The population of SPION@SiO 2 was observed to be dependent on the interaction between the number of moles of TEOS and the number of moles of NH 4 OH. The term was estimated to have a negative effect on the population if the number of moles of both simultaneously increased or decreased. If the number of moles of either TEOS or NH 4 OH increased, while the other decreased, an increase in population of SPION@SiO 2 would be observed. These trends can be found in the regression equation 4 and contour-map in Fig. , where the contour planes are curved and the map has a paraboloid-structure. It is interesting to note that the fractionated addition of TEOS was determined to have no effect on the population of core@shell particles formed, contrary to what is reported in literature. Instead, we found that fractionated additions of TEOS contributed only to the shell growth and monodispersity and hence the mechanism of growth, rather than population of SPION@SiO 2 formed.