Colloid particle formulations for antimicrobial applications

High-performance photocatalytic degradation and antifungal activity of chromium-doped nickel oxide nanoparticles

The elimination of pollutants such as dyes and fungi has become a tedious process hence there is a need for multifunctional materials that can be used for the removal or degradation of various pollutants from wastewater. Here, a nickel oxide nanoparticle (NiONPs) was synthesized by the co-precipitation method. In the current study, a composite of nickel oxide nanoparticles (NiONPs) was synthesized using nitrogen and chromium as dopants to create (N/NiONPs) and (Cr/N/NiONPs), respectively and used for the removal of dyes and fungi. The synthesized nanocomposites were characterized using zeta potential (ZP), scanning electron microscopy (SEM), X-rays diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The NiONPs, N/NiONPs and Cr/N/NiONPs were tested for the degradation of two dye pollutants, Reactive blue 13 (RB13) and eosin dye. The obtained results showed that Cr/N/NiONPs were more efficient than NiONPs and N/NiONPs for dye degradation by applying the same irradiation conditions. The Cr/N/NiONPs nanocomposites showed very good degradation efficiency of dye up to 94.2% for the RB13 and 90.8% for the eosin. We also examined the antifungal action of the NiONPs, N/NiONPs and Cr/N/NiONPs against Trichoderma fungus. The results showed that the Cr/N/NiONPs have an extremely strong antifungal impact on Trichoderma. This could be explained by the strong adhesion of Cr/N/NiONPs to the Trichoderma surface due to electrostatic attraction. This work has demonstrated that it is possible to create environmentally safe materials that can be used for the degradation of different dyes and the improvement of more effective antifungal treatments with lower active agent doses for fungus control with potential big economic benefits.

Green One-Step Synthesis of Silver Nanoparticles Obtained from Schinus areira Leaf Extract: Characterization and Antibacterial Mechanism Analysis

The increased emergence of antibiotic-resistant bacteria is a serious health problem worldwide. In this sense, silver nanoparticles (AgNPs) have received increasing attention for their antimicrobial activity. In this context, the goal of this study was to produce AgNPs by a green synthesis protocol using an aqueous leaf extract of Schinus areira as biocomposite to later characterize their antimicrobial action. The nanomaterials obtained were characterized by UV‒vis spectroscopy, DLS, TEM, and Raman, confirming the presence of quasi-spherical AgNPs with a negative surface charge and diameter around 11 nm. Afterward, the minimum inhibitory and bactericidal concentration of the AgNPs against Staphylococcus aureus and Escherichia coli were obtained, showing high antibacterial activity. In both of the examined bacteria, the AgNPs were able to raise intracellular ROS levels. In E. coli, the AgNPs can harm the bacterial membrane as well. Overall, it can be concluded that it was possible to obtain AgNPs with colloidal stability and antibacterial activity against Gram-positive and Gram-negative bacteria. Our findings point to at least two separate mechanisms that can cause cell death, one of which involves bacterial membrane damage and the other of which involves intracellular ROS induction.

Probing analysis of Cu-doping on the structural, optical, morphological and magnetic properties of hematite nanoparticles and their antibacterial activity

The present study describes the synthesis of pure and Cu doped α-Fe2O3nanoparticles (with various concentrations of Copper 1, 3, 6, and 9 wt%) by conventional chemical precipitation technique and examines their structural, morphological, optical, magnetic, and antibacterial capabilities. The XRD pattern of pure and Cu-doped α-Fe2O3 nanoparticles exhibit rhombohedral structure and the estimated crystalline sizes were ranged from 39 to 58 nm. It is discovered that the estimated density dislocations linked to the agglomeration/cluster formations diminish when interstitial vacancies are filled with copper. The obtained bandgap from Tauc's plot, 2.07 eV of pure α-Fe2O3 is found to less than Cu doped α-Fe2O3 nanoparticles (2.9-3.4 eV), due to the structural changes and the tailing of localised states into deep bandgap energy levels. The intense blue emission bands (410-490 nm) arised due to the movement of trapped electrons from the donor level to the valance band and broad green emission bands (522-560 nm) are due to deep level CuO defect to the Fe2O3. The fundamental stretching of Fe-O vibrations and the presence of Cu in prepared samples were identified in FTIR and Raman spectra. SEM micrograph shows the uniform distribution of spherical nanoparticles with size ranged from 39 to 61 nm, which is in good accord with XRD studies. Further, the magnetic characteristics of the pure and Cu-doped α-Fe2O3 samples were assessed using a vibrating sample magnetometer (VSM); the ensuing hysteresis loop of the Cu-doped α-Fe2O3 displays weaker ferromagnetic behaviour. In the present investigations, the disc diffusion technique has been used to examine the antibacterial activity. Thus, the results of antibacterial activities demonstrated that at concentrations of 200 and 500 μg/ml of pure and Cu-doped α-Fe2O3 NPs, the highest zone of inhibition was found against gram (+ve) positive bacteria and was followed by the gram (-ve) negative bacteria's.

Outstanding Performance of Mg/g-C3N4-Doped Al2O3 Serving as a Nanocatalyst and Its Bactericidal Behavior: An In Silico Molecular Docking Study

A coprecipitation approach was employed to synthesize aluminum oxide (Al2O3) with a fixed quantity of graphitic carbon nitride (g-C3N4) and various concentrations of Mg (2 and 4 wt. %). The main objective of this research is to explore and enhance the dye degradation potential and antimicrobial efficacy of synthesized pristine and doped Al2O3 with molecular docking analysis. Al2O3 has potent mechanical, thermal, antimicrobial, phosphoric, optical, and electrical properties, but it leaches into water and has a high band gap and low refractive index. g-C3N4 was incorporated into Al2O3 to increase the degradation potency. The incorporation of Mg enhances the metal oxide characteristics and performance in catalysis. XRD patterns revealed the orthorhombic phase of Al2O3. The SAED pattern of Al2O3 and (2 and 4 wt %) Mg/g-C3N4-Al2O3 nanostructures (NSs) showed bright polycrystalline rings. UV-visible spectra showed the absorption of Al2O3 at 289 nm, and upon doping, a blue shift was accompanied. The EDS spectra indicated the existence of Al, O, Na, and Mg, thereby verifying the elemental composition of the pristine and doped samples. TEM images revealed the nanowires (NWs) of Al2O3. The NSs demonstrated outstanding catalytic performance for the remediation of RhB dye in a basic medium of around 97.36%. Mg/g-C3N4-Al2O3 (4 wt %) exhibited a notable augmentation in the inhibition zone, measuring 5.25 mm, when exposed to high-level doses against Staphylococcus aureus. In silico predictions have recently shed light on the underlying mystery of the bactericidal actions of these doped NSs against specific enzyme targets such as DNA gyraseS. aureus.

