Biomedical Engineering Reference
In-Depth Information
One of the nanoparticle-based contrast agents undergoing developments on
the MICAD list is called FANPs (flower-like gold nanoparticles). The FANPs
consists of Cy5.5-Gly-Pro-Leu-Gly-Val-Arg-Gly-(Lys-TDOPA)
3
-flower-
like gold-Fe
3
O
4
optical NPs and have been evaluated for imaging protease
expression
in vivo
. The peptide sequence with a Cy5.5 NIR dye molecule is
attached to AuNPs to form fluorescence-quenched NPs (Cy5.5-Gly-Pro-Leu-
Gly-Val-Arg-Gly-Cys-AuNPs (Cy5.5-MMP-AuNPs or GANPs)). The pres-
ence of Cy5.5 molecules in close proximity result in fluorescence quenching
from the efficient fluorescence resonance energy transfer to Au.
275
When the
Leu-Gly bond is cleaved by matrix metalloproteinases (MMPs), the NIR fluo-
rescence signal from the Cy5.5 will increase as the Cy5.5-containing fragments
is released. The Cy5.5 has a NIR absorbance maximum at 675 nm, an emis-
sion maximum at 694 nm, and an extinction coefficient of 250,000 M
−1
cm
−1
.
The FANPs are being developed for NIR fluorescence imaging of MMPs that
are expressed in tumors, atherosclerosis, myocardial infarction, and other dis-
eases.
276
Xie et al.
276
modified the FANPs by replacing the AuNP with Au-
Fe
3
O
4
, to induce a fluorescently quenched state to the overall nanostructure. The
composite NP which is shaped like a flower has three IO “petals” on each AuNP.
The gold surface was passivated with a thiolated PEG (SH-PEG
5000
) while the
MMP peptide was covalently linked to the Lys-tridihydrophenylalanine (Lys-
TDOPA) on the surface of the IO NMs. This Cy5.5-Gly-Pro-Leu-Gly-Val-
Arg-Gly-(Lys-TDOPA)
3
-flower-like gold-Fe
3
O
4
optical NPs (FANPs) have
been evaluated for imaging protease expression in vivo. The following process
was used in the synthesis of the FANPs.
(1)
The Fe
3
O
4
was allowed to grow on the surface of AuNPs (8 nm) through pyrol-
ysis of Fe(CO)
5
for 10 min at 220 °C to form flower-like gold-Fe
3
O
4
NPs.
(2)
Standard solid-phase peptide synthesis was used to prepare the Gly-Pro-
Leu-Gly-Val-Arg-Gly-(Lys-TDOPA)
3
.
(3)
Standard methods of conjugation was applied to attach the Cy5.5 to the
N
-terminus of Gly-Pro-Leu-Gly-Val-Arg-Gly-(Lys-TDOPA)
3
to pro-
duce Cy5.5-Gly-Pro-Leu-Gly-Val-Arg-Gly-(Lys-TDOPA)
3
.
(4)
To 0.4 mg of the Cy5.5-Gly-Pro-Leu-Gly-Val-Arg-Gly-(Lys-TDOPA)
3
and 25 mg SH-PEG
5000
in 0.9 mL DMSO was added to 2 mL gold-Fe
3
O
4
NPs (27 mg) in CHCl
3
.
(5)
The mixture was incubated at room temperature for ~18 h to form the
FANPs.
(6)
The mixture was centrifuged and the FANPs pellet was collected.
(7)
This pellet was reconstituted and characterized.
The IO “petals” showed a diameter of 13.4 ± 3.5 nm.
276
The overall diameter of
FANPs was 40.0 ± 4.3 nm, as determined with dynamic light scattering. There
were 152 ± 12 molecules of Cy5.5-Gly-Pro-Leu-Gly-Val-Arg-Gly-(Lys-
TDOPA)
3
per FANP and the quenching efficiency of a single FANP for the
Cy5.5 was estimated to be >95%.
276
Stability of the FANPs were observed
