Facile synthesis of magnetic–plasmonic nanocomposites as T₁ MRI contrast enhancing and photothermal therapeutic agents

Nanocomposites combining magnetic and plasmonic components have received widespread attention in recent years due to their potential applications in biomedical research. Herein, we describe a facile method for growing small iron oxide nanoparticles on various plasmonic core materials with different shapes and surfaces by utilizing a polypyrrole interlayer. By focusing on Au nanorod@polypyrrole@iron oxide (Au NR@PPy@Fe_xO) nanocomposites, we show that these systems exhibit a low r₂/r₁ ratio of 4.8, making them efficient T₁ positive contrast-enhancing agents for magnetic resonance imaging (MRI). Moreover, we show that the nanocomposites are excellent photothermal agents in the second near infrared region, with high photothermal conversion efficiency, reaching up to 46%. In addition, the Au NR@PPy@Fe_xO nanocomposites show very low cytotoxicity. In summary, the present results highlight the great potential of the synthetic method and the nanocomposites developed in this study for T₁ MRI and/or infrared thermal imaging-guided photothermal cancer therapeutic applications.