Quantitative Analysis of Metal Impurities in Carbon Nanotubes: Efficacy of Different Pretreatment Protocols for ICPMS Spectroscopy

Determination of Metallic Impurities in Carbon Nanotubes by Glow Discharge Mass Spectrometry

A method for the rapid assessment of metallic impurities in carbon nanotubes (CNTs) by pin-cell source geometry glow discharge mass spectrometry (GDMS) is presented. Pins were prepared by pressing CNT powder onto an indium substrate. GDMS analysis was performed using high-carbon-content nanotube and coal-certified reference materials for calibration purposes. This approach enables the calibrated measurement of 41 elemental impurities in CNTs. The method was validated by the analysis of NIST SRM 2483 single-wall CNTs (raw soot) with good agreement with the certified values. The proposed measurement approach could also be applied not only for CNTs but also for the assessment of precursor materials used in the synthesis of CNTs and for quality control during the entire manufacturing process. The ability to assess the presence of all metallic impurities in a simple, reliable, high-throughput manner will allow the industry to real-time monitor any changes in the product process, access its toxicity, and environmental impact. As sample preparation is maintained to a minimum, this allows the determination of metallic impurities at concentration levels that are usually not attainable by most techniques.

Recent advances in graphene nanoribbons for biosensing and biomedicine

In recent years, a new type of quasi-one-dimensional graphene-based material, graphene nanoribbons (GNRs), has attracted increasing attention. The limited domain width and rich edge configurations of GNRs endow them with unique properties and wide applications in comparison to two-dimensional graphene. This review article mainly focuses on the electrical, chemical and other properties of GNRs, and further introduces the typical preparation methods of GNRs, including top-down and bottom-up strategies. Then, their biosensing and biomedical applications are highlighted in detail, such as biosensors, photothermal therapy, drug delivery, etc. Finally, the challenges and future prospects in the synthesis and application of functionalized GNRs are discussed. It is expected that GNRs will have significant practical use in biomedical applications in the future.

Toxicological Aspects of Carbon Nanotubes, Fullerenes and Graphenes

Nanomedicines exhibit unbelievable capability in overcoming the hurdles faced in biological applications. Carbon nanotubes (CNTs), graphene-family nanomaterials and fullerenes are a class of engineered nanoparticles that have emerged as a new option for possible use in drug/gene delivery for life-threatening diseases. Their adaptability to pharmaceutical applications has opened new vistas for biomedical applications. Successful applications of this family of engineered nanoparticles in various fields may not support their use in medicine due to inconsistent data on toxicity as well as the lack of a centralized toxicity database. Inconsistent toxicological studies and lack of mechanistic understanding have been the reasons for limited understanding of their toxicological aspects. These nanoparticles, when underivatized or pristine, are considered as safe, however less reactive. The derivatized forms or functionalization changes their chemistry significantly to modify their biological effects including toxicity. They can cause acute and long term injuries in tissues by penetration through the the blood-air barrier, blood-alveolus barrier, blood-brain barrier, and blood-placenta barrier. and by accumulating in the lung, liver, and spleen . The toxicological effects are manifested through inflammatory response, DNA damage, apoptosis, autophagy and necrosis. Other factors that largely influence the toxicity of carbon nanotubes, graphenes and fullerenes are the concentration, functionalization, dimensional and surface topographical factors. Thus, a better understanding of the toxicity profile of CNTs, graphene-family nanomaterials and fullerenes in humans, animals and the environment is of significant importance, to improve their biological safety, to facilitate their wide biological application and for the successful commercial application. The exploration of appropriate cell lines to investigate specific receptors and intracellular targets as well as chronic toxicity beyond the proof-of-concept is required.

Carbon black nanoparticles induce cell necrosis through lysosomal membrane permeabilization and cause subsequent inflammatory response

