Distinctly different chemical functionalities on the internal and the external surfaces of silica nanotubes, and their applications as multi-chemosensors

Article abstract of DOI:10.1002/chem.201100011

Inside and out: The external and internal surface of silica nanotubes (SNTs) can be independently modified by a sol-gel grafting reaction. The azobenzene-based ligands on the external surface recognize Hg²⁺ through a color change, whereas the B

Full text of DOI:10.1002/chem.201100011

COMMUNICATION
DOI: 10.1002/chem.201100011
Distinctly Different Chemical Functionalities on the Internal and the
External Surfaces of Silica Nanotubes, and Their Applications as Multi-
Chemosensors
Sungmin Seo,[a] Ji Ha Lee,[a] Youngje Cho,[a] Jin-Gyu Kim,[b] Changyeon Kim,[b] and
Jong Hwa Jung*[a]
Nanomaterials modified with multiple functionalizations
are fundamentally advantageous for modern environmental,
biomedical, and biological applications, including catalysis,
filtration, separation, molecular collection, storage, nanoflui-
dics, medical imaging, drug delivery, and sensors.[1] Unlike
spherical nanoparticles, nanotubes have two distinct surfaces
that can be independently modified with the desired func-
tional groups by using template synthesis. Our research and
that of others led us to develop smart silica multifunctional-
ized nanotubes for single-molecule sensing, bioseparation,
and drug/gene delivery carriers.[2–8] Martin and colleagues
reported the separate functionalization of the inner and
outer surfaces of silica nanotubes (SNTs)[4] and demonstrat-
ed the extraction of lipophilic molecules from an aqueous
solution phase. However, a general method for the selective
introduction of separate functional groups to the internal
and the external surfaces of SNTs still remains a challenge.[9]
Metal ions can pose severe risks for human health and the
environment, and methods for the facile preparation of fluo-
rogenic and chromogenic receptors with high selectivity and
sensitivity for heavy metal ions have continued to receive
much interest.[10] Of the known heavy metal ions, Hg2+ and
Pb2+ are two of the most dangerous; lead can cause adverse
health effects on exposure, particularly in children.[11] A vari-
ety of symptoms have been attributed to lead poisoning.
Once introduced into the body, Hg2+ and Pb2+ can cause
abdominal pain and vomiting. The long-term accumulation
of Hg2+ and Pb2+ in the human body leads to many serious
afflictions, including muscle paralysis, mental confusion,
memory loss, and anemia, which suggest that Hg2+ and Pb2+
affect multiple targets in vivo.[12] Plausible molecular targets
of lead include calcium- and zinc-binding proteins that con-
trol cell signaling and gene expression, respectively.[13] Thus,
it is important to develop a safe and effective procedure to
detect and remove heavy metal ions from the body follow-
ing toxic heavy metal contamination.[14]
In particular, there are several advantages to using multi-
functionalized organic–inorganic hybrid nanomaterials as
chemo-sensors in the environment. First, multifunctionalized
nanomaterials can rapidly and easily detect two metal ions
at the same time. Second, these nanomaterials would be
useful as highly selective and efficient adsorbents for specif-
ic guest molecules in environmental pollutants due to the
competition complex reaction. Third, the nanomaterials can
be easily controlled to interact with target guest molecules
for detection among various guest molecules in real analyti-
cal samples. Herein, we describe a procedure to selectively
functionalize the internal and the external surfaces of SNTs
and we apply the new nanomaterial as a dual chemosensor
for Hg2+ and Pb2+ ions in aqueous solution.
The methodology is outlined in Scheme 1. First, the SNTs
were prepared by using an organogel fiber as a template
(Scheme S1).[15] By vigorous mixing of the SNTs with recep-
tor 1 in toluene overnight before removal of the organogel
fiber, we were able to specifically modify the external sur-
face of the SNTs. By this process, azobenzene-coupled re-
ceptor 1 was attached onto the external surface of SNTs as
a chromogenic receptor for Hg2+. Then, after removal of
the organogel from the inner cavity of the SNTs, the
1-modified silica nanotubes (A-SNTs; Scheme S2) were
characterized by scanning electron microscopy (SEM),
transmission electron microscopy (TEM), FTIR, thermogra-
vimetric analysis (TGA), UV/Vis spectroscopy, and X-ray
photoelectron spectroscopy (XPS).
