Facile fabrication of amphiphilic AIE active glucan: Via formation of dynamic bonds: Self assembly, stimuli responsiveness and biological imaging

Article abstract of DOI:10.1039/c6tb00776g

Fluorescent organic nanoparticles (FONs) with aggregation induced emission (AIE) properties have recently emerged as one of the most promising luminescent nanomaterials for biomedical applications due to their unique AIE feature. In this study, we reporte

Full text of DOI:10.1039/c6tb00776g

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Facile Fabrication of Amphiphilic AIE active Glucan via Formation
of Dynamic Bonds: Self Assembly, Stimuli Responsiveness and
Biological Imaging
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Qing Wana,#, Meiying Liua,#, Dazhuang Xua, Hongye Huanga, Liucheng Maoa, Guangjian Zenga,
Fengjie Denga,*, Xiaoyong Zhanga,*, Yen Weib,*
www.rsc.org/
Fluorescent organic nanoparticles (FONs) with aggregation induced emission (AIE) properties have recently emerged as
one of the most promising luminescent nanomaterials for biomedical applications due to their unique AIE feature. In this
work, we reported the preparation of AIE active FONs through mixing AIE dye (TPE-CHO), 3-Aminobenzeneboronic acids
(ABBA) and Glucan in one-pot. ABBA was acted as molecular “bridge” to conjugate TPE-CHO with Glucan via formation of
Schiff base and phenyl borate. The resultant products (Glu-TPE FONs) showed amphiphilic properties and could self-
assemble into nanoparticles in aqueous solution. Glu-TPE FONs showed strong luminescence intensity and high water
dispersibility because of the AIE properties of TPE-CHO and hydrophilic nature of Glucan. To examine the biomedical
application potential of Glucan-AIE FONs, the responsiveness, biocompatibility and cell uptake behavior of Glu-TPE FONs
were subsequently examined. We demonstrated that Glu-TPE FONs possess good biocompatibility and can be potentially
used for biological imaging applications. More importantly, it is well known that the Schiff base and phenyl borate can
response to pH and glucose. Therefore, Glu-TPE FONs can be used for fabrication of multifunctional biomaterials with
stimuli responsiveness.
However, the drawbacks of fluorescent inorganic nanomaterials
such as poor biodegradable capability, toxicity to living
1. Introduction
organisms and low quantum yields etc. have largely impeded
their bioimaging applications. On the other hand, the
fluorescent organic nanoparticles (FONs) based on
conventional organic dyes such as fluorescein, Rhodamine and
quinine sulfate often suffer from quenching phenomenon when
they are dispersed in aqueous solution or interact with
biomacromolecules in living cells due to their aggregated state
or high concentration in human body. The phenomenon was
named as aggregation caused quenching (ACQ) effect, which
makes preparation of ultrabright FONs based on conventional
organic dyes problematic.
The development of luminescent nanoparticles with great
sensitivity, selectivity and biocompatibility is of critical
importance for bioscience and biotechnology application due to
their achievement for detecting biological macromolecules and
tracking biological activity.1ꢀ5 As compared with the small
organic dyes, fluorescent nanoparticles that integrated more
fluorescent chromophores into ones possess many advantages
for biological and biomedicine applications for their better
photophysical properties, amplication of fluorescent signal and
multifunctional potential. Over the past few decades, numerous
fluorescent nanoprobes based on inorganic components,
organic components and the inorganic/organic hybrids have
been reported.6ꢀ12 The inroganic nanoparticles (e.g.
semiconductor quantum dots,13ꢀ17 carbon quantum dots, Ln ions
doped nanomaterials and luminescent silica nanoparticles) have
Recently, some organic molecules with unique aggregated
induced emission (AIE) feature have drawn increasingly
attention and provided effective platform for the research and
development of unique fluorescent nanomaterials due to their
obvious enhancement fluorescence at aggregated state. Since
the first report for facile preparation of AIE active luminophors
for biological imaging by research Park group,22, 23 numerous
attention has been attracted by these types of fluorescent
materials, which showed unique properties for the practical
18ꢀ21
been reported and utilized for bioimaging applications.7,
a.Department of Chemistry and Jiangxi Provincial Key Laboratory of New Energy
Chemistry, Nanchang University, 999 Xuefu Avenue, Nanchang 330031, China.
