Carbon Nanotube Probes Research Articles

Manipulation of quantum spin transport of TM (Mn, Fe, Co, and Ni) (II) phthalocyanines coupled to carbon nanotube leads applicable in spintronic devices

We conducted a theoretical scrutiny on the quantum spin transport characteristics of a class of open-shell 3d-transition metal (TM = Mn, Fe, Co, and Ni) (II) phthalocyanines (TMPcs) molecules sandwiched between two semi-infinite armchair single-walled carbon nanotube probes. Herein, the spin density functional formalism is utilized in conjunction with state-of-the-art non-equilibrium Green's function technique. Molecular junctions composed of MnPc and FePc have higher local magnetic spin moments than CoPc and NiPc because of the strong exchange spin-splitting between the 3d-states of the Mn or Fe cation atoms and the p-states of the N anion atom. This indicates that TMPc molecules (TM = Mn, and Fe) bridged between two single-walled carbon nanotube (SWCNT) electrodes with a π-type geometry demonstrate a pronounced transmission near the Fermi level. Furthermore, the sign and robustness of spin filter efficiency are tailored by manipulating the central atom of 3d-transition metal and the contact SWCNT electrodes. Subsequently, FePc and MnPc molecular junctions have the advantage of operating practically as ideal spin filter devices compared to CoPc and NiPc molecular structures. Moreover, the tunneling magnetoresistance (TMR) of these molecular devices is assessed. For MnPc and FePc molecular junctions, the estimated total conductance exhibited a robust trend at zero bias voltage, whereas the magnitudes of spin-up and spin-dn quantum conductances increased significantly in CoPc and NiPc molecular configurations with bias voltages range between ±0.45 and ±0.95 Volt. Spin-down carriers essentially govern the quantum conductance of TMPc (Mn, Fe, Co, and Ni) molecular junctions at bias voltage around ±0.75 Volt. By examining their I-V characteristics, it has been established that MnPc, and FePc molecular junctions exhibit metal-like behavior, whereas CoPc and NiPc molecular devices are subject to negative differential resistance. As a result of our theoretical findings, it is found that TMPcs (TM = Fe, Mn) coupled to SWCNT probes yield a robust spin filter efficiency that may be of interest for prospective technological realizations in organic-inorganic molecular spintronic devices.

Studies of probe tip materials by atomic force microscopy: a review.

As a tool that can test insulators' surface morphology and properties, the performance index of atomic force microscope (AFM) probes is the most critical factor in determining the resolution of microscopy, and the performance of probes varies in various modes and application requirements. This paper reviews the latest research results in metal, carbon nanotube, and colloidal probes and reviews their related methods and techniques, analyses the advantages and disadvantages of the improved probes compared with ordinary probes by comparing the differences in spatial resolution, sensitivity, imaging, and other performance aspects, and finally provides an outlook on the future development of AFM probes. This paper promotes the development of AFM probes in the direction of new probes and further promotes the broader and deeper application of scanning probe microscope (SPM).

Controlled optical near-field growth of individual free-standing well-oriented carbon nanotubes, application for scattering SNOM/AFM probes.

Exploiting localized heat-generation density and the resulting enhanced temperature-rise for controlled growth of carbon nanotubes (CNTs) is reported, and its potentials for batch-production of high-quality CNT probes are demonstrated. Optical near field chemical vapor deposition (ONF-CVD) benchtop fabrication schemes are developed for the localized integration of individual well-aligned carbon nanotubes without bending/buckling exactly at desired nanoscale sites. It is demonstrated that generating self-aligned catalyst nanoparticles superimposed on top of silicon nanotips, along with near-field induced absorption confinement, provide the ability to localize the generated heat at the nanotips apexes, and control the CNT growth locations. The nanoscale maskless controllability of the growth site is shown by properly tailoring ONF-CVD conditions to overcome overall heat exposure of the substrate for selective activation of catalyst nanoparticles located at apexes, from those dispersing all over the tips. The calculated local power densities and temperature profiles of the simulated tips, clearly demonstrate the confined heat and optimal gradient of generated temperature rise as the main factors affecting the growth. In addition to determining necessary processing conditions to control the localization and orientation of the growth, parameters affecting the length and diameter of the localized individually grown nanotubes are also presented. Optical near-field-based growth schemes can be extended for localized maskless fabrication of other nanoscale devices, beyond the diffraction limit, using photothermal effects.

Single-Walled Carbon Nanotube Probes for the Characterization of Biofilm-Degrading Enzymes Demonstrated against Pseudomonas aeruginosa Extracellular Matrices.

