Topology of DNA: a honeycomb stable structure under salt effect

Atomic Force Microscopy analysis is employed to study the geometrical and topological properties of $3000$kbp DNA molecules fixed in mica substrates with $MgCl_{2}$. We found that the aggregates on the substrate surface for certain salt concentrations form a honeycomb stable structure with the addition of salt. The honeycomb, and the transition to other structures, were characterized by the \emph{Betti numbers}, which is a topological invariant property and by \emph{Hausdorff-Besicovitch fractal dimension}.