Single molecule mechanical testing

Single molecule mechanical testing performed with the AFM has distinct advantages over other force measuring devices due mainly to the very precise displacement measurements afforded by the AFM scanner. This allows for the examination of single molecules that are much smaller that those examined by other techniques including the optical tweezers. The molecules examined in this study would not be able to be examined by any other means than AFM. Typical molecules examined with the optical trap are usually several microns in length to allow for better displacement measurements. The use of the AFM to perform these mechanical tests has allowed for the investigation of ever-smaller single molecules.; In this study the use of covalent attachment chemistry was employed to make one point of attachment to the single molecule. The second point of attachment was made using the molecular recognition of the biotin-streptavidin conjugate. This empowered a rapid investigation of the mechanical properties of several single molecules. The streptavidin molecular recognition system was explored both attached directly to a cantilever and as a bridge between two molecules. The results show that although the biotin-streptavidin linker does unfold, the response is reproducible and subtractable from the overall response of the molecular ensemble. Using this attachment chemistry allowed for the examination of the effect of structure, point of attachment, and GC content on the mechanical properties of DNA.