Additive-manufacturing (3D-printing) is a fabrication procedure based on melting and solidification, widely used for production of engineering components. Among 3D-printing technologies, fused deposition modeling (FDM) is the most common and inexpensive one.[1] In recent years, this technology has been also extended to the fabrication of electrochemical sensors.  In biomedicine, the electrochemical sensors are largely studied and used to make quantitative assessment of biomolecules. These devices work under the influence of oxidation and reduction processes and the presence of analytes at the surface of conductive electrode material causes changes in the electrical potential and/or current recorded, that are taken as a function of the analytes concentration.[2] The utilization of FDM technology in the fabrication of electrochemical sensors provides a number of advantages, however, the applicability of 3D-printing to fabricate electrochemical sensors is restricted by the availability of conductive filaments. In this work we propose a smart and simple strategy for the preparation of electrochemical multi-sensors. Recently applied by our group for biodegradable polymers [3], and now under investigation for not absorbable and biocompatible materials (polypropylene (PP), polyurethane (PU)) largely used as textiles in the biomedical field. These polymers are directly transformed into an electroresponsive material without adding any conductive material. More specifically, 3D-printed specimens are chemically modified by low pressure O2-plasma treatments. The excited species introduced onto the polymer surface, after the application of the electric discharge, are responsible of the chemical functionalization (confirmed by characterization techniques such as XPS, FTIR and SEM) of the specimens and make them able to act as functional working electrodes. The oxidation of biomolecules as dopamine (DA) and serotonin (SA)  was assessed by cyclic voltammetry (CV) leading to a sensitivity of  1.45 µA/(cm2·µM), while the limit of detection (LOD), is 1.34 µM, for DA and SA detection, respectively. Finally, the simultaneous detection of DA and SA was performed. The results here reported led to define a new way for the manufacture of electrodes for electrochemical sensors based on 3D printing without using conducting materials at any stage of the process.