The monodispersity of the NPs, as determined from nanoparticle size distribution was assessed using nanoparticle entropy (E n ). Size distribution was analysed using a modified Shannon entropy, equation 1. By using this approach, a system can be described as either highly monodisperse, monodisperse, near-monodisperse, or polydisperse, based on the normalised nanoparticle entropy, E n . If E n falls in the range 0 to 0.125, it is classified as highly monodisperse, it is monodisperse if E n is between 0.125 and 0.206, it is near-monodisperse between 0.206 and 0.618, and anything above 0.618 is classified as polydisperse. Following this classification, all SPION@SiO 2 NPs formed were classified as monodisperse or near-monodisperse, excluding treatments 111 and 113, which were classified as polydisperse. Treatments 112 and 331 were excluded from analysis due to an insufficient sample size.