Small (d∼ 8 nm) magnetite nanoparticles, Fe3O4NP, are prepared and coated with mercaptopropyl trimethoxysilane (MPTS) to form Fe3O4NP@MPTS. In the coating step controlled MPTS/Fe3O4NP molar ratios are used, ranging from 1 to 7.8 × 10(4). The total quantity of MPTS per Fe3O4NP is determined by SEM-EDS analysis and the average number of free, reactive -SH groups per Fe3O4NP is calculated by a colorimetric method. At very low molar ratios MPTS forms a submonolayer on the Fe3O4NP surface with all -SH free to react, while on increasing the MPTS/Fe3O4NP molar ratio the (CH3O)3Si- groups of MPTS polymerize, forming a progressively thicker shell, in which only a small fraction of the -SH groups, positioned on the shell surface, is available for further reaction. The MPTS shell reduces the magnetic interactions occurring between the magnetite cores, lowering the occurrence and strength of collective magnetic states, with Fe3O4NP@MPTS showing the typical behaviour expected for a sample with a mono-modal size distribution of superparamagnetic nanoparticles. Interaction of Fe3O4NP@MPTS with gold nanostars (GNS) was tested, using both Fe3O4NP@MPTS with a MPTS submonolayer and with increasing shell thickness. Provided that a good balance is used between the number of available -SH and the overall size of Fe3O4NP@MPTS, the free thiols of such nanoparticles bind GNS decorating their surface, as shown by UV-Vis spectroscopy and TEM imaging.

Magnetite nanoparticles have been prepared by oriented aggregation exploiting the action of calix[8]arene, an organic macrocycle capable of complexing Fe ions, during the synthesis. Control over the degree of aggregation enables tuning of the morphology of the product, which can vary from multicore aggregated nanoparticles to nano-octahedra, with a dramatic change in the magnetic properties. Octahedral magnetite nanoparticles display ferrimagnetic behavior, which is typical of magnetite above 40 nm in size. In contrast, multicore nanostructures exhibit a narrower hysteresis loop and remarkable heating capacity under an alternating magnetic field. With the aim of producing a material useful for biomedical applications, all samples were made to be dispersible in water and biocompatible by ligand exchange with 2,3dimercaptosuccinic acid. Their morphology and magnetic properties were maintained after functionalization, as well as their good colloidal properties, which were characterized by dynamic light scattering.

Interface and morphology determine the magnetic, plasmonic and magnetic hyperthermia properties of Au/iron oxide nanocrystal heterostructures.