Inactivation of bacterial pathogens by carbon nanotubes in suspensions

Surface-anchored carbon nanomaterials for antimicrobial surfaces

Carbon nanomaterials (CNMs) are known for their antimicrobial (antibacterial and antiviral) activity when dispersed in a liquid, but whether this can be transferred to the surface of common materials has rarely been investigated. We have compared two typical CNMs (double-walled carbon nanotubes and few-layer graphene) in their non-oxidised and oxidised forms in terms of their antibacterial (Pseudomonas aeruginosa and Staphylococcus aureus) and antiviral (SARS-CoV2) activities after anchoring them onto the surface of silicone. We propose a very simple and effective protocol using the air-brush spray deposition method to entrap CNMs on the surfaces of two different silicone materials and demonstrate that the nanomaterials are anchored within the polymer while still being in contact with bacteria. We also investigated their antiviral activity against SARS-COV2 after deposition on standard surgical respiratory masks. Our results show that while suspensions of double-walled carbon nanotubes had a moderate effect on P. aeruginosa, this was not transferred after anchoring them to the surface of silicone. In contrast, graphene oxide showed a very strong antibacterial effect on P. aeruginosa and oxidised double-walled carbon nanotubes on S. aureus only when anchored to the surface. No significant antiviral activity was observed. This work paves the way for new antibacterial surfaces based on CNMs.

Effects of Graphene-Based Nanomaterials on Microorganisms and Soil Microbial Communities

The past decades have witnessed intensive research on the biological effects of graphene-based nanomaterials (GBNs) and the application of GBNs in different fields. The published literature shows that GBNs exhibit inhibitory effects on almost all microorganisms under pure culture conditions, and that this inhibitory effect is influenced by the microbial species, the GBN's physicochemical properties, the GBN's concentration, treatment time, and experimental surroundings. In addition, microorganisms exist in the soil in the form of microbial communities. Considering the complex interactions between different soil components, different microbial communities, and GBNs in the soil environment, the effects of GBNs on soil microbial communities are undoubtedly intertwined. Since bacteria and fungi are major players in terrestrial biogeochemistry, this review focuses on the antibacterial and antifungal performance of GBNs, their antimicrobial mechanisms and influencing factors, as well as the impact of this effect on soil microbial communities. This review will provide a better understanding of the effects of GBNs on microorganisms at both the individual and population scales, thus providing an ecologically safe reference for the release of GBNs to different soil environments.

Water-based technologies for improving water quality at the point of use: A review

Water safety concerns are increasing tremendously as a result of the rising population and environmental pollution. As a result, viable water treatment approaches need to be designed to meet the water consumption demands of the population, particularly in developing countries. The recent technological advances in water treatment and purification are well articulated in this review. The efficiency of the materials used for purification and their affordability for people living in rural and remote settlements in various parts of the world have been discussed. Water treatment techniques prior to the rapid advancement of science and technology included a variety of strategies such as coagulation/flocculation, filtration, disinfection, flotation and pH correction. The use of nanotechnology in water treatment and purification has modernized the purification process. Therefore, efficient removal of microbes such as bacteria and viruses are exquisitely accomplished. These technologies may include membrane filtration, ultraviolet irradiation, advanced oxidation ion-exchange and biological filtration technologies. Thus, nanotechnology allows for the fabrication of less expensive systems, allowing even low-income people to benefit from it. Most developing countries find these technologies particularly valuable because access to clean and safe water for drinking and residential needs is critical. This is because access to municipal water supplies is also difficult. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Antibiofilm Effect of Nitric Acid-Functionalized Carbon Nanotube-Based Surfaces against E. coli and S. aureus

Chemically modified carbon nanotubes are recognized as effective materials for tackling bacterial infections. In this study, pristine multi-walled carbon nanotubes (p-MWCNTs) were functionalized with nitric acid (f-MWCNTs), followed by thermal treatment at 600 °C, and incorporated into a poly(dimethylsiloxane) (PDMS) matrix. The materials' textural properties were evaluated, and the roughness and morphology of MWCNT/PDMS composites were assessed using optical profilometry and scanning electron microscopy, respectively. The antibiofilm activity of MWCNT/PDMS surfaces was determined by quantifying culturable Escherichia coli and Staphylococcus aureus after 24 h of biofilm formation. Additionally, the antibacterial mechanisms of MWCNT materials were identified by flow cytometry, and the cytotoxicity of MWCNT/PDMS composites was tested against human kidney (HK-2) cells. The results revealed that the antimicrobial activity of MWCNTs incorporated into a PDMS matrix can be efficiently tailored through nitric acid functionalization, and it can be increased by up to 49% in the absence of surface carboxylic groups in f-MWCNT samples heated at 600 °C and the presence of redox activity of carbonyl groups. MWCNT materials changed the membrane permeability of both Gram-negative and Gram-positive bacteria, while they only induced the production of ROS in Gram-positive bacteria. Furthermore, the synthesized composites did not impact HK-2 cell viability, confirming the biocompatibility of MWCNT composites.

Automatic classification of microplastics and natural organic matter mixtures using a deep learning model

Several preprocessing procedures are required for the classification of microplastics (MPs) in aquatic systems using spectroscopic analysis. Procedures such as oxidation, which are employed to remove natural organic matter (NOM) from MPs, can be time- and cost-intensive. Furthermore, the identification process is prone to errors due to the subjective judgment of the operators. Therefore, in this study, deep learning (DL) was applied to improve the classification accuracies for mixtures of microplastic and natural organic matter (MP-NOM). A convolutional neural network (CNN)-based DL model with a spatial attention mechanism was adopted to classify substances from their Raman spectra. Subsequently, the classification results were compared with those obtained using conventional Raman spectral library software to evaluate the applicability of the model. Additionally, the crucial spectral band for training the DL model was investigated by applying gradient-weighted class activation mapping (Grad-CAM) as a post-processing technique. The model achieved an accuracy of 99.54%, which is much higher than the 31.44% achieved by the Raman spectral library. The Grad-CAM approach confirmed that the DL model can effectively identify MPs based on their visually prominent peaks in the Raman spectra. Furthermore, by tracking distinctive spectra without relying solely on visually prominent peaks, we can accurately classify MPs with less prominent peaks, which are characterized by a high standard deviation of intensity. These findings demonstrate the potential for automated and objective classification of MPs without the need for NOM preprocessing, indicating a promising direction for future research in microplastic classification.

Oxidative Stress Response and E. coli Biofilm Formation under the Effect of Pristine and Modified Carbon Nanotubes

The article investigates the expression of oxyR and soxS oxidative stress genes in E. coli under the effect of pristine multi-walled carbon nanotubes (MWCNTs) and pristine single-walled carbon nanotubes (SWCNTs), MWCNTs and SWCNTs functionalized with carboxyl groups (MWCNTs-COOH and SWCNTs-COOH, respectively), SWCNTs functionalized with amino groups (SWCNTs-NH₂) and SWCNTs functionalized with octadecylamine (SWCNTs-ODA). Significant differences were found in the expression of the soxS gene, while no changes were observed in the expression level of the oxyR gene. The pro-oxidant effect of SWCNTs, SWCNTs-COOH, SWCNTs-NH₂, and SWCNTs-ODA is presented, and the contrary antioxidant effect of pristine MWCNTs and MWCNTs-COOH in the presence of methyl viologen hydrate (paraquat) is shown. The article shows that SWCNTs-COOH, SWCNTs-NH₂, and SWCNTs-ODA added to the medium generate the production of reactive oxygen species (ROS) in bacterial cells. SWCNTs-COOH intensified the E. coli biofilm formation, and the biofilm biomass exceeded the control by 25 times. Additionally, it is shown that the rpoS expression increased in response to MWCNTs-COOH and SWCNTs-COOH, and the effect of SWCNTs-COOH was more significant. SWCNTs-COOH and SWCNTs-NH₂ initiated an increase in ATP concentration in the planktonic cells and a decrease in the biofilm cells. The atomic force microscopy (AFM) method showed that the volume of E. coli planktonic cells after the exposure to carbon nanotubes (CNTs) decreased compared to that without exposure, mainly due to a decrease in cell height. The absence of a strong damaging effect of functionalized SWCNTs on E. coli K12 cells, both in suspension and in biofilms, is shown. Contact with functionalized SWCNTs initiated the aggregation of the polymeric substances of the biofilms; however, the cells did not lyse. Among the studied CNTs, SWCNTs-COOH caused an increased expression of the soxS and rpoS, the formation of ROS, and stimulation of the biofilm formation.

