Direct measurement of the mechanism by which magnesium specifically modifies the mechanical properties of DNA.

We examine the effect of physiological cations Na ⁺ , K ⁺ , Mg ²⁺ , and Ca ²⁺ on the mechanical properties of bundles of λ-phage DNA using silicon nanotweezers (SNTs). Integrating SNTs with a microfluidic device allows us to perform titration experiments while measuring the effect in real-time. The results show that only for Mg ²⁺ and in particular, at the intra-nuclear concentration (100 mM), the interaction occurs.