Functional Mesoporous Silica Nanoparticles with a Core-Shell Structure for Controllable Drug Delivery - Advanced Bioactive Inorganic Materials for Bone Regeneration and Drug Delivery - page 57

(a)

CTAB

Self-assembly

Heating Sol-Gel reaction

Fe 3 O 4 nanoparticles
in organic phase

Fe 3 O 4 nanoparticles
in aqueous phase

Fe 3 O 4 nanoparticles
embedded in
mesoporous silica spheres

(b) (c) (d)

50 nm

200 nm 200 nm

FIGURE 3.4
(a) Synthetic procedure of monodisperse and size-controllable core-shell Fe 3 O 4 @mSiO 2
nanoparticles. (b) FE-SEM. (c) TEM and (d) HRTEM images of Fe 3 O 4 @mSiO 2 nanoparticles.
(Reprinted with permission from Kim J., Lee J. E., Lee J., et al., J. Am. Chem. Soc. 128: 688-699,
Copyright 2006, American Chemical Society.)

magnetic Fe 3 O 4 nanocrystals were first transferred from the organic phase to
the aqueous phase using CTAB surfactant. The subsequent sol-gel reaction
of TEOS in the aqueous solution containing CTAB and oleic acid-stabilized
magnetic nanocrystals resulted in magnetic mesoporous silica nanoparticles
with a core-shell structure. Here, CTAB serves not only as the stabilizing
surfactant for the transfer of hydrophobic Fe 3 O 4 nanocrystals to the aque-
ous phase but also as the organic template for the formation of mesopores
in the sol-gel reaction. The Fe 3 O 4 @mSiO 2 particles can be collected after the
removal of the CTAB templates from the as-synthesized nanoparticles by
extraction in acidic ethanol solution (pH 1.4). The same research group also
reported the synthesis of magnetic fluorescent delivery vehicles by encapsu-
lating monodisperse magnetic and semiconductor nanocrystals in uniform
mesoporous silica nanoparticles (Kim et al. 2008). Similarly, Zhao et al. (2005)
synthesized magnetic silica nanoparticles with highly ordered mesostruc-
tures by using the phase transfer method. For this approach, the resulting
magnetic mesoporous silica nanoparticles possess a uniform nanosize (≈90-
140 nm) and a highly ordered mesostructure, and, more important, the pore
size can be changed from 2.4 to 3.4 nm and the saturation magnetization
values can be changed from 0.43 to 7.62 emu/g (Zhao et al. 2005).