Superior antibacterial activity of zinc oxide/graphene oxide composites originating from high zinc concentration localized around bacteria

Rational Design and Fabrication of ZnONPs Functionalized Sericin/PVA Antimicrobial Sponge

The interests of developing antimicrobial biomaterials based on silk sericin from Bombyx mori cocoon, have been shooting up in the last decades. Sericin is a valuable natural protein owing to its hydrophilicity, biodegradability, and biocompatibility. Here, we fabricated a sponge with antibacterial capacities for potential wound dressing application. By co-blending of sericin, polyvinyl alcohol (PVA) and zinc oxide nanoparticles (ZnONPs), the ZnONPs-sericin/PVA composite sponge (ZnONPs-SP) was successfully prepared after freeze-drying. Scanning electron microscopy showed the porous structure of ZnONPs-SP. Energy dispersive spectroscopy indicated the existence of Zn in the sponge. X-ray diffractometry revealed the hexagonal wurtzite structure of ZnONPs. Fourier transform infrared spectroscopy showed the biologic coupling of ZnONPs and sericin resulted in a decrease of α-helix and random coil contents, and an increase of β-sheet structure in the sponge. The swelling experiment suggested ZnONPs-SP has high porosity, good hydrophilicity, and water absorption capability. The plate bacterial colony counting coupled with growth curve assays demonstrated that the composite sponge has an efficiently bacteriostatic effect against Staphylococcus aureus and Escherichia coli, respectively. Furthermore, the cell compatibility analysis suggested the composite sponge has excellent cytocompatibility on NIH3T3 cells. In all, ZnONPs-SP composite sponge has significant potentials in biomaterials such as wound dressing and tissue engineering.

Nanomaterials as Delivery Vehicles and Components of New Strategies to Combat Bacterial Infections: Advantages and Limitations

Life-threatening bacterial infections have been well-controlled by antibiotic therapies and this approach has greatly improved the health and lifespan of human beings. However, the rapid and worldwide emergence of multidrug resistant (MDR) bacteria has forced researchers to find alternative treatments for MDR infections as MDR bacteria can sometimes resist all the present day antibiotic therapies. In this respect, nanomaterials have emerged as innovative antimicrobial agents that can be a potential solution against MDR bacteria. The present review discusses the advantages of nanomaterials as potential medical means and carriers of antibacterial activity, the types of nanomaterials used for antibacterial agents, strategies to tackle toxicity of nanomaterials for clinical applications, and limitations which need extensive studies to overcome. The current progress of using different types of nanomaterials, including new emerging strategies for the single purpose of combating bacterial infections, is also discussed in detail.

Zinc oxide-coated zeolite adsorbs and inactivates waterborne Staphylococcus aureus

Zinc oxide-coated zeolite (ZOCZ) and zinc oxide (ZnO) were compared in terms of their effectiveness in removing Staphylococcus aureus (S. aureus) from nutrient broth and phosphate-buffered saline (PBS) solution. ZOCZ was found to be extremely efficient in removing S. aureus. ZnO initially was much less effective. Photographs of removal S. aureus from PBS solution with ZOCZ confirmed that a multilayer of S. aureus cells forms on the surface of ZOCZ particles. The comparison of the images of confocal laser scanning microscope and inverted contrast fluorescence microscope further proved that a multilayer of S. aureus cells formed on the surface of ZnO-30N-zeolite. The FESEM images showed that the cell membranes of S. aureus attached to the surface of ZnO-30N-zeolite collapsed. Energy Dispersive X-Ray Spectrum and the atomic absorption spectroscopic analysis confirmed that zinc ions penetrate into S. aureus cells, causing their death. The dead cells were easily removed, allowing ZOCZ to be reused.

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.

