Antibacterial Nanomaterials Research Articles

The Inhibition Effect of Graphene Oxide Nanosheets on the Development ofStreptococcus mutansBiofilms

Bacterial biofilms play a critical role in dental pathogenic mechanisms due to their ability to tolerate many traditional antibacterial agents. Thus, it is crucial to find effective methods to inhibit the occurrence and development of biofilms. Recently, graphene oxide (GO) nanosheets have become a promising antibacterial nanomaterial for use in various applications. This study focuses on the effect of GO nanosheets on the development of Streptococcus mutans biofilms. It is found that GO nanosheets are highly effective at inhibiting the formation of bacterial biofilms at concentrations ranging from low to high in early development stages. After GO treatment, the ratio of living cells in the biofilm decreases significantly, and the biofilm structure is destroyed. In contrast, GO has a minimal effect on mature biofilms.

Synthesis and Applications of Antibacterial N-Halamine Polymers and Nanomaterials

Synthesis and Applications of Antibacterial N-Halamine Polymers and Nanomaterials

{101}-{001} Surface Heterojunction-Enhanced Antibacterial Activity of Titanium Dioxide Nanocrystals Under Sunlight Irradiation.

The {101}-{001} surface heterojunction constructed on polyhedral titanium dioxide (TiO2) nanocrystals has recently been proposed to be favorable for the efficient electron-hole spatial separation due to the preferential accumulation of electron and hole on {101} and {001} facets, respectively. The formed free electron and hole can promote reactive oxygen species (ROS) production, which potentially can be used for inactivation of bacteria. In the present study, a series of truncated octahedral bipyramid TiO2 nanocrystals (T1, T2, T3, and T4) coexposed with {101} and {001} facets were prepared to form various ratios of {101} to {001} facet for optimization of electron-hole spatial separation efficiency. All these polyhedral TiO2 nanocrystals could more significantly produce ROS than spherical TiO2 nanocrystals (Ts), exhibiting the higher antibacterial activity against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria under simulated sunlight irradiation. Among these polyhedral TiO2 nanocrystals, T3 with a {101}/{001} ratio of 1.78 was found to be the best one showing the highest ROS and the most potent antibacterial performance. Scanning electron microscope images of bacteria displayed that the surface membrane structure of both E. coli and S. aureus bacteria was influenced to different extents by these TiO2 nanocrystals, where T3 caused the most severe membrane damage. The molecular mechanism underlying the high antibacterial activity of TiO2 nanocrystals was ascribed to activation of oxidative stress as evidenced by intracellular ROS production, glutathione depletion, and membrane lipid peroxidation in bacteria. The surface heterojunction as a completely new strategy holds great promise to develop effective antibacterial nanomaterials.

Development and Antibacterial Performance of Novel Polylactic Acid-Graphene Oxide-Silver Nanoparticle Hybrid Nanocomposite Mats Prepared By Electrospinning.

Antibacterial nanomaterials have attracted great interest in recent years, especially with an increase in antibiotic resistance of microbial organisms. However, deleterious properties such as aggregation, toxicity of nanoparticles, and low stability limit their practical application. In this respect, we have developed novel PLA-based fibrous mats with GO-Ag hybrid nanofillers through electrospinning for minimizing bacterial attachment and growth for biomedical applications. Polylactic acid (PLA) exhibits low tensile modulus and strength as well as no bactericidal ability. To enhance its tensile and bactericidal performances, 1 wt % graphene oxide (GO), and 1-7 wt % silver nanoparticle (AgNP) are incorporated into the PLA matrix. For comparison, electrospun PLA-1 wt % GO and PLA-AgNP nanocomposites have also been prepared. The morphological, mechanical and thermal properties as well as bactericidal activities of electrospun PLA-based nanocomposite fibrous mats have been investigated. Tensile tests show that the addition of 1 wt % GO or 1-7 wt % AgNPs to PLA leads to a drastic increase in its elastic modulus. Further enhancements in tensile modulus and strength of PLA can be obtained by adding GO-AgNP nanohybrids. The thermal stability of PLA is greatly improved by adding GO-AgNP nanohybrids. Agar disk diffusion test results indicate that the PLA-1 wt %GO nanocomposite has no inhibition zones against Esherichia coli (E. coli) and Staphylococcus aureus (S. aureus). However, GO nanofillers with lateral width of micrometer range act as effective anchoring sites for AgNPs. Thus, PLA-1 wt %GO-(1-7) wt % Ag hybrid fibrous mats exhibit excellent antibacterial effect against E. coli, while the PLA-1 wt %GO-Ag mats with higher AgNP loadings show bacterial inhibition toward S. aureus. The bactericidal effects of PLA-1 wt %GO-(1-7)%Ag hybrids are studied and analyzed using live/dead fluorescent imaging assay, quantitative antibacterial efficacy test, SEM examination and residual oxygen species measurement. Our work highlights the development of electrospun nanocomposite mats as promising antibacterial materials for biomedical applications and systematically depicts the bactericidal mechanism of PLA-GO-Ag nanocomposites.

