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Published online by Cambridge University Press: 10 February 2011
A method for covalent immobilization of a single dextran polymer between a gold surface and the tip of an atomic force microscope (AFM) is presented. Carboxymethylated dextran immobilized on gold by epoxythiol chemistry was activated with N-hydroxysuccinimide (NHS) and N-ethyl-N'-(dimethylaminopropyl) carbodiimide hydrochloride (EDC) in order to make the dextran polymer reactive for the amino groups present on the previously aminosilanized AFM tip. By measuring force vs extension curves we have shown that it is possible to catch such an activated dextran polymer with an AFM tip through the formation of a covalent bond. Dextran polymers were attached even without any detectable indentation of the tip in the dextran-coated gold surface. In this so-called fly-fishing mode, attachment of multiple dextran polymers, which typically occurs when the tip is indented into the surface, are efficiently avoided.