Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants

Noncovalent Modification of Single-Walled Carbon Nanotubes Using Thermally Cleavable Polythiophenes for Solution-Processed Thermoelectric Films

Four thermally cleavable polythiophene derivatives containing carbonate and solubilizing groups were synthesized for noncovalent modification of single-walled carbon nanotubes (SWCNTs). A well-dispersed polythiophene/SWCNTs composite was obtained by adsorption of the polymer at the SWCNT surface. The solution-processed composite film exhibited solid-state thermal cleavage of the insulating solubilizing group through decarboxylation, producing an insoluble composite film. The thermally cleavable composite film was evaluated for potential application as a thermoelectric (TE) material. The electrical conductivity (σ) of the thermally treated composite film was up to 250 times higher than that of the as-prepared composite film. The increased σ contributed to an increase in the power factor (PF). The ethanol-processed composite film could be applicable for green processing of a TE material using the less-toxic solvent. The substrate-free polythiophene/SWCNTs composite film prepared by simple solvent evaporation yielded a figure-of-merit of 3.1 × 10^-2 with a PF of 28.8 μW m^-1 K^-2 at 25 °C. This solution-processed methodology is beneficial for the development of a flexible TE material.

Role of Molecular Weight in Polymer Wrapping and Dispersion of MWNT in a PVDF Matrix

The thermal and electrical properties of a polymer nanocomposite are highly dependent on the dispersion of the CNT filler in the polymer matrix. Non-covalent functionalisation with a PVP polymer is an excellent driving force towards an effective dispersion of MWNTs in the polymer matrix. It is shown that the PVP molecular weight plays a key role in the non-covalent functionalisation of MWNT and its effect on the thermal and electrical properties of the polymer nanocomposite is reported herein. The dispersion and crystallisation behaviour of the composite are also evaluated by a combination of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC).

Polyampholytic graft copolymers based on polydehydroalanine (PDha) – synthesis, solution behavior and application as dispersants for carbon nanotubes

We herein introduce a versatile platform of graft copolymers featuring a polyampholytic backbone and side chains of varying length and polarity using post-polymerization modification of polydehydroalanine (PDha).

Long Carbon Nanotubes Functionalized with DNA and Implications for Spintronics

Helical molecules such as DNA have recently been found to behave as an efficient source and detector of spin-polarized charge carriers. This phenomenon, often dubbed as chirality-induced spin selectivity or CISS, could be used to significantly improve the performance of spintronic devices, which utilize carrier spins (rather than charge) to realize electronic and sensing functions. Recently, it has been reported that carbon nanotubes, helically wrapped with DNA, can also act as an efficient source and detector of spin-polarized carriers, by virtue of spin-orbit coupling originating from the helical potential. It has been postulated that spin polarization should increase with the length of the wrapped tubes. However, in literature, most fabrication processes yield tubes with submicron lengths, which can produce ∼70% spin polarization. In an effort to enhance this effect further, here, we report a fabrication process that can yield DNA-wrapped nanotubes of length ∼1-4 microns. Detailed characterization of these devices, using atomic force microscopy, Raman, UV-vis, and temperature-dependent transport, has been presented. Initial transport measurements indicate the presence of strong magnetoresistance in these tubes, which could be attributed to spin-dependent effects. Systematic fabrication of long DNA-wrapped nanotubes, which has hitherto not been reported, is expected to enable further investigation into the spin-dependent properties of these ultimate one-dimensional nanoscale hybrids and may have a significant impact on nanoscale spintronics.

