Fabrication of Low‐cost Screen‐printed Electrode in Paper Using Conductive Inks of Graphite and Silver/Silver Chloride

The fabrication of the Screen-Printed Electrode (SPE) was performed using the graphite ink to print the working (WE) and counter electrodes (CE), and silver/silver chloride path as reference electrode (RE). All the electrodes are printed in a paper substrate using screen-printing technique. The resulting SPE is characterized using scanning electron microscopy, showing all the ink layer, and subsequently optimized. The paper sample presented the cellulose fibers entanglement, extremely rough, with highly porous network. Then the graphite ink was deposited and the surface became flat, thinner and very smooth. When the silver ink was painted on top of the graphite ink, the spherical silver particles, ranged from 2-3.5 mu m in size, were observed. And finally, the silver ink was covered with a AgCl layer and the particle size becomes larger with an irregular sphere-like phase. The images showed that the layers appear to be homogeneously distributed with good coverage. Then fabrication process was optimized concerning type of paper, the sanding process, the hydrophobic barrier, the electrode design and size. In summary, the optimized values included using the previously sanded matte paper with a mineral spirit layer. The design and size of the electrode were also tested to achieve the best electrochemical performance (design 3 with 3.5 cm). The final SPE was a miniaturized and flexible paper-based electrochemical electrode. In order to evaluate the electrical properties, the ohmic resistance of each ink was tested using a multimeter and the obtained values were 2.18 k omega for the graphite ink, 2.27 omega for the silver ink and 38.33 k omega for the silver/silver chloride ink. That can indicate the good conductivity of each ink used in the fabrication of the electrode and the correct deposition of Ag/AgCl. Finally, the electrode was used to measure the electrochemical response of K-4[Fe(CN)(6)] in different concentrations. Then a calibration curve was obtained from the voltammograms and a linearity was observed between the current and concentration in the range of 0.50-2.00 mM. That indicates that the SPE has potential to be used as a voltammetric electrode.