Reversible, meniscus-free molecular combing of long-chain DNA.

We introduce a method for reversibly orienting long-chain DNA on solid hydrophilic substrates without a fluid meniscus. End-tethered lambda-DNA mushrooms are elongated by a hydrodynamic flow in the presence of trivalent cations, resulting in electrostatic adsorption of the extended DNA to the surface. By complexation of the cations the part of the DNA which is unspecifically bound to the surface desorbs quantitatively, and the mushroom conformation is restored. With the use of multiple deposition-combing steps, combined with a final desorption step, tethering densities higher than attainable with single deposition steps can be obtained.