Alexander Star

Hybrid nanomaterials comprising metal–graphitic interfaces are uniquely suitable to probe molecular interactions and the associated phenomena such as charge transfer and adsorbate spillover effects. Herein, we study the modulation of the electronic and chemical properties of gold nanoparticle-decorated single-walled carbon nanotubes (SWCNT) using Raman spectroscopy and measurements of field-effect transistor (FET) characteristics. SWCNT are extremely sensitive to changes in the local electronic environment and therefore gold-analyte interactions may be probed both through changes in FET characteristics (as an electrical transducer) and in surface-enhanced Raman scattering (as a chromophore). We study these changes both experimentally and theoretically in order to elucidate the electronic structure of complex nanocomposites, and the information gathered from these experiments is applied to the study of biomolecular interactions with gold nanoparticle-decorated SWCNT. This study, in addition to providing deeper understanding of metal–graphitic interfaces, will offer a combined approach to SWCNT biosensing methodology based on the dual monitoring of the FET–Raman characteristics, which we demonstrate through detection of glutathione.

Nanoelectronic Discrimination of Nonmalignant and Malignant Cells Using Nanotube Field-Effect Transistors

Co-reporter:Guilherme O. Silva, Zachary P. Michael, Long Bian, Galina V. Shurin, Marcelo Mulato, Michael R. Shurin, and Alexander Star

ACS Sensors August 25, 2017 Volume 2(Issue 8) pp:1128-1128

Publication Date(Web):July 31, 2017

DOI:10.1021/acssensors.7b00383

Detection of malignant cells in tissue is a difficult hurdle in medical diagnostics and screening. Carbon nanotubes are extremely sensitive to their local environments, and nanotube-based field-effect transistors (NTFETs) provide a plethora of information regarding the mechanism of interaction with target analytes. Herein, we use a series of functionalized metal nanoparticle-decorated NTFET devices forming an array with multiple nonselective sensor units as the electronic “tongue”, sensing all five basic tastes. By extraction of selected NTFET characteristics and using linear discriminant analysis, we have successfully detected and discriminated between malignant and nonmalignant tissues and cells. We also studied the sensing mechanism and what NTFET characteristics are responsible for the variation of response between cell types, allowing for the design of future studies such as detection of malignant cells in a biopsy or the effects of malignant cells on healthy tissue.Keywords: biosensors; carbon nanotubes; electronic tongue; linear discriminant analysis; metal nanoparticle;

Defect-Induced Near-Infrared Photoluminescence of Single-Walled Carbon Nanotubes Treated with Polyunsaturated Fatty Acids

Co-reporter:Cheuk Fai Chiu, Wissam A. Saidi, Valerian E. Kagan, and Alexander Star

Journal of the American Chemical Society April 5, 2017 Volume 139(Issue 13) pp:4859-4859

Publication Date(Web):March 13, 2017

DOI:10.1021/jacs.7b00390

Single-walled carbon nanotubes (SWCNTs) have been incorporated in many emerging applications in the biomedical field including chemical sensing, biological imaging, drug delivery, and photothermal therapy. To overcome inherent hydrophobicity and improve their biocompatibility, pristine SWCNTs are often coated with surfactants, polymers, DNA, proteins, or lipids. In this paper, we report the effect of polyunsaturated fatty acids (PUFAs) on SWCNT photoluminescence. A decrease in the SWCNT bandgap emission (E11) and a new red-shifted emission (E11–) were observed in the presence of PUFAs. We attribute the change in SWCNT photoluminescence to the formation of oxygen-containing defects by lipid hydroperoxides through photo-oxidation. The observed changes in near-infrared emission of SWCNTs are important for understanding the interaction between SWCNTs and lipid biocorona. Our results also indicate that photoexcited SWCNTs can catalyze lipid peroxidation similarly to lipoxygenases.

Nanoemitters and innate immunity: the role of surfactants and bio-coronas in myeloperoxidase-catalyzed oxidation of pristine single-walled carbon nanotubes

Co-reporter:Cheuk Fai Chiu;Haider H. Dar;Alexandr A. Kapralov;Renã A. S. Robinson;Valerian E. Kagan

Nanoscale (2009-Present) 2017 vol. 9(Issue 18) pp:5948-5956

Publication Date(Web):2017/05/11

DOI:10.1039/C6NR07706D

Single-walled carbon nanotubes (SWCNTs) are experimentally utilized in in vivo imaging and photothermal cancer therapy owing to their unique physicochemical and electronic properties. For these applications, pristine carbon nanotubes are often modified by polymer surfactant coatings to improve their biocompatibility, adding more complexity to their recognition and biodegradation by immuno-competent cells. Here, we investigate the oxidative degradation of SWCNTs catalyzed by neutrophil myeloperoxidase (MPO) using bandgap near-infrared (NIR) photoluminescence and Raman spectroscopy. Our results show diameter-dependence at the initial stages of the oxidative degradation of sodium cholate-, DNA-, and albumin-coated SWCNTs, but not phosphatidylserine-coated SWCNTs. Moreover, sodium deoxycholate- and phospholipid-polyethylene glycol coated SWCNTs were not oxidized under the same reaction conditions, indicating that a surfactant can greatly impact the biodegradability of a nanomaterial. Our data also revealed that possible binding between MPO and surfactant coated-SWCNTs was unfavorable, suggesting that oxidation is likely caused by a hypochlorite generated through halogenation cycles of free MPO, and not MPO bound to the surface of SWCNTs. The identification of SWCNT diameters and coatings that retain NIR fluorescence during the interactions with the components of an innate immune system is important for their applications in in vivo imaging.

Single-walled carbon nanotubes templated CuO networks for gas sensing

Co-reporter:Guiming Peng, Suqin Wu, James E. Ellis, Xueqing Xu, Gang Xu, Changlin Yu and Alexander Star

Journal of Materials Chemistry A 2016 vol. 4(Issue 27) pp:6575-6580

Publication Date(Web):16 Jun 2016

DOI:10.1039/C6TC01722C

The design and synthesis of materials that can be used for sensing gases and vapors at ambient temperature is of much significance to environmental monitoring, public health and safety. Herein, single-walled carbon nanotubes (SWCNTs) templated CuO networks (SWCNT/CuO) were synthesized via a facile sol–gel method. Raman and XPS characterization proved that CuO was covalently linked to SWCNTs via Cu–O–C bonds. After deposition of the obtained SWCNT/CuO onto the interdigitated gold electrodes to assemble gas sensors, both ethanol and water vapors were successfully detected by the sensors at ambient temperature. Electron donation from both analytes to the p-type sensing material results in a conductance decrease effect on the SWCNT/CuO sensor. The ambient operating temperature overcomes the high operating temperature shortcoming of most reported CuO-based sensors. Meanwhile, the high sensitivity (2 ppm for ethanol) indicates promising sensing applications for the as-prepared SWCNT/CuO material described in this study.

