The experimental design was produced and studied using the statistical software JMP (version 15). To establish the local re- sponse surface, a 3 3 full-factorial design was chosen to study the synthesis of SPION@SiO 2 (Fig. ). This design allowed for the identification of main effects and interactions, in addition to nonlinear effects, which were modelled as quadratic functions. Three experimental variables were selected for investigation: moles of TEOS, moles of NH 4 OH, and the number of fractionated additions of TEOS, as stated in Table . These experimental factors and their upper and lower limits were chosen based on literature evidence, being previously identified as important parameters in the hydrolysis and condensation mechanism for the silica shell formation. The concentration and size of the SPION NP core and the concentration of the core stabilising agent, IGEPAL-co-520 were fixed, and not included in the study, as the growth of a silica shell is primarily controlled by the aforementioned experimental factors. The centre point treatment, labelled 222, was repeated five times, totalling 31 experimental runs. These were randomised to avoid bias. It is worth noting that for ease of comparison between factors and the responses, the experimental treatments have been arranged based on the DoE pattern of the experimental factors (1,2,3). In this study, the silica shell thickness, monodispersity and population of SPION@SiO 2 NP formed were used as response variables. The null hypothesis, H 0 , states that the experimental factors (number of mole of TEOS, number of moles of NH 4 OH, and the number of fractionated additions of TEOS) have no effect on the SPION@SiO 2 NP formed. The alternative hypothesis, H a , states that the experimental factors do effect the SPION@SiO 2 NP formed.