Electrochemical behavior of needle-like and forest-like single-walled carbon nanotube electrodes

Mediated Electron Transfer at Vertically Aligned Single-Walled Carbon Nanotube Electrodes During Detection of DNA Hybridization

Vertically aligned single-walled carbon nanotube (VASWCNT) assemblies are generated on cysteamine and 2-mercaptoethanol (2-ME)-functionalized gold surfaces through amide bond formation between carboxylic groups generated at the end of acid-shortened single-walled carbon nanotubes (SWCNTs) and amine groups present on the gold surfaces. Atomic force microscopy (AFM) imaging confirms the vertical alignment mode of SWCNT attachment through significant changes in surface roughness compared to bare gold surfaces and the lack of any horizontally aligned SWCNTs present. These SWCNT assemblies are further modified with an amine-terminated single-stranded probe-DNA. Subsequent hybridization of the surface-bound probe-DNA in the presence of complementary strands in solution is followed using impedance measurements in the presence of Fe(CN)6 (3-/4-) as the redox probe in solution, which show changes in the interfacial electrochemical properties, specifically the charge-transfer resistance, due to hybridization. In addition, hybridization of the probe-DNA is also compared when it is attached directly to the gold surfaces without any intermediary SWCNTs. Contrary to our expectations, impedance measurements show a decrease in charge-transfer resistance with time due to hybridization with 300 nM complementary DNA in solution with the probe-DNA attached to SWCNTs. In contrast, an increase in charge-transfer resistance is observed with time during hybridization when the probe-DNA is attached directly to the gold surfaces. The decrease in charge-transfer resistance during hybridization in the presence of VASWCNTs indicates an enhancement in the electron transfer process of the redox probe at the VASWCNT-modified electrode. The results suggest that VASWCNTs are acting as mediators of electron transfer, which facilitate the charge transfer of the redox probe at the electrode-solution interface.

Electrochemistry at carbon nanotube forests: sidewalls and closed ends allow fast electron transfer

The electrochemical properties of the closed ends and sidewalls of pristine carbon nanotube forests are investigated directly using a nanopipet electrochemical cell. Both are shown to promote fast electron transfer, without any activation or processing of the carbon nanotube material required, in contrast to the current model in the literature.

The new age of carbon nanotubes: an updated review of functionalized carbon nanotubes in electrochemical sensors

Since the discovery of carbon nanotubes (CNTs), they have drawn considerable research attention and have shown great potential application in many fields due to their unique structural, mechanical, and electronic properties. However, their native insolubility severely holds back the process of application. In order to overcome this disadvantage and broaden the scope of their application, chemical functionalization of CNTs has attracted great interest over the past several decades and produced various novel hybrid materials with specific applications. Notably, the rapid development of functionalized CNTs used as electrochemical sensors has been successfully witnessed. In this featured article, the recent progress of electrochemical sensors based on functionalized CNTs is discussed and classified according to modifiers covering organic (oxygen functional groups, small organic molecules, polymers, DNA, protein, etc.), inorganic (metal nanoparticles, metal oxide, etc.) and organic-inorganic hybrids. By employing some representative examples, it will be demonstrated that functionalized CNTs as templates, carriers, immobilizers and transducers are promising for the construction of electrochemical sensors.

Prussian Blue Modified Solid Carbon Nanorod Whisker Paste Composite Electrodes: Evaluation towards the Electroanalytical Sensing ofH2O2

Metallic impurity free solid carbon nanorod “Whiskers” (SCNR Whiskers), a derivative of carbon nanotubes, are explored in the fabrication of a Prussian Blue composite electrode and critically evaluated towards the mediated electroanalytical sensing of H2O2. The sensitivity and detection limits for H2O2on the paste electrodes containing 20% (w/w) Prussian Blue, mineral oil, and carbon nanorod whiskers were explored and found to be 120 mA/(M cm2) and 4.1 μM, respectively, over the concentration range 0.01 to 0.10 mM. Charge transfer constant for the 20% Prussian Blue containing SCNR Whiskers paste electrode was calculated, for the reduction of Prussian Blue to Prussian White, to reveal a value of1.8±0.2 1/s (α=0.43,N=3). Surprisingly, our studies indicate that these metallic impurity-free SCNR Whiskers, in this configuration, behave electrochemically similar to that of an electrode constructed from graphite.

