We have shown previously that single-walled carbon nanotubes can be catalytically biodegraded over several weeks by the plant-derived enzyme, horseradish peroxidase. However, whether peroxidase intermediates generated inside human cells or biofluids are involved in the biodegradation of carbon nanotubes has not been explored. Here, we show that hypochlorite and reactive radical intermediates of the human neutrophil enzyme myeloperoxidase catalyse the biodegradation of single-walled carbon nanotubes in vitro, in neutrophils and to a lesser degree in macrophages. Molecular modelling suggests that interactions of basic amino acids of the enzyme with the carboxyls on the carbon nanotubes position the nanotubes near the catalytic site. Importantly, the biodegraded nanotubes do not generate an inflammatory response when aspirated into the lungs of mice. Our findings suggest that the extent to which carbon nanotubes are biodegraded may be a major determinant of the scale and severity of the associated inflammatory responses in exposed individuals.

Carbon nanotubes have aroused great interest since their discovery in 1991. Because of the vast potential of these materials, researchers from diverse disciplines have come together to further develop our understanding of the fundamental properties governing their electronic structure and susceptibility towards chemical reaction. Carbon nanotubes show extreme sensitivity towards changes in their local chemical environment that stems from the susceptibility of their electronic structure to interacting molecules. This chemical sensitivity has made them ideal candidates for incorporation into the design of chemical sensors. Towards this end, carbon nanotubes have made impressive strides in sensitivity and chemical selectivity to a diverse array of chemical species. Despite the lengthy list of accomplishments, several key challenges must be addressed before carbon nanotubes are capable of competing with state-of-the-art solid-state sensor materials. The development of carbon nanotube based sensors is still in its infancy, but continued progress may lead to their integration into commercially viable sensors of unrivalled sensitivity and vanishingly small dimensions.

We report carbon nanotube network field-effect transistors (NTNFETs) that function as selective detectors of DNA immobilization and hybridization. NTNFETs with immobilized synthetic oligonucleotides have been shown to specifically recognize target DNA sequences, including H63D single-nucleotide polymorphism (SNP) discrimination in the HFE gene, responsible for hereditary hemochromatosis. The electronic responses of NTNFETs upon single-stranded DNA immobilization and subsequent DNA hybridization events were confirmed by using fluorescence-labeled oligonucleotides and then were further explored for label-free DNA detection at picomolar to micromolar concentrations. We have also observed a strong effect of DNA counterions on the electronic response, thus suggesting a charge-based mechanism of DNA detection using NTNFET devices. Implementation of label-free electronic detection assays using NTNFETs constitutes an important step toward low-cost, low-complexity, highly sensitive and accurate molecular diagnostics.hemochromatosis ͉ SNP ͉ biosensor T he development of nucleic acids diagnostics has become the subject of intense research, especially in the postgenome era. Current methods have mainly focused on optical detection using fluorescence-labeled oligonucleotides with dyes (1), quantum dots (2), or enhanced absorption of light by oligonucleotidemodified gold nanoparticles (3). On the other hand, label-free electronic methods promise to offer sensitivity, selectivity, and low cost for the detection of DNA hybridization (4). For example, microfabricated silicon field-effect sensors can monitor directly the increase in surface charge when DNA was hybridized on the sensor surface (5). Nanomaterials possess unique properties that are amenable to biosensor applications; they are one-dimensional structures that are extremely sensitive to electronic perturbations, readily functionalized with biorecognition layers, and compatible with many semiconducting manufacturing processes. Thus, one-dimensional silicon nanowires (6-8) and indium oxide nanowires (9) have shown promising performance, because their electronic conductance is more sensitive to DNA-associated charges as a result of their high surface-tovolume ratio. Using smaller nanowires with virtually all atoms on their surface, such as single-walled carbon nanotubes (SWNTs), will provide additional advantages in DNA detection. To date, there are several reports on electrochemical detection of DNA hybridization using multi-walled carbon nanotube electrodes (ref. 10 and references therein, and ref. 11). Whereas electrochemical methods rely on electrochemical behavior of the labels, measurement of direct electron transfer between SWNTs and DNA molecules paves the way for label-free DNA detection. SWNT-based field-effect transistors (12) have excellent operating characteristics (13), and they have already been explored for highly sensitive electronic detection of gases (14, 15) and biomolecules such as antibodies (16,17).Single-stranded DNA (ssDNA) has been recently demons...

We have used nanoscale field effect transistor devices with carbon nanotubes as the conducting channel to detect protein binding. A PEI/PEG polymer coating layer has been employed to avoid nonspecific binding, with attachment of biotin to the layer for specific molecular recognition. Biotin-streptavidin binding has been detected by changes in the device characteristic. Nonspecific binding was observed in devices without the polymer coating, while no binding was found for polymer-coated but not biotinylated devices. Streptavidin, in which the biotin-binding sites were blocked by reaction with excess biotin, produced essentially no change in device characteristic of the biotinylated polymer-coated devices.