To confirm whether receptor 1 was immobilized onto the
external or internal surface of the SNTs before calcinations,
A-SNTs were examined by using TEM with the electron
energy-loss spectroscopic (EELS) technique (Figure S1). Sil-
icon, oxygen, carbon, and nitrogen components were homo-
geneously deposited onto the surface of the A-SNTs, which
supports the idea that receptor 1 is homogenously attached
to the external surface of the SNTs. In particular, the color
contrast for the distribution of nitrogen atom in both edge
[a] S. Seo, J. H. Lee, Y. Cho, Prof. Dr. J. H. Jung
Department of Chemistry and Research Institute of Natural Sciences
Gyeongsang National University
Jinju 660-701 (Korea)
Fax : (+82)55-758-6027
E-mail: jonghwa@gnu.ac.kr
[b] J.-G. Kim, C. Kim
Division of Electron Microscopic Research
Korea Basic Science Institute
Daejeon 305-333 (Korea)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100011.
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parts was higher than that of the central part
in A-SNT, which indicates that receptor 1 was
immobilized onto the external surface of the
SNTs. As shown in Figure S2, we further mea-
sured the TGA thermogram of A-SNTs. The
result of the TGA experiment (Figure S2)
showed that the modified SNTs consisted of
only 65.5 wt% of receptor 1 (Scheme 1d). We
also calculated the concentration of receptor 1
attached to the surface of SNT, the surface
density, and the surface coverage.[9c] The re-
sulting concentration, loading density, and sur-
face coverage of receptor 1 were 1.05 mm,
0.60 moleculesnmÀ2, and 80.5%, respectively.
A value of 80.5% surface coverage was deter-
mined to be the maximum, due to the steric
hindrance and hydrophobicity of receptor 1.
For structural proof that receptor 1 was at-
tached to the external or the internal surfaces
of A-SNTs, we compared the IR spectra of
SNTs and A-SNTs. For the SNTs, IR peaks ap-
peared atn˜ =3450, 1658, and 1084 cmÀ1. For A-
SNT (Figure S3), peaks appeared at n˜ =3382,
2976, 2933, 2884, 1626, 1615, 1570, 1471, 1446,
1428, and 1382 cmÀ1. These new peaks origi-
nate from the acyclic azobenzene-coupled re-
ceptor 1, providing solid evidence that 1 is
indeed attached to the external surface of the
SNT. The components of A-SNT were also
confirmed by XPS (Figure 1). The XPS spec-
trum of A-SNT shows C1s, N1s, O1s and Si2p
binding energies (Figure 1b), in which N1s
originates from nitrogen atoms of the azoben-
zene-based receptor 1, whereas no N1s for ni-
trogen was detected for SNTs (Figure 1a). Fur-
thermore, the UV/Vis spectrum of A-SNT dis-
persed in aqueous solution shows an absorp-
tion peak with maximum at l=320 nm, which
indicates that the azobenzene-coupled receptor
was immobilized onto the external surface of
SNTs.
To selectively modify the internal surface of
A-SNTs, BODIPY-based fluorogenic receptor
2 (Scheme S3) was reacted with A-SNTs dis-
persed in toluene at reflux for 24 h, as de-
scribed above. Because the external surfaces of
the A-SNTs were already occupied by chromo-
genic receptor 1, as shown in Figure S1, recep-
tor 2 was selectively attached to the internal
surface of the A-SNTs. After cooling to room
temperature, the pink solid product was fil-
tered, washed with THF, and dried (Fig-
ure 2A). Then IR and TOF-SIMS spectra of
the A-SNTs modified with immobilized
BODIPY derivative 2 (A-SNT-B) were record-
ed. In the IR spectrum of A-SNT-B, in addi-
tion to the bands attributed to A-SNTs, strong
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Figure 1. XPS spectra of a) SNT, b) A-SNT, and c) A-SNT-B.
Figure 3. A) UV/Vis spectra of A-SNT-B (10 mm) before (a) and after
(b) the addition of Hg2+ (10 equiv) in aqueous solution (pH 7.4). Spectra
c) and d) were separated by curve fitting from spectrum b). B) Photo-
graph of A-SNT-B a) before and b,c) after the addition of Hg2+
(10 equiv) and Pb2+ (10 equiv), respectively, in aqueous solution.
