The high dispersion of DNA-multiwalled carbon nanotubes and their properties

DNA-wrapped multiwalled carbon nanotubes (MWCNTs) were successfully obtained by a simple sonication treatment method. The obtained materials were characterized in detail by Raman spectroscopy and scanning electron microscopy (SEM). An SEM image showed that MWCNTs were dispersed sufficiently and covered entirely with DNA. This resulted in high aqueous solubility of the products, with a stability of more than several months. The interaction between DNA and MWCNTs was confirmed by Raman measurements and was ascribed to the strong π-π interactions between the backbones of DNA and the surface of carbon nanotubes. The cyclic voltammograms showed that the composite exhibited excellent electrochemical properties. Experimental results also revealed that the high dispersion of DNA-assisted MWCNTs presented a better property compared with pristine MWCNTs. This facile method for obtaining water-soluble MWCNTs has great potential application for both bioscience and biotechnology.     

Different multiwalled carbon nanotubes-enzyme system and enzymatic activity

The interactions between enzyme and nanoparticles (NPs) are governed by the key properties of NPs, such as structure, size, surface chemistry, charge, and surface shape. In this report, we compared the effect of oxidized multiwalled carbon nanotubes (OXWNT) and irradiated multiwalled carbon nanotubes (IRWNT) on the enzymatic activity of PchPipA. Both OXWNT and IRWNT decreased the biocatalytic activity of PchPipA to some extent when they were added in the reaction system, while OXWNT exhibited higher inhibition of the activity of PchPipA than IRWNT. These results suggested that the water solubility may be another property that can affect the interaction of bio-macromolecular products and nanoparticles.     

A rapid assay for assessment of sphingosine kinase inhibitors and substrates

The effect of incorporating carbon nanotubes (CNTs) in the gel matrix on the electrophoretic mobility of proteins based on their molecular weight differences was investigated using sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE). More specifically, a reduction in standard deviation in the molecular weight calibration plots by 55% in the case of multiwalled carbon nanotubes (MWCNTs) and by 34% in the case of single-walled carbon nanotubes (SWCNTs) compared with that of pristine polyacrylamide gels was achieved after incorporating an insignificant amount of functionalized CNTs into the gel matrix. A mechanism based on a more uniform pore size distribution in CNT modified polyacrylamide gel matrix is proposed. Furthermore, the impact of SWCNTs and MWCNTs on the mobility of proteins in different molecular weight regimes at a given acrylamide concentration offers a tunable gel matrix in terms of the selection of molecular weight ranges of proteins. The robustness and excellent reproducibility of the CNT–PAGE protocol are expected to have a significant impact on the molecular weight determination of newly isolated proteins.     

Spontaneous exfoliation of single-walled carbon nanotubes dispersed using a designed amphiphilic peptide

We have observed concentration dependent exfoliation of single-walled carbon nanotubes dispersed in solutions of the synthetic peptide nano-1. As the nanotube concentration is reduced, the bundle diameters tend to decrease before saturating at <2.0 nm for concentrations below 6 x 10(-3) mg/mL. The fraction of individual nanotubes increases with decreasing concentration, saturating at approximately 95% at low concentration. This concentration dependent exfoliation happens even if the dispersions are not sonicated on dilution, albeit over a longer time scale. The populations both of individual nanotubes and of bundles are much higher than expected at high concentrations, indicating the presence of repulsive internanotube interactions stabilizing the dispersions.     

Alteration of deposition pattern and pulmonary response as a result of improved dispersion of aspirated single-walled carbon nanotubes in a mouse model

Nanoparticles have a fundamental dimension of <100 nm. However, on suspension in media, agglomerates of nanoparticles are the more common structure. This is particularly evident in prior intratracheal instillation or aspiration studies of single-walled carbon nanotubes (SWCNT), in which granulomatous lesions encased by epithelioid macrophages were produced by large agglomerates. In this study, we tested the hypothesis of whether exposure to more dispersed SWCNT structures would alter pulmonary distribution and response. A dispersed preparation of single-walled carbon nanotubes (DSWCNT) with a mean diameter of 0.69 microm was given by pharyngeal aspiration to C57BL/6 mice. Electron microscopy demonstrated a highly dispersed, interstitial distribution of DSWCNT deposits by 1 day postexposure. Deposits were generally <1 microm. Macrophage phagocytosis of DSWCNT was rarely observed at any time point. Lung responses were studied by lavage and morphometry at 1 h, 1 day, 7 day, and 1 mo after a single DSWCNT exposure of 10 microg/mouse. Lung sections and lavage cells demonstrated an early, transient neutrophilic and inflammatory phase that rapidly resolved and was similar to that observed with large agglomerates. No granulomatous lesions or epithelioid macrophages were detected. Morphometric measurement of Sirius red staining was used to assess the connective tissue response. The average thickness of connective tissue in alveolar regions was 0.10 +/- 0.02, 0.09 +/- 0.02, 0.10 +/- 0.01, 0.48 +/- 0.04, and 0.88 +/- 0.19 microm for PBS and 1-h, 1-day, 7-day, and 1-mo postexposure groups, respectively. The results demonstrate that dispersed SWCNT are rapidly incorporated into the alveolar interstitium and that they produce an increase in collagen deposition.     