In Situ Grown TiO2 Nanospindles Facilitate the Formation of Holey Reduced Graphene Oxide by Photodegradation

Co-reporter:Guiming Peng, James E. Ellis, Gang Xu, Xueqing Xu, and Alexander Star

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 11) pp:7403

Publication Date(Web):March 1, 2016

DOI:10.1021/acsami.6b01188

Titanium dioxide (TiO2) nanostructures and TiO2/graphene nanocomposites are intensively studied materials for energy conversion, energy storage, and organic contaminant photodegradation. However, for TiO2/graphene composites, impermeability across the graphitic basal plane for electrolytes, metal ions, and gas molecules hinders their practical applications. Herein we report a simple, environmentally friendly synthetic route for mesoporous anatase TiO2 nanospindles, and successfully apply this method to obtain in situ grown TiO2 nanospindles/graphene oxide composite. After a thermal reduction at 400 °C, holes are created in the reduced graphene oxide (RGO) sheets through a photocatalytic oxidation mechanism. The formation of holes in RGO is promoted by photogenerated hydroxyl radicals that oxidize and subsequently decarboxylate the graphitic surface of RGO. The proposed mechanism was supported by photocatalytic electrochemical properties of the nanomaterials. The resulting TiO2/holey RGO composites may overcome the original impermeability of graphene sheets and find applications in catalysis, energy conversion/storage devices, and sensors.Keywords: carbon nanotubes; catalysis; graphene; oxidation; oxygen reduction reaction; titanium dioxide;

Payload drug vs. nanocarrier biodegradation by myeloperoxidase- and peroxynitrite-mediated oxidations: pharmacokinetic implications

Co-reporter:Wanji Seo, Alexandr A. Kapralov, Galina V. Shurin, Michael R. Shurin, Valerian E. Kagan and Alexander Star

Nanoscale 2015 vol. 7(Issue 19) pp:8689-8694

Publication Date(Web):16 Apr 2015

DOI:10.1039/C5NR00251F

With the advancement of nanocarriers for drug delivery into biomedical practice, assessments of drug susceptibility to oxidative degradation by enzymatic mechanisms of inflammatory cells become important. Here, we investigate oxidative degradation of a carbon nanotube-based drug carrier loaded with Doxorubicin. We employed myeloperoxidase-catalysed and peroxynitrite-mediated oxidative conditions to mimic the respiratory burst of neutrophils and macrophages, respectively. In addition, we revealed that the cytostatic and cytotoxic effects of free Doxorubicin, but not nanotube-carried drug, on melanoma and lung carcinoma cell lines were abolished in the presence of tumor-activated myeloid regulatory cells that create unique myeloperoxidase- and peroxynitrite-induced oxidative conditions. Both ex vivo and in vitro studies demonstrate that the nanocarrier protects the drug against oxidative biodegradation.

Oxidative Unzipping of Stacked Nitrogen-Doped Carbon Nanotube Cups

Co-reporter:Haifeng Dong, Yong Zhao, Yifan Tang, Seth C. Burkert, and Alexander Star

ACS Applied Materials & Interfaces 2015 Volume 7(Issue 20) pp:10734

Publication Date(Web):May 6, 2015

DOI:10.1021/acsami.5b00447

We demonstrate a facile synthesis of different nanostructures by oxidative unzipping of stacked nitrogen-doped carbon nanotube cups (NCNCs). Depending on the initial number of stacked-cup segments, this method can yield graphene nanosheets (GNSs) or hybrid nanostructures comprised of graphene nanoribbons partially unzipped from a central nanotube core. Due to the stacked-cup structure of as-synthesized NCNCs, preventing complete exposure of graphitic planes, the unzipping mechanism is hindered, resulting in incomplete unzipping; however, individual, separated NCNCs are completely unzipped, yielding individual nitrogen-doped GNSs. Graphene-based materials have been employed as electrocatalysts for many important chemical reactions, and it has been proposed that increasing the reactive edges results in more efficient electrocatalysis. In this paper, we apply these graphene conjugates as electrocatalysts for the oxygen reduction reaction (ORR) to determine how the increase in reactive edges affects the electrocatalytic activity. This investigation introduces a new method for the improvement of ORR electrocatalysts by using nitrogen dopants more effectively, allowing for enhanced ORR performance with lower overall nitrogen content. Additionally, the GNSs were functionalized with gold nanoparticles (GNPs), resulting in a GNS/GNP hybrid, which shows efficient surface-enhanced Raman scattering and expands the scope of its application in advanced device fabrication and biosensing.Keywords: carbon nanotubes; graphene−carbon nanotube hybrid structure; nitrogen doped; optimized morphology; unzipping;

Indium Oxide—Single-Walled Carbon Nanotube Composite for Ethanol Sensing at Room Temperature

Co-reporter:James E. Ellis; Uri Green; Dan C. Sorescu; Yong Zhao

The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 4) pp:712-717

Publication Date(Web):February 2, 2015

DOI:10.1021/jz502631a

Utilizing a sol-gel synthesis, indium oxide is grown on the surface of oxidized single-walled carbon nanotubes (SWCNT) to form a hybrid material with high conductivity and sensitivity toward certain organic vapors. The room-temperature sensing of dilute ethanol and acetone vapors on the surface of indium oxide/SWCNT hybrid material is studied using electrical conductance experiments in a nonoxidizing environment. Through testing of variously calcinated materials, it was observed that the degree of annealing greatly affects the material’s response to acetone and ethanol, such that the intermediate calcination condition yields the best sensitivity. DFT simulations are used to study the interface between defective SWCNT and indium oxide, as well as the interaction between ethanol and acetone molecules with the indium oxide/SWCNT hybrid material.

Nano-Gold Corking and Enzymatic Uncorking of Carbon Nanotube Cups

Co-reporter:Yong Zhao; Seth C. Burkert; Yifan Tang; Dan C. Sorescu; Alexandr A. Kapralov; Galina V. Shurin; Michael R. Shurin; Valerian E. Kagan

Journal of the American Chemical Society 2014 Volume 137(Issue 2) pp:675-684

Publication Date(Web):December 21, 2014

DOI:10.1021/ja511843w

Because of their unique stacked, cup-shaped, hollow compartments, nitrogen-doped carbon nanotube cups (NCNCs) have promising potential as nanoscale containers. Individual NCNCs are isolated from their stacked structure through acid oxidation and subsequent probe-tip sonication. The NCNCs are then effectively corked with gold nanoparticles (GNPs) by sodium citrate reduction with chloroauric acid, forming graphitic nanocapsules with significant surface-enhanced Raman signature. Mechanistically, the growth of the GNP corks starts from the nucleation and welding of gold seeds on the open rims of NCNCs enriched with nitrogen functionalities, as confirmed by density functional theory calculations. A potent oxidizing enzyme of neutrophils, myeloperoxidase (MPO), can effectively open the corked NCNCs through GNP detachment, with subsequent complete enzymatic degradation of the graphitic shells. This controlled opening and degradation was further carried out in vitro with human neutrophils. Furthermore, the GNP-corked NCNCs were demonstrated to function as novel drug delivery carriers, capable of effective (i) delivery of paclitaxel to tumor-associated myeloid-derived suppressor cells (MDSC), (ii) MPO-regulated release, and (iii) blockade of MDSC immunosuppressive potential.

