Multiwall carbon nanotubes (MWCNTs) are filled in the cavity at the tip of a microelectrode to form a carbon nanotubes powder microelectrode (CNTs-PME). CNTs-PME was used to study electrochemical properties of superoxide anion in aprotic media. The reversibility of the oxygen/superoxide anion couple (O(2)/O(2)(.-)) at the different powder microelectrode in different aprotic media was compared by cyclic voltammetry (CV). The result indicated that the nearly reversible redox process of the O(2)/O(2)(.-) couple was obtained at a CNTs-PME. The heterogeneous electron transfer rate constant (k(s)) can be measured by steady-state voltammogram and the result is 4.7 x 10(-3) cm s(-1), suggesting that the electrode reaction is a nearly reversible process as expected. The scavenging activities of bilirubin, alpha-tocopherol (vitamin E), are examined, and the experimental results confirm that alpha-tocopherol is the better scavenger toward O(2)(.-) between them. 相似文献
A facile approach to polymer nanocomposites with single‐wall carbon nanotubes and cationic polymers is reported. The composite material was synthesized by producing carboxylic acid groups at the nanotube termini followed by a reaction with poly(allylamine) in water. Fourier transform infrared spectral and thermogravimetric analyses corroborate that the poly(allylamine) chains were wrapped on the surface of the carbon nanotubes. The scanning electron microscopic (SEM) image shows that the nanotubes were dispersed with little aggregation, thus, strongly suggesting that the poly(allylamine) chains have covered the single‐wall carbon nanotubes, which was further evidenced by transmission electron microscopy. The composites are soluble in water, and this solubilization process opens up new opportunities in the solution chemistry on pristine nanotubes.
In this paper, we report a new technique to pattern carbon microelectrodes for use in microfluidics. This technique, termed micromolding of carbon inks, uses poly(dimethylsiloxane)(PDMS) microchannels to define the size of the microelectrode. First, PDMS microchannels of the approximate dimensions desired for the microelectrode are made by soft lithography. The PDMS is then reversibly sealed to a substrate and the microchannels are filled with carbon ink. After a heating step the PDMS mold is removed, leaving a carbon microelectrode with a size slightly smaller than the original PDMS microchannel. The resulting microelectrode (27 microm wide and 6 microm in height) can be reversibly sealed to a PDMS-based flow channel. Fluorescence microscopy showed that no leakage occurred around the chip/electrode seal, even up to flow rates of 10 microL min(-1). The electrode was characterized by microchip-based flow injection analysis. Injections of catechol in Hank's Balanced Salt Solution (pH 7.4), showed a linear response from 2 mM to 10 microM (r(2)= 0.995), with a sensitivity of 56.5 pA microM(-1) and an estimated limit of detection of 2 microM (0.27 picomole, S/N=3). Reproducibility of the electrode response was shown by repeated injections (n= 10) of a 500 microM catechol solution, resulting in a RSD of 4.6%. Finally, selectivity was demonstrated by coating the microelectrode with Nafion, a perfluoronated cation exchange polymer. Dopamine exhibited a response at the modified microelectrode while ascorbic acid was rejected by the Nafion-coating. These electrodes provide inexpensive detectors for microfluidic applications while also being viable alternatives to use of other carbon microelectrode materials, such as carbon fibers. Furthermore, the manner in which the microelectrodes are produced will be of interest to researchers who do not have access to state of the art microfabrication facilities. 相似文献
Carboxylated carbon nanotubes were coated onto carbon microfiber electrodes to create a micron-scale bioelectrode. This material has a high surface area and can serve as a support for immobilization of enzymes such as glucose oxidase. A typical carbon nanotube loading of 13???g?cm?1 yields a coating thickness of 17???m and a 2000-fold increase in surface capacitance. The modified electrode was further coated with a biocatalytic hydrogel composed of a conductive redox polymer, glucose oxidase, and a crosslinker to create a glucose bioelectrode. The current density on oxidation of glucose is 16.6?mA?cm?2 at 0.5?V (vs. Ag/AgCl) in oxygen-free glucose solution. We consider this approach to be useful for designing and characterizing surface treatments for carbon mats and papers by mimicking their local microenvironment.
Figure
Carboxylated carbon nanotubes were coated on a carbon fiber microelectrode as a support for a glucose-oxidizing bioelectrode. Glucose oxidation current density increased linearly with nanotube surface area up to 16.6?mA?cm?2 at 0.5?V (vs. Ag/AgCl) in oxygen-free glucose solution. 相似文献
An ultra-trace voltammetric method was developed for the determination of single strand DNA (ss-DNA) related to the human immunodeficiency virus type 1 (HIV-1). It is based on the signal amplification of carbon nanotubes loaded with silver nanoparticles and placed on a gold microelectrode. The capture ss-DNA (a 21-mer) possessing a thiol group at the 3?? end was self-assembled onto the surface of the gold microelectrode. It was then hybridized with target HIV-1 ss-DNA (a 42-mer) and further hybridized with the electrochemical probe (a 18-mer ss-DNA) tagged with multiwall carbon nanotubes and loaded with silver nanoparticles. The resulting formation of a DNA sandwich conjugate led to a strong electrochemical oxidation signal that was linearly proportional to the concentration of HIV-1 ss-DNA in the range from 1.0 to 100?pM. The detection limit was 0.5?pM (at an S/N of 3). This was equivalent to 0.05?fmol of HIV-1 ss-DNA in a volume of 20???L. The relative standard deviation was 4.0% at 1.0?pM (n?=?11). Non-complementary ss-DNA of HIV-1 ss-DNA was effectively discriminated. This work demonstrates that the employment of the microelectrode and a sandwich hybridization model is promising in terms of sensitive and selective electrochemical detection of DNA.
Figure
Schematic diagram of the sandwich electrochemical detection for DNA hybridization 相似文献
