Contrast silver ct scan

1. Size-controlled synthesis of dendrimer-stabilized silver nanoparticles for
X-ray computed tomography imaging applications†
Hui Liu,ab
Han Wang,c
Rui Guo,b
Xueyan Cao,b
Jinglong Zhao,c
Yu Luo,b
Mingwu Shen,b
Guixiang Zhang*c
and Xiangyang Shi*ab
Received 13th July 2010, Accepted 18th August 2010
DOI: 10.1039/c0py00218f
We report a facile size-controlled synthesis of dendrimer-stabilized silver nanoparticles (Ag DSNPs) for
X-ray computed tomography (CT) imaging applications. Amine-terminated generation 5
poly(amidoamine) dendrimers were used as templates to complex Ag(I) ions for subsequent reductive
formation of dendrimer-entrapped Ag nanoparticles. Following a one-step acetylation reaction to
transform dendrimer terminal amine to acetyl groups, Ag DSNPs can be formed. The formed Ag
DSNPs were characterized using 1
H NMR, UV-Vis spectrometry, transmission electron microscopy,
and z-potential measurements. We show that through the variation of the dendrimer/Ag salt molar
ratio, the size of Ag DSNPs can be controlled at the range of 8.8–23.2 nm. The formed Ag DSNPs are
stable not only in water, PBS buffer, and fetal bovine serum, but also at different pH conditions
(pH 5–8) and temperatures (20–50
C). X-Ray absorption coefficient measurements show that the
attenuation of Ag DSNPs is size-dependent, and the Ag DSNPs with a diameter of 16.1 nm display an
X-ray attenuation intensity close to that of a clinically used iodine-based contrast agent (Omnipaque) at
the same molar concentration of the active element (Ag versus iodine). This suggests that Ag DSNPs
with an appropriate size have a great potential to be used as a CT imaging contrast agent, although the
atomic number of Ag is lower than that of iodine. Furthermore, CT scanning showed prolonged
enhancement at the point of mice injected subcutaneously with Ag DSNPs, rendering them as
a promising contrast agent in CT imaging applications.
Introduction
Noble metal nanoparticles (NPs) continue to receive immense
scientific and technological interest in applications including but
not limited to optoelectronics,1,2
sensing,3–5
biomedicine,6–10
and
catalysis.11–13
In particular, silver (Ag) NPs (AgNPs) have been
proved to be promising candidates for use in catalysis and
biomedicine.3,14–16
For biomedical applications, the concerns
over the toxicity of AgNPs can be usually resolved by appro-
priate surface modification.17,18
In general, most of the potential
applications related to AgNPs require that the synthesized
AgNPs should be size-tunable and colloidally stable under
different conditions, which still remains a great challenge.
Among many synthetic methodologies developed to synthesize
AgNPs,14,19–21
the approaches to using dendrimers as templates
or stabilizers have been proved to be quite promising. Den-
drimers are a family of highly branched, monodispersed,
synthetic macromolecules with well-defined composition and
architecture.22,23
The unique structural features allow them to be
employed as either templates or stabilizers to form AgNPs.24–28
In general, two types of dendrimer-protected AgNPs can be
formed: (1) dendrimer-entrapped AgNPs (Ag DENPs) and (2)
dendrimer-stabilized AgNPs (Ag DSNPs). Ag DENPs with a size
generally smaller than 5 nm are formed using dendrimers as
templates under fast reduction and nucleation chemistry, having
a structure where each AgNP is entrapped within each dendrimer
molecule,24,26,27,29
while Ag DSNPs with a size usually larger than
5 nm are formed using dendrimers as stabilizers under mild
reduction conditions, having a structure where each AgNP
is surrounded by multiple dendrimer molecules on its
surface.7,14,27,28,30–32
For biological applications, it is ideal for Ag DENPs or
DSNPs to have a neutral surface charge in order to avoid non-
specific binding and toxicities. In this context, Ag DENPs or
DSNPs formed using amine-terminated dendrimers as templates
or stabilizers should be functionalized to neutralize the den-
drimer terminal amines. Literature data have shown that acety-
lation is one of the key steps to form biocompatible and
multifunctional gold DENPs and DSNPs for biomedical appli-
cations.5,10,33–35
For the case of Ag DENPs or DSNPs, we show
that acetylation of Ag DENPs formed using generation 5 (G5)
poly(amidoamine) (PAMAM) dendrimers as templates (with
dendrimer/Ag salt molar ratio of 1 : 51.2) could significantly
change the size and size distribution of the particles.27
The size of
partially acetylated Ag DENPs displays a bimodal distribution
(2.9 nm and 11.0 nm), whereas the pristine amine-terminated Ag
DENPs and the completely acetylated Ag DENPs are relatively
a
State Key Laboratory for Modification of Chemical Fibers and Polymer
Materials, Donghua University, Shanghai, 201620, P. R. China
b
College of Chemistry, Chemical Engineering and Biotechnology, Donghua
University, Shanghai, 201620, P. R. China. E-mail: xshi@dhu.edu.cn; Fax:
+0086-21-67792306-804; Tel: +0086-21-67792656
c
Department of Radiology, Affiliated Shanghai First People’s Hospital,
Medical College, Shanghai Jiaotong University, Shanghai, 200080, P. R.