Electronic Detection of Bacteria Using Holey Reduced Graphene Oxide

Co-reporter:Yanan Chen, Zachary P. Michael, Gregg P. Kotchey, Yong Zhao, and Alexander Star

ACS Applied Materials & Interfaces 2014 Volume 6(Issue 6) pp:3805

Publication Date(Web):February 28, 2014

DOI:10.1021/am500364f

Carbon nanomaterials have been widely explored for diverse biosensing applications including bacterial detection. However, covalent functionalization of these materials can lead to the destruction of attractive electronic properties. To this end, we utilized a new graphene derivative, holey reduced graphene oxide (hRGO), functionalized with Magainin I to produce a broad-spectrum bacterial probe. Unlike related carbon nanomaterials, hRGO retains the necessary electronic properties while providing the high percentage of available oxygen moieties required for effective covalent functionalization.Keywords: antimicrobial peptides; graphene; nanomaterials; nanotechnology; semiconductors;

Insight into the Mechanism of Graphene Oxide Degradation via the Photo-Fenton Reaction

Co-reporter:Hao Bai ; Wentao Jiang ; Gregg P. Kotchey ; Wissam A. Saidi ; Benjamin J. Bythell ; Jacqueline M. Jarvis ; Alan G. Marshall ; Renã A. S. Robinson

The Journal of Physical Chemistry C 2014 Volume 118(Issue 19) pp:10519-10529

Publication Date(Web):April 15, 2014

DOI:10.1021/jp503413s

Graphene represents an attractive two-dimensional carbon-based nanomaterial that holds great promise for applications such as electronics, batteries, sensors, and composite materials. Recent work has demonstrated that carbon-based nanomaterials are degradable/biodegradable, but little work has been expended to identify products formed during the degradation process. As these products may have toxicological implications that could leach into the environment or the human body, insight into the mechanism and structural elucidation remain important as carbon-based nanomaterials become commercialized. We provide insight into a potential mechanism of graphene oxide degradation via the photo-Fenton reaction. We have determined that after 1 day of treatment intermediate oxidation products (with MW 150–1000 Da) were generated. Upon longer reaction times (i.e., days 2 and 3), these products were no longer present in high abundance, and the system was dominated by graphene quantum dots (GQDs). On the basis of FTIR, MS, and NMR data, potential structures for these oxidation products, which consist of oxidized polycyclic aromatic hydrocarbons, are proposed.

Sensing Reversible Protein–Ligand Interactions with Single-Walled Carbon Nanotube Field-Effect Transistors

Co-reporter:Alexandra M. Münzer ; Wanji Seo ; Gregory J. Morgan ; Zachary P. Michael ; Yong Zhao ; Katharina Melzer ; Giuseppe Scarpa

The Journal of Physical Chemistry C 2014 Volume 118(Issue 31) pp:17193-17199

Publication Date(Web):July 11, 2014

DOI:10.1021/jp503670a

We report on the reversible detection of CaptAvidin, a tyrosine modified avidin, with single-walled carbon nanotube (SWNT) field-effect transistors (FETs) noncovalently functionalized with biotin moieties using 1-pyrenebutyric acid as a linker. Binding affinities at different pH values were quantified, and the sensor’s response at various ionic strengths was analyzed. Furthermore, protein “fingerprints” of NeutrAvidin and streptavidin were obtained by monitoring their adsorption at several pH values. Moreover, gold nanoparticle decorated SWNT FETs were functionalized with biotin using 1-pyrenebutyric acid as a linker for the CNT surface and (±)-α-lipoic acid linkers for the gold surface, and reversible CaptAvidin binding is shown, paving the way for potential dual mode measurements with the addition of surface enhanced Raman spectroscopy (SERS).

Efficient separation of nitrogen-doped carbon nanotube cups

Co-reporter:Yifan Tang, Yong Zhao, Seth C. Burkert, Mengning Ding, James E. Ellis, Alexander Star

Carbon 2014 80() pp: 583-590

Publication Date(Web):

DOI:10.1016/j.carbon.2014.09.001

Sweet carbon nanostructures: carbohydrate conjugates with carbon nanotubes and graphene and their applications

Co-reporter:Yanan Chen, Alexander Star and Sébastien Vidal

Chemical Society Reviews 2013 vol. 42(Issue 11) pp:4532-4542

Publication Date(Web):17 Dec 2012

DOI:10.1039/C2CS35396B

Because of their unique physicochemical properties, carbon nanotubes and graphene can find promising applications in many fields of biomedical research. However, the pristine nanomaterials suffer from low solubility in aqueous systems which results in their limited biocompatibility. Through the introduction of carbohydrates, the surface properties of these graphitic carbon nanostructures can be modified not just to improve their water solubility but also to enable these versatile nanostructures to interact selectively with biological systems. This review will highlight the synthetic strategies that have been reported for the covalent and noncovalent functionalization of carbon nanostructures with carbohydrates, as well as their applications in biosensing and biomedicine.

Photoinduced Charge Transfer and Acetone Sensitivity of Single-Walled Carbon Nanotube–Titanium Dioxide Hybrids

Co-reporter:Mengning Ding ; Dan C. Sorescu

Journal of the American Chemical Society 2013 Volume 135(Issue 24) pp:9015-9022

Publication Date(Web):May 21, 2013

DOI:10.1021/ja402887v

The unique physical and chemical properties of single-walled carbon nanotubes (SWNTs) make them ideal building blocks for the construction of hybrid nanostructures. In addition to increasing the material complexity and functionality, SWNTs can probe the interfacial processes in the hybrid system. In this work, SWNT–TiO2 core/shell hybrid nanostructures were found to exhibit unique electrical behavior in response to UV illumination and acetone vapors. By experimental and theoretical studies of UV and acetone sensitivities of different SWNT–TiO2 hybrid systems, we established a fundamental understanding on the interfacial charge transfer between photoexcited TiO2 and SWNTs as well as the mechanism of acetone sensing. We further demonstrated a practical application of photoinduced acetone sensitivity by fabricating a microsized room temperature acetone sensor that showed fast, linear, and reversible detection of acetone vapors with concentrations in few parts per million range.

Enzyme-Catalyzed Oxidation Facilitates the Return of Fluorescence for Single-Walled Carbon Nanotubes

Co-reporter:Cheuk Fai Chiu ; Brian A. Barth ; Gregg P. Kotchey ; Yong Zhao ; Kristy A. Gogick ; Wissam A. Saidi ; Stéphane Petoud

Journal of the American Chemical Society 2013 Volume 135(Issue 36) pp:13356-13364

Publication Date(Web):May 15, 2013

DOI:10.1021/ja400699y

In this work, we studied enzyme-catalyzed oxidation of single-walled carbon nanotubes (SWCNTs) produced by the high-pressure carbon monoxide (HiPco) method. While oxidation via strong acids introduced defect sites on SWCNTs and suppressed their near-infrared (NIR) fluorescence, our results indicated that the fluorescence of SWCNTs was restored upon enzymatic oxidation, providing new evidence that the reaction catalyzed by horseradish peroxidase (HRP) in the presence of H2O2 is mainly a defect-consuming step. These results were further supported by both UV–vis–NIR and Raman spectroscopy. Therefore, when acid oxidation followed by HRP-catalyzed enzyme oxidation was employed, shortened (<300 nm in length) and NIR-fluorescent SWCNTs were produced. In contrast, upon treatment with myeloperoxidase, H2O2, and NaCl, the oxidized HiPco SWCNTs underwent complete oxidation (i.e., degradation). The shortened, NIR-fluorescent SWCNTs resulting from HRP-catalyzed oxidation of acid-cut HiPco SWCNTs may find applications in cellular NIR imaging and drug delivery systems.

