A general strategy to construct fluorogenic probes from charge-generation polymers (CGPs) and AIE-active fluorogens through triggered complexation

Article abstract of DOI:10.1002/anie.201105735

Trip the light of plastic: An aqueous fluorogenic sensing system consisting of selective and specific analyte-triggerable charge-generation polymers (CGPs) and a negatively charged aggregation-induced emission active fluorogen (TPE-COOH₄) is pr

Full text of DOI:10.1002/anie.201105735

Angewandte
Chemie
DOI: 10.1002/anie.201105735
Sensors
A General Strategy To Construct Fluorogenic Probes from Charge-
Generation Polymers (CGPs) and AIE-Active Fluorogens through
Triggered Complexation**
Changhua Li, Tao Wu, Chunyan Hong, Guoqing Zhang,* and Shiyong Liu*
Fluorescent probes have been extensively used in chemical
biology, clinical diagnosis, and biosensing because of their
high sensitivity, fast response, and excellent spatial and
temporal resolution.[1] On the basis of photo-induced electron
transfer (PET), internal charge transfer (ICT), fluorescence
resonance energy transfer (FRET), and excited-state intra-
molecular proton transfer (ESIPT) mechanisms, various
fluorometric probes based on small molecule fluorophores,
quantum dots, and conjugated polymers have been devel-
oped.[2] The concept of aggregation-induced emission (AIE)[3]
or aggregation-induced enhanced emission (AIEE)[4] has
emerged to be a powerful and versatile strategy for the design
of novel types of fluorescent probes.[5] Typical AIE-active
molecules, such as tetraphenylethene (TPE), are non-emis-
sive in the molecularly dissolved state, whereas enhanced
fluorescence emission was achieved when they are in the
aggregated state.[6] In recent years, a great variety of AIE-
based small-molecule chemosensors and biosensors for ana-
lytes ranging from heavy-metal ions, thiols, explosives, gas,
carbohydrates, and DNA, to proteins and enzymes have been
fabricated.[5–7] Current research trends in this field involve the
development of general strategies towards water-soluble
fluorogenic probes selective and sensitive for variable ana-
lytes.
envisaged that the intrinsic multivalent nature of polyelec-
trolytes should enable the design of a new-generation of
fluorometric probes when integrated with water-soluble AIE-
active fluorogens.
By taking advantage of the fact that small molecule amine
moieties can be caged by carbamate functionalization and
selectively decaged on demand,[9] we recently designed
charge-generation polymers (CGPs) possessing pendent car-
bamate-masked amine functionalities, which can undergo
stimuli-triggered transition from the initially neutral state to a
charged one in the presence of a specific analyte of
interest.[10a] The charge-generation process was then coupled
with the induced aggregation of Au nanoparticles to design
colorimetric probes. We hypothesize that the integration of
appropriately designed CGPs possessing varying triggerable
motifs with AIE-active charged fluorogens, such as the TPE
derivative bearing four carboxyl acid moieties (TPE-
COOH4), should allow the construction of CGP-based
fluorogenic probes with enhanced detection sensitivity and
designing flexibility (Scheme 1). In the presence of triggering
analyte of interest, electrostatic complexation between TPE-
COOH4 and the newly generated cationic polyelectrolytes
can “turn on” the fluorescence emission through induced
aggregation of TPE-COOH4. Owing to the versatile design
and facile synthesis of CGPs bearing different analyte-specific
charge-generation moieties, this conceptual strategy is
Polyelectrolytes undergo aggregation and assembly in the
presence of oppositely charged polyelectrolytes, multivalent
small organic molecules, and inorganic nanoparticles owing to
electrostatic interactions.[8] However, to the best of our
knowledge, polyelectrolyte-induced aggregation of AIE-
active charged fluorogens has not been utilized in sensing
and detection systems, mainly because of the lack of suitable
smart polyelectrolytes exhibiting specific analyte-triggerable
charge generation or conversion characteristics. It can be
[*] C. Li, T. Wu, Prof. Dr. C. Hong, Prof. Dr. G. Zhang, Prof. Dr. S. Liu
CAS Key Laboratory of Soft Matter Chemistry, Hefei National
Laboratory for Physical Sciences at the Microscale, Department of
Polymer Science and Engineering, University of Science and
Technology of China, Hefei, Anhui 230026 (China)
E-mail: sliu@ustc.edu.cn
gzhang@ustc.edu.cn
[**] Financial support from the National Natural Scientific Foundation
of China (NNSFC) (20874092, 91027026, and 51033005) and
Fundamental Research Funds for the Central Universities is grate-
fully acknowledged.
