Among these parameters, the surface charge is the one that determines how the nanoparticles interact with their environment in conjunction with the neighbouring nanoparticles. It is a measure of the electrokinetic potential in colloidal systems between the bulk solution and the particle surface. In the context of drug delivery systems, the total charge on the particle surface is formally referred to as the zeta potential, which is determined using laser Doppler anemometry. A high absolute value of the zeta potential -more than 30 mV (on both the negative and positive sides) -indicates a high surface charge on the drug-loaded CSHNs, which leads to strong repulsive forces between the particles, thereby preventing aggregation of the nanoparticles. However, if the value of the zeta potential is below 5 mV, agglomeration occurs . In addition to the surface charge, some other properties of the solution (e.g., the pH, the ionic strength, and the type of solution) are also crucial for the surface charge of the core-shell structures and thus for the agglomeration state of the nanoparticles in solution. When nanoparticles aggregate, they are no longer on the nanoscale but form larger clusters whose physical properties are significantly different from those of particles dispersed in solution. In summary, the zeta potential is recognized as a measure of the stability and durability of nanoparticles.