Transducers conductometric

Conductometric transducers, as the oldest electrochemical devices, seem not to enjoy wide applications due to their poor selectivity. For example, Yagiuda et al. proposed a conductometric immunosensor for the determination of methamphetamine (MA) in urine [89], The decrease in the conductivity between a pair of platinum electrodes might result from the direct attachment of MA onto the anti-MA antibodies immobilized on the electrode surface. The system was claimed to be a useful detection technique of MA in comparison with a gas chromatography-mass spectrometry method. 

Combined scanning probe techniques 932 Compartmentalized surfaces 921 Competitive immunoassay el80 Composite electrodes 145 material 916 Concanavalin A 313, 317 Conducting polymer 44, 73 based ISE 74 Conductivity e62 Conductometric transducers 241 Conjugate 650 polymer 74... 

Conductometric transducers consist of two pairs of identical electrodes, one of which contains an immobilized enzyme. As the enzyme-catalyzed reaction causes concentration changes in the electrolyte the conductivity alters and can be detected. 

Ivanov, S. Tsakova, V. Mirsky, V. M. Conductometric transducing in electrocatalytical sensors Detection of ascorbic acid. Electrochem. Commun. 2006, 8, 643-646... 

This principle is widely applicable and more or less independent of the nature of the analyte. Another sensor design belonging to the same group is based on conductometric transducers [6-8]. Here, two electrodes are separated by an imprinted polymer, often in the form of a membrane. Binding of the analyte to the polymer changes its conductivity, which is translated into an electrical signal. Acoustic and conductometric transducers are described more in detail below. 

In the sensor technology, conductometric transducer principle is the oldest and widely used strategy. In this type of sensor the detection... 

An ideal sensor recognizes analytes in a sensitive, selective, and reversible manner. This recognition is in turn reported as a clear response. In recent years, conducting polymers have emerged as practical and viable transducers for translating analyte-receptor and nonspecific interactions into observable signals. Transduction schemes include electronic sensors using conductometric and potentiometric methods and optical sensors based on colorimetric and fluorescence methods [1]. 

Electrochemical transducers can be divided into conductometric, potentio-metric and amperometric measuring principles. 

Electrochemical transducers work based on either an amperometric, potentio-metric, or conductometric principle. Further, chemically sensitive semiconductors are under development. Commercially available today are sensors for carbohydrates, such as glucose, sucrose, lactose, maltose, galactose, the artificial sweetener NutraSweet, for urea, creatinine, uric acid, lactate, ascorbate, aspirin, alcohol, amino acids and aspartate. The determinations are mainly based on the detection of simple co-substrates and products such as 02, H202, NH3, or C02 [142]. 

Enzyme sensors can measure analytes that are the substrates of enzymatic reactions. Thermometric sensors can measure the heat produced by the enzyme reaction [31], while optical or electrochemical transducers measure a product produced or cofactor consumed in the reaction. For example, several urea sensors are based on the hydrolysis of urea by urease producing ammonia, which can be detected by an ammonium ion-selective ISE or ISFET [48] or a conductometric device [49]. Amperometric enzyme sensors are based on the measurement of an electroactive product or cofactor [50] an example is the glucose oxidase-based sensor for glucose, the most commercially successful biosensor. Enzymes are incorporated in amperometric sensors in functionalised monolayers [51], entrapped in polymers [52], carbon pastes [53] or zeolites [54]. Other catalytic biological systems such as micro-organisms, abzymes, organelles and tissue slices have also been combined with electrochemical transducers. 

Electrochemical immunoassays include a wide variety of devices based on the coupling of immunological reactions with electrochemical transduction. All of them involve the immobilization of an immunoreagent component on the surface of the electrode transducer. Electrochemical detection is based on the direct intrinsic redox behavior either of an analyte species or of some reporter molecule. For the detection no expensive equipment is needed, with the measurement of either a simple current or a voltage charge. Different electrochemical detection strategies are used, but ampero-metric detection is most widely used. Potentiometric and conductometric detection are applied in different assays as well. 

The type of molecular recognition reaction determines the form of the transducer used (Table 5.3). Enzymatic reactions often involve an electron transfer. This electrical activity can be measured with amperometric, potentiometric or conductometric sensors. If the bioreaction includes the generation of H+ or OH ions, then a pH sensitive dye in combination with an optical device can be used. For antibody-antigen binding, the mass change on the surface of the transducer can be detected with a piezoelectric device. Exothermic or endothermic reactions can be followed with a temperature sensor. 

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