“Single-” and “multi-core” FePt nanoparticles: from controlled synthesis via zwitterionic and silica bio-functionalization to MRI applications

Abstract

The value of the magnetization has a strong influence on the performance of nanoparticles that act as the contrast agent material for MRI. In this article, we describe processing routes for the synthesis of FePt nanoparticles of different sizes, which, as a result, exhibit different magnetization values. “Single-core” FePt nanoparticles of different sizes (3–15 nm) were prepared via one-step or two-step synthesis, with the latter exhibiting twice the magnetization (m (1.5T) = 14.5 emu/g) of the nanoparticles formed via the one-step synthesis (m (1.5T) 20 nm) leads to an increase in the magnetization m (1.5T) from 8 to 19.5 emu/g, without exceeding the superparamagnetic limit. Stable water suspensions were prepared using two different approaches: (a) functionalization with a biocompatible, zwitterionic, catechol ligand, which was used on the FePt nanoparticles for the first time, and (b) coating with SiO2 shells of various thicknesses. These FePt-based nanostructures, the catechol- and SiO2-coated “single-core” and “multi-core” FePt nanoparticles, were investigated in terms of the relaxation rates. The higher r 2 values obtained for the “multi-core” FePt nanoparticles compared to that for the “single-core” ones indicate the superiority of the “multi-core” FePt nanoparticles as T 2 contrast agents. Furthermore, it was shown that the SiO2 coating reduces the r 1 and r 2 relaxation values for both the “single-core” and “multi-core” FePt nanoparticles. The high r 2/r 1 ratios obtained in our study put FePt nanoparticles near the top of the list of candidate materials for use in MRI.