Labeling of Aptamers

A general overview of labeling methods for different compound classes with both single photon emitters for SPECTand positron emitters for PET has been extensively reviewed elsewhere (Younes et al., 2002).

Without influencing their binding affinities, radiolabeling of aptamers is pursued either via site-specific conjugation of a bifunctional chelator or by attaching a radiolabeled precursor. In order to establish a stable position for the radioisotope, often the 3' end of the aptamer is chosen for chelator conjugation or, if the 5' end is radiolabeled, the 3' end is simultaneously capped, preventing exonu-clease activity. Radiolabeling conditions such as high temperatures, the use of organic solvents, and pH ranges between 4 and 9 can be applied, because these conditions do not harm the aptamer structure, stability or specificity.

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