Chemistry Reference
In-Depth Information
: Yb, Er were deposited
onto iron oxide nanoparticles in the presence of EDTA [84]. These
core/shell nanoparticles emitted at 539 nm and 658 nm when
excited with a 980 nm laser. The hybrid particles were found to stack
in chainlike assemblies when subjected to an external magnetic field.
They bound specifically to a glass slide spotted with biotinylated IgG
and showed upconversion fluorescence, confirming the successful
binding with the protein.
Streptavidin bounded upconverting NaYF
4
5.2.1.3 Dy-based multifunctional nanomaterials
Dysprosium is another lanthanide ion that has been investigated as
a T
contrast agents. The present trend in clinical MRI is towards
higher magnetic field strength for a better signal-to-noise ratio,
enhanced resolutions as well as larger acquisition rates [85]. The
current commercial Gd(III)-chelates contrast agents exhibited poor
water relaxivity, especially under high field. As a result, the interests
for Dy-based complex or Dy-based nanoparticles as MRI contrast
agents is increasing due to its short relaxation time (~0.5 ps) and
high magnetic moment (10.6 uB), thus giving high contrasts in
higher field strength [86].
The incorporation of Dy and other rare earth ions into a matrix
for both fluorescent and MR imaging is rarely reported. Dy
3+
coupled
to a noncytotoxic indium phosphide/zinc sulfide (InP/ZnS) QDs that
provides fluorescence detection, MR responsiveness, and payload
delivery were reported by Grant and coworkers [87]. By surface
modifying the QDs with a cell-penetrating peptide sequence coupled
to an MR contrast agent, the bimodal nanomaterials functioned as a
self-transfecting high-field MR/optical contrast agent for nonspecific
intracellular labeling. Fluorescent images confirmed sequestration
in perinuclear vesicles of labeled cells, with no apparent toxicity.
These techniques could be extended to impart cell selectivity or act
as a delivery vehicle for genetic or pharmaceutical interventions.
NaDyF4:Tb
2
3+
nanocrystals were also investigated as multifunctional
negative
MRI contrast agents in high magnetic field and
fluorescence imaging [88]. Yet, in another study, Das
T
2
et al
. reported
:Tb
3+
nanocrystals as dual modal-
contrast agent [89]. Interestingly, the phantom images taken at 7.0 T
MRI and
single-phased ultrasmall Dy
O
2
3
MRI images of a mouse model demonstrated that the
4 nm nanocrystals exhibit excellent positive
in vivo
contrast, which was
due to the small r2 relaxivity (2.17 mM
-1
s
-1
) (Fig. 5.20). Contrast
T
2