Rationale: The adverse health effects of nano-particulate pollutants have attracted much attention in recent years. Carbon nanomaterials are recognized as risk factors for prolonged inflammatory responses and diffuse alveolar injury. Previous research indicated a central role of alveolar macrophages in the pathogenesis of particle-related lung disease, but the underlying mechanism remains largely unknown. Methods: C57BL/6 mice were intratracheally instilled with carbon black nanoparticles (CBNPs). Cell necrosis and the infiltrated neutrophils in the lungs were detected by flow cytometry. Release of mitochondria was observed with Mito Tracker and mitochondrial DNA (mtDNA) was quantified by qPCR via Taqman probes. TLR9-p38 MAPK signaling pathway was detected by Western blotting. The production of lipid chemoattractant leukotriene B4 (LTB4) in the supernatant and bronchoalveolar lavage fluid (BALF) was quantitated using an enzyme immunoassay (EIA). Results: In the present study, we found that a single instillation of CBNPs induced neutrophil influx in C57BL/6 mice as early as 4 h post-exposure following the rapid appearance of cell damage indicators in BALF at 30 min. Macrophages exposed to CBNPs showed necrotic features and were characterized by lysosome rupture, cathepsin B release, reactive oxygen species generation, and reduced intracellular ATP level. Necrosis was partly inhibited by a specific lysosomal cathepsin B inhibitor CA074 Me. Further analyses suggested that the resulting leakage of mtDNA from the necrotic cells activated neutrophils and triggered severe inflammation in vivo. Pulmonary neutrophilic inflammation induced by mtDNA was reduced in TLR9-/- mice. Additionally, mtDNA induced LTB4 production from macrophages, which may contribute to neutrophil recruitment. Conclusion: We demonstrated here that CBNPs induce acute cell necrosis through lysosomal rupture and that mtDNA released from necrotic cells functions as a key event mediating pulmonary neutrophilic inflammation. This study described a novel aspect of the pathogenesis of particle-induced inflammatory response and provided a possible therapeutic target for the regulation of inflammation.

Yttrium Residues in MWCNT Enable Assessment of MWCNT Removal during Wastewater Treatment

Many analytical techniques have limited sensitivity to quantify multi-walled carbon nanotubes (MWCNTs) at environmentally relevant exposure concentrations in wastewaters. We found that trace metals (e.g., Y, Co, Fe) used in MWCNT synthesis correlated with MWCNT concentrations. Because of low background yttrium (Y) concentrations in wastewater, Y was used to track MWCNT removal by wastewater biomass. Transmission electron microscopy (TEM) imaging and dissolution studies indicated that the residual trace metals were strongly embedded within the MWCNTs. For our specific MWCNT, Y concentration in MWCNTs was 76 µg g⁻¹, and single particle mode inductively coupled plasma mass spectrometry (spICP-MS) was shown viable to detect Y-associated MWCNTs. The detection limit of the specific MWCNTs was 0.82 µg L⁻¹ using Y as a surrogate, compared with >100 µg L⁻¹ for other techniques applied for MWCNT quantification in wastewater biomass. MWCNT removal at wastewater treatment plants (WWTPs) was assessed by dosing MWCNTs (100 µg L⁻¹) in water containing a range of biomass concentrations obtained from wastewater return activated sludge (RAS) collected from a local WWTP. Using high volume to surface area reactors (to limit artifacts of MWCNT loss due to adsorption to vessel walls) and adding 5 g L⁻¹ of total suspended solids (TSS) of RAS (3-h mixing) reduced the MWCNT concentrations from 100 µg L⁻¹ to 2 µg L⁻¹. The results provide an environmentally relevant insight into the fate of MWCNTs across their end of life cycle and aid in regulatory permits that require estimates of engineered nanomaterial removal at WWTPs upon accidental release into sewers from manufacturing facilities.

Cellular Toxicity and Immunological Effects of Carbon-based Nanomaterials

BACKGROUND

Carbon nanomaterials are a growing family of materials featuring unique physicochemical properties, and their widespread application is accompanied by increasing human exposure.

MAIN BODY

Considerable efforts have been made to characterize the potential toxicity of carbon nanomaterials in vitro and in vivo. Many studies have reported various toxicology profiles of carbon nanomaterials. The different results of the cytotoxicity of the carbon-based materials might be related to the differences in the physicochemical properties or structures of carbon nanomaterials, types of target cells and methods of particle dispersion, etc. The reported cytotoxicity effects mainly included reactive oxygen species generation, DNA damage, lysosomal damage, mitochondrial dysfunction and eventual cell death via apoptosis or necrosis. Despite the cellular toxicity, the immunological effects of the carbon-based nanomaterials, such as the pulmonary macrophage activation and inflammation induced by carbon nanomaterials, have been thoroughly studied. The roles of carbon nanomaterials in activating different immune cells or inducing immunosuppression have also been addressed.

CONCLUSION

Here, we provide a review of the latest research findings on the toxicological profiles of carbon-based nanomaterials, highlighting both the cellular toxicities and immunological effects of carbon nanomaterials. This review provides information on the overall status, trends, and research needs for toxicological studies of carbon nanomaterials.