Hydrolase co-therapies that degrade biofilm extracellular polymeric substances (EPS) allow for a better diffusion of antibiotics and more effective treatment; current methods for quantitatively measuring the enzymatic degradation of EPS are not amendable to high-throughput screening. Herein, we present biofilm EPS-functionalized single-walled carbon nanotube (SWCNT) probes for rapid screening of hydrolytic enzyme selectivity and activity on EPS. The extent of biofilm EPS degradation is quantified by monitoring the quenching of the SWCNT fluorescence. We used this platform to screen 16 hydrolases with varying bond breaking selectivity against a panel of wild-type Pseudomonas aeruginosa and mutants deficient or altered in one or more EPS. Next, we performed concentration-dependent studies of six enzymes on two common strains found in cystic fibrosis (CF) environments and, for each enzyme, extracted three first-order rate constants and their relative contributions by fitting a parallel, multi-site degradation model, with a good model fit (R2 from 0.65 to 0.97). Reaction rates (turnover rates) are dependent on the enzyme concentration and range from 6.67 × 10-11 to 2.80 × 10-3 *s-1 per mg/mL of enzymes. Lastly, we confirmed findings from this new assay using an established crystal-violet staining assay for a subset of hydrolase panels. In summary, our work shows that this modular sensor is amendable to the high-throughput screening of EPS degradation, thereby improving the rate of discovery and development of novel hydrolases.

Controlled growth of a single carbon nanotube on an AFM probe

Carbon nanotubes (CNTs) can be used as atomic force microscopy (AFM) tips for high-resolution scanning due to their small diameter, high aspect ratio and outstanding wear resistance. However, previous approaches for fabricating CNT probes are complex and poorly controlled. In this paper, we introduce a simple method to selectively fabricate a single CNT on an AFM tip by controlling the trigger threshold to adjust the amount of growth solution attached to the tip. The yield rate is over 93%. The resulting CNT probes are suitable in length, without the need for a subsequent cutting process. We used the CNT probe to scan the complex nanostructure with a high aspect ratio, thereby solving the long-lasting problem of mapping complex nanostructures.

(Invited) Mechanistic Study of the Covalent Bond-Mediated Charge Transfer between Carbon Nanotubes and Molecular Probes

The noncovalent interaction between carbon nanotubes and molecular groups leads to hybrid systems with low stability and poorly defined structure in terms of the density of functional groups, their relative positions and orientation. Since these factors are affected by microenvironmental parameters, studying the charge transfer of such dynamic systems is challenging. Covalent attachment of molecular probes, on the other hand, disturb the π-conjugated integrity of carbon nanotubes and suppress their light emission1,2. In 2017, we explored a nondestructive covalent functionalization (NCF) that opens up new avenues to overcome the aforementioned challenges3. NCF is an effective strategy for the preparation of stable carbon nanotube hybrids with defined functionality and preserved photoluminescence property4. In this work, we have used NCF for the mechanistic study of covalent bond-mediated charge transfer between molecular probes and carbon nanotubes by manipulating the structure of the probes. Different molecular probes with the same backbone but different functionality were synthesized by reaction between aniline derivatives and cyanuric chloride (Figure 1a). The conjugation of the molecular probes to the surface of carbon nanotubes by nitrene [2+1] cycloaddition reaction resulted in hybrid systems with the preserved physicochemical properties. π conjugated system of carbon nanotubes was integrated outwards into the backbone of molecular probes upon opening the aziridine ring in the bridge position and resulted in charge transfer between these two components (Figure 1b). Due to the same chemical backbone but different number of electron donating groups, variation in the optical properties of carbon nanotubes was assigned to the contribution of these groups in doping through which a mechanism for the covalent bond-mediated charge transfer was proposed. As a proof of concept, we have demonstrated a new way to forward the π conjugated system of carbon nanotubes outwards into other (macro)molecules which results in new systems with the unique optoelectronic properties. References Cognet, L. et al. Science 2007, 316, 1465.Piao, Y. et al. Chem. 2013, 5, 840.Setaro et al. Nat Commun. 2017, 8, 14281.Godin et al. Science Advances, 2019, 5, eaax116. Figure 1

Determination of Hamaker constant for CNT and AFM probe configuration inside SEM

Mounting the atomic force microscope (AFM) probe on the gripper of the robotic nanoscale manipulators system enables the combination of the AFM and scanning electron microscope (SEM). The AFM–SEM-based method of determining Hamaker constant for carbon nanotube (CNT) and AFM cantilever in the vacuum condition of SEM, which is completed through a robotic nanoscale manipulators system, is presented for the first time. During Hamaker constant determining experiment, the elastic force is measured utilising integrated AFM–SEM imaging technique through detecting the deflection of AFM cantilever that actually equals van der Waals adhesion force. The van der Waals attraction force between CNT and AFM cantilever is calculated through the modelling of a cylindrical nanotube and a flat gold-coated surface. The experiment results indicate that Hamaker's constant measured are comparable to typical values published by previous researchers, being of the order of 100 zJ, which indicates that the present approach is valid and reliable.