China. E-mail: guixiangzhang@sina.com
† Electronic supplementary information (ESI) available: Additional 1
H
NMR spectra and z-potential values of all Ag DSNPs and the
photographs of the Ag DSNP solutions dispersed in water, PBS buffer,
and fetal bovine serum. See DOI: 10.1039/c0py00218f
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2. monodispersed with a size of 2.9 nm and 11.0 nm, respectively.
This indicates that Ag DSNPs can be formed by complete
acetylation of the amine-surfaced Ag DENPs. This previous
study leads us to hypothesize that size-controlled synthesis of Ag
DSNPs may be realized by varying the initial dendrimer/Ag salt
molar ratio using a similar synthetic protocol.
One important biological application of noble metal NPs is to
use them as contrast agents for X-ray computed tomography
(CT) imaging. Recent advances of nanotechnology in medical
applications show that gold NPs display much higher X-ray
attenuation than the clinically used iodine-based contrast agent
(Omnipaque) and can be used for CT imaging of cells and tissue/
organs.36–40
The major advantage of using metal NPs as CT
imaging contrast agents is that the NPs have long blood circul-
ation times, thereby enabling prolonged imaging of tissues/
organs. In contrast, iodine-based small molecular agents are
quickly metabolized after injection, unable to prolong the
imaging time. Since AgNPs have structural and crystaline
similarity to gold NPs, it is expected that Ag DSNPs with tunable
sizes can be used for CT imaging applications.
In this present study, utilizing a similar approach reported by
our group,27
we report the size-controlled synthesis of Ag DSNPs
for CT imaging applications. The formed Ag DSNPs with
different sizes were characterized by nuclear magnetic resonance
(NMR) spectroscopy, UV-Vis spectrometry, transmission
electron microscopy (TEM), and z-potential measurements. The
stability of the Ag DSNPs under different pH and temperature
conditions was evaluated by UV-Vis spectrometry. Finally, the
X-ray attenuation properties and CT imaging capability were
compared with a clinically used iodine-based contrast agent,
Omnipaque. To our knowledge, this is the first report related to
size-controlled synthesis of surface neutralized Ag DSNPs for
CT imaging applications. Findings from this study are expected
to provide a basis for rational design of functionalized NPs for
medical imaging applications.
Experimental section
Materials
Ethylenediamine core amine-terminated G5 PAMAM dendrimers
(G5.NH2) with a polydispersity index less than 1.08 were purchased
from Dendritech (Midland, MI). All other chemicals were obtained
from Aldrich and used as received. The water used in all the
experimentswas purified using a Milli-QPlus 185 water purification
system (Millipore, Bedford, MA) with resistivityhigher than 18 MU
cm. Regenerated cellulose dialysis membranes (molecular weight
cut-off, MWCO ¼ 10 000) were acquired from Fisher.
