Ends Of Single-walled Carbon Nanotubes Research Articles

Carbon Nanotube Biohybrids: From Protein Site-Specific Coupling to the Fabrication of Reconfigurable (multi)Sensing Systems and Devices

We controlled the assembly of different biomolecules, from proteins to DNA and aptamer sequences, on carbon nanotubes (CNTs), so as to couple CNTs electronic output to biomolecular function. First we will present a facile strategy for the site-specific coupling of proteins to single walled carbon nanotubes (SWCNTs): i) in solution and with single-molecule control, with a focus on light harvesting and charge transfer investigations, as well as ii) in device configurations to investigate biomolecular (protein-protein) recognition in the context of antimicrobial resistance enzyme detection. Using an orthogonal Click reaction, Green Fluorescent Protein (GFP) was engineered to contain a genetically encoded azide group and then bound selectively to SWCNT ends in 1:1 nanohybrids with different protein orientations: in close proximity or at longer distances from the GFP’s functional center. Atomic force microscopy and fluorescence analysis in solution and on surfaces at the single-protein level confirmed the importance of bioengineering optimal protein attachment sites to achieve direct protein−nanotube communication and bridging.[1] We will then discuss the extension of this rationale into bioelectornic devices for the development of real-time biosensors with engineered protein interfacing. We assembled different variants of a b-lactamase (BL) inhibitory protein (BLIP) onto SWCNT sidewalls in electronic device configurations. We recorded the current responses in real-time for the detection of different concentrations of a class BL enzymes,[2] that degrade antibiotics, in the context of investigating antimicrobial resistance. (Resistance against the most useful antibiotics, the b-lactams, including the penicillins, is arguably the most pressing issue due to the prevalence of many different BL enzymes that degrade the antibiotic; BLIP acts as the ideal detection element in terms of its specificity to BLs and ability to bind a wide variety of different BLs). Employing a similar strategy, we will report on the fabrication of reconfigurable and solution processable nanoscale biosensing devices with multisensing capability based on SWCNTs functionalized with specific, and different, aptamer sequences employed as selective recognition elements. Distinct, hence water-soluble, SWCNT-aptamer hybrids were immobilized from solution onto different pre-patterned electrodes on the same chip, via a low-cost dielectrophoresis methodology. Multiplexed detection of three different biomarkers indicative of stress and neuro-trauma conditions was successfully performed, and real-time detection was achieved in serum down to physiologically relevant concentrations.[3] Finally, we present a strategy for the controlled assembly of stimuli-responsive end-to-end SWCNT junctions in aqueous solution, employing DNA as a molecular linker. The assembly/disassembly of the nanotubes was controlled via the intrinsic responsiveness to different stimuli of sequence-specific DNA linkers forming the junctions.[4] By and large, we demonstrate novel approaches for the designed assembly of solution-processable bioelectronic systems where single biomolecules modulate the properties of carbon nanotubes.This can yield new insights into biomolecular events down to single-molecule resolution and facilitate biomolecules’ use as integrated nanocomponents in molecular electronics and biosensing devices. [1] Journal of the American Chemical Society, 2017, 139, 17834-17840 [2] Submitted [3] Nano Letters, 2018, 18, 4130-4135 [4] Under 2nd review in Chemistry of Materials

Large magnetic moment at sheared ends of single-walled carbon nanotubes**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0208403 and 2016YFA0200403), the National Natural Science Foundation of China (Grant Nos. 51472057, 11874129, 91323304, and 11674387), the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA09040101), and the Baotou Rare Earth Research

In this work we report that after single-walled carbon nanotubes (SWNTs) are sheared with a pair of titanium scissors, the magnetization becomes larger than that of the corresponding pristine ones. The magnetization increases proportionally with the number of SWNTs with sheared ends, suggesting that there exist magnetic moments at the sheared ends of SWNTs. By using the coefficient of this linear relation, the average magnetic moment is estimated to be 41.5 ± 9.8 μB (Bohr magneton) per carbon atom in the edge state at temperature of 300.0 K, suggesting that ultrahigh magnetic fields can be produced. The dangling sigma and pi bonds of the carbon atoms at sheared ends play important roles in determining the unexpectedly high magnetic moments, which may have great potential applications.

