Antibodies affinity biosensors

Main types of biomolecular recognition elements used in affinity biosensors based on spectroscopy of guided modes include antibodies, nucleic acids and biomimetic materials. Antibodies are used most frequently because of their high affinity, versatility, and commercial availability. 

None of the involved species are fluorescent. Therefore, for fluorescence signaling of citrate recognition, carboxyfluorescein is first added to the medium because binding to the receptor in the absence of citrate is possible and causes deprotonation of carboxyfluorescein, which results in high fluorescence. Citrate is then added, and because it has a better affinity for the receptor than carboxyfluorescein, it replaces the latter, which emits less fluorescence in the bulk solvent as a result of protonation. Note that this molecular sensor operates in a similar fashion to antibody-based biosensors in immunoassays. It was succes-fully tested on a variety of soft drinks. 

Various types of biomolecular recognition elements have been exploited in affinity biosensors. These include antibodies ", aptamers, peptides , and... 

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... 

A biosensor is a sensing device that is integrated within or intimately associated with a physical transducer. Such a system quantifies electronic signals arising from the interaction between a biosensor and an analyte of interest. Catalytic biosensors use enzymes, microorganisms, or whole cells to catalyze a reaction with the target analyte, while affinity biosensors utilize antibodies, receptors, or nucleic acids to bind with the target analyte. 

Zeder-Lutz, G., Altschuh, D., Geysen, H. M., Trifilieff, E., Sommermeyer, G., Van and Rcgenmortel, M. H. V. Monoclonal antipeptide antibodies - Affinity and kinetic rate constants measured for the peptide and the cognate protein using a biosensor technology. Molec. Immunol. 1993, 30, 145-155. 

Bresler H S era/ 1992 Application of capacitive affinity biosensors HIV antibody and glucose detection Biosensor Design and Application ed P R Mathewson and J W Finley (Washington, DC American Chemical Society) pp 89-104 Keese C R and Giaver I 1994 A biosensor that monitors cell morphology with electrical fields IEEE Eng. Med. Biol. Mag. 13 402-8 Bao J-Z er al 1993 Impedance spectroscopy of human erythrocytes system calibration and nonlinear modelling IEEE Trans. Biomed. Eng. BME-40 364-78... 

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... 

Conversely, the development of affinity biosensors constitutes a field of application where monolayer-modified electrodes are of great importance, as testified by the abundant literature [135-142]. Antibodies, aptamers, and strands of nucleic acids are the most common biological recognition elements used for the selective detection of the target analyte. These biomolecules require to be stably grafted oti the electrode surface through a monolayer without losing their activity [143]. 

VACNT electrodes have been successfully employed with different immobilised biological materials, such as enzymes (catalytic biosensors) and antibodies or DNA (affinity biosensors), for the development of electrochemical biosensors. The characteristics of these different electrochemical biosensors are discussed in the next sections. 

The well-studied biotin-streptavidin system with its extremely high binding affinity (K 10 M" ) is chosen to illustrate the attributes of these LSPR-based nanoscale affinity biosensors. The biotin-streptavidin system has been studied in great detail by SPR spectroscopy and serves as an excellent model system for the LSPR nanosensor. Streptavidin, a tetrameric protein, can bind up to four biotinylated molecules (i.e. antibodies, inhibitors, nucleic acids, etc.) with minimal impact on its biological activity and, therefore, will provide a ready pathway for extending the analyte accessibility of the LSPR nanobiosensor. 

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