Figure 2. a) Photograph of A-SNT-B. b) SEM and c) TEM images of
A-SNT-B.
mophore. Thus, the observed color change is ascribed to the
formation of a complex with strong coordination bonding
[16]
between the bridgehead nitrogen atom of 1 and Hg2+
.
new bands at n˜ =2750, 1990, 1704, 1473, and 1210 cmÀ1 ap-
peared, which originate from receptor 2, indicating that 2 is
bound on the A-SNT (Figure S4). The TOF-SIMS spectrum
of A-SNT-B displays the fragments of 2 (m/z 427), which
confirms that 2 is covalently anchored onto the internal sur-
face of the A-SNT (Figure S5). Furthermore, the absorption
spectrum of A-SNT-B showed two visible absorption bands
at l=320 and 505 nm (Figure S6), which may arise from re-
ceptors 1 and 2, respectively. Furthermore, the XPS spec-
trum of A-SNT revealed C1s, N1s, O1s, Si2p, and F1s bind-
ing energies (Figure 1c), in which the F1s binding energy in
particular originates from BODIPY-based receptor 2. This
result indicates that fluorogenic receptor 2 is immobilized
onto the internal surface of A-SNTs. The SEM and TEM
images of A-SNT-B revealed a nanotubular structure with a
diameter of 120 nm (Figure 2).
With the exception of Hg2+, no significant color changes
were observed with other metal ions (Figure 3B,c). These
findings confirm that A-SNT-B could be useful as a colori-
metric sensing material for selective detection of Hg2+ in
the presence of other metal ions. As a reference experiment,
the color change in A-SNT upon the addition of Hg2+ was
performed under the same conditions. A-SNT also showed a
color change from yellow to pink upon the addition of Hg2+
in aqueous solution (Figure S7). The finding suggests that
Hg2+ ions are coordinated to receptor 1 immobilized onto
the external surface of A-SNT-B.
Next we observed the fluorescence changes in A-SNT-B
upon addition of Li+, Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+
,
Co2+, Cd2+, Pb2+, Ni2+, Zn2+, Fe3+, Cu2+, and Hg2+ in
aqueous solution (pH 7.4). As expected, A-SNT-B in the ab-
sence of metal ions is virtually nonfluorescent in its apo
state (F<0.003), which resulted from the efficient photoin-
duced electron transfer (PET)[17] quenching of the fluoro-
phore by the lone-pair electrons of the nitrogen atom in the
benzoyl moiety. Interestingly, upon the addition of increas-
To apply the chromogenic and fluorogenic chemosensors
for the detection of two different metal ions, we investigated
the chromogenic properties of A-SNT-B towards the metal
ions Li+, Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+, Co2+, Cd2+
,
Pb2+, Ni2+, Zn2+, Fe3+, Cu2+, and Hg2+ in aqueous solution
(pH 7.4). The absorption bands of A-SNT-B in the absence
of metal ions appear at l=320 and 505 nm, respectively
(Figure 3A,a). Interestingly, the addition of Hg2+ into a sus-
pension of A-SNT-B in H2O resulted in a color change from
pink to gray-brown (Figure 3B,b), accompanied by a new
absorption band at around l=480 nm (Figure 3A,b), which
consists of two different absorption bands for azobenezne-
based receptor 1 and BODIPY-based receptor 2, respective-
ly, by curve fitting (Figure 3A,c and d). The absorption
band at l=320 nm is shifted to l=480 nm, which is attribut-
ed a net electronic charge transfer from the donor end
(bridgehead nitrogen) to the acceptor end within the chro-
ing concentrations of Pb2+
, the emission spectrum of
A-SNT-B showed a large chelation-enhanced fluorescence
(CHEF) effect due to the blocking of the PET process. An
overall emission change of about 10-fold (F=0.019,
Figure 4) at the emission maximum (lem =510 nm) was ob-
served for Pb2+. On the other hand, no significant changes
in fluorescence emission were observed in parallel experi-
ments with Li+, Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+, Co2+
,
Cd2+, Ni2+, Zn2+, Fe3+, Cu2+, and Hg2+ (Figure 4). From
these fluorescence changes, we noticed that the A-SNT-B
revealed a high selectivity for Pb2+ ions over other metal
cations. These results are in good accord with our previous
report.[18] Furthermore, these results imply that BODIPY-
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J. H. Jung et al.
Figure 5. Photograph of pellets of A-SNT-B prepared in a) the absence
and the presence of b) Li+, c) Ca2+, d) Sr2+, e) Co2+, f) Cd2+, g) Zn2+
,
h) Pb2+, i) Hg2+, j) Cu2+, k) Fe2+, and l) Fe3+, under irradiation by a UV
lamp.
Figure 4. Fluorescence spectra of A-SNT-B (10 mm) on the addition of
metal ions (10 equiv) in aqueous solution (pH 7.4).
