The LD spectrum of free ctDNA shows a negative absorption band with a minimum at 258 nm, which indicates that the average orientation of the DNA bases was nearly perpendicular to the direction of flow (Figure ). The LD spectra of ctDNA with increasing concentrations of COSAN ([COSAN]/[ctDNA(pb)] = 0.1 to 0.7) show that the magnitude of the LD signal at 258 nm increases by approximately 9% at [COSAN]/[ctDNA(pb)] = 0.7, so adding COSAN slightly increases the orientation of DNA bases in the direction of flow. However, this effect is weak. To put this number into the context, for ethidium bromide (EB), the magnitude of the LD signal between free DNA and DNA with EB at a molar ratio of 0.1 increases by over 70%. Furthermore, no LD signal was detected at 282 nm (COSAN absorbance region), which suggests that COSAN does not bind to ctDNA in a way that promotes its orientation in the direction of flow along with ctDNA. Overall, these LD measurements show that COSAN is not intercalated into DNA or bound to minor DNA grooves.