LD spectroscopy measures the difference between the absorption of linearly polarized light travelling parallel and perpendicular to the orientation of a sample. CtDNA consists of dsDNA strands long enough to be oriented in the Couette flow and has a negative LD band in its absorbance region. In contrast, COSAN is a small molecule and is not oriented in the flow, thus lacking an LD signal. However, COSAN may be oriented in the flow along with DNA and acquire an LD signal by interacting with DNA either through intercalation or minor-grove binding. Although the absorbance spectra of COSAN and DNA overlap, COSAN clearly contributed to the absorbance spectra (Figure ).