## Materials and Methods  
### Materials and Manufacturing  
Figure 1 is an illustration, including photographic images of the connected components, of the fabrication process followed to manufacture the paper-based potentiostat.  
The global interconnections of the paper-based potentiostat consist of conductive tracks and component pads that were inkjet-printed with a nanosilver ink (NPS-JL, Harima Chemicals, Tokyo, Japan) onto a photo paper substrate (NB-RC-3 GR120, Mitsubishi, Tokyo, Japan) using a drop-and-demand piezo inkjet-printer (DMP-2831 Materials printer, Dimatix, Santa Clara, CA, USA). Printing was performed using a single nozzle, jetting at 40 V, a nozzle temperature of 28 \({}^{\circ}\)C and a platen temperature of 30 \({}^{\circ}\)C. This was followed by a thermal curing step at a 100 \({}^{\circ}\)C for an hour in a convection oven (276 digital EcoTherm convection oven, Labotec, Midrand, South Africa). Surface  
Figure 1: A flow diagram of the steps followed to fabricate the printed paper-based potentiostat.  
mount components were mechanically connected to the paper substrate using Superglue (Precision Superglue(r), Henkel Loctite, Dusseldorf, Germany) and the through-hole pin connectors were adhered to the paper using an 0.9 mm needle and Superglue. The components were electrically connected by hand-painted silver conductive paste (CircuitWorks Conductive Epoxy, Chemtronics, Kennesaw, GA, USA). The process was concluded by a 10 min curing step at 66 \({}^{\circ}\)C in the convection oven.  
The effectiveness of the tracks and connections were validated using a multimeter (Agilent U1242B True RMS Multimeter, Agilent technologies, Santa Clara, CA, USA), and track parameters were characterized in detail using an impedance analyzer (GW-Instek LCR-8110G, New Taipei City, Taiwan). The LCR measurement instrument was connected to the tracks via 1 mm round-tip pogo pins. DC four-point probing, with calibration on the pogo pins, was used to characterize and compare the resistance of the silver tracks printed on paper substrate to that of copper PCB tracks.  
The Fujifilm-supplied ACE7000 software permits the conversion of layout data in various design formats to a pattern file, which the Dimatix printer uses. Therefore, direct transfer from the design of the PCB potentiostat to a paper-based design is possible as illustrated in Figure 2. This approach enables parallel product development, allowing the paper-based circuitry and back-end development to occur independently, and then integrated.  
The paper-based potentiostat, the PCB potentiostat and the development board (LMP91000 EVM, Texas Instruments, Dallas, TX, USA) consist of a sensing chip (LMP91000, Texas Instruments, USA) and required electronic circuitry connected to an Arduino Uno (Arduino, Ivrea, Turin, Italy) which controls and communicates with the potentiostat front-end. The Arduino Uno transmits the sensor data to a personal computer (PC) where the data is saved to a Microsoft Excel (2010) template file and graphed. The results of each system were compared to the results obtained from the laboratory-based potentiostat (Autolab PGSTAT, Metrohm, Germany).  
An 80 \(\mu\)L sample of 5 mM ferri-ferrocyanide ([Fe(CN)6]\({}^{3-/4-}\)) redox coupled with 0.1 M potassium chloride (KCI) electrolyte was drop-cast onto a commercially available screen-printed carbon ceramic electrochemical sensor (DS-C110, Dropsens, Asturias, Spain) for each experiment.