In situ Raman spectroelectrochemical study of potential-induced molecular encapsulation of β-carotene inside single-walled carbon nanotubes

The effect of the electrochemical potential of single-walled carbon nanotubes (SWCNTs) on the encapsulation behavior of β-carotene inside the SWCNT cavities was investigated by in situ Raman spectroelectrochemistry. Prior to Raman measurement, the electrochemical behavior of β-carotene at SWCNT electrodes was investigated. Weak adsorption of β-carotene was observed, whereas at glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG) electrodes, β-carotene showed diffusion-controlled reactions and was not adsorbed. Furthermore, a negative potential shift of the oxidation reaction of β-carotene was observed at the SWCNT surface compared with that at other carbon materials such as GC and HOPG. To remove the ends of SWCNTs to allow encapsulation of β-carotene and minimize damage of the side wall of SWCNTs, we used finely controlled potential oxidation method. Results of the in situ Raman measurements indicated that encapsulation of β-carotene into the SWCNT cavity occurred most smoothly when a potential of 0.3V (vs. Ag/Ag+) was applied to the SWCNTs. When the applied potential was >0.4V, the encapsulated β-carotene could be oxidized and decomposed through formation of cation radical and dication forms of β-carotene, even though the β-carotene was encapsulated in the SWCNTs. Applied potentials of –0.2~0.2V did not result in smooth encapsulation compared with that at 0.3V. Overall, we found that the encapsulation behavior of β-carotene in SWCNTs depended on the potential of the SWCNTs.

Beam-Induced Nonuniform Shrinkage of Single-Walled Carbon Nanotube and Passivation Effect of Metal Nanoparticle

Electron-beam-induced nonuniform shrinkage of single-walled carbon nanotube (SWCNT) and the passivation effect of catalyst metal nanoparticle on the shrinkage were reported for the first time. It was found that pristine SWCNT shrank in its axial direction preferentially from the most curved, free cap end of the tube whereas the shrinkage of the tube diameter was almost offset by the axial shrinkage. However, once being attached to Fe nanoparticle, the most curved cap end of SWCNT became intriguingly passivated. As a consequence, the axial shrinkage of the SWCNT was retarded and the shrinkage of the tube diameter was revealed. A new mechanism of atom “diffusion” combined with atom “evaporation” as athermally driven by the nanocurvature of SWCNT and electron beam activation was proposed to elucidate the observed new phenomenon, which is different from the existing knock-on mechanism.

Thermal Transport Across the Interface Between a Suspended Single-Walled Carbon Nanotube and Air

The heat transfer coefficients of several individual single-walled carbon nanotubes (SWCNTs) were measured using a micro-Raman spectroscopy technique in an atmosphere environment. A 514 nm laser was focused in the middle of a suspended SWCNT and the local temperature rise was measured by monitoring the downshifts of the G-band frequency. The heat transfer coefficient can be extracted from the measured midpoint temperature rise. Because there are no temperature drops at the ends of SWCNTs, the thermal contact resistance can be ignored. A detailed kinetic model was developed to predict the heat transfer coefficient quantitatively from the free molecular regime to the continuum regime. The theoretical prediction agrees well with the experimental data. Based on the present model, a maximum heat transfer coefficient occurs in the transition regime at a diameter of several nanometers, which is the competition result of the thermal resistances of the noncontinuum layer and continuum layer. The maximum value agrees with the prediction of kinetic theory of gases. The noncontact Raman measurement technique and prediction model will benefit the thermal design of carbon nanotube-based heat spreaders.

Controlled Formation of Carbon Nanotube Junctions via Linker-Induced Assembly in Aqueous Solution

Here we present a simple approach for the controlled formation of one-dimensional and multiterminal nanotube junctions. We describe a facile bottom-up strategy for joining the ends of single-walled carbon nanotubes. The geometry of the junctions can be varied and controlled by linker-induced assembly of DNA-wrapped nanotubes.

Effect of Competitive Surface Functionalization on Dual-Modality Fluorescence and Magnetic Resonance Imaging of Single-Walled Carbon Nanotubes.

