단일벽 탄소나노튜브의 미량유해물질 흡착거동에서 양이온 계면활성제의 영향에 관한 연구

The interaction of molecules and material surfaces is one of the fundamental topics in surface science. Also, understanding the behavior of molecules in nano-space is increasingly important in nano- and biotechnologies. A single-walled carbon nanotube (SWNT) is a monolayered material composed of all surface atoms, which provide a simple van der Waals potential originated from a single layer both for the outer surface (quasi 2D) and inner nano-space (quasi 1D). Furthermore, the quasi 1D electronic structure of SWNT allows resonant optical transitions, which are sensitively affected by the surrounding environment of SWNT. SWNTs are thus an ideal material for examining the behaviors of molecules on the surface or in the nano-space by means of optical spectroscopy. We use a singly suspended SWNT between mesa structures to minimize the interactions with the substrate and other nanotubes, and expose it directly to the ambient gas. Semiconducting SWNTs suspended in space exhibit resonant photoluminescence (PL) and Raman scattering, and their optical responses depend on the state of molecules adsorbed on the SWNT surface or encapsulated in the tube [1-3]. Therefore, gas molecule adsorption/desorption on the SWNT surface or inside of the tube can be probed by PL and Raman spectroscopy. We have found that water molecules form an adsorption layer of two-monolayer thickness on the hydrophobic SWNT surface as a result of hydrogen-bonding network of water molecules [2]. The water adsorption layer has a sizable effect on the radial breathing mode frequency in Raman scattering [4]. The phase of water molecules can also affect those properties of SWNTs. The phase diagrams of the water both outside and inside of SWNT will be constructed based on the results of spectroscopy. Furthermore, PL peak energies from hybrids of single-stranded DNA and SWNT were found to depend on the DNA base type, namely thymine, adenine, cytosine, and guanine [5]. The base type dependence was attributed to the adsorption energy of the DNA bases on the SWNT surface. [1] S. Chiashi, et al. Nano Lett. 8, 3097 (2008). [2] Y. Homma, et al. Phys. Rev. Lett. 110, 157402 (2013). [3] S. Chiashi, et al. J. Phys. Chem. Lett. 5, 408 (2014). [4] S. Chiashi, et al. Phys. Rev. B 91, 155415 (2015). [5] M. Ito, et al. J. Phys. Chem. C 119, 21141 (2015).

Prostate-specific antigen (PSA) is used to detect prostate cancer. RNA aptamers against this protein have been reported previously. In this work, the stability and interaction mechanism of aptamer with PSA and single-wall carbon nanotube (SWCNT) was studied by computational techniques. Molecular dynamics simulations were used to investigate the interaction of aptamer segments with the surfaces of SWCNT and prostate-specific antigen (PSA) protein in an aqueous solution by two steps. Firstly, the interaction of aptamer and SWCNT was studied by the molecular dynamic simulation method. Our results showed that an aptamer segment can attach to the surface of SWCNT with its helix axis perpendicularly. Our analysis shows that the π–π stacking interactions play an important role in the binding of the aptamer to carbon rings. Secondly, we analysed the interaction of PSA protein with aptamer in the aptamer–SWCNT assemble. We found that the 3D structure of aptamer in the presence of PSA protein and SWCNT was stable. Finally, this study provides evidence about the stability of aptamer as a sensor on the surface of SWCNT (as a fixed surface) for PSA protein as a ligand. This finding can help to improve new biosensors for detecting cancer protein markers.