Effect of antioxidants on enzyme-catalysed biodegradation of carbon nanotubes

Co-reporter:Gregg P. Kotchey, James A. Gaugler, Alexander A. Kapralov, Valerian E. Kagan and Alexander Star

Journal of Materials Chemistry A 2013 vol. 1(Issue 3) pp:302-309

Publication Date(Web):25 Oct 2012

DOI:10.1039/C2TB00047D

The growing applications of carbon nanotubes (CNTs) inevitably increase the risk of exposure to this potentially toxic nanomaterial. In an attempt to address this issue, research has been implemented to study the biodegradation of CNTs. In particular, myeloperoxidase (MPO), an enzyme expressed by inflammatory cells of animals including humans, catalyse the degradation of oxidized carbon nanomaterials. While reactive intermediates generated by MPO efficiently degrade oxidized single-walled carbon nanotubes (o-SWCNTs); the exact mechanism of enzyme-catalysed biodegradation remains ambiguous. In this work, we tried to explain enzymatic oxidation in terms of redox potentials by employing competitive substrates for MPO such as chloride, which is oxidized by MPO to form a strong oxidant (hypochlorite), and antioxidants that have lower redox potentials than CNTs. Employing transmission electron microscopy, Raman spectroscopy, and vis-NIR absorption spectroscopy, we demonstrate that the addition of antioxidants, L-ascorbic acid and L-glutathione, with or without chloride significantly mitigates MPO-catalysed biodegradation of o-SWCNTs. This study focuses on a fundamental understanding of the mechanisms of enzymatic biodegradation of CNTs and the impact of antioxidants on these pathways.

Synthesis of One-Dimensional SiC Nanostructures from a Glassy Buckypaper

Co-reporter:Mengning Ding and Alexander Star

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 6) pp:1928

Publication Date(Web):February 21, 2013

DOI:10.1021/am3031008

A simple and scalable synthetic strategy was developed for the fabrication of one-dimensional SiC nanostructures—nanorods and nanowires. Thin sheets of single-walled carbon nanotubes (SWNTs) were prepared by vacuum filtration and were washed repeatedly with sodium silicate (Na2SiO3) solution. The resulting “glassy buckypaper” was heated at 1300–1500 °C under Ar/H2 to allow a solid state reaction between C and Si precursors to form a variety of SiC nanostructures. The morphology and crystal structures of SiC nanorods and nanowires were characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray spectroscopy (EDX), electron diffraction (ED), and X-ray diffraction (XRD) techniques. Furthermore, electrical conductance measurements were performed on SiC nanorods, demonstrating their potential applications in high-temperature sensors and control systems.Keywords: carbon nanotubes; high-temperature sensors; SiC nanorods; SiC nanowires; silicate;

Understanding Interfaces in Metal–Graphitic Hybrid Nanostructures

Co-reporter:Mengning Ding, Yifan Tang, and Alexander Star

The Journal of Physical Chemistry Letters 2013 Volume 4(Issue 1) pp:147-160

Publication Date(Web):December 13, 2012

DOI:10.1021/jz301711a

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.

Rigid versus Flexible Ligands on Carbon Nanotubes for the Enhanced Sensitivity of Cobalt Ions

Co-reporter:Pingping Gou, Nadine D. Kraut, Ian Matthew Feigel, and Alexander Star

Macromolecules 2013 Volume 46(Issue 4) pp:1376-1383

Publication Date(Web):February 5, 2013

DOI:10.1021/ma400113m

Carbon nanotubes have shown great promise in the fabrication of ultracompact and highly sensitive chemical and biological sensors. Additional chemical functionalization schemes can controllably improve selectivity of the carbon nanotube-based sensors; however, the exact transduction mechanism is still under debate. In this article we detail the synthesis and selective response of single-walled carbon nanotubes (SWNTs) functionalized with polyazomethine (PAM) polymer toward the application of a specific trace metal ion detector. The response of the polymer system was compared to shape persistent macrocycle (MAC) comprised of identical ion coordination ligands. While ion detection with rigid MAC/SWNT chemiresistor was comparable to bare SWNT, flexible PAM offers significant SWNT signal amplification, allowing for picomolar detection of Co2+ ions with both selectivity and a fast response. We hypothesized that rearrangement of the flexible PAM on the SWNT network is a sensing mechanism which allows for ultrasensitive detection of metal ions. The electron transfer and polymer rearrangement on the SWNT were studied by a combination of optical spectroscopy and electrical measurements—ultimately allowing for a better understanding of fundamental mechanisms that prompt device response.

The Effect of Metal Catalyst on the Electrocatalytic Activity of Nitrogen-Doped Carbon Nanotubes

Co-reporter:Yifan Tang, Seth C. Burkert, Yong Zhao, Wissam A. Saidi, and Alexander Star

The Journal of Physical Chemistry C 2013 Volume 117(Issue 48) pp:25213-25221

Publication Date(Web):November 12, 2013

DOI:10.1021/jp403033x

Nitrogen-doped and undoped carbon nanotubes (CNTs) were synthesized from ferrocene, nickelocene, and cobaltocene metal catalysts. Electrochemical testing for an oxygen reduction reaction (ORR) showed that nitrogen-doped CNTs synthesized from ferrocene had improved catalytic activity while nanotubes synthesized from nickelocene and cobaltocene, doped with a comparable amount of nitrogen and having similar stacked-cups structure as nitrogen doped CNTs from ferrocene, had a performance only slightly better than that of undoped CNTs. Ferrocene-based nitrogen-doped CNTs also demonstrated similar long-term stability and higher CO tolerance compared to Pt/C catalyst. Detailed ORR mechanisms were also studied and carbon nanomaterials showed different ORR processes as a result of the metal catalyst utilized in the chemical synthesis. Nitrogen-doped and undoped CNTs synthesized from nickelocene show a preferential 4-electron process as compared to materials synthesized from ferrocene and cobaltocene. We believe that the metal used in the growth process regulates the mechanism of oxygen reduction and can be used to develop improved nitrogen-doped carbon nanomaterials as nonprecious-metal catalysts for fuel cells.

Carbon Nanotubes for the Label-Free Detection of Biomarkers

Co-reporter:Alexandra M. Münzer, Zachary P. Michael, and Alexander Star

ACS Nano 2013 Volume 7(Issue 9) pp:7448

Publication Date(Web):September 13, 2013

DOI:10.1021/nn404544e

Carbon nanotubes (CNTs) have been of high interest because of their potential to complement or to replace current biomedical sensor and assay techniques. By taking advantage of their unique electrical and optical properties, CNTs can be integrated into highly sensitive sensors and probes. We highlight recent advances toward applying CNTs to the biomedical field, focusing on a report by Reuel et al. in this issue of ACS Nano, wherein the inherent near-infrared (NIR) fluorescence of functionalized arrays of single-walled carbon nanotubes (SWNTs) is utilized for detection of several important biological markers.

