Site-specific assembly of DNA and appended cargo on arrayed carbon nanotubes

DNA-Mediated Assembly of Carbon Nanomaterials

Carbon nanomaterials (CNMs) have attracted extensive attentions on account of their superior electrical, mechanical, optical, and biological properties. However, the dimensional limit and irregular arrangement have hampered their further application. It is necessary to find an easy, efficient and controllable way to assemble CNMs into well-ordered array. DNA nanotechnology, owning to the advantages of precise programmability, highly structural predictability and spatial addressability, has been widely applied in the assembly of CNMs. Summarizing the progress and achievements in this field will be of great value to related studies. Herein, based on the different dimensions of CNMs containing 0-dimensional (0D) carbon dots (CDs), fullerenes, 1-dimensional (1D) carbon nanotubes (CNTs) and 2-dimensional (2D) graphene, we introduced the conjugation strategies between DNA and CNMs, their different assembly methods and their applications. In addition, we also discuss the existing challenges and future opportunities in the field.

Carbazochrome carbon nanotube as drug delivery nanocarrier for anti-bleeding drug: quantum chemical study

The interaction between drugs and single-walled carbon nanotubes is proving to be of fundamental interest for drug system of delivery and nano-bio-sensing. In this study, the interaction of pristine CNT with carbazochrome, an anti-hemorrhagic or hemostatic agent, was investigated with M06-2X functional and 6-31G^* basis set. All probable positions of related adsorption for these kind drugs were thought-out to find out which one is energetically suitable. Based on the achieved data, the stronger interactions appeared the oxygen atom of C = O group and nitrogen atom of imine groups. The topology analysis of QTAIM (quantum theory of atoms in a molecule) method was accomplished to understand the properties of interactions between the CNT and carbazochrome. Frontier molecular orbital energies of all systems, global index including stiffness, softness, chemical Gibbs energies, and electrophilicity parameters, as well as some other important physical data such as dipole moment, polarizability, anisotropy polarisibility, and hyperpolaribility were calculated, evaluated, and then compared together. The essence of the formed bonding model progress along the reaction roots was further validated using electron localization function (ELF) calculations. The highest values of adsorption energies were determined in the range of 18.24 up to 22.12 kcal mol^-1 for these kind systems. The acceptable recovery time of 849 s was obtained for the desorption of carbazochrome from the CNT surface under UV-light. The final results exhibit that carbazochrome can serve as a promising carrier and also as sensitive sensors in any kind of practical application.

Effect of Acid Treatment on the Functionalization of Surface, Structural and Textural Properties of Carbon Nanotubes Taunit

The role of acid treatment of Taunit carbon nanotubes in the formation of oxygen-containing functional groups on its surface as well as morphological and textural properties was studied. Acid treatment was carried out in an HNO3 solution or its mixture with H2SO4 under mild conditions (85 °C/1 h) with subsequent washing with distilled water or without washing. Properties of the initial and oxidized samples were investigated using elemental carbon, hydrogen, nitrogen, oxygen (CHNO) analysis, BET (Brunauer-Emmett-Teller) determination of surface area, X-ray diffraction, Raman and Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy, and hydrogen temperature-programmed reduction. Treatment with HNO3 and HNO3/H2SO4 mixture was shown to be efficient for the formation of various oxygen-containing groups on the Taunit surface; therewith, the water washing step also contributed to functionalization of the surface. Depending on the oxidant, acid treatment increased graphite and oxygen content in the samples by a factor of 3‒4.5. Treatment with HNO3 without water washing exerted a weak effect on the graphite structure ordering, the concentration of aliphatic groups was high as compared to other oxidation conditions. Treatment of Taunit with the HNO3/H2SO4 mixture, on the contrary, increased the number of defects in graphite layers and decreased the concentration of aliphatic structures.

Bioelectrocatalysis at carbon nanotubes

This paper summarizes several examples of enzyme immobilization and bioelectrocatalysis at carbon nanotubes (CNTs). CNTs offer substantial improvements on the overall performance of amperometric enzyme electrodes mainly due to their unique structural, mechanical and electronic properties such as metallic, semi-conducting and superconducting electron transport. Unfortunately, their water insolubility restrains the kick-off in some particular fields. However, the chemical functionalization of CNTs, non-covalent and covalent, attracted a remarkable interest over the past several decades boosting the development of electrochemical biosensors and enzymatic fuel cells (EFCs) based on two different types of communications: mediated electron transfer (MET)-type, where the use of redox mediators, small electroactive molecules (freely diffusing or bound to side chains of flexible redox polymers), which are able to shuttle the electrons between the enzyme active site and the electrode (second electron transfer generation system); direct electron transfer (DET)-type between the redox group of the enzyme and the electrode surface (third electron transfer generation system).

