Recognition elements in sensors

Self-supported photoresponsive MIP membranes synthesised using a photosensitive monomer, p-phenylazo-acrylanilide, and dansylamine as template, have been applied as recognition element in sensors [207, 208]. The binding capacity of the membrane for dansylamide could be reversibly modified by changing the illumination of membrane. Other examples are NADH and NADPH imprinted membranes... 

Haupt, K. (2004) Molecularly imprinted polymers as recognition elements in sensors. In O.S. Wolfbeis (Ed.) Ultrathin Electrochemical Chemo-and Biosensors. Springer. 

The great potential of this technology has been recognised recently there is now strong development towards the use of molecularly imprinted polymers (MIPs) as recognition elements in sensors [15]. 

Direct measurement of the interaction between the network and the guest molecule, when it is possible to quantify the variations of a property depending on these interactions. For instance, the introduction of fluorescent probes, either via the functionalised monomer or via the guest would allow accurate assessment of any change in the immediate environment of the probes [ 136]. The use of MIPs as recognition elements in sensors led to the development of this approach (see below). 

One of the most promising applications of imprinted networks is their use as recognition elements in sensors [ 145]. A reminder of the principle of action of these sensors is given in Fig. 18. 

Molecularly Imprinted Polymers as Recognition Elements in Sensors Mass and Electrochemical Sensors... 

MIPs can be used as recognition elements in sensors in the same way as other chemical or biochemical... 

MIPs can be used as recognition elements in sensors due to their excellent affinity and cavity for analytes. However, the generation of transducers is still a big challenge. In this section, interesting examples of optical, electrochemical, and mass-sensitive MIP sensors are discussed. 

Another class of biomolecules that can be used as recognition elements in sensors are bioreceptors. These are proteineous species that normally are found in the membranes of biological cells. Many of these proteins have been identified that have a role as signaling agents to provide information transfer between the two sides of a cell membrane— in other words, these molecules are the primitive manifestation of senses (taste, touch, smell, vision) for single cells. Membrane bioreceptors have been identified with a responsiveness to many different substances that either excite cells or to regulate the cell s behavior. Some examples are given below. 

The type of matrix used for immobilization of the recognition element for bacterial cell detection is crucial to achieve high sensitivity. Two important conditions should be considered specifically for bacterial detection (1) the accessibility of the recognition elements in the immobilization matrix for bacteria binding on the sensor surface and (2) to obtain the binding of the analytes within the most sensitive region of the evanescent field, immediately adjacent to the sensor surface. 

The second group of properties is concerned with sensor operation in general and the peculiarities of the recognition element in particular. Ideally, a sensor should be fully reversible. Otherwise, it should lend itself readily to rapid, effective, reliable regeneration in order to be actually reusable. If... 

Kriz D, Kempe M, Mosbach K. Introduction of molecularly imprinted polymers as recognition elements in conductometric chemical sensors. Sens Actual B 1996 33 178-181. 

This technique has also been employed for the preparation of a catalytic imprinted membrane by coating a cellulose membrane with a polymer incorporating particles imprinted with the transition-state analogue of a dehydrofluorination reaction [264]. The application of such an MIP composite membrane as the recognition element in an optical sensor has been reported for digitoxin analysis in serum samples by embedding digitoxin-MIP particles in polyvinyl chloride film in presence of plasticizer by the dry inversion process [265],... 

Most ISEs are based on purely physicochemical and non-catalytic recognition elements solid membranes with fixed ionic sites (e.g. the glass pH electrode), ion-exchange polymer membranes or plasticised hydrogel membranes incorporating ionophores [9], Silicon oxide or metal oxides act as the recognition element in pH-ISFETs, gas-sensitive FETs, solid-state electrolyte, solid-state semiconductor and many conductometric gas sensors. 

During the initial stage of development of UA sensor, researchers used uricase enzyme (UOx) based electrodes for the determination of UA where UOx serves as a molecular recognition element. In the enzyme based electrodes UOx will oxidize UA to allantoin in the presence of 02 and gives away C02 and H202 as side products. The equation for the enzymatic oxidation of UA is ... 

During the last decade the number of application of MIP-based sensors has increased dramatically. The high selectivity and affinity of MIPs for target analytes make them ideal recognition elements in the development of sensors. Capacitive (Panasyuk etal., 2001), conductimetric (Piletsky et al., 1995), field effect (Lahav et al., 2004), amper-ometric (Kritz and Mosbach, 1995), and voltammetric (Pizzariello et al., 2001), electrochemical transduction systems have been used. Sensors based on conductimetric transduction have been developed by Piletsky et al. (1995) for the analysis of herbicides. A system using a TiC>2 sol-gel system, and with a linear range of 0.01-0.50 mg L-1 for atrazine, without interference of simazine, and chloroaromatic acids has been described by Lahav et al. (2004). 

Molecular imprinted polymer-based CL imaging sensors. When using MIP as the recognition element in a CL sensor, the selectivity of the CL method can be greatly improved and the interference of some species commonly present in samples can be eliminated. So, an MIP-based CL sensor can be used directly to determine the analyte in real samples. 

The simplicity of use, the relatively low cost and the broad range of possible guest molecules (small organic molecules, ions but also biological macromolecules) have since led to the important development of this technique, as illustrated by the increasing numbers of publications over recent years [17-25]. The fields of application of these imprinted polymer networks are very diverse. We can mention chromatographic supports (particularly for the separation of enantiomers) recognition elements in the preparation of specific sensors, catalysts, systems for stereospecific synthesis, and selective adsorbents. 

MIPs find uses in four main types of application separation of molecules, preparation of antibody analogues, recognition elements for sensors, stereoselective reactions and catalysis. 

The simplest approach to sensor 20 was to start with the diamine recognition elements in place.Thus, trityl alcohol 24a was prepared in three steps from ethyl aminobenzoate as shown in Scheme 10. Conversion of the trityl alcohol to the trityl acetylene was attempted using the typical procedure. Unfortunately, the diamine recognition elements did not survive these conditions, yielding only decomposition, though a variety of permutations were explored. A similar fate was met with several potential precursors to the desired diamine appended trityl acetylene (e.g., 24b and... 

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