Evaluation of the antibacterial power and biocompatibility of zinc oxide nanorods decorated graphene nanoplatelets: new perspectives for antibiodeteriorative approaches

Evaluating the adverse effects and mechanisms of nanomaterial exposure on longevity of C. elegans: A literature meta-analysis and bioinformatics analysis of multi-transcriptome data

Exposure to large-size particulate air pollution (PM2.5 or PM10) has been reported to increase risks of aging-related diseases and human death, indicating the potential pro-aging effects of airborne nanomaterials with ultra-fine particle size (which have been widely applied in various fields). However, this hypothesis remains inconclusive. Here, a meta-analysis of 99 published literatures collected from electronic databases (PubMed, EMBASE and Cochrane Library; from inception to June 2023) was performed to confirm the effects of nanomaterial exposure on aging-related indicators and molecular mechanisms in model animal C. elegans. The pooled analysis by Stata software showed that compared with the control, nanomaterial exposure significantly shortened the mean lifespan [standardized mean difference (SMD) = -2.30], reduced the survival rate (SMD = -4.57) and increased the death risk (hazard ratio = 1.36) accompanied by upregulation of ced-3, ced-4 and cep-1, while downregulation of ctl-2, ape-1, aak-2 and pmk-1. Furthermore, multi-transcriptome data associated with nanomaterial exposure were retrieved from Gene Expression Omnibus (GSE32521, GSE41486, GSE24847, GSE59470, GSE70509, GSE14932, GSE93187, GSE114881, and GSE122728) and bioinformatics analyses showed that pseudogene prg-2, mRNAs of abu, car-1, gipc-1, gsp-3, kat-1, pod-2, acdh-8, hsp-60 and egrh-2 were downregulated, while R04A9.7 was upregulated after exposure to at least two types of nanomaterials. Resveratrol (abu, hsp-60, pod-2, egrh-2, acdh-8, gsp-3, car-1, kat-1, gipc-1), naringenin (kat-1, egrh-2), coumestrol (egrh-2) or swainsonine/niacin/ferulic acid (R04A9.7) exerted therapeutic effects by reversing the expression levels of target genes. In conclusion, our study demonstrates the necessity to use phytomedicines that target hub genes to delay aging for populations with nanomaterial exposure.

Antimicrobial mechanisms of ZnO nanoparticles to phytopathogen Pseudomonas syringae: Damage of cell envelope, suppression of metabolism, biofilm and motility, and stimulation of stomatal immunity on host plant

Nanoparticles have recently been employed as a new strategy to act as bactericides in agricultural applications. However, the effects and mechanisms of foliar deposition of nanoparticles on bacterial pathogens, plant physiology and particularly plant immunity have not been sufficiently understood. Here, we investigated the effects and mechanisms of ZnO NPs in controlling of tobacco wildfire caused by Pseudomonas syringae pv. tabaci, through the comprehensive analysis of biological changes of both bacteria and plants. The global gene expression changes of Pseudomonas syringae pv. tabaci supported that the functions of "protein secretion", "membrane part", "signal transducer activity", "locomotion", "chemotaxis" and "taxis" in bacteria, as well as the metabolic pathways of "bacterial chemotaxis", "two-component system", "biofilm formation", "ABC transporters" and "valine, leucine and isoleucine degradation" were significantly down-regulated by ZnO NPs. Correspondingly, we reconfirmed that the cell envelope structure, biofilm and motility of Pseudomonas syringae pv. tabaci were directly disrupted or suppressed by ZnO NPs. Different from completely killing Pseudomonas syringae pv. tabaci, ZnO NPs (0.5 mg/mL) potentially improved plant growth and immunity through enzymatic activity and global molecular response analysis. Furthermore, the changes of gene expression in ABA signaling pathway, ABA concentration and stomatal aperture all supported that ZnO NPs can specifically stimulate stomatal immunity, which is important to defend bacterial infection. Taken together, we proposed that both the inhibition or damage of motility, biofilm, metabolisms, virulence and cell envelope on P. syringae pv. tabaci, and the activation of the stomatal immunity formed two-layered antibacterial mechanisms of ZnO NPs on phytopathogenic bacteria.

