Biosensors functional matrices

Some non-silica sol-gel materials have also been developed to immobilize bioactive molecules for the construction of biosensors and to synthesize new catalysts for the functional devices. Liu et al. [33] proved that alumina sol-gel was a suitable matrix to improve the immobilization of tyrosinase for detection of trace phenols. Titania is another kind of non-silica material easily obtained from the sol-gel process [34, 35], Luckarift et al. [36] introduced a new method for enzyme immobilization in a bio-mimetic silica support. In this biosilicification process precipitation was catalyzed by the R5 peptide, the repeat unit of the silaffin, which was identified from the diatom Cylindrotheca fusiformis. During the enzyme immobilization in biosilicification the reaction mixture consisted of silicic acid (hydrolyzed tetramethyl orthosilicate) and R5 peptide and enzyme. In the process of precipitation the reaction enzyme was entrapped and nm-sized biosilica-immobilized spheres were formed. Carturan et al. [11] developed a biosil method for the encapsulation of plant and animal cells. 

The construction of a biosensor, a biochip, or a bioreactor frequently requires the fixation of corresponding biomacromolecules, especially proteins, on an electrode without denaturation. Protein functions have been studied only in an aqueous medium. However, the aqueous medium is not the best matrix from in practical applications. The available temperature range of an aqueous system is not sufficiently wide, and it is scarcely possible to maintain long-term stability of the proteins in an aqueous medium. It is therefore important to find a nonaqueous medium in... 

Functionalization of surfaces with photopolymerized monomers or sol-gel matrices has also been used. In this case, the biomolecules can be physically entrapped within the supporting matrix. The method is applicable for almost all types of surfaces, it is easy to handle, and the large spectrum of monomer precursors commercially available permits the immobilization of basically all biological elements. In this case, the absence of chemical bond formation helps to preserve the activity of the bioreagent during the immobilization process. However, several drawbacks such as leaking of biocomponent and possible diffusion barriers restrict the performance of biosensor devices fabricated using this procedure. 

D.A., Sultanov, Y.M., Efendiev, A.A., and Schuhmann, W. (2007) Parallel synthesis of libraries of anodic and cathodic functionalized electrodeposition paints as immobilization matrix for amperometric biosensors. Bioelectrochemistry, 71 (1), 81-90. 

As a biosensor, by definition, consists of a biological recognition system in intimate physical and functional contact with an artificial transducer, among the possible combinations the most efHcient ones have to be conceived with regard to the demands of the actual analytical problem. The choice will not only be determined by the optimum sensitivity or the response time to be attained, but also by the properties of the matrix and the concentration range of the substance to be monitored. This may be explained by means of an example. 

Since the mediators should be mobile in order to provide the electron flow between the enzyme catalytic centre and electrode, they are usually soluble in the electrolytic medium, and therefore could be lost during the repetitive measurements. This, in combination with inactivation of enzyme, due to its denaturing leads to the loss of sensitivity of the biosensor with time. The possible solution to this problem is using an excess of enzyme and mediators in the measurement. Recendy, a new technique has been developed where redox polymers were used in dual function as immobilisation matrix and as materials facilitating electron-transfer. In materials such as these, the mediator redox... 

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