Figure 1.

DNA minicircles of 168 bp in 1 mM MgCl₂ (A) and 1 mM ZnBr₂ (B). (C) Circles of 126 bp in 1 mM ZnBr₂. (D) Linear 126-bp oligomers are shown in the same electrolyte. All four images are scaled as shown by the bar in D. Molecules were spontaneously adsorbed onto mica from solution and imaged in situ by using MAC mode AFM. The cantilever, with a spring constant 0.6 N/m, was oscillated at 5 nm p/p at 25 kHz and the set point decrease was 0.3 nm. The images (512 lines of data) were each acquired in 5 min.