New conductive filament ready-to-use for 3D-printing electrochemical (bio)sensors: Towards the detection of SARS-CoV-2

The 3D printing technology has gained ground due to its wide range of applicability. The development of new conductive filaments contributes significantly to the production of improved electrochemical devices. In this context, we report a simple method to producing an efficient conductive filament, containing graphite within the polymer matrix of PLA, and applied in conjunction with 3D printing technology to generate (bio)sensors without the need for surface activation. The proposed method for producing the conductive filament consists of four steps: (i) mixing graphite and PLA in a heated reflux system; (ii) recrystallization of the composite; (iii) drying and; (iv) extrusion. The produced filament was used for the manufacture of electrochemical 3D printed sensors. The filament and sensor were characterized by physicochemical techniques, such as SEM, TGA, Raman, FTIR as well as electrochemical techniques (EIS and CV). Finally, as a proof-of-concept, the fabricated 3D-printed sensor was applied for the determination of uric acid and dopamine in synthetic urine and used as a platform for the development of a biosensor for the detection of SARS-CoV-2. The developed sensors, without pre-treatment, provided linear ranges of 0.5–150.0 and 5.0–50.0 μmol L(−1), with low LOD values (0.07 and 0.11 μmol L(−1)), for uric acid and dopamine, respectively. The developed biosensor successfully detected SARS-CoV-2 S protein, with a linear range from 5.0 to 75.0 nmol L(−1) (0.38 μg mL(−1) to 5.74 μg mL(−1)) and LOD of 1.36 nmol L(−1) (0.10 μg mL(−1)) and sensitivity of 0.17 μA nmol(−1) L (0.01 μA μg(−1) mL). Therefore, the lab-made produced and the ready-to-use conductive filament is promising and can become an alternative route for the production of different 3D electrochemical (bio)sensors and other types of conductive devices by 3D printing.