The Most Recent Advances in the Application of Nano-Structures/Nano-Materials for Single-Cell Sampling.

The research in endogenous biomolecules from a single cell has grown rapidly in recent years since it is critical for dissecting and scrutinizing the complexity of heterogeneous tissues, especially under pathological conditions, and it is also of key importance to understand the biological processes and cellular responses to various perturbations without the limitation of population averaging. Although conventional techniques, such as micromanipulation or cell sorting methods, are already used along with subsequent molecular examinations, it remains a big challenge to develop new approaches to manipulate and directly extract small quantities of cytosol from single living cells. In this sense, nanostructure or nanomaterial may play a critical role in overcoming these challenges in cellular manipulation and extraction of very small quantities of cells, and provide a powerful alternative to conventional techniques. Since the nanostructures or nanomaterial could build channels between intracellular and extracellular components across cell membrane, through which cytosol could be pumped out and transferred to downstream analyses. In this review, we will first brief the traditional methods for single cell analyses, and then shift our focus to some most promising methods for single-cell sampling with nanostructures, such as glass nanopipette, nanostraw, carbon nanotube probes and other nanomaterial. In this context, particular attentions will be paid to their principles, preparations, operations, superiorities and drawbacks, and meanwhile the great potential of nano-materials for single-cell sampling will also be highlighted and prospected.

A study on the mechanical properties of a carbon nanotube probe with a high aspect ratio

Carbon nanotube (CNT) probes are used in atomic force microscopes (AFMs) for high-resolution imaging, especially in the measurement of high aspect ratio micro/nano structures. Due to the use of a longer CNT tip leading to the degradation of image resolution, researchers have used several methods to cut CNTs. However, the principle of the selection of the cutting length has hardly been reported. Moreover, the influence of the effect of size on the mechanical properties of a CNT tip is not fully understood. In this study, an accurate model of finite element simulations is constructed on the basis of scanning electron microscopy data to investigate the mechanical properties of a CNT probe. An elastic model is employed to study the factors that influence the critical buckling force at the CNT tip during the measurement process. The calculation shows that the mechanical stiffness of the probe is affected by the diameter and the length-to-diameter ratio of the CNT tip. The changes in the von Mises stress at the bond between the AFM probe and the CNT tip as well as the variation of the strain energy at the CNT tip are discussed. It is hoped that this study will provide guidance for the selection of the cutting length of CNT-AFM probes and propose a basis for probe selection and design in practical measurements.

Phenylboronic acid derivative-modified (6,5) single-wall carbon nanotube probes for detecting glucose and hydrogen peroxide.

In this paper, we presented a new method for constructing near-infrared fluorescence probes and their applications in detecting glucose and hydrogen peroxide (H2O2). We used purified (6,5) single-wall carbon nanotubes (SWCNTs) separated by a polyethylene glycol/dextran aqueous two-phase system as the basis for near-infrared probes. Different phenylboronic acids were used for non-covalent modification of SWCNTs (6,5). Glucose was detected by the specific binding of the boronic acid group with cis-diol. Hydrogen peroxide was detected by horseradish peroxidase (HRP) combined with phenylboronic-acid-modified SWCNTs. The results revealed that the fluorescence intensity of purified SWCNTs was significantly enhanced without other chiral nanotube interactions compared to that of the raw SWCNT material. The fluorescence responses of 3-carboxy-5-nitrophenylboronic acid-modified purified CNTs could be used to effectively measure glucose in the concentration range from 0.01 mM to 0.50 mM with an interval linear index of R2 = 0.996 (LOD = 1.7 μM, S/N = 3). The detected H2O2 with the 3-aminobenzeneboronic acid-modified (6,5) SWCNT with HRP was in the concentration range from 5.0 μM to 40 μM with an interval linear index of R2 = 0.997 (LOD = 0.85 μM, S/N = 3). Moreover, this sensor exhibited a strong anti-interference effect without biological matrix fluorescence effects above 1000 nm wavelength. Thus, the proposed novel near-infrared fluorescence probes employed for reducing the interference of the biomatrix in this region are expected to be used in subsequent biosensor investigations.

