Methylene blue as a DNA probe for a comparative study of Cd2+, Pb2+ and Cr3+ ions binding to calf thymus DNA

► Methylene blue (MB) as a DNA probe was developed for the study of heavy metal ions binding with ctDNA. ► MB was first used to compare the binding affinity of heavy metal ions with ctDNA. ► The interaction mechanisms are related to the concentration ratios of heavy metal ions to DNA.