Assessment of differential magnetic susceptibility in nanoparticles: Effects of changes in viscosity and immobilisation

Abstract The nonlinear magnetic behaviour of superparamagnetic iron-oxide nanoparticles (SPIONs) has attracted interest as a valuable feature for upcoming medical applications. Injecting SPIONs into the human body affects their magnetic properties through the formation of protein corona or cell immobilisation. It is therefore important to study the effects of environmental changes on the magnetic susceptibility of SPIONs. A superparamagnetic quantifier (SPaQ) is used here to assess the differential magnetic susceptibility of three commercially available SPIONs: Synomag®, Resovist® and Sienna+®. The following experiments were carried out to mimic the influence of the biological environment on the magnetic responses of SPIONs: (i) varying the viscosity of the medium; and (ii) immobilising the nanoparticles by freeze-drying. Differential magnetisation curves as a function of the applied magnetic field were visualised to reveal the dynamic magnetic behaviour of SPIONs in both experiments. Synomag® displayed the lowest decrease (~5%) in differential magnetic susceptibility compared to Resovist® (~33%) and Sienna+® (~21%), for a change from water to a high-viscosity fluid. Although Synomag® showed a clear drop in differential magnetic susceptibility (~58%) after freeze-drying, it still appears to be a promising candidate for clinical applications due to its low sensitivity to changes in viscosity.