Synthesis of Ag DSNPs
Following a similar protocol to that reported in our previous
work,27
Ag DSNPs with tunable sizes were synthesized (Fig. 1).
In the preparation procedure, Ag DENPs were first prepared by
NaBH4 reduction of Ag(I) ions complexed with G5.NH2 den-
drimers with different dendrimer/Ag salt molar ratios (1 : 25,
1 : 50, 1 : 75, and 1 : 100). This was followed by complete
acetylation of the dendrimer terminal amines, forming Ag
DSNPs with a neutral surface charge. In a typical synthesis of Ag
DSNPs with dendrimer/Ag salt molar ratio of 1 : 25, an aqueous
AgNO3 solution (83.1 mL, 118.6 mM) was added to G5.NH2
aqueous solution (1 mL, 0.394 mM) under vigorous stirring.
After 30 min, a water–methanol mixture solution (v/v ¼ 2 : 1) of
NaBH4 (192.6 mL, 153.5 mM) was dropwise added to the den-
drimer/Ag salt mixture solution while stirring. The stirring was
continued for 2 h to complete the reaction. The reaction mixture
was extensively dialyzed against water (6 times, 4 L) for 3 days to
remove the excess reactants and by-products, followed by
lyophilization to give [(Ag0
)25-G5.NH2] DENPs.
The acetylation reaction procedure used to modify Ag DENPs
with acetamide groups is similar to that described in our previous
work.27
Taking the acetylation of [(Ag0
)25-G5.NH2] DENPs as
an example, triethylamine (36.6 mL) was added to an aqueous
solution of [(Ag0
)25-G5.NH2] DENPs (11.3 mg, 5 mL). After 2 h
stirring, acetic anhydride (20.7 mL) was added to the Ag DENPs/
triethylamine mixture solution while stirring, and the mixture
was allowed to react for 24 h. The crude product was extensively
dialyzed against PBS buffer (3 times, 4 L) and water (3 times, 4 L)
for 3 days to remove the excess of reactants and by-products,
followed by lyophilization to get [(Ag0
)25-G5.NHAc] DSNPs.
[(Ag0
)50-G5.NHAc], [(Ag0
)75-G5.NHAc], and [(Ag0
)100-
G5.NHAc] DSNPs were obtained with the same procedure.
Characterization techniques
1
H NMR spectra of Ag DSNPs were recorded on a Bruker DRX
400 nuclear magnetic resonance spectrometer. Samples were
dissolved in D2O before measurements. z-Potential measure-
ments were performed using a Malvern Zetasizer Nano ZS model
ZEN3600 (Worcestershire, UK) equipped with a standard 633
nm laser. UV-Vis spectra were collected using a Lambda 25
UV-Vis spectrometer (Perkin-Elmer, United States). Samples
were dissolved in water before the experiments. TEM was per-
formed with a JEM 2100 analytical electron microscope oper-
ating at 200 kV. Five microlitres of an aqueous solution of Ag
DSNPs (1 mg mLÀ1
) were dropped onto a carbon-coated copper
grid and air dried before measurements. The size distribution
histogram of Ag DSNPs was analyzed using ImageJ software
(http://rsb.info.nih.gov/ij/download.html). For each sample, 300
NPs from different images were randomly selected to analyze the
size and size distribution.
X-Ray CT imaging
Ag DSNPs or iohexol 300 (Omnipaque 300 mg I/mL, GE
Healthcare) solutions with different concentrations were
prepared in 100 mL Eppendorf tubes and placed in a self-designed
scanning holder. CT scans were performed using a Micro-CT
imaging system (eXplore Locus, GE) with 80 kV, 450 mA, and
a slice thickness of 45 mm. Evaluation of the contrast enhance-
ment of Ag DSNPs was carried out by loading the digital CT
images in a standard display program and then selectingFig. 1 A schematic illustration of the preparation of Ag DSNPs.
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3. a uniform round region of interest on the resultant CT image for
each sample. Contrast enhancement was determined in Houns-
field units (HU) for each concentration of Ag DSNPs with
different compositions and Omnipaque.
