Reversible Binding of DNA on NiCl2-Treated Mica by Varying the Ionic Strength

The atomic force microscope is a key tool for investigating DNA conformation and DNA−protein interactions in liquid. The main advantage of this technique is that moving molecules can be studied in real time provided that molecules are sufficiently bound to the surface. Mg 2+ ions with a very low concentration of monovalent salt are generally used to attach DNA on mica because monovalent counterions inhibit the DNA electrostatic attraction with the surface. However, monovalent counterions at physiological concentrations are necessary to obtain specific DNA/protein interactions. To solve this problem, we propose a new protocol to obtain a reversible binding of DNA on NiCl 2 -pretreated mica. This protocol uses Mg 2+ ions for monitoring DNA attachment on NiCl 2 -pretreated mica, which allows the DNA molecules to remain bound to the surface even at high NaCl concentration thanks to Ni 2+ ions adsorbed on the surface.