Nanoantibiotic effect of carbon-based nanocomposites: epicentric on graphene, carbon nanotubes and fullerene composites: a review

Carbon in many different forms especially, Graphene, Carbon nanotubes (CNTs), and Fullerene is emerging as an important material in the areas of the biomedical field for various applications. This review comprehensively describes the nano antibiotic effect of carbon-based nanocomposites: epicenter on graphene, carbon nanotubes, and fullerene Composites. It summarises the studies conducted to evaluate their antimicrobial applications as they can disrupt the cell membrane of bacteria resulting in cell death. The initial section gives a glimpse of both "Gram"-positive and negative bacteria, which have been affected by Graphene, CNTs, and Fullerene-based nanocomposites. These bacteria include Staphylococcus Aureus, Bacillus Thuringiensis, Enterococcus faecalis, Enterococcus faecium, Bacillus subtilis, Escherichia coli, Klebseilla pneumoniae, Pseudomonas aeroginosa, Pseudomonas syringae , Shigella flexneri,Candida Albicans, Mucor. Another section is dedicated to the insight of Graphene, and its types such as Graphene Oxide (GO), Reduced graphene oxide (rGO), Graphene Nanoplatelets (GNPs), Graphene Nanoribbons (GNRs), and Graphene Quantum Dots (GQDs). Insight into CNT, including both the types SWCNT and MWCNT, studied, followed by understanding fullerene is also reported. Another section is dedicated to the antibacterial mechanism of Graphene, CNT, and Fullerene-based nanocomposites. Further, an additional section is dedicated to a comprehensive review of the antibacterial characteristics of Graphene, CNT, and nanocomposites based on fullerene. Future perspectives and recommendations have also been highlighted in the last section.

The two faces of pyocyanin - why and how to steer its production?

The ambiguous nature of pyocyanin was noted quite early after its discovery. This substance is a recognized Pseudomonas aeruginosa virulence factor that causes problems in cystic fibrosis, wound healing, and microbiologically induced corrosion. However, it can also be a potent chemical with potential use in a wide variety of technologies and applications, e.g. green energy production in microbial fuel cells, biocontrol in agriculture, therapy in medicine, or environmental protection. In this mini-review, we shortly describe the properties of pyocyanin, its role in the physiology of Pseudomonas and show the ever-growing interest in it. We also summarize the possible ways of modulating pyocyanin production. We underline different approaches of the researchers that aim either at lowering or increasing pyocyanin production by using different culturing methods, chemical additives, physical factors (e.g. electromagnetic field), or genetic engineering techniques. The review aims to present the ambiguous character of pyocyanin, underline its potential, and signalize the possible further research directions.

In Vitro and In Vivo Biocompatibility Studies on Engineered Fabric with Graphene Nanoplatelets

To produce clothes made with engineered fabrics to monitor the physiological parameters of workers, strain sensors were produced by depositing two different types of water-based inks (P1 and P2) suitably mixed with graphene nanoplatelets (GNPs) on a fabric. We evaluated the biocompatibility of fabrics with GNPs (GNP fabric) through in vitro and in vivo assays. We investigated the effects induced on human keratinocytes by the eluates extracted from GNP fabrics by the contact of GNP fabrics with cells and by seeding keratinocytes directly onto the GNP fabrics using a cell viability test and morphological analysis. Moreover, we evaluated in vivo possible adverse effects of the GNPs using the model system Caenorhabditis elegans. Cell viability assay, morphological analysis and Caenorhabditis elegans tests performed on smart fabric treated with P2 (P2GNP fabric) did not show significant differences when compared with their respective control samples. Instead, a reduction in cell viability and changes in the membrane microvilli structure were found in cells incubated with smart fabric treated with P1. The results were helpful in determining the non-toxic properties of the P2GNP fabric. In the future, therefore, graphene-based ink integrated into elastic fabric will be developed for piezoresistive sensors.