Synthesis of Graphene Quantum Dot Magnesium Hydroxide Nanocomposites and Investigation of Their Antioxidant and Antimicrobial Activities

In this paper, we synthesized graphene quantum dots magnesium hydroxide nanocomposites (GQDs/Mg(OH)₂). The synthesized nanocomposites were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Malvern Zetasizer. The antimicrobial and antioxidant properties of the obtained GQDs/Mg(OH)₂ nanocomposites were investigated. GQDs/Mg(OH)₂ nanocomposites have MIC values of 15.625 μg/mL against fungi (C. metapsilosis and C. parapsilosis) and 62.5 μg/mL against Gram (+) (S. pneumonia and E. faecalis) and Gram (-) (E. coli). The synthesized GQDs/Mg(OH)₂ nanocomposites showed moderate antioxidant activity. The results showed that at 100-µg/mL GQDs/Mg(OH)₂ nanocomposite concentration, the H₂O₂ scavenging activity was 62.18%.

The improvement of periodontal tissue regeneration using a 3D-printed carbon nanotube/chitosan/sodium alginate composite scaffold

Periodontal disease is a common disease in the oral field, and many researchers are studying periodontal disease and try to find some biological scaffold materials to make periodontal tissue regenerative. In this study, we attempted to construct a carbon nanotube/chitosan/sodium alginate (CNT/CS/AL) ternary composite hydrogel and then prepare porous scaffold by 3D printing technology. Subsequently, characterizing the materials and testing the mechanical properties of the scaffold. Additionally, its effect on the proliferation of human periodontal ligament cells (hPDLCs) and its antibacterial effect on Porphyromonas gingivalis were detected. We found that CNT/CS/AL porous composite scaffolds with uniform pores could be successfully prepared. Moreover, with increasing CNT concentration, the degradation rate and the swelling degree of scaffold showed a downward trend. The compressive strength test indicated the elastic modulus of composite scaffolds ranged from 18 to 80 kPa, and 1% CNT/CS/AL group had the highest quantitative value. Subsequently, cell experiments showed that the CNT/CS/AL scaffold had good biocompatibility and could promote the proliferation of hPDLCs. Among 0.1%-1% CNT/CS/AL groups, the biocompatibility of 0.5% CNT/CS/AL scaffold performed best. Meanwhile, in vitro antibacterial experiments showed that the CNT/CS/AL scaffold had a certain bacteriostatic effect on P. gingivalis. When the concentration of CNT was more than 0.5%, the antimicrobial activity of composite scaffold was significantly promoted, and about 30% bacteria were inactivated. In conclusion, this 3D-printed CNT/CS/AL composite scaffold, with good material properties, biocompatibility and bacteriostatic activity, may be used for periodontal tissue regeneration, providing a new avenue for the treatment of periodontal disease.

Validating Methods To Eradicate Plant-Pathogenic Ralstonia Strains Reveals that Growth In Planta Increases Bacterial Stress Tolerance

Plant-pathogenic bacteria in the Ralstonia solanacearum species complex (RSSC) cause highly destructive bacterial wilt disease of diverse crops. Wilt disease prevention and management is difficult because RSSC persists in soil, water, and plant material. Growers need practical methods to kill these pathogens in irrigation water, a common source of disease outbreaks. Additionally, the R. solanacearum race 3 biovar 2 (R3bv2) subgroup is a quarantine pest in many countries and a highly regulated select agent pathogen in the United States. Plant protection officials and researchers need validated protocols to eradicate R3bv2 for regulatory compliance. To meet these needs, we measured the survival of four R3bv2 and three phylotype I RSSC strains following treatment with hydrogen peroxide, stabilized hydrogen peroxide (Huwa-San), active chlorine, heat, UV radiation, and desiccation. No surviving RSSC cells were detected after cultured bacteria were exposed for 10 min to 400 ppm hydrogen peroxide, 50 ppm Huwa-San, 50 ppm active chlorine, or temperatures above 50°C. RSSC cells on agar plates were eradicated by 30 s of UV irradiation and killed by desiccation on most biotic and all abiotic surfaces tested. RSSC bacteria did not survive the cell lysis steps of four nucleic acid extraction protocols. However, bacteria in planta were more difficult to kill. Stems of infected tomato plants contained a subpopulation of bacteria with increased tolerance of heat and UV light, but not oxidative stress. This result has significant management implications. We demonstrate the utility of these protocols for compliance with select agent research regulations and for management of a bacterial wilt outbreak in the field. IMPORTANCE Bacteria in the Ralstonia solanacearum species complex (RSSC) are globally distributed and cause destructive vascular wilt diseases of many high-value crops. These aggressive pathogens spread in diseased plant material and via contaminated soil, tools, and irrigation water. A subgroup of the RSSC, race 3 biovar 2, is a European and Canadian quarantine pathogen and a U.S. select agent subject to stringent and constantly evolving regulations intended to prevent pathogen introduction or release. We validated eradication and inactivation methods that can be used by (i) growers seeking to disinfest water and manage bacterial wilt disease outbreaks, (ii) researchers who must remain in compliance with regulations, and (iii) regulators who are expected to define containment practices. Relevant to all these stakeholders, we show that while cultured RSSC cells are sensitive to relatively low levels of oxidative chemicals, desiccation, and heat, more aggressive treatment, such as autoclaving or incineration, is required to eradicate plant-pathogenic Ralstonia growing inside plant material.

Anti-Infective and Toxicity Properties of Carbon Based Materials: Graphene and Functionalized Carbon Nanotubes

Recently, antimicrobial activities of various carbon-based nanomaterials against specific pathogens have become one of the most significant research interests in this field. Carbon nanotubes (CNTs) are promising multidisciplinary nanostructures in biomedicine, drug delivery, genetic engineering, biosensors, and artificial implants. However, the biomedical administration of CNTs is dependent on their solubility, toxicity, and biocompatibility, as well as novel drug-delivery applications through optimization of the drug's loading capacity, cellular absorption, and continuous release within the target cell. The usage of CNTs and Graphene materials as antimicrobial agents and nanocarriers for antibiotics delivery would possibly improve their bioavailability and facilitate better anti-infective therapy. However, it is worth mentioning that CNTs' antimicrobial activity and toxicity are highly dependent on their preparation and synthesis method. Various types of research have confirmed that diameter, length, residual catalyst, metal content, surface coating, electronic structure, and dispersibility would affect CNTs' toxicity toward bacteria and human cells. In this review article, a general study was performed on the antimicrobial properties of carbon-based nanomaterials, as well as their toxicity and applications in confronting different microorganisms. This study could be useful for researchers who are looking for new and effective drug delivery methods in the field of microbial resistance.