The highly selective recognition of Hg2+ and Pb2+ by
A-SNT-B demonstrates that the approach employed in the
present study is capable of cooperatively enhancing and con-
trolling selectivity towards Hg2+ and Pb2+. More important-
ly, quantitative measurements of the emission maximum of
Pb2+-bound A-SNT-B indicated that the fluorescence
change correlated linearly with [Pb2+] over the 0 to 40 ppb
range investigated (Figure S11). In addition, the absorption
change in A-SNT-B with Hg2+ exhibited linearity between
1.0 and 10 mm (Figure S12). We determined that the limits of
detection of A-SNT-B for Hg2+ and Pb2+ are ꢀ1.0 mm and
2.2 ppb, respectively.
Figure 6 shows a flow chart of the visual color and fluo-
rescence emission changes upon the addition of the metal
ions to dispersed solutions of A-SNT-B. Based on the visual
color and emission changes mentioned above, we propose a
two-step procedure for the qualitative analysis of an un-
known sample (see Figure 6). 1) An aliquot of an unknown
sample is dispersed into an aqueous solution of A-SNT-B. If
both the color and fluorescence emission changes, then both
Hg2+ and Pb2+ are present in the unknown sample. 2) If
only the fluorescence emission changes, the unknown
sample must contain Pb2+. On the other hand, if only the
visual color changes, but the background fluorescence emis-
based receptor 2 immobilized on the internal surface of
A-SNT-B was highly selective, recognizing only Pb2+ ions.
We also observed the fluorescence image of A-SNT-B by
fluorescence microscope (Figure S8). A-SNT-B showed non-
emission in the absence of Pb2+ whereas A-SNT-B showed
strong emission in the presence of Pb2+. These results indi-
cate that receptor 2 attached to the internal surface of
A-SNT-B is selectively bound to Pb2+
.
To evaluate further the utility of A-SNT-B as a dual ion-
selective colorimetric and fluorimetric probe for Hg2+ and
Pb2+, the competition-based color and emission changes in
A-SNT-B upon addition of various biologically and environ-
mentally relevant metal ions, such as Li+, Na+, K+, Mg2+
,
Ba2+, Ca2+, Sr2+, Co2+, Cd2+, Ni2+, Zn2+, Fe3+, and Cu2+
were investigated in aqueous solution (Figure S9). As ex-
pected, the color and emission changes in A-SNT-B upon
the addition of Hg2+ and Pb2+ in the presence of Li+, Na+,
K+, Mg2+, Ba2+, Ca2+, Sr2+, Co2+, Cd2+, Ni2+, Zn2+, Fe3+
,
and Cu2+ were also observed, which indicates that A-SNT-B
is a very promising tool for the selective detection of Hg2+
and Pb2+ in the presence of an excess of other metal ions.
The color and the fluorescence emission changes in
A-SNT-B are fully reversible; the addition of strong base
(0.01 n NaOH) to an acidic solution (0.01 n HCl) reversed
these effects (Figure S10). In addition, the color and the
emission changes could be reproduced over several cycles of
detection and separation.
To extend the above performance to a portable chemo-
sensor kit, disk-shaped pellets of A-SNT-B were prepared
by a simple and convenient method (Figure 5). The emission
of the disk of A-SNT-B was dramatically increased when
dipped in aqueous Pb2+ (10 mm) solution. In addition, the
pink color of the disk of A-SNT-B was immediately changed
into gray-brown when dipped in aqueous Hg2+ solution
(10 mm). Apart from Hg2+ and Pb2+ ions, no other changes
in the fluorescence emission or the color of A-SNT-B oc-
curred when the disk was dipped in other metal ions
(10 mm), such as Li+, Na+, K+, Mg2+, Ba2+, Ca2+, Sr2+
,
Co2+, Cd2+, Ni2+, Zn2+, Fe2+, Fe3+, and Cu2+. This result
implies that disks prepared from A-SNT-B are applicable as
a portable chemosensor for detection of Hg2+ and Pb2+ in
the environmental and biological fields.
Figure 6. Flow chart for the detection of Pb2+ and Hg2+ ions by using A-
SNT-B.
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sion is unchanged, then Hg2+ must be present in the un-
known sample.
Luckett, A. H. Gopalani, S. B. Lee, D. S. English, J. Am. Chem. Soc.
2005, 127, 17385.
