*2.2. Methods*

Microelectrophoretic Mobility Measurements

The purpose of the microelectrophoretic experiment was to obtain the dependence of the surface charge density on the pH of the electrolyte solution. Using a Zetasizer Nano ZS (Malvern Instruments, Malvern, UK) apparatus allowed us to obtain data on the microelectrophoretic mobility of the blood cells using the laser Doppler microelectrophoresis (LDE) technique. WTW InoLab 720 laboratory pH meter (WTW, Weinheim, Germany) use for all measurements was performed as a function of pH. Six measurements were made (each covering 100–200 series for a duration of 5 s) for each pH value for each sample.

Equation (1) allowed us to calculate of the surface charge density from electrophoretic mobility measurements [30]:

$$
\delta = \frac{\eta \cdot u}{d} \tag{1}
$$

where *η* is the viscosity of the solution, *u* is the electrophoretic mobility, and *d* is the diffusion layer thickness.

The thickness of the diffusion layer can be determined from the following formula (Equation (2)) [31]:

$$d = \sqrt{\frac{\varepsilon \cdot \varepsilon\_0 \cdot R \cdot T}{2 \cdot F^2 \cdot I}}\tag{2}$$

where *R* is the the gas constant, *T* is the temperature, *F* is the Faraday number, *I* is the ionic strength of 0.9% NaCl, and *εε*<sup>0</sup> is the permeability of the electric medium.
