi-complete inhibition of bacterial growth in wound-like medium and biofilm development, with values of 99% and 96%, respectively, with selectivity indices above the requirements for drugs to become promising agents for the topic preventive treatment of chronic wounds and burns.

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.

Nano Silver-Induced Toxicity and Associated Mechanisms

Nano silver is one of the most widely used engineering nanomaterials with antimicrobial activity against bacteria, fungi, and viruses. However, the widespread application of nano silver preparations in daily life raises concerns about public health. Although several review articles have described the toxicity of nano silver to specific major organs, an updated comprehensive review that clearly and systematically outlines the harmful effects of nano silver is lacking. This review begins with the routes of exposure to nano silver and its distribution in vivo. The toxic reactions are then discussed on three levels, from the organ to the cellular and subcellular levels. This review also provides new insights on adjusting the toxicity of nano silver by changing their size and surface functionalization and their combination with other materials to form a composite formulation. Finally, future development, challenges, and research directions are discussed.

Recent Advances and Mechanistic Insights into Antibacterial Activity, Antibiofilm Activity, and Cytotoxicity of Silver Nanoparticles

The substantial increase in multidrug-resistant (MDR) pathogenic bacteria is a major threat to global health. Recently, the Centers for Disease Control and Prevention reported possibilities of greater deaths due to bacterial infections than cancer. Nanomaterials, especially small-sized (size ≤10 nm) silver nanoparticles (AgNPs), can be employed to combat these deadly bacterial diseases. However, high reactivity, instability, susceptibility to fast oxidation, and cytotoxicity remain crucial shortcomings for their uptake and clinical application. In this review, we discuss various AgNPs-based approaches to eradicate bacterial infections and provide comprehensive mechanistic insights and recent advances in antibacterial activity, antibiofilm activity, and cytotoxicity (both in vitro and in vivo) of AgNPs. The mechanistic of antimicrobial activity involves four steps: (i) adhesion of AgNPs to cell wall/membrane and its disruption; (ii) intracellular penetration and damage; (iii) oxidative stress; and (iv) modulation of signal transduction pathways. Numerous factors affecting the bactericidal activity of AgNPs such as shape, size, crystallinity, pH, and surface coating/charge have also been described in detail. The review also sheds light on antimicrobial photodynamic therapy and the role of AgNPs versus Ag⁺ ions release in bactericidal activities. In addition, different methods of synthesis of AgNPs have been discussed in brief.

Polycationic Silver Nanoclusters Comprising Nanoreservoirs of Ag+ Ions with High Antimicrobial and Antibiofilm Activity

Silver-based nano-antibiotics are rapidly developing as promising alternatives to conventional antibiotics. Ideally, to remain potent against a wide range of drug-resistant and anaerobic bacteria, silver-based nano-antibiotics should easily penetrate through the bacterial cell walls and actively release silver ions. In this study, highly monodispersed, ultrasmall (<3 nm), polycationic silver nanoclusters (pAgNCs) are designed and synthesized for the elimination of a range of common Gram-negative and Gram-positive pathogens and their corresponding established and matured biofilms, including those composed of multiple species. The pAgNCs also show greatly enhanced antibacterial efficacy against anaerobic bacteria such as Fusobacterium nucleatum and Streptococcus sanguinis. These results demonstrate that the cationic nature facilitates better penetration to the bacterial cell membrane while the presence of a high percentage (>50%) of silver ions (i.e., Ag⁺ nanoreservoirs) on the cluster surface maintains their efficiency in both aerobic and anaerobic conditions. Significantly, the pAgNCs showed a strong capacity to significantly delay the development of bacterial resistance when compared to similar-sized negatively charged silver nanoparticles or conventional antibiotics. This study demonstrates a novel design strategy that can lay the foundation for the development of future highly potent nano-antibiotics effective against a broad spectrum of pathogens and biofilms needed in many everyday life applications and industries.