Broad-Spectrum Antibacterial Activity of Synthesized Carbon Nanodots from d-Glucose

Carbon nanodots, a class of carbon nano-allotropes, have been synthesized through different routes and methods from a wide range of precursors. The selected precursor, synthetic method, and conditions can strongly alter the physicochemical properties of the resulting material and their intended applications. Herein, carbon nanodots (CNDs) have been synthesized from d-glucose by combining pyrolysis and chemical oxidation methods. The effect of the pyrolysis temperature, equivalents of oxidizing agent, and refluxing time were studied on the product and quantum yield. In the optimum conditions (pyrolysis temperature of 300 °C, 4.41 equiv of H2O2, 90 min of reflux) CNDs were obtained with 40% and 3.6% of product and quantum yields, respectively. The obtained CNDs are negatively charged (ζ-potential = -32 mV), excellently dispersed in water, with average diameter of 2.2 nm. Furthermore, ammonium hydroxide (NH4OH) was introduced as dehydrating and/or passivation agent during CNDs synthesis resulting in significant improvement of both product and quantum yields of about 1.5 and 3.76-fold, respectively. The synthesized CNDs showed a broad spectrum of antibacterial activities toward different Gram-positive and Gram-negative bacteria strains. Both synthesized CNDs caused highly colony forming unit reduction (CFU), ranging from 98% to 99.99% for most of the tested bacterial strains. However, CNDs synthesized in the absence of NH4OH, due to a negatively charged surface enriched in oxygenated groups, performed better in zone inhibition and minimum inhibitory concentration. The elevated antibacterial activity of high-oxygen-containing carbon nanodots is directly correlated to their ROS formation ability.

Physicochemical Properties and Antibacterial Activity of Gellan Gum Incorporating Zinc Oxide/Carbon Nanotubes Bionanocomposite Film for Wound Healing

Wound healing dressing based on a natural polymer of gellan gum incorporating zinc oxide nanoparticles and multiwall carbon nanotubes (GG/ZnONP + MWCNT) bionanocomposite film was fabricated via the solution casting method. The physicochemical properties of the film were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM). Moreover, the antibacterial properties of the bionanocomposite film were investigated for wound healing applications. The characterization results confirmed the reinforcement of the gellan gum (GG) matrix with zinc oxide nanoparticles (ZnONP) and multiwall carbon nanotubes (MWCNT), as an amorphous GG/ZnONP + MWCNT bionanocomposite film was obtained. SEM morphological analysis shows that the addition of ZnONP and MWCNT nanofillers changed the film microstructure into a sponge-like structure that is more suitable for fluid uptake and thus more useful for wound healing. The GG/ZnONP + MWCNT bionanocomposite film demonstrated good antibacterial activity against all strains tested. Furthermore, macroscopic analysis shows that the wound treated with GG/ZnONP + MWCNT bionanocomposite film recovered completely (100%) in 14 days, compared to pure GG film (90.76%) and negative control (77.40%). As a result, the GG/ZnONP + MWCNT bionanocomposite film could be a promising wound dressing material.

Functionalization of Multi-Walled Carbon Nanotubes Changes Their Antibiofilm and Probiofilm Effects on Environmental Bacteria

Releasing multi-walled carbon nanotubes (MWCNTs) into ecosystems affects the biofilm formation and metabolic activity of bacteria in aquatic and soil environments. Pristine (pMWCNTs), oleophilic (oMWCNTs), hydrophilic (hMWCNTs), and carboxylated (cMWCNTs) carbon nanotubes were used to investigate their effects on bacterial biofilm. A pronounced probiofilm effect of modified MWCNTs was observed on the Gram-negative bacteria of Pseudomonas fluorescens C2, Acinetobacter guillouiae 11 h, and Alcaligenes faecalis 2. None of the studied nanomaterials resulted in the complete inhibition of biofilm formation. The complete eradication of biofilms exposed to MWCNTs was not observed. The functionalization of carbon nanotubes was shown to change their probiofilm and antibiofilm effects. Gram-negative bacteria were the most susceptible to destruction, and among the modified MWCNTs, oMWCNTs had the greatest effect on biofilm destruction. The number of living cells in the biofilms was assessed by the reduction of XTT, and metabolic activity was assessed by the reduction of resazurin to fluorescent resorufin. The biofilms formed in the presence of MWCNTs reduced tetrozolium to formazan more actively than the control biofilms. When mature biofilms were exposed to MWCNTs, dehydrogenase activity decreased in Rhodococcus erythropolis 4-1, A. guillouiae 11 h, and A. faecalis 2 in the presence of pMWCNTs and hMWCNTs, as well as in A. guillouiae 11 h exposed to cMWCNTs. When mature biofilms were exposed to pMWCNTs, hMWCNTs, and cMWCNTs, the metabolism of cells decreased in most strains, and oMWCNTs did not have a pronounced inhibitory effect. The antibiofilm and probiofilm effects of MWCNTs were strain-dependent.

Engineering plants with carbon nanotubes: a sustainable agriculture approach

Sustainable agriculture is an important conception to meet the growing food demand of the global population. The increased need for adequate and safe food, as well as the ongoing ecological destruction associated with conventional agriculture practices are key global challenges. Nanomaterials are being developed in the agriculture sector to improve the growth and protection of crops. Among the various engineered nanomaterials, carbon nanotubes (CNTs) are one of the most promising carbon-based nanomaterials owing to their attractive physiochemical properties such as small size, high surface area, and superior mechanical and thermal strength, offering better opportunities for agriculture sector applications. This review provides basic information about CNTs, including their history; classification; and electrical, thermal, and mechanical properties, with a focus on their applications in the agriculture field. Furthermore, the mechanisms of the uptake and translocation of CNTs in plants and their defense mechanisms against environmental stresses are discussed. Finally, the major shortcomings, threats, and challenges of CNTs are assessed to provide a broad and clear view of the potential and future directions for CNT-based agriculture applications to achieve the goal of sustainability.

A review on removal strategies of microorganisms from water environment using nanomaterials and their behavioural characteristics

Significant findings for microbial removal have led to expertise on several kinds of nanomaterials that made new paths for removing various biological contaminants in a variety of water resources in recent years. Furthermore, advancements in multifunctional nanocomposites synthesis pave the enhanced possibility for their use in water treatment system design. The adsorption towards microbial elimination has been reviewed and compared in this review article using four common kinds of nanomaterials: carbon materials, metal oxides, metal/metal oxides, polymeric metal oxide nanocomposites and their most important mechanistic behavior also discussed. We also describe and analyze recent findings on the effects of engineered nanomaterials on microbial communities in natural and artificial environments. Understanding the removal mechanistic strategy is crucial to improving the nanoparticles (NPs) efficiency and increasing their applicability against a variety of bacteria in various environmental conditions. Also, our study focused on their behavioral effects on microbial structure and functionality towards the removal. Future research opportunities connected to the use of nanomaterials in microbial control and inactivation with societal and health implications are also discussed. We also highlight a number of interesting research subjects that might be of futuristic interest to the scientific community.

Advanced metal and carbon nanostructures for medical, drug delivery and bio-imaging applications

Nanoparticles (NPs) offer great promise for biomedical, environmental, and clinical applications due to their several unique properties as compared to their bulk counterparts. In this review article, we overview various types of metal NPs and magnetic nanoparticles (MNPs) in monolithic form as well as embedded into polymer matrices for specific drug delivery and bio-imaging fields. The second part of this review covers important carbon nanostructures that have gained tremendous attention recently in such medical applications due to their ease of fabrication, excellent biocompatibility, and biodegradability at both cellular and molecular levels for phototherapy, radio-therapeutics, gene-delivery, and biotherapeutics. Furthermore, various applications and challenges involved in the use of NPs as biomaterials are also discussed following the future perspectives of the use of NPs in biomedicine. This review aims to contribute to the applications of different NPs in medicine and healthcare that may open up new avenues to encourage wider research opportunities across various disciplines.