[7] a) H.-J. Wang, W.-H. Zhou, X.-F. Yin, Z.-X. Zhung, H.-H. Yang, X.-
R. Wang, J. Am. Chem. Soc. 2006, 128, 15954; b) R. Fan, R. Karnik,
M. Yue, D. Li, A. Majumdar, P. Yang, Nano Lett. 2005, 5, 1633.
[8] a) S. Kapoor, A. J. Bhattacharyya, J. Phys. Chem. C 2009, 113, 7155;
b) H. Ma, J. Tarr, M. A. DeCoster, J. McNamara, D. Caruntu, J. F.
Chen, C. J. O’Connor, W. L. Zhou, App. Phy. 2009, 105, 07B309–2;
c) Q.-G. Xiao, X. Tao, J.-P. Zhang, J.-F. Chen, J. Mol. Catal. B 2006,
42, 14; d) Q.-G. Xiao, X. Tao, J.-F. Chen, Ind. Eng. Chem. Res. 2007,
46, 459.
[9] a) N. Gartmann, D. Brꢂhwiler, Angew. Chem. 2009, 121, 6472;
Angew. Chem. Int. Ed. 2009, 48, 6354; b) K. A. Kilian, T. Bçcking,
K. Gaus, J. J. Gooding, Angew. Chem. 2008, 120, 2737; Angew.
Chem. Int. Ed. 2008, 47, 2697; c) K. Cheng, C. C. Landry, J. Am.
Chem. Soc. 2007, 129, 9674.
In conclusion, we have demonstrated the selective immo-
bilization of two different receptors on the internal and ex-
ternal surfaces of SNTs by simple sol-gel grafting reactions.
The A-SNT-B sensor was successfully applied to the highly
selective detection of Hg2+ and Pb2+ ions, and the new mul-
tifunctionalized nanostructure was easily recycled by chemi-
cal treatment. This simple and convenient method for sepa-
rate functionalization of both the external and the internal
surfaces of SNTs could be very effective for recognition and
separation of specific target molecules. We believe that con-
trol over the interior and exterior surface chemistry will
have a broad impact for the study and application of porous
materials.
[10] a) R. Krꢃmer, Angew. Chem. 1998, 110, 804; Angew. Chem. Int. Ed.
1998, 37, 772; b) L. Fabbrizzi, A. Poggi, Chem. Soc. Rev. 1995, 24,
197.
[11] H. L. Needleman, Human Lead Exposure, CRC Press, Boca Raton,
FL, 1992.
Acknowledgements
[12] a) S. Araki, H. Sato, K. Yokoyama, K. Murata, Am. J. Ind. Med.
2000, 37, 193; b) N. Rifai, G. Cohen, M. Wolf, L. Cohen, C. Faser, J.
Savory, L. DePalma, Ther. Drug Monit. 1993, 15, 71; c) D. A. Cory-
Slechta, Adv. Behav. Pharmacol. 1984, 4, 211; d) C. Winder, N. G.
Carmichael, P. D. Lewis, Trends Neurosci. 1982, 5, 207; e) X. Chen,
S.-W. Kim, M. J. Jou, Y. Kim, S.-J. Kim, S. Park, J. Yoon, Org. Lett.
2008, 10, 5235; f) E. M. Nolan, S. J. Lippard, Chem. Rev. 2008, 108-
108, 3443; g) X. Guo, X. Qian, L. Jia, J. Am. Chem. Soc. 2004, 126,
2272; h) Y.-K. Yang, S.-K. Ko, I. Shun, J. Tae, Org. Biomol. Chem.
2009, 4590; i) S. Yoon, A. E. Albers, A. P. Wong, C. J. Chang, J. Am.
Chem. Soc. 2005, 127, 16030.
This work was supported by a grant from NRF (2011-0003903 and 2011-
0016922) and the WCU (World Class University) Program (R32-2008-
000-20003-0) supported by the Ministry of Education, Science and Tech-
nology, and the Next-Generation BioGreen 21 Program (SSAC, grant
No PJ008109), Rural Development Administration, S. Korea.
Keywords: chromophores
·
fluorophores
·
hybrid
nanomaterials · lead · mercury · sensors
[13] E. S. Claudio, H. A. Godwin, J. S. Magyar, Prog. Inorg. Chem. 2003,
51, 1 and references therein.
[14] a) Q. He, E. W. Miller, A. P. Wong, C. J. Chang, J. Am. Chem. Soc.
2006, 128, 9316; b) M. Sun, D. Shangguan, H. Ma, L. Nie, X. Li, S.
