Nitric oxide microsensors

Nitric oxide can be electrochemically oxidized to nitrite and then to nitrate via a three-electron transfer reaction. The overall reaction is  

The oxidation of NO to nitrite and the subsequent oxidation of nitrite to nitrate cannot be clearly discriminated due to their similar oxidation potentials (8). To detect NO electrochemically, the complete three-electron oxidation of NO to nitrate (at ca. 0.9 V vs. Ag/AgCl) at the surface of a working electrode is accomplished (9,10) amperometrically 

Electrochemical oxidation of NO at the surfaces of novel electrode materials (e.g., platinum, gold, glassy carbon, carbon fiber) is known to be kinetically slow. However, accelerated electron-transfer kinetics of NO oxidation have been reported for a variety of chemically modified electrodes with polymeric metalloporphyrin films (11,12) and platinized Pt (13). These electrodes require less positive potentials for NO oxidation to nitrate ( 0.65-0.75 V vs. Ag/AgCl) and generate higher current (5-10 fold) than bare metal electrodes. 

To fabricate NO sensors, chemically modified electrodes are commonly covered with an additional membrane layer. This increases the selectivity for NO by cutting off other easily oxidized and interfering species. A variety of membranes (e.g., cellulose acetate (14, 15), Nafion (16)) have been used to modify the surface of working electrodes via electropolymerization or classic dip coating methods. 

Planar NO microsensors are constructed similarly to the planar metal disk microelectrodes commonly used in scanning electrochonical microscopy (SECM, see Chapter 12). The working electrodes are prepared as follows (i) The metal (e.g., Pt) disk electrode is encased in glass and the surrounding glass sheath reduced as described in Section 6.3.1 and in reference (19). The bare metal electrode is then chonicaUy modified to enhance the kinetics for electrochemical oxidation of NO on its surface. 

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J.H. Shin, S.W. Weinman, and M.H. Schoenfisch, Sol-gel derived amperometric nitric oxide microsensor. Anal. Chem. 77, 3494-3501 (2005). 

X.J. Zhang, L. Cardosa, M. Broderick, H. Fein, and I.R. Davies, Novel calibration method for nitric oxide microsensors by stoichiometrical generation of nitric oxide from SNAP. Electroanalysis 12, 425—428 (2000). 

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T. Malinski and Z. Taha, Nitric-oxide release from a single cell measured in situ by a porphyrinic-based microsensor. Nature 358, 676-678 (1992). 

T. Malinski, F. Bailey, Z.G. Zhang, and M. Chopp, Nitric-oxide measured by a porphyrinic microsensor in rat-brain after transient middle cerebral-artery occlusion. J. Cereb. Blood Flow Metab. 13, 355-358 (1993). 

A. J. Cunningham and J. B. Justice, Jr., Approaches to Voltammetric and Chromatographic Monitoring of Neurochemicals in Vivo, J. Chem. Ed. 1987, 64, A34. Another Nafion-coated electrode can detect 10 10 mol of the neurotransmitter nitric oxide within a single cell [T. Malinski and Z. Taha, Nitric Oxide Release from a Single Cell Measured in Situ by a Porphyrinic-Based Microsensor, Nature 1992, 358, 676]. 

Steven R. Tannenbaum, a member of the Institute of Medicine, has a Ph.D. in food science and technology from the Massachusetts Institute of Technology, where he is currently the codirector and Underwood-Prescott Professor, Division of Bioengineering and Environmental Health, and professor of chemistry, Department of Chemistry. Dr. Tannenbaum s research interests include the chemistry and pathophysiology of nitric oxide, the quantitative measurement of human exposure to carcinogens, and tissue-based microsensors for toxin detection and drug metabolism. He has been a member of the NRC Board on Environmental Studies and Toxicology and has served on several NRC committees. 

Malinski, T., Z. Taha, S. Grunfeld, S. Patton, M. Kapturczak, and P. Tomboulian (1993). Diffusion of nitric-oxide in the aorta wall monitored in-situ by porphyrinic microsensors. Sjoc/jem. Biophys. Res. Commun. 193(3), 1076-1082. 

Kanai, A.J., H.C. Strauss, G.A. Truskey, A. L. Crews, S. Grunfeld, and T. Malinski (1995). Shear-stress induces ATP-independent transient nitric-oxide release from vascular endothelial-cells, measured directly with a porphyrinic microsensor. Cir. Res. 77(2), 284-293. 

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