Bioactive ZnO Nanoparticles: Biosynthesis, Characterization and Potential Antimicrobial Applications

In recent years, biosynthesized zinc oxide nanoparticles (ZnONPs) have gained tremendous attention because of their safe and non-toxic nature and distinctive biomedical applications. A diverse range of microbes (bacteria, fungi and yeast) and various parts (leaf, root, fruit, flower, peel, stem, etc.) of plants have been exploited for the facile, rapid, cost-effective and non-toxic synthesis of ZnONPs. Plant extracts, microbial biomass or culture supernatant contain various biomolecules including enzymes, amino acids, proteins, vitamins, alkaloids, flavonoids, etc., which serve as reducing, capping and stabilizing agents during the biosynthesis of ZnONPs. The biosynthesized ZnONPs are generally characterized using UV-VIS spectroscopy, TEM, SEM, EDX, XRD, FTIR, etc. Antibiotic resistance is a serious problem for global public health. Due to mutation, shifting environmental circumstances and excessive drug use, the number of multidrug-resistant pathogenic microbes is continuously rising. To solve this issue, novel, safe and effective antimicrobial agents are needed urgently. Biosynthesized ZnONPs could be novel and effective antimicrobial agents because of their safe and non-toxic nature and powerful antimicrobial characteristics. It is proven that biosynthesized ZnONPs have strong antimicrobial activity against various pathogenic microorganisms including multidrug-resistant bacteria. The possible antimicrobial mechanisms of ZnONPs are the generation of reactive oxygen species, physical interactions, disruption of the cell walls and cell membranes, damage to DNA, enzyme inactivation, protein denaturation, ribosomal destabilization and mitochondrial dysfunction. In this review, the biosynthesis of ZnONPs using microbes and plants and their characterization have been reviewed comprehensively. Also, the antimicrobial applications and mechanisms of biosynthesized ZnONPs against various pathogenic microorganisms have been highlighted.

Mechanistic insights into the cinnamaldehyde modification of lignin for sustainable anti-fungal reagent

The limited anti-fungal activity of enzymatic hydrolysis lignin (EHL) has been a challenge in its direct application as a bamboo preservative. To address this issue, the cinnamaldehyde modification of EHL was carried out to introduce anti-fungal structures into the lignin matrix, effectively enhancing its anti-fungal activity. The results demonstrated that the minimal inhibitory concentrations of the modified lignin (EHL-DC) against Aspergillus niger significantly improved from 16 mg/mL to 1 mg/mL, with comparable enhancements in anti-fungal activity against other fungi. As a result of the modification, the EHL-DC is more prone to interact with fungal cell membranes, contributing to a roughened, shrunken hyphal surface and a decrease in mycelial biomass. Multiple characterization methods were employed to better grapple with the EHL-DC chemical changes. The nitrogen content increased from 2.3 % to 8.3 %, and alterations in elemental compositions further support the proposed reaction mechanism and its role in enhancing EHL's anti-fungal activity. This study offers novel insights into the high-value utilization of enzymatic hydrolysis lignin based on green chemistry principles.

Superior possibilities and upcoming horizons for nanoscience in COVID-19: noteworthy approach for effective diagnostics and management of SARS-CoV-2 outbreak

The outbreak of COVID-19 has caused great havoc and affected many parts of the world. It has imposed a great challenge to the medical and health fraternity with its ability to continue mutating and increasing the transmission rate. Some challenges include the availability of current knowledge of active drugs against the virus, mode of delivery of the medicaments, its diagnosis, which are relatively limited and do not suffice for further prognosis. One recently developed drug delivery system called nanoparticles is currently being utilized in combating COVID-19. This article highlights the existing methods for diagnosis of COVID-19 such as computed tomography scan, reverse transcription-polymerase chain reaction, nucleic acid sequencing, immunoassay, point-of-care test, detection from breath, nanotechnology-based bio-sensors, viral antigen detection, microfluidic device, magnetic nanosensor, magnetic resonance platform and internet-of-things biosensors. The latest detection strategy based on nanotechnology, biosensor, is said to produce satisfactory results in recognizing SARS-CoV-2 virus. It also highlights the successes in the research and development of COVID-19 treatments and vaccines that are already in use. In addition, there are a number of nanovaccines and nanomedicines currently in clinical trials that have the potential to target COVID-19.

Nanostructured γ-Al2O3 Synthesis Using an Arc Discharge Method and its Application as an Antibacterial Agent against XDR Bacteria

In the last few years, many efforts have been devoted to investigating the antibacterial activity of metal nanoparticles, especially against multidrug-resistant bacteria. Recently extensively drug-resistant (XDR) bacteria have emerged and caused a global threat. The purpose of this manuscript was to synthesize nanostructured γ-Al2O3 as an antibacterial agent against some XDRs. The results showed that Al2O3 was a mix of rod and spherical shapes in the nano range with diameters of less than 30 nm. The zeta potential was determined to estimate the surface charge for the synthesized γ-Al2O3, which was recorded as −34 ± 1.8 mV, indicating good stability. The synthesized nanostructured γ-Al2O3 showed a potent antibacterial activity against extensively drug-resistant Acinetobacter baumanii, with an inhibition zone diameter that reached 19 mm and a minimum inhibitory concentration (MIC) value that reached 2 µg/mL. The observed antibacterial activity of the prepared Al2O3 nanoparticles confirmed that the main mechanistic actions include bacterial cells apoptosis, ROS increment, cellular membrane disruption, and DNA damage. The cytotoxic effect (CC50) of the prepared γ-Al2O3-NPs was 1250 µg/mL in a normal human lung fibroblast cell line (WI-38 cells). It can be concluded that the synthesized γ-Al2O3 had an acceptable toxicity, which may pave the way for its use as a potent agent in the fight against XDR bacteria.

Synthesis, biomedical applications, and toxicity of CuO nanoparticles

Versatile nature of copper oxide nanoparticles (CuO NPs) has made them an imperative nanomaterial being employed in nanomedicine. Various physical, chemical, and biological methodologies are in use for the preparation of CuO NPs. The physicochemical and biological properties of CuO NPs are primarily affected by their method of fabrication; therefore, selectivity of a synthetic technique is immensely important that makes these NPs appropriate for a specific biomedical application. The deliberate use of CuO NPs in biomedicine questions their biocompatible nature. For this reason, the present review has been designed to focus on the approaches employed for the synthesis of CuO NPs; their biomedical applications highlighting antimicrobial, anticancer, and antioxidant studies; and most importantly, the in vitro and in vivo toxicity associated with these NPs. This comprehensive overview of CuO NPs is unique and novel as it emphasizes on biomedical applications of CuO NPs along with its toxicological assessments which would be useful in providing core knowledge to researchers working in these domains for planning and conducting futuristic studies. KEY POINTS: • The recent methods for fabrication of CuO nanoparticles have been discussed with emphasis on green synthesis methods for different biomedical approaches. • Antibacterial, antioxidant, anticancer, antiparasitic, antidiabetic, and antiviral properties of CuO nanoparticles have been explained. • In vitro and in vivo toxicological studies of CuO nanoparticles exploited along with their respective mechanisms.

Recent Trends in Composite Nanozymes and Their Pro-Oxidative Role in Therapeutics

Nanozymes are inorganic nanostructures whose enzyme mimic activities are increasingly explored in disease treatment, taking inspiration from natural enzymes. The catalytic ability of nanozymes to generate reactive oxygen species can be used for designing effective antimicrobials and antitumor therapeutics. In this context, composite nanozymes are advantageous, particularly because they integrate the properties of various nanomaterials to offer a single multifunctional platform combining photodynamic therapy (PDT), photothermal therapy (PTT), and chemodynamic therapy (CDT). Hence, recent years have witnessed great progress in engineering composite nanozymes for enhanced pro-oxidative activity that can be utilized in therapeutics. Therefore, the present review traverses over the newer strategies to design composite nanozymes as pro-oxidative therapeutics. It provides recent trends in the use of composite nanozymes as antibacterial, antibiofilm, and antitumor agents. This review also analyzes various challenges yet to be overcome by pro-oxidative composite nanozymes before being used in the field.