Single-walled carbon nanotube/pyrenecyclodextrin nanohybrids for ultrahighly sensitive and selective detection of p-nitrophenol

Electrochemical detection of p-nitrophenol (P-NP) using a highly sensitive and selective platform based on single-walled carbon nanotube/pyrenecyclodextrin (SWCNT/PyCD) nanohybrids is described for the first time. The electrochemical performance of the SWCNT/PyCD nanohybrid electrode was fully compared with bare glassy carbon, single-SWCNT, single-PyCD, and SWCNT/CD (without pyrene rings) electrodes. Besides the techniques of cyclic voltammetry and chronoamperometric transients, differential pulse voltammetry (DPV) has been used for the detection of P-NP without any interference from o-nitrophenol (O-NP) at the potentials of -0.80 and -0.67 V, respectively. The SWCNT/PyCD nanohybrid electrode is highly sensitive, and it shows an ultrahigh sensitivity of 18.7 μA/μM toward P-NP in contrast to the values reported previously. The detection limit (S/N = 3) of the SWCNT/PyCD nanohybrid electrode toward P-NP is 0.00086 μM (0.12 ppb), which is well below the allowed limit in drinking water, 0.43 μM, given by the U.S. Environmental Protection Agency (EPA). The analytical performance of the SWCNT/PyCD nanohybrid electrode toward P-NP is superior to the existing electrodes.

Vertically aligned single-walled carbon nanotubes by chemical assembly--methodology, properties, and applications

Single-walled carbon nanotubes (SWNTs), as one of the most promising one-dimension nanomaterials due to its unique structure, peculiar chemical, mechanical, thermal, and electronic properties, have long been considered as an important building block to construct ordered alignments. Vertically aligned SWNTs (v-SWNTs) have been successfully prepared by using direct growth and chemical assembly strategies. In this review, we focus explicitly on the v-SWNTs fabricated via chemical assembly strategy. We provide the readers with a full and systematic summary covering the advances in all aspects of this area, including various approaches for the preparation of v-SWNTs using chemical assembly techniques, characterization, assembly kinetics, and electrochemical properties of v-SWNTs. We also review the applications of v-SWNTs in electrochemical and bioelectrochemical sensors, photoelectric conversion, and scanning probe microscopy.

Covalent assembly and micropatterning of functionalized multiwalled carbon nanotubes to monolayer-modified Si(111) surfaces

Multiwalled carbon nanotubes (MWNTs) covalently bound to monocrystalline p-type Si(111) surfaces have been prepared by attaching soluble amine-functionalized MWNTs onto a preassembled undecanoic acid monolayer using carbodiimide coupling. SEM analysis of these functionalized surfaces shows that the bound MWNTs are parallel to the surface rather than perpendicular. The voltammetric and electrochemical impedance spectroscopy measurements reveal that the electron transfer at the MWNT-modified surface is faster than that observed at a MWNT-free alkyl monolayer. We have also demonstrated that it is possible to prepare MWNT micropatterns using this surface amidation reaction and a "reagentless" UV photolithography technique. Following this approach, MWNT patterns surrounded by n-dodecyl areas have been produced and the local electrochemical properties of these micropatterned surfaces have been examined by scanning electrochemical microscopy. In particular, it is demonstrated that the MWNT patterns allow a faster charge transfer which is consistent with the results obtained for the uniformly modified surfaces.

Optimized carbon nanotube fiber microelectrodes as potential analytical tools

The preparation and interesting electrochemical properties of carbon nanotube (CNT) fiber microelectrodes are reported. By combining the advantages of CNT with those of fiber electrodes, this type of microelectrode differs from CNT-modified or CNT-containing composite electrodes, because they are made solely of CNT without other components, for example additives or binders. The performance of these electrodes has been characterized with regard to, among others, the electrocatalytic oxidation of analytes via dehydrogenase-mediated reactions. In this context the reversible regeneration of the coenzyme NAD(+) using a mediator is a key step in the development of new amperometric sensor devices and we have successfully immobilized mediator molecules that are very efficient for this purpose on the surface of the CNT fiber electrode. The microelectrodes thus obtained have been compared with classic carbon microelectrodes and have promising behavior in biosensing applications, especially after specific pretreatments such as CNT alignment inside the fiber or expansion of the specific surface by chemically induced swelling.

Wet chemical needlelike assemblies of single-walled carbon nanotubes on a silicon surface

Single-walled carbon nanotubes (SWCNT) have been organized covalently to form a uniform needlelike structure on a silicon surface using a wet chemical assembly technique. In this work, we successfully combine silanization with the condensation reaction of the carboxylic group with the amino group.