Thermo-responsive nanoarrays of silver nanoparticle, silicate nanoplatelet and PNiPAAm for the antimicrobial applications

The ternary nanohybrids of silver nanoparticles (AgNPs) in combination with silicate nanoplatelets (NSP) and thermally sensitive poly(N-isopropylacrylamide) (PNiPAAm) were fabricated for antibacterial applications. PNiPAAm were chemically grafted on the NSP by atom-transfer radical polymerization (ATRP) via polymerizing N-isopropylacrylamide monomers with sol-gel linkers (BBTES). The nanoparticles of AgNPs then were adsorbed on NSP-PNiPAAm nanosheets through in situ reduction reaction of AgNO3 in aqueous dispersion. The particle sizes of AgNPs were estimated to be 7–12nm in diameter with different composition ratios of AgNPs to NSP-PNiPAAm, evaluated by transmission electron microscope (TEM). The nanohybrids of AgNP/NSP-PNiPAAm exhibited the unique property of lowest critical solution temperature (LCST) at 32°C. The thermo-responsive antibacterial efficacy of the ternary nanohybrids was demonstrated by Bacillus subtilis (B. subtilis) and Escherichia coli (E. coli) at lower than the LCST (28°C) and higher than the LCST (37°C). The result show that the great antibacterial ability was observed in the hydrophilic bacteria (B. subtilis) at 28°C. In contrast, the excellent antibacterial ability was found in the hydrophobic bacteria (E. coli) at 37°C, due to the surface energy modulation of AgNP/NSP-PNiPAAm. The tailoring of silver-containing ternary nanohybrids allow the new antibacterial nanomaterials to selectively affect the surface of bacteria by varying temperature.

Selective in vitro photothermal nano-therapy of MRSA infections mediated by IgG conjugated gold nanoparticles.

There are serious systemic infections associated with methicillin-resistant Staphylococcus aureus (MRSA) and several other types of bacteria leading to the deaths of millions of people globally. This type of mortality is generally caused by the increasing number of antibiotic-resistant organisms, a consequence of evolution via natural selection. After the synthesis of gold nanoparticles (GNPs) by wet chemistry, bio-functionalization with IgG molecules was performed. Following administration of IgG-GNPs to MRSA cultures at various concentrations and various incubation time laser irradiation was performed. To assess the selectivity and specificity of the proposed treatment the following methods were used: flow cytometry, contrast phase microscopy, and by fluorescence microscopy. The results in our study indicate that following administration of IgG-GNPs biomolecule an extended and selective bacterial death occurs following laser irradiation in a dose dependent manner. Therefore, the new findings might impel studies on these antibacterial nanomaterials and their biological and medical applications.

Preparation and Antibacterial Mechanism Insight of Polypeptide-Based Micelles with Excellent Antibacterial Activities.

