Functionalized Biocompatible Nanoparticles for Site-Specific Imaging and Therapeutics - Polymers in Nanomedicine - page 257

efficient bioseparation and biodelivery, highly sensitive biolabeling, and MRI with
enhanced contrast.
Human epidermal growth factor receptor 2 (HER2/neu) antibodies were conjugated
to the surface of poly(amino acid)-coated iron oxide nanoparticles (PAIONs) for the
detection of breast cancer (Fig. 24 )[ 79 ]. The method of antibody conjugation was
briefly: 0.57 nmol PAION (4 mg) was washed with 4 mL of a phosphate-buffered
saline (PBS) solution by vortexing and sonication. The washed particles were collected
in a Microcon Centrifugal Filter Device (molecular weight cutoff 100 kDa). After
being washed twice, the particles were suspended with 4 mL of 25% glutaraldehyde
solution (final concentration of 1mg/mL) and incubated overnight at room temperature
with shaking. Glutaraldehyde-functionalized particles were washed with a PBS solu-
tion, as performed in the previous washing step, and this was repeated three times.
HER2/neu antibodies were then conjugated to the glutaraldehyde-functionalized
nanoparticles as follows: PAION (2 mg, 0.285 nmol) dispersed in 400 m LofPBS
was mixed with 100 m Lof200 m g/mL antibody solution (0.054 mM). A BSA-
conjugated PAION was used as a negative control which was prepared with the
remaining 2 mg of functionalized nanoparticles by suspending them in 500 m Lof
3% BSA in PBS. The mixture was kept at 4 C and maintained overnight to allow
stable binding between the protein and PAION. The antibody- and BSA-conjugated
particles were then washed with a PBS solution and incubated with excess ethanol-
amine for 1 h at room temperature to block nonspecific binding sites. Finally, 1 mg/mL
antibody- and BSA-conjugated PAIONs in PBS solution were stored at 4 C until use.

6.6 MR Contrast Agents

6.6.1 Nonspecific Contrast Agents

Nonspecific contrast agents are low molecular weight contrast agents, e.g.,
Gd-DTPA, and high molecular weight blood pool agents [ 84 ], such as high
generation dendrimers [ 85 ]. These agents can be used for MR angiography and to
measure the perfusion and permeability properties of tissues.

6.6.2 Targeted Contrast Agents

Targeted contrast agents are specific and directed to a specific molecular or cellular
target with an appropriate targeting ligand molecule. Recombinant high density
lipoprotein (HDL)-like nanoparticles, a specific contrast agent for MRI of athero-
sclerotic plaques, has been reported [ 86 ] (Fig. 25 ).
Sipkins et al. [ 87 ] described the detection of tumor angiogenesis with an
a v b 3-specific antibody that was conjugated to polymerized paramagnetic
liposomes [ 87 ]. The red fluorescence represents the liposomes (Fig. 26c ) and
the green fluorescence represents blood vessels.

In Fig. 26 , we see that