Magnetic iron oxide nanoparticle functionalization: isocyanate moiety as a suitable monodentate anchoring group

From the Shelf to the Particle: Preparation of Highly Organic-Functionalized Magnetic Composites via 4-Nitrophenyl Reactive Ester

Preparation of chemically tunable magnetic nanoparticles (MNPs) is of great interest in many technological fields. Although numerous methods have been developed to prepare MNPs coated with functional organic moieties, most of them are complex, multistep, and involve the preparation of a specific ligand to be inserted on the particle surface. Herein, we describe the preparation of MNPs covered with reactive polymer poly(4-nitrophenyl methacrylate). The composite was prepared by the dispersion polymerization of 4-nitrophenyl methacrylate in the presence of magnetite nanoparticles stabilized by oleic acid. The novel material can be easily modified with amines to give chemically stable amide bonds without installation of pH-dependent features in the link. The extent of particle modification is readily monitored by the release of 4-nitrophenol from the polymer using UV-vis spectrophotometry. Good agreement between the degree of functionalization assessed by colorimetry and elemental analysis was obtained, and functionalization up to 3 mmol g^-1 is easily attained. To illustrate the applicability of the method for catalyst development, we prepared imidazole-covered MNPs that accelerate the hydrolysis of a model organophosphate, with rate constants approximately 10⁵-fold higher than the spontaneous hydrolysis. The catalyst can be recovered by a magnet and recycled without appreciable loss of catalytic activity.

Orthogonal Clickable Iron Oxide Nanoparticle Platform for Targeting, Imaging, and On-Demand Release

A versatile iron oxide nanoparticle platform is reported that can be orthogonally functionalized to obtain highly derivatized nanomaterials required for a wide variety of applications, such as drug delivery, targeted therapy, or imaging. Facile functionalization of the nanoparticles with two ligands containing isocyanate moieties allows for high coverage of the surface with maleimide and alkyne groups. As a proof-of-principle, the nanoparticles were subsequently functionalized with a fluorophore as a drug model and with biotin as a targeting ligand towards tumor cells through Diels-Alder and azide-alkyne cycloaddition reactions, respectively. The thermoreversibility of the Diels-Alder product was exploited to induce the on-demand release of the loaded molecules by magnetic hyperthermia. Additionally, the nanoparticles were shown to target cancer cells through in vitro experiments, as analyzed by magnetic resonance imaging.