Chemistry Reference
In-Depth Information
QD surface. The third method preserves the native TOP/TOPO on
the QD and uses variants of amphiphilic “diblock” and ”triblock”
copolymers and phospholipids to tightly interleave/interdigitate the
alkylphosphine ligands through hydrophobic attraction, whereas
the hydrophilic outer block permits aqueous dispersion and further
derivitization.
These three strategies (Scheme 4.7) were applied for
derivatizing fluorescent QD with gadolinium chelates. To add
the MRI contrast ability, QD can be functionalized with Gd
3+
-
DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid)
complexes as shown by the study of Jin
[51]. For achieving this,
TOP/TOPO layer was first replaced by glutathione, which is composed
of a thiol function for the immobilization of the ligand onto the NIR-
emitting QD, an amine group for further functionalization and of
two carboxylic moieties for water compatibility and also for further
functionalization. The addition of DOTA NHS ester to glutathione-
coated QD led to the covalent grafting of DOTA through the formation
of amide bond (Schemes 4.4 and 4.5). In a last functionalization
step, QD are made paramagnetic by the capture of gadolinium (III)
ions from DOTA (Gd-DOTA-QD). The functionalization induces
an increase in the hydrodynamic diameter from 7 to 10 nm. This
strategy seems to be efficient since Gd-DOTA-QD exhibit a relatively
high longitudinal relaxivity
et al.
r
(365 mM
−1
s
−1
). Moreover, these
1
paramagnetic QD have a great potential for
imaging since the
implantation of a tube filled with Gd-DOTA-QD into the abdomen of a
mouse can be detected by NIR FI and by MRI. Unfortunately, no data
were given about the intravenous injection of these nanopaticles and
their biodistribution, which is a key parameter for the biomedical
applications of these QD.
in vivo
demonstrated that QD can be functionalized by
gadolinium(III) chelates after their encapsulation in a silica shell [52].
The shell was obtained in two steps. After a priming step replacing
trioctylphosphine oxide (TOPO) surfactants on the QD surface with
mercaptopropyltrimethoxysilane (MPTMS), polymerization of
siloxane was performed in methanol under slightly basic conditions.
In the second step, addition of fresh MPTMS and poly(ethylene)
glycol(PEG)-propyltrimethoxysilane permitted the introduction
of functional (SH) and stabilizing PEG groups on the surface of the
SiO
Gerion
et al.
shell. As reported in the section devoted to fluorescent silica
nanoparticles (see Section 4.2.2), ligands used for the immobilization
2
