Affinity biosensors compounds

Results on DNA-based biosensors will be presented they have been used mainly for two kind of applications 1) for the determination of low-molecular weight compounds witlr affinity for nucleic acids and 2) for the detection of hybridization reaction. 

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]. 

Surface-bound, neutral, hydrophilic polymers such as polyethers and polysaccharides dramatically reduce protein adsorption [26-28], The passivity of these surfaces has been attributed to steric repulsion, bound water, high polymer mobility, and excluded volume effects, all of which render adsorption unfavorable. Consequently, these polymer modified surfaces have proven useful as biomaterials. Specific applications include artificial implants, intraocular and contact lenses, and catheters. Additionally, the inherent nondenaturing properties of these compounds has led to their use as effective tethers for affinity ligands, surface-bound biochemical assays, and biosensors. 

Amperometric or voltammetric biosensors typically rely on an enzyme system that catalyt-ically converts electrochemically non-active analytes into products that can be oxidized or reduced at a working electrode. Although these devices are the most commonly reported class of biosensors, they tend to have a small dynamic range due to saturation kinetics of the enzyme, and a large overpotential is required for oxidation of the analyte this may lead to oxidation of interfering compounds as well (e.g., ascorbate in the detection of hydrogen peroxide). In addition to the use in enzyme-based biosensors, amperometric transducers have also been used to measure enzyme-labelled tracers for affinity-based biosensor (mainly immunosensors and genosensors). Enzymes which are commonly used for this purpose include horseradish peroxidase (HRP) [17] and alkaline phosphatase (AP) [18,19,21]. 

In essence, this technique allows for the detection of surface binding interactions in real time without the use of labels. Immunosensors that rely on these principles are commercially available from Biacore AB (formerly Pharmacia Biosensor). These are based on the popular BIACORE 3000, BIACORE 2000 and BIACORE probe instruments in conjunction with disposable sensor chips, which may be purchased with affinity capture chemistries in place (e.g. SA5 Sensor Chips with streptavidin bearing surfaces for capture of biotinylated compounds) [92]. These devices incorporate micro-fluidic systems for delivery of reagents required for analysis and are capable of measuring affinities and kinetics of antibody-antigen interactions in addition to analyte concentrations, which can be determined to the picomolar range [93]. 

DNA or RNA aptamers - the single stranded nucleic acids with high affinity to proteins or to other low and macromolecular compounds, which is comparable with that of antibodies. These special characteristics open new routes in biosensor assembling for further practical applications, such as detection of toxicants in food or environment. 

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