New highly sensitive voltammetric DNA-sensors have been developed for the detection of cytostatic drug doxorubicin based on Azure A electropolymerized on various carbon nanomaterials, i.e., functionalized multi-walled carbon nanotubes (fMWCNTs) and carbon black (CB). Carbon materials promote electropolymerization of the Azure A dye applied as a matrix for DNA molecules saturated with methylene blue (MB) molecules. Interaction with the intercalator (doxorubicin) liberates the MB molecules and changes redox activity. The doxorubicin concentration ranges reached by cyclic voltammetry were from 0.1 pM to 100 nM (limit of detection, LOD, 0.03 pM) for the biosensor based on CB, and from 0.3 pM to 0.1 nM (LOD 0.3 pM) for that based on fMWCNTs. DNA-sensors were tested on spiked samples of artificial serum, and biological and pharmaceutical samples. The DNA-sensors can find further application in the monitoring of the doxorubicin residuals in cancer treatment, as well as for pharmacokinetics studies.