Scheme 1. Construction of fluorogenic sensors through the integration
of negatively charged AIE-active fluorogens (TPE-COOH4) with water-
soluble amine-caged charge-generation polymers (CGPs) exhibiting
selective and specific analyte-triggered switching from the initially
uncharged state to cationic polyelectrolytes.
Supporting information for this article, including experimental
details, characterization methods, and all relevant characterization
data, is available on the WWW under http://dx.doi.org/10.1002/
anie.201105735.
Angew. Chem. Int. Ed. 2012, 51, 455 –459
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
455

.
Angewandte
Communications
expected to provide a general approach toward engineering a
broad range of fluorogenic probes with diverse sensing
functions. Herein, we report proof-of-concept examples for
the fabrication of fluorogenic probes for two types of
biologically relevant species, namely, H2O2 and thiols, on
the basis of newly designed amine-caged CGPs and negatively
charged AIE-active fluorogens (Scheme 1 and Scheme 2). In
addition, preliminary results concerning their application for
the fluorogenic assay of glucose and d-glucose 6-phosphate
(G6P) are also presented.
as evidenced by 1H NMR spectroscopic analysis from the
complete disappearance of signals characteristic of carbamate
protecting groups (Figures S2 and S3). Since pendent ali-
phatic amine moieties typically possess a pKa value of 8–
9,[10,11] decaged amine residues are mainly in the protonated
state under neutral conditions.
The negatively charged AIE-active TPE derivative bear-
ing four carboxy acid moieties (TPE-COOH4) was then
synthesized (Scheme S3 and Figure S5).[12] TPE-COOH4 has a
pKa value of 4–5 is soluble in water, and exists in its ionized
form at pH 7.4, exhibiting essentially no fluorescence emis-
sion, whereas at pH 3.0 it forms aggregates as a result of
decreased solubility upon protonation and emits intense blue
emission (Figure S6). This result confirms that TPE-COOH4
retains similar AIE features to that of TPE.[6] The colorless
aqueous solution of TPE-COOH4 at pH 7.4 remains non-
fluorescent upon the sole addition of H2O2 or dithiothreitol
(DTT), indicating that they do not induce the aggregation of
TPE-COOH4 (Figure S6).
The aqueous based fluorogenic sensing system for H2O2
was then optimized to consist of negatively charged TPE-
COOH4 (7.5 mm) and the CGP, P(OEGMA0.86-co-
PBMA0.14
)
copolymer ([PBMA] = 30.0 mm) in buffer solu-
410
tion (PBS; pH 7.4). Initially, TPE-COOH4 exhibits no fluo-
rescence emission (Figure 1a–c), which is quite reasonable
considering that negatively charged TPE-COOH4 does not
exhibit any specific interactions with the uncharged amine-
caged copolymer.
Scheme 2. Schematic illustration of the stimuli-triggered charge-gener-
ation process of amine-caged CGPs bearing a) H2O2- and b) thiol-
reactive moieties.
Upon addition of H2O2 (30 equiv relative to PBMA
residues) to the sensing mixture, the emission intensity
increases gradually with time and then stabilizes after
around 180 min (Figure 1a and Figure S7). Concomitantly,
the solution gradually turns from clear to a bluish tinge
(Figure 1b), indicating the formation of colloidal nanoparti-
cles. In addition, the H2O2-induced fluorescence can also be
visualized by the naked eye, as evidenced by the transition
from nonfluorescent to the intense blue emission (Figure 1c).
