Carbon nanotubes paste electrode

Electrochemical investigation of dopamine at the water/1,2-dichloroethane interface

Dopamine is an important neurotransmitter in mammalian central and peripheral nervous systems and is also a medicament to cure some neuropsychosis. In this work, ion transfer (IT), facilitated ion transfer (FIT) of protonated dopamine, and electron transfer (ET) between dopamine and ferrocene are investigated at the water/1,2-dichloroethane (W/DCE) interface. The IT and FIT reactions of protonated dopamine can be observed simultaneously within the same potential window. The experimental results demonstrate that dibenzo-18-crown-6, dibenzo-24-crown-8, and benzo-15-crown-5 work well with the protonated dopamine. The amperometric detection of dopamine based on either the IT or the FIT of protonated dopamine can get rid of the interference of ascorbic acid, and the lowest concentration that can be determined is approximately 0.05 microM by differential pulse voltammetry. For the ET reaction, its kinetics can be evaluated by scanning electrochemical microscopy, and the results show that the relationship between rate constants and driving force at the unmodified W/DCE interface obeys the Butler-Volmer equation in a rather wide potential region. When the W/DCE interface is modified by egg lecithin, the ET rate constants decrease with increasing concentration of egg lecithin, which indicates that egg lecithin hinders the ET reaction. When the driving force is increased to a certain degree, the linear relationship between ET rate constants and the driving force is distorted. These results will be helpful to understand both the pharmacodynamics and the neural signal transmission mechanism of dopamine at biological membranes and also provide a novel way to detect dopamine.

Electrochemical sensing platform based on the carbon nanotubes/redox mediators-biopolymer system

A new electrochemical sensing platform was developed that relied on synergy between carbon nanotubes (CNT) and redox mediators that were co-immobilized in the biopolymer chitosan (CHIT). To demonstrate the concept, the redox mediator Toluidine Blue O (TBO) and CNT were integrated in CHIT and used for the determination of a reduced form of nicotinamide adenine dinucleotide (NADH). As compared to CHIT-TBO, the CHIT-TBO/CNT films displayed large amplification of a current due to the TBO-mediated oxidation of NADH at -0.10 V. This was discussed in terms of the TBO/CNT synergy that resulted in the improved charge propagation through the CHIT-TBO/CNT matrix.

Study of carbon nanotube modified biosensor for monitoring total cholesterol in blood

A carbon nanotube modified biosensor for monitoring total cholesterol in blood was studied. This sensor consists of a carbon working electrode and a reference electrode screen-printed on a polycarbonate substrate. Cholesterol esterase, cholesterol oxidase, peroxidase and potassium ferrocyanide were immobilized on the screen-printed carbon electrodes. Multi-walled carbon nanotubes (MWCN) were added to prompt electron transfer. Experimental results show that the carbon nanotube modified biosensor offers a reliable calibration profile and stable electrochemical properties.

Chemically functionalized carbon nanotubes

Since their discovery, carbon nanotubes have attracted the attention of many a scientist around the world. This extraordinary interest stems from their outstanding structural, mechanical, and electronic properties. In fact, apart from being the best and most easily available one-dimensional (1D) model system, carbon nanotubes show strong application potential in electronics, scanning probe microscopy, chemical and biological sensing, reinforced composite materials, and in many more areas. While some of the proposed applications remain still a far-off dream, others are close to technical realization. Recent advances in the development of reliable methods for the chemical functionalization of the nanotubes provide an additional impetus towards extending the scope of their application spectrum. In particular, covalent modification schemes allow persistent alteration of the electronic properties of the tubes, as well as to chemically tailor their surface properties, whereby new functions can be implemented that cannot otherwise be acquired by pristine nanotubes.

Electrochemistry and Electroanalytical Applications of Carbon Nanotubes: A Review

This review addresses recent developments in electrochemistry and electroanalytical chemistry of carbon nanotubes (CNTs). CNTs have been proved to possess unique electronic, chemical and structural features that make them very attractive for electrochemical studies and electrochemical applications. For example, the structural and electronic properties of the CNTs endow them with distinct electrocatalytic activities and capabilities for facilitating direct electrochemistry of proteins and enzymes from other kinds of carbon materials. These striking electrochemical properties of the CNTs pave the way to CNT-based bioelectrochemistry and to bioelectronic nanodevices, such as electrochemical sensors and biosensors. The electrochemistry and bioelectrochemistry of the CNTs are summarized and discussed, along with some common methods for CNT electrode preparation and some recent advances in the rational functionalization of the CNTs for electroanalytical applications.