A Natural Vanishing Act: The Enzyme-Catalyzed Degradation of Carbon Nanomaterials

Co-reporter:Gregg P. Kotchey, Saad A. Hasan, Alexander A. Kapralov, Seung Han Ha, Kang Kim, Anna A. Shvedova, Valerian E. Kagan, and Alexander Star

Accounts of Chemical Research 2012 Volume 45(Issue 10) pp:1770

Publication Date(Web):July 23, 2012

DOI:10.1021/ar300106h

Over the past three decades, revolutionary research in nanotechnology by the scientific, medical, and engineering communities has yielded a treasure trove of discoveries with diverse applications that promise to benefit humanity. With their unique electronic and mechanical properties, carbon nanomaterials (CNMs) represent a prime example of the promise of nanotechnology with applications in areas that include electronics, fuel cells, composites, and nanomedicine. Because of toxicological issues associated with CNMs, however, their full commercial potential may not be achieved. The ex vitro, in vitro, and in vivo data presented in this Account provide fundamental insights into the biopersistence of CNMs, such as carbon nanotubes and graphene, and their oxidation/biodegradation processes as catalyzed by peroxidase enzymes. We also communicate our current understanding of the mechanism for the enzymatic oxidation and biodegradation. Finally, we outline potential future directions that could enhance our mechanistic understanding of the CNM oxidation and biodegradation and could yield benefits in terms of human health and environmental safety.The conclusions presented in this Account may catalyze a rational rethinking of CNM incorporation in diverse applications. For example, armed with an understanding of how and why CNMs undergo enzyme-catalyzed oxidation and biodegradation, researchers can tailor the structure of CNMs to either promote or inhibit these processes. In nanomedical applications such as drug delivery, the incorporation of carboxylate functional groups could facilitate biodegradation of the nanomaterial after delivery of the cargo. On the other hand, in the construction of aircraft, a CNM composite should be stable to oxidizing conditions in the environment. Therefore, pristine, inert CNMs would be ideal for this application. Finally, the incorporation of CNMs with defect sites in consumer goods could provide a facile mechanism that promotes the degradation of these materials once these products reach landfills.

Welding of Gold Nanoparticles on Graphitic Templates for Chemical Sensing

Co-reporter:Mengning Ding ; Dan C. Sorescu ; Gregg P. Kotchey

Journal of the American Chemical Society 2012 Volume 134(Issue 7) pp:3472-3479

Publication Date(Web):January 22, 2012

DOI:10.1021/ja210278u

Controlled self-assembly of zero-dimensional gold nanoparticles and construction of complex gold nanostructures from these building blocks could significantly extend their applications in many fields. Carbon nanotubes are one of the most promising inorganic templates for this strategy because of their unique physical, chemical, and mechanical properties, which translate into numerous potential applications. Here we report the bottom-up synthesis of gold nanowires in aqueous solution through self-assembly of gold nanoparticles on single-walled carbon nanotubes followed by thermal-heating-induced nanowelding. We investigate the mechanism of this process by exploring different graphitic templates. The experimental work is assisted by computational studies that provide additional insight into the self-assembly and nanowelding mechanism. We also demonstrate the chemical sensitivity of the nanomaterial to parts-per-billion concentrations of hydrogen sulfide with potential applications in industrial safety and personal healthcare.

Electronic Detection of Lectins Using Carbohydrate-Functionalized Nanostructures: Graphene versus Carbon Nanotubes

Co-reporter:Yanan Chen, Harindra Vedala, Gregg P. Kotchey, Aymeric Audfray, Samy Cecioni, Anne Imberty, Sébastien Vidal, and Alexander Star

ACS Nano 2012 Volume 6(Issue 1) pp:760

Publication Date(Web):December 2, 2011

DOI:10.1021/nn2042384

Here we investigated the interactions between lectins and carbohydrates using field-effect transistor (FET) devices comprised of chemically converted graphene (CCG) and single-walled carbon nanotubes (SWNTs). Pyrene- and porphyrin-based glycoconjugates were functionalized noncovalently on the surface of CCG-FET and SWNT-FET devices, which were then treated with 2 μM nonspecific and specific lectins. In particular, three different lectins (PA-IL, PA-IIL, and ConA) and three carbohydrate epitopes (galactose, fucose, and mannose) were tested. The responses of 36 different devices were compared and rationalized using computer-aided models of carbon nanostructure/glycoconjugate interactions. Glycoconjugate surface coverage in addition to one-dimensional structures of SWNTs resulted in optimal lectin detection. Additionally, lectin titration data of SWNT- and CCG-based biosensors were used to calculate lectin dissociation constants (Kd) and compare them to the values obtained from the isothermal titration microcalorimetry technique.Keywords: carbohydrate; carbon nanotubes; graphene; lectin; sensors

Selecting Fruits with Carbon Nanotube Sensors

Co-reporter:Mengning Ding; Alexer Star

Angewandte Chemie International Edition 2012 Volume 51( Issue 31) pp:7637-7638

Publication Date(Web):

DOI:10.1002/anie.201203387

Corking Carbon Nanotube Cups with Gold Nanoparticles

Co-reporter:Yong Zhao, Yifan Tang, Yanan Chen, and Alexander Star

ACS Nano 2012 Volume 6(Issue 8) pp:6912

Publication Date(Web):July 13, 2012

DOI:10.1021/nn3018443

Nitrogen doping of carbon nanotubes during chemical vapor deposition synthesis can create unique stacked cup-shaped structures termed as nitrogen-doped carbon nanotube cups (NCNCs). These cups have semielliptical hollow cavities and elevated reactivity which could lead to various applications. In this work, by applying intense ultrasonication to the as-synthesized NCNCs, we demonstrated an effective mechanical method to isolate the individual cups with opened cavities from their stacks. The graphitic structures of the isolated cups and their inherent nitrogen functionalities were characterized by comprehensive microscopic and spectroscopic methods. In particular, we quantitatively determined the existence of amine functionalities on NCNCs and found that they were preferentially distributed at the open edges of the cups, providing localized reactive sites. Further, by thiolating the amine groups with 3-mercapto-propionic acid, we were able to effectively cork the isolated cups by gold nanoparticles with commensurate diameters. These cup-shaped carbon nanomaterials with controlled inner volumes and gold nanoparticle corks could find potential applications as nanoscale reaction containers or drug delivery vehicles.Keywords: carbon nanotubes; chemical vapor deposition; gold nanoparticles; nitrogen doping

Selektiver Nachweis von Ethylengas aus Frchten mit Kohlenstoffnanorhren-Sensoren

Co-reporter:Mengning Ding; Alexer Star

Angewandte Chemie 2012 Volume 124( Issue 31) pp:7755-7756

Publication Date(Web):