Design strategies for antiviral coatings and surfaces: A review☆

The routine disinfection and sanitization of surfaces, objects, and textiles has become a time-consuming but necessary task for managing the COVID-19 pandemic. Nonetheless, the excessive use of sanitizers and disinfectants promotes the development of antibiotic-resistant microbes. Moreover, that improper disinfection could lead to more virus transfer, which leads to more viral mutations. Recently developed antiviral surface coatings can reduce the reliance on traditional disinfectants. These surfaces remain actively antimicrobial between periods of active cleaning of the surfaces, allowing a much more limited and optimized use of disinfectants. The novel nature of these surfaces has led, however, to many inconsistencies within the rapidly growing literature. Here we provide tools to guide the design and development of antimicrobial and antiviral surfaces and coatings. We describe how engineers can best choose testing options and propose new avenues for antiviral testing. After defining testing protocols, we summarize potential inorganic and organic materials able to serve as antiviral surfaces and present their antiviral mechanisms. We discuss the main limitations to their application, including issues related to toxicity, antimicrobial resistance, and environmental concerns. We propose solutions to counter these limitations and highlight how the context of specific use of an antiviral surface must guide material selection. Finally, we discuss how the use of coatings that combine multiple antimicrobial mechanisms can avoid the development of antibiotic resistance and improve the antiviral properties of these surfaces.

The influence of nanomaterials on pyocyanin production by Pseudomonas aeruginosa

Pseudomonas aeruginosa is a bacterium producing industrially utile metabolites, such as rhamnolipids, biopolymers, and pigments. Pyocyanin, the most studied example of pigments, is a virulence factor that also shows the potential for application in, e.g., agriculture, anticancer therapy, and energy production. Therefore, potential inhibitors and stimulants of pyocyanin production by P. aeruginosa should be studied, and nanomaterials may cause both effects. The study aimed to examine the influence of zinc oxide and multi-walled carbon nanotubes (pristine or dispersed with alginic acid) on pyocyanin production by P. aeruginosa. First, the influence of different concentrations of nanomaterials (500.00–0.06 µg/mL) on culture optical density and biofilm formation was studied. These results helped select concentrations for further tests, i.e., growth curves and fluorescence measurements. Pyocyanin production was assessed by the chloroform–hydrochloric acid method. SEM analysis was conducted to assess the influence of nanomaterials on the cell's integrity and biofilm structure. Pristine multi-walled carbon nanotubes exhibited a stimulative effect on pigment production when applied in high concentrations (500.00 µg/mL), while dispersed material enhanced the production in lowered dosages (125.00 µg/mL). On the other hand, high concentrations of zinc oxide inhibited pyocyanin production, while minor increased bioproduct production. The research indicates the potential to use nanomaterials as the modulators of pyocyanin production and other metabolites.

The antibacterial property of zinc oxide/graphene oxide modified porous polyetheretherketone against S. sanguinis, F. nucleatum and P. gingivalis

About 30% failures of implant are caused by peri-implantitis. Subgingival plaque, consisting of S. sanguinis, F. nucleatum, P. gingivalis et. al, is the initiating factor of peri-implantitis. Polyetheretherketone(PEEK) is widely used for the fabrication of implant abutment, healing cap and temporary abutment in dental applications. As a biologically inert material, PEEK has shown poor antibacterial properties. To promote the antibacterial activity of PEEK, we loaded ZnO/GO on sulfonated PEEK. We screened out that when mass ratio of ZnO/GO was 4:1, dip-coating time was 25 min, ZnO/GO modified SPEEK shown the best physical and chemical properties. At the meantime, the ZnO/GO-SPEEK samples possess a good biocompatibility. The ZnO/GO-SPEEK inhibits P. gingivalis obviously, and could exert an antibacterial activity to S. sanguinis in the early stage, prevents biofilm formation effectively. With the favorable in vitro performances, the modification of PEEK with ZnO/GO is promising for preventing peri-implantitis.

Performance of Graphene/Polydimethylsiloxane Surfaces against S. aureus and P. aeruginosa Single- and Dual-Species Biofilms