Green preparation and characterization of graphene oxide/carbon nanotubes-loaded carboxymethyl cellulose nanocomposites

In this study, a homogeneous and stable dispersion of graphene oxide (GO)/carbon nanotube (CNT) complexes (GCCs) was obtained by dispersing CNTs in an aqueous solution using GO in the absence of dispersing agents. Furthermore, carboxymethyl cellulose/GCC (CMC/GCC) nanocomposite films were prepared by a simple solution mixing-evaporation method. The dispersibility of the GCCs with different CNT contents was investigated by UV-Vis spectrophotometry. The morphological and crystalline structures of the samples were analyzed by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were conducted to identify the chemical composition of GO, CNTs, and GCCs. These results revealed that CNTs could be stably dispersed in water using GO. In addition, when CMC/GCC nanocomposite films were prepared by mixing CMC and GCCs, CNTs were uniformly dispersed in the CMC matrix. The tensile behavior was investigated using a universal testing machine. The tensile strength and Young’s modulus of the CMC/GCC nanocomposite films were significantly improved by up to about 121% and 122%, respectively, compared to those of pure CMC because of uniform and strong π-π interfacial interactions between CNTs and CMC polymer.

Rational Design of 1D Partially Graphitized N-Doped Hierarchical Porous Carbon with Uniaxially Packed Carbon Nanotubes for High-Performance Lithium-Ion Batteries

N-doped hierarchical porous carbon with uniaxially packed carbon nanotubes (CNTs) was prepared by copolymer single-nozzle electrospinning, carbonization, and KOH activation. Densely and uniaxially aligned CNTs improve the electrical conductivity and act as a structural scaffold, enhancing the electrochemical performance of the anode. A partially graphitized N-doped carbon shell, which has a rapid ion accessible pore network and abundant redox sites, was designed to expand the redox sites from the surface of the material to the whole material, including the inner part. As an anode, this material exhibited a superior reversible capacity of 1814.3 mA h g^-1 at 50 mA g^-1 and of 850.1 mA h g^-1 at 1000 mA g^-1. Furthermore, the reversible capacity decreased by only 36% after 400 cycles and showed superior rate capability to that of the same material without CNTs, indicating that the CNT acted successfully as a structural scaffold and enhanced the electrical conductivity. This study not only allowed the rational design of the ideal structure of CNT-based carbonaceous anode material, which has both a rapid ion accessible structure and fast electron-transfer path, but also shed light on a potential strategy by which to use CNTs to modify the nitrogen bonding configuration in N-doped carbon for better electrochemical performance.

Designed Functional Dispersion for Insulin Protection from Pepsin Degradation and Skeletal Muscle Cell Proliferation: In Silico and In Vitro Study

Functionalized single-walled carbon nanotubes with polyethylene glycol (PEGylated SWCNTs) are a promising nanomaterial that recently has emerged as the most attractive "cargo" to deliver chemicals, peptides, DNA and RNAs into cells. Insulin therapy is a recommended therapy to treat diabetes mellitus despite its side effects. Recently, functional dispersion made up of bioactive peptides, bioactive compounds and functionalized carbon nanomaterials such as PEGylated SWCNTs have proved to possess promising applications in nanomedicine. In the present study, molecular modeling simulations are utilized to assist in designing insulin hormone-PEGylated SWCNT composites, also called functional dispersion; to achieve this experimentally, an ultrasonication tool was utilized. Enzymatic degradation assay revealed that the designed functional dispersion protects about 70% of free insulin from pepsin. In addition, sulforhodamine B (SRB) assay, the quantification of insulin and glucose levels in differentiated skeletal muscle cell supernatants, reveals that functional dispersion regulates glucose and insulin levels to promote skeletal muscle cell proliferation. These findings offer new perspectives for designed functional dispersion, as potential pharmaceutical preparations to improve insulin therapy and promote skeletal muscle cell health.

Oxidised carbon nanotubes as dual-domain synergetic stabilizers in electroconductive carbon nanotube flexible coatings

We report that combining oxidised carbon nanotubes (O-CNTs) and pristine CNTs may be the answer for more electroconductive composites. Short (<1 μm) oxidised multi-wall CNTs (O-MWCNTs) acted as an unobvious and excellent conductivity enhancer in MWCNT-based composite thin films. 'Blending' O-MWCNTs (1.5 wt%) with 250 μm-long MWCNTs (98.5 wt%), both of well-defined morphology and physicochemistry, led to a 3- and 26-fold increase in specific conductivity as compared to purely MWCNT- or purely O-MWCNT-based thin films, respectively. We explain the enhanced conductivity by the effect of a dual-domain structure of O-MWCNTs. The scale-up method, i.e. screen-printing, opens a route to application in textronics (i.e. electrical and electronic textiles) and hence targets for medicine, civil/military engineering, wellness, etc.

