Methylene blue redox label

E. E. Ferapontova and K. V. Gothelf, Optimization of the electrochemical RNA-aptamer based biosensor fo theophylline by using a methylene blue redox label. Electroanalysis, 21, 261-1266 [2009a],... 

The formation of aptamer-substrate complexes was also followed by the use of redox-active intercalators73 (Fig. 12.18d). A nucleic acid hairpin structure that contained in its single-stranded loop the antithrombin base sequence was assembled on a Au electrode, and methylene blue was intercalated as a redox label in the double-stranded stem of the hairpin structure. The hairpin was, then, opened in the presence of thrombin, by generating the respective G-quadruplex-thrombin complex, and as a result, the redox label was removed from the nucleic structure, showing a decrease in the voltammetric response with the increase in the concentration of thrombin. This method enabled the analysis of thrombin with a detection limit that corresponded to... 

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.

Labels such as enzymes, NPs, and redox species, such as ferrocene (Fc) or methylene blue (MB), are often used for recognition processes. Electrochemical aptasensors with a label have received and yet continue to receive considerable attention because they combine the specificity of the aptamer-analyte recognition to the advantages of an amplified signal. These strategies are generally highly sensitive due to the analytical characteristics of the label used. 

The DNA duplex formation can be detected based on the incorporation or association of a hybridization indicator or changes accrued from the hybridization event. Different indicators can be used in detection of DNA based on the appropriate electrochemical activity selected, it can be either label-free (e.g. guanine, adenine), or label-based (enz5nne-based, ferrous and ferricyanide. Ruthenium bipyridine [Ru (bpy)], methylene blue, Ethidium bromide etc). The hybridization event is detected via the increase or decrease in signal of the redox indicator or changes in conductivity or impedance/capacitance. 

Sensors for accurate detection of the bacteria N. gonotrhoeae causing the sexually transmitted disease gonorrhea have been developed by Singh et al. [49]. The sensor is based on the detection of DNA hybridization using methylene blue as redox indicator. It was prepared by electropolymerization of aniline in presence of camphor sulfonic acid and c-MWCNTs followed by covalent immobilization of amino labeled ss-DNA on the film surface. 

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