Enzyme biosensor

Toxin (Enzyme Inhibition) Biosensors Enzyme affectors (inhibitors and activators) that influence the rate of biocatalytic reactions can also be measured. Sensing probes for organophosphate and carbamate pesticides, for the respiratory... 

Blum L.J., Chemiluminescent flow injection analysis of glucose in drinks with a bienzyme fiber optic biosensor, Enzyme Microb. Technol. 1993 15 407-411. 

The cholinesterase to determine the toxic activity may be chosen (i) in pure form of commercial enzyme from animals in a water buffer solution or using biosensors, enzyme preparation impregnated into a rigid matrix that significantly activates the enzymic activity and (ii) in the form of crude extracts from plant or animal tissues. 

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. 

Biocatalytic recognition by purified enzymes is the most common mechanism used in design of biosensors. Enzymes are biological catalysts that facilitate conversion of substrate into products by lowering activation energy of the reaction. They are proteins or glycoproteins, and biorecognition properties depend almost entirely on the amino acids of the exposed surface of enzyme molecule. 

Keywords Biosensors, Enzyme thermistor, Process monitoring, Enzyme Technology, Biotransformation. 

Different biospecific interaction processes may be considered for the construction of biosensors. Enzymes, antibodies, lectins, hormones, microorganisms, organelles, or tissue sections can be used to act as molecular... 

Two fundamentally different types of competing reactions can be utilized in biosensors enzyme competition, i.e., the competition of different enzymes for one and the same substrate, and substrate competition,... 

Faschi S., Ogoriczyk D., Palchetti I., Mascini M., (2007) Evaluation of pesticide-induced acetylcholinesterase inhibition by means of disposable carbon-modified electrochemical biosensors. Enzyme Microb. Technol., 40, 485-489... 

One can conclude that the use of amperometric and potenriometric biosensots has achieved a considerable progress in the determination of hydrogen peroxide. The redox-enzyme and electrode structure achieved by many provides the basis for electrochemical biosensors. Enzymes need to be modified either by mutagenesis, or site-specific reactions that would provide structures with readily accessible sites. Many of the latter could be accomplished with the aid of a mediator. 

Glassy carbon Protein fusion to affinity tag Biosensor/enzyme-Unked immunoassays [95]... 

The most often used recognition elements for the construction of biosensors are enzymes. Their catalytic activity usually derives from prosthetic groups (nonproteins such as heme, FAD, or pyridox-alphosphate) or metal ions. The prosthetic groups are usually covalently bound to the enzyme, while coenzymes or cosubstrates are only associated with it, binding in close proximity to the substrate binding site during the catalytic action. For their application in biosensors, enzymes have to be isolated from the biological... 

Kang CD, Lee SW, Park TH, Sim SJ. Performance enhancement of real-time detection of protozoan parasite, Cryptosporidium oocyst by a modified surface plasmon resonance (SPR) biosensor. Enzyme Microb Technol 2006 39 387-390. 

Langmuir-Blodgett layers have a structure similar to that of natural cell membranes. They thus play an important role in biosensors. Enzymes and antibodies can be attached in this way to ISFET gates or to surface acoustic wave (SAW) sensors. 

In order to make a useful biosensor, enzyme has to be properly attached to the transducer with maintained enzyme activity. This process is known as enzyme immobilization. The choice of immobilization method depends on many factors such as the nature of the enzyme, the type of transducer used, the physiochemical properties of analyte, and the operating conditions [73]. The major requirement out of all these is its maximum activity in immobilized microenvironment. Enzyme-based electrodes provide a tool to combine selectivity of enzyme toward particular analyte and the analytical power of electrochemical devices. The amperometric transducers are highly compatible when enzymes such as urease, generating electro-oxidizable ions, are used [74]. The effective fabrication of enzyme biosensor based on how well the enzyme bounds to the transducer surface and remains there during use. The enzyme molecules dispersed in solutions will have a freedom of their movement randomly. Enzyme immobilization is a technique that prohibits this freedom of movement of enzyme molecules. There are four basic methods of immobilizing enzymes on support materials [75] and they are physical adsorption, entrapment, covalent bonding, and cross-linking, as shown in the Fig. 36. 

Tkac, J., Navratil, M., Sturdik, E., et al., 2001. Monitoring of dihydroxyacetone production during oxidation of glycerol by immobilized Gluconobacter oxydans cells with an enzyme biosensor. Enzyme and Microbial Technology 28,383-388. 

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