The reaction of the CGP with H2O2 can chemoselectively de-
cage boronate-based carbamate protecting groups,[9b–e] lead-
ing to the generation of amine moieties and spontaneous
transformation from the uncharged state into a cationic
polyelectrolyte (Scheme 2a). Subsequently, the newly gener-
ated cationic polyelectrolyte electrostatically interacts with
negatively charged TPE-COOH4 molecules to form polyion
complex (PIC) nanoparticles,[8] leading to fluorescence emis-
sion (Scheme 1). TEM and AFM analyses revealed the
presence of robust spherical nanoparticles with diameters in
the range 30–40 nm (Figures S8 and S9). Electrophoresis
measurements further indicated that micellar nanoparticles
possess a zeta potential of approximately ꢀ8 mV. Dynamic
laser light scattering (LLS) revealed an intensity-average
hydrodynamic radius hRhi of 47 nm and polydispersity (m2/G2)
of 0.12 (Figure S10). Static LLS measurements revealed an
apparent molar mass Mw,app of 2.33 ꢀ 107 gmolꢀ1 and average
radius of gyration hRgi of 38 nm (Figure S11). Note that the
hRgi/hRhi ratio of 0.81 is quite close to that theoretically
predicted for hard spheres (0.774). Assuming that all charged
species have participated in the formation of PIC micelles, we
can roughly estimate that, on average, each micellar nano-
According to the above design (Scheme 1), two polymer-
izable and analyte-triggerable carbamate-based monomers,
H2O2-reactive PBMA (Scheme S1 in the Supporting Infor-
mation) and thiol-reactive SSMA (Scheme S1 and Figure S1),
were synthesized at first by the reaction of 2-isocyanatoethyl
methacrylate with hydroxy-functionalized precursors bearing
boronate and disulfide moieties, respectively. Since these two
monomers lack sufficient water solubility, we then opted to
prepare triggering moiety-loaded water-soluble polymers by
reversible addition–fragmentation chain transfer (RAFT)
copolymerization of PBMA or SSMA with oligo(ethylene
glycol) methyl ether methacrylate (OEGMA) (Scheme S2).
1H NMR spectroscopic analysis (Figures S2a and S3a)
revealed overall degrees of polymerization (DPs) of 410 and
400 and functional comonomer contents of 14 and 15 mol%,
respectively, for P(OEGMA-co-PBMA) and P(OEGMA-co-
SSMA) copolymers. Moreover, relatively narrow-disperse
copolymers were obtained (Figure S4).
P(OEGMA-co-PBMA) and P(OEGMA-co-SSMA)
copolymers are water-soluble and remain in the uncharged
state when dissolved in water. As both of them contain
carbamate-caged amine moieties, we can visualize that they
will undergo the transition from the initially uncharged state
to positively charged one upon addition of H2O2[9b–e] and thiol
compounds,[9f–h] respectively (Scheme 2). This is indeed the
case, and it was found that the presence of H2O2 or thiol
groups can selectively deprotect carbamate caging moieties,
456
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 455 –459

Angewandte
Chemie
the final stable state was estimated to be 180 min (Figure 1a
and Figure S7). To maintain the consistency and repeatability
of the sensing system, in subsequent experiments all aqueous
mixtures were then incubated for 180 min upon addition of
H2O2. Typical fluorescence emission intensity obtained for the
aqueous sensing mixture upon addition of H2O2 (0–60.0 equiv
relative to PBMA moieties) are shown in Figure 1c and
Figure S12. The emission intensity dramatically increases with
the H2O2 concentration and tends to stabilize out at more
than 60.0 equiv H2O2, exhibiting approximately 40-fold
cumulative enhancement in emission intensity.
The detection limit at which a 10% increase in emission
intensity can be achieved was determined to be 30 mm
(1.02 mgLꢀ1) (Figure 1d), which is quite comparable to
those of fluorescent sensors based on small molecule aryl
boronates.[9b,d] On the basis of the above results, we estab-
lished that highly sensitive fluorogenic H2O2 detection system
can be constructed by integrating negatively charged AIE-
active fluorogen, TPE-COOH4, with the novel type of CGP
exhibiting H2O2-triggerable transformation from the initially
uncharged state to a cationic polyelectrolyte.
To evaluate the generality of the proposed strategy
(Scheme 1), we then replaced H2O2-reactive CGP,
P(OEGMA0.86-co-PBMA0.14
)
410
copolymer, with the thiol-
reactive one, P(OEGMA0.85-co-SSMA0.15
)
copolymer. The
400
latter contains disulfide moieties as the triggerable motif
(Scheme 2b). Thus, it should allow for the construction of
fluorogenic sensor for thiol compounds. The optimized thiol-
sensing system consists of TPE-COOH4 (7.5 mm) and
P(OEGMA0.85-co-SSMA0.15
)
copolymer at a SSMA con-
400
centration of 30.0 mm in aqueous medium (pH 7.4). Previous
studies have demonstrated that thiols can selectively trigger
the cleavage of disulfide-based carbamate protecting groups
and spontaneously release primary amine moieties.[9f–h]
Figure 1. a) Time evolution of fluorescence emission spectra
(lex =390 nm, slit widths for excitation and emission: 5 nm) of the
fluorogenic sensing mixture (pH 7.4) consisting of TPE-COOH4
(7.5 mm) and P(OEGMA0.86-co-PBMA0.14
)
410
([PBMA]=30.0 mm) upon
Thus, the reaction of P(OEGMA0.85-co-SSMA0.15
)
400
co-
addition of 30.0 equiv H2O2 (relative to PBMA moieties) at 258C.