Since their discovery [1] in 1993, single-walled carbon nanotubes (SWNTs) have found numerous applications [2] in chemistry and physics on account of their anisotropic shapes (diameters of around 1 nm and lengths of micrometers), remarkable strengths and elasticities, and unique physical properties, for example, high thermal and electrical conductivities. By contrast, and despite their clear potential, SWNTs have not yet been fully integrated into biological systems, [3] mainly because of the considerable difficulty in rendering them soluble in aqueous solutions.Initially, the challenge of achieving soluble SWNTs in organic solvents was addressed by their covalent modification-examples include both end-group [4] and side-wall [5] functionalization. Covalent modification, however, has the disadvantage that it impairs their physical properties. For these, and other reasons, we have been attracted by a supramolecular approach [6] to the solubilization problemnamely, the noncovalent functionalization of SWNTs by wrapping polymers around them in the knowledge that desired features can be grafted onto the polymers, prior to their being self-assembled around the SWNTs. Considerable progress [6, 7] has been made in the use of synthetic polymers to render SWNTs soluble in organic solvents. However, while some water-soluble polymers [8] and surfactants [9] can bring aqueous solubilities to SWNTs, they may not be as biocompatible as would be desirable.It was for this reason, amongst others, that we decided to explore the possibility of solubilizing SWNTs in aqueous solutions of starch. [10] We knew from our knowledge of the supramolecular chemistry of fullerenes [11] that cyclodextrins (CDs) of the appropriate dimensions (g-CD commonly and d-CD occasionally), and in the correct stoichiometries, will dissolve fullerenes (C 60 and C 70 , for example) in water. [12] CDs are the macrocyclic analogues [13] of starch. The connection is clear. Here, we report 1) that common starch, provided it is activated toward complexation by wrapping itself helically around small molecules, will transport SWNTs competitively into aqueous solutions, 2) that the process is sufficiently reversible at high temperatures to permit the separation of SWNTs in their supramolecular starch-wrapped form by a series of physical manipulations from amorphous carbon, and 3) that the addition of glucosidases to these starched carbon nanotubes results in the precipitation of the SWNTs from aqueous solution.

Here we demonstrate design, fabrication, and testing of electronic sensor array based on single-walled carbon nanotubes (SWNTs). Multiple sensor elements consisting of isolated networks of SWNTs were integrated into Si chips by chemical vapor deposition (CVD) and photolithography processes. For chemical selectivity, SWNTs were decorated with metal nanoparticles. The differences in catalytic activity of 18 catalytic metals for detection of H(2), CH(4), CO, and H(2)S gases were observed. Furthermore, a sensor array was fabricated by site-selective electroplating of Pd, Pt, Rh, and Au metals on isolated SWNT networks located on a single chip. The resulting electronic sensor array, which was comprised of several functional SWNT network sensors, was exposed to a randomized series of toxic/combustible gases. Electronic responses of all sensor elements were recorded and the sensor array data was analyzed using pattern-recognition analysis tools. Applications of these small-size, low-power, electronic sensor arrays are in the detection and identification of toxic/combustible gases for personal safety and air pollution monitoring.

Two-dimensional graphitic carbon is a new material with many emerging applications, and studying its chemical properties is an important goal. Here, we reported a new phenomenon -the enzymatic oxidation of a single layer of graphitic carbon by horseradish peroxidase (HRP). In the presence of low concentrations of hydrogen peroxide (~40 µM), HRP catalyzed the oxidation of graphene oxide, which resulted in the formation of holes on its basal plane. During the same period of analysis, HRP failed to oxidize chemically reduced graphene oxide (RGO). The enzymatic oxidation was characterized by Raman, UV-Vis, EPR and FT-IR spectroscopy, TEM, AFM, SDS-PAGE, and GC-MS. Computational docking studies indicated that HRP was preferentially bound to the basal plane rather than the edge for both graphene oxide and RGO. Due to the more dynamic nature of HRP on graphene oxide, the heme active site of HRP was in closer proximity to graphene oxide compared to RGO, thereby facilitating the oxidation of the basal plane of graphene oxide. We also studied the electronic properties of the reduced intermediate product, holey reduced graphene oxide (hRGO), using field-effect transistor (FET) measurements. While RGO exhibited a V-shaped transfer characteristic similar to a single layer of graphene that was attributed to its zero band gap, hRGO demonstrated a p-type semiconducting behavior with a positive shift in the Dirac points. This p-type behavior rendered hRGO, which can be conceptualized as interconnected graphene nanoribbons, as a potentially attractive material for FET sensors. Keywords graphene; oxidation; microscopy; peroxidase; field-effect transistor Graphene has captured the attention of the scientific community due to its novel electronic properties 1,2 coupled with its mechanical strength, 2,3 both of which may make graphene integral in future generations of electronics, batteries, sensors, and composites.1 , 2 , 4 -6 One of the current methods of synthesizing graphene entails exfoliating graphite through astar@pitt.edu. Supporting Information Available: Supplemental TEM micrographs for the graphene oxide and RGO experiments ( Figure S1); Amplex Red assay for days 1 and 20 of RGO oxidation ( Figure S2); electron paramagnetic resonance (EPR) spectroscopy data ( Figure S3); AFM images with section analysis of graphene oxide, HRP, and RGO ( Figure S4); details of the predicted interaction sites for RGO, graphene oxide, and holey graphene oxide on HRP (Table S1); back gate FET data for hRGO and RGO ( Figure S5); and FT-IR and UV-vis spectra of hRGO, RGO, and graphene oxide ( Figure S6). This material is available free of charge via the Internet at

The electrochemical activity of stacked nitrogen-doped carbon nanotube cups (NCNCs) has been explored in comparison to commercial Pt-decorated carbon nanotubes. The nanocup catalyst has demonstrated comparable performance to that of Pt catalyst in oxygen reduction reaction. In addition to effectively catalyzing O(2) reduction, the NCNC electrodes have been used for H(2)O(2) oxidation and consequently for glucose detection when NCNCs were functionalized with glucose oxidase (GOx). Creating the catalysts entirely free of precious metals is of great importance for low-cost fuel cells and biosensors.