DOI:10.1002/ange.201203387

Chemical Sensing with Polyaniline Coated Single-Walled Carbon Nanotubes

Co-reporter:Mengning Ding;Yifan Tang;Pingping Gou;Michael J. Reber ;Alexer Star

Advanced Materials 2011 Volume 23( Issue 4) pp:536-540

Publication Date(Web):

DOI:10.1002/adma.201003304

Nanoelectronic Detection of Lectin-Carbohydrate Interactions Using Carbon Nanotubes

Co-reporter:Harindra Vedala, Yanan Chen, Samy Cecioni, Anne Imberty, Sébastien Vidal, and Alexander Star

Nano Letters 2011 Volume 11(Issue 1) pp:170-175

Publication Date(Web):December 6, 2010

DOI:10.1021/nl103286k

We have used single-walled carbon nanotube field-effect transistor (NTFET) devices to probe the interactions between carbohydrates and their recognition proteins called lectins. These interactions are involved in a wide range of biological processes, such as cell−cell recognition, cell−matrix interaction as well as viral and bacterial infections. In our experiments, NTFETs were functionalized noncovalently with porphyrin-based glycoconjugates synthesized using “click” azide−alkyne chemistry, and change in electrical conductance was measured upon specific binding of two bacterial lectins that present different carbohydrate preference, namely PA-IL, PA-IIL from Pseudomonas aeruginosa and a plant lectin Concanavalin A. However, no significant change in the device characteristics was observed when the devices were exposed to other lectins with different specificity. Detection of PA-IL binding to galactosylated NTFETs was highly sensitive (2 nM) with a measured dissociation constant (Kd = 6.8 μM) corresponding to literature data. Fluorescence microscopy, atomic force microscopy, UV−vis-NIR spectroscopy, and several control measurements confirmed the NTFET response to selective interactions between carbohydrates and lectins.

Chemical Sensitivity of Graphene Edges Decorated with Metal Nanoparticles

Co-reporter:Harindra Vedala, Dan C. Sorescu, Gregg P. Kotchey, and Alexander Star

Nano Letters 2011 Volume 11(Issue 6) pp:2342-2347

Publication Date(Web):May 17, 2011

DOI:10.1021/nl2006438

Graphene is a novel two-dimensional nanomaterial that holds great potential in electronic and sensor applications. By etching the edges to form nanoribbons or introducing defects on the basal plane, it has been demonstrated that the physical and chemical properties of graphene can be drastically altered. However, the lithographic or chemical techniques required to reliably produce such nanoribbons remain challenging. Here, we report the fabrication of nanosensors based on holey reduced graphene oxide (hRGO), which can be visualized as interconnected graphene nanoribbons. In our method, enzymatic oxidation generated holes within the basal plane of graphene oxide, and after reduction with hydrazine, hRGO was formed. When decorated with Pt nanoparticles, hRGO exhibited a large and selective electronic response toward hydrogen gas. By combining experimental results and theoretical modeling, we propose that the increased edge-to-plane ratio, oxygen moieties, and Pt nanoparticle decoration were responsible for the observed gas sensing with hRGO nanostructures.

Biosensors based on one-dimensional nanostructures

Co-reporter:Ian Matthew Feigel, Harindra Vedala and Alexander Star

Journal of Materials Chemistry A 2011 vol. 21(Issue 25) pp:8940-8954

Publication Date(Web):11 Apr 2011

DOI:10.1039/C1JM10521C

Over the past decade, one-dimensional nanostructures (1D-NS) have been studied for the detection of biological molecules. These nanometre-scale materials, with diameters comparable to the size of individual biomolecules, offer the advantage of high sensitivity. In this feature article we discuss different techniques of biosensing using 1D-NS, namely electrical, electrochemical, optical, and mechanical methods, with a focus on the advancement of these techniques. Advantages and disadvantages of various synthesis and functionalization methods of 1D-NS, as well as biosensor device fabrication procedures are discussed. The main focus of this review is to demonstrate the progress of protein and DNA sensors based on 1D-NS over the past decade, and in addition we present an outlook for the future of this technology.

Enzymatic Degradation of Multiwalled Carbon Nanotubes

Co-reporter:Yong Zhao, Brett L. Allen, and Alexander Star

The Journal of Physical Chemistry A 2011 Volume 115(Issue 34) pp:9536-9544

Publication Date(Web):February 24, 2011

DOI:10.1021/jp112324d

Because of their unique properties, carbon nanotubes and, in particular, multiwalled carbon nanotubes (MWNTs) have been used for the development of advanced composite and catalyst materials. Despite their growing commercial applications and increased production, the potential environmental and toxicological impacts of MWNTs are not fully understood; however, many reports suggest that they may be toxic. Therefore, a need exists to develop protocols for effective and safe degradation of MWNTs. In this article, we investigated the effect of chemical functionalization of MWNTs on their enzymatic degradation with horseradish peroxidase (HRP) and hydrogen peroxide (H2O2). We investigated HRP/H2O2 degradation of purified, oxidized, and nitrogen-doped MWNTs and proposed a layer-by-layer degradation mechanism of nanotubes facilitated by side wall defects. These results provide a better understanding of the interaction between HRP and carbon nanotubes and suggest an eco-friendly way of mitigating the environmental impact of nanotubes.

The Enzymatic Oxidation of Graphene Oxide

Co-reporter:Gregg P. Kotchey, Brett L. Allen, Harindra Vedala, Naveena Yanamala, Alexander A. Kapralov, Yulia Y. Tyurina, Judith Klein-Seetharaman, Valerian E. Kagan, and Alexander Star

ACS Nano 2011 Volume 5(Issue 3) pp:2098

Publication Date(Web):February 23, 2011

DOI:10.1021/nn103265h

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, ultraviolet-visible, electron paramagnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, atomic force microscopy, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and gas chromatography−mass spectrometry. Computational docking studies indicated that HRP was preferentially bound to the basal plane rather than the edge for both graphene oxide and RGO. Owing 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 (keywords): field-effect transistor; graphene; microscopy; oxidation; peroxidase

Understanding the Sensor Response of Metal-Decorated Carbon Nanotubes

Co-reporter:Douglas R. Kauffman, Dan C. Sorescu, Daniel P. Schofield, Brett L. Allen, Kenneth D. Jordan and Alexander Star

Nano Letters 2010 Volume 10(Issue 3) pp:958-963

Publication Date(Web):February 15, 2010

DOI:10.1021/nl903888c

We have explored the room temperature response of metal nanoparticle decorated single-walled carbon nanotubes (NP-SWNTs) using a combination of electrical transport, optical spectroscopy, and electronic structure calculations. We have found that upon the electrochemical growth of Au NPs on SWNTs, there is a transfer of electron density from the SWNT to the NP species, and that adsorption of CO molecules on the NP surface is accompanied by transfer of electronic density back into the SWNT. Moreover, the electronic structure calculations indicate dramatic variations in the charge density at the NP-SWNT interface, which supports our previous observation that interfacial potential barriers dominate the electrical behavior of NP-SWNT systems.