Antibacterial Properties of Graphene-Based Nanomaterials

Bacteria mediated infections may cause various acute or chronic illnesses and antibiotic resistance in pathogenic bacteria has become a serious health problem around the world due to their excessive use or misuse. Replacement of existing antibacterial agents with a novel and efficient alternative is the immediate demand to alleviate this problem. Graphene-based materials have been exquisitely studied because of their remarkable bactericidal activity on a wide range of bacteria. Graphene-based materials provide advantages of easy preparation, renewable, unique catalytic properties, and exceptional physical properties such as a large specific surface area and mechanical strength. However, several queries related to the mechanism of action, significance of size and composition toward bacterial activity, toxicity criteria, and other issues are needed to be addressed. This review summarizes the recent efforts that have been made so far toward the development of graphene-based antibacterial materials to face current challenges to combat against the bacterial targets. This review describes the inherent antibacterial activity of graphene-family and recent advances that have been made on graphene-based antibacterial materials covering the functionalization with silver nanoparticles, other metal ions/oxides nanoparticles, polymers, antibiotics, and enzymes along with their multicomponent functionalization. Furthermore, the review describes the biosafety of the graphene-based antibacterial materials. It is hoped that this review will provide valuable current insight and excite new ideas for the further development of safe and efficient graphene-based antibacterial materials.

Zinc-Based Biomaterials for Regeneration and Therapy

Zinc has been described as the 'calcium of the twenty-first century'. Zinc-based degradable biomaterials have recently emerged thanks to their intrinsic physiological relevance, biocompatibility, biodegradability, and pro-regeneration properties. Zinc-based biomaterials mainly include: metallic zinc alloys, zinc ceramic nanomaterials, and zinc metal-organic frameworks (MOFs). Metallic zinc implants degrade at a desirable rate, matching the healing pace of local tissues, and stimulating remodeling and formation of new tissues. Zinc ceramic nanomaterials are also beneficial for tissue engineering and therapy thanks to their nanostructures and antibacterial properties. MOFs have large surface areas and are easily functionalized, making them ideal for drug delivery and cancer therapy. This review highlights recent developments in zinc-based biomaterials, discusses obstacles to overcome, and pinpoints directions for future research.

Generation of engineered core-shell antibiotic nanoparticles

Well-defined nanocomposite structures have received significant attention due to their superior combinatorial properties. Rational tuning of the core and shell of the nanostructure(s) can offer potent antibacterial activity. Such advanced core–shell nanocomposite methodologies allow not only the incorporation of antibacterial agents on the shell but also provide its stability and nurture antibacterial activity. Herein, antibiotic zinc oxide–curcumin (ZnO–Cum) core–shell nanoparticles for antibacterial application were synthesised. The ZnO–Cum core–shell nanoparticles were prepared by curcumin nanolayer deposition on zinc oxide nanoparticles via a sonication process. The resulting ZnO–Cum core–shell nanoparticles were spiracle in shape with a ∼45 nm ZnO core and ∼12 nm curcumin shell layer size, respectively, determined by transmission electron microscopy. X-ray diffraction analysis confirmed the formation of a core–shell crystal structure. Additionally, UV-DRS and ATR-FTIR spectral analysis support the existence of ZnO and curcumin in a core–shell nanocomposite. The antibacterial activities of nanoparticles developed were studied against Staphylococcus aureus and Streptococcus pneumoniae and Escherichia coli and Shigella dysenteriae bacterial stains using the diffusion method. A greater inhibition of the growth of Gram positive and negative bacteria was noticed upon treatment with core–shell ZnO and curcumin nanoparticles than the commercial antibiotic amoxicillin which indicates their antibacterial property. The findings of this study provide evidence that the zinc oxide–curcumin core–shell nanoparticles may be highly promising for antibacterial and biomedical applications.

Antibiotic ZnO–curcumin core–shell nanoparticles were prepared via an ultra-sonication process. ZnO–curcumin exhibited excellent antibacterial capacity compared to the commercial antibiotic amoxicillin.

