This study focuses on identifying DNA sequences capable of selectively binding 6-mercaptopurine (6MP) or its analog, azathioprine (Aza), as a potential bioreceptor for biosensing methods. The approach used in the study is based on instrumental analysis methods such as UV-Vis spectroscopy, high performance liquid chromatography (HPLC), and nuclear magnetic resonance techniques to describe the interaction, its mode, and strength as well as selectivity of selected DNA sequences toward thiopurines. Thus, of the sequences tested, dsDNA GGCAGGACGGAG poses the ability to form complexes with 6MP, with an affinity constant of 2.52·10