b.Department of Chemistry and the Tsinghua Center for Frontier Polymer Research,
Tsinghua University, Beijing, 100084, P. R. China.
applications in organic lightꢀemitting diode (OLED),24 chemꢀ
c. # These authors contributed equally to this work
28
biosensors25ꢀ27 and fluorescent probes.26,
In the past few
† Footnotes relaꢀng to the ꢀtle and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [The AIE properties of TPE-
CHO, TEM images of Glu-TPE FONs and cell viability of Glu-TPE FONs were provided
in supplementary information]. See DOI: 10.1039/x0xx00000x
years, many simple and effective strategies have been
developed for fabrication of AIEꢀactive polymeric
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nanoprobes.29ꢀ35 For instance, hydrophobic AIE dyes can be
facilely incorporated into amphiphilic macromolecules such as
Scheme 1 Schematic showing the synthetic procedure of TPE-CHO and Glu-TPE FONs
Bovine serum albumin (BSA), commercial available surfactants via a facile one-pot method.
and synthetic copolymers to increase their biocompatibility and
water dispersibility in aqueous solution via noncovalent self
assembly procedure.36 On the other hand, a number of covalent
methods such covalent conjugation, ringꢀopening reaction,
Schiff base condensation, free radical polymerization,
reversible additionꢀfragmentation chain transfer polymerization
(RAFT)37 and emulsion polymerization38 have been also been
developed for fabrication of AIE polymeric nanoprobes with
well controlled properties and functions.32, 38ꢀ40 Carbohydrate
polymers are types of polymers from natural living organisms.
Some of them have demonstrated to be potentially utilized for
different biomedical applications due to their hydrophilic
nature, biological activity and low cost etc. Among them,
Glucan have great potential for biomimicry and wide
biomedical applications such as therapeutic drugs, drug
delivery and bioactive hydrogels.41, 42 However, to the best of
the authors knowledge, only very few studies have reported the
fabrication of AIEꢀactive carbohydrate polymers thus far. The
fabrication of stimuli responsive AIEꢀactive Glucan through
formation of dynamic bonds has not been demonstrated before.
In this contribution, a facile and fast strategy for preparation
of amphiphilic AIE active Glucan is developed by oneꢀpot
2. Experiment
2.1 measurements and materials
All available starting materials contained reaction materials,
reagents and solvents were used from commercially purchased.
The raw materials for the synthesis of TPEꢀCHO were 2ꢀ
Bromoꢀ1,1,2ꢀtriphenylethylene (MW: 335.24 Da, > 98.0%,
purchased from Tokyo Chemical Industry Co. LTD.), 4ꢀ
Acetylphenylboronic acid (MW:163.97 Da,
>
98.0%)
Bis(triphenylphosphine) palladium(II) diacetate (MW: 749.08,
Pd: 14.2%) and Potassium bicarbonate (MW:100.12 Da,
99.7%), were offered from Aladdin. Glucan (MW: 10000 Da)
and ABBA monohydrate were also purchased from Aladdin,
which was used to fabricate FONs. Other dry solvents were
directly used without other purification.
1H NMR spectra were recorded on Bruker Avanceꢀ400
spectrometer with D2O and CDCl3 as the solvents. The
synthetic polymers were characterized by Fourier transform
infrared spectroscopy (FTꢀIR) using KBr pellets, FTꢀIR spectra
were supplied from Nicolet5700 (Thermo Nicolet corporation).
Transmission electron microscopy (TEM) images were
recorded on a Hitachi 7650B microscope operated at 80 Kv.
