Chemistry Reference
In-Depth Information
Fluoride host materials offer distinct advantages over oxide
materials, as the fluoride matrix has low absorbency and the
emitter can be excited directly. The quenching of excited state
rare earth ions is minimized when lanthanide ions are doped into
fluoride hosts, which leads to long emission lifetimes and high
luminescence intensities even in the case of IR-emitting ion [72].
Wong
. investigated the magnetic and luminescent properties
of multifunctional GdF
et al
: Eu nanoparticles [73]. The nanoparticles
showed downconversion and exhibited paramagnetism at both 293
and 77 k. They later doped upconversion emitting ions Yb, Tm in
the same host nanoparticles [74]. The GdF
3
: Yb, Tm nanoparticles
exhibited nearly pure NIR-to-NIR upconversion, which achieved
deeper tissue penetration and reduced autofluorescence from
biological tissues. The nanoparticles also showed paramagnetism
due to the presence of Gd ion. This indicated that these nanoparticles
were promising in bioimaging and bioseparation. Kumar
3
et al
.
reported lanthanide ion doped NaYF
nanocrystals for optical and
magnetic resonance bioimaging [75]. Lanthanide ions Gd
4
3+
and
3+
3+
3+
Er
were co-doped into fluoride nanoparticles, and the
nanoparticles were then modified with tumor-specific antibodies.
The
/Yb
/Eu
targeted imaging of live cancer cells showed no sign of
cellular toxicity. Gd
in vitro
3+
co-doped nanoparticles imparted strong
T
1
contrast effect and strong upconversion fluorescence, as shown in
Fig. 5.14. Thus these fluoride nanoparticles doped with lanthanide
ions may be used as dual-modal contrast agents in optical imaging
and MRI.
Yet in another study, by replacing yttrium (Y) with paramagnetic
gadolium (Gd), Heyon
et al
. reported uniform and monodisperse
3+
3+
Yb/Er co-doped NaGdF
: Yb
, Er
nanocrystal as bimodal contrast
4
agent [77]. The core NaGdF
: Yb, Er upconversion nanoparticles were
first synthesized by a thermal decomposition method, and an inert
NaGdF
4
layer was further coated protection to provide for the doped
absorption/emission centers (Yb
4
). The nanoparticles
were found to be extremely resistant to photobleaching, and no
photoblinking occurred. Good T
3+
and Er
3+
T1-weighted MRI contrast was
obtained in 1% agarose solution and in cells (SK-BR-3) incubated
with nanoparticles (Fig. 5.15a,b). Besides,
1
upconversion
cellular imaging data (in SK-BR-3 cells) revealed cellular uptake of
nanoparticles with a complete absence of autofluorescence at NIR
(980 nm) excitation (Fig. 5.15c-f).
in vitro
