Figure 1.

(A) Picture of conventional electrochemical cells with pen-like electrodes. (B) Examples of commercial screen-printed electrode cards from DropSens (ceramic substrate [13]) and MicruX (polymeric substrate [14]). (C) Schematic drawing of the stencil-printing process to fabricate several low-cost electrodes on a transparency sheet, with pictures showing the integration of the transparency electrode onto the cap of a sample vial for on-site water analysis. (D) Pictures of a paper-based electrochemical cell containing the three electrodes (top and bottom views), also inserted in a commercial interface that connects electrodes to the potentiostat. (C) and (D) are reprinted from [15] (Chapters 4 and 25), Copyright (2020), with permission from Elsevier.