Similarly, Jaiswal et al. [22] reported a porous surface ofCu–chitosan NPs. Qi et al. [28] described the Cu sorption mecha-nism by ion-exchange resins and surface chelating which furtherfacilitated by a porous surface of chitosan nanomaterials. Interest-ingly, in our study ESD spectra of porous chitosan nanomaterialsmanifest higher Cu deposition in porous area which clearly sup-ports the mechanism described by Qi et al. [28]. In the presentstudy, 80% of Cu was embedded in chitosan nanoformulation whichis higher than our previous finding [18]. Based on this study, wepresent here a hypothetical model of Cu–chitosan NPs synthesisthrough chitosan, TPP and Cu interaction and encapsulation ofCu into chitosan (Fig. 6). In our model, Cu–chitosan NPs exhib-ited +22.6 mV zeta potential that indicated substantial stabilitythrough electrostatic repulsion of positively charged nanoparti-cles. In addition, positive value of the zeta potential provides moreelectrostatic interaction with biological membranes and therebymore antifungal activity [18,20]. Based on the observations, weassume that the zeta potential of Cu–chitosan NPs is critical fordetermining the antifungal activity and nanoparticle stability. Inthe present study, Cu–chitosan NPs (at concentration of 0.10 and0.12%) significantly impeded fungal mycelia growth and spore ger-mination. These results are comparable with our earlier reportswhere Cu–chitosan NPs exhibited substantial in vitro antifungalactivity against A. alternata, M. phaseolina and R. solani [18]. Fur-thermore,