Solution and on-surface synthesis of structurally defined graphene nanoribbons as a new family of semiconductors

Graphene nanoribbons (GNRs) are quasi-one-dimensional subunits of graphene and have open bandgaps in contrast to the zero-bandgap graphene. The high potential of GNRs as a new family of carbon-based semiconductors, e.g. for nanoelectronic and optoelectronic applications, has boosted the research attempts towards fabrication of GNRs. The predominant top-down methods such as lithographical patterning of graphene and unzipping of carbon nanotubes cannot prevent defect formation. In contrast, bottom-up chemical synthesis, starting from tailor-made molecular precursors, can achieve atomically precise GNRs. In this account, we summarize our recent research progress in the bottom-up synthesis of GNRs through three different methods, namely (1) in solution, (2) on-surface under ultrahigh vacuum (UHV) conditions, and (3) on-surface through chemical vapour deposition (CVD). The solution synthesis allows fabrication of long (>600 nm) and liquid-phase-processable GNRs that can also be functionalized at the edges. On the other hand, the on-surface synthesis under UHV enables formation of zigzag GNRs and in situ visualization of their chemical structures by atomic-resolution scanning probe microscopy. While the on-surface synthesis under UHV is typically costly and has limited scalability, the industrially viable CVD method can allow lower-cost production of large GNR films. We compare the three methods in terms of the affordable GNR structures and the resulting control of their electronic and optical properties together with post-processing for device integration. Further, we provide our views on future perspectives in the field of bottom-up GNRs.

Determination of inorganic contaminants in carbon nanotubes by plasma-based techniques: Overcoming the limitations of sample preparation

In this work, sample preparation of carbon nanotubes (CNTs) for further determination of inorganic contaminants was investigated using a microwave-assisted wet digestion single reaction chamber system (MAWD-SRC). Analytes (Al, As, Ca, Cd, Co, Cr, Fe, La, Mg, Mo, Ni, Pb and Zn) were determined in CNTs by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS, except for Al, Ca, Fe and Mg). Method parameters were evaluated, as the mass of CNT (25-300 mg), the temperature (220-270 °C) and the time (35-75 min) of irradiation program. The accuracy was evaluated by using a certified reference material (CRM) of CNT and also by comparison of the results with those obtained using neutron activation analysis (NAA) and high resolution continuum source graphite furnace atomic absorption spectrometry with direct solid sampling (DSS-HR-CS-GF AAS). Quantitative recoveries for all elements were obtained using 275 mg of CNTs, 6 mL of 14.4 mol L^-1 HNO₃ and 0.5 mL of 30% H₂O₂ with an irradiation program of 65 min (35 min at 270 °C). No statistical difference was observed between the results obtained after the decomposition of CNTs by MAWD-SRC with those obtained by NAA and DSS-HR-CS-GF AAS. No difference was also observed for the results using the proposed method and the values for the CRM of CNT. The use of MAWD-SRC showed good performance for CNTs digestion using relatively high sample mass (up to 275 mg), contributing to low limits of quantification (LOQs) and overcoming the current limitations of sample preparation. To the best knowledge of the authors, this work reports the highest sample mass feasible to be decomposed using wet digestion for CNTs among the methods proposed in literature.

NanoRelease: Pilot interlaboratory comparison of a weathering protocol applied to resilient and labile polymers with and without embedded carbon nanotubes

A major use of multi-walled carbon nanotubes (MWCNTs) is as functional fillers embedded in a solid matrix, such as plastics or coatings. Weathering and abrasion of the solid matrix during use can lead to environmental releases of the MWCNTs. Here we focus on a protocol to identify and quantify the primary release induced by weathering, and assess reproducibility, transferability, and sensitivity towards different materials and uses. We prepared 132 specimens of two polymer-MWCNT composites containing the same grade of MWCNTs used in earlier OECD hazard assessments but without UV stabilizer. We report on a pilot inter-laboratory comparison (ILC) with four labs (two US and two EU) aging by UV and rain, then shipping for analysis. Two labs (one US and one EU) conducted the release sampling and analysis by Transmission Electron Microscopy (TEM), Inductively Coupled Plasma- Mass Spectrometry (ICP-MS), UltravioleteVisible Spectroscopy (UVeVis), Analytical Ultracentrifugation (AUC), and Asymmetric Flow Field Flow Fractionation (AF4). We compare results between aging labs, between analysis labs and between materials. Surprisingly, we found quantitative agreement between analysis labs for TEM, ICP-MS, UVeVis; low variation between aging labs by all methods; and consistent rankings of release between TEM, ICP-MS, UVeVis, AUC. Significant disagreement was related primarily to differences in aging, but even these cases remained within a factor of two.

