Molecular-basis of single-walled carbon nanotube recognition by single-stranded DNA

Hybrids of biological molecules and single-walled carbon nanotubes (SWCNT) have proven useful for SWCNT sorting and are enabling several biomedical applications in sensing, imaging, and drug delivery. In the DNA-SWCNT system, certain short (10-20mer) sequences of single-stranded DNA recognize specific SWCNT, allowing the latter to be sorted from a chirality diverse mixture. (1) However, little is known about the DNA secondary structures that underlie their recognition of SWCNTs. Using replica exchange molecular dynamics (REMD) of multiple strands on a single SWCNT, we report that DNA forms ordered structures on SWCNTs that are strongly DNA sequence and SWCNT dependent. DNA sequence (TAT)(4) on its recognition partner, the (6,5) SWCNT, (1) forms an ordered right-handed helically wrapped barrel, stabilized by intrastrand, self-stitching hydrogen bonds and interstrand hydrogen bonding. The same sequence on the larger diameter (8,7)-SWCNT forms a different and less-stable structure, demonstrating SWCNT selectivity. In contrast, homopolymer (T)(12), with weaker tendency for intrastrand hydrogen bonding, forms a distinctly left-handed wrap on the (6,5)-SWCNT, demonstrating DNA sequence specificity. Experimental measurements show that (TAT)(4) selectively disperses smaller diameter SWCNTs more efficiently than (T)(12), establishing a relationship between recognition motifs and binding strength. The developing understanding of DNA secondary structure on nanomaterials can shed light on a number of issues involving hybrids of nanomaterials and biological molecules, including nanomedicine, health-effects of nanomaterials, and nanomaterial processing.     

Direct discrimination between semiconducting and metallic single-walled carbon nanotubes with high spatial resolution by SEM

Single-walled carbon nanotube (SWCNT) films with a high density exhibit broad functionality and great potential in nanodevices,as SWCNTs can be either metallic or semiconducting in behavior.The films greatly benefit from characterization technologies that can efficiently identify and group SWCNTs based on metallic or semiconducting natures with high spatial resolution.Here,we developed a facile imaging technique using scanning electron microscopy (SEM) to discriminate between semiconducting and metallic SWCNTs based on black and white colors.The average width of the single-SWCNT image was reduced to ～9 nm,～1/5 of previous imaging results.These achievements were attributed to reduced surface charging on the SiO2/Si substrate under enhanced accelerating voltages.With this identification technique,a CNT transistor with an on/off ratio of ＞105 was fabricated by identifying and etching out the white metallic SWCNTs.This improved SEM imaging technique can be widely applied in evaluating the selective growth and sorting of SWCNTs.     

High-quality single-walled carbon nanotubes synthesis by hot filament CVD on Ru nanoparticle catalyst

We investigated the single-walled carbon nanotubes (SWCNTs) growth on Ru nanoparticle catalyst via hot filament assisted chemical vapor deposition (HFCVD) with two independent W filaments for the carbon precursor (methane) and the hydrogen dissociation respectively. The Ru nanoparticles were obtained following a two-step strategy. At first the growth substrate is functionalized by silanisation, then a self assembly of a ruthenium porphyrin complex monolayer on pyridine-functionalized metal oxide substrates. We have studied the impact of the filaments power and we optimized the SWCNTs growth temperature. The as grown SWCNTs were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. It was found that the quality, density and the diameter of SWCNTs depends on the filament and growth temperature. Results of this study can be used to improve the understanding of the growth of SWCNTs by HFCVD.     

A facile, one-step nanocarbon functionalization for biomedical applications

Despite their immense potential in biomedicine, carbon nanomaterials suffer from inefficient dispersion and biological activity in vivo. Here we utilize a single, yet multifunctional, hyaluronic acid-based biosurfactant to simultaneously disperse nanocarbons and target single-walled carbon nanotubes (SWCNTs) to CD44 receptor positive tumor cells with prompt uptake. Cellular uptake was monitored by intracellular enzyme-activated fluorescence, and localization of SWCNTs within cells was further confirmed by Raman mapping. In vivo photoacoustic, fluorescence, and positron emission tomography imaging of coated SWCNTs display high tumor targeting capability while providing long-term, fluorescence molecular imaging of targeted enzyme events. By utilizing a single biomaterial surfactant for SWCNT dispersion without additional bioconjugation, we designed a facile technique that brings nanocarbons closer to their biomedical potential.     