It is well-known that ionic surfactant coated single-walled carbon nanotubes (SWNTs) possess higher near-infrared fluorescence (NIRF) quantum yield than nonionic polymer functionalized SWNTs. However, the influence of surface functionalization on the magnetic properties of SWNTs for T2-weighted magnetic resonance imaging (MRI) has not been reported. Here, we demonstrate that SWNTs functionalized by nonionic polymers display superior T2 relaxivity for MRI as compared to those coated by ionic surfactants. This difference may indicate that micelle structures formed by ionic surfactants are sufficiently tight to partially exclude water protons from the iron catalysts attached to the ends of SWNTs. On the basis of the different effects of the two types of suspension agents on NIRF and MRI of functionalized SWNTs, we further explore the competitive surface functionalization between ionic surfactants and nonionic polymers by stepwise replacing ionic surfactant molecules in a nanotube suspension with nonionic polymers. The superior NIRF of ionic surfactant coated SWNTs gradually quenches whereas no improvement on T2 relaxivity is observed during this replacement process. This result may indicate that nonionic polymers wrap around the outside of micelle structures to form small nanotube bundles rather than replacing ionic surfactants in the micelle structures to directly interact with the SWNT surface. Finally, we demonstrate the feasibility of dual-modality NIRF and MRI of nonionic polymer functionalized SWNTs in brain cells.

Quantitative nanoscale visualization of heterogeneous electron transfer rates in 2D carbon nanotube networks

Carbon nanotubes have attracted considerable interest for electrochemical, electrocatalytic, and sensing applications, yet there remains uncertainty concerning the intrinsic electrochemical (EC) activity. In this study, we use scanning electrochemical cell microscopy (SECCM) to determine local heterogeneous electron transfer (HET) kinetics in a random 2D network of single-walled carbon nanotubes (SWNTs) on an Si/SiO(2) substrate. The high spatial resolution of SECCM, which employs a mobile nanoscale EC cell as a probe for imaging, enables us to sample the responses of individual portions of a wide range of SWNTs within this complex arrangement. Using two redox processes, the oxidation of ferrocenylmethyl trimethylammonium and the reduction of ruthenium (III) hexaamine, we have obtained conclusive evidence for the high intrinsic EC activity of the sidewalls of the large majority of SWNTs in networks. Moreover, we show that the ends of SWNTs and the points where two SWNTs cross do not show appreciably different HET kinetics relative to the sidewall. Using finite element method modeling, we deduce standard rate constants for the two redox couples and demonstrate that HET based solely on characteristic defects in the SWNT side wall is highly unlikely. This is further confirmed by the analysis of individual line profiles taken as the SECCM probe scans over an SWNT. More generally, the studies herein demonstrate SECCM to be a powerful and versatile method for activity mapping of complex electrode materials under conditions of high mass transport, where kinetic assignments can be made with confidence.

An Electrochemical Immunosensor Based on Chemical Assembly of Vertically Aligned Carbon Nanotubes on Carbon Substrates for Direct Detection of the Pesticide Endosulfan in Environmental Water

A glassy carbon substrate was covalently modified with a mixed layer of 4-aminophenyl and phenyl via in situ electrografting of their aryldiazonium salts in acidic solutions. Single-walled carbon nanotubes (SWNTs) were covalently and vertically anchored on the electrode surface via the formation of amide bonds from the reaction between the amines located on the modified substrate and the carboxylic groups at the ends of the nanotubes. Ferrocenedimethylamine (FDMA) was subsequently attached to the ends of SWNTs through amide bonding followed by the attachment of an epitope, i.e., endosulfan hapten to which an antibody would bind. Association or dissociation of the antibody with the sensing interface causes a modulation of the ferrocene electrochemistry. Antibody-complexed electrodes were exposed to samples containing spiked endosulfan (unbound target analyte) in environment water and interrogated using the square wave voltammetry (SWV) technique. The modified sensing surfaces were characterized by atomic force microscopy, XPS, and electrochemistry. The fabricated electrochemical immunosensor can be successfully used for the detection of endosulfan over the range of 0.01-20 ppb by a displacement assay. The lowest detection limit of this immunosensor is 0.01 ppb endosulfan in 50 mM phosphate buffer at pH 7.0.

