Enzyme electrode-based biosensors

One of the primary applications of entrapment immobilization has been to prepare enzyme-electrode-based biosensors [27], and one of the first functional enzyme electrodes utilized urease entrapped in an acrylamide film to detect urea using an ammonium ion selective electrode [28]. Highly hydrophobic bilayer lipid membranes and liposomes have also been used to entrap highly labile biomolecules (see chapter 9). Such films and layers are, however, inherently unstable themselves and are useful primarily as research tools. 

Many of the latter requirements are being met for many chemical sensors and for enzyme-electrode-based biosensors and products based on these sensors are commercially available (see chapter 23). Other, more advanced sensors, such as antibody- and receptor-based biosensors, have been commercialized to only a limited extent, primarily due to fabrication and cost limitations. New, simpler, and more cost-effective immobilization methods now being developed will be the driving force for the commercial emergence of these sensors within the next 5-10 years. 

S. Akgol and E. Dinckaya, A novel biosensor for specific determination of hydrogen peroxide catalase enzyme electrode based on dissolved oxygen probe. Talanta 48, 363-367 (1999). 

The quality assessment of food and fodder products requires analysis of protein, carbohydrates and fat. The enzyme electrode-based analyzers originally developed for clinical chemistry have found only limited application in food analysis because they are only suitable for the determination of one parameter, mostly glucose or a disaccharide. The increasing concern for food quality require new types of biosensors allowing residual and hygiene control and on-line measurement of age and freshness (Tschannen, 1988). 

Other biosensor-based diagnostic instruments, such as the enzyme-electrode-based analyzers of YSI for glucose and lactate, are utilized routinely in many clinical laboratories. i-Stat recently introduced a portable analyzer for bedside use which utilizes enzyme-electrode-based assays for glucose and urea, as well as chemical sensor tests for nitrogen, sodium, potassium, and chloride. 

Kulys, J. J., Enzyme Electrodes Based on Organic Metals , Biosensors 2 (1986) 3-13. 

Different lactate oxidising enzymes use different co-substrates and, therefore, a variety of electrochemical indicator reactions in biosensors can be utilised. Most of the lactate biosensors are based on enzymes like lactate oxidase (LOD) and lactate dehydrogenase (LDH). A needle-type lactate biosensor has been recently developed by Yang and coworkers who fabricated poly (1,3-phenylenediamine) electrodes immobilised with LOD for continuous intravascular lactate monitoring [185]. In the enzyme electrodes based on LDH, the biochemical reaction has been coupled to the electrode via NADH oxidation, either directly [119,123,163], or by using mediators [186] or additional enzymes [119]. This may lead to a shift of the unfavourable reaction equilibrium by partial trapping of the reduced cofactor. Direct oxidation of NADH requires potentials of more than 0.4 V ... 

Tliis work demonstrates the potential for application of potentiometric enzyme electrodes based on mediatorless enzyme electrocatalysis for fast and sensitive assay of organophosphorus pesticides. The sensing element based on screen-printed carbon material pomits mass fabrication of the electrodes at a low cost which is essential for the disposable sensor concept. The biosensor does not require any low-molecular weight mediator and can be arranged as an all-solid-state device. Such electrodes. 

In another biosensor construction variant, an enzyme electrode based on tyrosinase immobilized with ordered mesoporous carbon-Au (OMC-Au), L-lysine membrane and Au nanoparticles (tyrosinase/OMC-Au/L-lysine/Au) was combined with ANNs for the simultaneous determination of catechol and hydroquinone in compost bioremediation of municipal solid waste [35]. Limits of detection achieved were below 1 pM, demonstrating this is an appropriate tool for the quantitative study of a composting system. 

Kulys J.J. (1986) Enzymes electrodes based on organic metals. Biosensors, 2, 3-13. 

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. 

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