Nanotechnology in combating biofilm: A smart and promising therapeutic strategy

Since the birth of civilization, people have recognized that infectious microbes cause serious and often fatal diseases in humans. One of the most dangerous characteristics of microorganisms is their propensity to form biofilms. It is linked to the development of long-lasting infections and more severe illness. An obstacle to eliminating such intricate structures is their resistance to the drugs now utilized in clinical practice (biofilms). Finding new compounds with anti-biofilm effect is, thus, essential. Infections caused by bacterial biofilms are something that nanotechnology has lately shown promise in treating. More and more studies are being conducted to determine whether nanoparticles (NPs) are useful in the fight against bacterial infections. While there have been a small number of clinical trials, there have been several in vitro outcomes examining the effects of antimicrobial NPs. Nanotechnology provides secure delivery platforms for targeted treatments to combat the wide range of microbial infections caused by biofilms. The increase in pharmaceuticals' bioactive potential is one of the many ways in which nanotechnology has been applied to drug delivery. The current research details the utilization of several nanoparticles in the targeted medication delivery strategy for managing microbial biofilms, including metal and metal oxide nanoparticles, liposomes, micro-, and nanoemulsions, solid lipid nanoparticles, and polymeric nanoparticles. Our understanding of how these nanosystems aid in the fight against biofilms has been expanded through their use.

An injectable mesoporous silica-based analgesic delivery system prolongs the duration of sciatic nerve block in mice with minimal toxicity

The major limitation of traditional local anesthetics is the finite duration of a single injection. The present study developed two kinds of novel injectable anesthetic nanocomposites based on mesoporous silica, and evaluated their long-lasting analgesic effect and biosafety. The nanoparticulate carriers, mesoporous silica nanoparticles (MSNs) and mesoporous silica-coated gold nanorods (GNR@MSN), were firstly constructed using the oil-water biphase reaction approach and then ropivacaine (RPC), a local anesthetic, was loaded into the mesoporous carriers by vacuum suction. Transmission electron microscopic images showed the well-ordered mesoporous structure for drug loading. RPC-loaded MSNs and RPC-loaded GNR@MSN exhibited a sustained-release pattern in vitro, and the latter also showed a controlled-release manner triggered by near-infrared (NIR) irradiation. RPC-loaded MSNs and RPC-loaded GNR@MSN caused an initial sensory blockade in mice that lasted for 6 h, almost 2.5 folds of that from free RPC solution. Furthermore, upon NIR irradiation, the latter induced three additional periods of the blockade. Neither of them showed motor nerve block, which may be due to the sustained release manner. The low myotoxicity and low neurotoxicity of the two nanocomposites were presented both in vitro and in vivo. These results demonstrate the potential of the mesoporous silica-based analgesic nanocomposites in effectively controlling postoperative pain, maybe RPC-loaded MSNs for moderate pain and RPC-loaded GNR@MSN for severe pain. STATEMENT OF SIGNIFICANCE: Adequate postoperative analgesia helps early functional exercise after surgery and accelerates rapid recovery, while uncontrolled postoperative pain probably develops chronic post-surgical pain that impacts the life quality of patients for a long time. However, postoperative pain management is still a challenge. The current treatment drugs are always accompanied by some side effects due to their systemic effect. Opioids have risks of addiction and respiratory depression, and nonsteroidal anti-inflammatory drugs can lead to gastrointestinal reaction. Therefore, the long-lasting local anesthetic formulation with good biocompatibility is the most promising solution to manage post-surgical pain. The present study developed novel injectable anesthetic nanocomposites based on mesoporous silica, providing long-lasting pain relief in mice with minimal toxicity.

Mesoporous silica nanoparticles containing copper or silver synthesized with a new metal source: Determination of their structure parameters and cytotoxic and irritating effects

One of the potential implementation of mesoporous silica nanomaterials (MSNs) is their use in biomedical applications as adsorbents or carriers of various bioactive substances. In this study, we attempted to fabricate silica nanomaterials containing copper and silver that were introduced into the MSN matrix, for the first time using oxalate compounds as a metal source. The syntheses were carried out using hydrothermal and impregnation methods. Structure studies revealed that the obtained nanoparticles were of a spheroidal shape and most had diameters in the range 200-500 nm. Silver and copper were found to be grouped into clusters in most samples, except in copper-decorated MSNs prepared with the impregnation method, which had an even distribution of metal atoms throughout the volume of the granule. An evaluation of the cytotoxic and irritating effects revealed that the preferred candidates for potential future applications in medicine or cosmetology among materials obtained with the presented method are the copper-conjugated MSNs.