Sensing DNA through DNA Charge Transport

DNA charge transport chemistry involves the migration of charge over long molecular distances through the aromatic base pair stack within the DNA helix. This migration depends upon the intimate coupling of bases stacked one with another, and hence any perturbation in that stacking, through base modifications or protein binding, can be sensed electrically. In this review, we describe the many ways DNA charge transport chemistry has been utilized to sense changes in DNA, including the presence of lesions, mismatches, DNA-binding proteins, protein activity, and even reactions under weak magnetic fields. Charge transport chemistry is remarkable in its ability to sense the integrity of DNA.

Recent Advances in Nucleic Acid Targeting Probes and Supramolecular Constructs Based on Pyrene-Modified Oligonucleotides

In this review, we summarize the recent advances in the use of pyrene-modified oligonucleotides as a platform for functional nucleic acid-based constructs. Pyrene is of special interest for the development of nucleic acid-based tools due to its unique fluorescent properties (sensitivity of fluorescence to the microenvironment, ability to form excimers and exciplexes, long fluorescence lifetime, high quantum yield), ability to intercalate into the nucleic acid duplex, to act as a π-π-stacking (including anchoring) moiety, and others. These properties of pyrene have been used to construct novel sensitive fluorescent probes for the sequence-specific detection of nucleic acids and the discrimination of single nucleotide polymorphisms (SNPs), aptamer-based biosensors, agents for binding of double-stranded DNAs, and building blocks for supramolecular complexes. Special attention is paid to the influence of the design of pyrene-modified oligonucleotides on their properties, i.e., the structure-function relationships. The perspectives for the applications of pyrene-modified oligonucleotides in biomolecular studies, diagnostics, and nanotechnology are discussed.

Non-covalent anchoring of oligonucleotides on single-walled carbon nanotubes via short bioreducible linker

This paper describes a simple approach to obtain hybrids of single-walled carbon nanotubes with therapeutically relevant oligonucleotides that are able to be released upon glutathione treatment at physiological concentrations.

Application of Carbon Nanotubes in Nanomedicine

Carbon Nanotubes (CNTs) have become a technological field with great potential since they can be applied in almost every aspect of modern life. One of the sectors where CNTs are expected to play a vital role is the field of medical science. This chapter focuses on the latest developments in applications of CNTs for nanomedicine. A brief history of CNTs and a general introduction to the field are presented. Then, the preparation of CNTs that makes them ideal for use in medical applications is highlighted. Examples of common applications, including cell penetration, drug delivery, and gene delivery and imaging are given. Finally, the toxicity of carbon nanotubes is discussed.

Sequence specific detection of restriction enzymes at DNA-modified carbon nanotube field effect transistors

Protein-DNA interactions play a central role in many cellular processes, and their misregulation has been implicated in a number of human diseases. Thus, there is a pressing need for the development of analytical strategies for interrogating the binding of proteins to DNA. Herein, we report the electrical monitoring of a prototypical DNA-binding protein, the PvuII restriction enzyme, at microfluidic-encapsulated, DNA-modified carbon nanotube field effect transistors. Our integrated platform enables the sensitive, sequence specific detection of PvuII at concentrations as low as 0.5 pM in a volume of 0.025 μL (corresponding to ~7500 proteins). These figures of merit compare favorably to state of the art values reported for alternative fluorescent and electrical assays. The overall detection strategy represents a step toward the massively parallel electrical monitoring, identification, and quantification of protein-DNA interactions at arrayed nanoscale devices.

Novel multifunctional hybrids of single-walled carbon nanotubes with nucleic acids: synthesis and interactions with living cells

Novel hybrids of fluorescein-labeled poly(ethylene glycol)-modified single-walled carbon nanotubes (SWCNTs) with nucleic acids were prepared. 5'-Pyrene conjugates of oligodeoxyribonucleotides were used to construct the noncovalent hybrids, with the pyrene residues acting as anchor groups, immobilizing an oligonucleotide on the SWCNT surface. The hybrid formation characteristics were studied using ζ-potential measurements and adsorption isotherm plots. Transmission electron microscopy (TEM) of the samples stained with contrast agents proved that the pyrene conjugates of oligonucleotides were adsorbed onto the surfaces of the functionalized SWCNTs. On the basis of the MTT assay, the functionalized SWCNTs and their hybrids with oligonucleotides exhibited low toxicity toward HeLa, KB-3-1, and KB-8-5 cells. A TEM study of ultrathin sections of cells treated with SWCNTs revealed that the nanotubes directly interacted with the cellular surface.

