Review: The increasing importance of carbon nanotubes and nanostructured conducting polymers in biosensors

The growing need for analytical devices requiring smaller sample volumes, decreased power consumption and improved performance have been driving forces behind the rapid growth in nanomaterials research. Due to their dimensions, nanostructured materials display unique properties not traditionally observed in bulk materials. Characteristics such as increased surface area along with enhanced electrical/optical properties make them suitable for numerous applications such as nanoelectronics, photovoltaics and chemical/biological sensing. In this review we examine the potential that exists to use nanostructured materials for biosensor devices. By incorporating nanomaterials, it is possible to achieve enhanced sensitivity, improved response time and smaller size. Here we report some of the success that has been achieved in this area. Many nanoparticle and nanofibre geometries are particularly relevant, but in this paper we specifically focus on organic nanostructures, reviewing conducting polymer nanostructures and carbon nanotubes

Indirect electroanalytical detection of phenols

A novel indirect electrochemical protocol for the electroanalytical detection of phenols is presented for the first time. This methodology is demonstrated with the indirect determination of the target analytes phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol through an electrochemically adapted optical protocol. This electrochemical adaptation allows the determination of the above mentioned phenols without the use of any oxidising agents, as is the case in the optical method, where pyrazoline compounds (mediators) chemically react with the target phenols forming a quinoneimine product which is electrochemically active providing an indirect analytical signal to measure the target phenol(s). A range of commercially available pyrazoline substitution products, namely 4-dimethylaminoantipyrine, antipyrine, 3-methyl-1-(2-phenylethyl)-2-pyrazolin-5-one, 3-amino-1-(1-naphthylmethyl)-2-Pyrazolin-5-one, 4-amino-1,2-dimethyl-3-pentadecyl-3-pyrazolin-5-one hydrochloride, 3-amino-1-(2-amino-4-methylsulfonylphenyl)-2-pyrazolin-5-one hydrochloride and 4-aminoantipyrine are evaluated as mediators for the indirect detection of phenols. The indirect electrochemical detection of phenol, 2-chlorophenol, 4-chlorophenol and 2,4-dichlorophenol through the use of 4-aminoantipyrine as a mediator are successfully determined in drinking water samples at analytically useful levels. Finally, the comparison of the direct (no mediator) and the proposed indirect determination (with 4-aminoantipyrine) towards the analytical detection of the target phenols in drinking water is presented. The limitation of the proposed electroanalytical protocol is quantified for all the four target phenols

Carbon-Supported Palladium-Cobalt-Noble Metal (Au, Ag, Pt) Nanocatalysts as Methanol Tolerant Oxygen-Reduction Cathode Materials in DMFCs

The carbon-supported nanoparticles of Pd–Co–M (M = Pt, Au, Ag) catalysts for direct methanol fuel cells (DMFCs) in a ratio of (70:20:10) were prepared through reverse microemulsion method. The X-ray diffraction (XRD) analysis showed well-defined reflections corresponding to a face centered cubic phase of palladium. From transmission electron microscopy analysis, the particle size after heat-treatment at 500°C was found to be approximately 20 nm, which was also confirmed by XRD analysis. Polarization data indicated Pd–Co–Pt to have better oxygen reduction reaction (ORR) activity than the other combinations with Ag and Au, in terms of shift in onset potential to a positive value of more than 100 mV and increased reduction current. The ORR kinetics on Pd–Co–Pt was analyzed by using rotating disk electrode to follow a 4 electron pathway, the order of the reaction being unity. The peroxide formation estimated from the rotating ring disk electrode measurements was found to be a negligibly small amount of 1.1%. An additional advantage observed with Pd–Co–Pt was its high methanol tolerance and ORR activity nearly equal to Pt

Synthesis of Nitrogen Doped Carbon and Its Enhanced Electrochemical Activity towards Ascorbic Acid Electrooxidation

Nitrogen doped carbon, synthesized by a novel way of carbonizing polyaniline in an inert atmosphere at a constant temperature of 800∘C, exhibits several unique features.The carbon: nitrogen ratio is found to increase with the treatment duration up to 120 minutes and a mass reduction of 60 wt% is observed with an interesting observation of the retention of the bulk polymer morphology, surprisingly, even after the carbonization process. The electrochemical activity evaluated with potassium hexacyanoferrate and hexamine ruthenium redox systems at a regular time interval helps to tune the catalytic activity. This type of nitrogen doped carbon prepared from polyaniline base exhibits excellent electrocatalytic activity as illustrated by the oxidation of ascorbic acid in neutral mediu

Inhibition of corrosion of mild steel by ammonium pyrrolidene dithiocarbamate in 1 m hydrochloric acid

Inhibition of corrosion of mild steel in 1 M hydrochloric acid solution by Ammonium pyrrolidene dithiocarbamate (APDe) was evaluated using weight loss, polarisation and electrochemical impedance techniclues. Uesults obtained through the above mentioned techniques indicated that inhibition efl"iciency (IE) increased with concentration of inhibitor, thus reaching a maximum efficiency of 95% at 1 x to-I M. The rise in temperature did not alter the corrosion rate of mild steel drastically at higher inhibitor concentration. The adsorption of inhibition followed Langmuir isotherm. TIle activation energies generally increased with concentration revealing chemisorption of inhibitor on the mild steel surface. Surface analysis by XRD and {IV-luminescence emission spectra were also carried out to establish the mechanism of corrosion inhibition

Carbon-Supported Palladium–Polypyrrole Nanocomposite for Oxygen Reduction and Its Tolerance to Methanol

Carbon-supported palladium–polypyrrole Pd–PPy/C nanocomposite was synthesized by oxidative polymerization of pyrrole and reduction of palladium(II) precursor salt in the presence of Vulcan XC-72R. The Pd–PPy/C composites were characterized by X-ray diffraction (XRD), Fourier transform IR, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The XRD analysis of Pd–PPy/C shows the formation of the face-centered cubic structure of Pd particles and the mean particle size calculated from TEM was 5.3 2.0 nm. The electrochemical stability of Pd–PPy/C was examined by cyclic voltammetry in an acid solution. The thermal stability and Pd loading in the composite was assessed using TGA. The introduction of Pd in the conducting PPy/C matrix gives better catalytic activity toward oxygen reduction with resistance to methanol oxidation. This was further elucidated by the XPS analysis showing d-band vacancy that is attributed to metal–polymer interaction. From the polarization studies, it is observed that even in the presence of methanol there is no significant cathodic shift in the half-wave potential, revealing that Pd–PPy/C is tolerant to methanol. Rotating ring disk electrode studies show that there is only a negligible quantity of hydrogen peroxide produced in the potential region where its production is expected to be high. This confirms that Pd–PPy/C catalyzes reduction of oxygen directly to water through a four-electron pathway

Cyclic voltammetric studies on the electrochemical behaviour of cupronickel in sodium chloride solution

The electrochemical behavior of the dissolution of cupronickel in aqueous sodium chloride solutions was investigated through cyclic voltammetric and X-ray diffraction studies. The investigation analyses the discrepancies existing in the ideas related to cupronickel dissolution whether selective dissolution/simultaneous dissolution. Anodic dissolution of cupronickel alloys is found to be potential dependent. Selective dissolution takes place at lower potentials and simultaneous dissolution at higher potentials. The rate of simultaneous dissolution of the alloy is lower than that of the anodic dissolution of pure coppe