Enzyme electrode-based biosensors glucose sensor

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. 

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. 

In recent years, there are more applications based on the layer-by-layer fabrication techniques for CNT-modified electrodes. This technique clearly provides thinner and more isolated CNTs compared with other methods such as CNT-composite and CNT coated electrodes in which CNTs are in the form of big bundles. This method should help biomolecules such as enzymes and DNA to interact more effectively with CNTs than other methods, and sensors based on this technique are expected to be more sensitive. Important biosensors such as glucose sensors have been developed using this technique, and further development of other sensors based on the layer-by-layer technique is expected. 

Several implanted biosensors have been developed and evaluated in both animals and humans (see Chapter 4). Detection systems are based on enzymes, electrodes, or fluorescence. The most widely studied method is an electrochemical sensor that uses glucose oxidase. This sensor can be implanted intravenously or subcutaneously. Intravenous implantation in dogs for up to 3 months has demonstrated the feasibility of this approach. Alternatives to enzymes are being developed, including artificial glucose receptors. Less success has been achieved with subcutaneous implants. Implantation of a needle type of sensor into the subcutaneous tissue induces a host of inflammatory responses that alters the sensitivity of the device. Microdialysis with hoUow fibers or ultrafiltration with biologically inert material can decrease this problem. 

In a biosensor application, Wolfson and his research group [10] employed microfabrication techniques to produce miniature electrodes for potential implantable, non-enzyme-based glucose sensors. Thin-film techniques, such as DC magnetron-sputtered processing, were used to deposit platinum film or platinum film enhanced with titanium film on quartz substrates. The geometric shapes of the quartz substrate include cylindrical rods and rectangular plates in a... 

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