Elemental Quantification and Residues Characterization of Wet Digested Certified and Commercial Carbon Materials

Inductively coupled plasma optical emission spectroscopy (ICP-OES) is a common, relatively low cost, and straightforward analytical technique for the study of trace quantities of metals in solid materials, but its applicability to nanocarbons (e.g., graphene and nanotubes) has suffered from the lack of efficient digestion steps and certified reference materials (CRM). Here, various commercial and certified graphitic carbon materials were subjected to a "two-step" microwave-assisted acid digestion procedure, and the concentrations of up to 18 elements were analyzed by ICP-OES. With one exception (Sm), successful quantification of all certified elements in the two reference nanocarbons studied was achieved, hence validating the sample preparation approach used. The applicability of our "two-step" protocol was further confirmed for a commercial single-walled carbon nanotube sample. However, the digestion was markedly incomplete for all other commercial materials tested. Where possible, the digestion residues of the carbon materials analyzed (CRM included) were characterized to understand the structural changes that take place and how this may explain the challenge of disintegrating graphitic carbon. In this respect, it was found that solid state nuclear magnetic resonance holds considerable promise as a nonlocalized, easily interpretable, and reliable tool to access the efficient disintegration of these materials.

Determination of Metal Impurities in Carbon Nanotubes Sampled Using Surface Wipes

Residual metal impurities in carbon nanotubes (CNTs) provide a means to distinguish CNT from non-CNT sources of elemental carbon in environmental samples. A practical and cost-effective analytical approach is needed to support routine surface monitoring of CNT metal tracers using wipe sampling. Wipe sampling for CNT metal tracers is considered a qualitative indicator of the presence of CNTs, not a quantitative exposure metric. In this study, two digestion approaches (microwave-assisted nitric acid/H₂O₂ digestion and ultrasonic nitric/HF acid digestion) in conjunction with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) determination were evaluated for their ability to extract metal impurities from CNT particles captured on wipe substrates. Aliquots of different carbon nanotubes (including NIST 2483 single-wall CNT) with and without GhostWipes™ (ASTM E-1792 compliant) were used to compare the performance of the digestion methods. The microwave digestion method accommodated the bulky wipe sample and also eliminated potential ICP-MS signal interferences related to incomplete digestion. Although quantitative recoveries requiring lengthy multistep digestion protocols may be necessary in other applications, the near-total recoveries achieved in the present study for CNT catalyst elements were adequate for identifying surface contamination of CNTs in the workplace using wipe sampling.

Aerosol generation and characterization of multi-walled carbon nanotubes exposed to cells cultured at the air-liquid interface

Aerosol generation and characterization are critical components in the assessment of the inhalation hazards of engineered nanomaterials (NMs). An extensive review was conducted on aerosol generation and exposure apparatus as part of an international expert workshop convened to discuss the design of an in vitro testing strategy to assess pulmonary toxicity following exposure to aerosolized particles. More specifically, this workshop focused on the design of an in vitro method to predict the development of pulmonary fibrosis in humans following exposure to multi-walled carbon nanotubes (MWCNTs). Aerosol generators, for dry or liquid particle suspension aerosolization, and exposure chambers, including both commercially available systems and those developed by independent researchers, were evaluated. Additionally, characterization methods that can be used and the time points at which characterization can be conducted in order to interpret in vitro exposure results were assessed. Summarized below is the information presented and discussed regarding the relevance of various aerosol generation and characterization techniques specific to aerosolized MWCNTs exposed to cells cultured at the air-liquid interface (ALI). The generation of MWCNT aerosols relevant to human exposures and their characterization throughout exposure in an ALI system is critical for extrapolation of in vitro results to toxicological outcomes in humans.

Magnetic impurities in single-walled carbon nanotubes and graphene: a review

A review on magnetic impurities in single-walled carbon nanotubes and graphene: purification and detection of impurities and impurity-induced magnetism.