Torsional vibration of carbon nanotube–buckyball systems based on nonlocal elasticity theory

In this paper, torsional vibration analysis of single-walled carbon nanotube–buckyball systems is carried out. The buckyball is attached to single-walled carbon nanotube (SWCNT) at one end and the other end of SWCNT is fixed. Such nanostructures are promising for tunable nanoresonators whose frequency can be altered by attaching different buckyballs. Nonlocal elasticity is utilized to examine the small-scale effect on the nanoresonators and derive the torsional frequency equation and nonlocal transcendental equation. Based on these equations, numerical results are obtained for the dependence of the frequency on the mass moment of inertia. The analytical expressions of nonlocal frequencies are also derived when the buckyballs mass moment of inertias are much larger than that of SWCNTs. In addition, effort is made to study the influence of nonlocal parameter and attached buckyball on the torsional frequency of the nanoresonators.

Controlled Assembly of Ag Nanoparticles and Carbon Nanotube Hybrid Structures for Biosensing

Here we report a chemical-free, simple, and novel method in which a part from a silver-based anode is controllably used in a straightforward manner to produce silver nanoparticles (Ag NPs) in order to fabricate a controlled assembly of Ag NPs and single walled carbon nanotube (SWCNT) hybrid structures. The attachment and distribution of Ag NPs along SWCNTs have been investigated and characterized by field emission scanning electron microscopy (FESEM). We have achieved the decoration of SWCNTs with different densities of Ag NPs by changing the deposition time, the applied voltage, and the location of carbon nanotubes with respect to the anode. At low voltage, single silver nanoparticle is successfully attached at the open ends of SWCNTs whereas at high voltage, intermediate and full coverage densities of Ag NPs are observed. As voltage is further increased, fractals of Ag NPs along SWCNTs are observed. In addition, a device based on a Ag NPs-SWNT hybrid structure is used for the label-free detection of ssDNA molecules immobilized on it. We believe that the proposed method can be used to decorate and/or assemble metal nanoparticles or fractal patterns along SWCNTs with different novel metals such as gold, silver, and copper and can be exploited in various sensitive applications for fundamental research and nanotechnology.

Antibacterial Activity of Electrospun Polymer Mats with Incorporated Narrow Diameter Single-Walled Carbon Nanotubes

Polymer coatings featuring nonleaching antibacterial agents are needed to significantly reduce bacterial colonization and subsequent biofilm formation. Previously, single-walled carbon nanotubes (SWNTs) have been reported to be strong antimicrobial agents that kill microbes on contact. However, the antibacterial activity of freestanding polymer mats with a low weight percent of incorporated SWNTs has not been demonstrated. In this study, four different weight percents of well characterized, small diameter (0.8 nm) SWNTs were incorporated into electrospun polysulfone (PSf) mats. Electrospun PSf-SWNT mats were observed to be flexible and composed of continuous, cylindrical, and randomly oriented fibers. SEM micrographs revealed that SWNT ends were distributed along the longitudinal fiber axis. Loss of bacteria (Escherichia coli) viability was observed to directly correlate to increased SWNT incorporation within the mat, ranging from 18% for 0.1 wt % SWNTs to 76% for 1.0 wt % SWNTs. Time-dependent bacterial cytotoxicity studies indicated that the antimicrobial action of the PSf-SWNT mats occurs after a short contact time of 15 min or less. This study demonstrates the potential applicability of electrospun PSf-SWNT mats as antibacterial coatings.

Length-Dependent Photoluminescence Lifetimes in Single-Walled Carbon Nanotubes

We describe the length-dependent exciton dynamics in DNA-wrapped single-walled carbon nanotubes (SWNTs) using time-resolved photoluminescence (PL) excitation correlation spectroscopy. We demonstrate that the effective PL lifetimes have substantial upper limits in longer SWNTs. Our results suggest that the exciton diffusion to the ends of the nanotube has only a limited contribution to the net nonradiative relaxation rate, and the nonradiative processes that occur before the excitons reach the ends of SWNT are the dominant contribution to the nonradiative lifetime. From the length-dependent PL lifetimes and relative intensities in DNA-wrapped SWNTs, the exciton diffusion length was found to be ∼50 nm, and the diffusion coefficient was ∼1 cm2/s.