Adsorption mechanism of an antimicrobial peptide on carbonaceous surfaces: A molecular dynamics study

Peptides are versatile molecules with applications spanning from biotechnology to nanomedicine. They exhibit a good capability to unbundle carbon nanotubes (CNT) by improving their solubility in water. Furthermore, they are a powerful drug delivery system since they can easily be uptaken by living cells, and their high surface-to-volume ratio facilitates the adsorption of molecules of different natures. Therefore, understanding the interaction mechanism between peptides and CNT is important for designing novel therapeutical agents. In this paper, the mechanisms of the adsorption of antimicrobial peptide Cecropin A-Magainin 2 (CA-MA) on a graphene nanosheet (GNS) and on an ultra-short single-walled CNT are characterized using molecular dynamics simulations. The results show that the peptide coats both GNS and CNT surfaces through preferential contacts with aromatic side chains. The peptide packs compactly on the carbon surfaces where the polar and functionalizable Lys side chains protrude into the bulk solvent. It is shown that the adsorption is strongly correlated to the loss of the peptide helical structure. In the case of the CNT, the outer surface is significantly more accessible for adsorption. Nevertheless when the outer surface is already covered by other peptides, a spontaneous diffusion, via the amidated C-terminus into the interior of the CNT, was observed within 150 ns of simulation time. We found that this spontaneous insertion into the CNT interior can be controlled by the polarity of the entrance rim. For the positively charged CA-MA peptide studied, hydrogenated and fluorinated rims, respectively, hinder and promote the insertion.

A Facile Electrochemical Sensor Based on PyTS⁻CNTs for Simultaneous Determination of Cadmium and Lead Ions

A simple and easy method was implemented for the contemporary detection of cadmium (Cd²⁺) and lead (Pb²⁺) ions using 1,3,6,8-pyrenetetrasulfonic acid sodium salt-functionalized carbon nanotubes nanocomposites (PyTS⁻CNTs). The morphology and composition of the obtained PyTS⁻CNTs were characterized using scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and X-ray photoelectron spectroscopy (XPS). The experimental results confirmed that the fabricated PyTS⁻CNTs exhibited good selectivity and sensitivity for metal ion-sensing owing to the insertion of sulfonic acid groups. For Cd²⁺ and Pb²⁺, some of the electrochemical sensing parameters were evaluated by varying data such as the PyTS⁻CNT quantity loaded on the pyrolytic graphite electrode (PGE), pH of the acetate buffer, deposition time, and deposition potential. These parameters were optimized with differential pulse anodic sweeping voltammetry (DPASV). Under the optimal condition, the stripping peak current of the PyTS⁻CNTs/Nafion/PGE varies linearly with the heavy metal ion concentration, ranging from 1.0 μg L^-1 to 90 μg L^-1 for Cd²⁺ and from 1.0 μg L^-1 to 110 μg L^-1 for Pb²⁺. The limits of detection were estimated to be approximately 0.8 μg L^-1 for Cd²⁺ and 0.02 μg L^-1 for Pb²⁺. The proposed PyTS⁻CNTs/Nafion/PGE can be used as a rapid, simple, and controllable electrochemical sensor for the determination of toxic Cd²⁺ and Pb²⁺.

Dopant-Modulated Conjugated Polymer Enrichment of Semiconducting SWCNTs

Conjugated polymer extraction (CPE) is a low-cost, scalable process that can enrich single-walled carbon nanotube (SWCNT) materials in organic media. For other separation methods in aqueous phases, redox chemistry and/or pH control dramatically affect the sorting process of the SWCNTs. We have previously determined that the CPE process can be fine-tuned by adjusting the pH on the tube surface. Here, we systematically studied the effect of redox chemistry on the CPE process by adding organic p-/n-dopants. At a very strong p-/n-doping level, static repulsions dominated the interactions between the tubes and the CPE lost selectivity. When the doping level changed from a medium p-doping to a neutral state, the yield of CPE increased and the selectivity was compromised. We also observed chiral selectivity when a weak p-dopant was used. A photoluminescence excitation mapping under different titration conditions provided more insight into the doping level of the tubes relative to their diameters, chiralities, and redox potentials. We proposed a mechanism for the CPE process. The semiconducting and metallic tubes are separated because of their different solubilities, which are determined by the bundling energy between the tubes and are related to their doping level in polymer solutions.

