A convenient method of aligning large DNA molecules on bare mica surfaces for atomic force microscopy

Large DNA molecules remain difficult to be imaged by atomic force microscopy (AFM) because of the tendency of aggregation. A method is described to align long DNA fibers in a single direction on unmodified mica to facilitate AFM studies. The clear background, minimal overstretching, high reproducibility and convenience of this aligning procedure make it useful for physical mapping of genome regions and the studies of DNA–protein complexes. Atomic force microscopy (AFM) has displayed great potential in the study of the structure of DNAs and DNA–protein complexes. The complications in sample preparation, however, have until now hindered AFM from contributing vigorously to this field. This is especially the case for imaging long strands of DNA (1–3)