A comparison of the characteristics of polyurethane-based sealers including various antimicrobial agents

An obturation biomaterial that possess inherent antibacterial activity has been developed to create a tight seal for the root canal space in treatment. Novel castor oil-based polyurethane sealers composited with different proportions of silver phosphate or zinc oxide nanoparticles were synthesized to investigate the physicochemical properties, antibacterial effect on Enterococcus faecalis, and cytotoxicity on murine fibroblasts compared with commercially available products. The results showed that the physical properties of all of the polyurethane sealers could meet with the standards expected. The microdilatancy character of the polyurethane sealers was particularly preferable for the three dimensional obturation of root canal space. Compared with the silver-loaded polyurethane series, the zinc-loaded polyurethane series showed better antibacterial properties based on the contact mode. Analysis of the kinetics indicated that the setting process of the polyurethane sealers supported a first-order reaction and the setting process was highly effective, with more than 90% of the isocyanate groups participating in the setting reaction within 12 h. This is beneficial for the rapid consumption of monomers, efficiently avoiding inflammation. The in vitro results showed that the polyurethane sealers loaded with zinc oxide nanoparticles or 1 wt% silver phosphate were desirable for cell attachment and proliferation compared with the commercial sealers. In conclusion, the castor oil-based polyurethane-zinc sealers, especially PU-Zn5, present good physicochemical and antibacterial properties and cytocompatibility, and could be a promising candidate for application in the field of root canal treatment.

Environmental performance of graphene-based 3D macrostructures

Three-dimensional macrostructures (3DMs) of graphene and graphene oxide are being developed for fast and efficient removal of contaminants from water and air. The large specific surface area, versatile surface chemistry and exceptional mechanical properties of graphene-based nanosheets enable the formation of robust and high-performance 3DMs such as sponges, membranes, beads and fibres. However, little is known about the relationship between the materials properties of graphene-based 3DMs and their environmental performance. In this Review, we summarize the self-assembly and environmental applications of graphene-based 3DMs in removing contaminants from water and air. We also develop the critical link between the materials properties of 3DMs and their environmental performance, and identify the key parameters that influence their capacities for contaminant removal.

Polydopamine-Based Surface Modification of ZnO Nanoparticles on Sericin/Polyvinyl Alcohol Composite Film for Antibacterial Application

Silk sericin (SS) is a type of natural macromolecular protein with excellent hydrophilicity, biocompatibility and biodegradability, but also has very poor mechanical properties. To develop sericin-based wound dressings, we utilized polyvinyl alcohol (PVA) to reinforce the mechanical property of sericin by blending PVA and sericin, then modified zinc oxide nanoparticles (ZnO NPs) on SS/PVA film with the assistance of polydopamine (PDA) to endow SS/PVA film with antibacterial activity. Scanning electron microscopy, energy dispersive spectroscopy and X-ray powder diffraction demonstrated ZnO NPs were well grafted on PDA-SS/PVA film. Fourier transform infrared spectra suggested PDA coating and ZnONPs modification did not alter the structure of sericin and PVA. Water contact angle and swelling tests indicated the excellent hydrophilicity and swellability of ZnO NPs-PDA-SS/PVA composite film. Mass loss analysis showed ZnO NPs-PDA-SS/PVA film had excellent stability. The mechanical performance test suggested the improved tensile strength and elongation at break could meet the requirement of ZnO NPs-PDA-SS/PVA film in biomaterial applications. The antibacterial assay suggested the prepared ZnO NPs-PDA-SS/PVA composite film had a degree of antimicrobial activity against Escherichia coli and Staphylococcus aureus. The excellent hydrophilicity, swellability, stability, mechanical property and antibacterial activity greatly promote the possibility of ZnO NPs-PDA-SS/PVA composite film in antibacterial biomaterials application.