Xiong, G. Liu, W. Thiemann, Biopolymers 2003, 72, 413; c) J. Liu, Y.
Lu, J. Am. Chem. Soc. 2003, 125, 6642; d) C.-T. Chen, W.-P. Huang,
J. Am. Chem. Soc. 2002, 124, 6246; e) J. Li, Y. Lu, J. Am. Chem.
Soc. 2000, 122, 10466; f) S. Deo, H. A. Godwin, J. Am. Chem. Soc.
2000, 122, 174.
[15] a) J. H. Jung, Y. Ono, K. Hanabusa, S. Shinkai, J. Am. Chem. Soc.
2000, 122, 5008; b) J. H. Jung, Y. Ono, S. Shinkai, Chem. Eur. J.
2000, 6, 4552.
[16] a) E. Kim, H. E. Kim, S. J. Lee, S. S. Lee, M. L. Seo, J. H. Jung,
Chem. Commun. 2008, 3921; b) S. J. Lee, J.-E. Lee, J. Seo, I. Y.
Jeong, S. S. Lee, J. H. Jung, Adv. Funct. Mater. 2007, 17, 3441.
[17] a) S. J. Lee, J.-E. Lee, J. Seo, I. Y. Jeong, S. S. Lee, J. H. Jung, Adv.
Funct. Mater. 2007, 17, 3441; b) S. J. Lee, J. H. Jung, J. Seo, I. Yoon,
K.-M. Park, L. F. Lindoy, S. S. Lee, Org. Lett. 2006, 8, 1641.
[18] H. Y. Lee, D. R. Bae, J. C. Park, H. Song, W. S. Han, J. H. Jung,
Angew. Chem. 2009, 121, 1265–1269; Angew. Chem. Int. Ed. 2009,
48, 1239–1243.
[1] a) C. R. Martin, P. Kohli, Nat. Rev. Drug Discovery 2003, 2, 29;
b) G. M. Whitesides, Nat. Biotechnol. 2003, 21, 1161; c) M. Ferrari,
Nat. Rev. Cancer 2005, 5, 161.
[2] a) N. H. Kim, H. Y. Lee, Y. J. Cho, W. S. Han, D. Kang, S. S. Lee,
J. H. Jung, J. Mater. Chem. 2010, 20, 2139; b) D. R. Bae, S. J. Lee,
S. W. Han, J. M. Lim, D. Kang, J. H. Jung, Chem. Mater. 2008, 20,
3809; c) J. H. Jung, M. Park, S. Shinkai, Chem. Soc. Rev. 2010, 39,
4009.
[3] a) J. Goldberger, R. Fan, P. Yang, Acc. Chem. Res. 2006, 39, 239;
b) C. C. Chen, Y. C. Liu, C. H. Wu, C. C. Yeh, M. T. Su, Y. C. Wu,
Adv. Mater. 2005, 17, 404; c) N. W. Shi Kam, M. OꢁConnell, J. A.
Wisdom, H. Dai, Proc. Natl. Acad. Sci. USA 2005, 102, 11600.
[4] a) D. T. Mitchell, S. B. Lee, L. Trofin, N. Li, T. K. Nevanen, H. Sç-
derlund, C. R. Martin, J. Am. Chem. Soc. 2002, 124, 11864; b) P.
Kohil, C. R. Martin, J. Drug Delivery Sci. Technol. 2005, 15, 49;
c) H. Hillebrenner, F. Buyukserin, M. Kang, M. O. Mota, J. D. Stew-
art, C. R. Martin, J. Am. Chem. Soc. 2006, 128, 4236.
[5] a) S. J. Son, J. Reichel, B. He, M. Schuchman, S. B. Lee, J. Am.
Chem. Soc. 2005, 127, 7316; b) A. Nan, S. J. Son, S. B. Lee, H. Ghan-
dehari, Nano Lett. 2008, 8, 2150; c) S. J. Son, X. bai, H. Ghandehari,
S. B. Lee, J. Controlled Release 2006, 114, 143; d) B. He, S. J. Son,
S. B. Lee, Langmuir 2006, 22, 8263.
Received: January 3, 2011
Revised: March 3, 2011
Published online: May 26, 2011
[6] a) K. Okamoto, C. J. Shook, L. Bivona, S. B. Lee, D. S. English,
Nano Lett. 2004, 4, 233; b) K. Jayaraman, K. Okamoto, S. J. Son, C.
Chem. Eur. J. 2011, 17, 7433 – 7437
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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