Response surface analysis: SPION@SiO 2 particle design SPION@SiO 2 NPs prepared according to the conditions outlined by the DoE were characterised using TEM, and PPMS-VSM. TEM analysis determined the NP size, monodispersity, and population of SPION@SiO 2 NPs formed. Figure shows TEM images of the NPs generated at level 1 of number of moles of TEOS (0.16 mmol); TEM images of samples prepared at TEOS levels 2 and 3, and centre point conditions can be found in Fig. , ESI †. Boxplots showing the size distribution of the measured total diameter (d TEM ) of the core@shells produced in this study can be observed in Fig. , ESI †. Response surface analysis was used to explore relationships and interactions between experimental factors and their effect on the response variables (Table and Table , ESI †). Across all particles produced, the d TEM of particles ranged from 15 nm to 75 nm; the thickness of the silica shell (t shell ) ranged 2 nm to 32 nm; the normalised entropy (E n ) ranged 0.15 to 0.65 (characterising all particles to be either monodisperse or near monodisperse (vide infra)); and a single-core@shell population of 35 % to 99 % was observed. The SPION@SiO 2 were found to be weakly superparamagnetic; the mass susceptibility plots can be found in Fig. , ESI †.