Electrochemical study of dsDNA on carbon nanotubes paste electrodes applying cyclic and differential pulse voltammetry

Abstract Carbon nanotubes paste electrodes (CNTPEs) in combination with adsorptive transfer stripping voltammetry are shown to be very suitable for the determination of calf thymus double-stranded DNA (dsDNA). The performance of three types of multi-walled carbon nanotubes paste electrodes (MWCNTPEs) is investigated. The effects of surface pre-treatment and accumulation conditions on the adsorption and electrooxidation of the dsDNA at MWCNTPEs are also described. The results indicate that the electroactivity inherent to carbon nanotubes/paste electrodes allows a large enhancement of the guanine oxidation signal compared to that obtained at the conventional carbon paste electrodes (CPEs). Moreover, the extent of the enhancement dependents on the type of MWCNTs incorporated into the paste. Based on the signal of guanine, under optimal conditions, very low levels of dsDNA can be detected following short accumulation times for all three types of MWCNTPEs (MWCNTPE1, MWCNTPE2, MWCNTPE3), with detection limits of 2.64 mg L−1, 2.02 mg L−1 and 1.46 mg L−1, respectively. Additionally, the dsDNA isolated from rat liver tissues is determined by use of the previously mentioned MWCNTPEs. Graphical abstract

Understanding Interfaces in Metal-Graphitic Hybrid Nanostructures

Metal-graphitic interfaces formed between metal nanoparticles (MNPs) and carbon nanotubes (CNTs) or graphene play an important role in the properties of such hybrid nanostructures. This Perspective summarizes different types of interfaces that exist within the metal-carbon nanoassemblies and discusses current efforts on understanding and modeling the interfacial conditions and interactions. Characterization of the metal-graphitic interfaces is described here, including microscopy, spectroscopy, electrochemical techniques, and electrical measurements. Recent studies on these nanohybrids have shown that the metal-graphitic interfaces play critical roles in both controlled assembly of nanoparticles and practical applications of nanohybrids in chemical sensors and fuel cells. Better understanding, design, and manipulation of metal-graphitic interfaces could therefore become the new frontier in the research of MNP/CNT or MNP/graphene hybrid systems.

Enzymes immobilized on carbon nanotubes

Enzyme immobilizations on carbon nanotubes for fabrication of biosensors and biofuel cells and for preparation of biocatalysts are rapidly emerging as new research areas. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. The method of immobilization has an effect on the preservation of the enzyme structure and retention of the native biological function of the enzyme. In this review, we focus on recent advances in methodology for enzyme immobilization on carbon nanotubes.

Crucial functionalizations of carbon nanotubes for improved drug delivery: a valuable option?

Amidst the myriad of drug delivery systems able to enhance delivery, absorption and intracellular uptake of a bioactive molecule while protecting it from deactivation, Carbon Nanotubes (CNTs) have emerged as a recent and promising option especially in cancer therapy. This is mainly due to their unique properties, which render them extremely versatile through the incorporation of several functional groups and targeting molecules at the same time, while their natural shape allows them to selectively penetrate across biological barriers in a non-invasive way. In this expert review we aim to evaluate whether this innovative material, once chemically-modified with suitable functionalizations, can be considered as a valuable system in comparison to the already existing nanodevices. This will include the estimation of the most recent advances in the field of nanotechnology, together with a cautious evaluation of potential risks and hazards associated with the extensive use of this fascinating, but still unknown, nanomaterial.