Traditional antibiotics usually sterilize in chemical ways, which may lead to serious drug resistance. By contrast, peptide-based antibacterial materials are less susceptible to drug resistance. Herein we report the preparation of an antibacterial peptide-based copolymer micelle and the investigation of its membrane-penetration antibacterial mechanism by transmission electron microscopy (TEM). The copolymer is poly(l-lactide)-block-poly(phenylalanine-stat-lysine) [PLLA31-b-poly(Phe24-stat-Lys36)], which is synthesized by ring-opening polymerization. The PLLA chains form the core, whereas the polypeptide chains form the coronas of the micelle in aqueous solution. This micelle boasts excellent antibacterial efficacy against both Gram-positive and Gram-negative bacteria. Furthermore, TEM studies clearly reveal that the micelles pierce and then destroy the cell membrane of the bacteria. We also compared the advantages and disadvantages of two general methods for measuring the Minimal Inhibitory Concentration (MIC) values of antibacterial micelles. Overall, this study provides us with direct evidence for the antibacterial mechanism of polypeptide-based micelles and a strategy for synthesizing biodegradable antibacterial nanomaterials without antibiotic resistance.

"Race for the Surface": Eukaryotic Cells Can Win.

With an aging population and the consequent increasing use of medical implants, managing the possible infections arising from implant surgery remains a global challenge. Here, we demonstrate for the first time that a precise nanotopology provides an effective intervention in bacterial cocolonization enabling the proliferation of eukaryotic cells on a substratum surface, preinfected by both live Gram-negative, Pseudomonas aeruginosa, and Gram-positive, Staphylococcus aureus, pathogenic bacteria. The topology of the model black silicon (bSi) substratum not only favors the proliferation of eukaryotic cells but is biocompatible, not triggering an inflammatory response in the host. The attachment behavior and development of filopodia when COS-7 fibroblast cells are placed in contact with the bSi surface are demonstrated in the dynamic study, which is based on the use of real-time sequential confocal imaging. Bactericidal nanotopology may enhance the prospect for further development of inherently responsive antibacterial nanomaterials for bionic applications such as prosthetics and implants.

Carbon Nanomaterials as Antibacterial Colloids.

Carbon nanomaterials like graphene, carbon nanotubes, fullerenes and the various forms of diamond have attracted great attention for their vast potential regarding applications in electrical engineering and as biomaterials. The study of the antibacterial properties of carbon nanomaterials provides fundamental information on the possible toxicity and environmental impact of these materials. Furthermore, as a result of the increasing prevalence of resistant bacteria strains, the development of novel antibacterial materials is of great importance. This article reviews current research efforts on characterizing the antibacterial activity of carbon nanomaterials from the perspective of colloid and interface science. Building on these fundamental findings, recent functionalization strategies for enhancing the antibacterial effect of carbon nanomaterials are described. The review concludes with a comprehensive outlook that summarizes the most important discoveries and trends regarding antibacterial carbon nanomaterials.

Rapidly Probing Antibacterial Activity of Graphene Oxide by Mass Spectrometry-based Metabolite Fingerprinting.

Application of nanomaterials as anti-bacteria agents has aroused great attention. To investigate the antibacterial activity and antibacterial mechanism of nanomaterials from a molecular perspective is important for efficient developing of nanomaterial antibiotics. In the current work, a new mass spectrometry-based method was established to investigate the bacterial cytotoxicity of graphene oxide (GO) by the metabolite fingerprinting of microbes. The mass spectra of extracted metabolites from two strains DH5α and ATCC25922 were obtained before and after the incubation with nanomaterials respectively. Then principal component analysis (PCA) of these spectra was performed to reveal the relationship between the metabolism disorder of microbes and bactericidal activity of GO. A parameter “D” obtained from PCA scores was proposed that is capable to quantitatively evaluate the antibacterial activity of GO in concentration and time-dependent experiments. Further annotation of the fingerprinting spectra shows the variabilities of important metabolites such as phosphatidylethanolamine, phosphatidylglycerol and glutathione. This metabolic perturbation of E. coli indicates cell membrane destruction and oxidative stress mechanisms for anti-bacteria activity of graphene oxide. It is anticipated that this mass spectrometry-based metabolite fingerprinting method will be applicable to other antibacterial nanomaterials and provide more clues as to their antibacterial mechanism at molecular level.

Synthesis and Mechanism Insight of a Peptide-Grafted Hyperbranched Polymer Nanosheet with Weak Positive Charges but Excellent Intrinsically Antibacterial Efficacy.

