In QDFM, a small volume of isolated DNA molecules in aquous solution is placed on glass (51,53) or freshly cleaved sheets of mica (54) surface function-alized so that most DNA molecules attach at one or both ends. The DNA solution is then spread over a larger area by placing a cover slip on top; additional DNA molecules bind to the surface. During the subsequent drying step, molecules tethered to the support via either one or both ends (if linear) or via intermediate nicks in the double-stranded molecule (if the molecule is circular) are straightened and uniformly stretched by the hydrodynamic action of the receed-ing meniscus, i.e., the surface tension at the water-air interface.

0 0

Post a comment