Methylene Blue (MB) is a water-soluble dye which can physically absorb on single-wall carbon nanotube (SWCNT) surface. We discovered the dye can quench SWCNT fluorescence when it is added to a SWCNT dispersions in water. At the same time its own fluorescence is quenched. Analyzing the parameters of both these quenching processes we observed that the attachment of the dye to a SWCNT depends strongly on the quality of the SWCNT coating. As a result the quenching of specific SWCNT species can be used as a specific indicator of the species “protection” and its affinity to a dispersing agent. We have observed that the SWCNT quenching by MB is relatively weak in a case of good ionic surfactants, and such a quenching process does not indicate any specific or unexpected trends. Lowing stability of the protective layer due to lower surfactant concentration or unfavorable pH was causing an increasing quenching. More specific effects were detected with more selective process or SWCNT suspended with single-stranded DNA (ssDNA). Relative quenching of SWCNT species in this case was not constant, and could be used as a measure of adhesion strength or density of the SS-DNA on these species. The process of MB attachment was found to be dynamic, and it be described by an temporal attachment of MB molecules to a SWCNT. A quenching model was developed, resulting in a mathematical description with only two parameters. One of them is the adhesion strength (or binding energy), and another is the available volume (space) near a nanotube surface. The most obvious parameter, the available volume, was increasing in a case of a weaker (sparse or thin) coating of SWCNT surface by ssDNA, that was associated with a lower affinity of such ssDNA type to a SWCVNT species. The volume was becoming much smaller with a good ssDNA-SWCNT affinity, preventing in this way the interaction of the quencher with this SWCNT species. The studied process has appeared to be a simple and reliable tool for quick comparison of the affinity between specific SWCNT and ssDNA in bulk SWCNT solutions. Physical and mathematical models can also help to understand and analyze a wider variety of interactions between SWCNT and suspending agents or wrappers. The attachment of external ionic molecules, such as MB, may also help in development of SWCNT separation methods.

The assembly of sodium polystyrene sulfonate (Na+-PSS) at the surface of single-walled carbon nanotubes (SWNTs) in pH 3 aqueous solution is described. Rather than forming linear or sheet-like chain morphologies over SWNT surfaces, Na+-PSS adopts a spherically collapsed conformation believed to be the result of cation (either Na+ or H+) condensation onto the ionized polymer chain. It is well reported that cations (and also anions) adsorb preferentially onto single-walled and multi-walled carbon nanotube surfaces leading to an increased ion concentration in the near surface regions relative to the bulk solution. This work provides experimental evidence for preferentially absorbed cation condensation onto PSS anions until those cations are spaced at distances corresponding to the Bjerrum length ( B), as defined by the Manning theory of ion condensation, at the SWNT surface. The resulting electrostearic repulsions allow the SWNTs to remain suspended for days. Furthermore , coulombic repulsion among SWNT bundles after cation adsorption alone is not sufficient to form stable suspensions—but rather the stearic repulsions associated with spherically collapsed PSS at the nanotube surface is responsible for suspension stability. It is believed that the ultrasonic agitation drives cations into the small spaces between SWNT bundles and coulombic potential attracts the PSS to those regions.

The mechanism of CO oxidation by O2 on a single Au atom supported on pristine, mono atom vacancy (m), di atom vacancy (di) and the Stone Wales defect (SW) on single walled carbon nanotube (SWCNT) surface is systematically investigated theoretically using density functional theory. We determine that single Au atoms can be trapped effectively by the defects on SWCNTs. The defects on SWCNTs can enhance both the binding strength and catalytic activity of the supported single Au atom. Fundamental aspects such as adsorption energy and charge transfer are elucidated to analyze the adsorption properties of CO and O2 and co-adsorption of CO and O2 molecules. It is found that CO binds stronger than O2 on Au supported SWCNT. We clearly demonstrate that the defected SWCNT surface promotes electron transfer from the supported single Au atom to O2 molecules. On the other hand, this effect is weaker for pristine SWCNTs. It is observed that the high density of spin-polarized states are localized in the region of the Fermi level due to the strong interactions between Au (5d orbital) and the adjacent carbon (2p orbital) atoms, which influence the catalytic performance. In addition, we elucidate both the Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms of CO oxidation by O2. For the LH pathway, the barriers of the rate-limiting step are calculated to be 0.02 eV and 0.05 eV for Au/m-SWCNT and Au/di-SWCNT, respectively. To regenerate the active sites, an ER-like reaction occurs to form a second CO2 molecule. The ER pathway is observed on Au/m-SWCNT, Au/SW-SWCNT and Au/SWCNT in which the Au/m-SWCNT has a smaller barrier. The comparison with a previous study (Lu et al., J. Phys. Chem. C, 2009, 113, 20156-20160.) indicates that the curvature effect of SWCNTs is important for the catalytic property of the supported single Au. Overall, Au/m-SWCNT is identified as the most active catalyst for CO oxidation compared to pristine SWCNT, SW-SWCNT and di-SWCNT. Our findings give a clear description on the relationship between the defects in the support and the catalytic properties of Au and open a new avenue to develop carbon nanomaterial-based single atom catalysts for application in environmental and energy related fields.