Sustainable Antibacterial and Antiviral High-Performance Copper-Coated Filter Produced via Ion Beam Treatment

With the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), disease prevention has become incredibly important. Consequently, mask and air-purifier use has increased. The filter is the core component of these items. However, most filter materials lack antimicrobial properties. Copper is a sustainable antimicrobial material. When copper is deposited onto the filter’s surface, the microorganisms that come into contact with it can be effectively inactivated. In this study, we used an oxygen ion beam with a controlled process temperature to treat filter surfaces with copper. This enabled a strong adhesion of at least 4 N/cm between the copper and the filter fibers without damaging them. Upon exposing the filter to bacteria (Staphylococcus aureus ATCC 6538, Klebsiella pneumoniae ATCC 4352, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853) for one hour, a >99.99% removal rate was attained; when the filter was exposed to SARS-CoV-2 virus for one hour, it inactivated more than 99%. These beneficial properties minimize the risk of secondary infections, which are significantly more likely to occur when a conventional filter is replaced or removed.

Activity of Fusarium oxysporum-Based Silver Nanoparticles on Candida spp. Oral Isolates

Candida spp. resistant to commercially available antifungals are often isolated from patients with oral candidiasis, a situation that points to the need for the development of new therapies. Thus, we evaluated the activity of Fusarium oxysporum-based silver nanoparticles (AgNPs) on Candida spp. isolated from denture stomatitis lesions. Candida isolates were molecularly identified and submitted to susceptibility assays using AgNPs and commercial fungicides. The interference on biofilm formation and the mechanisms of action of AgNPs on Candida spp. were also investigated. Scanning electron microscopy was used to evaluate the morphology of AgNP-treated Candida. Candida albicans was the most frequent species isolated from denture stomatitis cases. All Candida spp. were susceptible to AgNPs at low concentrations, except Candida parapsilosis. AgNPs caused surface damage, cell disruption, and biofilm formation inhibition. The ergosterol supplementation protected C. albicans against the AgNP action. AgNPs are effective against Candida spp. and can be faced as a promising new therapeutic agent against oral candidiasis.

A review on coronavirus survival on impermeable and porous surfaces

We review recent studies on fomite transmission of COVID-19, caused by the novel coronavirus. In particular, we focus on survival time of coronavirus on solid and porous surfaces. Since the aqueous phase of a respiratory droplet serves as a medium for virus survival, evaporation of the droplet on a surface plays a crucial role in determining the virus survival time. While the bulk of the droplet takes a few seconds to evaporate, previous virus titer measurements revealed that the virus can survive for several hours or days on a surface. This long survival of virus has been attributed to a residual thin-liquid film which remains after drying of the bulk droplet. The evaporation of the thin-film is governed by the disjoining pressure within it and therefore, is a much slower process which causes the virus to survive longer. However, the aforesaid disjoining pressure is significantly modulated for the case of porous surfaces due to their typical geometries. This accelerates the thin-film evaporation on porous surfaces and thereby making them lesser susceptible to virus survival. Therefore, porous materials are deemed to be relatively safer for mitigating the spread of COVID-19 via fomite transmission. Using results of the reported research, we briefly discuss the possible recommendations to mitigate the spread of the disease.

Selective strategies for antibacterial regulation of nanomaterials

Recalcitrant bacterial infection, as a worldwide challenge, causes large problems for human health and is attracting great attention. The excessive antibiotic-dependent treatment of infections is prone to induce antibiotic resistance. A variety of unique nanomaterials provide an excellent toolkit for killing bacteria and preventing drug resistance. It is of great importance to summarize the design rules of nanomaterials for inhibiting the growth of pathogenic bacteria. We completed a review involving the strategies for regulating antibacterial nanomaterials. First, we discuss the antibacterial manipulation of nanomaterials, including the interaction between the nanomaterial and the bacteria, the damage of the bacterial structure, and the inactivation of biomolecules. Next, we identify six main factors for controlling the antibacterial activity of nanomaterials, including their element composition, size dimensions, surface charge, surface topography, shape selection and modification density. Every factor possesses a preferable standard for maximizing antibacterial activity, providing universal rules for antibacterial regulation of nanomaterials. We hope this comprehensive review will help researchers to precisely design and synthesize nanomaterials, developing intelligent antibacterial agents to address bacterial infections.

This review builds universal design rules for the antibacterial regulation of nanomaterials.

Polymeric Nanomaterials for Efficient Delivery of Antimicrobial Agents

Bacterial infections have threatened the lives of human beings for thousands of years either as major diseases or complications. The elimination of bacterial infections has always occupied a pivotal position in our history. For a long period of time, people were devoted to finding natural antimicrobial agents such as antimicrobial peptides (AMPs), antibiotics and silver ions or synthetic active antimicrobial substances including antimicrobial peptoids, metal oxides and polymers to combat bacterial infections. However, with the emergence of multidrug resistance (MDR), bacterial infection has become one of the most urgent problems worldwide. The efficient delivery of antimicrobial agents to the site of infection precisely is a promising strategy for reducing bacterial resistance. Polymeric nanomaterials have been widely studied as carriers for constructing antimicrobial agent delivery systems and have shown advantages including high biocompatibility, sustained release, targeting and improved bioavailability. In this review, we will highlight recent advances in highly efficient delivery of antimicrobial agents by polymeric nanomaterials such as micelles, vesicles, dendrimers, nanogels, nanofibers and so forth. The biomedical applications of polymeric nanomaterial-based delivery systems in combating MDR bacteria, anti-biofilms, wound healing, tissue engineering and anticancer are demonstrated. Moreover, conclusions and future perspectives are also proposed.

Biocidal activity of Ba2+-doped CeO2 NPs against Streptococcus mutans and Staphylococcus aureus bacterial strains

Mishandling of antibiotics often leads to the development of multiple drug resistance (MDR) among microbes, resulting in the failure of infection treatments and putting human health at great risk. As a response, unique nanomaterials with superior bioactivity must be developed to combat bacterial infections. Herein, CeO2-based nanomaterials (NMs) were synthesized by employing cerium(iii) nitrate and selective alkaline ions. Moreover, the influence of alkaline ions on CeO2 was investigated, and their characteristics, viz.: biochemical, structural, and optical properties, were altered. The size of nano Ba-doped CeO2 (BCO) was ∼2.3 nm, relatively smaller than other NMs and the antibacterial potential of CeO2, Mg-doped CeO2 (MCO), Ca-doped CeO2 (CCO), Sr-doped CeO2 (SCO), and Ba-doped CeO2 (BCO) NMs against Streptococcus mutans (S. mutans) and Staphylococcus aureus (S. aureus) strains was assessed. BCO outperformed all NMs in terms of antibacterial efficacy. In addition, achieving the enhanced bioactivity of BCO due to reduced particle size facilitated the easy penetration into the bacterial membrane and the presence of a sizeable interfacial surface. In this study, the minimum quantity of BCO required to achieve the complete inhibition of bacteria was determined to be 1000 μg mL-1 and 1500 μg mL-1 for S. mutans and S. aureus, respectively. The cytotoxicity test with L929 fibroblast cells demonstrated that BCO was less toxic to healthy cells. Furthermore, BCO did not show any toxicity and cell morphological changes in the L929 fibroblast cells, which is similar to the control cell morphology. Overall, the results suggest that nano BCO can be used in biomedical applications, which can potentially help improve human health conditions.

