Regression analysis of SPION@SiO 2 indicated that the number of moles of TEOS, number of moles of NH 4 OH and fractionated addition of TEOS were important parameters in determining the size, monodispersity and overall quality of the population of particles formed. Throughout each of the different response models, the experimental parameters of TEOS and NH 4 OH number of moles were statistically relevant, regardless of the nature of their effect. On the other hand, the number of fractionated additions of TEOS was found to be significant only as part of an interaction effect in combination with either the number of moles of TEOS or number of moles of NH 4 OH. The cause of these dependencies lies in the mechanism of the growth of NPs.