Differentiation of chemical reaction activity of various carbon nanotubes using redox potential: Classification by physical and chemical structures

The present study systematically examined the kinetics of a hydroxyl radical scavenging reaction of various carbon nanotubes (CNTs) including double-walled and multi-walled carbon nanotubes (DWCNTs and MWCNTs), and carbon nano peapods (AuCl₃@DWCNT). The theoretical model that we recently proposed based on the redox potential of CNTs was used to analyze the experimental results. The reaction kinetics for DWCNTs and thin MWCNTs agreed well with the theoretical model and was consistent with each other. On the other hand, thin and thick MWCNTs behaved differently, which was consistent with the theory. Additionally, surface morphology of CNTs substantially influenced the reaction kinetics, while the doped particles in the center hollow parts of CNTs (AuCl₃@DWCNT) shifted the redox potential in a different direction. These findings make it possible to predict the chemical and biological reactivity of CNTs based on the structural and chemical nature and their influence on the redox potential.

Carbon Nanomaterials in Electrochemical Detection

This chapter overviews the use of carbon nanomaterials in the field of electroanalysis and considers why carbon-based nanomaterials are widely utilized and explores the current diverse range that is available to the practising electrochemist, which spans from carbon nanotubes to carbon nanohorns through to the recent significant attention given to graphene.

Simple and Precise Quantification of Iron Catalyst Content in Carbon Nanotubes Using UV/Visible Spectroscopy

Iron catalysts have been used widely for the mass production of carbon nanotubes (CNTs) with high yield. In this study, UV/visible spectroscopy was used to determine the Fe catalyst content in CNTs using a colorimetric technique. Fe ions in solution form red-orange complexes with 1,10-phenanthroline, producing an absorption peak at λ=510 nm, the intensity of which is proportional to the solution Fe concentration. A series of standard Fe solutions were formulated to establish the relationship between optical absorbance and Fe concentration. Many Fe catalysts were microscopically observed to be encased by graphitic layers, thus preventing their extraction. Fe catalyst dissolution from CNTs was investigated with various single and mixed acids, and Fe concentration was found to be highest with CNTs being held at reflux in HClO4/HNO3 and H2SO4/HNO3 mixtures. This novel colorimetric method to measure Fe concentrations by UV/Vis spectroscopy was validated by inductively coupled plasma optical emission spectroscopy, indicating its reliability and applicability to asses Fe content in CNTs.

Radical scavenging reaction kinetics with multiwalled carbon nanotubes

Progress in the development of carbon nanotubes (CNTs) has stimulated great interest among industries providing new applications. Meanwhile, toxicological evaluations on nanomaterials are advancing leading to a predictive exposure limit for CNTs, which implies the possibility of designing safer CNTs. To pursue safety by design, the redox potential in reactions with CNTs has been contemplated recently. However, the chemical reactivity of CNTs has not been explored kinetically, so that there is no scheme to express a redox reaction with CNTs, though it has been investigated and reported. In addition, the reactivity of CNTs is discussed with regard to impurities that consist of transition metals in CNTs, which obfuscates the contribution of CNTs to the reaction. The present work aimed at modeling CNT scavenging in aqueous solution using a kinetic approach and a simple first-order reaction scheme. The results show that CNTs follow the redox reaction assumption in a simple chemical system. As a result, the reaction with multiwalled CNTs is semi-quantitatively denoted as redox potential, which suggests that their biological reactions may also be evaluated using a redox potential scheme.

Electrochemical sensors and biosensors based on redox polymer/carbon nanotube modified electrodes: a review

The aim of this review is to present the contributions to the development of electrochemical sensors and biosensors based on polyphenazine or polytriphenylmethane redox polymers together with carbon nanotubes (CNT) during recent years. Phenazine polymers have been widely used in analytical applications due to their inherent charge transport properties and electrocatalytic effects. At the same time, since the first report on a CNT-based sensor, their application in the electroanalytical chemistry field has demonstrated that the unique structure and properties of CNT are ideal for the design of electrochemical (bio)sensors. We describe here that the specific combination of phenazine/triphenylmethane polymers with CNT leads to an improved performance of the resulting sensing devices, because of their complementary electrical, electrochemical and mechanical properties, and also due to synergistic effects. The preparation of polymer/CNT modified electrodes will be presented together with their electrochemical and surface characterization, with emphasis on the contribution of each component on the overall properties of the modified electrodes. Their importance in analytical chemistry is demonstrated by the numerous applications based on polymer/CNT-driven electrocatalytic effects, and their analytical performance as (bio) sensors is discussed.