The increasing incidence of implant-associated infections has prompted the development of effective strategies to prevent biofilm formation on these devices. In this work, pristine graphene nanoplatelet/polydimethylsiloxane (GNP/PDMS) surfaces containing different GNP loadings (1, 2, 3, 4, and 5 wt%) were produced and evaluated on their ability to mitigate biofilm development. After GNP loading optimization, the most promising surface was tested against single- and dual-species biofilms of Staphylococcus aureus and Pseudomonas aeruginosa. The antibiofilm activity of GNP/PDMS surfaces was determined by the quantification of total, viable, culturable, and viable but nonculturable (VBNC) cells, as well as by confocal laser scanning microscopy (CLSM). Results showed that 5 wt% GNP loading reduced the number of total (57%), viable (69%), culturable (55%), and VBNC cells (85%) of S. aureus biofilms compared to PDMS. A decrease of 25% in total cells and about 52% in viable, culturable, and VBNC cells was observed for P. aeruginosa biofilms. Dual-species biofilms demonstrated higher resistance to the antimicrobial activity of GNP surfaces, with lower biofilm cell reductions (of up to 29% when compared to single-species biofilms). Still, the effectiveness of these surfaces in suppressing single- and dual-species biofilm formation was confirmed by CLSM analysis, where a decrease in biofilm biovolume (83% for S. aureus biofilms and 42% for P. aeruginosa and dual-species biofilms) and thickness (on average 72%) was obtained. Overall, these results showed that pristine GNPs dispersed into the PDMS matrix were able to inhibit biofilm growth, being a starting point for the fabrication of novel surface coatings based on functionalized GNP/PDMS composites.

Anti-pathogenic activity of graphene nanomaterials: A review

Graphene and its derivatives are promising candidates for a variety of biological applications, among which, their anti-pathogenic properties are highly attractive due to the outstanding physicochemical characteristics of these novel nanomaterials. The antibacterial, antiviral and antifungal performances of graphene are increasingly becoming more important due to the pathogen's resistance to existing drugs. Despite this, the factors influencing the antibacterial activity of graphene nanomaterials, and consequently, the mechanisms involved are still controversial. This review aims to systematically summarize the literature, discussing various factors that affect the antibacterial performance of graphene materials, including the shape, size, functional group and the electrical conductivity of graphene flakes, as well as the concentration, contact time and the pH value of the graphene suspensions used in related microbial tests. We discuss the possible surface and edge interactions between bacterial cells and graphene nanomaterials, which cause antibacterial effects such as membrane/oxidative/photothermal stresses, charge transfer, entrapment and self-killing phenomena. This article reviews the anti-pathogenic activity of graphene nanomaterials, comprising their antibacterial, antiviral, antifungal and biofilm-forming performance, with an emphasis on the antibacterial mechanisms involved.

Pristine and Antibiotic-Loaded Nanosheets/Nanoneedles-Based Boron Nitride Films as a Promising Platform to Suppress Bacterial and Fungal Infections

In recent years, bacteria inactivation during their direct physical contact with surface nanotopography has become one of the promising strategies for fighting infection. Contact-killing ability has been reported for several nanostructured surfaces, e.g., black silicon, carbon nanotubes, zinc oxide nanorods, and copper oxide nanosheets. Herein, we demonstrate that Gram-negative antibiotic-resistant Escherichia coli (E. coli) bacteria are killed as a result of their physical destruction while contacting nanostructured h-BN surfaces. BN films, made of spherical nanoparticles formed by numerous nanosheets and nanoneedles with a thickness <15 nm, have been obtained through a reaction of ammonia with amorphous boron. The contact-killing bactericidal effect of BN nanostructures has been compared with a toxic effect of gentamicin released from them. For a wider protection against bacterial and fungal infection, the films have been saturated with a mixture of gentamicin and amphotericin B. Such BN films demonstrate a high antibiotic/antimycotic agent loading capacity and a fast initial and sustained release of therapeutic agents for 170-260 h depending on the loaded dose. The pristine BN films possess high antibacterial activity against E. coli K-261 strain at their initial concentration of 10⁴ cells/mL, attaining >99% inactivation of colony forming units after 24 h, same as gentamicin-loaded (150 μg/cm²) BN sample. The BN films loaded with a mixture of gentamicin (150 and 300 μg/cm²) and amphotericin B (100 μg/cm²) effectively inhibit the growth of E. coli K-261 and Neurospora crassa strains. During immersion in the normal saline solution, the BN film generates reactive oxygen species (ROS), which can lead to accelerated oxidative stress at the site of physical cell damage. The obtained results are valuable for further development of nanostructured surfaces having contact killing, ROS, and biocide release abilities.

