Antibody bioreceptors

The potential use of SERS in biodiagnostic tests has been demonstrated through the use of immobilized monolayers of bioreceptors, including oligonucleotides and antibodies. The use of surface-enhanced Raman gene... 

Bioreceptors Antibodies Lectins Cell membrane receptors Nucleic acids Synthetic molecules... 

The role of bioreceptor can be also played by viruses covalently attached to the electrode surface, which was shown for resistance detection of antibody and prostate-specific membrane antigen.135 Taking into account up to 1020 unique species, phage-displayed libraries provide a vast pool of candidate receptors to practically any analyte, including small molecules, proteins and nucleic acids. Piezoelectric virus sensor has been developed e.g. for detection of distinctive antigens of the human cytomegalovirus.136... 

Use splice by overlap extension (SOE) PCR (43) to randomize up to a five amino acid stretch of the bioreceptor (e.g., a ligand-binding loop of an antibody). A schematic for this technique is shown in Fig. 4. 

Some values of association and dissociation reaction constants for bimolecular bioreceptors are given in figure 7.15, where data are shown for a single analyte, dinitrophenol (DNP), and a variety of monoclonal antibodies. Note that although the equilibrium binding constants range over one millionfold. 

A bioreceptor must be able to react specifically with an analyte of interest. For example, a bioreceptor for cholesterol should react only with cholesterol and not with any other compound in the sample. Biological recognition systems such as enzymes or antibodies offer this high specificity and, in addition, ensure high sensitivity and fast response. Usually, the bioreceptor molecules are immobilised at, or close to, the surface of the transducer. Immobilisation can be achieved by physical adsorption or entrapment by an inert membrane. The bioreceptor can also be covalently bound to functional groups on the surface of the transducer. 

Enzymatic bioreceptors have an advantage insofar as the enzyme regenerates itself after reaction. The enzyme is then available for further reaction with the sample. Thus, the response output is directly related to concentration changes in the sample. Antibodies on the other hand can only be used for a one-time measurement. They have to be disposed after reaction or the antigens have to be washed off with suitable reagents. 

The bioreceptor does not have to be an enzyme or antibody, virtually any compound that exhibits molecular recognition for an analyte is suitable. This could be a piece of DNA, a cell, a microorganism, an organelle or a plant or even mammalian tissue. Enzymes and antibodies are used most often, as they are relatively simple to incorporate into a device. This is more difficult with tissue slices and biological cells as they must be supplied with nutrients and have waste fluids removed in order to keep them alive. 

The functioning of a biosensor can thus be summarised as shown in Fig. 5.18. The analyte is recognised by the bioreceptor, which is usually a protein such as an enzyme or antibody. The protein is in close proximity to the detector. This transduces the recognition event into a signal, which can be amplified and displayed. 

When the immobilized sensing reagent also contains a bioreceptor, such as an enzyme or an antibody, the device is regarded as a biosensor (23). Such sensors hold great promise as they exploit the inherent ability of the bio molecule to selectively and sensitively recognize a particular chemical spedesln a complex matrix. Enzyme-based sensors produce a signal due to a selective enzyme-catalyzed chemical reaction of an analyte and form a product that is detected by a transduction element in the sensor. The... 

Biocomposites can also be easily prepared by adding the bioreceptor (an enzyme [18] and antibody [23], or an affinity receptor such as Protein A [73] or avidin [74,75]). 

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