Enzymatically cross-linked hyaluronic acid/graphene oxide nanocomposite hydrogel with pH-responsive release

Hyaluronic acid (HA) is made up of repeating disaccharide units (β-1,4-d-glucuronic acid and β-1,3-N-acetyl-d-glucosamine) and is a major constituent of the extracellular matrix. HA and its derivatives which possess excellent biocompatibility and physiochemical properties have been studied in drug delivery and tissue engineering applications. Tyramine-based HA hydrogel with good compatibility to cell and tissue has been reported recently. However, inferior mechanical property may limit the biomedical application of the HA hydrogel. In this study, HA/graphene oxide (GO) nanocomposite (NC) hydrogel was prepared through a horseradish peroxidase catalyzed in situ cross-linking process. As compared with pure HA hydrogels, incorporation of GO to the HA matrix could significantly enhance the mechanical properties (storage moduli 1800 Pa) of the hydrogel and prolong the release of rhodamine B (RB) as the model drug from the hydrogel (33 h) as well. In addition, due to the multiple interactions between GO and RB, the NC hydrogels showed excellent pH-responsive release behavior. The release of RB from the NC hydrogel was prolonged at low pH (pH 4.0) in the presence of GO, which could be attributed to the enhanced interactions between GO and HA as well as with RB. In situ three-dimensional encapsulation of mouse embryonic fibroblasts (BALB 3T3 cells) in the NC hydrogels and cytotoxicity results indicated the cytocompatibility of both the enzymatic cross-linking process and HA/GO NC hydrogels (cell viability 90.6 ± 4.25%). The enzymatically catalyzed fabrication of NC hydrogels proved to be an easy and mild approach, and had great potential in the construction of both tissue engineering scaffolds and stimuli-responsive drug release matrices.

Size- and surface chemistry-dependent pharmacokinetics and tumor accumulation of engineered gold nanoparticles after intravenous administration

It is important and essential to study the pharmacokinetics and biodistribution of gold nanoparticles for safer and more efficient therapeutic purposes.

A versatile method for direct determination of iron content in multi-wall carbon nanotubes by inductively coupled plasma atomic emission spectrometry with slurry sample introduction

Determination of iron in MWCNTs takes about 15 min using the slurry ICP-AES method.

Genotoxicity of multi-walled carbon nanotubes at occupationally relevant doses

Carbon nanotubes are commercially-important products of nanotechnology; however, their low density and small size makes carbon nanotube respiratory exposures likely during their production or processing. We have previously shown mitotic spindle aberrations in cultured primary and immortalized human airway epithelial cells exposed to single-walled carbon nanotubes (SWCNT). In this study, we examined whether multi-walled carbon nanotubes (MWCNT) cause mitotic spindle damage in cultured cells at doses equivalent to 34 years of exposure at the NIOSH Recommended Exposure Limit (REL). MWCNT induced a dose responsive increase in disrupted centrosomes, abnormal mitotic spindles and aneuploid chromosome number 24 hours after exposure to 0.024, 0.24, 2.4 and 24 μg/cm² MWCNT. Monopolar mitotic spindles comprised 95% of disrupted mitoses. Three-dimensional reconstructions of 0.1 μm optical sections showed carbon nanotubes integrated with microtubules, DNA and within the centrosome structure. Cell cycle analysis demonstrated a greater number of cells in S-phase and fewer cells in the G2 phase in MWCNT-treated compared to diluent control, indicating a G1/S block in the cell cycle. The monopolar phenotype of the disrupted mitotic spindles and the G1/S block in the cell cycle is in sharp contrast to the multi-polar spindle and G2 block in the cell cycle previously observed following exposure to SWCNT. One month following exposure to MWCNT there was a dramatic increase in both size and number of colonies compared to diluent control cultures, indicating a potential to pass the genetic damage to daughter cells. Our results demonstrate significant disruption of the mitotic spindle by MWCNT at occupationally relevant exposure levels.

A new approach to design safe CNTs with an understanding of redox potential

BACKGROUND

Carbon nanotubes (CNTs) are being increasingly industrialized and applied for various products. As of today, although several toxicological evaluations of CNTs have been conducted, designing safer CNTs is not practiced because reaction kinetics of CNTs with bioactive species is not fully understood.

RESULTS

The authors propose a kinetic mechanism to establish designing safe CNTs as a new goal. According to a literature search on the behavior of CNTs and the effects of impurities, it is found that chemical reactions on CNT surface are attributed to redox reactions involving metal impurities and carbon structures at the CNT surface.

CONCLUSION

A new goal is proposed to design safer CNTs using the redox potential hypothesis. The value of this hypothesis must be practically investigated and proven through the further experiments.