Enhanced Antimicrobial Action of Chlorhexidine Loaded in Shellac Nanoparticles with Cationic Surface Functionality

We report on an active nanocarrier for chlorhexidine (CHX) based on sterically stabilized shellac nanoparticles (NPs) with dual surface functionalization, which greatly enhances the antimicrobial action of CHX. The fabrication process for the CHX nanocarrier is based on pH-induced co-precipitation of CHX-DG from an aqueous solution of ammonium shellac and Poloxamer 407 (P407), which serves as a steric stabilizing agent. This is followed by further surface modification with octadecyl trimethyl ammonium bromide (ODTAB) through a solvent change to yield cationic surface functionality. In this study, we assessed the encapsulation efficiency and release kinetics of the novel nanocarrier for CHX. We further examined the antimicrobial effects of the CHX nanocarriers and their individual components in order to gain better insight into how they work, to improve their design and to explore the impacts of their dual functionalization. The antimicrobial actions of CHX loaded in shellac NPs were examined on three different proxy microorganisms: a Gram-negative bacterium (E. coli), a yeast (S. cerevisiae) and a microalgae (C. reinhardtii). The antimicrobial actions of free CHX and CHX-loaded shellac NPs were compared over the same CHX concentration range. We found that the non-coated shellac NPs loaded with CHX showed inferior action compared with free CHX due to their negative surface charge; however, the ODTAB-coated, CHX-loaded shellac NPs strongly amplified the antimicrobial action of the CHX for the tested microorganisms. The enhancement of the CHX antimicrobial action was thought to be due to the increased electrostatic adhesion between the cationic surface of the ODTAB-coated, CHX-loaded shellac NPs and the anionic surface of the cell walls of the microorganisms, ensuring direct delivery of CHX with a high concentration locally on the cell membrane. The novel CHX nanocarriers with enhanced antimicrobial action may potentially find applications in dentistry for the development of more efficient formulations against conditions such as gingivitis, periodontitis and other oral infections, as well as enabling formulations to have lower CHX concentrations.

Modulation of Quorum Sensing and Biofilms in Less Investigated Gram-Negative ESKAPE Pathogens

Pathogenic bacteria have the ability to sense their versatile environment and adapt by behavioral changes both to the external reservoirs and the infected host, which, in response to microbial colonization, mobilizes equally sophisticated anti-infectious strategies. One of the most important adaptive processes is the ability of pathogenic bacteria to turn from the free, floating, or planktonic state to the adherent one and to develop biofilms on alive and inert substrata; this social lifestyle, based on very complex communication networks, namely, the quorum sensing (QS) and response system, confers them an increased phenotypic or behavioral resistance to different stress factors, including host defense mechanisms and antibiotics. As a consequence, biofilm infections can be difficult to diagnose and treat, requiring complex multidrug therapeutic regimens, which often fail to resolve the infection. One of the most promising avenues for discovering novel and efficient antibiofilm strategies is targeting individual cells and their QS mechanisms. A huge amount of data related to the inhibition of QS and biofilm formation in pathogenic bacteria have been obtained using the well-established gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa models. The purpose of this paper was to revise the progress on the development of antibiofilm and anti-QS strategies in the less investigated gram-negative ESKAPE pathogens Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter sp. and identify promising leads for the therapeutic management of these clinically significant and highly resistant opportunistic pathogens.

The Molecular Basis of COVID-19 Pathogenesis, Conventional and Nanomedicine Therapy

In late 2019, a new member of the Coronaviridae family, officially designated as "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2), emerged and spread rapidly. The Coronavirus Disease-19 (COVID-19) outbreak was accompanied by a high rate of morbidity and mortality worldwide and was declared a pandemic by the World Health Organization in March 2020. Within the Coronaviridae family, SARS-CoV-2 is considered to be the third most highly pathogenic virus that infects humans, following the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV). Four major mechanisms are thought to be involved in COVID-19 pathogenesis, including the activation of the renin-angiotensin system (RAS) signaling pathway, oxidative stress and cell death, cytokine storm, and endothelial dysfunction. Following virus entry and RAS activation, acute respiratory distress syndrome develops with an oxidative/nitrosative burst. The DNA damage induced by oxidative stress activates poly ADP-ribose polymerase-1 (PARP-1), viral macrodomain of non-structural protein 3, poly (ADP-ribose) glycohydrolase (PARG), and transient receptor potential melastatin type 2 (TRPM2) channel in a sequential manner which results in cell apoptosis or necrosis. In this review, blockers of angiotensin II receptor and/or PARP, PARG, and TRPM2, including vitamin D3, trehalose, tannins, flufenamic and mefenamic acid, and losartan, have been investigated for inhibiting RAS activation and quenching oxidative burst. Moreover, the application of organic and inorganic nanoparticles, including liposomes, dendrimers, quantum dots, and iron oxides, as therapeutic agents for SARS-CoV-2 were fully reviewed. In the present review, the clinical manifestations of COVID-19 are explained by focusing on molecular mechanisms. Potential therapeutic targets, including the RAS signaling pathway, PARP, PARG, and TRPM2, are also discussed in depth.

Effective Antibacterial Activity of Degradable Copper-Doped Phosphate-Based Glass Nanozymes

Copper-containing antimicrobials are highly valuable in the field of medical disinfectants owing to their well-known high antimicrobial efficacy. Artificially synthesized nanozymes which can increase the level of reactive oxygen species (ROS) in the bacterial system have become research hotspots. Herein, we describe the design and fabrication of degradable Cu-doped phosphate-based glass (Cu-PBG) nanozyme, which can achieve excellent antibacterial effects against Gram-positive and Gram-negative bacteria. The antibacterial mechanism is based on the generation of ROS storm and the release of copper. It behaves like a peroxidase in wounds which are acidic and exerts lethal oxidative stress on bacteria via catalyzing the decomposition of H₂O₂ into hydroxyl radicals (^•OH). Quite different from any other reported nanozymes, the Cu-PBG is intrinsically degradable due to its phosphate glass nature. It gradually degrades and releases copper ions in a physiological environment, which further enhances the inhibition efficiency. Satisfactory antibacterial effects are verified both in vitro and in vivo. Being biodegradable, the prepared Cu-PBG exhibits excellent in vivo biocompatibility and does not cause any adverse effects caused by its long-time residence time in living organisms. Collectively, these results indicate that the Cu-PBG nanozyme could be used as an efficient copper-containing antimicrobial with great potential for clinical translation.

Enhanced Antimould Action of Surface Modified Copper Oxide Nanoparticles with Phenylboronic Acid Surface Functionality

Antimould agents are widely used in different applications, such as specialty paints, building materials, wood preservation and crop protection. However, many antimould agents can be toxic to the environment. This work aims to evaluate the application of copper oxide nanoparticles (CuONPs) surface modified with boronic acid (BA) terminal groups as antimould agents. We developed CuONPs grafted with (3-glycidyloxypropyl) trimethoxysilane (GLYMO), coupled with 4-hydroxyphenylboronic acid (4-HPBA), which provided a strong boost of their action as antimould agents. We studied the antimould action of the 4-HPBA-functionalized CuONPs against two mould species: Aspergillus niger (A. niger) and Penicillium chrysogenum (P. chrysogenum). The cis-diol groups of polysaccharides expressed on the mould cell walls can form reversible covalent bonds with the BA groups attached on the CuONPs surface. This allowed them to bind strongly to the mould surface, resulting in a very substantial boost of their antimould activity, which is not based on electrostatic adhesion, as in the case of bare CuONPs. The impact of these BA-surface functionalized nanoparticles was studied by measuring the growth of the mould colonies versus time. The BA-functionalized CuONPs showed significant antimould action, compared to the untreated mould sample at the same conditions and period of time. These results can be applied for the development of more efficient antimould treatments at a lower concentration of active agent with potentially substantial economic and environmental benefits.