Dispersant Effects on Single-Walled Carbon Nanotube Antibacterial Activity

There is significant interest in understanding whether nanomaterials with outstanding mechanical or electrical properties also possess antibacterial properties. However, assessment of antibacterial activity is a complex problem at the interface of chemistry and microbiology. Results can be affected by many factors including nanomaterial size, surface chemistry, concentration, and the dispersion media. The difficulty of dispersing nanomaterials such as single-walled carbon nanotubes (SWNTs) has resulted in many studies being conducted in the presence of dispersion aides which may themselves contribute to bacterial stress. The recent discovery that a standard microbial growth media, tryptic soy broth (TSB), is an effective SWNT dispersant provides a new opportunity to investigate the potential antibacterial activity of SWNTs using dispersants that range from antibacterial to growth-supporting. The five dispersants chosen for this work were Sodium dodecyl sulfate (SDS), pluronic, lysozyme, DNA, and tryptic soy broth. Staphylococcus aureus and Salmonella enterica were used as the model Gram-positive and Gram-negative bacteria. Activity was measured in terms of colony forming unit (CFU) and optical density measurements. None of the systems exhibited activity against Salmonella. SDS was fatal to Staph. aureus regardless of the presence of SWNTs. The activity of pluronic and lysozyme against Staph. aureus was enhanced by the presence of SWNTs. In contrast, the DNA and TSB dispersions did not have any activity regardless of the presence of SWNTs. These results highlight that the purported antibacterial activity of SWNTs may only be effective against bacteria that are sensitized by the dispersant and suggests the need for additional research on the mechanisms by which SWNT-dispersant interactions can result in antibacterial activity.

Composites based on graphite oxide and zirconium phthalocyanines with aromatic amino acids as photoactive materials

This article is a part of a scientific project focused on obtaining a new type of composite materials that are characterized by singlet oxygen generation upon irradiation with red light, which can be used as antibacterial agents. The composite material is nanoscale graphite oxide (GO) particles covalently bonded to an axially substituted zirconium phthalocyanine complex. For this purpose, two phthalocyanine zirconium complexes, axially mono-substituted with 4-aminosalicylic or 4-aminophthalic acids, were prepared and measured in terms of structure, morphology, and spectroscopic properties. The zirconium phthalocyanines are photosensitizers, and the axial ligands are bridging links connecting the complexes to the GO carrier (due to their terminal amino groups and carboxyl groups, respectively). The axial ligand in zirconium phthalocyanine complexes has a strong influence on the stability and optical properties of composite materials and, consequently, on reactive oxygen species (ROS) generation. In this paper, the effect of composite components (4-aminophthalato or 4-aminosalicylato substituted zirconium phthalocyanine complex as a photosensitizer and graphite oxide as a carrier and modulator of the action of active components) on ROS generation for potential antibacterial use is discussed.

Joint effects of carbon nanotubes and copper oxide nanoparticles on fermentation metabolism towards Saccharofermentans acetigenes: Enhancing environmental adaptability and transcriptional expression

In this study, the joint effects of widely used copper oxide nanoparticles (CuO NPs) and multi-walled carbon nanotubes (MWCNTs) on the fermentation metabolism of a model acetogenic bacterium Saccharofermentans acetigenes were investigated and the underlying mechanisms were further explored. The presence of sole CuO NPs or MWCNTs severely inhibited the acetate generation, while their co-existences did not further decrease the acetate yield as expected. Further analysis indicated the joint effects facilitated the enhancement of bacterial stimulus response to the environment and interspecies communication, which improved adaptive capacity to the adverse environment involved in nanomaterials. Meanwhile, the co-existence reduced inhibitory effects of sole nanomaterial on the gene expressions and catalytic activities of key enzymes involved in glycolysis and pyruvate metabolism. Therefore, the joint effects could enhance environmental adaptation of S. acetigenes and transcriptional expressions of key enzymes for acetic acid production-related processes, alleviating the inhibition of CuO NPs to acetate production.

An Overview of Antimicrobial Properties of Carbon Nanotubes-Based Nanocomposites

The development of carbon-based nanomaterials has extensively facilitated new discoveries in various fields. Carbon nanotube-based nanocomposites (CNT-based nanocomposites) have lately recognized as promising biomaterials for a wide range of biomedical applications due to their unique electronic, mechanical, and biological properties. Nanocomposite materials such as silver nanoparticles (AgNPs), polymers, biomolecules, enzymes, and peptides have been reported in many studies, possess a broad range of antibacterial activity when incorporated with carbon nanotubes (CNTs). It is crucial to understand the mechanism which governs the antimicrobial activity of these CNT-based nanocomposite materials, including the decoupling individual and synergistic effects on the cells. In this review, the interaction behavior between microorganisms and different types of CNT-based nanocomposites is summarized to understand the respective antimicrobial performance in different conditions. Besides, the current development stage of CNT-based nanocomposite materials, the technical challenges faced, and the exceptional prospect of implementing potential antimicrobial CNT-based nanocomposite materials are also discussed.

Detoxification of Ciprofloxacin in an Anaerobic Bioprocess Supplemented with Magnetic Carbon Nanotubes: Contribution of Adsorption and Biodegradation Mechanisms

In anaerobic bioreactors, the electrons produced during the oxidation of organic matter can potentially be used for the biological reduction of pharmaceuticals in wastewaters. Common electron transfer limitations benefit from the acceleration of reactions through utilization of redox mediators (RM). This work explores the potential of carbon nanomaterials (CNM) as RM on the anaerobic removal of ciprofloxacin (CIP). Pristine and tailored carbon nanotubes (CNT) were first tested for chemical reduction of CIP, and pristine CNT was found as the best material, so it was further utilized in biological anaerobic assays with anaerobic granular sludge (GS). In addition, magnetic CNT were prepared and also tested in biological assays, as they are easier to be recovered and reused. In biological tests with CNM, approximately 99% CIP removal was achieved, and the reaction rates increased ≈1.5-fold relatively to the control without CNM. In these experiments, CIP adsorption onto GS and CNM was above 90%. Despite, after applying three successive cycles of CIP addition, the catalytic properties of magnetic CNT were maintained while adsorption decreased to 29 ± 3.2%, as the result of CNM overload by CIP. The results suggest the combined occurrence of different mechanisms for CIP removal: adsorption on GS and/or CNM, and biological reduction or oxidation, which can be accelerated by the presence of CNM. After biological treatment with CNM, toxicity towards Vibrio fischeri was evaluated, resulting in ≈ 46% detoxification of CIP solution, showing the advantages of combining biological treatment with CNM for CIP removal.

