Exploring Interdigitated Electrode Arrays Screen-Printed on Paper Substrates for Steady-State Electrochemical Measurements

Abstract

This research explores the use of interdigitated electrode arrays (IDE) screen-printed on paper substrate for electrochemical measurements in steady state. Since the steady state is strongly related to IDE dimensions, the accuracy and reproducibility of the fabrication process were assessed for stencils of 120- and 200-mesh. Simulations were used to predict the limiting current and time response, and as a benchmark for comparison with the experimental results. For accurate an comparison, evaporation was prevented by using a homemade humidity box, which enabled measurements for periods as long as 30 min. Although cyclic voltammetry measurements in steady state were possible, this required at least 15 min per cycle when using the smallest electrodes (band width of 0.205 mm). Chronoamperometric measurements reaching steady state were also possible, requiring nearly 5 min for the largest electrodes (band width of 0.376 mm). Regarding the reproducibility of measurements, the relative standard deviations (RSD) of current and response time were near 12% and 26%, respectively. We attribute this mainly to the reproducibility of IDE fabrication (8% RSD). Experimental currents were approximately 30% to 34% of their simulated counterparts. Conversely, the simulated response times were about 30% to 50% of their experimental counterparts. We ascribe these discrepancies to the porosity of the paper (Whatman 2 CHR), estimated to be near 31% under wet conditions. This suggests that fibers inside the paper substrate block the passage of electrochemical species, thereby delaying their diffusion and decreasing the current. Steady-state voltammetry needs 15 min when using electrode bands of 0.205 mm Chronoamperometry needs 5 min to steady state when using electrode bands of 0.376 mm Measured current in wet paper was 30% to 34% of that simulated in free solution Time constant simulated in free solution was 30% to 50% of that measured in paper Diffusion coefficients in paper and free solution are related by the paper porosity