Amplitude response of conical multiwalled carbon nanotube probes for atomic force microscopy.

Carbon nanotubes are considered as great candidates for atomic force microscopy (AFM) probes because of their high aspect ratio and outstanding mechanical properties. In this work, we report that a conical AFM probe can be fabricated with arc discharge prepared multiwalled carbon nanotubes (MWCNTs) with an individual MWCNT at the apex by dielectrophoresis. The amplitude–displacement curve of the conical MWCNT probe demonstrates that this structure can remain stable until the force exerted on it increases to 14.0 ± 1.5 nN (nanonewton). Meanwhile, the conical MWCNT probes are able to resolve complex structure with high aspect ratio compared to commercial AFM probes, suggesting great potential for various AFM applications.

Characterization of Surface Interaction between Chitosan-modified Liposomes and Mucin Layer by Using CNT Probe AFM Method

In order to characterize the adhesion and deformation behavior between chitosan-modified liposomes and the mucin layer of the small intestine, mucin was coated on hydrophobic surface-modified carbon nanotube (CNT) probe of an atomic force microscope. The interaction between this mucin layer and the liposomes with or without chitosan modification in phosphoric acid buffer solution was determined by atomic force microscopy. The pH of the buffer solution was controlled at 2.8 and 7.0. The chitosan modification increased the attractive force between the liposomes and mucin layer during the separation process under both pH conditions. This result corresponded with that from a previous study about the liposome adhesion behavior on the surface of the small intestine of rats. By using the mucin-coated CNT probe, the long range and different types of attractive forces between the chitosan-modified liposomes and mucin layer was observed. Furthermore, the small-scaled deformation behavior change on the liposomal surfaces due to chitosan modification was also observed by the CNT probe. The detail deformation and adhesion behavior of the liposomes with or without chitosan modification was detected.

Nanometer-precise optical length measurement using near-field scanning optical microscopy with sharpened single carbon nanotube probe

We have developed and characterized a plasmon-excitation scattering-type near-field scanning optical microscope with sharpened single carbon nanotube probe. The developed microscope can optically capture differences in the refractive index of single-nanometer surface structures. Statistical analysis enabled us to estimate the precision of the optical length measurement to 1.8 nm.

Optical imaging of nanosized structures by using plasmonically excited cascade near-field coupling with a carbon nanotube probe

Near-field scanning optical microscopy (NSOM) overcomes the diffraction limit, thereby realizing a spatial resolution far beyond the wavelength of light used. However, NSOM still has a problem in repeatable imaging at the high spatial resolution and high contrast with conventional aperture or apertureless probes that are needed for practical applications. Here, we describe an optical imaging technique based on plasmonically excited cascade near-field coupling that has the potential to achieve single-nanometer spatial resolution with high imaging repeatability. This technique makes use of a plasmon waveguide coupled with a high-stiffness carbon nanotube optical probe. Through the action of surface plasmon polaritons, the input far-field light is converted into an optical near field that is used as an excitation source. This excitation near field is strongly enhanced and concentrated on the probe tip such that it generates a second near field as a nanosized probe spot on the apex of the tip. Extremely high-resolution optical imaging is accomplished by scanning the sample surface with the probe spot. At a wavelength of 850 nm, a 5-nm-wide metallic striped pattern on a cross-sectional superlattice sample was clearly resolved as a permittivity distribution.

Gold nanoparticles decorated carbon nanotube probe based immunochromatographic assay on cotton thread

A novel cotton thread immunochromatographic assay device was successfully developed based on gold nanoparticles decorated carbon nanotube nanocomposite probe (CNT/GNPs). Squamous cell carcinoma antigen (SCCA), a protein biomarker related to lung cancer, was used as an analyte to demonstrate the principle of immunochromatograpgic assay on cotton thread biosensor. Results indicated that CNT/GNPs exhibited good stability and superior sensitivity comparing with individual carbon nanotubes as reporter probe. Under optimal conditions, the biosensor was capable of measuring 3.03ng/mL SCCA which is 10 and 5000 folds more sensitive than previous reported CNT based lateral flow assay. The combination of CNT/GNPs nanocomposite probe with cotton thread based biosensor provide an alternative path for clinical diagnosis of other protein or nucleic acid biomarkers.

