DNA properties investigated by dynamic force microscopy

In this work, we show that by varying the experimental conditions, the driving amplitude, a dynamic force microscope allows DNA properties to be selectively imaged. The substrate on which the DNA is fixed is a silica surface grafted with silane molecules terminated with amine groups. Use of small oscillation amplitudes favors the attractive interaction between the tip and the sample, while the use of large amplitudes renders the contribution of the attractive interaction negligible. In particular, at small amplitudes, the images show that the attractive interaction is strongly enhanced along the DNA. This enhancement is found to be amenable with a model considering a narrow strip of randomly oriented dipoles on each side of the molecule. This work should provide new insights on the DNA interaction and conformational changes with localized charges.