This communication demonstrates that a 3D printing pen, commercially-available as a toy for kids, can be used to draw thermoplastic electrochemical sensors using conductive filaments over any desirable format and substrate. A polylactic acid filament containing graphene or carbon black was passed through the 3D pen that works as a handheld 3D printer (fused deposition modeling type). As proof-of-concepts, we select three designs, the first one analogous to a conventional carbon-paste electrode, the second one containing the three electrodes in a cylindrical tube and the third one similar to commercial screen-printed electrodes. The 3D pen was used to draw the thermoplastic electrodes inside the pockets of all devices until reaching the copper wires to establish electric contact. Customized 3D printed substrates were used to guide the application of the 3D pen. The fabricated electrodes were applied for the detection of dopamine and trace metals as well as to generate electrochemically a Prussian Blue modified sensor. Many other designs, conductive filaments and substrates can be combined with a 3D pen to draw electrochemical sensors as well as other electrochemical devices, with applications ranging from medical point-of-care platforms, energy-storage devices as well as for teaching purpose.

This work demonstrates the application of batch-injection analysis (BIA) with amperometric detection on a multi-walled carbon nanotube (MWCNT) modified electrode for the sensitive determination of the antioxidant pyrogallol in biodiesel. Samples were diluted in electrolyte (0.1 mol L-1 HClO4) before injection using an electronic micropipette on the BIA cell. The size effect of MWCNTs on electrochemical oxidation of pyrogallol was investigated and 3.5-fold increase in the amperometric sensitivity using the modified electrode with MWCNTs of shorter dimensions was obtained. This result was in agreement with cyclic voltammetry and electrochemical impedance spectroscopy measurements. After optimization of BIA parameters for the amperometric detection on the MWCNT-modified electrode, the proposed method presented a linear range from 0.3 to 1000 µmol L-1, detection limit of 0.013 µmol L-1, precision of 3%, and sample throughput of 240 h-1. Spiked biodiesel samples were analyzed and recovery values between 95-99% were obtained.