Fluorescence anisotropy using highly polarized emitting dyes confined inside BNNTs

Polarized fluorescence emission of nanoscale emitters has been extensively studied for applications such as bioimaging, displays, and optical communication. Extending the polarization properties in large assemblies of compact emitters is, however, challenging because of self-aggregation processes, which can induce depolarization effects, quenching, and cancellations of molecular dipoles. Here we use α-sexithiophene (6T) molecules confined inside boron nitride nanotubes (6T@BNNTs) to induce fluorescence anisotropy in a transparent host. The experiments first indicate that individual 6T@BNNTs exhibit a high polarization extinction ratio, up to 700, at room temperature. Using aberration-corrected HRTEM, we show that the fluorescence anisotropy is consistent with a general alignment of encapsulated 6T molecules along the nanotube axis. The molecular alignment is weakly influenced by the nanotube diameter, a phenomenon ascribed to stronger molecule-to-sidewall interactions compared to intermolecular interactions. By stretching a flexible thin film made of transparent polymers mixed with 6T@BNNTs, we induce a macroscopic fluorescence anisotropy within the film. This work demonstrates that the dyes@BNNT system can be used as an easy-to-handle platform to induce fluorescence anisotropy in photonic materials.

Applicability of OECD TG 201, 202, 203 for the aquatic toxicity testing and assessment of 2D Graphene material nanoforms to meet regulatory needs

Tests using algae and/or cyanobacteria, invertebrates (crustaceans) and fish form the basic elements of an ecotoxicological assessment in a number of regulations, in particular for classification of a substance as hazardous or not to the aquatic environment according to the Globally Harmonised System of Classification and Labelling of Chemicals (GHS-CLP) (GHS, 2022) and the REACH regulation (Registration, Evaluation, Authorisation and Restriction of Chemicals, EC, 2006). Standardised test guidelines (TGs) of the Organisation for Economic Co-operation and Development (OECD) are available to address the regulatory relevant endpoints of growth inhibition in algae and cyanobacteria (TG 201), acute toxicity to invertebrates (TG 202), and acute toxicity in fish (TG 203). Applying these existing OECD TGs for testing two dimensional (2D) graphene nanoforms may require more attention, additional considerations and/or adaptations of the protocols, because graphene materials are often problematic to test due to their unique attributes. In this review a critical analysis of all existing studies and approaches to testing used has been performed in order to comment on the current state of the science on testing and the overall ecotoxicity of 2D graphene materials. Focusing on the specific tests and available guidance's, a complete evaluation of aquatic toxicity testing for hazard classification of 2D graphene materials, as well as the use of alternative tests in an integrated approach to testing and assessment, has been made. This information is essential to ensure future assessments generate meaningful data that will fulfil regulatory requirements for the safe use of this "wonder" material.

Kondo effect and enhanced magnetic properties in gadolinium functionalized carbon nanotube supramolecular complex

We report on the enhancement of magnetic properties of multiwalled carbon nanotubes (MWNTs) functionalized with a gadolinium based supramolecular complex. By employing a newly developed synthesis technique we find that the functionalization method of the nanocomposite enhances the strength of magnetic interaction leading to a large effective moment of 15.79 µ_B and non-superparamagnetic behaviour unlike what has been previously reported. Saturating resistance at low temperatures is fitted with the numerical renormalization group formula verifying the Kondo effect for magnetic impurities on a metallic electron system. Magnetoresistance shows devices fabricated from aligned gadolinium functionalized MWNTs (Gd-Fctn-MWNTs) exhibit spin-valve switching behaviour of up to 8%. This study highlights the possibility of enhancing magnetic interactions in carbon systems through chemical modification, moreover we demonstrate the rich physics that might be useful for developing spin based quantum computing elements based on one-dimensional (1D) channels.

Interaction of graphene-related materials with human intestinal cells: an in vitro approach

Graphene-related materials (GRM) inherit unique combinations of physicochemical properties which offer a high potential for technological as well as biomedical applications. It is not clear which physicochemical properties are the most relevant factors influencing the behavior of GRM in complex biological environments. In this study we have focused on the interaction of GRM, especially graphene oxide (GO), and Caco-2 cells in vitro. We mimiked stomach transition by acid-treatment of two representative GRM followed by analysis of their physicochemical properties. No significant changes in the material properties or cell viability of exposed Caco-2 cells in respect to untreated GRM could be detected. Furthermore, we explored the interaction of four different GO and Caco-2 cells to identify relevant physicochemical properties for the establishment of a material property-biological response relationship. Despite close interaction with the cell surface and the formation of reactive oxygen species (ROS), no acute toxicity was found for any of the applied GO (concentration range 0-80 μg ml(-1)) after 24 h and 48 h exposure. Graphene nanoplatelet aggregates led to low acute toxicity at high concentrations, indicating that aggregation, the number of layers or the C/O ratio have a more pronounced effect on the cell viability than the lateral size alone.

