Sensors mediator-based

Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

Yet the majority of cation sensors are mediator-based sensing. One type of optical sensor is based on the fluorescence quenching of fluor-ophore Rhodamine 6G by transition metals such as Co(II), Cr(III),... 

The fourth type of mediator-based cation optical sensing is using potential sensitive dye and a cation selective ionophore doped in polymer membrane. Strong fluorophores, e.g. Rhodamine-B C-18 ester exhibits differences in fluorescence intensity because of the concentration redistribution in membranes. PVC membranes doped with a potassium ionophore, can selectively extract potassium into the membrane, and therefore produce a potential at the membrane/solu-tion interface. This potential will cause the fluorescent dye to redistribute within the membrane and therefore changes its fluorescence intensity. Here, the ionophore and the fluorescence have no interaction, therefore it can be applied to develop other cation sensors with a selective neutral ionophore. 

Alternatively, mediator-based sensors have been marketed as Glucose Pens - The Medisense Pen - in which the pen s nib is in fact attached to the external part of the sensor. With this sensor, the finger of a patient is pricked and a drop of blood is then placed on the sensor tip. These electroanalytical... 

Ion-selective electrodes (ISEs) with sensor membranes based on sensor molecules plus suitable plasticising solvent mediators are best fabricated with such components physically entangled in a thin poly(vinyl chloride) (PVC) membrane. 

One of the most important categories of ion selective chemical sensors is based on what are called liquid membranes. This term was flrst used in 196U to describe a matrix that is not water soluble it contains either anionic or cationic sites (liquid ion exchangers), which can selectivity facilitate the exchange of inorganic ions. In order to study the active carrier-mediated ion transport through these liquid membranes, a cell such as the one shown in Figure 3.4.4 has been employed. 

Amperometric sensors are based on heterogeneous electron transfer reactions, i.e., the oxidation and reduction of electroactive substances (Fig. 10). Oxygen and H2O2, being the cosubstrate and the product of several enzyme reactions, as well as artificial redox mediators, such as ferricyanide, N-methylphenazinium ion (NMP+), ferrocene, and benzo-quinone may be determined amperometrically. 

Different electrochemical sensors have been developed for cell concentration measurement. The most promising of these sensors are based on impedimetric measurements. A commercial version of a sensor that measures the frequency-dependent i)ermittivity is available from Aber Instruments Ltd [137-139]. Another type of electrochemical probe measures the potential changes in the cell suspension caused by the production of electroactive substances during cell growth [140-143]. To date, no on-line applications of these potentiometric sensors under real cultivation conditions have been reported. Other types of probes, such as amperometric and fuel-cell sensors, measure the current produced during the oxidation of certain compounds in the cell membrane. Mediators are often used to increase the sensitivity of the technique [143-145]. 

Mizaikoff, B. Lendl, B. (2002). Sensor Systems Based on Mid-infrared Transparent Fibers, In Handbook of Vibratkmal Spectroscopy, J. M. Chalmers P. R. Griffiths (Eds.), John Wiley Sons Ltd., ISBN 0471988472, Chichester Pippel, D. J. Weisenburger, G. A. Faibish, N. C. Beak, P. (2001). Kinetics and Mechanism of the (-)-Sparteine-Mediated Deprotonation of (E)-N-Boc-N-(p>-methoxyphenyl)-3-cyclohexylallylamine. Journal of the American Chemical Society Vol.123, pp. 4919-4927, ISSN 0002-7863... 

Second-Generation (Mediator-Based) Glucose Sensors... 

Oxygen present in the analyte solution presents a potential problem for enzyme/mediator-based sensors of this type. This is because O2 can also oxidize... 

The mediator-based chemistry used here to detect glucose is well know and interference fix>m other molecules, that might be present in the analyte solution, have been studied in detail (10). For this reason (and because the primary object of the work, to date, has been to provide proof of concept for a general sensor design) we have not yet investigated the effects of these interferences on the response of this prototjnpe sensor. It is important to point out, however, that a number of these potential interferents are anionic (10). Because the rates of anion transport in the sulfonated film used here is low (vide supra), this film should provide some level of protection against these anionic interferents. 

Currently, aU available continuous glucose sensors are based on mediation of electron transfer from the active center of GOx by oxygen or by an immobilized... 

P. Dutta, C.A. Tipple, N.V. Lavrik, P.G. Datskos, H. Hofstetter, O. Hofstetter, and M.J. Sepaniak, Enantioselective sensors based on antibody-mediated nanomechanics. Anal. Chem. 75, 2342—2348 (2003). 

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