The immobilization procedure to a biosensor surface has a major influence on the measurement results. To characterize the immobilization onto various biolayers, the interaction of DNA anti-thrombin aptamer with the protein thrombin was used as a model system. The aptamer was immobilized to a two-dimensional alkanethiol SAM via carboxylamide bonds and to a three-dimensional dextran matrix via streptavidin–biotin interaction. The calculatedKD values of about 260 and 267 nM, respectively, were comparable, while the amount of bound analyte varied by a factor of 2, depending on the accessibility of the immobilized aptamer. Differences in the specificity were shown by use of the similar protein elastase.
