## 3 Results and Discussion
### EIS Measurements  
The impedance measurements were performed on our fabricated textile-based microfluidic platform for each type of EO in different concentrations. Firstly, a dry platform (dry chip) was applied without delivering any solution, followed by the application of EOs to detect differences in the modulus of impedance. The tea tree, clary sage, and cinnamon bark EOs, at 0.2% concentrations, were studied. Figure 3 presents Nyquist plots of the studied EOs, presenting an imaginary part of impedance (\(Z\)\") as a function of a real part of impedance (\(Z\)\") measured at four terminals, as labeled in Figure 1 (at the same sides, Z12 and Z24, and diagonally, Z13 and Z24). Figure 2: (**a**) Experimental setup for EIS, (**b**) injection of EO solution onto the sensing part of the device. Figure 3: [PERSON]’s plots measured using all four electrode terminals for dry chip (black curves) and for (**a**) cinnamon EO, (**b**) tea tree EO, and (**c**) clary sage EO. It can be concluded from Figure 3 that the injection of EOs resulted in increasing the real part of the electrical impedance compared to the dry textile chip. Minor differences in impedance at different terminals are a consequence of the different distances between contacts on the one side and contacts on diagonal sides. Moreover, this small difference can be attributed to the non-ideal distribution of the applied solution in the knitted silver thread structure. However, this difference in impedance is negligible and, in further steps of our study, the results obtained between terminals 1 and 3 (labels shown in Figure 1)--Z13, will be shown. In addition to the visual differentiation in the Nyquist plots between tested EOs, for the development of a portable measurement device with limited processing capabilities, we propose the use of the root-mean-square deviation (RMSD) of the real part of the impedance. The result is a scalar value that can easily be used to compare EOs when compared to the baseline (dry sample). The RMSD for the real part of the impedance is defined as:  
\[\text{RMSD}\;=\;\sum_{i\;=\;1}^{N}\left[\frac{(\text{Re}(\text{Y}_{i,1})\;- \;\text{Re}(\text{Y}_{i,2}))^{2}}{\left(\text{Re}(\text{Y}_{i,1})\right)^{2}} \right]^{\frac{1}{2}} \tag{1}\]  
where the real part of the impedance of the first measurement (dry chip) is Re(Y\({}_{i,1}\)), the real part of impedance for different solutions is Re(Y\({}_{i,2}\)), and N is the number of measurement points in frequency sweep. Normally, RMSD values are used in the field of protein structure studies as a quantitative measure of similarity between two or more protein structures [24; 25]. However, in our study the significance of RMSD calculations is based on the fact that RMSD elements are estimated for each measurement point, requiring small memory resources. Therefore, high memory demand is eliminated, as there is no need for a buffer to store and process all data points simultaneously. Moreover, as it is a scalar value it does not require the graphical analysis of the complete dataset. Finally, the RMSD values obtained during the calibration process can be easily stored in the microcontroller's internal memory for the fast in situ differentiation of various EOs. Calculated RMSD values in the frequency range from 100 Hz to 10 kHz were 55.37 for clary sage, 34.66 for tea tree, and 34.03 for cinnamon bark EOs. The ratio between the modulus of Z13 for a chip with applied solutions of 0.2% for all three types of EOs and for a dry chip is presented in Figure 4.  
We performed a linear regression analysis of the curves shown in Figure 4. Using the ratio presented in Figure 4, at four frequencies (10 Hz, 100 Hz, 1 Hz, and 10 kHz), linear  
Figure 4: Impedance ratio of EOs and dry chip as a function of frequency. equations were determined, followed by R\({}^{2}\) calculations. Equations are included in Figure 4. With the calculations of R\({}^{2}\) values, we wanted to compare the linearity of curves for three different EOs.