Figure 7.

(a,b) Measured impedance spectrum (10 Hz–100 kHz) of the proposed f-EIS (the fitting residual r² = 0.9248). (c) $\left|\Delta Z/Z_{\mathrm{b}}\right|$ at 100Hz vs. concentration for the three methods. (d) Slope of Figure 7a ($\left|\Delta Z/Z_{\mathrm{b}}\right|$ (y) vs. concentration (x) [pg/mL]); nf-EIS: y = 0.4231 × ln(x) + 3.0236, r² = 0.9671; f-EIS: y = 0.6164 × ln(x) + 10.924, r² = 0.9446; proposed f-EIS: y = 4.5859 × ln(x) + 7.4451, r² = 0.9382.