Antimicrobial resistance is an increasingly problematic issue in the world and there is a present and urgent need to develop new antimicrobial therapies without drug resistance. Antibacterial polymers are less susceptible to drug resistance but they are prone to inducing serious side effects due to high positive charge. Herein we report a peptide-grafted hyperbranched polymer which can self-assemble into unusual nanosheets with highly effective intrinsically antibacterial activity but weak positive charges (+ 6.1 mV). The hyperbranched polymer was synthesized by sequential Michael addition-based thiol-ene and free radical mediated thiol-ene reactions, and followed by ring-opening polymerization of N-carboxyanhydrides (NCAs). The nanosheet structure was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies. Furthermore, a novel "wrapping and penetrating" antibacterial mechanism of the nanosheets was revealed by TEM and it is the key to significantly decrease the positive charges but have a very low minimum inhibitory concentration (MIC) of 16 μg mL(-1) against typical Gram-positive and Gram-negative bacteria. Overall, our synthetic strategy demonstrates a new insight for synthesizing antibacterial nanomaterials with weak positive charges. Moreover, the unique antibacterial mechanism of our nanosheets may be extended for designing next-generation antibacterial agents without drug resistance.

Surface arming magnetic nanoparticles with amine N-halamines as recyclable antibacterial agents: Construction and evaluation

Magnetic recyclable antibacterial nanomaterials, i.e., magnetic amine N-halamine nanoparticles (Fe3O4@SiO2/CTMP NPs), were constructed by arming magnetic silica nanoparticles (Fe3O4@SiO2 NPs) with amine N-halamine (CTMP). Magnetic iron oxide nanoparticles were encapsulated into silica layers followed by anchoring antibacterial amine N-halamines to give magnetic/antibacterial bi-functional agents with core-shell structure. Since the presence of Fe3O4 NPs in core, the products offer super-paramagnetic behavior, which made them separable magnetically after the antibacterial behavior. Their sterilizing effect on bacterial strain was evaluated using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as model bacteria via the plate counting technique, zone of inhibition study, and time kill assay. Antibacterial mechanism study illustrated that the products integrate both the contact mechanism and the release mechanism for attacking bacteria. The significant effect of oxidative chlorine content and concentration of the products on antibiotic action were confirmed. Thanks to the magnetic property, the potential recyclability of the products was achieved. Most significantly, the products retain effective antibacterial action even after five cycles. These findings revealed that the products Fe3O4@SiO2/CTMP NPs have promising applications in the antibacterial fields.

Can carbon-based nanomaterials revolutionize membrane fabrication for water treatment and desalination?

Due to their exceptional mechanical, conductive and antibacterial properties carbon-based nanomaterials (CNMs) have been widely used in attempts to fabricate novel membranes for water treatment and desalination with advanced characteristics. This paper reviews the current state of the application of CNMs, including carbon nanotubes, graphene, graphene oxide, carbon nanofibers, MXene, carbide derived carbon and fullerene for membrane preparation. A brief description of different CNMs and their properties has been provided with reference to membrane requirements. Thereafter the recent studies on the membrane fabrication/modification with CNMs as well as the properties of the developed membranes have been critically summarised. It was shown that, in some cases, using CNMs results in novel membranes with high flux, high rejection, low-fouling, and enhanced conductive, thermal and mechanical properties. However, further research including determining the optimum CNM quantity and characteristics, feed-specific membrane performance and long-term operability should be conducted to better evaluate the feasibility of CNM-based membranes in water treatment and desalination. This review paper is potentially important for researchers involved in the membrane fabrication using CNMs.

High antibiofouling property of vertically aligned carbon nanotube membranes at a low cross-flow velocity operation in different bacterial solutions

While membranes have been widely applied in water and wastewater treatment, further studies are still needed on the fouling issues. Vertically aligned carbon nanotube (VA CNT), an antibacterial nanomaterial, is a promising candidate for a membrane because of its superfast water permeability. The antibacterial and antibiofouling properties of VA CNT membranes were reported with a high permeate flux. This study showed the high antibiofouling property of VA CNT membranes at low cross-flow velocity operation in different bacterial solutions, resulting from its high antibacterial property, along with a quantitative comprehension of the relation between biofilms and fouling resistance of VA CNT membranes after membrane operation. These results facilitated the possibility of using VA CNT membranes for wastewater treatment, such as membrane bioreactors, even at a very low cross-flow velocity.

