In the personalized medicine era, affordable and portable devices for quicker cancer monitoring, even in remote areas, are crucial. To address this need, we have developed an enzyme-assisted electrochemical point-of-care (POC) test for application toward liquid biopsy. In particular, miR-200a-5p has been taken into account as the model target due to its correlation for triple negative breast cancer (TNBC) prognosis. The proposed platform has been conceived as signal-ON, and the detection architecture is based on the presence of a duplex-specific nuclease (DSN) that is selective for DNA-RNA heteroduplexes. When the miRNA is recognized by an ad-hoc designed DNA probe, the DSN enzyme enables for the isothermal target recycling and signal enhancement, which is essential for detecting the miRNA trace in biofluids. Introducing a methylene blue (MB) modification on the DNA probe, a single miRNA strand is capable of triggering multiple DSN cleavage circles, increasing the free MB and thus the electrochemical signal recorded. All the optimization studies have been carried out using a screen-printed strip, resulting in a dynamic range comprised between 0.1 pM and 100 nM and a detection limit down to the fM level. A satisfactory selectivity was highlighted by interrogating the system toward random miRNA target mixtures, and the platform was also tested in spiked commercial serum samples.