Study of DNA in "glasslike state" by atomic force microscopy: Importance of substrates

An atomic force microscopy (AFM) system operating at low temperatures and under ultra high vacuum (UHV) conditions is presented. file AFM system uses the laser beam deflection method to detect the cantilever deflection. The system was completely developed ill our laboratory for Studying biological samples [A. Radenovic et al.: Rev. Sci. Instrum. 74 (2003) 1022]. To Study DNA by AFM requires a Substrate oil which the DNA call be adsorbed from all aqueous solution. Images of DNA at room temperature and at tow temperatures oil three different surfaces are presented, including the first images of DNA oil the treated HOPG obtained at 82 K. The importance of the hydrophobic degree of the substrate for imaging DNA at low temperatures is discussed.