Abstract
λ-DNA as well as plasmids can be successfully deposited by molecular combing onhydrophobic surfaces, for pH values ranging from 4 to 10. On polydimethylsiloxane(PDMS) substrates, the deposited DNA molecules are overstretched by about 60–100%.There is a significant influence of sodium ions (NaCl) on the surface density of thedeposited DNA, with a maximum near to 100 mM NaCl for a DNA solution (28 ng µl − 1) at pH 8. The combing process can be described by a micromechanical modelincluding: (i) the adsorption of free moving coiled DNA at the substrate;(ii) the stretching of the coiled DNA by the preceding meniscus; (iii) therelaxation of the deposited DNA to the final length. The sticky ends ofλ-DNA cause an adhesion force in the range of about 400 pN which allows a stableoverstretching of the DNA by the preceding meniscus. The exposing of hidden hydrophobicbonds of the overstretched DNA leads to a stable deposition on the hydrophobic substrate.The pH-dependent density of deposited DNA as well as the observed influence of sodiumions can be explained by their screening of the negatively charged DNA backbone andsticky ends, respectively. The final DNA length can be derived from a balance of thestored elastic energy of the overstretched molecules and the energy of adhesion.
Published Version
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