The intercalation of small molecules into DNA separates DNA base pairs, lengthening the DNA, as shown by the increased viscosity of the DNA solution. We measured the viscosity of a solution with a constant concentration of ctDNA (0.24 mM (pb)) at increasing COSAN concentrations (from 0 to 0.12 mM). The data were plotted as the (η/η0) 1/3 function of the [COSAN]/[ctDNA(pb)] ratio, where η is the intrinsic viscosity of the solution containing ctDNA and COSAN, and η0 is the intrinsic viscosity of the solution containing free ctDNA (Figure ). At [COSAN]/[ctDNA(pb)] ratios ranging from 0.083 to 0.25, (η/η0) 1/3 remained unchanged and close to 1. At [COSAN]/[ctDNA(pb)] ratios ranging from 0.25 to 0.417, (η/η0) 1/3 slightly decreased to 0.96, albeit nonsignificantly. At a [COSAN]/[ctDNA(pb)] ratio of 0.5, the trend reversed, and (η/η0) 1/3 returned to approximately 1. Overall, we did not detect any significant changes in DNA viscosity after adding COSAN. These findings also indicate that COSAN does not intercalate into DNA.