Metal-film-assisted ultra-clean transfer of single-walled carbon nanotubes

Transfer printing of nanomaterials onto target substrates has been widely used in the fabrication of nanodevices, but it remains a challenge to fully avoid contamination introduced in the transfer process. Here we report a metal-film- assisted method to realize an ultra-clean transfer of single-walled carbon nanotubes （SWCNTs） mediated by poly（methyl methacrylate） （PMMA）. The amount of PMMA residue can be greatly reduced due to its strong physical adhesion to the metal film, leading to ultra-clean surfaces of both the SWCNTs and the substrates. This metal-film-assisted transfer method is efficient, nondestructive, and scalable. It is also suitable for the transfer of graphene and other nanostructures. Furthermore, the relatively low temperature employed allows this technique to be compatible with nanomaterial-based flexible electronics.     

Photothermal properties of inorganic nanomaterials as therapeutic agents for cancer thermotherapy

In recent years, gold (Au) nanoparticles (NPs) and single-walled carbon nanotubes (SWCNTs) have attracted significant attention as potent therapeutic agents for cancer thermotherapy. In this paper the photothermal properties of inorganic nanomaterials including porous silicon (PSi), titania (TiO2) nanotubes (NTs), TiO2 NPs, and multiwalled carbon nanotubes (MWCNTs), Au NPs and SWCNTs have been systematically investigated. PSi shows by far the largest temperature rise (deltaT), TiO2 NTs the second largest deltaT, and MWCNTs the smallest deltaT upon exposure to near-infrared (NIR) laser. The high photothermal effect of PSi has been found to be attributed to the high absorbance and the high surface-to-volume ratio due to the numerous micropores in PSi In addition, the factors affecting the photothermal effects of nanomaterials have been discussed. Our results suggest that PSi and TiO2 NTs are also potential therapeutic agents for cancer thermotherapy with excellent photothermal properties as well as high biocompatibility.     

Recent Advances in Managing Atherosclerosis via Nanomedicine

Atherosclerosis, driven by chronic inflammation of the arteries and lipid accumulation on the blood vessel wall, underpins many cardiovascular diseases with high mortality rates globally, such as stroke and ischemic heart disease. Engineered bio‐nanomaterials are now under active investigation as carriers of therapeutic and/or imaging agents to atherosclerotic plaques. This Review summarizes the latest bio‐nanomaterial‐based strategies for managing atherosclerosis published over the past five years, a period marked by a rapid surge in preclinical applications of bio‐nanomaterials for imaging and/or treating atherosclerosis. To start, the biomarkers exploited by emerging bio‐nanomaterials for targeting various components of atherosclerotic plaques are outlined. In addition, recent efforts to rationally design and screen for bio‐nanomaterials with the optimal physicochemical properties for targeting plaques are presented. Moreover, the latest preclinical applications of bio‐nanomaterials as carriers of imaging, therapeutic, or theranostic agents to atherosclerotic plaques are discussed. Finally, a mechanistic understanding of the interactions between bio‐nanomaterials and the plaque (“athero–nano” interactions) is suggested, the opportunities and challenges in the clinical translation of bio‐nanomaterials for managing atherosclerosis are discussed, and recent clinical trials for atherosclerotic nanomedicines are introduced.     

