Binding Sensors

2 AFFINITY SENSORS BASED ON PROTEINS AND ENZYMES 4.2.1 Binding Sensors 

Many binding sensors make use of the unique, antibody-like properties of lectins. These plant proteins are capable of binding certain 

Aizawa (1982) patented a lectin electrode based on the binding of horseradish peroxidase via its carbohydrate groups to con A immobilized on a hydrogen peroxide sensitive probe. The bound enzyme activity was determined from the H2O2 consumption catalyzed by HRP. 

Analyte Immobilized species Principle Transducer References 

Mannan con A difference measurement between active and blocked con A electrode Pt electrode Janata (1975) 

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In the literature the two basic types of biosensors are also called binding sensors and catalytic sensors. 

Affinity sensors The biologically active components of affinity sensors represent affinity ligands whose behavior has already been explained (see 3.3). The interaction between the sensor-attached affinity ligand and the corresponding counterpart of the chosen affinity interaction (i.e., analyte) may be monitored either directly (these biosensors are called direct or binding sensors) or indirectly by using a suitable label (e.g., an enzyme). 

A dye displacement assay is primarily a colorimetric competitive binding sensor system where an analyte displaces a dye from a receptor this displacement results in some color change that can be related to the amount of analyte present. Pioneering reports in this arena include the seminal protocols of Anslyn " and Buryak and Severin. ... 

Radloff D, Matern C, Plaschke M, Simon D, Reichert J, Ache HJ (1996) Stability improvement of an optochemical heavy metal ion sensor by covalent receptor binding. Sensor Acmat B Chem 35 207-211... 

Lawrence, D. S. Sharma, V. Agnes, R. S. Deeply quenched enzyme sensors and protein-protein binding sensors. PCX Int. Appl. WO 2008070152, 2008 Chem. Abstr. 2008, 149, 26898. 

Enzyme Immunosensors. Enzyme immunosensors are enzyme immunoassays coupled with electrochemical sensors. These sensors (qv) require multiple steps for analyte determination, and either sandwich assays or competitive binding assays maybe used. Both of these assays use antibodies for the analyte of interest attached to a membrane on the surface of an electrochemical sensor. In the sandwich assay type, the membrane-bound antibody binds the sample antigen, which in turn binds another antibody that is enzyme-labeled. This immunosensor is then placed in a solution containing the substrate for the labeling enzyme and the rate of product formation is measured electrochemically. The rate of the reaction is proportional to the amount of bound enzyme and thus to the amount of the analyte antigen. The sandwich assay can be used only with antigens capable of binding two different antibodies simultaneously (53). 

The eonerete examples of seleetive binding eeotoxieants of different nature are eonsidered with partieipation of paramagnetie eenters. The questions of ereation on the base of this materials sensitive sensor and materials -eoneentrators for analytieal determination of eeotoxieants traees in water medium are diseussed. 

Possible applications of MIP membranes are in the field of sensor systems and separation technology. With respect to MIP membrane-based sensors, selective ligand binding to the membrane or selective permeation through the membrane can be used for the generation of a specific signal. Practical chiral separation by MIP membranes still faces reproducibility problems in the preparation methods, as well as mass transfer limitations inside the membrane. To overcome mass transfer limitations, MIP nanoparticles embedded in liquid membranes could be an alternative approach to develop chiral membrane separation by molecular imprinting [44]. 

Dihydropyridine receptor (DHPR) is a member of voltage-dqiendent Ca2+ channels (CaVi, L-type), which specifically binds to dihydropyridine derivatives, a group of the Ca2+ channel blockers. Cav 1.1 works as the voltage sensor for skeletal muscle contraction, and Cay 1.2, as Ca2+-influx channel for cardiac muscle contraction. 

Conventional and novel PKC isozymes are potently activated by phorbol esters, heterocyclic compounds found in the milky sap exuded by plants of the Euphorbiaccae family. This sap was used medicinally as a counterirritant and cathartic agent over the millennia we now know that the active ingredients, phorbol esters, specifically bind to the Cl domain, the diacylglycerol sensor described above. In fact, their ability to recruit PKC to membranes is so effective that phorbol esters cause maximal activation of conventional PKCs, bypassing the requirement for Ca2+. This module is found in a number of other proteins in addition to PKC, so the profound effects of phorbol esters on cells are mediated by other proteins in addition to PKC. 

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