The TEM specimens were got by putting a drop of the
nanoparticle ethanol suspension on a carbonꢀcoated copper
grid. The fluorescence data were obtained from the
Fluorescence spectrophotometer (FSP, model: C11367ꢀ11),
which purchased from Hamamatsu (Japanese). UVꢀVis spectra
were obtained from a Perkin Elmer LAMBDA 35 UV/Vis
system.
procedure for
the first time. 1,1,2ꢀtriphenylꢀ2ꢀ(pꢀ
formyl)ethylene (TPEꢀCHO) can be synthesized based on
Suzuki reaction. Then TPEꢀCHO was conjugated with Glucan
using 3ꢀAminobenzeneboronic acids (ABBA) as the molecular
“bridge”, which can form Schiff base and phenyl borate with
TPEꢀCHO and Glucan, respectively (Scheme 1). The method
described in this work is especially attractive due to its easy
handle, mild reaction conditions (atmosphere and room
temperature) and environmentally benign (without catalysis and
only water as byꢀproducts). More importantly, both Schiff base
and phenyl borate can response to pH and glucose.43 Therefore,
this work could provide an important tool for fabrication of
stimuli responsive AIE active carbohydrate polymers.
2.2 Synthesis of TPE-CHO
The AIE dye (TPEꢀCHO) was synthesized according the
previous report.44 2ꢀBromoꢀ1,1,2ꢀtriphenylethylene (1.67 g, 5
mM) and 4ꢀAcetylphenylboronic acid (1.23 g, 7.5 mM) were
dissolved in the mixture solution, which contained toluene (50
mL), TBAB (200 mg, 0.7 mM) and 2 M Potassium bicarbonate
were dissolved in 20 mL water. The mixture solution was
sharply stirring at room temperature for 30 min under nitrogen
atmosphere. Afterward, Pd(PPh3)4 (10 mg) was quickly put into
reaction bottle and refluxed at 90 °C for 24 h. When the raw
reaction chemical agents were disappeared via evaluation of
silica gel column, the mixture was poured into water and
extracted three times with ethyl acetate (100 mL). The organic
layer was obtained and dried with anhydrous sodium sulfate.
After removing the organic solvent by rotary evaporation, the
purified products could be obtained via chromatographic
separation on a silica gel column with nꢀhexane/CH2Cl2 (2/1) as
eluent solvents.
Glu
ABBA
TPE-CHO
Glu-TPE FONs
2.3 Preparation of Glu-TPE FONs
GluꢀTPE FONs were prepared via a facile oneꢀpot procedure as
described follows. TPEꢀCHO (35.8 mg, 0.1 mM) and ABBA
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(13.7 mg, o.1 mM) were dissolved in the 10 mL THF solution, report.44 The structure information of TPEꢀCHO was confirmed
while Glucan (100 mg, 0.1 mM) was dissolved in a bit of water. by the 1H NMR
13C NMR and FTꢀIR spectra (Fig.S1-3). The
、
Mixing THF solution and water and adding several drops of amphipathic GluꢀTPE polymers were facilely prepared via a
TEA and stirring at room temperature for 8 h under nitrogen “oneꢀpot” procedure based on TPEꢀCHO and Glucan using
atmosphere. The resulting white solid could be obtained via ABBA as “bridge”. In order to confirm the successful
1
perticipating using cool diethyl ether and washed with ethyl preparation of GluꢀTPE FONs, the H NMR spectra of Glucan
acetate three times to remove unreacted TPEꢀCHO. The final and GluꢀTPE are shown in Fig. 1. After conjugating TPEꢀCHO
1
products were dried by vacuum oven at 50 °C for 24 h.
with Glucan using ABBA as “bridge”, the H NMR spectrum
of GluꢀTPE is found to possess integrated chemical shift from
Glucan and TPEꢀCHO. The chemical shift ranging from 3.0 to
2.4 Cytotoxicity evaluation of Glu-TPE FONs
In order to evaluate the toxic effects of GluꢀTPE FONs for 4.0 ppm could be contributed to methylene and methane groups
living cells, the cell viability of GluꢀTPE FONs with strong of Glucan. After modification with TPEꢀCHO via formation of
green fluorescence on HeLa cells was evaluated by cell phenyl borate and Schiff base, the signal about the protons of
counting kitꢀ8 (CCKꢀ8) assay.45ꢀ48 The experimental procedure aromatic rings were located between 5.5 to 8.0 ppm. Normally,
could be demonstrated by follows: Cells were put into 96ꢀwell the chemical shift of benzene ring locat at 6.0 to 8.0 ppm,
microplates at a density of 5×104 cells mL–1 in 160 ꢁL of however, the formation of Schiff base in GluꢀTPE FONs results
respective media containing 10% fetal bovine serum (FBS). in increasing electron cloud density around bezene rings, which
After 24 h of cell attachment, the cells were incubated with make the chemical shift (δ) of aromatic hydrogens shift to high
different concentrations of FONs (10ꢀ100 µg mL–1) for 12 and magnetic field. On the other hand, the peaks of aromatic
24 h. Then nanoparticles were removed and cells were washed hydrogens between 5.5 and 8.0 ppm were weaken, which could
with PBS three times. 10 ꢁL of CCKꢀ8 dye and 100 ꢁL of be explained by the poor solubility of GluꢀTPE FONs in D2O.