Templated Mesoporous Silica Outer Shell for Controlled Silver Release of a Magnetically Recoverable and Reusable Nanocomposite for Water Disinfection

In this work, we encapsulated Fe₃O₄@SiO₂@Ag (MS-Ag), a bifunctional magnetic silver core-shell structure, with an outer mesoporous silica (mS) shell to form an Fe₃O₄@SiO₂@Ag@mSiO₂ (MS-Ag-mS) nanocomposite using a cationic CTAB (cetyltrimethylammonium bromide) micelle templating strategy. The mS shell acts as protection to slow down the oxidation and detachment of the AgNPs and incorporates channels to control the release of antimicrobial Ag⁺ ions. Results of TEM, STEM, HRSEM, EDS, BET, and FTIR showed the successful formation of the mS shells on MS-Ag aggregates 50-400 nm in size with highly uniform pores ∼4 nm in diameter that were separated by silica walls ∼2 nm thick. Additionally, the mS shell thickness was tuned to demonstrate controlled Ag⁺ release; an increase in shell thickness resulted in an increased path length required for Ag⁺ ions to travel out of the shell, reducing MS-Ag-mS' ability to inhibit E. coli growth as illustrated by the inhibition zone results. Through a shaking test, the MS-Ag-mS nanocomposite was shown to eradicate 99.99+% of a suspension of E. coli at 1 × 10⁶ CFU/mL with a silver release of less than 0.1 ppb, well under the EPA recommendation of 0.1 ppm. This high biocidal efficiency with minimal silver leach is ascribed to the nanocomposite's mS shell surface characteristics, including having hydroxyl groups and possessing a high degree of structural periodicity at the nanoscale or "smoothness" that encourages association with bacteria and retains high Ag⁺ concentration on its surface and in its close proximity. Furthermore, the nanocomposite demonstrated consistent antimicrobial performance and silver release levels over multiple repeated uses (after being recovered magnetically because of the oxidation-resistant silica-coated magnetic Fe₃O₄ core). It also proved effective at killing all microbes from Long Island Sound surface water. The described MS-Ag-mS nanocomposite is highly synergistic, easy to prepare, and readily recoverable and reusable and offers structural tunability affecting the bioavailability of Ag⁺, making it excellent for water disinfection that will find wide applications.

Computational Appraisal of Silver Nanocluster Evolution on Epitaxial Graphene: Implications for CO Sensing

Early stages of silver nucleation on a two-dimensional (2D) substrate, here, monolayer epitaxial graphene (MEG) on SiC, play a critical role in the formation of application-specific Ag nanostructures. Therefore, it is of both fundamental and practical importance to investigate the growth steps when Ag adatoms start to form a new phase. In this work, we exploit density functional theory to study the kinetics of early-stage nuclei Ag n (n = 1-9) assembly of Ag nanoparticles on MEG. We find that the Ag1 monomer tends to occupy hollow site positions of MEG and interacts with the surface mainly through weak dispersion forces. The pseudoepitaxial growth regime is revealed to dominate the formation of the planar silver clusters. The adsorption and nucleation energies of Ag n clusters exhibit evident odd-even oscillations with cluster size, pointing out the preferable adsorption and nucleation of odd-numbered clusters on MEG. The character of the interaction between a chemisorbed Ag3 cluster and MEG makes it possible to consider this trimer as the most stable nucleus for the subsequent growth of Ag nanoparticles. We reveal the general correlation between Ag/MEG interaction and Ag-Ag interaction: with increasing cluster size, the interaction between Ag adatoms increases, while the Ag/MEG interaction decreases. The general trend is also supported by the results of charge population analysis, according to which the average charge per Ag adatom in a Ag n cluster demonstrates a drastic decrement with cluster size increase. 2D-3D structural transition in Ag n clusters was investigated. We anticipate that the present investigation is beneficial by providing a better understanding of the early-stage nucleation of Ag nanoparticles on MEG at the atomic scale. Specific interaction between odd-numbered Ag clusters preadsorbed onto the MEG surface and carbon monoxide (CO) as well as clusters' stability at 300 K is discussed in terms of sensing applications.