Flexible electrical probes made of carbon nanotube bundles

Carbon nanotube (CNT) bundles are extracted from vertically aligned CNT array by tungsten probes and attached on the tips of these tungsten probes strongly by van der waals forces, forming flexible microprobes, with tip radii varying from 100 nm to 1 μm. The geometries and electrical properties of these original probes are adjusted by laser beam irradiation, electric current application, and alcohol treatment. The resistance measurement of a carbon nanocoil using bundled CNT probes as sensing probes by four-probe method demonstrates great advantages of bundled CNT probes in measuring the system with continuous deformation varying with time. Verification for the flexibility of bundled CNT probes with ultrathin carbon film shows the great application potential in non-destructive testing. This research demonstrates the potential application of bundled CNT as flexible microprobes.

In situ, controlled and reproducible attachment of carbon nanotubes onto conductive AFM tips

Owing to the small diameter, wear resistance, high aspect ratio of their cylindrical structure and outstanding young's modulus, carbon nanotubes are regarded as excellent probes for atomic force microscope (AFM) imaging and various applications. To take the best out of carbon nanotubes’ potentials as AFM probes, we present a facile and reliable method to attach a single carbon nanotube onto an AFM probe covered with conductive Au layer. The method involves the following steps: positioning the AFM probe exactly onto a designated multiple-walled carbon nanotube growing vertically on a conductive substrate, establishing physical contact of the probe apex to the carbon nanotube with an appropriate force, and finally flowing a DC current of typically 100μA from the AFM probe to the substrate through the carbon nanotube. The current flow results in the fracture and attachment of the carbon nanotube onto the AFM probe. Our method is similar to that reported in previous studies to cut and assemble carbon nanotubes by flowing current under SEM, but by our method we succeed to achieve superior control of protruding length and reproducible attachment angle of the carbon nanotube in one step. Moreover, it is now possible to reliably prepare carbon nanotube probes in-situ during AFM experiments.

Static and dynamic pull-in instability of multi-walled carbon nanotube probes by He’s iteration perturbation method

A continuum model is utilized to extract the nonlinear governing equation for Carbon nanotube (CNT) probes near graphite sheets. The van der Waals (vdW) intermolecular force and electrostatic actuation are included in the equation of motion. Static and dynamic pull-in behavior of the system is investigated in this paper. To this end, a new asymptotic procedure is presented to predict the pull-in instability of electrically actuated CNTs by employing an analytic approach namely He’s iteration perturbation method (IPM). The effects of basic non-dimensional parameters such as initial amplitude, intermolecular force, geometrical parameter and actuation voltage on the pull-in instability as well as the fundamental frequency are studied. The obtained results from numerical simulations by employing three mode assumptions verify the strength of the analytical procedure. The qualitative analysis of the system dynamics shows that the equilibrium points of the autonomous system include stable center points and unstable saddle nodes. The phase portraits of the carbon nanotube actuator exhibit periodic and homoclinic orbits.

Frequency function in atomic force microscopy applied to a liquid environment.

Scanning specimens in liquids using commercial atomic force microscopy (AFM) is very time-consuming due to the necessary try-and-error iteration for determining appropriate triggering frequencies and probes. In addition, the iteration easily contaminates the AFM tip and damages the samples, which consumes probes. One reason for this could be inaccuracy in the resonant frequency in the feedback system setup. This paper proposes a frequency function which varies with the tip-sample separation, and it helps to improve the frequency shift in the current feedback system of commercial AFMs. The frequency function is a closed-form equation, which allows for easy calculation, as confirmed by experimental data. It comprises three physical effects: the quasi-static equilibrium condition, the atomic forces gradient effect, and hydrodynamic load effect. While each of these has previously been developed in separate studies, this is the first time their combination has been used to represent the complete frequency phenomenon. To avoid “jump to contact” issues, experiments often use probes with relatively stiffer cantilevers, which inevitably reduce the force sensitivity in sensing low atomic forces. The proposed frequency function can also predict jump to contact behavior and, thus, the probe sensitivity could be increased and soft probes could be widely used. Additionally, various tip height behaviors coupling with the atomic forces gradient and hydrodynamic effects are discussed in the context of carbon nanotube probes.

Material dependence of magnetic force microscopy performance using carbon nanotube probes: Experiments and simulation

We investigated the dependence of the performance of magnetic force microscopy (MFM) on magnetic coating materials by using carbon nanotube (CNT) probes. The magnetic structures of CNT-MFM probes with CoFe(80:20), CoFe(30:70), and CoCr(80:20) coatings were essentially the same in the simulations, but their magnetic properties, such as stability after magnetic reversal, varied slightly in the experiments. It was found that a larger saturation magnetic moment (Ms) is of advantage for attaining high spatial resolution. Although the distinction was hard to see in the MFM images, the experiments and simulations showed that CNT probes coated with high Ms materials gave stronger perturbations to soft magnetic materials than probes coated with low Ms materials.