Carbon-Nanotube-Based Thermoelectric Materials and Devices

Conversion of waste heat to voltage has the potential to significantly reduce the carbon footprint of a number of critical energy sectors, such as the transportation and electricity-generation sectors, and manufacturing processes. Thermal energy is also an abundant low-flux source that can be harnessed to power portable/wearable electronic devices and critical components in remote off-grid locations. As such, a number of different inorganic and organic materials are being explored for their potential in thermoelectric-energy-harvesting devices. Carbon-based thermoelectric materials are particularly attractive due to their use of nontoxic, abundant source-materials, their amenability to high-throughput solution-phase fabrication routes, and the high specific energy (i.e., W g^-1 ) enabled by their low mass. Single-walled carbon nanotubes (SWCNTs) represent a unique 1D carbon allotrope with structural, electrical, and thermal properties that enable efficient thermoelectric-energy conversion. Here, the progress made toward understanding the fundamental thermoelectric properties of SWCNTs, nanotube-based composites, and thermoelectric devices prepared from these materials is reviewed in detail. This progress illuminates the tremendous potential that carbon-nanotube-based materials and composites have for producing high-performance next-generation devices for thermoelectric-energy harvesting.

The role of the solvent and the size of the nanotube in the non-covalent dispersion of carbon nanotubes with short organic oligomers – a DFT study

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents. Recently, we have carried out two computational investigations on the intermolecular interactions between conjugated organic oligomers and SWCNTs in order to gain insight into an important process of the non-covalent dispersion of carbon nanotubes with short oligomers. These studies highlighted the fact that two additional factors, namely, the effects of the solvent and the carbon nanotube's size on these interactions need further investigation. In this work, with the help of model compounds (which are molecular fragments of the short oligomers used in our previous investigations), we analyze the significance of these two factors. We employ three dispersion corrected density functional theory (D-DFT) approximations (B97D, wB97XD, and B3LYP-D3) to assess the effect of the DFT method, and two basis sets (6-31G(d) and 6-31++G(d,p)) to assess the importance of using a higher basis set in our computations. The main focus of this work is to assess the effect of solvation and nanotube's size on the structure, electronic properties, and binding energies of the respective pairs of model compounds and segments of carbon nanotubes. No significant differences are found between the results of (6,5) and (8,7) SWCNTs in either the geometrical parameters of interacting oligomers or the general tendency of wrapping of their long side chains (SCs) around the nanotubes. However, we find that the binding energies per atom between nanotubes and model compounds are larger for nanotubes with the smaller diameter. The results of electronic properties also show that all model compounds interact more strongly with the (6,5) SWCNT than with the (8,7) SWCNT. Polar solvents such as chloroform show lower binding energies relative to those obtained without a solvent or with non-polar solvents such as hexane. It appears that the presence of a solvent weakens the oligomer/nanotube interactions and, presumably, strengthens the oligomer/solvent and nanotube/solvent interactions to facilitate dispersion of SWCNTs.

Among different dispersants of single-walled carbon nanotubes (SWCNTs), conjugated organic oligomers have the ability to interact strongly with SWCNTs and allow for effective dispersion in several organic solvents.

Switching the optical and electrical properties of carbon nanotube hybrid films using a photoresponsive dispersant as a dopant

The light-induced switching of the optical and electrical properties of single-walled carbon nanotubes hybrid films with photoresponsive dispersant.