DMEM cell culture medium were added to each well and The resulting GluꢀTPE FONs are well dispersed in aqueous
incubated for 2 h at room temperature. Afterward, plates were solution rather than dissolved in water. All of the above results
analyzed using a microplate reader (VictorШ, PerkinꢀElmer). could demonstrate the successful conjugation between TPEꢀ
Measurements of formazan dye absorbance were carried out at CHO and Glucan through the one pot strategy. Furthermore, the
450 nm, with the reference wavelength at 620 nm. The values strong peak at 8.3 ppm can be contributed to CH=N bond,
were proportional to the number of live cells. The percent further providing powerful evidence that triumphant
1
reduction of CCKꢀ8 dye was compared to controls, which preparation of GluꢀTPE FONs. Based on above analysis of H
represented 100% CCKꢀ8 reduction. Three replicate wells were NMR spectra, we can preliminarily draw a conclusion that
used per microplate, and the experiment was operated for three successful accomplishment for fabrication of AIE active
times. Cell survival was expressed as absorbance relative to that polymers through dynamic Schiff base and phenyl borate.
of untreated controls. Results are presented as mean ± standard
deviation (SD).
2.5 Confocal microscopic imaging
HeLa cells were cultured in Dulbecco’s modified eagle medium
(DMEM) supplemented with 10% heatꢀinactivated FBS, 2 mM
Glucantamine, 100 U mL–1 penicillin, and 100 ꢁg mL–1 of
streptomycin. Cell culture was controlled at 37 °C in a similar
humidified condition of 95% air and 5% CO2 in culture
medium. Culture medium should be updated every three days
for maintaining the exponential growth of the cells. Before
treatment, cells were seeded in a glass bottom dish with a
density of 1×105 cells per dish. On the day of treatment, the
cells were incubated with GluꢀTPE FONs at
a final
concentration of 20 µg mL–1 for 3 h at 37 °C. Afterward, the
cells were washed three times with PBS to remove the GluꢀTPE
FONs and then fixed with 4% paraformaldehyde for 10 min at
room temperature. Cell images were obtained using a confocal
laser scanning microscope (CLSM) Zesis 710 3ꢀchannel (Zesis,
Germany) with the excitation wavelength of 405 nm.
Fig. 1 1H NMR spectra of Glucan and Glu-TPE FONs.The chemical shift ranging from 3.0
to 4.0 ppm can be attributed to the methylene and methane groups, which is derived
from Glucan. The amplified 1H NMR spectrum of Glu-TPE ranging from 5.5 to 9.0 ppm
can be ascribed to the chemical shift of aromatic rings and formation of Schiff base.
3. Result and discussion
The TPEꢀCHO was synthesized based on 2ꢀBromoꢀ1,1,2ꢀ
triphenylethylene and 4ꢀAcetylphenylboronic acid as row
materials via Suzuki reaction according to our previous
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The successful formation of GluꢀTPE FONs was also Due to the amphiphilic properties of GluꢀTPE, the GluꢀTPE are
confirmed by TEM characterization. Due to their amphiphilic tended to self assemble into nanoparticles with great water
properties, GluꢀTPE could self assemble into nanoparticles, in dispersibility and strong luminescence. Therefore, the water
which the hydrophobic TPEꢀCHO was encapsulated in the core dispersibility and optical properties of GluꢀTPE FONs were
while the hydrophilic Glucan was coated on the hydrophobic further examined. As shown in the inset of Fig. 3A
,
core and as shell. As shown in Fig. S4, many spherical homogeneous suspension was observed when GluꢀTPE
nanoparticles with diameter between 80 and 250 nm could be polymers were dispersed in pure aqueous solution. The “AIE”
clearly observed, giving powerful and direct evidence for the marker with high transparency could be intuitively observed.
