Immobilization biorecognition

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. 

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

An electrochemical immunosensor includes a transducer (a current-conductive strip deposited on a polymer substrate) and a biorecognition substance (an antigen or antibodies) immobilized on the transducer surface. The formation of an immune complex and localization of non-antigen-specific antibodies (proteins) on this complex, which are usually labeled with enzymes, and a substrate in the solution, generates an active species capable of generating an electrochemical response. The sequential process, the use of enzymes, and occasionally unstable substrates limit and complicate a wide-scale application of such sensors. 

The main advantages of immobilizing whole cells over the isolated enzymes are (i) cells are more resistant to changes in pH or temperature and (ii) a single cell can contain all the enzymes and cofactors needed for bioconversion of the analyte [82], Most of the whole cell-based optical biosensors used in toxicity or bioremediation studies [83,84] employ microorganisms [85— 87], animal [88], plant tissues [89,90] or cell receptors [91] as biorecognition elements. 

Several strategies for immobilizing proteins on CNTs modified electrodes have been proposed. The step of immobilization is critical, since the enzyme has to remain as much active as possible in order to perform an efficient biorecognition of the substrate. The other aspect to consider is that the transducer where the protein will be immobilized has to allow a fast charge transfer to ensure a rapid and sensitive response. Therefore, it is important to take into account that the noncovalent functionalization of the sidewalls of SWCNTs is the best way to preserve the sp nanotube structure and their electronic characteristics. 

A different approach of site-specific polymerization and thus immobilization of a biorecognition element was shown by several research groups by utilizing electropolymerization [74-76]. In combination with microelectrodes in microchannel systems, a site directed simple immobilization of the biorecognition element could be achieved. Patterns can also be created by... 

As a flnal example, it should be pointed out that it is also possible to circumvent the need of immobilization of the biorecognition element in the microchannel system. Instead, it can be immobilized on superparamagnetic beads, silica beads, latex particles, etc. [79-81]. These beads are applied together with the sample into the microchannel system and can be collected on or near the transducer via magnetic or membrane separation. 

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