Eradication of Mature Bacterial Biofilms with Concurrent Improvement in Chronic Wound Healing Using Silver Nanoparticle Hydrogel Treatment

Biofilm-associated infections are a major cause of impaired wound healing. Despite the broad spectrum of anti-bacterial benefits provided by silver nanoparticles (AgNPs), these materials still cause controversy due to cytotoxicity and a lack of efficacy against mature biofilms. Herein, highly potent ultrasmall AgNPs were combined with a biocompatible hydrogel with integrated synergistic functionalities to facilitate elimination of clinically relevant mature biofilms in-vivo combined with improved wound healing capacity. The delivery platform showed a superior release mechanism, reflected by high biocompatibility, hemocompatibility, and extended antibacterial efficacy. In vivo studies using the S. aureus wound biofilm model showed that the AgNP hydrogel (200 µg/g) was highly effective in eliminating biofilm infection and promoting wound repair compared to the controls, including silver sulfadiazine (Ag SD). Treatment of infected wounds with the AgNP hydrogel resulted in faster wound closure (46% closure compared to 20% for Ag SD) and accelerated wound re-epithelization (60% for AgNP), as well as improved early collagen deposition. The AgNP hydrogel did not show any toxicity to tissue and/or organs. These findings suggest that the developed AgNP hydrogel has the potential to be a safe wound treatment capable of eliminating infection and providing a safe yet effective strategy for the treatment of infected wounds.

PVC-SiO2-Ag composite as a powerful biocide and anti-SARS-CoV-2 material

The ongoing COVID-19 pandemic has pushed scientists and technologists to find novel strategies to develop new materials to prevent the transmission, spread, and entry of pathogens into the human body. In this report, the fabrication of polyvinyl chloride (PVC)-SiO₂-Ag composite is presented, in which the percentage of Ag is 0.84% wt. Our findings render that this composite eliminates (> 99.8%) bacteria and fungus (Staphylococcus aureus, Escherichia coli, Penicillium funiculosum) and SARS-CoV-2, by surface contact in 2 h hours and 15 min, respectively. Specific migration analysis shown that the use of the PVC-SiO₂-Ag composite is considered safe and effective for food preservation. This research and innovation front can be considered a breakthrough for the design of biocide materials. Future directions for this exciting and highly significant research field can open the door to the development of new technologies for the fabrication of packaging films to protect consumer products (such as fruits, vegetables, and other foods).

Nanosilver-Decorated Biodegradable Mesoporous Organosilica Nanoparticles for GSH-Responsive Gentamicin Release and Synergistic Treatment of Antibiotic-Resistant Bacteria

PURPOSE

Antibiotic-resistant bacteria are pathogens that have emerged as a serious public health risk. Thus, there is an urgent need to develop a new generation of anti-bacterial materials to kill antibiotic-resistant bacteria.

METHODS

Nanosilver-decorated mesoporous organosilica nanoparticles (Ag-MONs) were fabricated for co-delivery of gentamicin (GEN) and nanosilver. After investigating the glutathione (GSH)-responsive matrix degradation and controlled release of both GEN and silver ions, the anti-bacterial activities of Ag-MONs@GEN were systematically determined against several antibiotic-susceptible and antibiotic-resistant bacteria including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis. Furthermore, the cytotoxic profiles of Ag-MONs@GEN were evaluated.

RESULTS

The GEN-loaded nanoplatform (Ag-MONs@GEN) showed glutathione-responsive matrix degradation, resulting in the simultaneous controlled release of GEN and silver ions. Ag-MONs@GEN exhibited excellent anti-bacterial activities than Ag-MONs and GEN alone via inducing ROS generation, especially enhancing synergetic effects against four antibiotic-resistant bacteria including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis. Moreover, the IC50 values of Ag-MONs@GEN in L929 and HUVECs cells were 313.6 ± 15.9 and 295.7 ± 12.3 μg/mL, respectively, which were much higher than their corresponding minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values.

CONCLUSION

Our study advanced the development of Ag-MONs@GEN for the synergistic and safe treatment of antibiotic-resistant bacteria.

