One-pot synthesis of maghemite nanocrystals across aqueous and organic solvents for magnetic hyperthermia

Superparamagnetic iron oxide nanocrystals (SPIONs) continue to receive intensive interest due to their significant prospects in biomedical applications. However, a critical requirement for such applications is the ability to synthesise high quality nanocrystals that are not only readily dispersible in aqueous solvents, but also retain good magnetic properties in an aqueous medium. This is not easy to achieve because, although organic solvent-based syntheses provide better control over SPIONs properties, their magnetic properties in particular, tend to deteriorate during aqueous phase transfer. In the current work, we propose a new route for the synthesis of high quality SPIONs using triethylamine (TEA) as a dynamic amphiphilic molecule. We demonstrate that in a single step, TEA can directly synthesise SPIONs that are readily dispersible in both aqueous and organic media. We further demonstrate the versatility of TEA in facilitating one-step phase transfer of SPIONs from organic to aqueous solvents. We then extend the applicability of this approach to demonstrate for the first time that organic molecules-capped SPIONs can also be directly dispersed in aqueous solvents. These SPIONs show remarkable potential for hyperthermia, as demonstrated through their outstanding magnetic field induced heating performance, which improves after their phase transfer to the aqueous phase. The current study establishes the importance of a suitable nanoparticle phase transfer protocol to ensure that the final product retains all the desirable application-focussed properties.