Red Microalgal Sulfated Polysaccharide-Cu2O Complexes: Characterization and Bioactivity

The anion-exchange capacity of the cell-wall sulfated polysaccharide of the red microalga Porphyridium sp. can be exploited for the complexation of metal ions (e.g., Cu, Zn, Ag) to produce novel materials with new bioactivities. In this study, we investigated this algal polysaccharide as a platform for the incorporation of copper as Cu₂O. Chemical and rheological characterization of the Cu₂O-polysaccharide complex showed that the copper is covalently bound to the polysaccharide and that the complex exhibits higher viscosity and conductivity than the native polysaccharide. Examination of the complex's inhibitory activity against the bacteria Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis and the fungus Candida albicans revealed a relatively high antimicrobial activity, especially against C. albicans (92% growth inhibition) as compared to the polysaccharide and to Cu₂O alone. The antibiofilm activity was also found against P. aeruginosa PA14 and C. albicans biofilms. An atomic force microscopy examination of the surface morphology of the complex revealed needle-like structures (spikes), approximately 10 nm thick, protruding from the complex surface to a maximum height of 1000 nm, at a density of about 5000/μm², which were not detected in the native polysaccharide. It seems that the spikes on the surface of the Cu₂O-polysaccharide complex are responsible for the antimicrobial activities of the complex, that is, for disruption of microbial membrane permeability, leading to cell death. The study thus indicates that the superior qualities of the novel material formed by complexion of Cu₂O to the polysaccharide should be studied further for various biotechnological applications.

Antimicrobial Nanomaterials and Coatings: Current Mechanisms and Future Perspectives to Control the Spread of Viruses Including SARS-CoV-2

The global COVID-19 pandemic has attracted considerable attention toward innovative methods and technologies for suppressing the spread of viruses. Transmission via contaminated surfaces has been recognized as an important route for spreading SARS-CoV-2. Although significant efforts have been made to develop antibacterial surface coatings, the literature remains scarce for a systematic study on broad-range antiviral coatings. Here, we aim to provide a comprehensive overview of the antiviral materials and coatings that could be implemented for suppressing the spread of SARS-CoV-2 via contaminated surfaces. We discuss the mechanism of operation and effectivity of several types of inorganic and organic materials, in the bulk and nanomaterial form, and assess the possibility of implementing these as antiviral coatings. Toxicity and environmental concerns are also discussed for the presented approaches. Finally, we present future perspectives with regards to emerging antimicrobial technologies such as omniphobic surfaces and assess their potential in suppressing surface-mediated virus transfer. Although some of these emerging technologies have not yet been tested directly as antiviral coatings, they hold great potential for designing the next generation of antiviral surfaces.

Mechanisms of nanotoxicity - biomolecule coronas protect pathological fungi against nanoparticle-based eradication

Whereas nanotoxicity is intensely studied in mammalian systems, our knowledge of desired or unwanted nano-based effects for microbes is still limited. Fungal infections are global socio-economic health and agricultural problems, and current chemical antifungals may induce adverse side-effects in humans and ecosystems. Thus, nanoparticles are discussed as potential novel and sustainable antifungals via the desired nanotoxicity but often fail in practical applications. In our study, we found that nanoparticles' toxicity strongly depends on their binding to fungal spores, including the clinically relevant pathogen Aspergillus fumigatus as well as common plant pests, such as Botrytis cinerea or Penicillum expansum. Employing a selection of the model and antimicrobial nanoparticles, we found that nanoparticle-spore complex formation is influenced by the NM's physicochemical properties, such as size, identified as a key determinant for our silica model particles. Biomolecule coronas acquired in pathophysiologically and ecologically relevant environments, protected fungi against nanoparticle-induced toxicity as shown by employing antimicrobial ZnO, Ag, or CuO nanoparticles as well as dissolution-resistant quantum dots. Mechanistically, dose-dependent corona-mediated resistance was conferred via reducing the physical adsorption of nanoparticles to fungi. The inhibitory effect of biomolecules on nano-based toxicity of Ag NPs was further verified in vivo, using the invertebrate Galleria mellonella as an alternative non-mammalian infection model. We provide the first evidence that biomolecule coronas are not only relevant in mammalian systems but also for nanomaterial designs as future antifungals for human health, biotechnology, and agriculture.

Combating Antibiotic-Resistant Gram-Negative Bacteria Strains with Tetracycline-Conjugated Carbon Nanoparticles

Nontoxic carbon nanoparticle samples prepared by both bottom-up and top-down approaches do not inhibit Gram-negative bacterial growth, indicating excellent biocompatibilities. However, cell growth inhibitory efficacies increase considerably when the carbon nanoparticles are conjugated with the antibiotic tetracycline. In tetracycline-resistant bacteria, these efficacies can approach tenfold higher activities when compared to tetracycline alone. No structural abnormality such as membrane disruptions is evident in the tested bacterial strains; this is in contrast with other nanocarbon systems such as graphene oxides, carbon nanotubes, and amine-functionalized carbon nanoparticles which do exhibit membrane disruptions. In comparison, the tetracycline-conjugated carbon nanoparticles induce membrane perturbations (but not membrane disruptions), inhibiting bacterial efflux mechanisms. It is proposed that when tetracycline is conjugated to the surface of carbon nanoparticles, it functions to direct the nanoparticles to membrane-associated tetracycline efflux pumps, thereby blocking and subsequently inhibiting their function. The conjugation between biocompatible carbon nanoparticles and subtherapeutic but well-established antibiotic molecules may provide hybrid antibiotic assembly strategies resulting in effective multidrug efflux inhibition for combating antibiotic resistance.

Carboxymethyl cellulose-based materials for infection control and wound healing: A review

The development of ideal wound dressing materials with excellent characteristics is currently a major demand in wound therapy. In recent years, carboxymethyl cellulose (CMC)-based wound dressing materials have been of immense attraction due to their noble properties, such as: biocompatibility, biodegradability, tissue resembling, low cost and non-toxic. It is used extensively, in a variety of applications in the biomedical and pharmaceutical fields. The hydrophilic nature of CMC, makes it possible to blend and cross-link with other materials, such as: synthetic polymers, natural polymers and inorganic materials and it enables the preparation of innovative wound dressing biomaterials. Hence, this review, focuses on the intrinsic characteristics of CMC-based wound dressing materials, including hydrogels, films, 3D printing, fibres, gauzes and their recent advancements in chronic wound healing.

Limitations of Recent Studies Dealing with the Antibacterial Properties of Silver Nanoparticles: Fact and Opinion

Due to the constant increase in the number of infectious diseases and the concomitant lack of treatment available, metallic nanoparticles (e.g., silver nanoparticles) have been of particular interest in the last decades. Indeed, several studies suggest that silver nanoparticles have valuable antimicrobial activities, especially against bacteria, which may lead us to think that these nanoparticles may one day be an attractive therapeutic option for the treatment of bacterial infections. Unfortunately, when we look a little closer to these studies, we can see a very great heterogeneity (e.g., in the study design, in the synthetic process of nanoparticles, in the methods that explore the antibacterial properties of nanoparticles and in the bacteria chosen) making cross-interpretation between these studies impossible, and significantly limiting the interest of silver nanoparticles as promising antibacterial agents. We have selected forty-nine international publications published since 2015, and propose to discuss, not the results obtained, but precisely the different methodologies developed in these publications. Through this discussion, we highlighted the aspects to improve, or at least to homogenize, in order to definitively establish the interest of silver nanoparticles as valuable antibacterial agents.

