Electrochemical sensors oxidation

The ISFET is an electrochemical sensor based on a modification of the metal oxide semiconductor field effect transistor (MOSFET). The metal gate of the MOSFET is replaced by a reference electrode and the gate insulator is exposed to the analyte solution or is coated with an ion-selective membrane as illustrated in Fig. 

Electrochemical Sensors for Nitrite and Nitric Oxide Determination 492... 

The first interest in the electroreduction of N02 or NO catalyzed by metal complexes is to model the activity of nitrite reductase enzymes.327 There is also an extensive growth in studies related to the development of metal complex-based electrochemical sensors for NO determination in biological and environmental samples 328 329 Nitrate disproportionates to nitric oxide and nitrate in aqueous solution. 

X. Zhang, Real time and in vivo monitoring of nitric oxide by electrochemical sensors - from dream to reality. Front. Biosci. 9, 3434-3446 (2004). 

Non-biological catalysts used for constructing flow-through sensors are typically metal oxides and complexes, in addition to some organic compounds. Most of them act via a redox effect, so they are primarily used with electrochemical sensors (amperometric ones in particular). 

An electrochemical sensor using an array microelectrode was tested for the detection of allergens such as mite and cedar pollen (Okochi et ah, 1999). Blood was used in the assay and the release of serotonin, a chemical mediator of allergic response, which is electrochemically oxidized at the potential around 300 mV, was monitored for electrochemical detection by cyclic voltammetry. 

The history of electrochemical sensors began in the thirties of the twentieth century, when the pH-sensitive glass electrode was deployed, but no noteworthy development was carried out till the middle of that century. In 1956, Clark invented his oxygen-sensor based on a Ft electrode in 1959, the first piezoelectric mass-deposition sensor (a quartz crystal microbal-ance) was produced. In the sixties, the first biosensors (Clark and Lyons, 1962) and the first metal oxide semiconductor-based gas sensors (Taguchi, 1962) started to appear. 

The physiological importance of nitric oxide should also be mentioned. It plays an important role in smooth muscle relaxation, platelet inhibition, neurotransmission, immune regulation, and penile erection (Nobel Prize in 1998 for the discovery of its role in the cardiovascular system). The importance of NO in biological systems stimulated the development of electrochemical sensors and the investigation of the electrochemical behavior of that compound. 

The most obvious way to incorporate this chemistry into an electrochemical sensor is to immobilize the enzyme onto an electrode surface and use this electrode to oxidize the hydrogen peroxide produced. An enzymatic sensor of this type was first prepared by Guilbault and Lubrano [91]. Numerous variations on this theme have since appeared, and sensors that employ this electrochemistry are now commercially available. 

An HPLC method using progressive electrochemical detection of SPA was described by McCabe and Acworth (128). Samples were mixed with hexane, and SPA were extracted with acetonitrile. An HPLC analysis of the extracts was performed, without an evaporation step, on a high-pressure Coul Array system in which analytes were detected on two coulometric array-cell modules, each containing four electrochemical sensors attached in series after the column. Analytes were separated on a Supelcosil LC-18, 5-/tm column using gradient elution and detected at potentials of —50, 0, 70, 250, 375, 500, 675, and 825 mV. To remove oxidative impurities to be coeluted with BHT, a guard cell with applied potential of 900 mV was also placed in the system. 

The four electrochemical sensors were carefully chosen and have two working electrodes of Au and two of Pt. One Au and one Pt electrode are operated at anodic potentials to facilitate oxidations, and the other two are operated at cathodic potentials to facilitate reductions. When an electroactive gas passes through this array, the half-wave potential of the chemical species is not measured. However, by comparing the signals from the sensors in the array, one can tell whether the half-wave potential is above or below 1.0 V vs. the standard hydrogen electrode (nhe). Thus, the array signals from these sensors, while not measuring the thermodynamic half-wave potential, do provide a set of chemical parameters related to the vapor s electrochemical properties. Hence, the term "chemical parameter spectrometry" was chosen to describe this technique. 

Electric arcs, in metal vapor synthesis, 1, 224 Electric-field-induced second harmonic generation Group 8 metallocenes, 12, 109 for hyperpolarizability measurement, 12, 107 Electrochemical cell assembly, in cyclic voltammetry, 1, 283 Electrochemical irreversibility, in cyclic voltammetry, 1, 282 Electrochemical oxidation, arene chromium carbonyls, 5, 258 Electrochemical properties, polyferrocenylsilanes, 12, 332 Electrochemical reduction, bis-Cp Zr(III) and (IV) compounds, 4, 745 Electrochemical sensors biomolecule—ferrocene conjugates... 

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