Sensitive detection of p53 tumor suppressor gene using an enzyme-based solid-state electrochemiluminescence sensing platform

An enzyme-based solid-state electrochemiluminescence (ECL) sensing platform for sensitive detection of a single point mutation is developed successfully using p53 tumor suppressor gene as a model analyte. A composite of multiwalled carbon nanotubes and Ruthenium (II) tris-(bipyridine) (MWNTs-Ru(bpy)(3)(2+)) was prepared and coated on an electrode surface, which was covered by polypyrrole (PPy) to immobilize ssDNA. Then, the ssDNA recognized the gold nanoparticle (AuNP)-labeled p53 tumor suppressor gene, and produced AuNP-dsDNA electrode with AuNP layer. The surface adsorbed the glucose-dehydrogenase (GDH) molecules for producing ECL signal. This system combined enzyme reaction with ECL detection, and it can recognize sequence-specific wild type p53 sequence (wtp53) and muted type p53 sequence (mtp53) with discrimination of up to 56.3%. The analytic results were sensitive and specific. It holds promise for the diagnosis and management of cancer.     

Horseradish peroxidase-driven fluorescent labeling of nanotubes with quantum dots

We describe the first enzyme-driven technique for fluorescent labeling of single-walled carbon nanotubes (SWNTs). The labeling was performed via enzymatic biotinylation of nanotubes in the tyramide-horseradish peroxidase (HRP) reaction. Both direct and indirect fuorescent labeling of SWNTs was achieved using either biotinyl tyramide or fluorescently tagged tyramides. Biotinylated SWNTs later reacted with streptavidin-conjugated fluorophores. Linking semiconductor nanocrystals, quantum dots (Q-dots), to the surface of nanotubes resulted in their fluorescent visualization, whereas conventional fluorophores bound to SWNTs directly or through biotin-streptavidin linkage, were completely quenched. Enzymatic biotinylation permits fluorescent visualization of carbon nanotubes, which could be useful for a number of biomedical applications. In addition, other organic molecules such as proteins, antibodies, or DNA can be conjugated to biotinylated SWNTs using this approach.     

Aptabodies - new type of artificial receptors for detection proteins

We report on a new type of artificial receptor formed by hybridization of two DNA aptamers for human thrombin (aptabody). This aptasensor based on multiwalled carbon nanotubes allowed us to detect thrombin with detection limit of 0.3 nM, which was 3 times better in comparison with conventional aptamer.     

Encapsulation of Pt-labelled DNA Molecules inside Carbon Nanotubes

Experiments on encapsulating Pt--labelled DNA molecules inside multiwalled carbon nanotubes (MWCNT) were performed under temperature and pressure conditions of 400K and 3 Bar. The DNA-CNT hybrids were purified via agarose gel electrophoresis and analyzed via high resolution transmission electron microscopy (HR-TEM) and energy dispersive X-ray spectroscopy (EDX). The results showed that the Pt-labelled DNA molecules attached to the outside walls of CNTs could be removed by electrophoresis. The HR-TEM and EDX results demonstrated that 2-3% of the Pt-labelled DNA molecules were successfully encapsulated inside the MWCNTs. The experimental study complements our previous molecular dynamics simulations on encapsulation of single stranded DNA oligonucleotides inside single wall carbon nanotubes under similar conditions in water. The van der Waals interaction between CNT and Pt-labelled DNA is believed to be the main driving force for this phenomenon. The DNA-CNT molecular complex could be further explored for potential applications in bio-nanotechnology.     

Aqueous suspension of carbon nanotubes enhances the specificity of long PCR

DNA manipulation technology is facing more challenges in the postgenomics era. More and more nanomaterials have been investigated for their potential implications in developing better gene technology. In this study, we reported the beneficial effect of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) in enhancing the specificity and total efficiency of long (14 kb) PCR. Hydroxylic and carboxylic carbon nanotubes (CNTs) had similar enhancing effects. Nanotubes could become another component for improvements in the amplification of long DNA.     