Fibrinogen binding-dependent cytotoxicity and degradation of single-walled carbon nanotubes

Carbon nanotubes are widely used in the area of biomedicine, and the binding of protein to carbon nanotubes are believed to play an important role in the potential cytotoxicity of nanomaterials. In this work, we investigated the effects of human fibrinogen-surface coatings on the biodegradation and cytotoxicity of carboxylated single-walled carbon nanotubes (SWCNTs). It was found that the electrostatic and π-π stacking interactions might be the crucial factors in stabilizing the binding of fibrinogen with SWCNTs by both theoretical and experimental approaches. Although naked SWCNTs could induce significant toxicity to macrophages, coating these nanomaterials with fibrinogen could greatly attenuate their toxicity. On the other hand, although SWCNTs and fibrinogen-preincubated SWCNTs were resistant to biodegradation in resting macrophages, both naked and fibrinogen-coated SWCNTs could be effectively and similarly degraded through myeloperoxidase (MPO) and peroxynitrite (ONOO^?)-dependent pathways in activated macrophages, where NADPH oxidase played a determinant role in the biodegradation process. Importantly, degraded SWCNTs by ONOO^? pathway in vitro induced less cytotoxicity than non-degraded nanotubes. These findings demonstrated that the binding of fibrinogen to SWCNTs could reduce cytotoxicity without affecting the biodegradation of nanotubes in activated inflammatory cells, providing a new route to design the safer nanotubes for future biomedical applications.     

The high current-carrying capacity of various carbon nanotube-based buckypapers

Buckypapers (BPs) are thin films made up of carbon nanomaterials, such as single-walled carbon nanotubes (SWCNTs) or mixtures of SWCNTs with multi-walled carbon nanotubes (MWCNTs) or vapor-grown carbon nanofibers (VGCNFs). In this research, BPs were exposed to high electrical current densities under different environments, and the effects on nanotube and BP breakdown were observed. In ambient conditions, SWCNT BP breakdown happened at around 430?°C with a flash of light. Mixed BPs of SWCNTs/MWCNTs and SWCNTs/VGCNFs showed higher ignition temperatures of over 500?°C. The results were compared to those from thermogravimetric analysis. In a vacuum, current-driven thermal heating from the samples can generate temperatures greater than 2000?°C. The breakdown current density increased to more than three times that in open air. The breakdown current density of a BP sample increased proportionally to its conductivity. A finite-element model based on Joule heating and heat convection was used to explain this relationship. Further experiments also proved that the high current-carrying capacity of microscale nanotube array samples improved to 10(6)?A?cm(-2) due to increased heat dissipation through the substrate.     

Oligodeoxyribonucleotide association with single-walled carbon nanotubes studied by SPM

Studies have been performed on both as-received and chemically oxidized single-walled carbon nanotubes (SWCNTs) grown by two different growth methods to better understand the preferential association of the oligodeoxyribonucleotide T30 (ODN) with SWCNTs. Samples of T30 ODN:SWCNT were examined under ambient conditions using non-contact scanning probe microscope (SPM) techniques. The resulting images show different morphologies ranging from tangled networks of SWCNTs to individual, well-dispersed isolated SWCNTs as the sonication time is increased. SPM images of well-dispersed, as-received SWCNTs reveal isolated features that are 1.4 to 2.8 nm higher than the bare SWCNT itself. X-ray photoemission spectroscopy (XPS) confirmed these features to be T30 ODN in nature. Chemically oxidizing the SWCNTs before sonication is found to be an effective way to increase the number of T30 ODN features.     

Finding a needle in a chemical haystack: tip-enhanced Raman scattering for studying carbon nanotubes mixtures

Tip-enhanced Raman scattering (TERS) has emerged as a powerful analytical tool for measuring chemical images with nanometre spatial resolution. In this paper, the application of TERS to study differentiation of single-walled carbon nanotubes (SWCNTs) with 14?nm spatial resolution is demonstrated by the measurement of a mixture of two different types of SWCNTs as the model sample. The results demonstrate that TERS is a viable tool for the detection and localization of different SWCNTs and amorphous carbon in mixed SWCNTs based on the spectral differences in the radial breathing mode and the D bands.     

Decoration of single-walled carbon nanotubes with Pt nanoparticles from an organometallic precursor

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt₂(dba)₃ (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2?C3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs.     

