COSAN has a strong absorption band at 282 nm (ε = 30,866 M -1 cm -1 , Figure and) and a weak absorption band at 448 nm (ε = 443.5 M -1 cm -1 , Figure and). The strong absorption band overlaps with the absorption band of DNA. Thus, to study the interaction between COSAN and DNA, we measured the absorbance of COSAN with increasing concentrations of DNA in the wavelength range of 380 -600 nm. Figure shows the absorption spectra of free COSAN and COSAN with increasing concentrations of ctDNA ([ctDNA(pb)]/[COSAN] ratios ranging from 0.25 to 1.5). We observed no changes in the absorption spectra of COSAN after adding DNA. Overall, these results indicate that no or only a very weak complex is formed between COSAN and ctDNA. Subsequently, we measured circular dichroism (CD) and linear dichroism (LD) spectra of DNA in the presence of COSAN. Both techniques provide information about DNA structural changes induced by ligand binding. Figure shows the CD spectra of ctDNA with COSAN ([COSAN]/[ctDNA(pb)] ratios ranging from 0 to 1).