Biomedical Engineering Reference
In-Depth Information
not only provided high quality in imaging enhancement to quantify
the targeting eficiency but also distinguished malignant cancerous
cells from nonmalignant epithelial cell lines (HaCat).
5
Recently, the
Au-Fe
3
O
4
heterostructures were fabricated as platform for a dual-
modelity bio-probe. The dumbbell structures were formed based on
the Au nanoparticles (3 nm or 8 nm) grown with Fe
3
O
4
nanoparticles
(20 nm).
64
Magnetic measurements (M-H curves) showed the
Au-Fe
3
O
4
heterostructures with superparamagnetic behavior
for MR imaging. Relection spectra of Au-Fe
3
O
4
heterostructures
exhibited characteristic relectance in the 590-650 nm range. Once
conjugation with epidermal growth factor receptor antibody (anti-
EGFR), the Au-Fe
3
O
4
showed higher speciicity targeting to A431
cells (overexpressed EGFR) than those without anti-EGFR. The dark-
ield microscope based on Au-Fe
3
O
4
relection provided long-term
cell tracking relection images.
Fluorescent contrast agents such as QDs and organic dyes have
been widely used for cell and intracellular imaging. However,
photobleaching occurs after a long time exposure for organic dyes.
The nonlinear optical effect of gold nanomaterials has attracted much
attention because of its excellent anti-photobleaching properties.
Multi-photon luorescence is an optical process, which is strongly
depended on the laser lux. For example, two-photon luorescence
(TPF) occurs when the luorophores are excited by simultaneous
absorption of two photons followed by a light emission from a
relaxation of a single photon. The LSPR of Au nanorods can locally
augment the ield of incident electromagnetic waves, increasing the
yield of nonlinear optical processes. Au nanorods are ideally suited
for nonlinear optical contrast agents in cell imaging using two-
photon-excited luminescence.
3
The TPF from a single Au nanorod
is 58 times that of a single rhodamine 6G molecule
65
and provides
cancer cell images to a depth of 75 μm.
66
Biofunctional Fe
3
O
4
-Ag
nanoparticles were used for TPF labeling of macrophage cells with
femtosecond infrared laser pulses (900 nm) as well.
63
2.4
Conclusion and Outlook
The bioconjugation of noble metal nanoparticles
via
covalent bonds
or electrostatic interactions is important for
in vitro
biolabeling and
bioimaging. The most important advantage is the selective and speciic
targeting of molecules, cells, or regions of interest, and observes
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