Optical photographs recorded under b) visible and c) UV (365 nm)
light for the aqueous fluorogenic sensing mixture (left) before and
(right) 180 min after the addition of 30.0 equiv H2O2. d) Relative
fluorescence intensity changes recorded for the aqueous fluorogenic
sensing system at 180 min after the addition of varying amounts of
H2O2 (0–60.0 equiv relative to PBMA moieties).
polymer with thiols can again chemoselectively transform
uncharged P(OEGMA0.85-co-SSMA0.15 into a cationic
)
400
polyelectrolyte (Scheme 2b and Figure S3). As shown in
Figure 2a and Figure S13, upon addition of DTT (500 equiv
relative to SSMA residues), the fluorescence emission
intensity increases gradually with time and then stabilizes
after 180 min. This result indicates that the above described
fluorogenic H2O2-sensing strategy can be further adapted for
fluorescent thiol detection (Scheme 1 and Scheme 2b).
Comparable time-dependent emission intensity changes
(i.e., both accomplished within around 3 h) were observed for
particle consists of 120 copolymer chains and 1710 TPE-
COOH4 moieties. In addition, the average chain density of
micellar nanoparticles was estimated to be 0.089 gcmꢀ3 based
on Mw,app and hRhi values, indicating that these colloidal
nanoparticles are highly hydrated. Note that the observed
enhanced emission of TPE-COOH4 within PIC micelles is
due to the restriction of intramolecular rotation of phenyl
rotors in complexed TPE-COOH4, which is, in principle,
independent of the presence of surrounding water
molecules.[5,6a–d]
P(OEGMA0.86-co-PBMA0.14
)
410
and P(OEGMA0.85
-
co-
SSMA0.15
)
copolymers in the presence of TPE-COOH4
400
upon addition of 30 equiv H2O2 (relative to PBMA) or
500 equiv DTT (relative to SSMA), respectively (Figures 1a
and 2a). This result must be a coincidence because in both
cases, the carbamate deprotection kinetics are quite depen-
dent on the H2O2 or DTT concentration (Scheme 2).[9]
Figure 2b and Figure S14 show that the emission intensity
increases considerably with increasing amount of DTT and
stabilizes at greater than 1000 equiv of DTT (relative to
SSMA moieties), exhibiting 42-fold cumulative enhancement
in the DTT range 0–1000 equiv and a detection limit of
0.5 mm. Thus, the integration of thiol-reactive CGP with TPE-
H2O2-triggered complexation between the CGP,
P(OEGMA0.86-co-PBMA0.14
)
410
copolymer, and TPE-
COOH4 can be further quantitatively determined by emission
intensity changes. Spectrofluorometric analysis was then
conducted to evaluate the H2O2 detection performance. The
time duration needed for the fluorometric changes to reach
Angew. Chem. Int. Ed. 2012, 51, 455 –459
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
457

.
Angewandte
Communications
organic pollutants (e.g., benzidine).[13c,d] Further work toward
this end are currently underway.
In summary, we have presented a general and conceptual
strategy for the construction of quantitative, selective, and
sensitive fluorogenic sensors by integrating a novel type of
stimuli-triggerable CGPs bearing caged amine moieties with
negatively charged AIE-active fluorogens, TPE-COOH4
(Scheme 1). The presence of specific biorelevant analytes,
H2O2 or thiols, can trigger the transformation of CGPs from
the initially uncharged state into a cationic polyelectrolyte
through the chemoselective cleavage of carbamate protecting
moieties. This transformation induces the aggregation of
negatively charged TPE-COOH4, leading to the dramatic
enhancement of fluorescence emission. Further applications
to the fluorogenic sensing of glucose and G6P were also
demonstrated. A variety of analyte-specific carbamate-based
amine-caging motifs could be incorporated into the CGP
design.[9a] We envisage that these proof-of-concept examples
can be further generalized to the design of more sophisticated
sensing systems.