Controlling the volumetric parameters of nitrogen-doped carbon nanotube cups

Co-reporter:Brett L. Allen, Matthew B. Keddie and Alexander Star

Nanoscale 2010 vol. 2(Issue 7) pp:1105-1108

Publication Date(Web):17 Mar 2010

DOI:10.1039/C0NR00043D

Analogous to multiwalled carbon nanotubes, nitrogen-doped carbon nanotube cups (NCNCs) have been synthesized with defined volumetric parameters (diameter and segment lengths) by controlling the catalyst particle size and the concentration of nitrogen precursor utilized in the chemical vapor deposition (CVD) reaction, allowing for tailored interior cavity space of cross-linked NCNCs, i.e. nanocapsules.

Graphene versus carbon nanotubes for chemical sensor and fuel cell applications

Co-reporter:Douglas R. Kauffman and Alexander Star

Analyst 2010 vol. 135(Issue 11) pp:2790-2797

Publication Date(Web):24 Aug 2010

DOI:10.1039/C0AN00262C

Graphene, an atomically thin layer of sp2 hybridized carbon, has emerged as a promising new nanomaterial for a variety of exciting applications including chemical sensors and catalyst supports. In this article, we survey modern methods of graphene production and functionalization with an emphasis on the development of chemical sensors and fuel cell electrodes with brief comparisons to state-of-the-art carbon nanotube-based systems.

Long-Term Performance of Pt-Decorated Carbon Nanotube Cathodes in Phosphoric Acid Fuel Cells

Co-reporter:Douglas R. Kauffman, Yifan Tang, Padmakar D. Kichambare, John F. Jackovitz and Alexander Star

Energy & Fuels 2010 Volume 24(Issue 3) pp:1877-1881

Publication Date(Web):January 29, 2010

DOI:10.1021/ef100013v

We report the electrochemical properties and performance of Pt-decorated carbon nanotube (Pt-CNT) catalysts for long-term operation in phosphoric acid fuel cells (PAFCs). Electrochemical measurements of Pt-CNT catalysts including cyclic voltammetry, rotating ring disk electrode voltammetry, and electrochemical impedance spectroscopy were conducted to evaluate the catalyzed oxygen reduction reaction (ORR). Furthermore, we tested the long-term performance of the Pt-CNT catalysts in 2′′ × 2′′ PAFC cathodes operating at 190 °C in 85% H3PO4 for extended periods (up to 240 days). Lifetime studies show that electrodes containing the Pt-CNT catalysts were approximately 20 times more stable than conventional Pt-C catalyst materials, even with a substantially thinner catalyst layer. This finding of the enhanced Pt-CNT catalyst stability bodes well for possible personal electronics or automotive applications, where catalyst longevity is an essential requirement.

Exploring the Chemical Sensitivity of a Carbon Nanotube/Green Tea Composite

Co-reporter:Yanan Chen, Yang Doo Lee, Harindra Vedala, Brett L. Allen, and Alexander Star

ACS Nano 2010 Volume 4(Issue 11) pp:6854

Publication Date(Web):November 2, 2010

DOI:10.1021/nn100988t

Single-walled carbon nanotubes (SWNTs) possess unique electronic and physical properties, which make them very attractive for a wide range of applications. In particular, SWNTs and their composites have shown a great potential for chemical and biological sensing. Green tea, or more specifically its main antioxidant component, epigallocatechin gallate (EGCG), has been found to disperse SWNTs in water. However, the chemical sensitivity of this SWNT/green tea (SWNT/EGCG) composite remained unexplored. With EGCG present, this SWNT composite should have strong antioxidant properties and thus respond to reactive oxygen species (ROS). Here we report on fabrication and characterization of SWNT/EGCG thin films and the measurement of their relative conductance as a function of H2O2 concentrations. We further investigated the sensing mechanism by Fourier transform infrared (FTIR) spectroscopy and field-effect transistor measurements (FET). We propose here that the response to H2O2 arises from the oxidation of EGCG in the composite. These findings suggest that SWNT/green tea composite has a great potential for developing simple resistivity-based sensors.Keywords: hydrogen peroxide; relative humidity; resistivity sensors; ROS

Graphitic Nanocapsules

Co-reporter:Brett L. Allen;Chad M. Shade;Adrienne M. Yingling;Stéphane Petoud;Alexer Star

Advanced Materials 2009 Volume 21( Issue 46) pp:4692-4695

Publication Date(Web):

DOI:10.1002/adma.200900851

Electrocatalytic Activity of Nitrogen-Doped Carbon Nanotube Cups

Co-reporter:Yifan Tang, Brett L. Allen, Douglas R. Kauffman and Alexander Star

Journal of the American Chemical Society 2009 Volume 131(Issue 37) pp:13200-13201

Publication Date(Web):September 1, 2009

DOI:10.1021/ja904595t

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 O2 reduction, the NCNC electrodes have been used for H2O2 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.

Electronically monitoring biological interactions with carbon nanotube field-effect transistors

Co-reporter:Douglas R. Kauffman and Alexander Star

Chemical Society Reviews 2008 vol. 37(Issue 6) pp:1197-1206

Publication Date(Web):07 Apr 2008

DOI:10.1039/B709567H

The year 2008 marks the 10th anniversary of the carbon nanotube field-effect transistor (NTFET). In the past decade a vast amount of effort has been placed on the development of NTFET based sensors for the detection of both chemical and biological species. Towards this end, NTFETs show great promise because of their extreme environmental sensitivity, small size, and ultra-low power requirements. Despite the great progress NTFETs have shown in the field of biological sensing, debate still exists over the mechanistic origins underlying the electronic response of NTFET devices, specifically whether analyte species interact with the carbon nanotube conduction channel or if interaction with the NTFET electrodes actually triggers device response. In this tutorial review, we describe the fabrication of NTFET devices, and detail several reports that illustrate recent advances in biological detection using NTFET devices, while highlighting the suggested mechanisms explaining the device response to analyte species. In doing this we hope to show that NTFET technology has the potential for low-cost and portable bioanalytical platforms.

Biodegradation of Single-Walled Carbon Nanotubes through Enzymatic Catalysis

Co-reporter:Brett L. Allen, Padmakar D. Kichambare, Pingping Gou, Irina I. Vlasova, Alexander A. Kapralov, Nagarjun Konduru, Valerian E. Kagan and Alexander Star

Nano Letters 2008 Volume 8(Issue 11) pp:3899-3903

Publication Date(Web):October 28, 2008

DOI:10.1021/nl802315h

We show here the biodegradation of single-walled carbon nanotubes through natural, enzymatic catalysis. By incubating nanotubes with a natural horseradish peroxidase (HRP) and low concentrations of H2O2 (∼40 μM) at 4 °C over 12 weeks under static conditions, we show the increased degradation of nanotube structure. This reaction was monitored via multiple characterization methods, including transmission electron microscopy (TEM), dynamic light scattering (DLS), gel electrophoresis, mass spectrometry, and ultraviolet−visible−near-infrared (UV−vis−NIR) spectroscopy. These results mark a promising possibility for carbon nanotubes to be degraded by HRP in environmentally relevant settings. This is also tempting for future studies involving biotechnological and natural (plant peroxidases) ways for degradation of carbon nanotubes in the environment.