Slime molds response to carbon nanotubes exposure: from internalization to behavior

Carbon nanotubes (CNTs) offer attractive opportunities due to their physical, electrical, mechanical, optical, and thermal properties. They are used in a wide range of applications and are found in numerous consumer products. On the downside, their increasing presence in the environment poses potential threats to living organisms and ecosystems. The aim of this study was to evaluate the toxicity of double-walled carbon nanotubes (DWCNTs) on a new model system: the acellular slime mold Physarum polycephalum. Despite its ecological significance, its simplicity of organization, and its behavioral complexity, exposure of such organisms to nanoparticles has been poorly investigated. Slime molds were exposed to DWCNTs using three routes of exposure (topical, food, environment). We first demonstrated that DWCNTs were rapidly internalized by slime molds especially when DWCNTs were mixed with the food or spread out in the environment. Secondly, we showed that a 6-week exposure to DWCNTs did not lead to bioaccumulation nor did it lead to persistence in the slime molds when they entered a resting stage. Thirdly, we revealed that 2 days following exposure, DWCNTs were almost entirely excreted from the slime molds. Lastly, we uncovered that DWCNTs exposure altered the migration speed, the pseudopods formation, and the expansion rate of the slime molds. Our results extend our current knowledge of CNTs cytotoxicity and introduce P. polycephalum as an ideal organism for nanotoxicology.

Proanthocyanin-Capped Biogenic TiO2 Nanoparticles with Enhanced Penetration, Antibacterial and ROS Mediated Inhibition of Bacteria Proliferation and Biofilm Formation: A Comparative Approach

Biofunctionalized TiO₂ nanoparticles with a size range of 18.42±1.3 nm were synthesized in a single-step approach employing Grape seed extract (GSE) proanthocyanin (PAC) polyphenols. The effect of PACs rich GSE corona was examined with respect to 1) the stability and dispersity of as-synthesized GSE-TiO₂ -NPs, 2) their antiproliferative and antibiofilm efficacy, and 3) their propensity for internalization and reactive oxygen species (ROS) generation in urinary tract infections (UTIs) causing Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus saprophyticus strains. State-of-the-art techniques were used to validate GSE-TiO₂ -NPs formation. Comparative Fourier transformed infrared (FTIR) spectral analysis demonstrated that PACs linked functional -OH groups likely play a central role in Ti⁴⁺ reduction and nucleation to GSE-TiO₂ -NPs, while forming a thin, soft corona around nascent NPs to attribute significantly enhanced stability and dispersity. Transmission electron microscopic (TEM) and inductively coupled plasma mass-spectroscopy (ICP-MS) analyses confirmed there was significantly (p<0.05) enhanced intracellular uptake of GSE-TiO₂ -NPs in both Gram-negative and -positive test uropathogens as compared to bare TiO₂ -NPs. Correspondingly, compared to bare NPs, GSE-TiO₂ -NPs induced intracellular ROS formation that corresponded well with dose-dependent inhibitory patterns of cell proliferation and biofilm formation in both the tested strains. Overall, this study demonstrates that -OH rich PACs of GSE corona on biogenic TiO₂ -NPs maximized the functional stability, dispersity and propensity of penetration into planktonic cells and biofilm matrices. Such unique merits warrant the use of GSE-TiO₂ -NPs as a novel, functionally stable and efficient antibacterial nano-formulation to combat the menace of UTIs in clinical settings.

A phytomass-inspired carbon and its importance as an antibacterial agent against human pathogens

Background

Imprudent use of antimicrobial drugs has resulted in the microbial resistance among the known microbes and hence we foresee a pressing need towards the development of novel, low-cost, and high potent antimicrobials which should be munificent by nature. In the pursuit of the above, phosphoric acid activated low-cost carbon was produced from a renewable phytomass precursor viz., leaves of Vitex negundo L. plant and explored for its antibacterial efficacy against four human pathogens viz., S. aureus, S. pyogenes (Gram-positive bacteria), and E. coli, P. aeruginosa (Gram-negative bacteria) by adopting well diffusion method. Carbon yield, burn-off, phase purity, elemental composition, particle morphology, and surface functionalities have been studied by ultimate elemental analysis, X-ray diffractometry, elemental analysis, scanning electron microscopy, and Fourier transform infrared spectrophotometry respectively. Minimal inhibition concentration (MIC) was also followed. Plausible mechanism of killing the pathogens by the above activated carbon was also provided.

Results

Vitex negundo leaves derived activated carbon (VNLAC) was found to contain large number of O-, S- and N-containing surface groups which are supposedly responsible for bestowing antibacterial properties to the carbon derived from Vitex negundo leaves. It has emerged as a potential antibacterial agent for many Gram-negative as well as Gram-positive bacteria. The inhibition zone of mean diameters ranged from 9 to 25 mm against all the pathogens was significantly (p < 0.05) less than that of the control viz., ciprofloxacin. Thus, the fundamental experimental results may extend the limits of carbon sources but also the conventional idea of obtaining active carbon to apply in technologies where carbon is inevitable.

Conclusion

The work not only demonstrates the promising potential of VNLAC as an efficient antibacterial agent but also presents a feasible mechanism of action of removing pathogens. Vitex negundo-derived carbon may become a cheap substitute for cost-prohibitive drugs. The findings of the work illustrate an easy choice as an antibacterial for topical application at infected sites.

Antimicrobial and anti-adhesive properties of carbon nanotube-based surfaces for medical applications: a systematic review

Although high-performance carbon materials are widely used in surface engineering, with emphasis on carbon nanotubes (CNTs), the application of CNT nanocomposites on medical surfaces is poorly documented. In this study, we aimed to evaluate the antimicrobial and anti-adhesive properties of CNT-based surfaces. For this purpose, a PRISMA-oriented systematic review was conducted based on predefined criteria and 59 studies were selected for the qualitative analysis. Results from the analyzed studies suggest that surfaces containing modified CNTs, and specially CNTs conjugated with different polymers, exhibited strong antimicrobial and anti-adhesive activities. These composites seem to preserve the CNT toxicity to microorganisms and promote CNT-cell interactions, as well as to protect them from nonspecific protein adsorption. However, CNTs cannot yet compete with the conventional strategies to fight biofilms as their toxicity profile on the human body has not been thoroughly addressed. This review can be helpful for the development of new engineered medical surfaces.

Review on Carbon Nanotube Varieties for Healthcare Application: Effect of Preparation Methods and Mechanism Insight

Many potential uses of carbon nanotubes (CNT) in various sectors have created an urge to assess their diverse range of properties pertaining to various applications like catalysis, biosensor, and antimicrobial activity. Increasing studies on the biosensor and antibacterial activity of CNT have prompted tremendous interest in the utilization of the carbon-based nanostructured material as an alternative to currently existing antibiotics. However, the study of bactericidal aspects of this nanomaterial is relatively new and hence the deeper understanding of the various physicochemical characteristics and antimicrobial nature of CNT is extremely wanted. This review covers the effect of framework substitution and explains the understanding of membrane disintegration and oxidative stresses upon nanomaterials for antimicrobial activity. The present article has also reviewed effect of preparation nanoparticle deposition and framework modification on carbon nanotube structure. The recent research on graphene-modified nanomaterials for biosensor applications related to healthcare/clinical applications have also been discussed. Major physicochemical contributing factors such as size, functionalization, high surface area, and aggregation features of CNT assisting in the bacterial killing have nicely been outlined. Hence, the present review explains the supporting information related with Single and multi-walled carbon nanotube and summarized the advantages of functionalized carbon nanotube/graphene-based nanostructured carbon-based materials towards protection and reduction of bacterial/viral infections in the healthcare sector.

