Biosensor architecture

The advantages of employing enzymes in biosensor architectures are the following ... 

A different approach to realize biosensor architectures is the immobihzation of a redox enzyme on the electrode surface in such a manner that direct ET is possible between the active side of the enzyme and the transducer [22, 140]. Thus, free-diffusing redox mediators are not necessary for these types of biosensors [164-169]. Biosensor designs based on direct ET have been investigated thoroughly and comprehensively reviewed [22-26, 170-182]. Figure 1.5 schematically illustrates how such direct ET can be realized within third-generation biosensors. 

Figure 1.5 Schematic representation of biosensor architectures based on direct ET (a) via an oriented adsorbed redox enzyme (b) via a redox enzyme coupled to a self-assembled monolayer (SAM).

The general advantages of reagentless biosensor structures can be summarized as follows. Since all components of the assay are securely immobilized on the electrode surface, there is no or just a negligible loss of redox mediators, cofactors, and/or enzymes over the time of operation. This is of importance for the performance and safety of a device because the impact of free-diffusing possibly toxic substances is minimized. Therefore, reagentless biosensor architectures are often used for in vitro and in vivo measurements as outlined in Sec lion 1.4.5. 

Figure 1.7 Parameters influencing the overall response of a specific biosensor architecture.

Knowing the most influential parameters of a specific biosensor architecture is the basis to understand and fine tune the performance of these devices in a rational manner. Figure 1.8 summarizes the key features of typical biosensors and lists several that are of additional importance for commercial devices. Among these, selectivity, sensitivity, accuracy, response, and recovery time as well as operating lifetime are some of the most important key factors. Keeping in mind the needs of the specific analytical task of interest, it seems to be necessary to characterize at least the key parameters mentioned in Figure 1.8 in order to specify the analytical performance of a biosensor design. 

There is an enormous variety of nanomaterials that can potentially be employed in biosensor architectures. The most prominent among them are metal nanoparticles [304], quantum dots [308], and carbon nanotubes [309-311]. AH of them have been employed in biosensors though not necessarily exclusively electrochemical biosensors. Quantum dots (QDs) offer unique absorption properties making them highly suitable for the construction of biosensors with optical readout. The most diverse electrochemical nanobiosensors are, however, obtained from carbon nanotubes (CNTs) which offer a wide range of different apphcations. 

The full potential of amperometric biosensors has not yet been tapped, especially with respect to the versatile and broad range of applications for which biosensors can be used. Many contributions to the field of biosensors and biofuel cells still are at the proof-of-concept stage. Thus, the authors hope that this chapter will promote lively and valuable discussions in order to generate new ideas and approaches towards the development and optimization of biosensor architectures. 

Table 3 Enzymatic biosensors architectures designed using VACNT electrodes.

Maciejewska M, Schafer D, Schuhmann W. SECM imaging of spatial variability in biosensor architectures. Electrochem Commun 2006 8 1119-1124. 

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