Antibacterial Activity against Staphylococcus Aureus of Titanium Surfaces Coated with Graphene Nanoplatelets to Prevent Peri-Implant Diseases. An In-Vitro Pilot Study

Dental implants are one of the most commonly used ways to replace missing teeth. Nevertheless, the close contact with hard and soft oral tissues expose these devices to infectious peri-implant diseases. To prevent such infection, several surface treatments have been developed in the last few years to improve the antimicrobial properties of titanium dental implants. In this in-vitro pilot study, the antimicrobial activity of titanium surfaces coated with different types of graphene nanoplatelets are investigated. Six different colloidal suspensions of graphene nanoplatelets (GNPs) were produced from graphite intercalated compounds, setting the temperature and duration of the thermal shock and varying the number of the exfoliation cycles. Titanium disks with sand-blasted and acid-etched surfaces were sprayed with 2 mL of colloidal GNPs suspensions. The size of the GNPs and the percentage of titanium disk surfaces coated by GNPs were evaluated through a field emission-scanning electron microscope. The antibacterial activity of the specimens against Staphylococcus aureus was estimated using a crystal violet assay. The dimension of GNPs decreased progressively after each sonication cycle. The two best mean percentages of titanium disk surfaces coated by GNPs were GNPs1050°/2 and GNPs1150°/2. The reduction of biofilm development was 14.4% in GNPs1150°/2, 20.1% in GNPs1150°/3, 30.3% in GNPs1050°/3, and 39.2% in GNPs1050°/2. The results of the study suggested that the surface treatment of titanium disks with GNPs represents a promising solution to improve the antibacterial activity of titanium implants.

Antibacterial Effect of Zinc Oxide-Based Nanomaterials on Environmental Biodeteriogens Affecting Historical Buildings

The colonization of microorganisms and their subsequent interaction with stone substrates under different environmental conditions encourage deterioration of materials by multiple mechanisms resulting in changes in the original color, appearance and durability. One of the emerging alternatives to remedy biodeterioration is nanotechnology, thanks to nanoparticle properties such as small size, no-toxicity, high photo-reactivity, and low impact on the environment. This study highlighted the effects of ZnO-based nanomaterials of two bacteria genera isolated from the Temple of Concordia (Agrigento’s Valley of the Temples in Sicily, Italy) that are involved in biodeterioration processes. The antimicrobial activities of ZnO-nanorods (Zn-NRs) and graphene nanoplatelets decorated with Zn-NRs (ZNGs) were evaluated against the Gram positive Arthrobacter aurescens and two isolates of the Gram negative Achromobacter spanius. ZNGs demonstrated high antibacterial and antibiofilm activities on several substrates such as stones with different porosity. In the case of ZNGs, a marked time- and dose-dependent bactericidal effect was highlighted against all bacterial species. Therefore, these nanomaterials represent a promising tool for developing biocompatible materials that can be exploited for the conservation of cultural heritage. These nanostructures can be successfully applied without releasing toxic compounds, thus spreading their usability.

Graphene-based nanomaterials: the promising active agents for antibiotics-independent antibacterial applications

Graphene-based nanomaterials, such as graphene oxide (GO) and reduced graphene oxide (rGO), have shown great potentials in drug delivery and photodynamic/photothermal therapy due to their featured structure and physicochemical properties. In recent years, their antibacterial potentials have also been exploited. The commonly recognized antibacterial mechanisms include sharp edge-mediated cutting effect, oxidative stress and cell entrapment. This antibacterial activity is very important for human health. As we know, infection with the pathogenic bacteria, especially the drug-resistant ones, is a great threat to human lives. Thus, the development of the antibiotics-independent and drug-free antibacterial agents is of great importance and significance. Graphene-based nanomaterials are a kind of such antibacterial agents. An insight into their properties and antibacterial mechanisms is necessary before they are developed into real products. Herein, we provide a comprehensive understanding of the antibacterial application of graphene-based nanomaterials via summarizing their antibacterial activities against some typical microbial species and discussing their unique mechanisms. In addition, the side-effects and problems in using these nanomaterials are also discussed.