Microbicidal Dispersions and Coatings from Hybrid Nanoparticles of Poly (Methyl Methacrylate), Poly (Diallyl Dimethyl Ammonium) Chloride, Lipids, and Surfactants

Hybrid and antimicrobial nanoparticles (NPs) of poly (methyl methacrylate) (PMMA) in the presence of poly (diallyl dimethyl ammonium) chloride (PDDA) were previously obtained by emulsion polymerization in absence of surfactant with low conversion. In the presence of amphiphiles such as cetyl trimethyl ammonium bromide (CTAB), dioctadecyl dimethyl ammonium bromide (DODAB) or soybean lecithin, we found that conversion increased substantially. In this work, the effect of the amphiphiles on the NPs core-shell structure and on the antimicrobial activity of the NPs was evaluated. NPs dispersions casted on silicon wafers, glass coverslips or polystyrene substrates were also used to obtain antimicrobial coatings. Methods for characterizing the dispersions and coatings were based on scanning electron microscopy, dynamic light scattering, determination of thickness, rugosity, and wettability for the coatings and determination of colony-forming unities (log CFU/mL) of microbia after 1 h interaction with the coatings or dispersions. The amphiphiles used during PMMA/PDDA/amphiphile NPs synthesis reduced the thickness of the NPs PDDA shell surrounding each particle. The antimicrobial activity of the dispersions and coatings were due to PDDA-the amphiphiles were either washed out by dialysis or remained in the PMMA polymeric core of the NPs. The most active NPs and coatings were those of PMMA/PDDA/CTAB-the corresponding coatings showed the highest rugosity and total surface area to interact with the microbes. The dispersions and coatings obtained by casting of the NPs dispersions onto silicon wafers were hydrophilic and exhibited microbicidal activity against Escherichia coli, Staphylococcus aureus, and Candida albicans. In addition, a major effect of reduction in particle size revealed the suitability of nanometric and cationic NPs (sizes below 100 nm) represented by PMMA/PDDA/CTAB NPs to yield maximal microbicidal activity from films and dispersions against all microbia tested. The reduction of cell viability by coatings and dispersions amounted to 6-8 logs from [PDDA] ≥ minimal microbicidal concentration.

"Ghost" Silica Nanoparticles of "Host"-Inherited Antibacterial Action

We fabricated surface-rough mesoporous silica nanoparticles ("ghost" SiO₂NPs) by using composite mesoporous copper oxide nanoparticles ("host" CuONPs) as templates, which allowed us to mimic their surface morphology. The "host" CuONPs used here as templates, however, had a very high antibacterial effect, with or without functionalization. To evaluate the surface roughness effect on the "ghost" SiO₂NPs antibacterial action, we functionalized them with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to permit additional covalent coupling of 4-hydroxyphenylboronic acid (4-HPBA). The diol groups on the bacterial membrane can form reversible covalent bonds with boronic acid (BA) groups on the "ghost" SiO₂NPs surface and bind to the bacteria, resulting in a very strong amplification of their antibacterial activity, which does not depend on electrostatic adhesion. The BA-functionalized "ghost" SiO₂NPs showed a very significant antibacterial effect as compared to smooth SiO₂NPs of the same surface coating and particle size. We attribute this to the "ghost" SiO₂NPs mesoporous surface morphology, which mimics to a certain extent those of the original mesoporous CuONPs used as templates for their preparation. We envisage that the "ghost" SiO₂NPs effectively acquire some of the antibacterial properties from the "host" CuONPs, with the same functionality, despite being completely free of copper. The antibacterial effect of the functionalized "ghost" SiO₂NPs/GLYMO/4-HPBA on Rhodococcus rhodochrous (R. rhodochrous) and Escherichia coli (E. coli) is much higher than that of the nonfunctionalized "ghost" SiO₂NPs or the "ghost" SiO₂NPs/GLYMO. The results indicate that the combination of rough surface morphology and strong adhesion of the particle surface to the bacteria can make even benign material such as silica act as a strong antimicrobial agent. Additionally, our BA-functionalized nanoparticles ("ghost" SiO₂NPs/GLYMO/4-HPBA) showed no detectable cytotoxic impact against human keratinocytes at particle concentrations, which are effective against bacteria.

Controlling the Antimicrobial Action of Surface Modified Magnesium Hydroxide Nanoparticles

Magnesium hydroxide nanoparticles (Mg(OH)2NPs) have recently attracted significant attention due to their wide applications as environmentally friendly antimicrobial nanomaterials, with potentially low toxicity and low fabrication cost. Here, we describe the synthesis and characterisation of a range of surface modified Mg(OH)2NPs, including particle size distribution, crystallite size, zeta potential, isoelectric point, X-ray diffraction (XRD), dynamic light scattering (DLS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). We explored the antimicrobial activity of the modified Mg(OH)2NPs on the microalgae (C. reinhardtii), yeast (S. cerevisiae) and Escherichia coli (E. coli). The viability of these cells was evaluated for various concentrations and exposure times with Mg(OH)2NPs. It was discovered that the antimicrobial activity of the uncoated Mg(OH)2NPs on the viability of C. reinhardtii occurred at considerably lower particle concentrations than for S. cerevisiae and E. coli. Our results indicate that the antimicrobial activity of polyelectrolyte-coated Mg(OH)2NPs alternates with their surface charge. The anionic nanoparticles (Mg(OH)2NPs/PSS) have much lower antibacterial activity than the cationic ones (Mg(OH)2NPs/PSS/PAH and uncoated Mg(OH)2NPs). These findings could be explained by the lower adhesion of the Mg(OH)2NPs/PSS to the cell wall, because of electrostatic repulsion and the enhanced particle-cell adhesion due to electrostatic attraction in the case of cationic Mg(OH)2NPs. The results can be potentially applied to control the cytotoxicity and the antimicrobial activity of other inorganic nanoparticles.

Self-grafting copper oxide nanoparticles show a strong enhancement of their anti-algal and anti-yeast action

We have developed and tested copper oxide nanoparticles (CuONPs) grafted with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) and coupled with 4-hydroxyphenylboronic acid (4-HPBA), which provides a very strong boost of their action as anti-algal and anti-yeast agents. The boronic acid terminal groups on the surface of the CuONPs/GLYMO/4-HPBA can form reversible covalent bonds with the diol groups of glycoproteins and carbohydrates expressed on the cell surface where they bind and accumulate, which is not based on electrostatic adhesion. Results showed that, the impact of the 4-HPBA grafted CuONPs on microalgae (C. reinhardtii) and yeast (S. cerevisiae) is several hundred percent higher than that of bare CuONPs and CuONPs/GLYMO at the same particle concentration. SEM and TEM imaging revealed that 4-HPBA-functionalized CuONPs nanoparticles can accumulate more on the cell walls than non-functionalized CuONPs. We found a marked increase of the 4-HPBA functionalized CuONPs action on these microorganisms at shorter incubation times compared with the bare CuONPs at the same conditions. We also showed that the anti-algal action of CuONPs/GLYMO/4-HPBA can be controlled by the concentration of glucose in the media and that the effect is reversible as glucose competes with the diol residues on the algal cell walls for the HPBA groups on the CuONPs. Our experiments with human cell lines incubated with CuONPs/GLYMO/4-HPBA indicated a lack of measurable loss of cell viability at particle concentrations which are effective as anti-algal agents. CuONPs/GLYMO/4-HPBA can be used to drastically reduce the overall CuO concentration in anti-algal and anti-yeast formulations while strongly increasing their efficiency.

