Polymer Coated Iron–Boron and Gold–Iron Alloy Nanoparticles for Magnetic Resonance Imaging and Near Infrared Photothermal Applications

Iron alloy nanoparticles (IA NPs) are appealing tools for nanomedicine because of their composition-dependent properties, including magnetism, near-infrared (NIR) absorption, radiosensitization, and biodegradability. However, NP stability in biological environments is a limiting factor in their use. The effective surface modification of IA NPs using hydrophilic biocompatible molecules is the only strategy to optimize the half-life in blood circulation, biodistribution, cellular absorption, and bioaccumulation. Here, IA NPs based on iron-boron (Fe-B) and gold-iron (Au-Fe) were surface stabilized using various polyethylene glycol derivatives or polyvinylpyrrolidone, which were then combined with silanes and citric acid to determine the best formulation in terms of nanometric size, biocompatible surface chemistry, and stability in biological fluids. The IA NPs were synthesized in a single step utilizing laser ablation in liquid, enabling the exploration of different types of surface coatings selected specifically for their affinity with the elements comprising the nanoalloys. Then, the most stable Fe-B and Au-Fe formulations were tested as contrast agents for magnetic resonance imaging (MRI) and as sensitizers for photothermal heating using NIR light, a property not previously investigated in these IA NPs but of interest for their application in photothermal therapy (PTT). Notably, the most stable Fe-B NPs performed well as MRI contrast agents and absorbed substantially in the NIR spectrum, making them viable candidates for use as photosensitizers. Preliminary <i>in vitro</i> tests confirmed the positive prospects of polymer-stabilized Fe-B NPs for PTT.