Facile Fabrication of Multifunctional ZnO Urchins on Surfaces

Functional ZnO nanostructured surfaces are important in a wide range of applications. Here we report the simple fabrication of ZnO surface structures at near room temperature with morphology resembling that of sea urchins, with densely packed, μm-long, tapered nanoneedles radiating from the urchin center. The ZnO urchin structures were successfully formed on several different substrates with high surface density and coverage, including silicon (Si), glass, polydimethylsiloxane (PDMS), and copper (Cu) sheets, as well as Si seeded with ZnO nanocrystals. Time-resolved SEM revealed growth kinetics of the ZnO nanostructures on Si, capturing the emergence of “infant” urchins at the early growth stage and subsequent progressive increases in the urchin nanoneedle length and density, whilst the spiky nanoneedle morphology was retained throughout the growth. ε-Zn(OH)2 orthorhombic crystals were also observed alongside the urchins. The crystal structures of the nanostructures at different growth times were confirmed by synchrotron X-ray diffraction measurements. On seeded Si substrates, a two-stage growth mechanism was identified, with a primary growth step of vertically aligned ZnO nanoneedle arrays preceding the secondary growth of the urchins atop the nanoneedle array. The antibacterial, anti-reflective, and wetting functionality of the ZnO urchins—with spiky nanoneedles and at high surface density—on Si substrates was demonstrated. First, bacteria colonization was found to be suppressed on the surface after 24 h incubation in gram-negative Escherichia coli (E. coli) culture, in contrast to control substrates (bare Si and Si sputtered with a 20 nm ZnO thin film). Secondly, the ZnO urchin surface, exhibiting superhydrophilic property with a water contact angle ~ 0°, could be rendered superhydrophobic with a simple silanization step, characterized by an apparent water contact angle θ of 159° ± 1.4° and contact angle hysteresis ∆θ < 7°. The dynamic superhydrophobicity of the surface was demonstrated by the bouncing-off of a falling 10 μL water droplet, with a contact time of 15.3 milliseconds (ms), captured using a high-speed camera. Thirdly, it was shown that the presence of dense spiky ZnO nanoneedles and urchins on the seeded Si substrate exhibited a reflectance R < 1% over the wavelength range λ = 200–800 nm. The ZnO urchins with a unique morphology fabricated via a simple route at room temperature, and readily implementable on different substrates, may be further exploited for multifunctional surfaces and product formulations.

Anti-Candidal Activity and In Vitro Cytotoxicity Assessment of Graphene Nanoplatelets Decorated with Zinc Oxide Nanorods

Candida albicans is the most common pathogenic fungus that is isolated in nosocomial infections in medically and immune-compromised patients. The ability of C. albicans to convert its form from yeast to hyphal morphology contributes to biofilm development that effectively shelters Candida against the action of antifungals molecules. In the last years, nanocomposites are the most promising solutions against drug-resistant microorganisms. The aim of this study was to investigate the antifungal activity of graphene nanoplateles decorated with zinc oxide nanorods (ZNGs) against the human pathogen Candida albicans. We observed that ZNGs were able to induce a significant mortality in fungal cells, as well as to affect the main virulence factors of this fungus or rather the hyphal development and biofilm formation. Reactive Oxygen Species (ROS) formation in yeast cells resulted one of the mechanisms of ZNGs to induce mortality. Finally, the toxicity of this nanomaterial was tested also on human keratinocyte cell line HaCaT. Our data indicated that ZNGs resulted not toxic when their aggregation state decreased by adding glycerol as emulsifier to ZNGs suspensions or when HaCaT cells were grown on ZNGs-coated glasses. Overall, the results that were obtained indicated that ZNGs could be exploited as an antifungal nanomaterial with a high degree of biocompatibility on human cells.

Tailored antimicrobial activity and long-term cytocompatibility of plasma polymer silver nanocomposites

The deposition of coatings enabling antibacterial properties in combination with cytocompatibility remains a challenge for biomaterial applications, such as in medical devices. Silver is one of the most utilized antibacterial surface components, due to its efficacy and extensive applicability. In this work, silver-containing plasma polymer nanocomposites (single layer and multilayers) were developed and tested, with a focus on cytotoxicity and bactericidal function, on the NIH3T3 mammalian cell line as well as Gram-negative ( Pseudomonas aeruginosa) and Gram-positive ( Staphylococcus aureus) bacterial strains. The data demonstrate that a tuneable Ag⁺ release is required, allowing sufficient antimicrobial activity while retaining appropriate cytocompatibility over the entire testing period of up to eight days.

Bacteria killing in ICU associated infections: antibacterial nanosheets as disinfectant

Here we propose Zn–CuO@GO nanosheets that induce rapid bacterial lysis via physically penetrating and wrapping into the cell wall. Such an irreversible damage make them promising as ICU disinfectants to combat ICU-associated multidrug resistant bacteria.