Antibacterial properties of Ag and Ag/AgCl nanoparticles from radish and tea extracts for water treatment applications

Silver nanoparticles (AgNPs) have antibacterial properties and are widely used for water disinfection. This technology is commercially applied in point-of-use water treatment as a post-treatment for filtrate water. However, the current process of synthesizing AgNPs has several disadvantages including the use of hazardous chemicals, consumption of a large amount of energy and the formation of hazardous byproducts. Here, we report an alternative and green synthesis using plant extracts. In this work, the plant extracts came from radish (R) and tea (T), and the AgNPs were derived from a microwave irradiation method. The AgNPs synthesized by chemical-based microwave irradiation (Ag-C) were also used as a control material. The novel method produced a smaller size of nanostructures with good dispersion ability and less agglomeration than those from chemical synthesis. The antibacterial properties of AgNPs on Gram-negative bacteria Escherichia coli (E. coli) and Gram-positive bacteria Staphylococcus aureus (S. aureus) were investigated. The results revealed that AgNPs from both green synthesis and chemical-based methods inactivated both types of bacteria. The green-synthesized AgNPs from radish juice provided a higher percentage of inhibition of E. coli than that of S. aureus. The inactivation rates of the AgNPs increased with increasing concentration of AgNPs. As the concentration of the Ag/AgCl-R and Ag-R increased from 150 μg/mL to 300 μg/mL, complete inactivation required a reduced time for the reaction from 300 minutes to only 30 minutes. Finally, the Ag/AgCl-R and Ag-R offered high antibacterial activity while the Ag-T provided the lowest antibacterial activity. This work provides an alternative method for the eco-synthesis of antibacterial nanomaterials for water treatment.

Reducing Environmental Toxicity of Silver Nanoparticles through Shape Control.

The use of antibacterial silver nanomaterials in consumer products ranging from textiles to toys has given rise to concerns over their environmental toxicity. These materials, primarily nanoparticles, have been shown to be toxic to a wide range of organisms; thus methods and materials that reduce their environmental toxicity while retaining their useful antibacterial properties can potentially solve this problem. Here we demonstrate that silver nanocubes display a lower toxicity toward the model plant species Lolium multiflorum while showing similar toxicity toward other environmentally relevant and model organisms (Danio rerio and Caenorhabditis elegans) and bacterial species (Esherichia coli, Bacillus cereus, and Pseudomonas aeruginosa) compared to quasi-spherical silver nanoparticles and silver nanowires. More specifically, in the L. multiflorum experiments, the roots of silver nanocube treated plants were 5.3% shorter than the control, while silver nanoparticle treated plant roots were 39.6% shorter than the control. The findings here could assist in the future development of new antibacterial products that cause less environmental toxicity after their intended use.

Computational modeling in nanomedicine: prediction of multiple antibacterial profiles of nanoparticles using a quantitative structure-activity relationship perturbation model.

We introduce the first quantitative structure-activity relationship (QSAR) perturbation model for probing multiple antibacterial profiles of nanoparticles (NPs) under diverse experimental conditions. The dataset is based on 300 nanoparticles containing dissimilar chemical compositions, sizes, shapes and surface coatings. In general terms, the NPs were tested against different bacteria, by considering several measures of antibacterial activity and diverse assay times. The QSAR perturbation model was created from 69,231 nanoparticle-nanoparticle (NP-NP) pairs, which were randomly generated using a recently reported perturbation theory approach. The model displayed an accuracy rate of approximately 98% for classifying NPs as active or inactive, and a new copper-silver nanoalloy was correctly predicted by this model with consensus accuracy of 77.73%. Our QSAR perturbation model can be used as an efficacious tool for the virtual screening of antibacterial nanomaterials.

Antibacterial wound dressing from chitosan/polyethylene oxide nanofibers mats embedded with silver nanoparticles.

