  By assuming that not only counter-ions but DNA molecules as well are
thermally distributed according to a Boltzmann law, we propose a modified
Poisson-Boltzmann equation at the classical level as starting point to compute
the effects of quantum fluctuations of the electric field on the interaction
among DNA-cation complexes. The latter are modeled here as infinite
one-dimensional wires ($\delta$-functions). Our goal is to single out such
quantum-vacuum-driven interaction from the counterion-induced and water-related
interactions. We obtain a universal, frustration-free Casimir-like (codimension
2) interaction that extensive numerical analysis show to be a good candidate to
explain the formation and stability of DNA aggregates. Such Casimir energy is
computed for a variety of configurations of up to 19 DNA strands in a hexagonal
array. It is found to be strongly many-body.
