Magnetic nanosheets: from iron oxide nanocubes to polydopamine embedded 2D clusters and their multi-purpose properties†

We here develop stable bidimensional magnetic nanoclusters (2D-MNCs) of iron oxide nanocubes (IONCs) arranged in thin nanosheets of closed-packed nanocubes. The assembly occurs by means of a two-step approach: in the first one, the ionic surfactant, sodium dodecyl sulfate (SDS), acts as a transient water transfer agent and as 2D clustering agent to induce formation of a monolayer of nanocubes arranged in thin nanosheets. Next, the addition of dopamine followed by solution basification, induces the in situ polymerization of dopamine with a tunable shell tickness depending on the dopamine amount, which helps to compact the clusters and ensures the long term water stability of the clusters. TEM, cryo-EM, and SAXS techniques helped to reveal structural features of the 2D-clusters. The pH-dependent degradation properties of polydopamine, enable to disassemble the clusters in acidic tumour microenviroment leading to a four-fold increase in the magnetic particle imaging signal and a concomitant increase of the magnetic heat losses of these clusters, makes them appealing in magnetic hyperthermia, while the shortening of T₂ relaxation time suggests their use as contrast in magnetic resonance imaging. Finally, with crystal violet dye, used as drug molecule, the feasibility to release payloads pre-encapsulated with the polydopamine polymer shell has been also shown.