Monocrystalline iron oxide nanocompounds (MION): Physicochemical properties

TLDR

MION is a stable monocrystalline iron oxide nanocompound that enables target‑specific MR imaging. This study reports the physicochemical properties of MION using multiple analytical techniques. The authors characterized MION with electron microscopy, X‑ray diffraction, chemical analysis, laser light scattering, Mössbauer spectroscopy, and phantom imaging. MION consists of 4.6 ± 1.2 nm hexagonal inverse‑spinel cores coated with ~25 dextran molecules, yielding a 20 nm hydrodynamic radius (8 nm in reverse micelles), exhibits superparamagnetism with 68 emu/g Fe at 1.5 T, a 505 kOe internal field, 100 K blocking temperature, R1 = 16.5 (mM‑s)⁻¹, R2 = 34.8 (mM‑s)⁻¹, and can be detected in liver tissue at <50 nmol Fe/g using gradient echo imaging.

Abstract

Abstract We have previously described a novel monocrystalline iron oxide nanocompound (MION), a stable colloid that enables target specific MR imaging. In this study, the physicochemical properties of MION are reported using a variety of analytical techniques. High resolution electron microscopy indicates that a MION consists of hexagonal shaped electron‐dense cores of 4.6 ± 1.2 nm in diameter. This iron oxide core has an inverse spinel crystal structure which was confirmed by x‐ray powder diffraction. Chemical analysis showed that each core has 25 ± 6 dextran molecules (10 kD) attached, resulting in a unimodal hydrodynamic radius of 20 nm by laser light scattering. Because of the flexibillity of the dextran layer, the radius is only 8 nm in nonaqueous reverse micelles. At room temperature, MION exhibit superparamagnetic behavior with an induced magnetization of 68 emu/g Fe at 1.5 T. Mössbauer studies show that the saturation internal magnetic field is 505 KOe, and blocking temperature is at 100 K. The R1 relaxivity of MION is 16.5 (mM‐sec)‐ 1 and the R2 relaxivity is 34.8 (mM‐sec)‐ 1 in aqueous solution at 37°C and 0.47 T. In vitro phantom studies show that the detectability of MION in liver tissue is less than 50 nmol Fe/g tissue using gradient echo imaging techniques.