This paper describes the fabrication and evaluation of a chemically modified carbon ink microelectrode to detect thiols of biological interest. The detection of thiols, such as homocysteine and cysteine, is necessary to monitor various disease states. The biological implications of these thiols generate the need for miniaturized detection systems that enable portable monitoring as well as quantitative results. In this work, we utilize a microchip device that incorporates a micromolded carbon ink electrode modified with cobalt phthalocyanine to detect thiols. Cobalt phthalocyanine (CoPC) is an electrocatalyst that lowers the potential needed for the oxidation of thiols. The CoPC/carbon ink composition was optimized for the micromolding method and the resulting microelectrode was characterized with microchip-based flow injection analysis. It was found that CoPC lowers the overpotential for thiols but, as compared to direct amperometric detection, a pulsed detection scheme was needed to constantly regenerate the electrocatalyst surface, leading to improved peak reproducibility and limits of detection. Using the pulsed method, cysteine exhibited a linear response between 10-250 microM (r(2) = 0.9991) with a limit of detection (S/N = 3) of 7.5 microM, while homocysteine exhibited a linear response between 10-500 microM (r(2) = 0.9967) with a limit of detection of 6.9 microM. Finally, to demonstrate the ability to measure thiols in a biological sample using a microchip device, the CoPC-modified microelectrode was utilized for the detection of cysteine in the presence of rabbit erythrocytes.

Dynorphin A 1–17 is an endogenous neuropeptide implicated in a variety of neurological disorders including Alzheimer’s and Parkinson’s diseases and neuropathic pain. Metabolites of this peptide can exhibit their own unique effects in vivo, and it is possible that one of these metabolites is responsible for the neurotoxicity. In this article, the use of CE for the separation of dynorphin A 1–17 from four of its metabolites is described. Buffer additives were investigated to eliminate peptide adsorption to the capillary wall and to improve resolution between closely related metabolites. On-capillary copper complexation was employed and was shown to improve separation efficiency as compared with the separation of native peptides. The method was then applied to in vitro dynorphin metabolism in human plasma as well as rat brain and rat spinal cord slices.

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Electrochemical detection has proved to be an invaluable tool for analytical applications in a variety of research areas including environmental analysis, materials research, bioanalysis, and neuroscience. While some electrochemical techniques function as stand‐alone methods, a few techniques, including amperometry, conductivity, and voltammetry, have been found to be useful as detectors for separation‐based methods. Electrochemistry (EC) has the ability to provide chemical reduction/oxidation (redox) information about the analytes of interest and can be utilized for direct, quantitative analysis if the number of electrons in the redox process is known. Additional advantages of electrochemical detection include low detection limits, high selectivity, portability, low cost, and the ability to miniaturize the system without a loss in sensitivity. This article focuses on the principles and applications of EC detection in liquid chromatography (LC), capillary electrophoresis (CE), and microchip electrophoresis (ME) systems. Topics include an overview of electrochemical detection schemes and electrode materials, a brief introduction to LC, CE, and ME, and discussions of applications of the above‐mentioned detection schemes to these separation methods.