Antigens affinity biosensors

Immunosensors are affinity biosensors and are defined as analytical devices that detect the binding of an antigen to its specific antibody by coupling the immunochemical reaction to the surface of a device... 

Antibodies, owing to their unparalleled ability to bind a diverse array of antigens with high affinity and specificity, are essential recognition reagents for numerous biosensor platforms. Most diagnostic immunoassays rely upon monoclonal or polyclonal antibodies derived from animals, and this source of recognition... 

Peptide nucleic acid (PNA) is a powerful new biomolecular tool with a wide range of important applications. PNA mimics the behavior of DNA and binds complementary nucleic acid strands and RNA sequences with high affinity and selectivity. The unique chemical, physical, and biological properties of PNA are exploited to produce powerful biomolecular tools, antisense and antigene agents, molecular probes, and biosensors [50-53]. 

Demonstration of immunospecificity and optimization of the assay for development of evanescent wave biosensors entails several steps. The choice of a fluorescently labeled Ag typically requires the evaluation of the binding characteristics of several tracers which are structurally related to the antigen. This allows the optimal choice of a fluorescent tracer. In the case of evanescent biosensors, the fluorescently labeled antigen tracer must bind to the antibody with sufficient affinity so that a relatively low concentration (e.g., 1 to 100 nM) will yield a reproducible signal, yet show a relatively low affinity as compared to the target analyte to be measured. 

The development of antibody-based biosensors presents more difficulties than enzyme-based biosensors as the antigen-antibody interactions are not readily reversible because of the high values of the affinity constants. Another limitation is that the physicochemical changes resulting from the immunochemical reaction are often insufficient to provide detection limits comparable with those of conventional analysis. As a consequence, indirect systems have been developed that rely on the use of enzyme-or fluorescent-tagged reagents. Both competitive and sandwich formats are used. Evanescent wave-induced fluorescence is frequently chosen to avoid possible interferences from the bulk media. For... 

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