Encapsulation of single-walled carbon nanotubes with asymmetric pyrenyl-gemini surfactants

Single-walled carbon nanotubes (SWCNTs) exhibit nonphotobleaching, near-infrared (NIR) fluorescence suitable for bioimaging applications. In particular, SWCNT fluorescence quenching induced by biopolymer dispersants facilitates flexible design of molecular nanosensors, yet challenges remain in analyte selectivity and lack of rational design strategies. A sought-after alternative to haphazard molecular modulation of SWCNT-based fluorescence is to couple the movement of a quencher to the SWCNT surface, enabling fluorescence energy transfer to modulate molecular recognition with high selectivity. This study presents the rational design of SWCNT-based nanosensors with fluorescence energy transfer, leveraging the unique properties of methylene blue (MB) proximity-mediated fluorescence quenching. MB-SWCNT-based nanosensors exhibit 1- stability in redox environments and 2- analyte-specific displacement-driven fluorescence modulation. By designing hybridization-induced displacement of MB-conjugated ssDNA from the SWCNT surface, we calculate that SWCNT fluorescence modulation can occur within a 6.8 nm fluorescence resonance energy transfer distance from the SWCNT surface and develop a robust and versatile platform to synthesize oligonucleotide nanosensors with tunable ΔF/F0 of up to 150%. Building upon this strategy, we developed four distinct nanosensors capable of selectively detecting tobacco mosaic virus (TMV) viral RNA fragments, which successfully differentiated TMV-infected plants from mock controls. Finally, we demonstrate the potential expansion of our design to target a wider scope of biomolecules using the biotin-avidin system as a model. Taken together, our study presents a generalizable platform that enables rational engineering of SWCNT NIR fluorescence intensity through MB distance-dependent fluorescence energy transfer, overcoming the intrinsic selectivity challenges of current SWCNT nanosensors.

Functionalized single-walled carbon nanotubes are currently being explored as novel delivery vehicles for proteins and therapeutic agents to treat various diseases. In order to maximize treatment efficacy, a strong binding between single-walled carbon nanotubes and their functionalized molecules is necessary. Glycated chitosan, a polymer with potent immunostimulatory properties for cancer treatment, has been used as a surfactant of single-walled carbon nanotubes to form an immunologically modified nanosystem for biomedical applications. In this study, we investigated the binding characteristics of single-walled carbon nanotube and glycated chitosan using molecular dynamics simulations. The mean square displacement, radius of gyration, interaction energy, and radial distribution function of the single-walled carbon nanotube-glycated chitosan system were analyzed. The results from the simulations demonstrated that glycated chitosan was bound to single-walled carbon nanotubes by a strong, noncovalent interaction. The stability of glycated chitosan on the single-walled carbon nanotubes surface was enhanced by the length of glycated chitosan, and the binding energy of the 2 molecules was closely related to the diameter and chirality of single-walled carbon nanotubes, with the most stable single-walled carbon nanotube-glycated chitosan system being formed by the combination of long polymer, large single-walled carbon nanotube, and armchair single-walled carbon nanotube. The understanding of the interactions between single-walled carbon nanotube and glycated chitosan and the structure of single-walled carbon nanotube-glycated chitosan allows the modifications of the novel nanosystem for disease diagnostics and therapeutics.