Tailoring Carbon Nanotubes to Enhance their Efficiency as Electron Shuttle on the Biological Removal of Acid Orange 10 Under Anaerobic Conditions

Anaerobic treatments have been described for the biodegradation of pollutants. However, the reactions proceed slowly due to the recalcitrant nature of these compounds. Carbon nanomaterials (CNM) intermediate in, and favor, the electron transfer, accelerating the anaerobic reduction of pollutants, which act as final electron acceptors. In the present work, different carbon nanotubes (CNT) with modified surface chemistry, namely CNT oxidized with HNO₃ (CNT_HNO₃) and CNT doped with nitrogen in a ball milling process (CNT_N_MB) were prepared using commercial CNT as a starting material. The new CNM were tested as redox mediators (RM), 0.1 g L^-1, in the biological reduction of the azo dye, Acid Orange 10 (AO10), with an anaerobic granular sludge, over 48 h of reaction. Methane production was also assessed to verify the microorganism's activity and the CNM's effect on the methanogenic activity. An improvement in the biological removal of AO10 occurred with all CNM (above 90%), when compared with the control without CNM (only 32.4 ± 0.3%). The best results were obtained with CNT_N_MB, which achieved 98.2 ± 0.1% biological AO10 removal, and an 11-fold reduction rate increase. In order to confer magnetic properties to the CNM, tailored CNT were impregnated with 2% of iron-samples: CNT@2%Fe, CNT@2%Fe_N_MB, and CNT@2%Fe_HNO₃. The better performance of the CNT doped with nitrogen was confirmed with CNT@2%Fe_N_MB, and the magnetic character facilitated its recovery after treatment, and did not affect its good catalytic properties. No dye removal was observed in the abiotic assays, so the removal was not due to adsorption on the CNM. Furthermore, the microorganism's viability was maintained during the assay and methane production was not affected by the presence of the CNM. Despite the toxic character of the aromatic amines formed, detoxification was observed after the biological process with thermally treated CNT.

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.

Advances in Biodegradable 3D Printed Scaffolds with Carbon-Based Nanomaterials for Bone Regeneration

Bone possesses an inherent capacity to fix itself. However, when a defect larger than a critical size appears, external solutions must be applied. Traditionally, an autograft has been the most used solution in these situations. However, it presents some issues such as donor-site morbidity. In this context, porous biodegradable scaffolds have emerged as an interesting solution. They act as external support for cell growth and degrade when the defect is repaired. For an adequate performance, these scaffolds must meet specific requirements: biocompatibility, interconnected porosity, mechanical properties and biodegradability. To obtain the required porosity, many methods have conventionally been used (e.g., electrospinning, freeze-drying and salt-leaching). However, from the development of additive manufacturing methods a promising solution for this application has been proposed since such methods allow the complete customisation and control of scaffold geometry and porosity. Furthermore, carbon-based nanomaterials present the potential to impart osteoconductivity and antimicrobial properties and reinforce the matrix from a mechanical perspective. These properties make them ideal for use as nanomaterials to improve the properties and performance of scaffolds for bone tissue engineering. This work explores the potential research opportunities and challenges of 3D printed biodegradable composite-based scaffolds containing carbon-based nanomaterials for bone tissue engineering applications.

Cytotoxicity Effects of Water-Soluble Multi-Walled Carbon Nanotubes Decorated with Quaternized Hyperbranched Poly(ethyleneimine) Derivatives on Autotrophic and Heterotrophic Gram-Negative Bacteria

Oxidized multi-walled carbon nanotubes (oxCNTs) were functionalized by a simple non-covalent modification procedure using quaternized hyperbranched poly(ethyleneimine) derivatives (QPEIs), with various quaternization degrees. Structural characterization of these hybrids using a variety of techniques, revealed the successful and homogenous anchoring of QPEIs on the oxCNTs' surface. Moreover, these hybrids efficiently dispersed in aqueous media, forming dispersions with excellent aqueous stability for over 12 months. Their cytotoxicity effect was investigated on two types of gram(-) bacteria, an autotrophic (cyanobacterium Synechococcus sp. PCC 7942) and a heterotrophic (bacterium Escherichia coli). An enhanced, dose-dependent antibacterial and anti-cyanobacterial activity against both tested organisms was observed, increasing with the quaternization degree. Remarkably, in the photosynthetic bacteria it was shown that the hybrid materials affect their photosynthetic apparatus by selective inhibition of the Photosystem-I electron transport activity. Cytotoxicity studies on a human prostate carcinoma DU145 cell line and 3T3 mouse fibroblasts revealed that all hybrids exhibit high cytocompatibility in the concentration range, in which they also exhibit both high antibacterial and anti-cyanobacterial activity. Thus, QPEI-functionalized oxCNTs can be very attractive candidates as antibacterial and anti-cyanobacterial agents that can be used for potential applications in the disinfection industry, as well as for the control of harmful cyanobacterial blooms.

Interactions of Fe-N-S Co-Doped Porous Carbons with Bacteria: Sorption Effect and Enzyme-Like Properties

Carbon-based (nano)materials doped with transition metals, nitrogen and other heteroatoms are considered active heterogeneous catalysts in a wide range of chemical processes. Recently they have been scrutinized as artificial enzymes since they can catalyze proton-coupled electron transfer reactions vital for living organisms. Herein, interactions between Gram-positive and Gram-negative bacteria and either metal-free N and/or S doped or metal containing Fe-N-S co-doped porous carbons are studied. The Fe- and N-co-doped porous carbons (Fe-N-C) exhibit enhanced affinity toward bacteria as they show the highest adsorption capacity. Fe-N-C materials also show the strongest influence on the bacteria viability with visible toxic effect. Both types of bacteria studied reacted to the presence of Fe-doped carbons in a similar manner, showing a decrease in dehydrogenases activity in comparison to controls. The N-coordinated iron-doped carbons (Fe-N-C) may exhibit oxidase/peroxidase-like activity and activate O2 dissolved in the solution and/or oxygen-containing species released by the bacteria (e.g., H2O2) to yield highly bactericidal reactive oxygen species. As Fe/N/ and/or S-doped carbon materials efficiently adsorb bacteria exhibiting simultaneously antibacterial properties, they can be applied, inter alia, as microbiological filters with enhanced biofouling resistance.

Synergistic effect of adding bioglass and carbon nanotubes on poly (lactic acid) porous membranes for guided bone regeneration

Polymer membranes have been widely used in guided bone regeneration (GBR), especially when it comes to their use in dentistry. Poly (lactic acid) (PLA) have good mechanical properties such as flexibility, which allows the material to be moldable and also has biocompatibility and biodegradation. Besides that, bioglass (BG) incorporated into the polymer matrix can promote osteoinduction properties and osteoconduction properties to the polymer-ceramic biocomposite. The membranes are also required to exhibit antimicrobial activity to prevent or control the proliferation of pathogenic microorganisms, and the addition of carbon nanotubes (CNT) can assist in this property. The porous membranes of PLA with the addition of different contents of BG and CNT were obtained by solvent casting in controlled humidity method, and the synergistic effect of the addition of both fillers were investigated. The membranes showed pores (3-11 μm) on their surface. The addition of 5 wt% BG causes an increase in the surface porosity and bioactivity properties of the PLA. The agar diffusion test showed antimicrobial activity in the membranes with addition of CNT. In vitro results showed that the porous membranes were not cytotoxic and allowed cell activity and differentiation. Thus, BG collaborated to increase biological activity while CNT contributed to microbial activity, creating a synergistic effect on PLA porous membranes, being this effect more evident for PLA/5BG/1.0CNT. These results indicated a promising use of this new biomaterial for the production of porous membranes for GBR.