Powerful antibacterial activity of graphene/nanoflower-like nickelous hydroxide nanocomposites

Aim: The development of new and efficient antibacterial agents is urgent to overcome emerging antimicrobial resistance. Materials & methods: Herein, we have presented a new type of 3D antibacterial system to prompt bacteria to contact with the any plane of nanocomposites. Results: Comparing the antibacterial activity of graphene oxide, reduced graphene oxide and graphene-loaded nanoflower-like nickelous hydroxide (GN/Ni(OH)2) nanocomposites; the GN/Ni(OH)2 showed stronger bactericidal capability toward Gram-negative/-positive bacteria. Moreover, the GN/Ni(OH)2 with low cytotoxicity can promote it as ‘green’ antimicrobial agents. And, the GN/Ni(OH)2 presented long-term stable antibacterial effectiveness after 2-month storage. The antibacterial mechanisms of GN/Ni(OH)2 were evidenced as the 3D contact and violent damage to the bacterial structure. Conclusion: The GN/Ni(OH)2 provides new insights into the antibacterial properties of 3D nanocomposites for effectively fighting pathogen threats in biomedicine and public health.

Fabrication of Bis-Quaternary Ammonium Salt as an Efficient Bactericidal Weapon Against Escherichia coli and Staphylococcus aureus

Combating bacterial pathogens has become a global concern, especially the emergence of drug-resistant bacteria have made conventional antibiotics lose their efficiency. This grim situation suggests the necessity to explore novel antibacterial agents with favorable safety and strong antibacterial activity. Here, we took the advantage of quaternary ammonium compounds and synthesized a long-chain high-molecular organic bis-quaternary ammonium salt (BQAS) with a broad-spectrum bactericidal activity through a facile one-pot reaction. The bactericidal effect of BQAS was evaluated by two bacterial human pathogens: Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), which are the major cause of diarrheal infections in children and adults. Our experimental results indicate that the bactericidal activity of BQAS is linked to the strong contact between the positively charged quaternary ammonium groups and the bacterial cells, thus leading to a temporary and locally high concentration of reactive oxygen species, which subsequently triggers oxidative stress and membrane damage in the bacteria. This mechanism was further confirmed by several assays, such as the membrane permeabilization assay, fluorescent-based cell live/dead test, scanning electron microscopy, transmission electron microscopy, together with the lactate dehydrogenase release assay, which all indicated that BQAS induced damage to the cytoplasmic membrane and the leakage of intracellular fluid containing essential molecules. The excellent bactericidal activity of BQAS suggests its great application potential as a promising candidate against the rapid emergence of drug-resistant bacterial pathogens.

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.

Antimicrobial graphene materials: the interplay of complex materials characteristics and competing mechanisms

Graphene materials (GMs) exhibit attractive antimicrobial activities promising for biomedical and environmental applications. However, we still lack full control over their behaviour and performance mainly due to the complications arising from the coexistence and interplay of multiple factors. Therefore, in this minireview, we attempt to illustrate the structure-property-activity relationships of GMs' antimicrobial activity. We first examine the chemical/physical complexity of GMs focusing on five aspects of their materials characteristics: (i) chemical composition, (ii) impurities and imperfections, (iii) lateral dimension, (iv) self-association (e.g., restacking), and (v) composite/hybrid formation. Next, we briefly summarise the current understanding of their antimicrobial mechanisms. Then, we assign the outlined materials characteristics of GMs to the proposed antimicrobial mechanisms. Lastly, we share our vision regarding the future of research and development in this fast-emerging field.

An overview of graphene materials: Properties, applications and toxicity on aquatic environments

Due to unique chemical and physical properties, nanomaterials from the Graphene family are being increasingly introduced in all fields of science. The specific roles they can occupy within different applications are attracting increased attention by several industrial sectors. These carbon nanoparticles are released into the environment especially accumulating in aquatic systems. Since the discovery of graphene, a number of research actives are being conducted to find out the toxic potential of the Graphene family materials to different organism's models. Although their toxicity effects are well described for biomedical applications, few data were produced with the specific aim of assessing the toxic effects of these carbon nanomaterials in the aquatic environment. The purpose of this review is to compile up-to-date information on properties, applications and characterization methods of graphene family materials in aquatic environments and identified biological toxic impacts of these NMs, with special focus on graphene oxide based on the most recent literature.

