# Trimodal Watch-Type Wearable Health Monitoring Device
## 3 Experimental Results
### Aqueous Phase Testing  
Before conducting aqueous phase testing, the accuracy of embedded CV technique was evaluated using a resistor array with values of 100 K\(\Omega\), 150 K\(\Omega\), 200 K\(\Omega\), 270 K\(\Omega\), and 300 K\(\Omega\). Figure 6 illustrates the results of the CV experiments. In these plots, the Y-axis represents current in the unit of \(\mu\)A, and the X-axis is voltage in the unit of mV. The potential sweep range was set from \(-900\) mV to \(+900\) mV with a sweep rate of 100 mV/s. Since discrete resistors were used to substitute the sensors, the result of the CV exhibited a linear relationship between output current and applied potentials, consistent with [PERSON]'s law. This observation confirms that the designed CV technique is functioning as anticipated. The error rate calculated using expected and measured current values is found to be 1% during the experiment.  
Figure 5: Gas phase testing results (**a**) Windows GUI; (**b**) Android app.  
Upon validating the accuracy of the embedded CV technique, aqueous phase testing is conducted using dopamine, a key analyte found in human sweat. Dopamine is often used as a model molecule for studying electrochemical processes because it undergoes oxidation and reduction reactions at specific potentials, making it a suitable compound for investigating electron transfer mechanisms during CV experimenst. A reference voltage is applied to an electrochemical cell containing the analyte (dopamine) and a WE. As the voltage is varied, current flows through the cell, and the current response is measured. The cyclic voltammogram, which is a plot of current versus applied potential, shows peaks corresponding to these oxidation and reduction reactions. The peak positions and shapes can provide information about the kinetics and thermodynamics of the electron transfer processes involved.  
The DRP-110 CNT SPES (Metrohm DropSens, Oviedo, Spain) was used in the experiment, which is a disposable screen-printed carbon electrode modified with carboxyl functionalized Multi-Walled Carbon Nanotubes (MWCNT-COOH). The WE is made of MWCNT-COOH, the CE is made of carbon, and the RE is made of silver. The electrode is pre-treated with 0.05 M phosphate-buffer solution (PBS). To pre-treat the electrode, 50 \(\mu\)L of PBS is drop-cast onto the WE, and CV is performed by applying +1.4 V for 300 s. The pre-treated electrode is then cleaned with de-ionized water. Stock solutions of dopamine are prepared in PBS at different concentrations (0.1 mM, 0.2 mM, 0.4 mM, 0.8 mM, and 1 mM). 50 \(\mu\)L of prepared solution is drop-cast on the WE. For CV, reference voltage of \(-200\) mV to +600 mV is applied to the SPES at a sweep rate of 25 mV/s and the corresponding current is measured. The experiment is repeated with different concentrations of dopamine. Figure 7a shows the cyclic voltammogram trace, with the current at the WE plotted against the applied voltage. These data are used to create a calibration curve in Figure 7b, where the current is plotted as a function of dopamine concentration. During the CV experiment, the applied potential is initially ramped from \(-200\) mV to +600 mV, resulting in five distinct peaks that correspond to different dopamine concentrations based on the redox reaction. The potential is then reversed and ramped back from +600 mV to \(-200\) mV. As the dopamine concentration increased, the current at the WE increased accordingly, showing an R\({}^{2}\) of 0.9579. This result confirms that the device responds to the CV technique when tested with dopamine solutions of different concentrations.  
Figure 6: Cyclic voltammetry test results with resistor array.