Suspended multiwalled, acid-functionalized carbon nanotubes promote aggregation of the opportunistic pathogen Pseudomonas aeruginosa

The increasing prevalence of carbon nanotubes (CNTs) as components of new functional materials has the unintended consequence of causing increases in CNT concentrations in aqueous environments. Aqueous systems are reservoirs for bacteria, including human and animal pathogens, that can form biofilms. At high concentrations, CNTs have been shown to display biocidal effects; however, at low concentrations, the interaction between CNTs and bacteria is more complicated, and antimicrobial action is highly dependent upon the properties of the CNTs in suspension. Here, impact of low concentrations of multiwalled CNTs (MWCNTs) on the biofilm-forming opportunistic human pathogen Pseudomonas aeruginosa is studied. Using phase contrast and confocal microscopy, flow cytometry, and antibiotic tolerance assays, it is found that sub-lethal concentrations (2 mg/L) of MWCNTs promote aggregation of P. aeruginosa into multicellular clusters. However, the antibiotic tolerance of these "young" bacterial-CNT aggregates is similar to that of CNT-free cultures. Overall, our results indicate that the co-occurrence of MWCNTs and P. aeruginosa in aqueous systems, which promotes the increased number and size of bacterial aggregates, could increase the dose to which humans or animals are exposed.

Polymethyl Methacrylate-Based Bone Cements Containing Carbon Nanotubes and Graphene Oxide: An Overview of Physical, Mechanical, and Biological Properties

Every year, millions of people in the world get bone diseases and need orthopedic surgery as one of the most important treatments. Owing to their superior properties, such as acceptable biocompatibility and providing great primary bone fixation with the implant, polymethyl methacrylate (PMMA)-based bone cements (BCs) are among the essential materials as fixation implants in different orthopedic and trauma surgeries. On the other hand, these BCs have some disadvantages, including Lack of bone formation and bioactivity, and low mechanical properties, which can lead to bone cement (BC) failure. Hence, plenty of studies have been concentrating on eliminating BC failures by using different kinds of ceramics and polymers for reinforcement and also by producing composite materials. This review article aims to evaluate mechanical properties, self-setting characteristics, biocompatibility, and bioactivity of the PMMA-based BCs composites containing carbon nanotubes (CNTs), graphene oxide (GO), and carbon-based compounds. In the present study, we compared the effects of CNTs and GO as reinforcement agents in the PMMA-based BCs. Upcoming study on the PMMA-based BCs should concentrate on trialing combinations of these carbon-based reinforcing agents as this might improve beneficial characteristics.

Elucidation of Antimicrobial Activity of Non-Covalently Dispersed Carbon Nanotubes

Microorganisms have begun to develop resistance because of inappropriate and extensive use of antibiotics in the hospital setting. Therefore, it seems to be necessary to find a way to tackle these pathogens by developing new and effective antimicrobial agents. Carbon nanotubes (CNTs) have attracted growing attention because of their remarkable mechanical strength, electrical properties, and chemical and thermal stability for their potential applications in the field of biomedical as therapeutic and diagnostic nanotools. However, the impact of carbon nanotubes on microbial growth has not been fully investigated. The primary purpose of this research study is to investigate the antimicrobial activity of CNTs, particularly double-walled and multi-walled nanotubes on representative pathogenic strains such as Gram-positive bacteria Staphylococcus aureus, Gram-negative bacteria Pseudomonas aeruginosa, Klebsiella pneumoniae, and fungal strain Candida albicans. The dispersion ability of CNT types (double-walled and multi-walled) treated with a surfactant such as sodium dodecyl-benzenesulfonate (SDBS) and their impact on the microbial growth inhibition were also examined. A stock concentration 0.2 mg/mL of both double-walled and multi-walled CNTs was prepared homogenized by dispersing in surfactant solution by using probe sonication. UV-vis absorbance, Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM) were used for the characterization of CNTs dispersed in the surfactant solution to study the interaction between molecules of surfactant and CNTs. Later, scanning electron microscopy (SEM) was used to investigate how CNTs interact with the microbial cells. The antimicrobial activity was determined by analyzing optical density growth curves and viable cell count. This study revealed that microbial growth inhibited by non-covalently dispersed CNTs was both depend on the concentration and treatment time. In conclusion, the binding of surfactant molecules to the surface of CNTs increases its ability to disperse in aqueous solution. Non-covalent method of CNTs dispersion preserved their structure and increased microbial growth inhibition as a result. Multi-walled CNTs exhibited higher antimicrobial activity compared to double-walled CNTs against selected pathogens.

Effects of carbon nanotubes on biodegradation of pollutants: Positive or negative?

Recently, a large quantity of carbon nanotubes (CNTs) enters the environment due to the increasing production and applications. More and more researches are focused on the fate and possible ecological risks of CNTs. Some literatures summarized the effects of CNTs on the chemical behavior and fate of pollutants. However, little reviewed the effects of CNTs on the biodegradation of pollutants. In general, the effects of CNTs on the biodegradation of pollutants and the related mechanisms were summarized in this review. CNTs have positive or negative effects on the biodegradation of contaminants by affecting the functional microorganisms, enzymes and the bioavailability of pollutants. CNTs may affect the microbial growth, activity, biomass, community composition, diversity and the activity of enzymes. The decrease of the bioavailability of pollutants due to the sorption on CNTs also causes the reduction of the biodegradation of contaminants. In addition, the roles of CNTs are controlled by multiple mechanisms, which are divided into three aspects i.e., properties of CNTs, environment condition, and microorganisms themself. The better understanding of the fate of CNTs and their impacts on the biochemical process in the environment is conducive to determine the release of CNTs into the environment.

Carbon Dots as Potent Antimicrobial Agents

Carbon dots (CDots) have emerged to represent a highly promising new platform for visible/natural light-activated microbicidal agents. In this article, the syntheses, structures, and properties of CDots are highlighted, representative studies on their activities against bacteria, fungi, and viruses reviewed, and the related mechanistic insights discussed. Also highlighted and discussed are the excellent opportunities for potentially extremely broad applications of this new platform, including theranostics uses.

Structure-Property-Toxicity Relationships of Graphene Oxide: Role of Surface Chemistry on the Mechanisms of Interaction with Bacteria

Graphene oxide (GO) is an antimicrobial agent with tunable surface chemistry. To identify the physicochemical determinants of GO's antimicrobial activity, we generated different modified Hummer's GO materials thermally annealed at 200, 500, or 800 °C (TGO200, TGO500, and TGO800, respectively) to modify the surface oxygen groups on the material. Plating assays show that as-received GO (ARGO) and TGO200, TGO500, and TGO800 reduce Escherichia coli viability by 50% (EC₅₀) at 183, 143, 127, and 86 μg/mL, respectively, indicating higher bacterial toxicity as ARGO is reduced. To uncover the toxicity mechanism of GO, fluorescent dye-based assays were used to measure oxidative stress at the EC₅₀. ARGO showed an increase in intracellular reactive oxygen species, measured as an increase in 2',7'-dichlorodihydrofluorescein diacetate fluorescence, whereas TGO500 and TGO800 induced an increase in the fluorescence of fluorescein diacetate (FDA) by 30 and 42%, suggesting a decrease in cell permeability. Because of a possible wrapping mechanism, plating assays after post-exposure sonication were performed to explain TGO's low oxidative response and high FDA levels. Results show no difference in colony-forming units, indicating that inhibition of cell growth is a result of the adsorption of bacterial cells on the GO material. By comparing different GO samples at their EC₅₀, this study reveals that reduction of GO alters both the mechanisms of cellular interaction and the degree of toxicity to bacteria.