Antibacterial and Photocatalytic Properties of ZnO-9-Aminoacridine Hydrochloride Hydrate Drug Nanoconjugates

The development of nanomaterial-based hybrid systems for healthcare and energy-related materials has attracted significant attention nowadays. Here, we have designed a nanocomposite of ZnO nanoparticles (NPs) with anticancer therapeutic drug 9-aminoacridine hydrochloride hydrate (9AA-HCl) for antibacterial and photocatalytic activities. Spectroscopic studies reveal that the photoinduced electron transfer from photoexcited 9AA-HCl to the conduction band of ZnO NP causes the generation of the reactive oxygen species (ROS), which is responsible for antibacterial activity and photocatalytic properties. It is seen that the efficiency of photodegradation of dye molecules increases in ZnO-9AA-HCl nanoconjugated systems than pure ZnO nanoparticles because of efficient charge separation. In addition, the antibacterial efficacy of the nanoconjugate is investigated using a strain of Gram-negative bacteria where the cell-killing activities are observed 99.99 and 100% for 20 and 21 μL/mL nanoconjugate, respectively, and very little cell-killing activity is observed for free ZnO NPs and free drug. Moreover, it is also observed that the nanoconjugate generates sufficient intracellular ROS that can hydrolyze 2',7'-dichlorodihydrofluoresceindiacetate (DCFH-DA) to highly fluorescent 2',7'-dichlorofluorescein (DCF). The outcome of the study will provide valuable information for designing new-edge nanoconjugate materials for potential applications in photocatalytic and antibacterial activities.

In Vitro Cytotoxicity and Morphological Assessments of GO-ZnO against the MCF-7 Cells: Determination of Singlet Oxygen by Chemical Trapping

Graphene-based materials have attracted considerable interest owing to their distinctive characteristics, such as their biocompatibility in terms of both their physical and intrinsic chemical properties. The use of nanomaterials with graphene as a biocompatible agent has increased due to an uptick in dedication from biomedical investigators. Here, GO-ZnO was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV-Vis) spectroscopy, energy dispersive X-ray analysis (EDAX), and Raman spectroscopy for structural, morphological, and elemental analysis. The toxic extent of GO-ZnO was noted by a methyl-thiazole-tetrazolium (MTT), while cellular morphology was observed towards the MCF-7 cells using an inverted microscope at magnification 40×. The cytotoxic effect of GO-ZnO investigated the cell viability reduction in a dose-dependent manner, as well as prompted the cell demise/destruction in an apoptotic way. Moreover, statistical analysis was performed on the experimental outcomes, with p-values < 0.05 kept as significant to elucidate the results. The generation of reactive oxygen species (ROS) demonstrated the potential applicability of graphene in tumor treatment. These key results attest to the efficacy of GO-ZnO nanocomposites as a substantial candidate for breast malignancy treatment.

A Review on Graphene-Based Nanomaterials in Biomedical Applications and Risks in Environment and Health

Graphene-based nanomaterials (GBNs) have attracted increasing interests of the scientific community due to their unique physicochemical properties and their applications in biotechnology, biomedicine, bioengineering, disease diagnosis and therapy. Although a large amount of researches have been conducted on these novel nanomaterials, limited comprehensive reviews are published on their biomedical applications and potential environmental and human health effects. The present research aimed at addressing this knowledge gap by examining and discussing: (1) the history, synthesis, structural properties and recent developments of GBNs for biomedical applications; (2) GBNs uses as therapeutics, drug/gene delivery and antibacterial materials; (3) GBNs applications in tissue engineering and in research as biosensors and bioimaging materials; and (4) GBNs potential environmental effects and human health risks. It also discussed the perspectives and challenges associated with the biomedical applications of GBNs.

