Table Parameter estimates that were deemed to be active in effecting the silica shell thickness of SPION@SiO 2 nanoparticles formed. The parameter estimates were calculated from the regression analysis and used in the prediction expression. In the case below, the fractionated addition of TEOS is included as a parameter, regardless of its p-value, due to its presence in the interaction term. Note that the t-ratio is the estimate divided by the standard error. If ≥ 1.96 (absolute value) the parameter is statistically significant. If the absolute value is < 1.96 the parameter is not statistically significant. The p-value is the probability of the null hypothesis (H 0 ) being true. The lower the p-value the less likely the H 0 is true. Herein, the null hypothesis assumes the experimental factors have no impact on the outcome. OH reduces the aqueous domains present which reduces the micelle size and quantity, therefore limiting places for shell growth to occur. Fewer fractionated additions of TEOS increase the amount of TEOS within each addition available for hydrolysis. With more hydrolysed TEOS present, there is competition between the formation of silica byproduct and growth of the silica shell. Due to the limited micelles available, this increased presence of hydrolysed TEOS therefore favours the formation of silica by-product. As such, these conditions encouraged the formation of non-defined core@shell structures, (as seen in the top row of Fig. ). As the number of moles of NH 4 OH and fractionated additions of TEOS increased, more defined core@shells were formed, and increasing t shell was observed.