Carbon Nanotube Gas and Vapor Sensors

Co-reporter:DouglasR. Kauffman ;Alexer Star

Angewandte Chemie International Edition 2008 Volume 47( Issue 35) pp:6550-6570

Publication Date(Web):

DOI:10.1002/anie.200704488

Abstract

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.

Synthesis, Characterization, and Manipulation of Nitrogen-Doped Carbon Nanotube Cups

Co-reporter:Brett L. Allen, Padmakar D. Kichambare and Alexander Star

ACS Nano 2008 Volume 2(Issue 9) pp:1914

Publication Date(Web):August 21, 2008

DOI:10.1021/nn800355v

Isolated, carbon nanotube cups with diameters of 12−40 nm have been synthesized by chemical vapor deposition through incorporation of nitrogen atoms into graphitic carbon structure and subsequent mechanical separation. Incorporation of nitrogen affords carbon nanotube cups with a unique composition comprising multiwalled, graphitic lattice with nitrogen groups on the exterior rim and hollow interior cavities. These nanostructures demonstrate the ability to participate in hydrogen bonding because of nitrogen functionalities on their open edges. Furthermore, reaction with these nitrogen functionalities results in the coupling of gold nanoparticles (GNPs) to the open rim of carbon nanotube cups. Through atomic force microscopy manipulation and adhesion force measurements, we compare the mobility of these structures on a hydrophilic surface before and after GNP coupling. Understanding of these forces will aid in useful nanostructure assembly for energy and biomedical applications.Keywords: atomic force microscopy; carbon nanotubes; chemical vapor deposition; gold nanoparticles

Gas- und Dampfsensoren auf der Basis von Kohlenstoff-Nanorhren

Co-reporter:DouglasR. Kauffman ;Alexer Star

Angewandte Chemie 2008 Volume 120( Issue 35) pp:6652-6673

Publication Date(Web):

DOI:10.1002/ange.200704488

Abstract

Seit ihrer Entdeckung im Jahr 1991 haben Kohlenstoff-Nanoröhren ein riesiges Interesse erfahren. Grund ist ihr enormes Anwendungspotenzial, und Forscher unterschiedlicher Fachrichtungen arbeiten heute gemeinsam daran, die elektronische Struktur und das Reaktionsverhalten von Kohlenstoff-Nanoröhren aufzuklären. Da ihre elektronische Struktur leicht von wechselwirkenden Molekülen beeinflusst wird, reagieren Kohlenstoff-Nanoröhren extrem empfindlich auf Änderungen in der lokalen chemischen Umgebung. Dies macht sie zu idealen Kandidaten für den Einsatz in chemischen Sensoren, und es wurden bemerkenswerte Fortschritte bezüglich der Empfindlichkeit und chemischen Selektivität gegenüber einer Vielzahl chemischer Spezies erzielt. Trotz der zahlreichen Verbesserungen sind aber noch einige wichtige Probleme zu lösen, bevor Kohlenstoff-Nanoröhren mit den modernsten Feststoff-Sensormaterialien konkurrieren können. Die Entwicklung von Sensoren auf der Basis von Kohlenstoff-Nanoröhren befindet sich zwar noch im Anfangsstadium, aber bei weiteren Fortschritten erscheint ihre Integration in kommerziell tragfähige Sensoren, die sich dann durch eine konkurrenzlose Empfindlichkeit und außerordentlich kleine Abmessungen auszeichnen werden, möglich.

Carbon Nanotube Field-Effect-Transistor-Based Biosensors

Co-reporter:B. L. Allen;P. D. Kichambare;A. Star

Advanced Materials 2007 Volume 19(Issue 11) pp:1439-1451

Publication Date(Web):30 APR 2007

DOI:10.1002/adma.200602043

There is an explosive interest in 1D nanostructured materials for biological sensors. Among these nanometer-scale materials, single-walled carbon nanotubes (SWNTs) offer the advantages of possible biocompatibility, size compatibility, and sensitivity towards minute electrical perturbations. In particular, because of these inherent qualities, changes in SWNT conductivity have been explored in order to study the interaction of biomolecules with SWNTs. This Review discusses these interactions, with a focus on carbon nanotube field-effect transistors (NTFETs). Recent examples of applications of NTFET devices for detection of proteins, antibody–antigen assays, DNA hybridization, and enzymatic reactions involving glucose are summarized. Examples of complementary techniques, such as microscopy and spectroscopy, are covered as well.

Label-free detection of DNA hybridization using carbon nanotube network field-effect transistors

Co-reporter:Eugene Tu;Joseph Niemann;Jean-Christophe P. Gabriel;C. Steve Joiner;Christian Valcke

PNAS 2006 Volume 103 (Issue 4 ) pp:921-926

Publication Date(Web):2006-01-24

DOI:10.1073/pnas.0504146103

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.

Peroxidase-mediated biodegradation of carbon nanotubes in vitro and in vivo

Co-reporter:Gregg P. Kotchey, Yong Zhao, Valerian E. Kagan, Alexander Star

Advanced Drug Delivery Reviews (December 2013) Volume 65(Issue 15) pp:1921-1932

Publication Date(Web):1 December 2013

DOI:10.1016/j.addr.2013.07.007

As a result of their unique electronic, optical, and mechanical properties, carbon nanotubes (CNTs) have been implemented in therapeutic and imaging applications. In an idealized situation, CNTs would be disposed of after they transport their theranostic payloads. Biodegradation represents an attractive pathway for the elimination of CNT carriers post-delivery and may be integral in catalyzing the release of the cargo from the delivery vehicle. Accordingly, recent research efforts have focused on peroxidase-driven biodegradation of CNTs. In this review, we not only summarize recent efforts to biodegrade CNTs in the test tube, in vitro, and in vivo, but also attempt to explore the fundamental parameters underlying degradation. Encouraged by the in vivo results obtained to date, we envision a future, where carbon-based nano-containers, which are specifically designed to target organs/cells, deliver their cargo, and biodegrade via peroxidase-driven mechanism, will represent an attractive therapeutic delivery option in nanomedicine.Download high-res image (376KB)Download full-size image

Biosensors based on one-dimensional nanostructures

Co-reporter:Ian Matthew Feigel, Harindra Vedala and Alexander Star

Journal of Materials Chemistry A 2011 - vol. 21(Issue 25) pp:NaN8954-8954

Publication Date(Web):2011/04/11

DOI:10.1039/C1JM10521C

Single-walled carbon nanotubes templated CuO networks for gas sensing

Co-reporter:Guiming Peng, Suqin Wu, James E. Ellis, Xueqing Xu, Gang Xu, Changlin Yu and Alexander Star

Journal of Materials Chemistry A 2016 - vol. 4(Issue 27) pp:NaN6580-6580

Publication Date(Web):2016/06/16

DOI:10.1039/C6TC01722C

Sweet carbon nanostructures: carbohydrate conjugates with carbon nanotubes and graphene and their applications

Co-reporter:Yanan Chen, Alexander Star and Sébastien Vidal