Electrochemical durability investigation of single-walled and multi-walled carbon nanotubes under potentiostatic conditions

Single-walled carbon nanotubes (SWCNTs) are near-infrared fluorescent substrates used in biological sensing, imaging, and delivery applications. These constructs are composed of SWCNTs in concert with an associated corona phase surrounding the nanotube. In this manner, noncovalent adsorption of polymers onto SWCNTs is typically implemented to disperse hydrophobic SWCNTs in solution, while also providing a functional handle such as a molecular recognition element that confers analyte specificity, giving rise to a nanosensor. For example, single-stranded DNA (ssDNA)-functionalized SWCNTs have been developed in which distinct ssDNA sequences confer specificity to different neurotransmitters for real-time brain sensing. However, this initial corona phase may be replaced by other biomolecules, predominantly proteins, once the SWCNT-based constructs are applied in the actual biological system of interest. Consequently, function of these and other nanoparticle-based biosensors is often hindered by protein corona formation, in which adsorbed proteins from the surrounding biofluid preclude interaction of the sensor with the target analyte. Establishing rational design rules to inform development and refinement of such nanosensors requires an understanding of both the initial nanoscale architectures and compositional changes upon application in complex biofluids.Herein, we describe methods and outcomes to investigate the carbon nanotube corona phase, both initially and upon interaction with proteins in the surrounding solution. To study the as-designed corona, we demonstrate a direct mode of measuring in-solution nucleic acid geometries on SWCNTs via X-ray scattering interferometry (XSI). This technique leverages the interference pattern produced by ordered gold nanoparticle tags conjugated to the DNA on the SWCNT surface. Using XSI, we quantify surface-adsorbed nucleic acid morphologies, ionic strength-dependent conformational changes, and the dopamine sensing mechanism of a DNA-SWCNT nanosensor, supported by ab initio modeling. To study the protein corona-covered SWCNT, we expand upon our previous work profiling protein adsorption on mixed-chirality SWCNTs that revealed the composition and driving forces of protein corona formation. We now characterize the protein corona across a panel of different nanosensor-relevant ssDNA sequences and single-chirality SWCNT substrates. Taken together, we aim to elucidate both the initial and end-state SWCNT surface to guide future nanobiotechnology design strategies.

Optical nanoscale technologies often implement covalent or noncovalent strategies for the modification of nanoparticles, whereby both functionalizations are leveraged for multimodal applications but can affect the intrinsic fluorescence of nanoparticles. Specifically, single‐walled carbon nanotubes (SWCNTs) can enable real‐time imaging and cellular delivery; however, the introduction of covalent SWCNT sidewall functionalizations often attenuates SWCNT fluorescence. Recent advances in SWCNT covalent functionalization chemistries preserve the SWCNT's pristine graphitic lattice and intrinsic fluorescence, and here, such covalently functionalized SWCNTs maintain intrinsic fluorescence‐based molecular recognition of neurotransmitter and protein analytes. The covalently modified SWCNT nanosensor preserves its fluorescence response towards its analyte for certain nanosensors, presumably dependent on the intermolecular interactions between SWCNTs or the steric hindrance introduced by the covalent functionalization that hinders noncovalent interactions with the SWCNT surface. These SWCNT nanosensors are further functionalized via their covalent handles with a targeting ligand, biotin, to self‐assemble on passivated microscopy slides, and these dual‐functionalized SWCNT materials are explored for future use in multiplexed sensing and imaging applications.

This article introduces sensing of nitrogen dioxide (NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) gas using horizontally aligned single walled carbon nanotubes (SWCNTs) in between gold interdigitated electrodes (IDEs). The fabrication process employed microelectromechanical system (MEMS), photolithography, thin film metallization, and dielectrophoresis (DEP) methods. Gold IDEs were fabricated using photolithography and thin film metallization techniques onto Si/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> substrate, and then, SWCNTs were horizontally aligned in between IDE using DEP. The fabricated sensor was characterized for sensing of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas in the range 1 to 5 ppm. The cardinal sensing principle involves the reduction of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules on interaction with horizontally aligned SWCNTs. This reduction of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> molecules is attributed to intratube and intertube electron modulation and charge transfer mechanisms on SWCNTs surface, which is manifested in terms of change in resistance of the SWCNTs. Therefore, change in resistance of SWCNTs on changing the concentration of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas was considered as the detection signal. The sensitivity of the present NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensor is found to be ~70%, which is better than the reported ones. The additional advantages of present study are that it is highly efficient, portable, compact, and cost effective technique for sensing of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas, which possesses potential applications in environmental monitoring of NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas and space flight demonstration.