A pyrazolate-supported Fe(3)(mu(3)-O) core: structural, spectroscopic, electrochemical, and magnetic study

A comparison is made between the structural, spectroscopic, electrochemical, and magnetic properties of pyrazolate versus carboxylate complexes [Fe3(mu3(mu3O)(mu-LL)6Cl3]2- containing the Fe3(mu3-O)-motif. While the Fe3(mu3-O)-cores are structurally indistinguishable in the two types of complexes, their magnetic properties deviate from the expected values as a result of a through-pyrazole contribution to the overall antiferromagnetic exchange with J1/hc = -80.1 cm(-1) and J2/hc = -72.4 cm(-1), or J1/hc = 70.6 cm(-1) and J2/hc = -80.8 cm(-1), (Hex = -J1(S1S2 + S2S3) - J2S1S3). The magnetic properties of the pyrazolate complexes are further tuned by an antisymmetric exchange interaction term.

Wiring efficiency of a metallizable DNA linker for site-addressable nanobioelectronic assembly

We report the first demonstration of DNA oligonucleotide tags used to address the site-specific assembly of multiple redox enzymes onto spatially distinct regions of a nanoelectronic platform, establishing a direct electrical contact. The resulting system constitutes a multiplexed carbon nanotube-redox protein biosensor capable of detecting varying concentrations of several different substances in real time. The efficiency and robustness of the enzyme linking scheme is explored in detail, showing a high degree of preservation of enzymatic activity and an efficient electrical contact at the enzyme-nanoelectrode interface. While five proteins have been used as a demonstration in this study, there is virtually no limit to the number of enzymes that could be bound in parallel using this linking strategy, which is universally applicable to all proteins due to the simple conjugation chemistry involved. We further demonstrate metallization of the linker in the presence of a divalent metal cation, inducing elevated electron transfer efficiency relative to the native DNA link.

Multifunctional nanorods for biomedical applications

Multifunctional nanorods have shown significant potential in a wide range of biomedical applications. Nanorods can be synthesized by a top down or bottom-up approach. The bottom-up approach commonly utilizes a template deposition methodology. A variety of metal segments can easily be incorporated into the nanorods. This permits high degrees of chemical and dimensional control. High aspect-ratio nanorods have a large surface area for functionalization. By varying the metal segments in the nanorods, spatial control over the binding of functional biomolecules that correspond with the unique surface chemistry of the metal segment can be achieved. Functionalized multicomponent nanorods are utilized in applications ranging from multiplexing, protein sensing, glucose sensing, imaging, biomolecule-associated nanocircuits, gene delivery and vaccinations.

Peptide nanowires for coordination and signal transduction of peroxidase biosensors to carbon nanotube electrode arrays

A strategy of metallizing peptides to serve as conduits of electronic signals that bridge between a redox enzyme and a carbon-nanotube electrode has been developed with enhanced results. In conjunction, a protocol to link the biological elements to the tips of carbon nanotubes has been developed to optimize contact and geometry between the redox enzyme and the carbon nanotube electrode array. A peptide nanowire of 33 amino acids, comprised of a leucine zipper motif, was mutated to bind divalent metals, conferring conductivity into the peptide. Reaction between a thiolate of the peptide with the sulfenic acid of the NADH peroxidase enzyme formed a peptide-enzyme assembly that are fully primed to transduce electrons out of the enzyme active site to an electrode. Scanning electron microscopy shows immobilization and linking of the assembly specifically to the tips of carbon nanotube electrodes, as designed. Isothermal titration calorimetry and mass spectrometry indicate a binding stoichiometry of at least three metals bound per peptide strand. Overall, these results highlight the gain that can be achieved when the signal tranducing units of a biosensor are aligned through directed peptide chemistry.

An Unexpected New Optimum in the Structure Space of DNA Solubilizing Single-Walled Carbon Nanotubes

Here we report quantitative data on the amount of single-walled carbon nanotubes that can be suspended with oligodeoxynucleotides in aqueous buffer, together with rate constants for the thermal denaturation of the resulting DNA-nanotube complexes at elevated temperatures. Sequence motifs d(GT)n and d(AC)n with n=2, 3, 5, 10, 20, or 40 were employed, both individually and as equimolar mixtures of the complementary strands. Unexpectedly, the greatest suspending efficiency was found for the mixture of short, complementary oligonucleotides d(GT)3 and d(AC)3. Unlike the suspending efficiency, the kinetic stability of the nanotube suspensions increases with increasing chain length of the DNA, with half life times of >25 h at 90 degrees C for the complexes of the longest strands. Our results identify a new, unexpected optimum in DNA sequence space for suspending carbon nanotubes. They also demonstrate that suspending power depends on the presence of complementary strands. Exploratory assays suggest that nanotubes can be deposited site-selectively from suspensions formed with short DNA sequences.