Breathing new life into old antibiotics: overcoming antibacterial resistance by antibiotic-loaded nanogel carriers with cationic surface functionality

Multidrug-resistant pathogens are prevalent in chronic wounds. There is an urgent need to develop novel antimicrobials and formulation strategies that can overcome antibiotic resistance and provide a safe alternative to traditional antibiotics. This work aimed to develop a novel nanocarrier for two cationic antibiotics, tetracycline hydrochloride and lincomycin hydrochloride which can potentially overcome antibiotic resistance. In this study, we report the use of surface functionalised polyacrylic copolymer nanogels as carriers for cationic antibiotics. These nanogels can encapsulate small cationic antimicrobial molecules and act as a drug delivery system. They were further functionalised with a biocompatible cationic polyelectrolyte, bPEI, to increase their affinity towards the negatively charged bacterial cell walls. These bPEI-coated nanocarrier-encapsulated antibiotics were assessed against a range of wound isolated pathogens, which had been shown through antimicrobial susceptibility testing (AST) to be resistant to tetracycline and lincomycin. Our data reveal that bPEI-coated nanogels with encapsulated tetracycline or lincomycin displayed increased antimicrobial performance against selected wound-derived bacteria, including strains highly resistant to the free antibiotic in solution. Additionally, our nanocarrier-based antibiotics showed no detectable cytotoxic effect against human keratinocytes. We attribute the increase in the antimicrobial activity of the cationically functionalised antibiotic-loaded nanogel carriers to specific electrostatic adhesion to the microbial cell wall delivering a higher local antibiotic concentration, confirmed by scanning electron microscopy. Such a nanotechnology based approach may enhance the effectiveness of a wide variety of existing antibiotics, offering a potentially new mechanism to overcome antibiotic resistance.

Biogenic Silver Nanoparticles as a Post-surgical Treatment for Corynebacterium pseudotuberculosis Infection in Small Ruminants

Caseous lymphadenitis (CL) is an infectious and zoonotic disease characterized by the development of granulomas in the lymph nodes and internal organs of small ruminants. The etiological agent of this disease is Corynebacterium pseudotuberculosis, a Gram-positive and facultative intracellular bacterium. The conventional treatment for CL consists of drainage and chemical cauterization of the lesions using a 10% iodine solution. However, this type of treatment is not effective, due to iodine's cytotoxic profile and low antibacterial activity. Currently, silver nanoparticles (AgNPs) can be seen as an alternative treatment for CL due to their antimicrobial activity and wound healing effects. Therefore, the present study aimed to evaluate AgNPs as a post-surgical treatment for CL. Twenty-nine goats and sheep with clinical signs of CL were selected. Surgical intervention was performed to excise the caseous lesions. To treat the lesions, an ointment formulation based on AgNP mixed with natural waxes and oils was used in the experimental group, and the conventional treatment with 10% iodine was used in the control group. Bacteria were isolated from the excised caseous material. The animals were observed for 8 weeks after the surgical treatment, and blood samples were taken weekly. The surgical wounds of sheep treated with AgNP healed faster, and the surgical wound area was smaller during the observation period; the latter effect was also observed in goats. AgNP-treated animals also had less purulent discharge and less moisture in the surgical wounds. The AgNP-treated animals had lower leukocyte counts and lower titers of anti-C. pseudotuberculosis antibodies. There was no statistically significant difference between the groups with regard to the hemogram results. The results of the susceptibility testing of C. pseudotuberculosis strains (T1, 1002, FRC41, and VD57 strains) and clinical isolates to AgNPs showed growth inhibition, even at low concentrations. It can be concluded that post-surgical treatment of CL using the AgNP-based ointment may be a promising tool in the control of CL, through faster healing, decreased wound contamination, and no apparent toxic effects.

Strongly Enhanced Antibacterial Action of Copper Oxide Nanoparticles with Boronic Acid Surface Functionality

Copper oxide nanoparticles (CuONPs) have been widely recognized as good antimicrobial agents but are heavily regulated due to environmental concerns of their postuse. In this work, we have developed and tested a novel type of formulation for copper oxide (CuONPs) which have been functionalized with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to allow further covalent coupling of 4-hydroxyphenylboronic acid (4-HPBA). As the boronic acid (BA) groups on the surface of CuONPs/GLYMO/4-HPBA can form reversible covalent bonds with the diol groups of glycoproteins on the bacterial cell surface, they can strongly bind to the cells walls resulting in a very strong enhancement of their antibacterial action which is not based on electrostatic adhesion. Scanning electron microscopy and transmission electron microscopy imaging revealed that 4-HPBA-functionalized CuO nanoparticles could accumulate more on the cell surface than nonfunctionalized ones. We demonstrate that the CuONPs with boronic acid surface functionality are far superior antibacterial agents compared to bare CuONPs. Our results showed that the antibacterial impact of the 4-HPBA-functionalized CuONPs on Rhodococcus rhodochrous and Escherichia coli is 1 order of magnitude higher than that of bare CuONPs or CuONPs/GLYMO. We also observed a marked increase of the 4-HPBA-functionalized CuONPs antibacterial action on these microorganisms at shorter incubation times compared with the bare CuONPs at the same conditions. Significantly, we show that the cytotoxicity of CuONPs functionalized with 4-HPBA as an outer layer can be controlled by the concentration of glucose in the media, and that the effect is reversible as glucose competes with the sugar residues on the bacterial cell walls for the BA-groups on the CuONPs. Our experiments with human keratinocyte cell line exposure to CuONPs/GLYMO/4-HPBA indicated lack of measurable cytotoxicity at particle concentration which are effective as an antibacterial agent for both R. rhodochrous and E. coli. We envisage that formulations of CuONPs/GLYMO/4-HPBA can be used to drastically reduce the overall CuO concentration in antimicrobial formulations while strongly increasing their efficiency.

Dual-functionalised shellac nanocarriers give a super-boost of the antimicrobial action of berberine

We have developed highly efficient antimicrobial nanocarriers for berberine (BRB) based on shellac nanoparticles (NPs) which were surface-functionalised with a surface active polymer, Poloxamer 407 (P407), and the cationic surfactant octadecyltrimethylammonium bromide (ODTAB). These shellac nanocarriers were produced in a two-step process which involves: (i) a pH change from aqueous ammonium shellac solution using P407 as a steric stabilizer in the presence of berberine chloride, and (ii) addition of ODTAB to yield shellac nanocarriers of cationic surface. We determined the BRB encapsulation efficiency and release profiles from such nanocarriers. We explored the antimicrobial action of these nanocarriers at different stages of their preparation which allowed us gain better understanding how they work, fine tune their design and reveal the impact of the nanoparticle coatings on to its antimicrobial effect. The antimicrobial action of BRB loaded within such shellac NPs with cationic surface functionality was examined on three different microorganisms, C. reinhardtii, S. cerevisiae and E. coli and compared with the effect of free BRB as well as non-coated BRB-loaded nanocarriers at the same BRB concentrations. We found that the cationic surface coating of the shellac NPs strongly amplified the efficiency of the encapsulated BRB across all tested microorganisms. The effect was attributed to the increased attraction between the ODTAB-coated BRB-loaded NPs and the anionic surface of the cell walls which delivers locally high BRB concentration. This nanotechnological approach could lead to more effective antimicrobial and disinfecting agents, dental formulations for plaque control, wound dressings, antialgal/antibiofouling formulations and antifungal agents.

Resistance to Nano-Based Antifungals Is Mediated by Biomolecule Coronas

Fungal infections are a growing global health and agricultural threat, and current chemical antifungals may induce various side-effects. Thus, nanoparticles are investigated as potential novel antifungals. We report that nanoparticles' antifungal activity strongly depends on their binding to fungal spores, focusing on the clinically important fungal pathogen Aspergillus fumigatus as well as common plant pathogens, such as Botrytis cinerea. We show that nanoparticle-spore complex formation was enhanced by the small nanoparticle size rather than the material, shape or charge, and could not be prevented by steric surface modifications. Fungal resistance to metal-based nanoparticles, such as ZnO-, Ag-, or CuO-nanoparticles as well as dissolution-resistant quantum dots, was mediated by biomolecule coronas acquired in pathophysiological and ecological environments, including the lung surfactant, plasma or complex organic matters. Mechanistically, dose-dependent corona-mediated resistance occurred via reducing physical adsorption of nanoparticles to fungal spores. The inhibitory effect of biomolecules on the antifungal activity of Ag-nanoparticles was further verified in vivo, using the invertebrate Galleria mellonella as an A. fumigatus infection model. Our results explain why current nanoantifungals often show low activity in realistic application environments, and will guide nanomaterial designs that maximize functionality and safe translatability as potent antifungals for human health, biotechnology, and agriculture.