Quantum yield in polymer wrapped single walled carbon nanotubes: a computational model

Quantum yield in polymer wrapped single walled carbon nanotubes (SWCNTs) has been computationally investigated using a 2D model of exciton decay with non-radiative channels due to the diffusive motion across the nanotube surface. Beside the role of SWCNT's ends as the exciton quenchers, we have considered the influence of the wrapping polymer through its chemistry and wrapping angle. The model has been solved exactly for zero-angle wrapping, a particular case when the polymer interfaces the nanotube along its axis. The general case has been treated numerically and it has been concluded that the wrapping angle has no relevant influence upon the quantum yield values which are of experimental interest. A wide range of quantum yield values computed in the present contribution can be helpful in understanding potentially available photoluminescence data of SWCNTs wrapped with a variety of polymer families.

Metallic versus Semiconducting SWCNT Chemiresistors: A Case for Separated SWCNTs Wrapped by a Metallosupramolecular Polymer

As-synthesized single-walled carbon nanotubes (SWCNTs) are a mixture of metallic and semiconducting tubes, and separation is essential to improve the performances of SWCNT-based electric devices. Our chemical sensor monitors the conductivity of an SWCNT network, wherein each tube is wrapped by an insulating metallosupramolecular polymer (MSP). Vapors of strong electrophiles such as diethyl chlorophosphate (DECP), a nerve agent simulant, can trigger the disassembly of MSPs, resulting in conductive SWCNT pathways. Herein, we report that separated SWCNTs have a large impact on the sensitivity and selectivity of chemical sensors. Semiconducting SWCNT (S-SWCNT) sensors are the most sensitive to DECP (up to 10000% increase in conductivity). By contrast, the responses of metallic SWCNT (M-SWCNT) sensors were smaller but less susceptible to interfering signals. For saturated water vapor, increasing and decreasing conductivities were observed for S- and M-SWCNT sensors, respectively. Mixtures of M- and S-SWCNTs revealed reduced responses to saturated water vapor as a result of canceling effects. Our results reveal that S- and M-SWCNTs compensate sensitivity and selectivity, and the combined use of separated SWCNTs, either in arrays or in single sensors, offers advantages in sensing systems.

Three-Dimensional Electroconductive Hyaluronic Acid Hydrogels Incorporated with Carbon Nanotubes and Polypyrrole by Catechol-Mediated Dispersion Enhance Neurogenesis of Human Neural Stem Cells

Electrically conductive hyaluronic acid (HA) hydrogels incorporated with single-walled carbon nanotubes (CNTs) and/or polypyrrole (PPy) were developed to promote differentiation of human neural stem/progenitor cells (hNSPCs). The CNT and PPy nanocomposites, which do not easily disperse in aqueous phases, dispersed well and were efficiently incorporated into catechol-functionalized HA (HA-CA) hydrogels by the oxidative catechol chemistry used for hydrogel cross-linking. The prepared electroconductive HA hydrogels provided dynamic, electrically conductive three-dimensional (3D) extracellular matrix environments that were biocompatible with hNSPCs. The HA-CA hydrogels containing CNT and/or PPy significantly promoted neuronal differentiation of human fetal neural stem cells (hfNSCs) and human induced pluripotent stem cell-derived neural progenitor cells (hiPSC-NPCs) with improved electrophysiological functionality when compared to differentiation of these cells in a bare HA-CA hydrogel without electroconductive motifs. Calcium channel expression was upregulated, depolarization was activated, and intracellular calcium influx was increased in hNSPCs that were differentiated in 3D electroconductive HA-CA hydrogels; these data suggest a potential mechanism for stem cell neurogenesis. Overall, our bioinspired, electroconductive HA hydrogels provide a promising cell-culture platform and tissue-engineering scaffold to improve neuronal regeneration.

