This work is directed to the development of nanosensors based on multi-walled carbon nanotubes (MWCNTs), aimed at the effective detection and monitoring of doxorubicin—a chemotherapy drug used in the treatment of breast cancer—in human blood and urine samples. The main goal is the design of nanosensors that provide precise and reliable detection and monitoring of doxorubicin concentration, offering an effective approach to monitoring drug levels during treatment. The research was carried out on screen-printed electrodes (SPEs) with a working electrode of commercial carbon nanotubes, as well as their modification by irradiation with electron radiation (50 kGy), or application of a polyvinylidene fluoride (PVDF)polymeric film. The electrochemical study, using cyclic voltammetry measurements, was performed to characterize and test the performance of the nanosensors. Structural changes resulting from the corresponding modifications were observed using scanning electron microscopy. The electrolyte was analyzed using UV-Vis spectroscopy before and after the cyclic voltammetry measurements. The current work presents the experimental procedures and describes the process leading to the final results.