A single-molecule approach to explore binding, uptake and transport of cancer cell targeting nanotubes

In the past decade carbon nanotubes (CNTs) have been widely studied as a potential drug-delivery system, especially with functionality for cellular targeting. Yet, little is known about the actual process of docking to cell receptors and transport dynamics after internalization. Here we performed single-particle studies of folic acid (FA) mediated CNT binding to human carcinoma cells and their transport inside the cytosol. In particular, we employed molecular recognition force spectroscopy, an atomic force microscopy based method, to visualize and quantify docking of FA functionalized CNTs to FA binding receptors in terms of binding probability and binding force. We then traced individual fluorescently labeled, FA functionalized CNTs after specific uptake, and created a dynamic 'roadmap' that clearly showed trajectories of directed diffusion and areas of nanotube confinement in the cytosol. Our results demonstrate the potential of a single-molecule approach for investigation of drug-delivery vehicles and their targeting capacity.

Mid-infrared Raman-soliton continuum pumped by a nanotube-mode-locked sub-picosecond Tm-doped MOPFA

We demonstrate a mid-infrared Raman-soliton continuum extending from 1.9 to 3 µm in a highly germanium-doped silica-clad fiber, pumped by a nanotube mode-locked thulium-doped fiber system, delivering 12 kW sub-picosecond pulses at 1.95 µm. This simple and robust source of light covers a portion of the atmospheric transmission window.

Design of double-walled carbon nanotubes for biomedical applications

Double-walled carbon nanotubes (DWNTs) prepared by catalytic chemical vapour deposition were functionalized in such a way that they were optimally designed as a nano-vector for the delivery of small interfering RNA (siRNA), which is of great interest for biomedical research and drug development. DWNTs were initially oxidized and coated with a polypeptide (Poly(Lys:Phe)), which was then conjugated to thiol-modified siRNA using a heterobifunctional cross-linker. The obtained oxDWNT-siRNA was characterized by Raman spectroscopy inside and outside a biological environment (mammalian cells). Uptake of the custom-designed nanotubes was not associated with detectable biochemical perturbations in cultured cells, but transfection of cells with DWNTs loaded with siRNA targeting the green fluorescent protein (GFP) gene, serving as a model system, as well as with therapeutic siRNA targeting the survivin gene, led to a significant gene silencing effect, and in the latter case a resulting apoptotic effect in cancer cells.

Carbon nanotubes have a deleterious effect on the nose: the first in vitro data

BACKGROUND

The information currently available concerning carbon nanotubes toxicity is disturbing and conflicting. Moreover, little is known about their effect on the nasal cavities, which are the first target for nanoparticles.

MATERIAL AND METHOD

We investigated the cytotoxicity (50 to 0.5 microg/mL) of double-walled carbon nanotube with two independent tests (MTT, Wst-1) on normal human nasal epithelial cells after 12-day exposure (control untreated nasal cells and A549). Nasal cell differentiation function, oxidative stress, the morphological features of cells in contact with DWCNTs and the localizations of the latter were also investigated.

RESULTS

Exposure revealed a dose-dependent decrease in cell metabolic activity and cell growth. In nearly all conditions, normal human nasal epithelial cells were more sensitive than malignant ones. Even with both tests, the cytotoxic threshold dose could not be accurately determined because of dye adsorption by DWCNTs. Nasal cells showed stronger cytokeratin 7 and persistent UEA-I immunostaining. Cytokeratin 19 production was increased at 25 microg/mL and mucus production was stimulated from 0.5 microg/mL. A significant increase in Reactive Oxygen Species was observed from 25 microg/mL. The cell plasma membrane showed several holes and DWCNTs were present in the cytoplasm.

CONCLUSION

DWCNTs seem to have a deleterious effect on nasal cells after 12-day exposure.

Magneto-Coulomb effect in carbon nanotube quantum dots filled with magnetic nanoparticles

Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot.

Ultrafast Raman laser mode-locked by nanotubes

We demonstrate passive mode-locking of a Raman fiber laser using a nanotube-based saturable absorber coupled to a net normal dispersion cavity. This generates highly chirped 500 ps pulses. These are then compressed down to 2 ps, with 1.4 kW peak power, making it a simple wavelength-versatile source for various applications.