Mechanical behaviors of single-walled carbon nanotube (SWCNT) and Ni-coated single-walled carbon nanotube (SWCNT-Ni) were investigated by using molecular dynamics (MD) simulation method. From these results of molecular dynamics simulation for two models of SWCNT and SWCNT-Ni, it was found that the Young's Modulus of SWCNT was higher than that of SWCNT-Ni, and failure stress and failure strain of SWCNT were also lower than that of SWCNT-Ni at same temperature point of 300K, 500K, and 700K. In order to understand compressing behaviors of different temperature, two different molecular models of SWCNT and SWCNT-Ni were analyzed at 300K, 500K and 700K respectively, and it was revealed that temperature fluctuation could also change the Young's Modulus, critical stress, and critical strain. In this work, it was very clear that nickel atoms on surface of SWCNT-Ni could retard local buckling at the processing of compressing. Coating nickel atoms on surface of SWCNT could improve some mechanical properties of SWCNT.

We report molecular dynamics simulations of DNA adsorption on a single-walled carbon nanotube (SWNT) in an aqueous environment. We have modeled a DNA segment with 12 base pairs (Dickerson dodecamer) and a (8,8) SWNT in water, with counterions to maintain total charge neutrality. Simulations show that DNA binds to the external surface of an uncharged or positively charged SWNT on a time scale of a few hundred picoseconds. The hydrophobic end groups of DNA are attracted to the hydrophobic SWNT surface of uncharged SWNTs, while the hydrophilic backbone of DNA does not bind to the uncharged SWNT. The binding mode of DNA to charged SWNTs is qualitatively different from uncharged SWNTs. The phosphodiester groups of the DNA backbone are attracted to a positively charged SWNT surface while DNA does not adsorb on negatively charged SWNTs. There is no evidence for canonical double-stranded DNA wrapping around either charged or uncharged SWNTs on the very short time scales of the simulations. The adsorption process appears to have negligible effect on the internal stacking structure of the DNA molecule but significantly affects the A to B form conversion of A-DNA. The adsorption of A-DNA onto an uncharged SWNT inhibits the complete relaxation of A-DNA to B-DNA within the time scale of the simulations. In contrast, binding of the A-DNA onto a positively charged SWNT may promote slightly the A to B conversion.

For elucidation of the adsorption effects on the vibration properties of single-walled carbon nanotubes (SWNTs), photoluminescence and Raman scattering spectra from SWNTs at different vapor pressure of water were simultaneously measured and a molecular dynamics (MD) simulation was performed. The water vapor pressure dependence and its tube diameter $({d}_{\mathrm{tube}})$ dependence of the frequency of the radial breathing mode (RBM) peaks $({\ensuremath{\omega}}_{\mathrm{RBM}})$ and the optical transition energy $({E}_{ii})$ indicate that the physical adsorption is quite important, and both ${\ensuremath{\omega}}_{\mathrm{RBM}}$ and ${E}_{ii}$ clearly depend on the number density of adsorption molecules on the SWNT surface. A simple adsorption model, where the vibrational coupling between the surrounding adsorption layer and SWNTs via van der Waals interaction is considered for RBM, reproduces the experimental and MD simulation results of ${\ensuremath{\omega}}_{\mathrm{RBM}}$ in a wide ${d}_{\mathrm{tube}}$ range for various SWNTs, such as isolated SWNTs in vacuum, SWNTs with adsorption water layer, and even bundled SWNTs. On the basis of the model, the variation of the relationship between ${\ensuremath{\omega}}_{\mathrm{RBM}}$ and ${E}_{ii}$ in a Kataura plot for various SWNT samples can also be understood generally as the ``environmental effects.''