Chemistry Reference
In-Depth Information
surfaces of the mesoporous silica particles strongly depends on the
pore size, the corresponding relaxivity is similarly affected by the
pore size.
Gd-load per nanomaterial is also key to increase the relaxivity in
a per contrast-agent basis. However, the relation between Gd-load
and relaxivity enhancement is not linear. Lin
. reported a higher
relaxivity for Gd-load ranging from 1.6% to 3.1% wt [38]. The
et al
r
value
1
reaches its maximum for 1.6% Gd-load (23.6 mM
at 9.4 T and
23°C) and decreases abruptly as the Gd loading increases from 2.3%
to 3.1%, falling to relaxivity values close to free Gd-DTPA at 6.8% (4.4
versus 3.9 mM
−1
s
−1
−1
−1
for Gd-DTPA at 9.4 T and 23°C). At such high Gd
loading, the dipole-dipole interaction among the paramagnetic ions
is presumed to be more significant, hence shortening the electronic
relaxation time.
The post-functionalization by silylated gadolinium chelates
(Si-Gd-DTPA, see reference [23]) constitutes another attractive
route for rendering mesoporous silica nanoparticles paramagnetic
[28]. The immobilization of the gadolinium chelates is performed
by the condensation of the trimethoxysilyl group of Si-Gd-DTPA
and the -OH groups present on the pore walls and on the surface
of the mesoporous nanoparticles. Such a post-functionalization
confers to the mesoporous nanoparticles' very high longitudinal
and transversal relaxivities
s
r
and
r
, which amounts to 7.0
×
10
5
1
2
−1
−1
×
5
−1
−1
×
6
−1
−1
mM
s
(3 T)/2.48
10
mM
s
(9.4 T) and 1.6
10
mM
s
×
6
−1
−1
(9.4 T) on a per millimolar particle basis,
respectively. These relaxivity values are much larger than the solid
silica nanoparticles coated with multilayers of the Gd-DTPA derivative
(see reference [23]). The enhanced magnetic resonance relaxivity
was attributed to the ready access of water molecules through the
nanochannels of mesoporous particles derivatized by gadolinium
chelates Si-Gd-DTTA. When the functionalization is performed
by a mixture of Si-Gd-DTTA and of rhodamine B conjugated to
aminopropyltriethoxysilane (4 mol %, relative to Gd-Si-DTTA), the
resulting mesoporous nanoparticles can behave as contrast agents
for fluorescence and magnetic resonance imaging. The uptake of
these fluorescent and paramagnetic mesoporous nanoparticles
by monocyte cells was revealed both by the fluorescence and the
contrast enhancement magnetic resonance images. Moreover, they
appeared well suited for
(3 T)/2.7
10
mM
s
MRI after intravenous injection
in the tail vein since aorta and liver are clearly visible on
in vivo
T
- and
1