ICR mice (20–25 g, Shanghai Laboratory Animal Center) were
anesthetized by intraperitoneal injection of 0.3 mL of 3%
pentobarbital sodium (12 mL kgÀ1
). [(Ag0
)75-G5.NHAc] (50 mL,
Ag concentration ¼ 0.1 mol LÀ1
) dispersed in PBS buffer was
then subcutaneously injected into the mouse’s back on the left.
For a control experiment, Omnipaque (50 mL, iodine concen-
tration ¼ 0.1 mol LÀ1
) was injected into the mouse’s back on the
right. CT scans were performed at 5 min and 25 min post
injection by a Micro-CT imaging system with a tube voltage of
80 kV, an electrical current of 450 mA, and a slice thickness of
92 mm. Images were reconstructed by GEHC microView soft-
ware based on voxels of 45 mm  45 mm  45 mm.
Results and discussion
Synthesis and characterization of Ag DSNPs
Metal DSNPs are often formed under mild reduction conditions,
including the use of mild reducing agents (e.g., hydrazine)41
and
physical treatments (e.g., UV-irradiation7,25
and thermo-treat-
ment).32,42
Our previous studies have shown that acetylation of
Ag DENPs formed with a G5 dendrimer/Ag salt molar ratio of
1 : 51.2 could readily convert Ag DENPs to Ag DSNPs.27
By
varying the molar ratio between G5.NH2 dendrimers and Ag
salt, it is expected that the size of the formed Ag DSNPs could be
controlled. We showed that when the molar ratio of G5.NH2/Ag
salt was beyond 1 : 100, the formed particles precipitated out at
the bottom of the vials. Therefore, the molar ratios of G5.NH2/
Ag salt were selected as 1 : 25, 1 : 50, 1 : 75, and 1 : 100.
The complete acetylation of all Ag DENPs was confirmed by 1
H
NMR. In the 1
H NMR spectra of all the formed Ag DSNPs
(Fig. S1†), the appearance of the proton signal at 1.87 ppm related
to the –CH3 protons of the acetyl group clearly indicates the
formation of acetamide groups on the dendrimer surface, similar
to the acetylated G5 dendrimers without AgNPs. These results
were in agreement with literature.27,43
The complete acetylation of
dendrimer terminal amines to acetamide groups was also verified
by z-potential measurements (Table S1). It is clear that all Ag
DSNPs have a surface potential close to zero after the acetylation
reaction, in agreement with the literature.27,34
The optical properties of Ag DSNPs were investigated using
UV-Vis spectrometry. Fig. 2a shows the UV-Vis spectra of Ag
DSNPs with different G5 dendrimer/Ag atom molar ratios. The
surface plasma resonance (SPR) peak27
around 412 nm clearly
indicates the existence of Ag NPs in solutions. Under similar
molar concentration of Ag DSNPs, the absorbance increased with
the increase of Ag content. When the G5 dendrimer/Ag atom
molar ratio reached up to 1 : 100, the absorbance value decreased,
and a broad band of absorbance at the region of 500 to 900 nm
appeared, indicating a relatively larger size or a certain degree of
aggregation of Ag DSNPs formed in the solution. From the
photograph of the [(Ag0
)25-G5.NHAc], [(Ag0
)50-G5.NHAc],
[(Ag0
)75-G5.NHAc], and [(Ag0
)100-G5.NHAc] DSNPs (Fig. 2b), it
is clear that the solution color deepens with the Ag content. The
[(Ag0
)25-G5.NHAc] DSNPs had a pale yellow color, whilst the
[(Ag0
)50-G5.NHAc] and [(Ag0
)75-G5.NHAc] DSNPs were quite
yellow. For [(Ag0
)100-G5.NHAc] DSNPs, a deep brown color was
shown. The gradually deepened color of Ag DSNPs is ascribed to
the gradual increase of the Ag content.
