# Development of Screen-Printable Nafion Dispersion for Electrochemical Sensor
## 3 Results
### Detection of Heavy Metals  
To evaluate the performance of the modified Nafion as an ion-exchange membrane (IEM) for electrochemical sensors, the ink was screen printed onto commercial sensors with screen-printed Ag as a working electrode (from BASi). The performance of the sensors with and without modified Nafion was evaluated by analyzing the concentrations of Pb(II) in 10 mM KNO3 buffer solution (pH = 5).  
Figure 8 shows the peak intensity (log10 scale) of the SWASV measurement of 100 ug/L and 500 ug/L Pb(II) using commercial sensors with and without the modified Nafion. The stripping peak currents of sensors without modified Nafion were at 0.0452 uA and 0.151 uA for 100 ug/L and 500 ug/L of Pb(II), respectively. With Nafion coating as the ion-exchange membrane, the peak current increased more than 50 times to 3.13 uA for 100 ug/L of  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Avg Height (\(\upmu\)m)** & **Roughness (Sa) (\(\upmu\)m)** \\ \hline Nafion Film 1 & 16.028 & 3.710 \\ Nafion Film 2 & 15.777 & 2.906 \\ Nafion Film 3 & 15.397 & 3.045 \\ \hline \hline \end{tabular}
\end{table}
Table 2: LSCM film thickness and roughness measurements of screen-printed Nafion membranes.  
Figure 7: High-resolution scan of Na1s of the modified Nafion material centered at 1070.74 eV. The black curve is the scan data; the blue curve is the fitted data, and the green curve is the baseline.  
Pb(II) and to 17.61 \(\upmu\)A for Pb(II) level of 500 \(\upmu\)g/L, respectively. The significant increase in peak intensity is due to the target Pb(II) ions being pre-concentrated by the sulfonated groups, which indicates that the modified Nafion material still possesses strong cation-exchange properties.  
The performance of the commercial sensors with modified Nafion was further characterized by analyzing Pb(II) with concentrations ranging from 1 \(\upmu\)g/L to 500 \(\upmu\)g/L in 10 mM KNO3 buffer solutions. The obtained voltammograms at various Pb(II) concentrations are shown in Figure 9. The anodic peak of Pb(II) has a peak potential of \(-\)0.74 V, and the peak intensity increases with the increase in Pb(II) concentrations. The peak shape and baseline are good at most concentrations except for those at 1 \(\upmu\)g/L, at which the signal-to-noise ratio (S/N) is slightly less than 3. Solutions containing different Pb(II) concentrations were analyzed in triplicate, and the average peak currents were plotted as a function of Pb(II) concentrations, as shown in Figure 10. Standard deviations at each level are also included in the calibration curve as Y-axis error bars. Overall, the commercial sensor with modified Nafion showed good linearity within the range of 5 \(\upmu\)g/L to 500 \(\upmu\)g/L of Pb(II) with an R-square value of 0.989. The detection limit for Pb(II) is estimated at around 2 \(\upmu\)g/L based on the S/N ratio. The obtained detection limit of sensors with the modified Nafion is below the EPA regulatory limit for Pb (15 \(\upmu\)g/L) and is also comparable to those with other electrode materials in previous reports [8; 9]. No delamination was found in those tested sensors and the Nafion membrane retained its integrity and functionality after 1 month of soaking in the buffer solutions. Again, this result demonstrates the superior application potential of modified Nafion as a screen-printable, cation-exchange membrane in electrochemical sensing and detection.  
Figure 8: Peak current (log\({}_{10}\) scale) of ASWV for detection of different Pb(II) concentrations using sensors with or without a Nafion membrane.