Determination of dissolved oxygen by catalytic reduction on Nafion-methyl viologen chemically modified electrode.
A small size Nafion-methyl viologen chemically modified electrode (Nafion-MV CME) together with a small size electrolytic cell were constructed for the purpose of dissolved oxygen (DO) determination. The catalytic reduction of DO on Nafion-MV CME results in fast and sensitive DO determination. The mechanism of such detection is also considered.
Metabolic Discrimination of Select List Agents by Monitoring Cellular Responses in a Multianalyte Microphysiometer
Harnessing the potential of cells as complex biosensors promises the potential to create sensitive and selective detectors for discrimination of biodefense agents. Here we present toxin detection and suggest discrimination using cells in a multianalyte microphysiometer (MMP) that is capable of simultaneously measuring flux changes in four extracellular analytes (acidification rate, glucose uptake, oxygen uptake, and lactate production) in real-time. Differential short-term cellular responses were observed between botulinum neurotoxin A and ricin toxin with neuroblastoma cells, alamethicin and anthrax protective antigen with RAW macrophages, and cholera toxin, muscarine, 2,4-dinitro-phenol, and NaF with CHO cells. These results and the post exposure dynamics and metabolic recovery observed in each case suggest the usefulness of cell-based detectors to discriminate between specific analytes and classes of compounds in a complex matrix, and furthermore to make metabolic inferences on the cellular effects of the agents. This may be particularly valuable for classifying unknown toxins.
Electrocatalysis of dioxygen reduction in aqueous acid and base by multimolecular layer films of electropolymerized cobalt tetra(o-aminophenyl)porphyrin
Abstract Films of cobalt(III) tetra(o-aminophenyl)porphyrin, poly-CoToAPP, electrooxidatively polymerized from acetonitriel solutions onto glassy carbon electrodes, exhibit two stable Co(III/II) cyclic voltammetric waves in 0.5 M H2SO4 and 1 M NaOH solutions. The more positive of the two waves predominates at low film coverages (a few monolayer equivalents); the more negative wave grows at high coverages (10–100 monolayers), especially in basic solutions. The two waves are ascribed to monomeric and to dimeric (or higher aggregate) poly-CoToAPP species, respectively, that are distributed unevenly within the film. Both waves exert pronounced catalysis of O2 reduction, but differently; rotated ring-disk voltammetry shows that H2O2 production at potentials of the first (“monomeric”) wave is much greater than that at the second. Electrocatalytic O2 reduction in 1 M NaOH with low coverage films produces considerable H2O2, but high coverage films produce no detectable H2O2 and are stable for a minimum of 104 turnovers of the film sites. The “dimer” poly-CoToAPP in the outer part of high coverage films may serve an efficient dismutase-like action on H2O2 escaping from the principal O2 reduction pathway in the inner, “monomer” part of the film. The rate constant of the O2 reduction on low coverage films is ca. 1×105 M−1 s−1, in acid and in base. Results for acid solutions of Co(III)ToAPP(Cl) are also reported, for comparison to the polymer film results.