Single-walled carbon nanotube induction of rat aortic endothelial cell apoptosis: Reactive oxygen species are involved in the mitochondrial pathway

The use of nano-sized materials offers exciting new options in technical and medical applications. Single-walled carbon nanotubes are emerging as technologically important in different industries. However, adverse effects on cells have been reported and this may limit their use. We previously found that 200μg/mL of single-walled carbon nanotubes induce apoptosis in rat aorta endothelial cells. The current study aimed to determine the signaling pathway involved in this process. We found that reactive oxygen species generation was involved in activation of the mitochondria-dependent apoptotic pathway. The finding of apoptosis was supported by a number of morphological and biochemical hallmarks, including chromatin condensation, internucleosomal DNA fragmentation, and caspase-3 activation. In conclusion, our results demonstrate that single-walled carbon nanotubes induce apoptosis in rat aorta endothelial cells and that reactive oxygen species are involved in the mitochondrial pathway.     

On the impact of nanotube diameter on biomembrane indentation – Computer simulations study

The influence of the single-walled carbon nanotubes on the phospholipid bilayer has been studied using steered molecular dynamics (SMD) simulations. The impact of different nanotubes on the phospholipid bilayer structure is discussed as well as the speed of indentation. Additionally, a series of simulations with pulling out of the nanotubes from the membrane were performed. The deflection of the membrane in both nanoindenation and extraction processes is also discussed. The self-sealing ability of membrane during this process is examined. Complete degradation of the bilayer was not observed even for the most invasive nanoindentation process studied. The obtained results show that carbon nanotubes can be regarded as potential drug carriers for targeted therapy.     

Effect of chirality,length and diameter of carbon nanotubes on the adsorption of 20 amino acids: a molecular dynamics simulation study

We carried out molecular dynamics simulations to study the adsorption of all the 20 amino acids (AAs; aromatic, polar and non-polar) on the surface of chiral, zigzag and armchair single-walled carbon nanotubes. The adsorption was occurring in all systems. In the aromatic AAs, the π–π stacking and the semi-hydrogen bond formation cause a strong interaction with the carbon nanotubes (CNTs). We also investigated the chirality, length and diameter dependencies on adsorption energies. We found that all AAs have more tendency to adsorption on the chiral and zigzag CNTs over the armchair. The results show that increasing both the diameter and the length causes the enhancement of the adsorption energy. But, the effect of the length is more than of the diameter. For example, the adsorption energy of Trp on the surface of CNT (4,1), with 2 nm length, is 20.4 kcal/mol. When the length of CNT becomes twice, the adsorption energy increases by 24 ± 0.3%. But by doubling the diameter, the adsorption energy increased only by 9.8 ± 0.25%.     

Polyamidoamine-grafted multiwalled carbon nanotubes for gene delivery: synthesis, transfection and intracellular trafficking

Functionalized multiwalled carbon nanotubes (f-MWNTs) are of great interest and designed as a novel gene delivery system. In this paper, we presented synthesis of polyamidoamine-functionalized multiwalled carbon nanotubes (PAA-g-MWNTs) and their application as a novel gene delivery system. The PAA-g-MWNTs, obtained from amide formation between PAA and chemically oxidized MWNTs, were stable in aqueous solution and much less toxic to cells than PAA and PEI 25KDa. More importantly, PAA-g-MWNTs showed comparable or even higher transfection efficiency than PAA and PEI at optimal w/w ratio. Intracellular trafficking of Cy3-labeled pGL-3 indicated that a large number of Cy3-labeled pGL-3 were attached to nucleus membrane, the majority of which was localized in nucleus after incubation with cells for 24 h. We have demonstrated that PAA modification of MWNTs facilitate higher DNA uptake and gene expression in vitro. All these facts suggest potential application of PAA-g-MWNTs as a novel gene vector with high transfection efficiency and low cytotoxicity.     

Characteristics of third-generation glucose biosensors based on Corynascus thermophilus cellobiose dehydrogenase immobilized on commercially available screen-printed electrodes working under physiological conditions