Ultrasensitive voltammetric detection of trace heavy metal ions using carbon nanotube nanoelectrode array

We describe an ultrasensitive voltammetric detection of trace heavy metal ions using nanoelectrode arrays (NEAs) that are based on low-site density carbon nanotubes (CNTs). The NEAs were prepared by sealing the side-walls of CNTs with an epoxy passive layer that reduces the current leakage and eliminates the electrode capacitance, leading to a low background current. This provides a high signal-to-noise ratio. The CNTs-NEAs coated with a bismuth film were used successfully for voltammetric detection of trace cadmium(II) and lead(II) at the sub-ppb level. The detection limit of 0.04 microg L(-1) was obtained under optimum experimental conditions. The attractive behavior of the new carbon NEA sensing platform holds great promise for onsite environmental monitoring and biomonitoring of toxic metals.

Basal plane pyrolytic graphite modified electrodes: comparison of carbon nanotubes and graphite powder as electrocatalysts

The oxidations of NADH, epinephrine, and norepinephrine are studied using carbon nanotube and graphite powder-modified basal plane pyrolytic graphite electrodes. Immobilization is achieved in two ways: first, via abrasive attachment of multiwall carbon nanotubes or graphite powder by gently rubbing the electrode surface on a fine quality paper supporting the desired material; second, via "film" modification from dispersing either graphite powder or nanotubes in acetonitrile and pipeting a small volume onto the electrode surface and allowing the solvent to volatilize. While electrocatalytic behavior of both types of nanotube-modified electrodes is shown, with enhanced currents and reduced peak-to-peak separations in the voltammetry in comparison with naked basal plane pyrolytic graphite, similar catalytic behavior is also seen at the graphite powder-modified electrodes. Caution is, therefore, suggested in assigning unique catalytic properties to carbon nanotubes.

Biosensing properties of diamond and carbon nanotubes

The biochemical properties of boron-doped diamond (BDD), carbon nanofiber, fullerene, and multiwalled carbon nanotube (MWCNT) electrodes have been investigated comparatively. Physiochemical factors which affect the biosensing properties such as surface hydrophobicities, effective surface area, and intrinsic material properties are studied. Voltammetric responses of the as-grown thin film electrode and surface-modified electrode to biomolecules such as L-ascorbic acid (L-AA), dopamine (DA), and uric acid are examined. As-grown MWCNT electrodes exhibit selective voltammetric responses to the different biomolecules and faster electron-transfer kinetics compared to BDD. The selective response is due to the considerably lower anodic potential of L-AA on MWCNT (-48 mVvs Ag/AgCl compared to 575 mV on BDD). This electrocatalytic response can be replicated on a nonselective carbon nanofiber electrode by coating it with gold nanoparticles. BDD has no intrinsic selective response to L-AA, and surface modification by anodic polarization is necessary for resolving L-AA and DA.

Ultrasensitive electrical biosensing of proteins and DNA: carbon-nanotube derived amplification of the recognition and transduction events

A new strategy for dramatically amplifying enzyme-linked electrical detection of proteins and DNA using carbon nanotubes (CNTs) for carrying numerous enzyme tracers and accumulating the enzymatically liberated product on CNT-modified transducer is described. Such a CNT-derived double-step amplification pathway (of both the recognition and transduction events) allows the detection of DNA and proteins down to 1.3 and 160 zmol, respectively, in 25-50 muL samples and indicates great promise for PCR-free DNA analysis. The new protocol is illustrated for monitoring sandwich hybridization and antibody-antigen interactions in connection with alkaline-phosphatase tracers. The DNA-linking of CNTs and particles holds promise also for assembling hybrid nanostructures relevant to molecular electronic devices.

A novel multi-walled carbon nanotube-based biosensor for glucose detection

The bioelectrochemical characteristics of a novel multi-walled carbon nanotube (MWNT)-based biosensor for glucose detection are studied and compared with those of glassy carbon (GC)-based biosensor. The MWNT-based biosensor exhibits a strong glucose response at applied potentials of 0.65 and 0.45 V versus Ag/AgCl, respectively, while GC-based biosensor shows a weak glucose response at 0.65 V and no response at 0.45 V. Besides, the MWNT-based biosensor shows a high stability of 86.7% of the initial activity to glucose after four-month storage, much higher than 37.2%, the corresponding value for a GC-based biosensor. The detection mechanism of the MWNT-based biosensor is also discussed in detail.