Chemisorption, immobilization sensor

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. 

Efficient immobilization of aptamers on surfaces is necessary for the construction of tongh, stable sensors and assay systems as one necessary step to overcome limitations for practical applications (Bini et al., 2007). Bini et al. (2007) have compared thrombin aptamers immobilized on a gold snrface by chemisorption (thiolated aptamer) and by biotin-streptavidin interaction (biotinylated aptamer carrying a linker) on a gold surface modified by a thiol-dextran-streptavidin layer. The linker-modified aptamer immobilized via streptavidin-biotin showed better reproducibility and sensitivity results for the quartz crystal sensor. Aptamers can be used for the functionalization of titanium-alloy surfaces (e.g., implant material, scaffolds) to enhance cell adhesion. The aptamers directed to osteoblasts are fixed electrochemically on the snrface of the alloy and promote cell adhesion (Gno et al., 2005, 2007). 

---