Mitchel J. Doktycz

Atomic force microscopy of single‐ and double‐stranded deoxyribonucleic acid

The atomic force microscope (AFM) was used to image double‐stranded DNA and single‐stranded DNA adsorbed onto mica modified by Ba (II). Images of double‐stranded DNA show an open circular shape without drastic contortions, and contour lengths that measure within 7% of the calculated length. Images of single‐stranded DNA show two distinct forms; compact open circles with ‘‘nodes’’ or lumps almost uniformly distributed are the most frequently observed while less abundant are highly elongated circles with a few nodes. Heating the single‐stranded DNA sample and altering the solvent conditions prior to adsorption was found to increase the number of elongated circular molecules observed in the AFM images.