The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes

The crystal growth behaviour and crystallography of a variety of metal halides incorporated within single walled carbon nanotubes (SWNTs) as determined by high resolution electron microscopy (HRTEM) is described. Simple packed structures, such as the alkali halides, form related structures within SWNTs that are found to be integral atomic layers in terms of their thickness as a function of the encapsulating SWNT diameter. An enhanced HRTEM image restoration technique reveals precise data concerning lattice distortions present in these crystals. More complex structures, such as those derived from 3D complex, layered and chain halides form related crystal structures within SWNTs. In narrow SWNTs (i.e. with diameters less than ca. 1.6 nm), structures consisting of individual 1D polyhedral chains (1D-PHCs) were obtained that were derived from the corresponding bulk halides structures. In the case of infinite 3D network and layered halides, the 1D polyhedral chains form with lower co-ordinations than in the bulk. Molecular halides also intercalate into SWNTs but these do not readily form organised structures within SWNTs.

Hydrophobic double walled carbon nanotubes interaction with phopholipidic model membranes: (1)H-, (2)H-, (31)P NMR and ESR study

The interactions of carbon nanotubes synthesized by catalytic chemical vapour deposition with phospholipidic bilayers, mimicking biological membranes, have been investigated using solid state (31)P- and (2)H NMR, (1)H- and (31)P NMR in liquids and ESR studies. It was found that carbon nanotubes can integrate the bilayer, depending on the overall cohesion of the membrane used. Whereas no direct interaction can be observed in small unilamellar vesicles or directly in the presence of short-chained phospholipids, carbon nanotubes incorporate into the membrane of multibilayers. The result is a significant 2-3K lowering of the transition temperature in multibilayers of dimyristoyl lecithins, which is more markedly associated with increased fluidity in the most superficial part of the membrane below the transition temperature (292-300K range). However, no ionophoric property was found on large unilamellar vesicles.

AFM imaging of functionalized carbon nanotubes on biological membranes

Multifunctional carbon nanotubes are promising for biomedical applications as their nano-size, together with their physical stability, gives access into the cell and various cellular compartments including the nucleus. However, the direct and label-free detection of carbon nanotube uptake into cells is a challenging task. The atomic force microscope (AFM) is capable of resolving details of cellular surfaces at the nanometer scale and thus allows following of the docking of carbon nanotubes to biological membranes. Here we present topographical AFM images of non-covalently functionalized single walled (SWNT) and double walled carbon nanotubes (DWNT) immobilized on different biological membranes, such as plasma membranes and nuclear envelopes, as well as on a monolayer of avidin molecules. We were able to visualize DWNT on the nuclear membrane while at the same time resolving individual nuclear pore complexes. Furthermore, we succeeded in localizing individual SWNT at the border of incubated cells and in identifying bundles of DWNT on cell surfaces by AFM imaging.

Writing simple RF electronic devices on paper with carbon nanotube ink

This paper shows that we can print on paper simple high-frequency electronic devices such as resistances, capacitances or inductances, with values that can be changed in a controllable manner by an applied dc voltage. This tunability is achieved with the help of an ink containing functionalized carbon nanotubes and water. After the water is evaporated from the paper, the nanotubes remain steadily imprinted on paper, showing a semiconducting behavior and tunable electrical properties.

Gate-dependent magnetoresistance phenomena in carbon nanotubes

We report on the first experimental study of the magnetoresistance of double-walled carbon nanotubes under a magnetic field as large as 50 T. By varying the field orientation with respect to the tube axis, or by gate-mediated shifting the Fermi level position, evidence for unconventional magnetoresistance is presented and interpreted by means of theoretical calculations.

Double-walled carbon nanotubes in composite powders

Double-walled carbon nanotubes (DWNTs) may be interesting in many applications since the outer wall would provide an interface with the rest of the system, without modifying the inner wall. CNT-Fe/Fe3C-Al2O3 composite powders containing carbon nanotubes (CNTs) (65% of which are DWNTs) are prepared by reduction of an oxide solid solution in a H2-CH4 gas mixture. The powders and CNTs are studied by both local and macroscopical techniques. The influence of the reducing atmosphere composition and of the dwell time at 1050 degrees C is studied. There is a 6-fold increase in CNT content upon the increase in the CH4 content from 3 to 30 mol.%, but the formation of undesirable carbon nanofibers can also be promoted. A CH4 content of 12-18 mol.% is adapted for the particular iron content in these powders. Increasing the dwell time at 1050 degrees C results in the formation of CNTs with more walls.