Multifunctional ultrasmall AgNP hydrogel accelerates healing of S. aureus infected wounds

The increasing emergence of antibiotic resistance coupled with the limited effectiveness of current treatments highlights the need for the development of new treatment modalities. Silver nanoparticles (AgNPs) are a promising alternative with broad-spectrum antibacterial activity. However, the clinical translation of AgNPs have been hampered primarily due to the delivery of unsafe levels of silver ions (Ag⁺) resulting in cellular toxicity and their susceptibility to aggregation resulting in loss of efficacy. Here, we describe a safe and effective, thermo-responsive AgNP hydrogel that provides antibacterial effects in conjunction with wound promoting properties. Using a murine model of wound infection, we demonstrate that the applied AgNP hydrogel to the wound (12 µg silver) not only provides superior bactericidal activity but also reduces inflammation leading to accelerated wound closure when compared to industry-standard silver sulfadiazine (302 µg silver). The AgNP hydrogel-treatment significantly accelerated wound closure at day 4 post-infection (56 closure) compared to both blank hydrogel or Ag SD (74% and 91% closure respectively) with a concurrent increase in PCNA-positive proliferating cells corresponding with a significant 32% improvement in wound re-epithelization compared to the blank hydrogel. Treatment of infected wounds with AgNP hydrogel also decreased neutrophil infiltration, increased anti-inflammatory Ym-1 positive M2 macrophages, and reduced the number of caspase-1 positive apoptotic cells. Therefore, this novel multifunctional AgNP thermo-responsive hydrogel is potentially a safe and effective treatment at much lower concentration for the treatment of wound infections. STATEMENT OF SIGNIFICANCE: In this study, we describe the development of a multifunctional thermo-responsive hydrogel of ultrasmall silver nanoparticles (AgNPs) for controlled and optimized delivery of silver to infected wounds. The in vivo biological effects of the developed hydrogel showed significant S. aureus elimination from infected mouse wounds compared to a commercial antibacterial formulation. The developed AgNP hydrogel optimally regulates inflammatory responses to promote wound healing as indicated by increased cell proliferation and wound re-epithelization. Additionally, AgNP hydrogel shows significant potential in regulating neutrophil infiltration while increasing levels of anti-inflammatory M2 macrophages and reduces the number of apoptotic cells. Therefore, the multifunctional properties of the developed AgNP thermo-responsive hydrogel offers great clinical potential to control bacterial infections and promote wound healing.

Toxicity-attenuated mesoporous silica Schiff-base bonded anticancer drug complexes for chemotherapy of drug resistant cancer

Multidrug resistance (MDR), evoked by improper chemotherapeutic practices, poses a serious threat to public health, which leads to increased medical burdens and weakened curative effects. Taking advantage of the enhanced pharmaceutical effect of Schiff base compounds, an aldehyde-modified mesoporous silica SBA-15 (CHO-SBA-15)-bonded anticancer drug combined with doxorubicin hydrochloride (DOX) was synthesized via a Schiff base reaction. Due to the acid-sensitive imine bonds formed between CHO-SBA-15 and DOX, the as-prepared nanocomposites exhibited pH-responsive drug releasing behaviours, resulting in a more enhanced cytotoxic effect on DOX-resistant tumour cells than that of free drugs. Notably, the in vivo studies indicated that mice treated with CHO-SBA-15/DOX composites evidently showed more attenuated systemic toxicity than the free drug molecules. The siliceous mesopore Schiff base-bonded anticancer drug nanocomposite, with minimal chemical modifications, provides a simplified yet efficient therapeutic nanoplatform to deal with drug-resistant cancer.

Novel Methotrexate-Ciprofloxacin Loaded Alginate-Clay Based Nanocomposite as Anticancer and Antibacterial Co-Drug Delivery System

