No abstract

Single molecule recognition imaging and dynamic force spectroscopy (DFS) analysis showed strong binding affinity between an aptamer and ricin, which was comparable with antibody-ricin interaction. Molecular simulation showed a ricin binding conformation with aptamers and gave different ricin conformations immobilizing on substrates that were consistent with AFM images.

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A simple two-step protocol for modification of atomic force microscopy tip and substrate by using a "click reaction" has been developed. The modified tip and substrate were applied to detect trace amounts of ricin by using single molecule recognition force microscopy (SMRFM1). A key feature of the approach is the use of a PEG derivative functionalized with a thiol and azide group end group. This compound could be attached to a gold coated AFM tip by a strong Au-thiol bond. The azide of the immobilized PEG was used for the attachment of an anti-ricin antibody modified with an alkyne group using a 'click reaction'. The latter reaction is highly efficient, compatible with the presence of many functional groups and proceeds under mild reaction conditions. In a separate step, ricin was immobilized on the gold substrate surface that was modified by active esters. For this process, a novel bifunctional reagent was employed containing an active ester and a thioctic acid moiety. The SMRFM results showed a sub fg/mL level of detection sensitivity. The unbinding force between the anti-ricin antibody and ricin was studied by the force-distance curves (F-D). The unbinding force between the ricin and the antibody was determined to be 64.89±1.67 pN by constructing a force histogram.