Figure 2. a) Time evolution of fluorescence emission spectra
(lex =390 nm, slit widths for excitation and emission: 5 nm) of the
fluorogenic sensing mixture (7.5 mm of TPE-COOH4 and P(OEGMA0.85
Received: August 13, 2011
Revised: October 23, 2011
Published online: December 1, 2011
-
co-SSMA0.15
)
400
with [SSMA]=30.0 mm) at pH 7.4 upon addition of
500 equiv DTT (relative to SSMA moieties) at 258C. b) Relative
fluorescence intensity changes recorded for the aqueous sensing
mixture at 180 min after the addition of varying amounts of DTT (0–
1000 equiv relative to SSMA moieties).
Keywords: biosensors · luminescence · polycations · polymers
.
[1] A. P. Demchenko, Introduction to Fluorescence Sensing,
Springer, Berlin, 2008.
COOH4 can further lead to the construction of highly
sensitive fluorogenic thiol-sensing assay.
Finally, we explored the applications of P(OEGMA0.86-co-
PBMA0.14)410 copolymer/TPE-COOH4 based sensing mixture
for the quantitative assay of two additional types of analytes,
glucose and d-glucose 6-phosphate (G6P), by taking advant-
age of glucose oxidase (GOx)-catalyzed[13a,b] and cascade acid
phosphatase (AP)/GOx-catalyzed[13c,d] production of H2O2,
respectively (Scheme S4). As shown in Figure S15, upon
addition of 60.0 equiv glucose (relative to PBMA) to the
[2] a) J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, Chem. Soc. Rev. 2011,
40, 3483 – 3495; b) K. E. Sapsford, L. Berti, I. L. Medintz,
Angew. Chem. 2006, 118, 4676 – 4704; Angew. Chem. Int. Ed.
2006, 45, 4562 – 4589; c) S. W. Thomas, G. D. Joly, T. M. Swager,
Chem. Rev. 2007, 107, 1339 – 1386; d) T. Schwarze, H. Mꢁller, C.
Dosche, T. Klamroth, W. Mickler, A. Kelling, H.-G. Lçhmanns-
rçben, P. Saalfrank, H.-J. Holdt, Angew. Chem. 2007, 119, 1701 –
1704; Angew. Chem. Int. Ed. 2007, 46, 1671 – 1674; e) K. Wang,
Z. Tang, C. J. Yang, Y. Kim, X. Fang, W. Li, Y. Wu, C. D. Medley,
Z. Cao, J. Li, P. Colon, H. Lin, W. Tan, Angew. Chem. 2009, 121,
870 – 885; Angew. Chem. Int. Ed. 2009, 48, 856 – 870; f) R. Hu, J.
Feng, D. Hu, S. Wang, S. Li, Y. Li, G. Yang, Angew. Chem. 2010,
122, 5035 – 5038; Angew. Chem. Int. Ed. 2010, 49, 4915 – 4918.
[3] J. Luo, Z. Xie, J. W. Y. Lam, L. Cheng, H. Chen, C. Qiu, H. S.
Kwok, X. Zhan, Y. Liu, D. Zhu, B. Z. Tang, Chem. Commun.
2001, 1740 – 1741.
mixture of P(OEGMA0.86-co-PBMA0.14)410, TPE-COOH4, and
GOx, we observed a time-dependent increase of fluorescence
emission, which essentially stabilizes after 210 min (Fig-
ure S16). This result is quite comparable to that observed
upon H2O2 addition (Figure 1a) and confirms that GOx-
assisted fluorogenic glucose sensing is feasible (Scheme S4).
Figure S17 indicates that the emission intensity after 210 min
incubation with glucose (0–120 equiv; 0–2.4 mm) exhibited
36-fold cumulative emission intensity increase. The two-
enzyme cascade reaction of G6P in the presence of AP and
GOx also results in the formation of H2O2, and this can be
utilized for fluorogenic G6P sensing (Scheme S4). We can
clearly tell from Figure S18 that the emission intensity at
487 nm dramatically increases with the G6P concentration in
the range 0–120 equiv after 300 min incubation with the
[4] B.-K. An, S.-K. Kwon, S.-D. Jung, S. Y. Park, J. Am. Chem. Soc.
2002, 124, 14410 – 14415.
[5] a) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Commun. 2009,
4332 – 4353; b) Y. Hong, J. W. Y. Lam, B. Z. Tang, Chem. Soc.