In this article, we describe a third-generation amperometric glucose biosensor working under physiological conditions. This glucose biosensor consists of a recently discovered cellobiose dehydrogenase from the ascomycete Corynascus thermophilus (CtCDH) immobilized on different commercially available screen-printed electrodes made of carbon (SPCEs), carboxyl-functionalized single-walled carbon nanotubes (SPCE-SWCNTs), or multiwalled carbon nanotubes (SPCE-MWCNTs) by simple physical adsorption or a combination of adsorption followed by cross-linking using poly(ethyleneglycol) (400) diglycidyl ether (PEGDGE) or glutaraldehyde (GA). The CtCDH-based third-generation glucose biosensor has a linear range between 0.025 and 30 mM and a detection limit of 10 μM glucose. Biosensors based on SWCNTs showed a higher sensitivity and catalytic response than the ones functionalized with MWCNTs and the SPCEs. A drastic increase in response was observed for all three electrodes when the adsorbed enzyme was cross-linked with PEGDGE or GA. The operational stability of the biosensor was tested for 7 h by repeated injections of 50 mM glucose, and only a slight decrease in the electrochemical response was found. The selectivity of the CtCDH-based biosensor was tested on other potentially interfering carbohydrates such as mannose, galactose, sucrose, and fucose that might be present in blood. No significant analytical response from any of these compounds was observed.     

On the elastic properties of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites using molecular dynamics simulations

Molecular dynamics simulations are used to study the physical and mechanical properties of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites. The effects of nanotube atomic structure, diameter, and volume fraction on the polymer density distribution, polymer atom distribution, stress–strain curves of nanocomposites and Young’s, and shear moduli of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites are explored. It is shown that the density of polymer, surrounding the nanotube surface, has a peak near the nanotube surface. However, increasing distance leads to dropping it to the value near the density of pure polymer. It is seen that for armchair nanotubes, the average polymer atoms distances from the single-walled carbon nanotubes are larger than the polymer atom distance from zigzag nanotubes. It further is shown that zigzag nanotubes are better candidates to reinforce poly (ethylene oxide) than their armchair counterparts.     

Single-walled carbon nanotubes are a new class of ion channel blockers

Here we identify a novel class of biological membrane ion channel blockers called single-walled carbon nanotubes (SWNTs). SWNTs with diameter distributions peaked at approximately 0.9 and 1.3 nm, C60 fullerenes, multi wall nanotubes (MWNTs), and hyperfullerenes (nano-"onions") were synthesized by several techniques and applied to diverse channel types heterologously expressed in mammalian cells. External as-fabricated and purified SWNTs blocked K+ channel subunits in a dose-dependent manner. Blockage was dependent on the shape and dimensions of the nanoparticles used and did not require any electrochemical interaction. SWNTs were more effective than the spherical fullerenes and, for both, diameter was the determining factor. These findings postulate new uses for SWNTs in biological applications and provide unexpected insights into the current view of mechanisms governing the interaction of ion channels with blocking molecules.     

A novel homogenous detection method based on the self-assembled DNAzyme labeled DNA probes with SWNT conjugates and its application in detecting pathogen

In this paper, a novel and cost-effective homogeneous detection method was constructed for the detection of genomic DNA and Staphylococcus aureus (S. aureus), based on the noncovalent assembly of DNAzyme-labeled detection probe and single-walled carbon nanotubes (SWNTs). When the target genomic DNA and hemin was existed in the detection solution, the detection probe wrapped on the SWNTs by π-stacking interactions would keep away from SWNTs and form a DNAzyme-self-assembly construction. This DNAzyme construction could catalyze 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS2?) and generate a colored product which could lead to the absorbance changes. Hence, according to its catalyzed capacity, the DNAzyme construction could amplify the detection signal. The concentration of target DNA could be quantified by exploiting their optical absorption changes at 414 nm and the concentration limit of detection of the method was 30 nM. And this detection method detected S. aureus quantitatively. In addition, this work proved that the method obtain higher detection sensitivity compared with the method without SWNTs because of the protection profile of SWNTs towards the detection probe.     

Ultrasonic Processing of Single-Walled Carbon Nanotube–Glucose Oxidase Conjugates: Interrelation of Bioactivity and Structure

Supramolecular conjugates of single-walled carbon nanotubes and glucose oxidase were prepared in aqueous solution using ultrasonication processing and then isolated by high-speed centrifugation. The conjugates of the single-walled carbon nanotubes and the pristine glucose oxidase, serving as control, were investigated for their enzymatic bioactivity. In addition, the effect of the extent of ultrasonication was studied. The conjugates were also characterized by UV–VIS and circular dichroism spectroscopy as well as by high-resolution transmission electron microscopic and thermogravimetric analysis. Ultrasonication is shown to reduce catalytic activity by ca. 30% (10 min) and that prolonged ultrasonication (up to 60 min) further reduces V _max by 40%. However, most of this decrease arises from ultrasonication itself. The presence of carbon nanotubes (CNTs), while not eliminating changes in catalytic activity, mitigates the magnitude of these changes and is effectively de-bundled by the presence of the surfactant properties of the protein. The enzymatic activity and conformation were found to be predominantly retained after the supramolecular conjugation process assisted by ultrasonication in the presence of the CNTs.