Quantitative Analysis of the Molecular Dynamics of P3HT:PCBM Bulk Heterojunction

The optoelectronic properties of blends of conjugated polymers and small molecules are likely to be affected by the molecular dynamics of the active layer components. We study the dynamics of regioregular poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) blends using molecular dynamics (MD) simulation on time scales up to 50 ns and in a temperature range of 250-360 K. First, we compare the MD results with quasi-elastic neutron-scattering (QENS) measurements. Experiment and simulation give evidence of the vitrification of P3HT upon blending and the plasticization of PCBM by P3HT. Second, we reconstruct the QENS signal based on the independent simulations of the three phases constituting the complex microstructure of such blends. Finally, we found that P3HT chains tend to wrap around PCBM molecules in the amorphous mixture of P3HT and PCBM; this molecular interaction between P3HT and PCBM is likely to be responsible for the observed frustration of P3HT, the plasticization of PCBM, and the partial miscibility of P3HT and PCBM.

Application of Carbon Nanotubes in Chiral and Achiral Separations of Pharmaceuticals, Biologics and Chemicals

Carbon nanotubes (CNTs) possess unique mechanical, physical, electrical and absorbability properties coupled with their nanometer dimensional scale that renders them extremely valuable for applications in many fields including nanotechnology and chromatographic separation. The aim of this review is to provide an updated overview about the applications of CNTs in chiral and achiral separations of pharmaceuticals, biologics and chemicals. Chiral single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) have been directly applied for the enantioseparation of pharmaceuticals and biologicals by using them as stationary or pseudostationary phases in chromatographic separation techniques such as high-performance liquid chromatography (HPLC), capillary electrophoresis (CE) and gas chromatography (GC). Achiral MWCNTs have been used for achiral separations as efficient sorbent objects in solid-phase extraction techniques of biochemicals and drugs. Achiral SWCNTs have been applied in achiral separation of biological samples. Achiral SWCNTs and MWCNTs have been also successfully used to separate achiral mixtures of pharmaceuticals and chemicals. Collectively, functionalized CNTs have been indirectly applied in separation science by enhancing the enantioseparation of different chiral selectors whereas non-functionalized CNTs have shown efficient capabilities for chiral separations by using techniques such as encapsulation or immobilization in polymer monolithic columns.

Green Processing of Carbon Nanomaterials

Carbon nanomaterials (CNMs) from fullerenes, carbon nanotubes, and graphene are promising carbon allotropes for various applications such as energy-conversion devices and biosensors. Because pristine CNMs show substantial van der Waals interactions and a hydrophobic nature, precipitation is observed immediately in most organic solvents and water. This inevitable aggregation leads to poor processability and diminishes the intrinsic properties of the CNMs. Highly toxic and hazardous chemicals are used for chemical and physical modification of CNMs, even though efficient dispersed solutions are obtained. The development of an environmentally friendly dispersion method for both safe and practical processing is a great challenge. Recent green processing approaches for the manipulation of CNMs using chemical and physical modification are highlighted. A summary of the current research progress on: i) energy-efficient and less-toxic chemical modification of CNMs using covalent-bonding functionality and ii) non-covalent-bonding methodologies through physical modification using green solvents and dispersants, and chemical-free mechanical stimuli is provided. Based on these experimental studies, recent advances and challenges for the potential application of green-processable energy-conversion and biological devices are provided. Finally, a conclusion section is provided summarizing the insights from the present studies as well as some future perspectives.

Multifunctional, biocompatible and pH-responsive carbon nanotube- and graphene oxide/tectomer hybrid composites and coatings

Here we present a route for non-covalent functionalization of carboxylated multi-walled carbon nanotubes and graphene oxide with novel two-dimensional peptide assemblies. We show that self-assembled amino-terminated biantennary and tetraantennary oligoglycine peptides (referred to as tectomers) effectively coat carboxylated multi-walled carbon nanotubes and also strongly interact with graphene oxide due to electrostatic interactions and hydrogen bonding as the driving force, respectively. The resulting hybrids can be made into free-standing conducting composites or applied in the form of thin, pH-switchable bioadhesive coatings onto graphene oxide fibers. Monitoring of cell viability of pancreatic cell lines, seeded on those CNT hybrids, show that they can be used as two- and three-dimensional scaffolds to tissue engineer tumour models for studying ex vivo the tumour development and response to treatment. This highly versatile method in producing pH-responsive hybrids and coatings offers an attractive platform for a variety of biomedical applications and for the development of functional materials such as smart textiles, sensors and bioelectronic devices.