Boosting the antimicrobial action of vancomycin formulated in shellac nanoparticles of dual-surface functionality

We demonstrate a strong enhancement of the antimicrobial action of vancomycin encapsulated in shellac nanocarriers with cationic surface functionality which concentrate on the microbial cell membranes.

The Pros and Cons of the Use of Laser Ablation Synthesis for the Production of Silver Nano-Antimicrobials

Silver nanoparticles (AgNPs) are well-known for their antimicrobial effects and several groups are proposing them as active agents to fight antimicrobial resistance. A wide variety of methods is available for nanoparticle synthesis, affording a broad spectrum of chemical and physical properties. In this work, we report on AgNPs produced by laser ablation synthesis in solution (LASiS), discussing the major features of this approach. Laser ablation synthesis is one of the best candidates, as compared to wet-chemical syntheses, for preparing Ag nano-antimicrobials. In fact, this method allows the preparation of stable Ag colloids in pure solvents without using either capping and stabilizing agents or reductants. LASiS produces AgNPs, which can be more suitable for medical and food-related applications where it is important to use non-toxic chemicals and materials for humans. In addition, laser ablation allows for achieving nanoparticles with different properties according to experimental laser parameters, thus influencing antibacterial mechanisms. However, the concentration obtained by laser-generated AgNP colloids is often low, and it is hard to implement them on an industrial scale. To obtain interesting concentrations for final applications, it is necessary to exploit high-energy lasers, which are quite expensive. In this review, we discuss the pros and cons of the use of laser ablation synthesis for the production of Ag antimicrobial colloids, taking into account applications in the food packaging field.

Green synthesis of catalytic gold/bismuth oxyiodide nanocomposites with oxygen vacancies for treatment of bacterial infections

We have developed a simple and green solution for the synthesis of catalytic gold-doped bismuth oxyiodide (Au/BiOI) nanocomposites at room temperature from an aqueous mixture of gold ions, bismuth ions, and iodide ions. Au nanoparticles (NPs) were formed in situ and doped into BiOI nanosheets. The oxygen vacancies generated in BiOI give rise to its oxidase-like activity, and Au doping facilitated the reaction leading to a 4-fold higher oxidase-like activity of the Au/BiOI nanocomposite. The Au/BiOI nanocomposites showed wide spectrum antimicrobial activity not only against non-multidrug-resistant E. coli, K. pneumoniae, S. enteritidis, S. aureus, and B. subtilis bacteria, but also against multidrug-resistant bacteria, methicillin-resistant S. aureus (MRSA). The gold doping reduced the minimal inhibitory concentration value by ∼2000-fold for the Au/BiOI nanocomposite, in comparison with only BiOI nanoparticles. The bactericidal property of the Au/BiOI nanocomposite arose from the combined effect of the disruption of the bacterial membrane through a strong interaction of the nanocomposite with the bacteria and the generation of reactive oxygen species. Also, the Au/BiOI nanocomposite is highly biocompatible, which has been demonstrated in vitro by analysis of cytotoxicity and hemolysis, and in vivo by evaluating ocular tissue responses. Furthermore, intrastromal administration of Au/BiOI nanocomposites can effectively alleviate S. aureus-induced bacterial keratitis in rabbits, suggesting a significant disinfectant benefit in preclinical studies. The Au/BiOI nanocomposites show great potential for the inactivation of bacterial pathogens in an aqueous environment and treatment of bacterial infection-induced diseases.

Toxicity of surface-modified copper oxide nanoparticles in a mouse macrophage cell line: Interplay of particles, surface coating and particle dissolution

The rapid dissolution of copper oxide (CuO) nanoparticles (NPs) with release of ions is thought to be one of the main factors modulating their toxicity. Here we assessed the cytotoxicity of a panel of CuO NPs (12 nm ± 4 nm) with different surface modifications, i.e., anionic sodium citrate (CIT) and sodium ascorbate (ASC), neutral polyvinylpyrrolidone (PVP), and cationic polyethylenimine (PEI), versus the pristine (uncoated) NPs, using a murine macrophage cell line (RAW264.7). Cytotoxicity, reactive oxygen species (ROS) production, and cellular uptake were assessed. The cytotoxicity results were analyzed by the benchmark dose (BMD) method and the NPs were ranked based on BMD₂₀ values. The PEI-coated NPs were found to be the most cytotoxic. Despite the different properties of the coating agents, NP dissolution in cell medium was only marginally affected by surface modification. Furthermore, CuCl₂ (used as an ion control) elicited significantly less cytotoxicity when compared to the CuO NPs. We also observed that the antioxidant, N-acetylcysteine, failed to protect against the cytotoxicity of the uncoated CuO NPs. Indeed, the toxicity of the surface-modified CuO NPs was not directly linked to particle dissolution and subsequent Cu burden in cells, nor to cellular ROS production, although CuO-ASC NPs, which were found to be the least cytotoxic, yielded lower levels of ROS in comparison to pristine NPs. Hierarchical cluster analysis suggested, instead, that the toxicity in the current in vitro model could be explained by synergistic interactions between the NPs, their dissolution, and the toxicity of the coating agents.

Contact killing and antimicrobial properties of copper

With the emergence of antibiotic resistance, the interest for antimicrobial agents has recently increased again in public health. Copper was recognized in 2008 by the United States Environmental Protection Agency (EPA) as the first metallic antimicrobial agent. This led to many investigations of the various properties of copper as an antibacterial, antifungal and antiviral agent. This review summarizes the latest findings about 'contact killing', the mechanism of action of copper nanoparticles and the different ways micro-organisms develop resistance to copper.

Enhanced antimicrobial effect of berberine in nanogel carriers with cationic surface functionality

We report a strong enhancement in the antimicrobial action of berberine encapsulated into polyacrylic acid-based nanogels followed by further surface functionalisation with a cationic polyelectrolyte (PDAC). Due to the highly developed surface area, the nanogel carrier amplifies the contact of berberine with microbial cells and increases its antimicrobial efficiency. We show that such cationic nanogel carriers of berberine can adhere directly to the cell membranes and maintain a very high concentration of berberine directly on the cell surface. We demonstrated that the antimicrobial action of the PDAC-coated nanogel loaded with berberine on E. coli and C. reinhardtii is much higher than that of the equivalent solution of free berberine due to the electrostatic adhesion between the positively charged nanogel particles and the cell membranes. Our results also showed a marked increase in their antimicrobial action at shorter incubation times compared to the non-coated nanogel particles loaded with berberine under the same conditions. We attribute this boost in the antimicrobial effect of these cationic nanocarriers to their accumulation on the cell membranes which sustains a high concentration of released berberine causing cell death within much shorter incubation times. This study can provide a blueprint for boosting the action of other cationic antimicrobial agents by encapsulating them into nanogel carriers functionalised with a cationic surface layer. This nanotechnology-based approach could lead to the development of more effective wound dressings, disinfecting agents, antimicrobial surfaces, and antiseptic and antialgal/antibiofouling formulations.