The size and morphology of Ag DSNPs with different
compositions were characterized with TEM (Fig. 3). The diameter
of [(Ag0
)25-G5.NHAc], [(Ag0
)50-G5.NHAc], [(Ag0
)75-G5.NHAc],
and [(Ag0
)100-G5.NHAc] DSNPs was 8.8, 12.4, 16.1, and 23.2 nm,
respectively. This implies that by simply varying the dendrimer/
Ag salt molar ratios, the size of Ag DSNPs can be controlled. The
diameter of [(Ag0
)50-G5.NHAc] DSNPs (12.4 nm) is very close to
that of [(Ag0
)51.2-G5.100Ac] (11.0 nm) reported in our previous
studies.27
In addition, all particles had a relatively narrow size
distribution except [(Ag0
)100-G5.NHAc] DSNPs. A small portion
of aggregated particles appeared in the size range of 50 to 70 nm
(Fig. 3d), in agreement with the UV-Vis spectrometry data
(Fig. 2a). It is worth noting that the TEM images shown in Fig. 3
are representative images for NPs with each composition.
However, the size distribution histograms of the Ag DSNPs were
based on the measurement of 300 NPs in different TEM images. In
this case, the selected TEM images for NPs with each composition
may not fully reflect the statistical results of the size distribution.
The crystalline nature of the Ag DSNPs was confirmed by
selected area electron diffraction (SAED). Fig. 4 shows a typical
SAED pattern of [(Ag0
)25-G5.NHAc] DSNPs. The (111), (200),
(220), and (311) rings in the SAED pattern clearly indicate the
face-centered cubic (fcc) crystal structure of Ag DSNPs.
Stability of Ag DSNPs
The stability of Ag DSNPs is of paramount importance for their
biological applications. Literature data show that the
Fig. 2 (a) UV-Vis spectra and (b) photographs of the aqueous solution
of Ag DSNPs with G5 dendrimer/Ag atom molar ratios of 1 : 25, 1 : 50,
1 : 75, and 1 : 100. In (b), the vials from left to right show the solution of
[(Ag0
)25-G5.NHAc], [(Ag0
)50-G5.NHAc], [(Ag0
)75-G5.NHAc], and
[(Ag0
)100-G5.NHAc] DSNPs.
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4. aggregation degree of metal nanoparticles could be effectively
reflected by changes of the absorption characteristics, especially
the SPR peak shifting in the UV-Vis spectrum.38,44
In this work,
we used UV-Vis spectroscopy to monitor the stability of Ag
DSNPs under different pH and temperature conditions. Fig. 5
shows the UV-Vis spectra of Ag DSNPs dispersed in water with
different pHs at room temperature (25
C). HCl or NaOH
(0.1 mol LÀ1
) was employed to adjust the pH value of the particle
suspension. We showed that at the pH range of 5 to 8, the SPR
peak position did not appreciably change in the spectra of all Ag
DSNPs with different compositions, suggesting that all the
formed Ag DSNPs are colloidally stable within this range of pH.
The stability of Ag DSNPs dispersed in water at different
temperatures was also investigated (Fig. 6). Similarly, in the UV-
Vis spectra of Ag DSNPs with different compositions, the SPR
peak position did not have any significant changes at the
temperatures of 25, 37, and 50
C. This implies that all Ag
DSNPs have a good colloidal stability and do not form aggre-
gates when temperature ranges from 25
C to 50
C. We noted
that the SPR peak intensity had a slight change for some cases of
Ag DSNPs under different pH and temperature conditions;
however, the SPR peak positions did not change significantly
under similar conditions. The SPR peak intensity changes only
reflected the slight concentration differences of the Ag DSNPs.
Furthermore, the colloidal stability of Ag DSNPs remained
identical when they were dispersed into water, PBS buffer, and
fetal bovine serum (Fig. S2†). No aggregation could be found
even after 4 months of storage at room temperature. Thus, the
Ag DSNPs prepared here possess good stability not only in
water, PBS buffer, and fetal bovine serum but also under
different pH and temperature conditions. The stability of all Ag
DSNPs is essential for their biological applications.
X-Ray CT imaging
Gold NPs have good X-ray attenuation properties, enabling
them to be used as contrast agents in CT imaging.38,39
The X-ray
Fig. 3 TEM images and size distribution histograms of
[(Ag0
)25-G5.NHAc] (a), [(Ag0
)50-G5.NHAc] (b), [(Ag0
)75-G5.NHAc] (c),
and [(Ag0
)100-G5.NHAc] (d) DSNPs, respectively.
