Biosensor transducing component

Bioanalyzer can be considered another version of commercial biosensors for off-line analysis. It was developed to have capabilities of complete analysis, short response time, specificity, and sensitivity that allows a quick clinical test. Abbott Vision, Boehringer-Mannheim Reflectron, and Kodak Ektachem DT60 (IBI Biolyzer is the new name) are used for cholesterol measurement in doctors offices. Bioanalyzer consists of biological and transducing component that are not physically connected. The uniqueness of this separation provides the versatility of analysis, i.e., use of disposable and different biological component for multi-components measurements. In authors laboratory, Kodak Ektachem DT60 was used successfully to determine cholesterol in some food matrices as well as in off-line process control. The analysis time was only 10 minutes compared to 1-2 days for the GC and HPLC methods. Complicated... 

Fig. 8. Basic components of a biosensor. In the case of an immunosensor, the antibody (or antigen) would be immobilized onto the transducer.

In recent years many efforts have been made to develop immunochemical techniques integrating the recognition elements and the detection components, in order to obtain small devices with the ability to carry out direct, selective, and continuous measurements of one or several analytes present in the sample. In this context biosensors can fulfill these requirements. Biosensors are analytical devices consisting of a biological component (enzyme, receptor, DNA, cell, Ab, etc.) in intimate contact with a physical transducer that converts the biorecognition process into a measurable signal (electrical or optical) (see Fig. 4). In... 

Fig. 4 Schematic representation of a generic biosensor with the essential components (biorecognition element, transducer, and electronic part involved in data processing and display)...

Biosensors are analytical devices that incorporate a biological component and a transducer. These must be in close proximity with one another and preferably in intimate contact, i.e. the biological component immobilized on to the transducer. Such devices are available in disposable forms, e.g. for measurement of blood glucose in diabetic patients, evaluation of the freshness of uncooked meat. Other designs are suitable for continuous use, e.g. on-line monitoring of fermentation processes, the detection of toxic substances. 

Field effect transistors are miniature, solid-state, potentiometric transducers (Figure 4.22) which can be readily mass produced. This makes them ideal for use as components in inexpensive, disposable biosensors and various types are being developed. The function of these semiconductor devices is based on the fact that when an ion is absorbed at the surface of the gate insulator (oxide) a corresponding charge will add at the semiconductor... 

Based on these chemosensors, biosensors can be set up such as glucose or H2O2 sensors. In this case the appropriate biological compound (glucose oxidase or catalase) must be immobilized on the chemosensor. Different optical sensors are also used as transducer elements for the production of biosensors, especially of immuno-sensors. Here the affinity component is immobilized on the tip of the fiber and all available immuno-sensing assays can be performed using this transducer element. Since these sensors cannot be sterilized and used for on-line monitoring in a bioprocess we refer to other publications [25-27]. 

The search for new approaches which can give increasing sensitivity to S PR-based biosensors is associated with the optimization of immobilization of the biological components on the transducer surface. 

Types of biosensors can be named either by the biological components, physical transducing devices, or the measured analytes. Researchers were originally using biological components to define types of biosensors (Table 2). Types of transducers had also been included in the name to identify the physical transducing device, i.e., enzyme electrodes, acoustic-immunosensors, optical biosensors, piezoelectric-immunosensors, and biochips. 

Redox enzymes are the active component in many electrochemical enzyme electrode biosensor devices.1821 The integration of two different redox enzymes with an electrode support, in which one of the biocatalysts is photoswitchable between ON and OFF states, can establish a composite multisensor array. The biomaterial interface that includes the photoswitchable enzyme in the OFF state electrochemi-cally transduces the sensing event of the substrate corresponding to the nonphoto-switchable enzyme. Photochemical activation of the light-active enzyme leads to the full electrochemical response, corresponding to the analysis of the substrates of the two enzymes. As a result, the processing of the signals transduced by the composite biomaterial interface in the presence of the two substrates permits the assay of the... 

The construction principle of any biosensor type is based on the use of two functionally different components (Figure 8.1) a bioselective membrane (a bioselector representing a biologically active, immobilized material) and a physical converter of the chemical signal (a transducer). The bioselector is applied directly to the transducer surface, which transforms... 

A biosensor utilizes a biological component to translate the concentration of a specific analyte of interest into a signal detectable by some chemical or physical means (7). Successful operation of a biosensor requires that the biological component and the signal it transduces be localized to and concentrated within a region in close proximity to the detection system. Immobilization of enzymes within a polymeric matrix ensures concentration and localization of the enzymic reaction, and creates a convective barrier, thus preventing dilution and convective removal of the product species before it is detected. Enzymes immobilized on or near the detection system are frequently used as the... 

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