Space durable polymer/carbon nanotube films for electrostatic charge mitigation

Low color, flexible, space environmentally durable polymeric materials possessing sufficient surface resistivity (10 6 –10 10 Ω/square) for electrostatic charge (ESC) mitigation are of interest for potential applications on Gossamer spacecraft as thin film membranes on antennas, large lightweight space optics, and second surface mirrors. One method of incorporating intrinsic ESC mitigation while maintaining low color, flexibility, and optical clarity is through the utilization of single-walled carbon nanotubes (SWNTs). However, SWNTs are difficult to uniformly disperse in the polymer matrix. The approach reported herein employed amide acid polymers endcapped with alkoxysilane groups that could condense with oxygen containing functionalities that were present on the ends of SWNTs as a result of the oxidative purification treatment. These SWNTs were combined with the endcapped amide acid polymers in solution and subsequently cast as unoriented thin films. Two examples possessed electrical conductivity (measured as surface resistance and surface resistivity) sufficient for ESC mitigation at loading levels of ≤0.08 wt% SWNT as well as good retention of thermo-optical properties. The percolation threshold was determined to lie between 0.03 and 0.04 wt% SWNT loading. Electrical conductivity of the film remained unaffected even after harsh mechanical manipulation.

Quantum chemistry study on the open end of single-walled carbon nanotubes

Geometrical and electronic structures of open-ended single-walled carbon nanotubes (SWCNTs) are calculated using density functional theory (DFT) with hybrid functional (B3LYP) approximation. Due to different distances between carbon atoms along the edge, reconstruction occurs at the open end of the (4,4) armchair SWCNT, i.e., triple bonds are formed in the carbon atom pairs at the mouth; however, for the (6,0) zigzag SWCNT, electrons in dangling bonds still remain at ‘no-bonding’ states. The ionization potential (IP) of both (4,4) and (6,0) SWCNTs is increased by their negative intrinsic dipole moments, and localized electronic states existed at both of their open ends.

Self-assembly of single-walled carbon nanotube based on diazoresin

The self-assembly film of single-walled carbon nanotube (SWCNT) based on diazoresin (DR) were prepared on CaF 2, mica substrates and Pt tip. After oxidation, the ends of SWCNT were opened and turned into carboxylic group, which can react with diazonium group via Coulombic attraction. The film formed was photosensitive. After UV irradiation, the ionic bond between carboxylic group and diazonium group would turn into covalent bond following the decomposition of the diazonium group. The self-assembly layer and the bond conversion between the layers of the film have been verified with infrared (IR) spectroscopy, UV-Vis spectroscopy and transmission electron microscope (TEM).

Influence of Oxygen on Field Emission from Single-Walled Carbon Nanotubes

The influence of oxygen on field emission properties of single-walled carbon nanotubes (SWCNTs) was studied experimentally. Field emission images and current–voltage curves acquired using a field emission microscope (FEM) showed that exposure to oxygen resulted in an increased work function of SWCNTs. Oxidation etching at high temperature sharpened the SWCNT ends and field emission was therefore enhanced.

Field-ion microscopy observation of single-walled carbon nanotubes

Field-ion microscopy (FIM), a tool for surface analysis with atomic resolution, has been employed to observe the end structure of single-walled carbon nanotubes (SWCNTs). FIM images revealed the existence of open SWCNT ends. Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them. Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles. Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.

Chemical vapor deposition of methane for single-walled carbon nanotubes

We report the synthesis of high-quality single-walled carbon nanotubes (SWNT) by chemical vapor deposition (CVD) of methane at 1000°C on supported Fe2O3 catalysts. The type of catalyst support is found to control the formation of individual or bundled SWNTs. Catalysts supported on crystalline alumina nanoparticles produce abundant individual SWNTs and small bundles. Catalysts supported by amorphous silica particles produce only SWNT bundles. Studies of the ends of SWNTs lead to an understanding of their growth mechanism. Also, we present the results of methane CVD on supported NiO, CoO and NiO/CoO catalysts.