Chemistry Reference
In-Depth Information
performed the post-functionalization of fluorescent silica
nanoparticles by two different gadolinium chelates, which carry one
(Gd-Si-DTTA) or two (Gd-Si-DTPA) propyltrimethoxysilyl moieties
[23]. After encapsulation of a luminescent [Ru(bpy)
Lin
et al.
core (bpy
= 2,2'-bypyridine) in an amorphous silica matrix, the surface of the
resulting nanoparticles was derivatized by condensation of silanol
(Si-OH) groups present on the nanoparticles and the methoxysilyl
groups of the gadolinium chelates. The authors noticed that
the functionalization with Gd-Si-DTTA led to the formation of a
monolayer of gadolinium chelates, whereas a thick paramagnetic
multilayered shell was provided when Gd-Si-DTPA is used for the
post-functionalization of the fluorescent nanoparticles. The final
size of the nanoparticles is around 37 and 40 nm, respectively.
The covalent immobilization of these gadolinium chelates confers
to nanoparticles the ability to enhance the positive contrast of the
MRI images since they exhibit higher longitudinal relaxivity values
per mM Gd
]Cl
3
2
3+
ions than the one for unbound gadolinium complexes.
Moreover each Gd-Si-DTTA chelate bound to the fluorescent silica
nanoparticles exhibits higher relaxivities
r
and
r
than those of Gd-
1
2
−1
−1
3+
Si-DTPA grafted to similar nanoparticles (
r
= 19.7 mM
s
Gd
and
1
−1
−1
3+
−1
−1
3+
−1
−1
r
= 60 mM
s
Gd
vs
r
= 7.8 mM
s
Gd
and
r
= 12.3 mM
s
2
1
2
3+
). This can be reasonably explained by a higher water exchange
rate since gadolinium chelates Gd-Si-DTTA coordinate two water
molecules whereas Gd-Si-DTPA chelates coordinate only one water
molecule. In addition, another feature of nanoparticles coated by
Gd-Si-DTTA plays in favor of a higher longitudinal relaxivity. Since
the surface functionalization of the fluorescent silica nanoparticles
by Gd-Si-DTTA yields a monolayered shell in contrast to the
derivatization of the nanoparticles by Gd-Si-DTPA, gadolinium (III)
ions are, therefore, more accessible. But the silica nanoparticles
coated by Gd-Si-DTPA exhibit a higher longitudinal relaxivity
Gd
r
1
when the comparison is based on the amount of particulate contrast
agents since each particle coated by Gd-Si-DTPA contains more
gadolinium (III) ions. It must be pointed out that these nanoparticles,
despite having different coatings, have an impressive longitudinal
relaxivity (
5
−1
−1
5
−1
−1
r
= 2.0 × 10
mM
s
and
r
= 6.1 × 10
mM
s
vs
r
=
1
2
1
5
−1
−1
5
−1
−1
4.9 × 10
for Gd-Si-DTTA and Gd-
Si-DTPA, respectively). The great potential of these luminescent and
paramagnetic nanoparticles was confirmed by
mM
s
and
r
= 7.8 × 10
mM
s
2
experiments
carried out on monocyte cells with Gd-Si-DTTA-coated nanoparticles.
in vitro
