Biorecognition molecules

Fig. 14.5 Surface chemistry The OFRR glass surface is biofunctionalized with 3APS. Then biorecognition molecules are immobilized using a cross linker...

One of the key factors in biosensor design is the immobilisation technique used to attach the biorecognition molecule to the transducer surface so as to render it in a stable and functional form. The challenge is to have a stable layer (or layers) of biorecognition molecules that do not desorb from the surface and that retain their activity. Entrapment or encapsulation techniques avoid the chemical changes that usually change the structure of the enzymes and modify their recognition capacity. 

It is well known that affinity biosensors, usually DNA sensors or immunosensors, require a biorecognition molecule that demonstrates a high affinity and specificity for the target biomarker. 

Besides synthetic polymers and small molecules, biological or bioactive species are used in the functionalization of carbon nanotubes not only for water solubility but also enhanced biocompatibilities and biorecognition capabilities. Various proteins, DNAs, and carbohydrates have been covalently or noncovalently functionalized with carbon nanotubes, producing highly aqueous stable and biocompatible... 

Immunoassays, along with all other methods based on biorecognition, are a great achievement for the field of analjdical chemistry. The first area to benefit from the advantages of this technique is probably chnical analysis, where selective and sensitive determination of macromolecules is often necessary, as it is very difficult, or sometimes impossible to identify and quantify macromolecules by any alternative method. Recently, the immunoassay application field was extended, more or less successfiilly, to the determination of small molecules (below 1000 Da) as well. The acceptance of immunoassays is, however, relatively hmited in some fields, probably due to the differences between the classical analytical methods and immunoassays, the latter requiring special conditions of operation, characterization and data interpretation, due to the extraordinary nature of the antibody-antigen interaction, as well as that of many possible interfering reactions. 

Biocatalytic recognition by purified enzymes is the most common mechanism used in design of biosensors. Enzymes are biological catalysts that facilitate conversion of substrate into products by lowering activation energy of the reaction. They are proteins or glycoproteins, and biorecognition properties depend almost entirely on the amino acids of the exposed surface of enzyme molecule. 

Some of the latest investigations show that on the base of smart polymers with simultaneously immobilized biorecognition molecules as enzymes, antibodies, nucleic acids with fluorescent dyes can be constructed biosensors by means of SPR measurements. 

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