Noncovalent Protein and Peptide Functionalization of Single-Walled Carbon Nanotubes for Biodelivery and Optical Sensing Applications

The exquisite structural and optical characteristics of single-walled carbon nanotubes (SWCNTs), combined with the tunable specificities of proteins and peptides, can be exploited to strongly benefit technologies with applications in fields ranging from biomedicine to industrial biocatalysis. The key to exploiting the synergism of these materials is designing protein/peptide-SWCNT conjugation schemes that preserve biomolecule activity while keeping the near-infrared optical and electronic properties of SWCNTs intact. Since sp² bond-breaking disrupts the optoelectronic properties of SWCNTs, noncovalent conjugation strategies are needed to interface biomolecules to the nanotube surface for optical biosensing and delivery applications. An underlying understanding of the forces contributing to protein and peptide interaction with the nanotube is thus necessary to identify the appropriate conjugation design rules for specific applications. This article explores the molecular interactions that govern the adsorption of peptides and proteins on SWCNT surfaces, elucidating contributions from individual amino acids as well as secondary and tertiary protein structure and conformation. Various noncovalent conjugation strategies for immobilizing peptides, homopolypeptides, and soluble and membrane proteins on SWCNT surfaces are presented, highlighting studies focused on developing near-infrared optical sensors and molecular scaffolds for self-assembly and biochemical analysis. The analysis presented herein suggests that though direct adsorption of proteins and peptides onto SWCNTs can be principally applied to drug and gene delivery, in vivo imaging and targeting, or cancer therapy, nondirect conjugation strategies using artificial or natural membranes, polymers, or linker molecules are often better suited for biosensing applications that require conservation of biomolecular functionality or precise control of the biomolecule's orientation. These design rules are intended to provide the reader with a rational approach to engineering biomolecule-SWCNT platforms, broadening the breadth and accessibility of both wild-type and engineered biomolecules for SWCNT-based applications.

Fabrication of durable and flexible single-walled carbon nanotube transparent conductive films

Highly flexible, durable, and transparent conducting films are fabricated from the de-bundled SWCNTs in aqueous solutions of SPES with high conductivity (125 Ω sq⁻¹) and good transmittance (87%) without adopting any binder or post treatment techniques.

Extreme Activity of Drug Nanocrystals Coated with A Layer of Non-Covalent Polymers from Self-Assembled Boric Acid

Non-covalent polymers have remarkable advantages over synthetic polymers for wide biomedical applications. In this study, non-covalent polymers from self-assembled boric acid were used as the capping reagent to replace synthetic polymers in drug crystallization. Under acidic pH, boric acid self-assembled on the surface of drug nanocrystals to form polymers with network-like structures held together by hydrogen bonds. Coating driven by boric acid self-assembly had negligible effects on drug crystallinity and structure but resulted in drug nanocrystals with excellent dispersion properties that aided in the formation of a more stable suspension. Boric acid coating improved drug stability dramatically by preventing drug molecules from undergoing water hydrolysis in a neutral environment. More importantly, the specific reactivity of orthoboric groups to diols in cell glycocalyx facilitated a rapid cross-membrane translocation of drug nanocrystals, leading to efficient intracellular drug delivery, especially on cancer cells with highly expressed sialic acids. Boric acid coated nanocrystals of camptothecin, an anticancer drug with poor aqueous solubility and stability, demonstrated extreme cytotoxic activity (IC₅₀ < 5.0 μg/mL) to cancer cells compared to synthetic polymer coated CPT nanocrystals and free CPT. Surface coating using non-covalent polymers from self-assembled boric acid will have wide biomedical applications especially in biomaterials and drug delivery field.