Purpose: In last decades, by increasing multi-drug resistant microbial pathogens an urgent demand was felt in the development of novel antimicrobial agents. Methods: Promising nanocomposites composed of clay/alginate/imidazolium-based ionic liquid, have been developed via intercalation of calcium alginate and ionic liquid by ion exchange method. These tailored nanocomposites were used as nanocarriers to simultaneously deliver methotrexate (MTX), and ciprofloxacin (CIP), as anticancer and antibacterial agents, respectively to MCF-7 breast cancer cells. Nanocomposites were fully characterized by scanning electron microscopy studies (SEM), X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, and thermogravimetric analysis (TGA) methods. The in vitro antimicrobial potential of the mentioned nanocomposites in free and dual-drug loaded form was investigated on Pseudomonas aeruginosa and Escherichia coli bacteria. The antitumor activity of nano-formulations was evaluated by both MTT assay and cell cycle arrest. Results: The dual drug-loaded nanocomposites with exceptionally high loading efficiency (MTX: 99 ±0.4% and CIP: 98 ±1.2%) and mean particle size of 70 nm were obtained with obvious pH-responsive MTX and CIP release (both drugs release rate was increased at pH 5.8 compared to 7.4). The antibacterial activity of CIP-loaded nanocomposites was significantly higher in comparison with free CIP (P <0.001). The antitumor activity results revealed that MTX cytotoxicity on MCF-7 cells was significantly higher in nano-formulations compared to free MTX (P <0.001). Both MTX-loaded nanocomposites caused S-phase arrest in MCF-7 cells compared to non-treated cells (P ˂ 0.001). Conclusion: Newly developed smart nanocomposites are potentially effective pH-sustainable delivery systems for enhanced tumor therapy.

The Antibacterial Effects of Supermolecular Nano-Carriers by Combination of Silver and Photodynamic Therapy

The over-use of antibiotics has promoted multidrug resistance and decreased the efficacy of antibiotic therapy. Thus, it is still in great need to develop efficient treatment strategies to combat the bacteria infection. The antimicrobial photodynamic therapy (aPDT) and silver nanoparticles have been emerged as effective antibacterial methods. However, the silver therapy may induce serious damages to human cells at high concentrations and, the bare silver nanoparticles may rapidly aggregate, which would reduce the antibacterial efficacy. The encapsulation of sliver by nano-carrier is a promising way to avoid its aggregation and facilitates the co-delivery of drugs for combination therapy, which does not require high concentration of sliver to exert antibacterial efficacy. This work constructed a self-assembled supermolecular nano-carrier consisting of the photosensitizers (PSs), the anti-inflammatory agent and silver. The synthesized supermolecular nano-carrier produced reactive oxygen species (ROS) under the exposure of 620-nm laser. It exhibited satisfying biocompatibility in L02 cells. And, this nano-carrier showed excellent antibacterial efficacy in Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as indicated by bacterial growth and colony formation. Its antibacterial performance is further validated by the bacteria morphology through the scanning electron microscope (SEM), showing severely damaged structures of bacteria. To summary, the supermolecular nano-carrier TCPP-MTX-Ag-NP combining the therapeutic effects of ROS and silver may serve as a novel strategy of treatment for bacterial infection.

Biomedical application of mesoporous silica nanoparticles as delivery systems: a biological safety perspective

The application of mesoporous silica nanoparticles (MSNs) as drug delivery systems to deliver drugs, proteins, and genes has expanded considerably in recent years, using in vitro and animal studies. For future translation to clinical applications, the biological safety aspects of MSNs must be considered carefully. This paper reviews the biosafety of MSNs, examining key issues such as biocompatibility, effects on immune cells and erythrocytes, biodistribution, biodegradation and clearance, and how these vary depending on the effects of the physical and chemical properties of MSNs such as particle size, porosity, morphology, surface charge, and chemical modifications. The future use of MSNs as a delivery system must extend beyond what has been learnt thus far using rodent animal models to encompass larger animals.

SiO2-Ag Composite as a Highly Virucidal Material: A Roadmap that Rapidly Eliminates SARS-CoV-2

COVID-19, as the cause of a global pandemic, has resulted in lockdowns all over the world since early 2020. Both theoretical and experimental efforts are being made to find an effective treatment to suppress the virus, constituting the forefront of current global safety concerns and a significant burden on global economies. The development of innovative materials able to prevent the transmission, spread, and entry of COVID-19 pathogens into the human body is currently in the spotlight. The synthesis of these materials is, therefore, gaining momentum, as methods providing nontoxic and environmentally friendly procedures are in high demand. Here, a highly virucidal material constructed from SiO2-Ag composite immobilized in a polymeric matrix (ethyl vinyl acetate) is presented. The experimental results indicated that the as-fabricated samples exhibited high antibacterial activity towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as towards SARS-CoV-2. Based on the present results and radical scavenger experiments, we propose a possible mechanism to explain the enhancement of the biocidal activity. In the presence of O2 and H2O, the plasmon-assisted surface mechanism is the major reaction channel generating reactive oxygen species (ROS). We believe that the present strategy based on the plasmonic effect would be a significant contribution to the design and preparation of efficient biocidal materials. This fundamental research is a precedent for the design and application of adequate technology to the next-generation of antiviral surfaces to combat SARS-CoV-2.

