Electrochemical aptasensors

Figure 12.18 (a) Electrochemical aptasensor for thrombin based on the control of electron... 

There is a limited number of studies on aptasensors (aptamer sensors), particularly for the detection of small organic molecules. An electrochemical aptasensor was developed by Kim et al. " for the detection of tetracycline using an ssDNA aptamer that selectively binds to tetracycline as the recognition element. The aptamer was highly selective for tetracycline and distinguishes minor structural... 

ELECTROCHEMICAL APTASENSOR BASED ON REDOX-ACTIVE APTAMER MONOLAYERS LINKED TO ELECTRODES... 

Figure 3.3 Electrochemical aptasensor for thrombin based on the control of electron transfer between redox-labeled aptamer and the electrode. (A) Controlling the orientation of the redox label with respect to the electrode upon formation of a thrombin-aptamer complex. (B) Differential pulse voltammetry corresponding to an analysis of different concentrations of thrombin by a ferrocene-tethered aptamer (a) 0, (b) 10, (c) 20, and (d) 30 nM. (Reprinted with permission from Radi et al., 2006. Copyright 2006 American Chemical Society.) (C) Activation of the electrical contact of methylene blue-tethered aptamer upon formation of the respective aptamer-thrombin complex. (D) Voltammo-grams corresponding to analysis of the thrombin by the configuration depicted in part (C) curves (a) no thrombin (b) thrombin 10 nM (c) thrombin 256 nM. (Reprinted with permission from Xiao et al., 2005. Copyright 2005 American Chemical Society.) (E) Blocking the electrical response of methylene blue intercalated into the stem of a DNA hairpin as a result of formation of an aptamer-thrombin complex.

A reusable electrochemical electrode for the use of low-molecular-weight molecules by its aptamers was demonstrated with the development of an electrochemical aptasensor for adenosine monophosphate (Wu et al., 2007). The anti-adenosine aptamer was functionalized at its end with a redox-active ferrocene unit. An electrode was functionalized with nucleic acid complementary to a region of the aptamer, and this was hybridized to the redox-tethered aptamer, giving rise to a redox response. In the presence of adenosine, an adenosine-aptamer complex was formed, resulting in dissociation of the redox-tethered aptamer from the surface and depletion of the redox signal. The extent of the decrease in electrical response was controlled by concentration of the adenosine analyte. 

Indirect amplified electrochemical analysis of aptamer-protein complexes has employed nanoparticles as labels for the development of electrochemical aptasensors. The use of metal nanoparticles as tracers for the analysis of nucleic acid... 

Electrochemical aptasensors have been developed widely for some period of time, especially in the most recent few years (Willner and Zayats, 2007). Due to the properties of the technique itself, most electrochemical aptasensors depend on electrodes for electron transfer. Thus, the SOALF mode could make sense. Here we introduce mainly easy routes in this mode rather than in the SFALF mode. 

Sandwich-type sensing platforms are also nsed widely in electrochemical aptasensors (Willner and Zayats, 2007), especially for common model molecnles such as a-thrombin (Mir et al., 2006 Polsky et al., 2006 Centi et al., 2007) and platelet-derived growth factor (PDGF) (Zhou et al., 2007), which possess two active aptamer-binding sites. This type of sensor usually... 

Obviously, the sensors above are fabricated relatively complicatedly, because most sensors need multiple steps of modification, label, or separation. These steps might display their advantages, such as high selectivity and sensitivity, but still not avoid the defaults that label usually faces. As a matter of fact, most electrochemical aptasensors have been designed for speed and simplicity, which exemplify the inherent advantages of electrochemistry. Hence, most electrochemical aptasensors reported are generally simpler. 

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