Immobilization of magnetic iron oxide nanoparticles on laponite discs - an easy way to biocompatible ferrofluids and ferrogels

Abstract

Magnetic nanocomposites containing iron oxide (maghemite) nanoparticles, well embedded in a synthetic clay matrix (laponite) were prepared by a new one step chemical route and characterized by TEM, XRD, magnetization measurements, Mössbauer spectroscopy, DLS, and MRI measurements. The synthetic procedure leads to non-stoichiometric γ-Fe(2)O(3) with a controllable content in the nanocomposite. Magnetic nanoparticles incorporated in the diamagnetic clay matrix exhibit a mean diameter of 13 nm, superparamagnetic behavior with a high saturation magnetization achievable at low applied magnetic fields. In-field Mössbauer spectra and ZFC/FC magnetization curves reveal a perfect ferrimagnetic ordering within nanoparticles with negligible spin frustration and interparticle interactions due to the complete coating of maghemite surfaces by the nanocrystalline laponite matrix. Magnetic iron oxide nanoparticles embedded in laponite matrix exhibit strong T(2) weighted MRI contrast. The maghemite/laponite composite particles have 200 nm hydrodynamic diameter and form very stable hydrosols and/or hydrogels depending on their concentration in water.

Figure 1

TEM images of Sample 1 and Sample 2. The inset demonstrates the crystal planes of the nanocrystalline laponite matrix covering the magnetic nanoparticles.

Figure 2

Powder XRD patterns of Sample 1 and Sample 2 magnetic nanocomposites.

Figure 3

Zero-field room temperature Mössbauer spectra of Sample 1 and Sample 2 with individual spectral components.

Figure 4

In-field low-temperature Mössbauer spectra of Sample 1 and Sample 2, measured at a temperature of 5 K and in an external magnetic field of 5 T.

Figure 5

ZFC and FC magnetization curves of Sample 1 and Sample 2 (left) and hysteresis loops (right) for both samples measured at a temperature of 2 and 300 K.

Figure 6

Particle size distribution of Sample 2 (50.2 wt. % iron oxide loading), derived from TEM image and measurement of the superparamagnetic hysteresis loop.

Figure 7

Optical photos of (a) ferrofluid, under an external magnetic field, (concentration of maghemite/laponite particles is about 15 mg/ml) and (b) ferrogel (concentration of maghemite/laponite particles is about 35 mg/ml).

Figure 8

(a) Intensity weighted particle size distribution of ~ 0.02 % w/v Sample 2 and laponite suspension as obtained from DLS measurements, (b) zeta-potential distribution diagram obtained from Sample 2.

Figure 9

(A) Transverse relaxation rate R₂ (or 1/T₂) of Sample 2 and mono-dispersed iron oxide nanoparticle (IONP) at different Fe concentrations were measured at a magnetic field strength of 3 Telsa using a multi-echo spin echo method. (B) T₂ weighted fast spin echo images showed Fe concentration dependent reduction of MRI signals, which is typically observed as the MRI contrast effect of magnetic iron oxide nanoparticles