SWCNT气体传感器的NO2气敏特性

为了提高NO2气体检测的灵敏度和速度,以单壁碳纳米管（SWCNT）为装配介质,采用介电电泳方法获得单壁碳纳米管场效应晶体管（SWCNT—FET）作为气体传感器检测装置,通过原子力显微镜（AFM）和扫描电子显微镜（SEM）表征,结果显示,利用介电电泳方法能够成功地把SWCNTs装配到芯片的源漏两极间;通入NO2气体前后电特性变化情况的测试结果表明,选择接入电场频率为2MHz,峰峰值电压10V,介电电泳持续时间10s时,制备出SWCNT—FET成功率高,通入NO2气体后的电导率增加三个数量级。利用紫外光持续照射10min,SWCNT上的气体分子解附,使气体传感器可重复利用。     

基于SEM图像的低维纳米材料自动分类方法

针对传统方法在低维纳米材料形貌检测和分类鉴别方面的不足,提出了一种基于扫描电子显微镜（SEM）图像的低维纳米材料自动分类方法．以纳米材料的SEM图像为基础,利用小波包分解技术对材料表面纹理特征进行提取,通过将纹理特征与支持向量机（SVM）相结合,实现了纳米材料的自动分类．该方法具有检测速度快、精度高、无损耗等诸多优点,可用于纳米材料大规模生产中的自动检测．对16种不同类别材料的SEM图像仿真结果表明,该方法的分类精度能够达到93．75％,证明了其在实际工程中的有效性．     

Polydiacetylene single-walled carbon nanotubes nano-hybrid for cellular imaging applications

The functionalization of single-walled carbon nanotubes (SWCNTs) by forming self-assembled supramolecular structure of 10,12-pentacosadiynoic acid (PCDA) on the carbon nanotube wall is reported. PCDA assemblies on SWCNTs (PCDA/SWCNTs) were polymerized by UV irradiation to extensively conjugated polydiacetylene (PDA). PDA/SWCNT was identified by absorption and emission spectroscopy, scanning and transmission electron microscopies (SEM and TEM) and atomic force microscopy (AFM). PDA/SCWNTs showed strong near-infrared (NIR) fluorescence caused by fluorescence resonance energy transfer (FRET) between PDA network and semiconducting SWCNT core. The micro-patterning of biotinylated PDA/SWCNT with FITC-avidin on biotinylated glass surface demonstrated the potential application for a bio-sensing device. Furthermore, the biocompatibility for mammalian cancer cells was tested by viability experiments, which revealed that the PDA/SWCNTs had very low toxicity below 31.3 mg/L in terms of pristine SWCNTs concentration. Also, PDA/SWCNTs inside the cells can be observed by NIR microscopy. This unique modular method of preparation can contribute to diverse functionalities for practical applications in various non-invasive cellular imaging.     

用FEM/FIM研究单壁碳纳米管束

利用范氏力将单壁碳纳米管样品组装到钨针尖上 ,用FEM/FIM对同一碳纳米管样品用热处理方法和场脱附方法进行了研究。场离子显微镜是具有原子级分辨能力的尖端表面分析工具 ,由场离子像推测这次组装的样品是由三根单壁碳纳米管突起组成的碳纳米管束。清洁碳纳米管束样品的场发射像和场离子像有极好的对应关系。场脱附后的碳纳米管束的场发射特性较好地符合Fowler Nordheim场发射模型。通过比较碳纳米管束吸附态和热处理后以及场脱附后的Fowler Nordheim曲线的斜率变化 ,得出碳纳米管束样品逸出功的变化 ,再结合场发射像的变化推断出场脱附与热处理结合是一种较理想的获得清洁碳纳米管表面的方法     

Localized growth of suspended SWCNTs by means of an "all-laser" process and their direct integration into nanoelectronic devices

We have successfully developed an "all-laser" processing for the localized growth of suspended single-wall carbon nanotubes (SWCNTs) on prepatterned SiO/sub 2//Si substrates. Our "all-laser" process stands out by its exclusive use of the same KrF excimer laser, first, to deposit the embedded-catalyst electrodes with a controllable architecture and, second, to grow SWCNTs through the pulsed laser ablation of a pure graphite target. Under the optimal growth conditions, the suspended SWCNTs are shown to bridge laterally adjacent electrodes separated by a gap of /spl sim/2 /spl mu/m. These SWCNTs (having diameters in the 1.25-1.64-nm range) generally tend to auto-assemble into bundles of /spl sim/5--15 nm in diameter. The "all-laser" process here developed offers the advantage of a direct integration of the SWCNTs into field-effect-transistor-like devices with no postprocessing, thereby permitting the investigation of their electrical transport properties. Thus, the suspended SWCNT bundles are shown to behave collectively as an ambipolar transistor with ON/OFF switching ratios as high as /spl sim/10/sup 4/.     