Multimetallic Microparticles Increase the Potency of Rifampicin against Intracellular Mycobacterium tuberculosis

Mycobacterium tuberculosis ( M.tb) has the extraordinary ability to adapt to the administration of antibiotics through the development of resistance mechanisms. By rapidly exporting drugs from within the cytosol, these pathogenic bacteria diminish antibiotic potency and drive the presentation of drug-tolerant tuberculosis (TB). The membrane integrity of M.tb is pivotal in retaining these drug-resistant traits. Silver (Ag) and zinc oxide (ZnO) nanoparticles (NPs) are established antimicrobial agents that effectively compromise membrane stability, giving rise to increased bacterial permeability to antibiotics. In this work, biodegradable multimetallic microparticles (MMPs), containing Ag NPs and ZnO NPs, were developed for use in pulmonary delivery of antituberculous drugs to the endosomal system of M.tb-infected macrophages. Efficient uptake of MMPs by M.tb-infected THP1 cells was demonstrated using an in vitro macrophage infection model, with direct interaction between MMPs and M.tb visualized with the use of electron FIB-SEM tomography. The release of Ag NPs and ZnO NPs within the macrophage endosomal system increased the potency of the model antibiotic rifampicin by as much as 76%, realized through an increase in membrane disorder of intracellular M.tb. MMPs were effective at independently driving membrane destruction of extracellular bacilli located at the exterior face of THP1 macrophages. This MMP system presents as an effective drug delivery vehicle that could be used for the transport of antituberculous drugs such as rifampicin to infected alveolar macrophages, while increasing drug potency. By increasing M.tb membrane permeability, such a system may prove effectual in improving treatment of drug-susceptible TB in addition to M.tb strains considered drug-resistant.

Toxicity assessment and mechanistic investigation of engineered monoclinic VO2 nanoparticles

Growing interest in monoclinic VO2 nanoparticles (NPs) among consumers and the industries of window coatings, solar sensors etc. has brought particular attention to their safety concerns. The toxicity of this new class of nanomaterials in bacterial ecosystems has not yet been evaluated. The degree of crystallinity is a significant parameter that determines the performance of materials. However, the previously reported methods for toxicity assessment have neglected its influence. In this work, we systematically evaluated the toxicity of VO2 NPs with different degrees of crystallinity to four typical bacterial strains and studied the influence of physicochemical properties and aging treatment on their antibacterial effect. The results showed that the toxicity of VO2 nanoparticles was very low. Interestingly, we found that antibacterial properties of VO2 NPs were dependent on both bacterial strains and VO2 particle properties. In addition, the highly crystalline VO2 NPs were more toxic than normal and industrial VO2 particles. We attribute the crystallinity-related toxicity to the dissolved vanadium, the physical interactions between the bacteria and particles, and the generation of reactive oxygen species, as supported by our experimental results and theoretical calculation.

The preparation and antibacterial activity of cellulose/ZnO composite: a review

The infectious diseases caused by various bacteria pose serious threat to human health. To solve this problem, antibacterial agents have been widely used in people’s daily life to deactivate or kill these bacteria. Among the antibacterial agents, ZnO is one of the most promising metal oxide antibacterial agents due to its non-toxic nature and safe properties. To expand its application, many composites of ZnO have been widely studied. Cellulose, as one of the most abundant biopolymers, has many merits like biodegradability, biocompatibility and low cost. Thus, many studies focus on synthesized cellulose/ZnO. The synthetic strategy includes both chemical and physical methods. Many of them have been shown that cellulose/ZnO composites have excellent antibacterial activity and are environment-friendly and have many applications for example food packing, antibacterial fibers and so on. This review mainly discusses the preparation methods of cellulose/ZnO and their effect on the morphology and properties.

