# Smartphone-Based NFC Potentiostat for Wireless Electrochemical Sensing
## 4 Discussion  
This study demonstrated the design and performance of an NFC potentiostat (Silicon Craft Technology PLC, Bangkok, Thailand), which is a battery-free and flat card-sized device that interfaces with a smartphone through near-field communication. The device was designed for electrochemical measurement in point-of-care testing and resource-limited settings that do not require technical users. These potentiostats have the following aspects: (1) portability: the device is credit-card-sized (5.5 cm \(\times\) 8.6 cm) and weighs only 8.07 g; (2) low cost: this potentiostat is designed to be used with a screen-printed electrode, which is low-cost, disposable and has ease of modification to detect various analytes [53; 54]; (3) ease of use: the NFC potentiostat is operated via a smartphone application. The smartphone application allows the user to set the parameters of an electrochemical experiment and receive the resulting data; (4) wireless and cloud connectivity: the connection of smartphones facilitates sharing and storage of all information to the database in order to minimize the  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Added (mg/mL)** & **Found (mg/mL)** & **Recovery (\%)** \\ \hline
0.2 & 0.197 \(\pm\) 0.009 & 98.78 \(\pm\) 4.74 \\
0.4 & 0.383 \(\pm\) 0.011 & 95.80 \(\pm\) 2.87 \\
0.6 & 0.556 \(\pm\) 0.014 & 92.69 \(\pm\) 2.35 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Analyses of ascorbic acid in spiked commercial drinking water measured by cyclic voltammetry (\(n=3\)).  
Figure 7: (**a**) Cyclic voltammograms of different concentrations of ascorbic acid (0.1–1.0 mg/mL). (**b**) The calibration curve between current (\(\mu\)A) and concentration of ascorbic acid (mg/mL). The current observed at 550 mV was used to plot the calibration curve to determine the ascorbic acid concentration.  
manual error and create big data for further analysis, such as machine learning or artificial intelligence.  
The performance of the NFC potentiostat was evaluated by comparing it to a commercial benchtop potentiostat. Cyclic voltammetry and chronoamperometry were carried out in a potassium ferricanide solution containing 0.1 M KCl. The results showed good agreement of cyclic voltammograms between the two devices, but current signals of our NFC potentiostat were lower than the commercial potentiostat. The deviation was from the difference of applied potential step voltage from the DAC and differences in sampling time and period designed for each potentiostat. For amperometric measurements, the slope of the current response obtained by the NFC potentiostat was similar to the commercial potentiostat with a reliability greater than 97%, although the signal from the NFC potentiostat was observed to have current noise, compared with the commercial potentiostat, which was free of noise. The noise was from a limitation of the analog-to-digital converter (ADC) resolution of the potentiostat, which is 12 bit and less than that of the commercial benchtop potentiostat. Note that the setting measurement range was \(\pm\)20 \(\mu\)A, hence, the noise floor should be around 10 nA.  
The first prototype of the NFC potentiostat can perform cyclic voltammetry and chronoamperometry with the input current \(\pm\)20 \(\mu\)A and the biasing voltage at \(\pm\)0.8 V. Although the benchtop potentiostats offer a wide operational window of current and voltage (\(\pm\)2 A, \(\pm\)10 V), they are too expensive and large for on-site measurement. Therefore, an NFC potentiostat can be an alternative device for electrochemical measurement in point-of-care testing and resource-limited settings. In a future prototype, the operation ranges will be expanded and the system will be developed to support various electrochemical techniques such as linear sweep voltammetry, square wave voltammetry and differential pulse voltammetry.