Fig. 4 A typical SAED pattern for [(Ag0
)25-G5.NHAc] DSNPs.
Fig. 5 UV-Vis spectra of [(Ag0
)25-G5.NHAc] (a), [(Ag0
)50-G5.NHAc]
(b), [(Ag0
)75-G5.NHAc] (c), and [(Ag0
)100-G5.NHAc] (d) DSNPs under
different pH conditions.
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5. attenuation properties of gold NPs are demonstrated to be both
size- and concentration-dependent.38,39,45
Due to the crystalline
and structural similarity, AgNPs may be another choice of CT
contrast agents. Theoretically, Ag element has a lower X-ray
absorption coefficient than iodine because of its lower atomic
number. However, the nanometre-sized AgNPs allow them to be
cleared from the blood much more slowly than commercial
iodine-based small molecular CT contrast agents, permitting
longer imaging times.
In this study, we investigated the effect of the size of Ag
DSNPs on the X-ray absorption characteristics. X-Ray absorp-
tion coefficient measurements revealed that Ag DSNPs with the
same Ag concentration and different sizes (8.8–23.2 nm) had
different X-ray attenuation intensity (Fig. 7a). The X-ray
attenuation intensity enhanced with the size of the Ag DSNPs.
This may be caused by the gradual increase of the local
concentration of Ag with the size of colloidally stable Ag DSNPs
within a certain range. When the size of Ag DSNPs increased to
23.2 nm ([(Ag0
)100-G5.NHAc] DSNPs), the intensity of X-ray
attenuation decreases. This suggests that the dependence of the
X-ray attenuation intensity on the particle sizes falls into
a certain range. When the particle size is beyond the threshold
(23.2 nm), the Ag DSNPs display larger size dispersity and more
aggregation, which is not beneficial for enhancing the effect of
the X-ray attenuation. This suggests that the colloidal stability of
the particles is important for particles with good X-ray attenu-
ation properties. In this case, [(Ag0
)75-G5.NHAc] DSNPs with
a diameter of 16.1 nm had the strongest X-ray attenuation
intensity.
In order to compare the X-ray attenuation properties of Ag
DSNPs with a clinically used iodine-based CT contrast agent
(Omnipaque), we selected [(Ag0
)75-G5.NHAc] DSNPs for
comparison (Fig. 7b). With the increase of the molar concen-
tration of the active element (i.e., Ag or iodine), the attenuation
coefficient of both [(Ag0
)75-G5.NHAc] DSNPs and Omnipaque
increased due to the concentration-dependent effect caused by
the change in mass ratio between Ag (or iodine) and water
molecules. At the concentration below 0.10 mol LÀ1
,
[(Ag0
)75-G5.NHAc] DSNPs displayed approximately similar
X-ray attenuation coefficients to Omnipaque. This implies that
Ag DSNPs with an appropriate size have an approximately
similar X-ray attenuation intensity to omnipaque with iodine
concentration similar to Ag, although the atomic number of Ag
is lower than that of iodine.
To further explore the potential to use Ag DSNPs as
CT contrast agents, [(Ag0
)75-G5.NHAc] DSNPs (50 mL,
[Ag] ¼ 0.1 mol LÀ1
) was subcutaneously injected into a mouse’s
back on the left and the cross-sectional CT image was collected
(Fig. 8). In CT images, parenchyma, including muscles and blood
vessels, are gray and even darker, while bones, such as the
mouse’s spondyle in our case, are white due to their higher
density and the resultant stronger X-ray absorption. Because
AgNPs have a much higher attenuation coefficient than paren-
chyma, the existence of AgNPs within the parenchyma can be
easily visualized in the CT image at 5 min and 25 min post-
injection (arrows in Fig. 8a and 8b). Thus, AgNPs can greatly
boost CT image contrast, providing that the administered
AgNPs are enriched in particular areas or tissues. In Fig. 8a and
8b, the arrow points to the Ag DSNP injection region at 5 min
and 25 min post injection, respectively. The inject region is
Fig. 6 UV-Vis spectra of [(Ag0
)25-G5.NHAc] (a), [(Ag0
)50-G5.NHAc]
(b), [(Ag0
)75-G5.NHAc] (c), and [(Ag0
)100-G5.NHAc] (d) DSNPs at
different temperatures.
