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Mechanism of Histamine Oxidation and Electropolymerization at Carbon Electrodes.

ABSTRACT: Histamine plays an important role in neuromodulation and the biological immune response. Although many electrochemical methods have been developed for histamine detection, the mechanism of its redox reaction has not been directly investigated. Here, we studied the mechanism of histamine oxidation at carbon electrodes and used that mechanistic information to design better fast-scan cyclic voltammetry (FSCV) methods for histamine. Using amperometry, cyclic voltammetry (CV), and X-ray photoelectron spectroscopy (XPS), we demonstrate that histamine oxidation requires a potential of at least +1.1 V vs Ag/AgCl. We propose that histamine undergoes one-electron oxidation on an imidazole nitrogen that produces a radical. The radical species dimerize and continue to undergo oxidation, leading to electropolymerization, which fouls the electrode. CV shows a peak at 1.3 V that is pH dependent, consistent with a one-proton, one-electron oxidation reaction. This mechanism is confirmed using 1- and 3-methylhistamine, which do not electropolymerize, compared to N?-methylhistamine, which does. XPS also revealed a nitrogen-containing product adsorbed on the electrode surface after histamine oxidation. For FSCV detection of histamine at carbon-fiber microelectrodes, histamine oxidation was adsorption-controlled, and the anodic peak was observed at +1.2 V on the backward scan because of the rapid scan rate. However, the oxidation fouled the electrode and convoluted the FSCV temporal response; therefore, we implemented Nafion coating to alleviate the electrode fouling and preserve the time response of FSCV. Knowing the mechanism of histamine oxidation will facilitate design of better electrochemical methods for real-time monitoring of histamine.

SUBMITTER: Puthongkham P

PROVIDER: S-EPMC6777000 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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Mechanism of Histamine Oxidation and Electropolymerization at Carbon Electrodes.

Puthongkham Pumidech P Lee Scott T ST Venton B Jill BJ

Analytical chemistry 20190613 13

Histamine plays an important role in neuromodulation and the biological immune response. Although many electrochemical methods have been developed for histamine detection, the mechanism of its redox reaction has not been directly investigated. Here, we studied the mechanism of histamine oxidation at carbon electrodes and used that mechanistic information to design better fast-scan cyclic voltammetry (FSCV) methods for histamine. Using amperometry, cyclic voltammetry (CV), and X-ray photoelectron ...[more]

PMID: 31194511

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Project description:This paper describes an electropolymerization-based on-chip valving system, accomplished by electrosynthesis of conductive polymeric ionic liquid (CPIL) films at selected points within an array of bipolar electrodes (BPEs), in which each of these wireless electrodes spans an IL-aqueous phase boundary. The low viscosity and high hydrophobicity of the CPIL precursor allow it to be patterned by established microfluidic methods. This advancement has the potential to impact microscale analysis because it allows on-demand creation of solid CPIL microstructures at locations specified by microfluidics, phase boundaries, and electrode potentials. To achieve this outcome, an imidazolium-based IL was functionalized with a pyrrole moiety, and the viscosity was tuned by choosing the appropriate counterion to form a CPIL with the desired viscosity, hydrophobicity, and oxidation potential. This monomer species was then introduced into a microfluidic device, which was prefilled with an aqueous buffer solution. The device comprised many parallel microchannels lined with nanoliter-scale chambers. BPEs interconnected the channels such that the BPE tips were each aligned to a chamber opening. The electrodes contacting the outermost channels were connected directly to a power supply and functioned as driving electrodes. The CPIL displaced the buffer in the channels and established a phase boundary at the opening of each chamber, thereby digitizing the aqueous phase. Finally, an alternating square waveform (under mode 1) was applied for 5 min to yield immobilized polymer films at a location defined by the BPE poles. In total, three modes were developed and three corresponding polymer film patterns were formed. Under mode 2, a DC power supply was used to achieve a dissymmetrical polymer film pattern, and, under mode 3, a regional polymer film pattern was formed under an AC potential with a DC offset. Our preliminary results demonstrate that the generated polymer films are immobile and sufficiently thick to seal the chambers at room temperature over the duration of our observation window (50 min), and this seal is maintained even at elevated temperatures that induce partial evaporation of the chamber contents. A key point is that this method is compatible with a preceding step─dielectrophoretic capture of single melanoma cells within the nanoliter-scale chambers.

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Mechanism of Histamine Oxidation and Electropolymerization at Carbon Electrodes.

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Mechanism of Histamine Oxidation and Electropolymerization at Carbon Electrodes.

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