Figure 3 d showed positive linear relationship between zeta potential and amount of chitosan used for developing the nanoparticles. The relationship was predictable since chitosan dissolves in an aqueous solvent, exhibiting net positive charges due to the protonated amine group (30). When the amount of lecithin used decreases, the zeta potential increases, proving that negatively charged lecithin had reacted with positively charged chitosan, producing a negative effect on zeta potential. The same trend can be seen in Fig. 3 e, where PEG 2000 with a surface charge of − 2 to − 7 mV also had a negative effect on zeta potential, but to a lower extent to that of lecithin (32). It can be seen that chitosan was capable of producing formulation with zeta potential greater than 50 mV. Still, the use of PEG 2000 and lecithin, or to be exact, the electrostatic interaction between chitosan and other components, causes the reduction of zeta potential. Figure 3 f further supported the point that lecithin and PEG 2000 were responsible for zeta potential decrement. When a higher proportion of PEG2000 (40 mg) and lecithin (300 mg) was used, the zeta potential significantly decreases in the nanoparticles.