Study of probes and substrates for low temperature atomic force microscopy and biological applications

The atomic force microscopy in ultrahigh vacuum and at low temperature demonstrated its excellent capability to reach atomic resolution. Nevertheless in the case of biological samples high resolution has been achieved only in very few cases. We demonstrated here the importance of the appropriate choice of probes and substrates in order to image DNA at low temperature with high resolution. We investigated properties of three types of cantilevers and they were studied by scanning electron microscopy as a function of temperature. A large bending of cantilevers, which were coated from both sides, was observed at low temperatures. Therefore uncoated cantilevers pare strongly recommended for low temperature applications. Different methods for immobilization of DNA on the substrate are examined at low temperatures. First images of linear DNA on graphite at 82 K under ultrahigh vacuum conditions are presented.