One-step synthesis of water-dispersible ultra-small Fe3O4 nanoparticles as contrast agents for T1 and T2 magnetic resonance imaging

Abstract

Uniform, highly water-dispersible and ultra-small Fe₃O₄ nanoparticles were synthesized via a modified one-step coprecipitation approach. The prepared Fe₃O₄ nanoparticles not only show good magnetic properties, long-term stability in a biological environment, but also exhibit good biocompatibility in cell viability and hemolysis assay. Due to the ultra-small sized and highly water-dispersibility, they exhibit excellent relaxivity properties, the 1.7 nm sized Fe₃O₄ nanoparticles reveal a low r₂/r₁ ratio of 2.03 (r₁ = 8.20 mM⁻¹ s⁻¹, r₂ = 16.67 mM⁻¹ s⁻¹); and the 2.2 nm sized Fe₃O₄ nanoparticles also appear to have a low r₂/r₁ ratio of 4.65 (r₁ = 6.15 mM⁻¹ s⁻¹, r₂ = 28.62 mM⁻¹ s⁻¹). This demonstrates that the proposed ultra-small Fe₃O₄ nanoparticles have great potential as a new type of T₁ magnetic resonance imaging contrast agents. Especially, the 2.2 nm sized Fe₃O₄ nanoparticles, have a competitive r₁ value and r₂ value compared to commercial contrasting agents such as Gd-DTPA (r₁ = 4.8 mM⁻¹ s ⁻¹), and SHU-555C (r₂ = 69 mM⁻¹ s⁻¹). In vitro and in vivo imaging experiments, show that the 2.2 nm sized Fe₃O₄ nanoparticles exhibit great contrast enhancement, long-term circulation, and low toxicity, which enable these ultra-small sized Fe₃O₄ nanoparticles to be promising as T₁ and T₂ dual contrast agents in clinical settings.