Antibacterial Nanocomposites Based on Thermosetting Polymers Derived from Vegetable Oils and Metal Oxide Nanoparticles

Thermosetting polymers derived from vegetable oils (VOs) exhibit a wide range of outstanding properties that make them suitable for coatings, paints, adhesives, food packaging, and other industrial appliances. In addition, some of them show remarkable antimicrobial activity. Nonetheless, the antibacterial properties of these materials can be significantly improved via incorporation of very small amounts of metal oxide nanoparticles (MO-NPs) such as TiO2, ZnO, CuO, or Fe3O4. The antimicrobial efficiency of these NPs correlates with their structural properties like size, shape, and mainly on their concentration and degree of functionalization. Owing to their nanoscale dimensions, high specific surface area and tailorable surface chemistry, MO-NPs can discriminate bacterial cells from mammalian ones, offering long-term antibacterial action. MO-NPs provoke bacterial toxicity through generation of reactive oxygen species (ROS) that can target physical structures, metabolic paths, as well as DNA synthesis, thereby leading to cell decease. Furthermore, other modes of action-including lipid peroxidation, cell membrane lysis, redox reactions at the NP-cell interface, bacterial phagocytosis, etc.-have been reported. In this work, a brief description of current literature on the antimicrobial effect of VO-based thermosetting polymers incorporating MO-NPs is provided. Specifically, the preparation of the nanocomposites, their morphology, and antibacterial properties are comparatively discussed. A critical analysis of the current state-of-art on these nanomaterials improves our understanding to overcome antibiotic resistance and offers alternatives to struggle bacterial infections in public places.

Antibacterial Carbon-Based Nanomaterials

The emergence and global spread of bacterial resistance to currently available antibiotics underscore the urgent need for new alternative antibacterial agents. Recent studies on the application of nanomaterials as antibacterial agents have demonstrated their great potential for management of infectious diseases. Among these antibacterial nanomaterials, carbon-based nanomaterials (CNMs) have attracted much attention due to their unique physicochemical properties and relatively higher biosafety. Here, a comprehensive review of the recent research progress on antibacterial CNMs is provided, starting with a brief description of the different kinds of CNMs with respect to their physicochemical characteristics. Then, a detailed introduction to the various mechanisms underlying antibacterial activity in these materials is given, including physical/mechanical damage, oxidative stress, photothermal/photocatalytic effect, lipid extraction, inhibition of bacterial metabolism, isolation by wrapping, and the synergistic effect when CNMs are used in combination with other antibacterial materials, followed by a summary of the influence of the physicochemical properties of CNMs on their antibacterial activity. Finally, the current challenges and an outlook for the development of more effective and safer antibacterial CNMs are discussed.

Antibacterial activity of chitosan nano-composites and carbon nanotubes: A review

Bacteriological contamination of water sources is a major challenge that has a detrimental impact on both the environment and human health. This imposes the search for the most efficient disinfectant. Despite their antibacterial efficiency, traditional methods can often form disinfection byproducts through their reaction with organic and inorganic compounds. Substitutes for conventional bacterial inactivation methods should not produce harmful byproducts and must also be cost effective. Nanotechnology is an attractive option that is suited for surface reactions as nanostructures offer large surface to volume ratios. Technologies using chitosan-modified nanocomposites and carbon nanotubes have proven to offer promising alternatives for bacterial inactivation. To enhance their antibacterial efficiency, such technologies have been modified chemically and physically and have as well been associated with other treatment techniques. However, despite their high bacterial disinfection efficacy and lack of treatment byproducts, the vagueness in bacterial inactivation mechanisms and complexity in materials preparation have often obscured their wide scale application. The aim of this manuscript is to review the recent advances in bacterial disinfection using nanomaterials, in the form of chitosan and carbon nanotubes. The rapid rate of research and the notable progress in this area dictate the frequent compilation and dissemination of recent introductions to this field. Existing gaps in the literature are thus also highlighted and reported discrepancies are pinpointed so that roadmaps for future studies may be figured.

Phage shock protein and gene responses of Escherichia coli exposed to carbon nanotubes

Two-dimensional electrophoretic, western blotting, and quantitative polymerase chain reaction analyses of Escherichia coli cells exposed to pristine single walled carbon nanotubes (SWCNTs), and hydroxyl and carboxylic functionalized SWCNTs (SWCNT-OHs and SWCNT-COOHs) were conducted. SWCNT concentration and length were experimental variables. Exposing E. coli cells to SWCNTs led to changes in protein and gene expressions. Several proteins altered their regulations at a low SWCNT concentration (10 μg/ml) and were shut down at a high SWCNT concentration (100 μg/ml). The expressions of the phage shock protein (psp) operon including pspA, pspB, and pspC genes responded to the membrane stressors, SWCNTs, were also examined. While pspA and pspC expressions were influenced by the length, concentration, and functional groups of SWCNTs, pspB expression was not induced by SWCNTs. The alterations in phage shock protein and gene expressions indicated that SWCNTs caused cell membrane perturbation.

Antibacterial activity of carbon nanoparticles isolated from chimney soot

Carbon nanoparticles (CNPs) are isolated from chimney soot and characterised by various tools such as X-ray diffraction, scanning electron microscopy, transmission electron microscopy and ultraviolet-visible spectroscopy. The X-ray diffraction studies confirm the presence of C₆₀ nanoparticles in the isolated sample. The thermal properties of the prepared CNPs are recorded using thermogravimetric analysis and differential thermal analysis. The analysis of the antibacterial activity of the synthesised CNPs against selected Gram-positive and Gram-negative bacterial strains is also investigated. The systematic study confirms that CNPs collected from chimney soot exhibit good antibacterial potency against Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumoniae, and Proteus mirabilis.

Culture of dental pulp stem cells on nanoporous alumina substrates modified by carbon nanotubes

PURPOSE

Alumina substrates are one of the commonly used scaffolds applied in cell culture, but in order to prevent formation of biofilm on the alumina substrate, these substrates are modified with carbon nanotube.

METHODS

The alumina substrate was made by a two-step anodization method and was then modified with carbon nanotubes by simple chemical reaction. The substrates were characterized with FTIR, SEM, EDX, 3D laser scanning digital microscope, contact angle (CA) and surface free energy (SFE). To determine how this modification influences the reduction of biofilm, biofilm of two various bacteria, Escherichia coli (E.coli) and Staphylococcus aureus (S. aureus), were investigated.

RESULTS

The biofilm on the modified substrate decreased due to the presence of carbon nanotubes and increased antibacterial properties. Dental pulp stem cells (DPSCs) were cultured onto flat alumina (FA) and nanoporous alumina-multiwalled carbon nanotubes (NAMC) substrates to examine how the chemical modification and surface topography affects growth of DPSCs.

CONCLUSION

Cell attachment and proliferation were investigated with SEM and Presto Blue assay, and the findings show that the NAMC substrates are suitable for cell culture.

Reduction in energy for electrochemical disinfection of E. coli in urine simulant

ABSTRACT

We report the development of novel modes of operation for electrochemical disinfection of E. coli in human urine simulant with an aim to minimize the energy required for disinfection. The system employs boron-doped diamond electrodes and will be part of an energy neutral, water and additive free outdoor toilet being developed for use in developing countries. Disinfection had been previously demonstrated with voltage being continuously applied to the electrode until disinfection was achieved. In the present study, a new pulsed mode of operation is investigated. This includes a continuous on mode, where oxidants are generated until disinfection is achieved, a single cycle mode, where oxidants are generated for a fixed time and the water is circulated so allow already generated oxidants to disinfect, and a pulsed mode with different duty cycles, which is like the single cycle mode but with multiple cycles. Disinfection was achieved with pulsed mode operation with a 68% energy reduction compared to the continuous on mode. Energy saving was most likely achieved by lengthening the contact time of the disinfectant with the bacteria and increased generation of non-chlorine disinfecting oxidants.

GRAPHICAL ABSTRACT