the nanostructures will decrease the solution potential,
while loaded nanopaticles will affect less the solution potential.
Thus, we could assume that at least part of the nanoparticles are still loaded since the nanoparticle potential is less negative for the loaded case.
Further more, in time, for booth cases of loaded and unloaded nanoparticles, the negative potential diminish, suggesting that some components of the FBS containing medium might attach to the structures, annihilated the particles negative potential.