2.2.3. Electrophoretic Light Scattering Measurements

Microelectrophoretic mobility of the liposomes was obtained by performing micro-electrophoretic assessments on samples using ELS technique. The measurements were performed by Zetasizer Nano ZS apparatus (Malvern Instruments, Malvern, United Kingdom). The xperiment was carried out as a function of pH using a WTW InoLab pH 720 laboratory meter (WTW, Weinheim, Germany). The samples were suspended in 155 mM/L NaCl solution and titrated to the desired pH (range 2–10, every ± 0.3 units) with HCl or NaOH. Six measurements were made (each covering 100–200 series for a duration of 5 s) for each pH value per sample. Experiments were performed three times with similar results.

The surface charge density δ depends on electrophoretic mobility as described by the following equation [43]:

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

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

The diffuse layer thickness is defined as [44]:

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

where: *R* represents the gas constant, *T*—the temperature, *F*—the Faraday constant, *I*—the ionic strength of 0.9% NaCl, and ε and ε<sup>0</sup> refer to the permeability of the electric medium.
