Atomic Force Microscopy of DNA in Aqueous Solutions

DNA on mica can be imaged in the atomic force microscope AFM in water or in some buffers if the sample has first been dehydrated thoroughly with propanol or by baking in vacuum and if the sample is imaged with a tip that has been deposited in the scanning electron microscope SEM. Without adequate dehydration or with an unmodified tip, the DNA is scraped off the substrate by AFM-imaging in aqueous solutions. The measured heights and widths of DNA are larger in aqueous solutions than in propanol. The measured lengths of DNA molecules are the same in propanol and in aqueous solutions and correspond to the base spacing for B-DNA, the hydrated form of DNA when the DNA is again imaged in propanol after buffer, however, it shortens to the length expected for dehydrated A-DNA.... Propanol, Scanning electron microscope, E. Coli RNA polymerase, Washing samples, Aqueous solutions electrostatic effects, Hydration, Salt concentration, Humidity, Rotation of scan direction