Electron Transfer Directed Antibacterial Properties of Graphene Oxide on Metals

Nanomaterials such as silver nanoparticles and graphene-based composites are known to exhibit biocidal activities. However, interactions with surrounding medium or supporting substrates can significantly influence this activity. Here, it is shown that superior antimicrobial properties of natural shellac-derived graphene oxide (GO) coatings is obtained on metallic films, such as Zn, Ni, Sn, and steel. It is also found that such activities are directly correlated to the electrical conductivity of the GO-metal systems; the higher the conductivity the better is the antibacterial activity. GO-metal substrate interactions serve as an efficient electron sink for the bacterial respiratory pathway, where electrons modify oxygen containing functional groups on GO surfaces to generate reactive oxygen species (ROS). A concerted effect of nonoxidative electron transfer mechanism and consequent ROS mediated oxidative stress to the bacteria result in an enhanced antimicrobial action of naturally derived GO-metal films. The lack of germicidal effect in exposed cells for GO supported on electrically nonconductive substrates such as glass corroborates the above hypothesis. The results can lead to new GO coated antibacterial metal surfaces important for environmental and biomedical applications.

Antibacterial [2-(Methacryloyloxy) ethyl] Trimethylammonium Chloride Functionalized Reduced Graphene Oxide/Poly(ethylene-co-vinyl alcohol) Multilayer Barrier Film for Food Packaging

The objective of present work was to construct antibacterial [2-(methacryloyloxy) ethyl] trimethylammonium chloride functionalized reduced graphene oxide/poly(ethylene-co-vinyl alcohol) (MTAC-rGO/EVOH) multilayer barrier films by using layer-by-layer assembly under a parallel electric field. Besides barrier and mechanical properties, the antibacterial activities of the film and cytotoxicity of MTAC-rGO nanosheets were extensively investigated. The functionalization of rGO was achieved by grafting MTAC onto a graphene framework through C (sp³)-C bonds. The assembly of MTAC-rGO on the EVOH matrix not only significantly improved film mechanical strength, but also endowed the targeting film with outstanding moisture barrier even under a relative humidity of 99% (e.g., 0.019 g m^-2 s^-1 atm^-1 for (MTAC-rGO/EVOH)₂₀) besides good oxygen barrier (e.g., 0.07 cm³ m^-2 d^-1 atm^-1 for (MTAC-rGO/EVOH)₂₀). Among the testing films, MTAC-rGO/EVOH film had the best antibacterial activity, and the activity against S. aureus was better than E. coli. Meanwhile, the cytotoxicity of MTAC-rGO nanosheets was very low. Results suggest that MTAC-rGO/EVOH film may have great potential in food active packaging.

Efficient coverage of ZnO nanoparticles on cotton fibres for antibacterial finishing using a rapid and low cost in situ synthesis

Antibacterial fabric using a simple, reproducible and low cost technique to synthesize high-quality ZnONPs was prepared and characterized.

Photo-enhanced antibacterial activity of ZnO/graphene quantum dot nanocomposites

Synthesis of new, highly active antibacterial agents has become increasingly important in light of emerging antibiotic resistance. In the present study, ZnO/graphene quantum dot (GQD) nanocomposites were produced by a facile hydrothermal method and characterized by an array of microscopic and spectroscopic measurements, including transmission electron microscopy, X-ray photoelectron spectroscopy, UV-vis and photoluminescence spectroscopy. Antibacterial activity of the ZnO/GQD nanocomposites was evaluated with Escherichia coli within the context of minimum inhibitory concentration and the reduction of the number of bacterial colonies in a standard plate count method, in comparison to those with ZnO and GQD separately. It was found that the activity was markedly enhanced under UV photoirradiation as compared to that in ambient light. This was ascribed to the enhanced generation of reactive oxygen species under UV photoirradiation, with minor contributions from membrane damage, as manifested in electron paramagnetic resonance and fluorescence microscopic measurements. The results highlight the significance of functional nanocomposites based on semiconductor nanoparticles and graphene derivatives in the development of effective bactericidal agents.

