Biosensors signaling aptamers

In this part we will describe recent achievements in the development of biosensors based on DNA/RNA aptamers. These biosensors are usually prepared by immobilization of aptamer onto a solid support by various methods using chemisorption (aptamer is modified by thiol group) or by avidin-biotin technology (aptamer is modified by biotin) or by covalent attachment of amino group-labeled aptamer to a surface of self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA). Apart from the method of aptamer immobilization, the biosensors differ in the signal generation. To date, most extensively studied were the biosensors based on optical methods (fluorescence, SPR) and acoustic sensors based mostly on thickness shear mode (TSM) method. However, recently several investigators reported electrochemical sensors based on enzyme-labeled aptamers, electrochemical indicators and impedance spectroscopy methods of detection. 

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],...

A novel signal-on junction-probe-based ECL aptamer biosensor for the detection of thrombin was constructed. Figure 6.6 shows experimental principle of the junction-probe ECL aptamer biosensor for the detection of thrombin. Compared with some other ECL aptamer sensors, the proposed ECL aptamer biosensor has the advantages of higher sensitivity, lower background current, better selectivity and reusability, fabrication easiness, and operation convenience. These features make it a promising alternative to conventional thrombin detection methods and this method is expected to be involved in biochip fabrication [25]. 

Zhang J, Chen P, Wu X, Chen J, Xu L, Chen G, Fu F (2011) A signal-on electrochemiluminescence aptamer biosensor for the detection of ultratrace thrombin based on junction-probe. Biosens Bioelectron 26(5) 2645-2650. doi 10.1016/j.bios.2010.11.028... 

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