Fig. 7 (a) X-Ray attenuation (HU) as a function of the size of Ag
DSNPs at the same Ag concentration (0.05 mol LÀ1
); (b) X-ray attenu-
ation (HU) of [(Ag0
)75-G5.NHAc] DSNPs and Omnipaque as a function
of the molar concentration of active element (Ag or iodine).
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6. displayed as a narrow bright strip in the CT image due to the
limited diffusion and localized distribution of Ag DSNPs. In
contrast, in the inject area of Omnipaque with iodine concen-
tration similar to Ag on the mouse’s back on the right (arrow
head in Fig. 8a and 8b), no such bright injection region can be
found in the CT image even at 5 min post injection. This is due to
the high diffusion rate of the small molecular contrast agent in
the subcutaneous tissues. Besides the ability of Ag DSNPs in
prolonging the CT imaging time at the localized region, the
injected Ag DSNPs did not show any toxicity to the mice. The
mice injected with the Ag DSNPs behaved healthy and normal as
compared with those before injection.
Conclusions
In summary, Ag DSNPs were formed by acetylation-mediated
conversion of amine-surfaced Ag DENPs. By simply varying the
molar ratio of G5 PAMAM dendrimer/Ag salt, the size of crystal-
line Ag DSNPs with fcc crystal structures can be controlled at the
range of 8.8–23.2 nm. The formed Ag DSNPs are stable not only in
water, PBS buffer, and fetal bovine serum but also at different pH
andtemperatureconditions.X-Rayabsorptionresults revealedthat
the attenuation intensity of Ag DSNPs was both size- and concen-
tration-dependent. The Ag DSNPs with a diameter of 16.1 nm were
found to have approximately similar X-ray attenuation intensity to
that of iodine-based contrast agents at the same molar concentra-
tion. Furthermore, we show that subcutaneously injected Ag
DSNPs can significantly increasethe contrastof the injection region
ofamouseinthe CTimage,suggestingthe useofAgDSNPs asanin
vivo contrast agent for CT imaging applications. Our future efforts
will be focused on the application of Ag DSNPs for blood pool
imaging in vivo through intravenous injection of the particles.
Moreover, taking into consideration the unique structural features
of PAMAM dendrimers and the capability for synthesis of multi-
functional metal DSNP,33,35
Ag DSNPs are expected to be a useful
platform for the construction of multifunctional theranostic nano-
agents for targeted CT imaging of various diseases with prolonged
imaging times.
Acknowledgements
This research is financially supported by the National Natural
Science Foundation of China (20974019 and 30901730), the
National Basic Research Program of China (973 Program,
2007CB936000), the Shanghai Pujiang Program (09PJ1400600),
the Program for Professor of Special Appointment (Eastern
Scholar) at Shanghai Institutions of Higher Learning, and the
Fundamental Research Funds for the Central Universities (For
R. G., X. C., M. S., and X. S.). R. G. thanks the supports from
Young Teacher Foundation of Donghua University (200802)
and Shanghai Natural Science Foundation (10ZR1400800).
G. Z. thanks the Ph.D. Programs Foundation of Ministry of
Education of China (No. 20090073110072).
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Fig. 8 CT image of a mouse with 50 mL of [(Ag0
)75-G5.NHAc] DSNPs
([Ag] ¼ 0.1 mol LÀ1
) subcutaneously injected into its back on the left at
5 min (a) and 25 min (b) post injection. The white arrow points to the Ag
DSNP injection region. For a control experiment, Omnipaque (50 mL,
iodine concentration ¼ 0.1 mol LÀ1
) was injected into the mouse’s back
on the right. The white arrow head points to the inject area of Omnipaque
with iodine concentration similar to Ag.
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