Amperometric detection in the presence of carbon nanotubes dispersed in background electrolyte: Evaluating its suitability for capillary electrokinetic chromatography separations of polyphenolic compounds.

This work reports on the positive effects observed upon both the separation and analytical signals in electrophoretic separations of selected phenolic compounds when using aqueous BGE containing carbon nanotubes (CNTs) in connection to electrochemical detection (ECD). The influence of the presence of surfactant-coated CNTs in the BGE upon the amperometric response of probe compounds was evaluated under hydrodynamic regime in capillary flow injection experiments as well as electrophoretic separations. Among the surfactants employed to disperse CNTs within BGE, SDS shows the best results in terms of dispersion stability and degree of dispersion of the CNTs. ECD allows working with BGEs containing CNTs concentrations of, at least, 24.0 mg/L without increasing of baseline noise, on the opposite to that reported when using UV-visible detection, and the presence of CNTs in the BGE improves the electrochemical response of some of the tested compounds. These benefits were reflected in higher sensibility in the electrochemical signal and additional improved resolution in the electrophoretic separation of (±)-catechin and sinapic acid when using these BGE containing CNTs.

Biocatalytically induced formation of cupric ferrocyanide nanoparticles and their application for electrochemical and optical biosensing of glucose.

The enzymatically controlled growth of cupric ferrocyanide nanoparticles in the presence of glucose oxidase, its ferricyanide electron acceptor, and copper ions is described. The biocatalytically stimulated growth of these nanoparticles on the surface of carbon-paste electrodes results in an amplified electrochemical detection of the glucose substrate. This concept can readily be expanded for monitoring a wide range of biocatalytic processes involving the ferricyanide electron acceptor.

Analytical applications of glassy carbon electrodes modified with multi-wall carbon nanotubes dispersed in polyethylenimine as detectors in flow systems.

This work reports the advantages of using glassy carbon electrodes (GCEs) modified with multi-wall carbon nanotubes (CNT) dispersed in polyethylenimine (PEI) as detectors in flow injection and capillary electrophoresis. The presence of the dispersion of CNT in PEI at the electrode surface allows the highly sensitive and reproducible determination of hydrogen peroxide, different neurotransmitters (dopamine (D) and its metabolite dopac, epinephrine (E), norepinephrine (NE)), phenolic compounds (phenol (P), 3-chlorophenol (3-CP) and 2,3-dichlorophenol (2,3CP)) and herbicides (amitrol). Sensitivities enhancements of 150 and 140 folds compared to GCE were observed for hydrogen peroxide and amitrol, respectively. One of the most remarkable properties of the resulting electrode is the antifouling effect of the CNT/PEI layer. No passivation was observed either for successive additions (30) or continuous flow (for 30 min) of the compounds under investigation, even dopac or phenol. A critical comparison of the amperometric and voltammetric signal of these different analytes at bare- and PEI-modified glassy carbon electrodes and pyrolytic graphite electrodes is also included, demonstrating that the superior performance of CNT is mainly due to their unique electrochemical properties. Glassy carbon electrodes modified with CNT-PEI dispersion also show an excellent performance as amperometric detector in the electrophoretic separation of phenolic compounds and neurotransmitters making possible highly sensitive and reproducible determinations.

Nanoparticle-based assays of antioxidant activity.

The antioxidant power of several phenolic acids and related food samples is estimated from the generation and growth of gold nanoparticles. The intensity of the resulting particle plasmon absorption bands correlates well with the redox characteristics of these phenolic acids estimated from cyclic voltammetry experiments. The highest capacity of reducing gold(III) to gold nanoparticles corresponds to the highest antioxidant activity, consistent with the tendency of phenolic acids to donate electrons.