Impedimetric biosensors

These impedimetric biosensors suffer from the virtually irreversible binding discussed in Chapter 2. This is the main reason why they do not qualify as direct biosensors. They have been used in conjunction with the ferro/ferricyanide redox couple as the indicator of the blocking of the surface (Radi et al., 2005). Unfortunately, the binding event is so strong that the analysis has to be run in an assay format. The result of such a procedure is shown in Fig. 8.2. 

Electrochemical biosensors have some advantages over other analytical transducing systems, such as the possibility to operate in turbid media, comparable instrumental sensitivity, and possibility of miniaturization. As a consequence of miniaturization, small sample volume can be required. Modern electroanalytical techniques (i.e., square wave voltammetry, chronopotentiometry, chronoamperometry, differential pulse voltammetry) have very low detection limit (1(T7-10 9 M). In-situ or on-line measurements are both allowed. Furthermore, the equipments required for electrochemical analysis are simple and cheap when compared with most other analytical techniques (2). Basically electrochemical biosensor can be based on amperometric and potentiometric transducers, even if some examples of conductimetric as well as impedimetric biosensor are reported in literature (3-5). 

Figure 4.16. Schematic outline of the label-free impedimetric biosensor for thrombin at an aptamer-functionalized Au electrode based on a three-level cascaded signal amplification (a) Formation of a mixed monolayer of thiolated aptamer and 6-mercaptohexanol on the AuE (b) thrombin addition and binding with aptamer (c) binding with Apt-Au-NPs to carry out the first-level signal amplification ( ] (d) the enlargement of the SDS-stabilized Apt-Au-NPs to achieve the second/third-level signal amplification CH/HO and (e) schematic outline of the electron-transfer resistance of different modified electrodes [82] (reprinted with permission of acs],...

Impedimetric Biosensors for Nano- and Mkrofluidks, Table 1 Impedance properties of common electrical elements... 

Impedimetric Biosensors for Nano- and Microfluidics, Fig. 6 Illustration of the immobilization... 

Impedimetric biosensors for whole cells have demonstrated two mechanisms in response. Considering the overall impedance of a biological cell as including the resistance and the capacitance of the cell membrane, the... 

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