dc.description.abstract | Iron oxide nanocrystals (IONCs) have attracted extensive interest due to their high
magnetization that efficiently decreases the transverse relaxation times of water
protons. The increase in their transverse relaxivities upon crystal clustering is also
considered as one of their important properties.
Nanoemulsions (NEs) were developed with oil-in-water emulsions containing IONCs
in an oil core stabilized by phospholipids (DSPC) and di-stearoyl-phosphatidylethanolamine-
N-methoxy(polyethylene glycol)(PEG-DSPE) lipid amphiliphiels. We
prepared two different NEs: NEs containing 10 mol% and 50 mol% PEG2000-DSPE
(P10 and P50), while their sizes were kept constant. Monodisperse aggregates for
P10 and unevenly dispersed IONCs for P50 batches were developed.
IONCs-loaded NEs were analyzed by Dynamic light scattering (DLS) to obtain
the hydrodynamic diameter, Inductively coupled plasma mass spectrometry (ICPMS)
to measure iron concentration, and Transmission Electron Microscopy (TEM)
to observe the IONCs in the NEs. Furthermore, transverse relaxivities, r2 were
measured at 0.47 T, 1.5 T, 3 T and 7 T.
The experimental relaxivities were interpreted based on two parameters: the number
of IONCs in each droplet and the magnetic field strengths. Experimental relaxivities
of P10 NEs were in good agreement with the theoretical studies. Relaxivities
increased with increased number of IONCs in each droplet and relaxivities increased
with increased magnetic field until they level of when magnetization saturation has
been attained. Experimental relaxivities of P50 were close to the prediction of
the static dephasing regime model and much higher than the fast diffusion model
predictions.
In the current work it is evident that there is a significant difference in the experimental
relaxivities of P10 and P50 batches. However, due to the difference in
geometry between P10 and P50, we are not able to make conclusions about the
effect of PEG density. A thorough preparation and characterization of NEs with a
numerical simulations may be needed to explain the effect of PEG density. | |