Polymeric Nanoparticles for Antimicrobial Therapies: An Up-To-Date Overview

Despite the many advancements in the pharmaceutical and medical fields and the development of numerous antimicrobial drugs aimed to suppress and destroy pathogenic microorganisms, infectious diseases still represent a major health threat affecting millions of lives daily. In addition to the limitations of antimicrobial drugs associated with low transportation rate, water solubility, oral bioavailability and stability, inefficient drug targeting, considerable toxicity, and limited patient compliance, the major cause for their inefficiency is the antimicrobial resistance of microorganisms. In this context, the risk of a pre-antibiotic era is a real possibility. For this reason, the research focus has shifted toward the discovery and development of novel and alternative antimicrobial agents that could overcome the challenges associated with conventional drugs. Nanotechnology is a possible alternative, as there is significant evidence of the broad-spectrum antimicrobial activity of nanomaterials and nanoparticles in particular. Moreover, owing to their considerable advantages regarding their efficient cargo dissolving, entrapment, encapsulation, or surface attachment, the possibility of forming antimicrobial groups for specific targeting and destruction, biocompatibility and biodegradability, low toxicity, and synergistic therapy, polymeric nanoparticles have received considerable attention as potential antimicrobial drug delivery agents. In this context, the aim of this paper is to provide an up-to-date overview of the most recent studies investigating polymeric nanoparticles designed for antimicrobial therapies, describing both their targeting strategies and their effects.

Catalytic Nanomaterials toward Atomic Levels for Biomedical Applications: From Metal Clusters to Single-Atom Catalysts

Single-atom catalysts (SACs) featuring the complete atomic utilization of metal, high-efficient catalytic activity, superior selectivity, and excellent stability have been emerged as a frontier in the catalytic field. Recently, increasing interests have been drawn to apply SACs in biomedical fields for enzyme-mimic catalysis and disease therapy. To fulfill the demand of precision and personalized medicine, precisely engineering the structure and active site toward atomic levels is a trend for nanomedicines, promoting the evolution of metal-based biomedical nanomaterials, particularly biocatalytic nanomaterials, from nanoparticles to clusters and now to SACs. This review outlines the syntheses, characterizations, and catalytic mechanisms of metal clusters and SACs, with a focus on their biomedical applications including biosensing, antibacterial therapy, and cancer therapy, as well as an emphasis on their in vivo biological safeties. Challenges and future perspectives are ultimately prospected for SACs in diverse biomedical applications.

Cetyltrimethylammonium Bromide (CTAB)-Loaded SiO2-Ag Mesoporous Nanocomposite as an Efficient Antibacterial Agent

To date, Ag-based nanomaterials have demonstrated a high potential to overcome antibiotic resistance issues. However, bare Ag nanomaterials are prone to agglomeration in the biological environment, which results in a loss of antibacterial activity over time. Furthermore, it is still challenging to collect small-sized Ag nanomaterials right after the synthesis process. In this study, spherical-shaped Ag nanoparticles (NPs) (~6–10 nm) were attached on the surface of cetyltrimethylammonium bromide (CTAB)-loaded mesoporous silica nanoparticles (MSNs) (~100–110 nm). Antibacterial activity tests suggested that the obtained nanocomposite can be used as a highly efficient antibacterial agent against both Gram-negative and Gram-positive bacterial strains. The minimum inhibitory concentration (MIC) recalculated to pure Ag weight in nanocomposite was found to be ~1.84 µg/mL (for Escherichia coli) and ~0.92 µg/mL (for Staphylococcus aureus)—significantly smaller compared to values reported to date. The improved antibacterial activity of the prepared nanocomposite can be attributed to the even distribution of non-aggregated Ag NPs per volume unit and the presence of CTAB in the nanocomposite pores.

pH-Responsive "Smart" Hydrogel for Controlled Delivery of Silver Nanoparticles to Infected Wounds