Rev. 2011, 40, 5361 – 5388.
[6] a) Y. Liu, C. Deng, L. Tang, A. Qin, R. Hu, J. Z. Sun, B. Z. Tang,
J. Am. Chem. Soc. 2011, 133, 660 – 663; b) Y. Hong, H. Xiong,
J. W. Y. Lam, M. Hꢂußler, J. Liu, Y. Yu, Y. Zhong, H. H. Y. Sung,
I. D. Williams, K. S. Wong, B. Z. Tang, Chem. Eur. J. 2010, 16,
1232 – 1245; c) Y. Hong, M. Hꢂußler, J. W. Y. Lam, Z. Li, K. K.
Sin, Y. Dong, H. Tong, J. Liu, A. Qin, R. Renneberg, B. Z. Tang,
Chem. Eur. J. 2008, 14, 6428 – 6437; d) J.-P. Xu, Z.-G. Song, Y.
Fang, J. Mei, L. Jia, A. J. Qin, J. Z. Sun, J. Ji, B. Z. Tang, Analyst
2010, 135, 3002 – 3007; e) J. Wang, J. Mei, W. Yuan, P. Lu, A. Qin,
J. Sun, Y. Ma, B. Z. Tang, J. Mater. Chem. 2011, 21, 4056 – 4059;
f) L. Tang, J. K. Jin, A. Qin, W. Zhang Yuan, Y. Mao, J. Mei, J.
Zhi Sun, B. Z. Tang, Chem. Commun. 2009, 4974 – 4976; g) M.
Nakamura, T. Sanji, M. Tanaka, Chem. Eur. J. 2011, 17, 5344 –
aqueous mixture containing P(OEGMA0.86-co-PBMA0.14
) ,
410
TPE-COOH4, AP, and GOx. In principle, this fluorogenic
assay system should also be applicable for the fluorometric
quantification of phosphatase activities and the detection of
AP-specific inhibitors such as pesticides (e.g., paraoxon) and
458
www.angewandte.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2012, 51, 455 –459

Angewandte
Chemie
5349; h) H. Tong, Y. Hong, Y. Dong, M. Hꢂussler, Z. Li, J. W. Y.
Lam, Y. Dong, H. H. Y. Sung, I. D. Williams, B. Z. Tang, J. Phys.
Chem. B 2007, 111, 11817 – 11823; i) Y. Liu, Y. Yu, J. W. Y. Lam,
Y. Hong, M. Faisal, W. Z. Yuan, B. Z. Tang, Chem. Eur. J. 2010,
16, 8433 – 8438; j) Y. Hong, C. Feng, Y. Yu, J. Liu, J. W. Y. Lam,
K. Q. Luo, B. Z. Tang, Anal. Chem. 2010, 82, 7035 – 7043.
[7] a) Y. Liu, Y. Tang, N. N. Barashkov, I. S. Irgibaeva, J. W. Y. Lam,
R. Hu, D. Birimzhanova, Y. Yu, B. Z. Tang, J. Am. Chem. Soc.
2010, 132, 13951 – 13953; b) P. S. Salini, A. P. Thomas, R.
Sabarinathan, S. Ramakrishnan, K. C. G. Sreedevi, M. L. P.
Reddy, A. Srinivasan, Chem. Eur. J. 2011, 17, 6598 – 6601; c) L.
Peng, M. Wang, G. Zhang, D. Zhang, D. Zhu, Org. Lett. 2009, 11,
1943 – 1946; d) T. Sanji, K. Shiraishi, M. Tanaka, ACS Appl.
Mater. Interfaces 2009, 1, 270 – 273; e) M. Zhao, M. Wang, H.
Liu, D. Liu, G. Zhang, D. Zhang, D. Zhu, Langmuir 2009, 25,
676 – 678.
M. Airiau, J. Am. Chem. Soc. 2006, 128, 1755 – 1761; k) J.
Fresnais, E. Ishow, O. Sandre, J.-F. Berret, Small 2009, 5, 2533 –
2536.
[9] a) P. G. M. Wuts, T. W. Greene, Greeneꢀs Protective Groups in
Organic Synthesis, 4th ed., Wiley-Interscience, Hoboken, NJ,
2006; b) L. C. Lo, C. Y. Chu, Chem. Commun. 2003, 2728 – 2729;
c) E. Sella, D. Shabat, Chem. Commun. 2008, 5701 – 5703; d) D.