Chemical mechanisms of the toxicological properties of nanomaterials: generation of intracellular reactive oxygen species

As more and more nanomaterials with novel physicochemical properties or new functions are created and used in different research fields and industrial sectors, the scientific and public concerns about their toxic effects on human health and the environment are also growing quickly. In the past decade, the study of the toxicological properties of nanomaterials/nanoparticles has formed a new research field: nanotoxicology. However, most of the data published relate to toxicological phenomena and there is less understanding of the underlying mechanism for nanomaterial-induced toxicity. Nanomaterial-induced reactive oxygen species (ROS) play a key role in cellular and tissue toxicity. Herein, we classify the pathways for intracellular ROS production by nanomaterials into 1) the direct generation of ROS through nanomaterial-catalyzed free-radical reactions in cells, and 2) the indirect generation of ROS through disturbing the inherent biochemical equilibria in cells. We also discuss the chemical mechanisms associated with above pathways of intracellular ROS generation, from the viewpoint of the high reactivity of atoms on the nanosurface. We hope to aid in the understanding of the chemical origin of nanotoxicity to provide new insights for chemical and material scientists for the rational design and creation of safer and greener nanomaterials.

Quantifying and imaging engineered nanomaterials in vivo: challenges and techniques

Quantifying and imaging the engineered nanomaterials (ENMs) in vivo can provide information on the bio-distribution and fate of ENMs in living systems. A necessary amount of in vivo quantitative data is indispensable to verify the extrapolation from in vitro tests, to modify the predictive models of ENM exposure, and to underpin the risk management strategy for ENMs. However, it remains a challenge to quantitatively assess the bio-distribution of ENMs under realistic exposure, their long-term deposition (especially in non-targeted tissues), their passage across the natural barriers, and the impacts of nano-bio interactions on their in vivo behaviors. Some commonly used techniques for in vivo ENM quantification, such as electron microscopy, fluorescence-based detection, atomic spectroscopy, radiotracing, and techniques basing on synchrotron radiation are reviewed, and their technical characteristics, the state of the art, limitations, and future prospects are addressed.

Short multiwall carbon nanotubes promote neuronal differentiation of PC12 cells via up-regulation of the neurotrophin signaling pathway

Numerous unique properties of carbon nanotubes make them attractive for applications in neurobiology such as drug delivery, tissue regeneration, and as scaffolds for neuronal growth. In this study, the critical roles of the length of multiwall carbon nanotubes (MWCNTs) on a neuronal-like model cell line PC12 cells are investiaged. Incubation of PC12 cells with carboxylated MWCNTs did not significantly affect cellular morphology and viability at lower concentrations. Short MWCNTs show higher cellular uptake and more obvious removal compared to longer ones, which can result in higher ability to promote PC12 cell differentiation. Pre-incubation of short MWCNTs can up-regulate the expression of neurotrophin signaling pathway-associated TrkA/p75 receptors and Pincher/Gap43/TH proteins, which might be the underlying mechanism for the improved differentiation in PC12 cells. The current results provide insight for future applications of MWCNTs in neuron drug delivery and neurodegenerative disease treatment.

Nano-bio effects: interaction of nanomaterials with cells

With the advancements in nanotechnology, studies on the synthesis, modification, application, and toxicology evaluation of nanomaterials are gaining increased attention. In particular, the applications of nanomaterials in biological systems are attracting considerable interest because of their unique, tunable, and versatile physicochemical properties. Artificially engineered nanomaterials can be well controlled for appropriate usage, and the tuned physicochemical properties directly influence the interactions between nanomaterials and cells. This review summarizes recently synthesized major nanomaterials that have potential biomedical applications. Focus is given on the interactions, including cellular uptake, intracellular trafficking, and toxic response, while changing the physicochemical properties of versatile materials. The importance of physicochemical properties such as the size, shape, and surface modifications of the nanomaterials in their biological effects is also highlighted in detail. The challenges of recent studies and future prospects are presented as well. This review benefits relatively new researchers in this area and gives them a systematic overview of nano-bio interaction, hopefully for further experimental design.