Carbon nanotube-DNA nanoarchitectures and electronic functionality

Biological molecules such as deoxyribonucleic acid (DNA) possess inherent recognition and self-assembly capabilities, and are attractive templates for constructing functional hierarchical material structures as building blocks for nanoelectronics. Here we report the assembly and electronic functionality of nanoarchitectures based on conjugates of single-walled carbon nanotubes (SWNTs) functionalized with carboxylic groups and single-stranded DNA (ssDNA) sequences possessing terminal amino groups on both ends, hybridized together through amide linkages by adopting a straightforward synthetic route. Morphological and chemical-functional characterization of the nanoarchitectures are investigated using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Electrical measurements (I-V characterization) of the nanoarchitectures demonstrate negative differential resistance in the presence of SWNT/ssDNA interfaces, which indicates a biomimetic route to fabricating resonant tunneling diodes. I-V characterization on platinum-metallized SWNT-ssDNA nanoarchitectures via salt reduction indicates modulation of their electrical properties, with effects ranging from those of a resonant tunneling diode to a resistor, depending on the amount of metallization. Electron transport through the nanoarchitectures has been analyzed by density functional theory calculations. Our studies illustrate the great promise of biomimetic assembly of functional nanosystems based on biotemplated materials and present new avenues toward exciting future opportunities in nanoelectronics and nanobiotechnology.

Electrochemistry using self-assembled DNA monolayers on highly oriented pyrolytic graphite

Duplex DNA functionalized with pyrene has been utilized to fabricate DNA-modified electrodes on highly oriented pyrolytic graphite (HOPG). Films have been characterized using AFM and radioactive labeling as well as electrochemically. The data obtained are consistent with a close-packed structure in the film with helices oriented in a nearly upright orientation, as seen earlier with the fabrication of thiol-tethered duplexes on gold. Also as on gold, we observe the reduction of DNA-bound intercalators in a DNA-mediated reaction. The reduction of the intercalator is attenuated in the presence of the single-base mismatches, CA and GT, independent of the sequence composition of the oligonucleotide. This sensitivity to single-base mismatches is enhanced when methylene blue reduction is coupled in an electrocatalytic cycle with ferricyanide. The extended potential range afforded by the HOPG surface has allowed us also to investigate the electrochemistry of previously inaccessible metallointercalators, Ru(bpy)2dppz2+ and Os(phen)2dppz2+, at the DNA-modified HOPG surface. These results support the application of DNA-modified HOPG as a convenient and reproducible surface for electrochemical DNA sensors using DNA-mediated charge transport.

Wrapping single-walled carbon nanotubes with long single-stranded DNA molecules produced by rolling circle amplification

Single-walled carbon nanotubes can be readily wrapped in and dispersed by long single-stranded DNA molecules (ssDNAs) synthesized by rolling circle amplification.

DNA-directed synthesis of zinc oxide nanowires on carbon nanotube tips

This paper describes a class of three component hybrid nanowires templated by DNA directed self-assembly. Through the modification of carbon nanotube (CNT) termini with synthetic DNA oligonucleotides, gold nanoparticles are delivered, via DNA hybridization, to CNT tips that then serve as growth sites for zinc oxide (ZnO) nanowires. The structures we have generated using DNA templating represent an advance toward building higher order sequenced one dimensional nanostructures with rational control.

Selective Heterogeneous Nucleation and Growth of Size-Controlled Metal Nanoparticles on Carbon Nanotubes in Solution

We present a novel approach to the in situ deposition of size-controlled platinum nanoparticles on the exterior walls of carbon nanotubes (CNTs). The reduction of metal ions in ethylene glycol (EG), by the addition of a salt such as sodium dodecyl sulfate (SDS), p-CH3C6H4SO3Na, LiCF3SO3, or LiClO4, results in high dispersions and high loadings of platinum nanoparticles on CNTs without aggregation. We have performed controlled experiments to elucidate the mechanism. By exploiting the salt effect, our method effectively depresses homogeneous nucleation, leading to selective heterogeneous metal nucleation and growth, even on unmodified CNTs. In the 2.3-9.6 nm size range, the size of platinum nanoparticles, at 50% loading, can be controlled by changing the concentration of metal ions, the reaction temperature, the reducing reagent or the means by which reactive solutions are added. Our method provides a flexible route towards the preparation of novel one-dimensional hybrid materials, for which a number of promising applications in a variety of fields can be envisioned.