Srikun, E. W. Miller, D. W. Dornaille, C. J. Chang, J. Am. Chem.
Soc. 2008, 130, 4596 – 4597; e) A. P. Esser-Kahn, N. R. Sottos,
S. R. White, J. S. Moore, J. Am. Chem. Soc. 2010, 132, 10266 –
10268; f) J. H. Lee, C. S. Lim, Y. S. Tian, J. H. Han, B. R. Cho, J.
Am. Chem. Soc. 2010, 132, 1216 – 1217; g) B. Zhu, X. Zhang, Y.
Li, P. Wang, H. Zhang, X. Zhuang, Chem. Commun. 2010, 46,
5710 – 5712; h) C. S. Lim, G. Masanta, H. J. Kim, J. H. Han,
H. M. Kim, B. R. Cho, J. Am. Chem. Soc. 2011, 133, 11132 –
11135.
[8] a) A. Harada, K. Kataoka, Macromolecules 1995, 28, 5294 –
5299; b) A. Harada, K. Kataoka, Science 1999, 283, 65 – 67;
c) Y. Lee, T. Ishii, H. J. Kim, N. Nishiyama, Y. Hayakawa, K.
Itaka, K. Kataoka, Angew. Chem. 2010, 122, 2606 – 2609; Angew.
Chem. Int. Ed. 2010, 49, 2552 – 2555; d) I. K. Voets, A. de Keizer,
P. de Waard, P. M. Frederik, P. H. H. Bomans, H. Schmalz, A.
Walther, S. M. King, F. A. M. Leermakers, M. A. C. Stuart,
Angew. Chem. 2006, 118, 6825 – 6828; Angew. Chem. Int. Ed.
2006, 45, 6673 – 6676; e) Y. Yan, N. A. M. Besseling, A. de Ke-
izer, A. T. M. Marcelis, M. Drechsler, M. A. C. Stuart, Angew.
Chem. 2007, 119, 1839 – 1841; Angew. Chem. Int. Ed. 2007, 46,
1807 – 1809; f) J. Zhang, Y. Zhou, Z. Zhu, Z. Ge, S. Liu,
Macromolecules 2008, 41, 1444 – 1454; g) X. Jia, D. Y. Chen, M.
Jiang, Chem. Commun. 2006, 1736 – 1738; h) J.-F. Berret, Adv.
Colloid Interface Sci. 2011, 167, 38 – 48; i) M. Beija, J.-D. Marty,
M. Destarac, Prog. Polym. Sci. 2011, 36, 845 – 886; j) J.-F. Berret,
N. Schonbeck, F. Gazeau, D. E. Kharrat, O. Sandre, A. Vacher,
[10] a) C. Li, J. Hu, T. Liu, S. Liu, Macromolecules 2011, 44, 429 – 431;
b) J. Hu, S. Liu, Macromolecules 2010, 43, 8315 – 8330; c) X. W.
Xu, A. E. Smith, C. L. McCormick, Aust. J. Chem. 2009, 62,
1520 – 1527; d) L. H. He, E. S. Read, S. P. Armes, D. J. Adams,
Macromolecules 2007, 40, 4429 – 4438.
[11] a) A. I. Petrov, A. A. Antipov, G. B. Sukhorukov, Macromole-
cules 2003, 36, 10079 – 10086; b) S. Mutka, B. Njegic-Dzakula, D.
Kovacevic, Croat. Chem. Acta 2008, 81, 593 – 597.
[12] P. P. Kapadia, L. R. Ditzler, J. Baltrusaitis, D. C. Swenson, A. V.
Tivanski, F. C. Pigge, J. Am. Chem. Soc. 2011, 133, 8490 – 8493.
[13] a) C. R. Gordijo, A. J. Shuhendler, X. Y. Wu, Adv. Funct. Mater.
2010, 20, 1404 – 1412; b) Y. Jiang, H. Zhao, Y. Q. Lin, N. N. Zhu,
Y. R. Ma, L. Q. Mao, Angew. Chem. 2010, 122, 4910 – 4914;
Angew. Chem. Int. Ed. 2010, 49, 4800 – 4804; c) F. Mazzei, F.
Botrꢃ, C. Botrꢃ, Anal. Chim. Acta 1996, 336, 67 – 75; d) N.
Jaffrezic-Renault, Sensors 2001, 1, 60 – 74.
Angew. Chem. Int. Ed. 2012, 51, 455 –459
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
459