Persistent wound infections have been a therapeutic challenge for a long time. Current treatment approaches are mostly based on the delivery of antibiotics, but these are not effective for all infections. Here, we report the development of a sensitive pH-responsive hydrogel that can provide controlled, pH-triggered release of silver nanoparticles (AgNPs). This delivery system was designed to sense the environmental pH and trigger the release of AgNPs when the pH changes from acidic to alkaline, as occurs due to the presence of pathogenic bacteria in the wound. Our results show that the prepared hydrogel restricts the release of AgNPs at acidic pH (pH = 4) but substantially amplifies it at alkaline pH (pH = 7.4 and pH = 10). This indicates the potential use of the hydrogel for the on-demand release of Ag+ depending on the environmental pH. In vitro antibacterial studies demonstrated effective elimination of both Gram-negative and positive bacteria. Additionally, the effective antibacterial dose of Ag+ showed no toxicity towards mammalian skin cells. Collectively, this pH-responsive hydrogel presents potential as a promising new material for the treatment of infected wounds.

Size-Dependent Bioactivity of Silver Nanoparticles: Antibacterial Properties, Influence on Copper Status in Mice, and Whole-Body Turnover

Purpose

The ability of silver nanoparticles (AgNPs) of different sizes to influence copper metabolism in mice is assessed.

Materials and Methods

AgNPs with diameters of 10, 20, and 75 nm were fabricated through a chemical reduction of silver nitrate and characterized by UV/Vis spectrometry, transmission and scanning electronic microscopy, and laser diffractometry. To test their bioactivity, Escherichia coli cells, cultured A549 cells, and C57Bl/6 mice were used. The antibacterial activity of AgNPs was determined by inhibition of colony-forming ability, and cytotoxicity was tested using the MTT test (viability, %). Ceruloplasmin (Cp, the major mammalian extracellular copper-containing protein) concentration and enzymatic activity were measured using gel-assay analyses and WB, respectively. In vitro binding of AgNPs with serum proteins was monitored with UV/Vis spectroscopy. Metal concentrations were measured using atomic absorption spectrometry.

Results

The smallest AgNPs displayed the largest dose- and time-dependent antibacterial activity. All nanoparticles inhibited the metabolic activity of A549 cells in accordance with dose and time, but no correlation between cytotoxicity and nanoparticle size was found. Nanosilver was not uniformly distributed through the body of mice intraperitoneally treated with low AgNP concentrations. It was predominantly accumulated in liver. There, nanosilver was included in ceruloplasmin, and Ag-ceruloplasmin with low oxidase activity level was formed. Larger nanoparticles more effectively interfered with the copper metabolism of mice. Large AgNPs quickly induced a drop of blood serum oxidase activity to practically zero, but after cancellation of AgNP treatment, the activity was rapidly restored. A major fraction of the nanosilver was excreted in the bile with Cp. Nanosilver was bound by alpha-2-macroglobulin in vitro and in vivo, but silver did not substitute for the copper atoms of Cp in vitro.

Conclusion

The data showed that even at low concentrations, AgNPs influence murine copper metabolism in size-dependent manner. This property negatively correlated with the antibacterial activity of AgNPs.

Self-assembled nanogels of luminescent thiolated silver nanoclusters and chitosan as bactericidal agent and bacterial sensor

Multifunctional theranostic agents with the features of good biocompatibility, long-term antibacterial efficacy, and rapid bacterial detection are the desired future medicine for infectious diseases, but which poses huge challenges on the design of such multifunctional nanocomposites in a single entity. Herein, self-assembled nanogels of thiolated silver nanoclusters (Ag NCs) and chitosan was designed and synthesized, which combines the desirable biocompatible, targeting specific, luminescent properties. This nanogel displays an amplified luminescence via strong matrix-ligand coordination between thiolate ligands and chitosan matrix to rigidify the molecular structure on the surface of Ag NCs. Concomitantly, this nanogel exhibits exceptional bactericidal activity, with approximately >10-fold stronger activity compared to its counterpart Ag NCs. Furthermore, a bacterial detection system was developed based on the bacterial binding on the fluorescent nanogels. This work provides a new strategy in designing multifunctional theranostic agents and this new composite Ag NC nanogel holds great promise for practical applications as the theranostic nanomedicines.