Specific Molecular Interaction and Recognition at Single-Walled Carbon Nanotube Surfaces

Carbon nanotubes (CNTs) are carbon clusters (polymers) with huge molecular weight and have been the central material in the field of nanomaterials science and nanotechnology because of their remarkable electronic, thermal, mechanical, optical, and electrical properties. In this review article, we first focus on the formation of self-assembled CNT superstructures and spontaneous conductive CNT-honeycomb structure formation from CNT/long-chain ammonium lipids by simple solvent casting. We also summarized our recent studies on specific molecular interactions and recognition at single-walled carbon nanotube surfaces and CNT chirality recognition using specific polymers. For such studies, the key issue is to develop a methodology to solubilize/disperse them in solvent because as-synthesized CNTs form tightly bundled structures as a result of their strong van der Waals interactions and are insoluble in many solvents. For the analysis of molecules and CNT surfaces, the introduction of thermodynamic treatment and an HPLC method using CNT-coated silica as a stationary phase was powerful.

pH-controlled doxorubicin anticancer loading and release from carbon nanotube noncovalently modified by chitosan: MD simulations

In the present study, we describe here the pH condition activating doxorubicin (DOX) anticancer drugs loading and release over single-wall carbon nanotube (SWNT) non-covalently wrapped with chitosan (CS). The possibility of drug displacement on DOX/CS/SWNT nanocarrier was investigated using molecular dynamics simulations. The drug loading and release were monitored via displacement analysis and binding energy calculations. The simulated results clearly showed that the drugs well interacted with the CS/SWNT at physiological pH (pH 7.4), where CS was in the deprotonated form. Contrastingly, in weakly acidic environments (pH 5.0-6.5) which is a pH characteristics of certain cancer environments, the protonated CS became loosen wrapped around the SWNT and triggered drugs release as a result of charge-charge repulsion between CS and drug molecules. The obtained data fulfil the understanding at atomic level of drug loading and release controlled by pH-sensitive polymer, which might be useful for further cancer therapy researches.

Nanoporous carbon materials with enhanced supercapacitance performance and non-aromatic chemical sensing with C1/C2 alcohol discrimination

We have investigated the textural properties, electrochemical supercapacitances and vapor sensing performances of bamboo-derived nanoporous carbon materials (NCM). Bamboo, an abundant natural biomaterial, was chemically activated with phosphoric acid at 400 °C and the effect of impregnation ratio of phosphoric acid on the textural properties and electrochemical performances was systematically investigated. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of various oxygen-containing surface functional groups (i.e. carboxyl, carboxylate, carbonyl and phenolic groups) in NCM. The prepared NCM are amorphous in nature and contain hierarchical micropores and mesopores. Surface areas and pore volumes were found in the range 218-1431 m² g^-1 and 0.26-1.26 cm³ g^-1, respectively, and could be controlled by adjusting the impregnation ratio of phosphoric acid and bamboo cane powder. NCM exhibited electrical double-layer supercapacitor behavior giving a high specific capacitance of c.256 F g^-1 at a scan rate of 5 mV s^-1 together with high cyclic stability with capacitance retention of about 92.6% after 1000 cycles. Furthermore, NCM exhibited excellent vapor sensing performance with high sensitivity for non-aromatic chemicals such as acetic acid. The system would be useful to discriminate C₁ and C₂ alcohol (methanol and ethanol).

Formation of Coaxial Nanocables with Amplified Supramolecular Chirality through an Interaction between Carbon Nanotubes and a Chiral π-Gelator

In an attempt to gather experimental evidence for the influence of carbon allotropes on supramolecular chirality, we found that carbon nanotubes (CNTs) facilitate amplification of the molecular chirality of a π-gelator (MC-OPV) to supramolecular helicity at a concentration much lower than that required for intermolecular interaction. For example, at a concentration 1.8×10(-4)  m, MC-OPV did not exhibit a CD signal; however, the addition of 0-0.6 mg of SWNTs resulted in amplified chirality as evident from the CD spectrum. Surprisingly, AFM analysis revealed the formation of thick helical fibers with a width of more than 100 nm. High-resolution TEM analysis and solid-state UV/Vis/NIR spectroscopy revealed that the thick helical fibers were cylindrical cables composed of individually wrapped and coaxially aligned SWNTs. Such an impressive effect of CNTs on supramolecular chirality and cylindrical-cable formation has not been reported previously.