Preparation and investigation on properties of lysozyme chemically bonded to single-walled carbon nanotubes

The purpose of this research is the preparation of a lysozyme-single-walled carbon nanotube (SWCNT) conjugate and investigation of the effect of conjugation on the structure and function of lysozyme. At first, SWCNTs were functionalised by oxygen and lysozyme was coupled to the SWCNTs by carbodiimide method. The high chemical stability of conjugation was purposed for the SWCNTs conjugated enzyme as approved by Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) images, agarose gel electrophoresis and X-ray diffraction (XRD) patterns. The degree of conjugation was determined by thermogravimetric analysis (TGA) process. The results showed no significant differences between the XRD patterns of the native lysozyme and conjugated lysozyme–SWCNTs and these indicated excellent capacity of the SWCNTs to conjugated enzyme. The gel electrophoresis studies and TEM image confirmed the covalent attachment of the enzyme to the functionalised SWCNTs. These results revealed that the enzyme retain a high fraction of their native structure and activity upon attachment to SWCNTs. Therefore, this conjugated protein represents novel preparations that make it an attractive choice as a natural antimicrobial agent.     

Photoacoustic Imaging: Contrast Agents and Their Biomedical Applications

Photoacoustic (PA) imaging as a fast‐developing imaging technique has great potential in biomedical and clinical applications. It is a noninvasive imaging modality that depends on the light‐absorption coefficient of the imaged tissue and the injected PA‐imaging contrast agents. Furthermore, PA imaging provides superb contrast, super spatial resolution, and high penetrability and sensitivity to tissue functional characteristics by detecting the acoustic wave to construct PA images. In recent years, a series of PA‐imaging contrast agents are developed to improve the PA‐imaging performance in biomedical applications. Here, recent progress of PA contrast agents and their biomedical applications are outlined. PA contrast agents are classified according to their components and function, and gold nanocrystals, gold‐nanocrystal assembly, transition‐metal chalcogenides/MXene‐based nanomaterials, carbon‐based nanomaterials, other inorganic imaging agents, small organic molecules, semiconducting polymer nanoparticles, and nonlinear PA‐imaging contrast agents are discussed. The applications of PA contrast agents as biosensors (in the sensing of metal ions, pH, enzymes, temperature, hypoxia, reactive oxygen species, and reactive nitrogen species) and in bioimaging (lymph nodes, vasculature, tumors, and brain tissue) are discussed in detail. Finally, an outlook on the future research and investigation of PA‐imaging contrast agents and their significance in biomedical research is presented.     

Micromachined silicon transmission electron microscopy grids for direct characterization of as-grown nanotubes

Transmission electron microscopy (TEM) is a key technique in the structural characterization of carbon nanotubes. For device applications, carbon nanotubes are typically grown by chemical vapour deposition (CVD) on silicon substrates. However, TEM requires very thin samples, which are electron transparent. Therefore, for TEM analysis, CVD grown nanotubes are typically deposited on commercial TEM grids by post-processing. However, this procedure can damage the nanotubes, and it does not work reliably if the nanotube density is too low. The ability to do TEM directly on as-grown nanotubes on the silicon substrate would solve these problems. For this purpose, we have fabricated micromachined silicon TEM grids with narrow open slits on them. Since the nanotubes grown on these substrates are suspended freely over the open slits, the micromachined substrates form a natural TEM grid for direct imaging of CVD grown nanotubes. Furthermore, the background noise is significantly reduced during micro-Raman spectroscopy, resulting in a better signal-to-noise ratio. As a result, these micromachined Si substrates provide a low cost, mass producible, efficient, and reliable platform for direct TEM, SEM, AFM, and Raman characterization of as-grown nanotubes. These grids can be used for characterizing a wide range of other nanomaterials, including peapods, nanowires, and nanofibres.