Understanding the toxicity of carbon nanotubes

Because of their unique physical, chemical, electrical, and mechanical properties, carbon nanotubes (CNTs) have attracted a great deal of research interest and have many potential applications. As large-scale production and application of CNTs increases, the general population is more likely to be exposed to CNTs either directly or indirectly, which has prompted considerable attention about human health and safety issues related to CNTs. Although considerable experimental data related to CNT toxicity at the molecular, cellular, and whole animal levels have been published, the results are often conflicting. Therefore, a systematic understanding of CNT toxicity is needed but has not yet been developed. In this Account, we highlight recent investigations into the basis of CNT toxicity carried out by our team and by other laboratories. We focus on several important factors that explain the disparities in the experimental results of nanotoxicity, such as impurities, amorphous carbon, surface charge, shape, length, agglomeration, and layer numbers. The exposure routes, including inhalation, intravenous injection, or dermal or oral exposure, can also influence the in vivo behavior and fate of CNTs. The underlying mechanisms of CNT toxicity include oxidative stress, inflammatory responses, malignant transformation, DNA damage and mutation (errors in chromosome number as well as disruption of the mitotic spindle), the formation of granulomas, and interstitial fibrosis. These findings provide useful insights for de novo design and safe application of carbon nanotubes and their risk assessment to human health. To obtain reproducible and accurate results, researchers must establish standards and reliable detection methods, use standard CNT samples as a reference control, and study the impact of various factors systematically. In addition, researchers need to examine multiple types of CNTs, different cell lines and animal species, multidimensional evaluation methods, and exposure conditions. To make results comparable among different institutions and countries, researchers need to standardize choices in toxicity testing such as that of cell line, animal species, and exposure conditions. The knowledge presented here should lead to a better understanding of the key factors that can influence CNT toxicity so that their unwanted toxicity might be avoided.

Detection of single walled carbon nanotubes by monitoring embedded metals

Detection of single walled carbon nanotubes (CNTs) was performed using single particle-inductively coupled plasma-mass spectrometry (spICPMS). Due to the ambiguities inherent in detecting CNTs by carbon analysis, particularly in complex environmental matrices, this study focuses on using trace catalytic metals intercalated in the CNT structure as proxies for the nanotubes. Using a suite of commercially available CNTs, the monoisotopic elements Co and Y were found to be the most effective for differentiation of particulate pulses from background. The small, variable, amount of trace metal in each CNT makes separation from instrumental background challenging; multiple cut-offs for determining CNT number concentration were investigated to maximize the number of CNTs detected and minimize the number of false positives in the blanks. In simple solutions the number of CNT pulses detected increased linearly with concentration in the ng L−1 range. However, analysis of split samples by both spICPMS and Nanoparticle Tracking Analysis (NTA) showed the quantification of particle number concentration by spICPMS to be several orders of magnitude lower than by NTA. We postulate that this is a consequence of metal content and/or size, caused by the presence of many CNTs that do not contain enough metal to be above the instrument detection limit, resulting in undercounting CNTs by spICPMS. However, since the detection of CNTs at low ng L−1 concentrations is not possible by other techniques, spICPMS is still a more sensitive technique for detecting the presence of CNTs in environmental, materials, or biological applications. To highlight the potential of spICPMS in environmental studies the release of CNTs from polymer nanocomposites into solution was monitored, showcasing the technique's ability to detect changes in released CNT concentrations as a function of CNT loading.

Response of soil microorganisms to As-produced and functionalized single-wall carbon nanotubes (SWNTs)

The use of single-wall carbon nanotubes (SWNTs) in manufacturing and biomedical applications is increasing at a rapid rate; however data on the effects of a potential environmental release of the materials remain sparse. In this study, soils with either low or high organic matter contents as well as pure cultures of E. coli are challenged with either raw as-produced SWNTs (AP-SWNTs) or SWNTs functionalized with either polyethyleneglycol (PEG-SWNTs) or m-polyaminobenzene sulfonic acid (PABS-SWNTs). To mimic chronic exposure, the soil systems were challenged weekly for six weeks; microbial activities and community structures for both the prokaryote and eukaryote community were evaluated. Results show that repeated applications of AP-SWNTs can affect microbial community structures and induce minor changes in soil metabolic activity in the low organic matter systems. Toxicity of the three types of SWNTs was also assessed in liquid cultures using a bioluminescent E. coli-O157:H7 strain. Although decreases in light were detected in all treated samples, low light recovery following glucose addition in AP-SWNTs treatment and light absorption property of SWNTs particles suggest that AP-SWNTs suppressed metabolic activity of the E. coli, whereas the two functionalized SWNTs are less toxic. The metals released from the raw forms of SWNTs would not play a role in the effects seen in soil or the pure culture. We suggest that sorption to soil organic matter plays a controlling role in the soil microbiological responses to these nanomaterials.