Chemistry Reference
In-Depth Information
emission peaks and longer lifetime of excited state. Gunlaugsson
et al.
demonstrated that the luminescence of europium buried into
a heptadendate ligand (a tetraazamacrocycle) can be modulated
by exploiting the deleterious quenching effect of water on the rare
earth luminescence [71]. The luminescence is switched of when two
water molecules are present in the coordination sphere, whereas the
displacement of water by a diketone derivative bearing an aromatic
ring re-establishes the light, which is even enhanced due to the
effect of the antenna from aromatic ring. This principle developed
for modulating fluorescence can be applied for “smart” MRI. When
water is present in the coordination sphere, these gold particles
can exert an enhancement of the positive contrast of magnetic
resonance images, whereas no enhancement is visible when water
was displaced by analytes. Therefore, MRI contrast agents, which are
sensitive to the presence of definite biomolecules, can be imagined.
Gold nanoparticles can also be rendered paramagnetic by the
covalent grafting of gadolinium (III) chelates to biomolecules,
which are then immobilized on the particles for targeting them to
the zone of interest. For instance, Chung
applied this strategy
for preparing paramagnetic gold nanostructures, which are able
to combine dual modality imaging (MRI and optical imaging) and
targeted therapy [72]. First, hollow gold nanoparticles coated with
thiol-ended PEG and cystein-protein-G were synthesized. Each
class of molecules grafted to the hollow nanoparticles ensures a
specific role. PEG was used for improving the colloidal stability and,
therefore, the particle blood circulation time and the efficiency of
particle internalization, while protein G molecules were introduced
to optimize the orientation of antibodies (anti-HER2) on the
surface of the hollow gold nanoparticles. Meanwhile, anti-HER2
antibodies were derivatized by gadolinium chelates by exploiting
the covalent coupling between the amino group of the antibody
and the isothiocyanate group of p-SCN-Bn-DTPA (Schemes 4.1 and
4.5). After chelation of gadolinium (III) ions by DTPA conjugated to
anti-HER2, the paramagnetic antibody (anti-HER2-Gd-DTPA) was
immobilized onto hollow gold nanoparticles. The resulting particles
were successfully applied as both MRI (
et al.
−1
−1
) and
optical imaging contrast enhancers of cancer cells since they can
be observed by optical microscopy (due to the optical properties
of hollow gold nanoparticles) and by MRI. The presence of anti-
HER2 onto the nanoparticles favors the internalization in SKBR3
r
= 23.7 mM
s
1