High-Density Assembly of Gold Nanoparticles on Multiwalled Carbon Nanotubes Using 1-Pyrenemethylamine as Interlinker

In this article, we describe the formation of carbon nanotube (CNT)-gold nanoparticle composites in aqueous solution using 1-pyrenemethylamine (Py-CH2NH2) as the interlinker. The alkylamine substituent of 1-pyrenemethylamine binds to a gold nanoparticle, while the pyrene chromophore is noncovalently attached to the sidewall of a carbon nanotube via pi-pi stacking interaction. Using this strategy, gold nanoparticles with diameters of 2-4 nm can be densely assembled on the sidewalls of multiwalled carbon nanotubes. The formation of functionalized gold nanoparticles and CNT-Au nanoparticle composites was followed by UV-vis absorption and luminescence spectroscopy. After functionalization of gold nanoparticles with 1-pyrenemethylamine, the distinct absorption vibronic structure of the pyrene chromophore was greatly perturbed and its absorbance value was decreased. There was also a corresponding red shift of the surface plasmon resonance (SPR) absorption band of the gold nanoparticles after surface modification from 508 to 556 nm due to interparticle plasmon coupling. Further reduction of the pyrene chromophore absorbance was observed upon formation of the CNT-Au nanoparticle composites. The photoluminescence of 1-pyrenemethylamine was largely quenched after attaching to gold nanoparticles; formation of the CNT-Au nanoparticle composites further lowered its emission intensity. The pyrene fluoroprobe also sensed a relatively nonpolar environment after its attachment to the nanotube surface. The present approach to forming high-density deposition of gold nanoparticles on the surface of multiwalled carbon nanotubes can be extended to other molecules with similar structures such as N-(1-naphthyl)ethylenediamine and phenethylamine, demonstrating the generality of this strategy for making CNT-Au nanostructure composites.

Modular, self-assembling peptide linkers for stable and regenerable carbon nanotube biosensor interfaces

As part of an effort to develop nanoelectronic sensors for biological targets, we tested the potential to incorporate coiled coils as metallized, self-assembling, site-specific molecular linkers on carbon nanotubes (CNTs). Based on a previously conceived modular anchor-probe approach, a system was designed in which hydrophobic residues (valines and leucines) form the interface between the two helical peptide components. Charged residues (glutamates and arginines) on the borders of the hydrophobic interface increase peptide solubility, and provide stability and specificity for anchor-probe assembly. Two histidine residues oriented on the exposed hydrophilic exterior of each peptide were included as chelating sites for metal ions such as cobalt. Cysteines were incorporated at the peptide termini for oriented, thiol-mediated coupling to surface plasmon resonance (SPR) biosensor surfaces, gold nanoparticles or CNT substrates. The two peptides were produced by solid phase peptide synthesis using Fmoc chemistry: an acidic 42-residue peptide E42C, and its counterpart in the heterodimer, a basic 39-residue peptide R39C. The ability of E42C and R39C to bind cobalt was demonstrated by immobilized metal affinity chromatography and isothermal titration calorimetry. SPR biosensor kinetic analysis of dimer assembly revealed apparent sub-nanomolar affinities in buffers with and without 1 mM CoCl2 using two different reference surfaces. For device-oriented CNT immobilization, R39C was covalently anchored to CNT tips via a C-terminal cysteine residue. Scanning electron microscopy was used to visualize the assembly of probe peptide (E42C) N-terminally labeled with 15 nm gold nanoparticles, when added to the R39C-CNT surface. The results obtained open the way to develop CNT tip-directed recognition surfaces, using recombinant and chemically synthesized chimeras containing binding epitopes fused to the E42C sequence domain.

Ultra-high redox enzyme signal transduction using highly ordered carbon nanotube array electrodes

We report on a highly ordered array of carbon nanotubes (CNTs) that serves as a universally direct nanoelectrode interface for redox proteins and provides an efficient conduit for electron transfer. The site-selective, covalent docking of the enzyme glucose oxidase (GO(x)) on the CNT tips is found to have a marked effect on enhancing electron transfer properties, as measured by cyclic voltammetry. A unimolecular electron transfer rate of 1500 s(-1) has been measured for this system, a value exceeding the rate of oxygen reduction by glucose oxidase. Furthermore, the redox enzyme-CNT array conjugate can be utilized as a quantitative, substrate-specific biosensor.