Study of Graphene Oxide Structural Features for Catalytic, Antibacterial, Gas Sensing, and Metals Decontamination Environmental Applications

This study represents a comprehensive review about the structural features of graphene oxide (GO) and its significance in environmental applications. Two dimensional (2D) GO is tremendously focused in advanced carbon-based nanomaterials for environmental applications due to its tunable physicochemical characteristics. Herein, we report foundational structural models of GO and explore the chemical bonding of oxygen moieties, with graphite basal plane using various characterization tools. Moreover, the impact of these oxygen moieties and the morphology of GO for environmental applications such as removal of metal ions and catalytic, antibacterial, and gas sensing abilities have here been critically reviewed for the first time. Environmental applications of GO are highly significant because, in the recent era, the fast progress of industries, even in the countryside, results in air and water pollution. GO has been widely investigated by researchers to eradicate such environmental issues and for potential industrial and clinical applications due to its 2D structural features, large surface area, presence of oxygen moieties, nonconductive nature, intense mechanical strength, excellent water dispersibility, and tunable optoelectronic properties. Thence, particular emphasis is directed toward the modification of GO by varying the number of its oxygen functional groups and by coupling it with other exotic nanomaterials to induce unique properties in GO for potential environmental remediation purposes.

Halloysite Nanotubes Supported Ag and ZnO Nanoparticles with Synergistically Enhanced Antibacterial Activity

Novel antimicrobial nanocomposite incorporating halloysite nanotubes (HNTs) and silver (Ag) into zinc oxide (ZnO) nanoparticles is prepared by integrating HNTs and decorating Ag nanoparticles. ZnO nanoparticles (ZnO NPs) and Ag nanoparticles (Ag NPs) with a size of about 100 and 8 nm, respectively, are dispersively anchored onto HNTs. The synergistic effects of ZnO NPs, Ag NPs, and HNTs led to the superior antibacterial activity of the Ag-ZnO/HNTs antibacterial nanocomposites. HNTs facilitated the dispersion and stability of ZnO NPs and brought them in close contact with bacteria, while Ag NPs could promote the separation of photogenerated electron-hole pairs and enhanced the antibacterial activity of ZnO NPs. The close contact with cell membrane enabled the nanoparticles to produce the increased concentration of reactive oxygen species and the metal ions to permeate into the cytoplasm, thus induced quick death of bacteria, indicating that Ag-ZnO/HNTs antibacterial nanocomposite is a promising candidate in the antibacterial fields.

NiO-nanoflakes grafted graphene: an excellent photocatalyst and a novel nanomaterial for achieving complete pathogen control

The increased levels of industrial pollutants in water and of drug-resistant pathogens more generally are a serious threat to human and aquatic life. Herein, we present the solar-light-induced dye removal and bactericidal properties of nickel oxide (NiO) and graphene nanoplatelet (GNP) nanocomposites. The conducting nature of GNPs is the key factor that accounts for the enhanced photocatalytic and antibacterial activity. Remarkably, the graphene/NiO nanocomposite shows outstanding photocatalytic activity (99% degradation) as compared to NiO (34%) alone, which makes it a potential candidate for the depollution of dye-contaminated water. In addition, the optimized amount of GNPs in the graphene/NiO nanocomposite renders it an exceptional antibacterial material, producing 100% growth inhibition of pathogenic microorganisms (both Gram-positive and Gram-negative bacteria). Therefore, the graphene/NiO nanocomposite can be an innovative material to achieve complete pathogen control, alongside being an economic solution for water treatment.

One-Pot Facile Methodology to Synthesize Chitosan-ZnO-Graphene Oxide Hybrid Composites for Better Dye Adsorption and Antibacterial Activity

Novel chitosan-ZnO-graphene oxide hybrid composites were prepared using a one-pot chemical strategy, and their dye adsorption characteristics and antibacterial activity were demonstrated. The prepared chitosan and the hybrids such as chitosan-ZnO and chitosan-ZnO-graphene oxide were characterized by UV-Vis absorption spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy. The thermal and mechanical properties indicate a significant improvement over chitosan in the hybrid composites. Dye adsorption experiments were carried out using methylene blue and chromium complex as model pollutants with the function of dye concentration. The antibacterial properties of chitosan and the hybrids were tested against Gram-positive and Gram-negative bacterial species, which revealed minimum inhibitory concentrations (MICs) of 0.1 µg/mL.