Novel antibacterial nanomaterials have been developed for biomedical applications. The present study involves the preparation and properties of antibacterial nanofibers from chitosan/polyethylene oxide electrospun nanofibers incorporated with silver nanoparticles. Silver nanoparticles were efficiently synthesized in situ after ultra violet (UV) with AgNO3 as precursor and chitosan/polyethylene oxide as reducing agent and protecting agent, respectively. Then the resultant solutions were electrospun into nanofibers. The formation of silver nanoparticles was confirmed with ultraviolet visible (UV-vis) and transmission electron microscopy (TEM), and the electrospun nanofibers were characterized by scanning electron microscopy and energy dispersive X-ray. The resultant fibers exhibited uniform morphology with silver nanoparticles distributed throughout the fiber. Also, the fibers showed certain tensile strength and excellent antibacterial activity against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Sustained release of silver nanoparticles from fibers could last for over 72 h. The silver-containing chitosan/polyethylene oxide nanofibers showed excellent cytocompatibility.

Ultrashort cationic naphthalene-derived self-assembled peptides as antimicrobial nanomaterials.

Self-assembling dipeptides conjugated to naphthalene show considerable promise as nanomaterial structures, biomaterials, and drug delivery devices. Biomaterial infections are responsible for high rates of patient mortality and morbidity. The presence of biofilm bacteria, which thrive on implant surfaces, are a huge burden on healthcare budgets, as they are highly resistant to current therapeutic strategies. Ultrashort cationic self-assembled peptides represent a highly innovative and cost-effective strategy to form antibacterial nanomaterials. Lysine conjugated variants display the greatest potency with 2% w/v NapFFKK hydrogels significantly reducing the viable Staphylococcus epidermidis biofilm by 94%. Reducing the size of the R-group methylene chain on cationic moieties resulted in reduction of antibiofilm activity. The primary amine of the protruding R-group tail may not be as readily available to interact with negatively charged bacterial membranes. Cryo-SEM, FTIR, CD spectroscopy, and oscillatory rheology provided evidence of supramolecular hydrogel formation at physiological pH (pH 7.4). Cytotoxicity assays against murine fibroblast (NCTC 929) cell lines confirmed the gels possessed reduced cytotoxicity relative to bacterial cells, with limited hemolysis upon exposure to equine erythrocytes. The results presented in this paper highlight the significant potential of ultrashort cationic naphthalene peptides as future biomaterials.

Impacts of size and shape of silver nanoparticles on Arabidopsis plant growth and gene expression

Silver nanoparticles (AgNPs) are widely used as antibacterial nanomaterials; however, the environmental impacts of AgNPs remain uncertain. In this study, Arabidopsis physiological responses and gene expression were investigated after exposure to 3 different morphologies of AgNPs. The triangular (47 ± 7 nm) and spherical (8 ± 2 nm) AgNPs exhibited the lowest and highest degrees of antimicrobial activity, respectively. The AgNP-induced phenotypic alterations in Arabidopsis were correlated with nanoparticle morphology and size, in which the decahedral AgNPs (45 ± 5 nm) induced the highest degree of root growth promotion (RGP); however, the spherical AgNPs exhibited no RGP and induced the highest levels of anthocyanin accumulation in Arabidopsis seedlings. The decahedral and spherical AgNPs induced the lowest and highest levels of Cu/Zn superoxide dismutase (CSD2) accumulation, respectively. Moreover, 3 morphologies of AgNPs induced protein accumulations including cell-division-cycle kinase 2 (CDC2), protochlorophyllide oxidoreductase (POR), and fructose-1,6 bisphosphate aldolase (FBA). Regarding transcription, the AgNPs induced the gene expression of indoleacetic acid protein 8 (IAA8), 9-cis-epoxycarotenoid dioxygenase (NCED3), and dehydration-responsive RD22. Additional studies have shown that AgNPs antagonized the aminocyclopropane-1-carboxylic acid (ACC)-derived inhibition of root elongation in Arabidopsis seedlings, as well as reduced the expression of ACC synthase 7 (ACS7) and ACC oxidase 2 (ACO2), suggesting that AgNPs acted as inhibitors of ethylene (ET) perception and could interfere with ET biosynthesis. In conclusion, AgNPs induce ROS accumulation and root growth promotion in Arabidopsis. AgNPs activate Arabidopsis gene expression involved in cellular events, including cell proliferation, metabolism, and hormone signaling pathways.