PHASE IMAGING OF MOVING DNA-MOLECULES AND DNA-MOLECULES REPLICATED INTHE ATOMIC-FORCE MICROSCOPE

Phase imaging with a tapping mode atomic force microscope (AFM) has ma ny advantages for imaging moving DNA and DNA-enzyme complexes in aqueo us buffers at molecular resolution. In phase images molecules can be r esolved at higher scan rates and lower forces than in height images fr om the AFM. Higher scan rates make it possible to image faster process es. At lower forces the molecules are imaged more gently. Moving DNA m olecules are also resolved more clearly in phase images than in height images; Phase images in tapping mode AFM show the phase difference be tween oscillation of the piezoelectric crystal that drives the cantile ver and oscillation of the cantilever as it interacts with the sample surface. Phase images presented here show moving DNA molecules that ha ve been replicated with Sequenase in the AFM and DNA molecules tethere d in complexes with Escherichia coli RNA polymerase.