self assembly of GluꢀTPE polymers in aqueous solution. Self The GluꢀTPE solution can suspend more than 24 h. The water
assembly of amphiphilic polymers in aqueous solution is a very dispersibility provided powerful evidence for the formation of
important route for fabrication of nanomaterials for biomedical amphiphilic polymers. The UVꢀVis spectrum was utilized to
applications. And the self assembly of AIE dyes contained prove the formation of nanoparticles of GluꢀTPE in water. As
amphiphilic polymers is of particular interest for fabrication of shown in Fig. 3A, two peaks at 407 and 337 nm were found in
luminescent nanoparticles because AIE active dyes could the UVꢀVis spectrum. The adsorption peak at 337 nm should be
effectively overcome the notorious ACQ effect of conventional ascribed to the n→π* transition of TPE conjugation structure,
organic dyes. Moreover, successful preparation of GluꢀTPE while the adsorption peak at 407 nm can be attributed to the
FONs are further confirmed by FTꢀIR spectra. As shown in Fig. formation of –CH=Nꢀ on the conjugated structure. The Schiff
2
, a new incisive peak at 1690 cmꢀ1 is emerged in the samples base will lead to the red shift of conjugated structure.26
of GluꢀTPE FONs as compared the spectrum of Glucan. This Furthermore, it could notice that whole absorption curve of
peak can be ascribed to the stretching viration of –CH=Nꢀ GluꢀTPE was started to increase ranging from 800 to 200 nm,
bond, indicating the successful formation of Schiff base which is ascribed to the Mie effect, indicating that successful
between the ABBA and TPEꢀCHO. Furthermore, another peak formation of GluꢀTPE nanoparticles in water. The AIE
at 1350 cmꢀ1 was also emerged in the sample of GluꢀTPE properties of TPEꢀCHO were evaluated by FL spectrometer. As
FONs. This peak can be attributed to the stretching viration of shown in Fig. S5, the fluorescent intensity was gradually
BꢀO bond. Moreover, many peaks between 500ꢀ1000 cm–1 and increased when the volume ratio of water to THF increase from
1300ꢀ1600–1 were observed in GluꢀTPE FONs. These peaks 10% to 90%. However, the maximum emission wavelength has
should be ascribed to deformaton vibration of aromatic rings not significantly changed (about 496 nm). It is well known that
from TPEꢀCHO and ABBA. Finally, a number of characteristic the polarity of solvents will in turn influence the dispersibility
peaks of Glucan were also found in GluꢀTPE FONs. Therefore, of TPEꢀCHO. When the ratio of water to THF increased, the
we can conclude that GluꢀTPE FONs have truly botained via dispersibility of TPEꢀCHO is poor, resulting in strong emission.
formation of dynamic Schiff base and phenyl borate based on In this case, the fluorescence intensity of TPEꢀCHO in 90%
the FTꢀIR spectra.
water is 47 folds to in 10% water. These results suggested that
TPEꢀCHO possess remarkable AIE properties. The PL spectra
of GluꢀTPE water suspension were displayed in Fig. 3B. It can
be seen that the maximum emission wavelength of GluꢀTPE
FONs was located at 516 nm. The emission wavelength is
obviously longer than that of TPEꢀCHO in water. The red shift
phenomenon also indicated that the formation of Schiff base
between TPEꢀCHO and ABBA. Well consistent with the
fluorescent spectra, bright and uniform green fluorescence can
be observed after GluꢀTPE FONs were irradiated with UV lamp
at 365 nm (Inset of Fig. 4A). The fluorescence picture was also
implied that GluꢀTPE FONs have dispersibility in aqueous
solution. Furthermore, the excitation spectrum of GluꢀTPE
FONs is rather broad with maximum peak at 417 nm when the
emission wavelength was set at 516 nm. As compared with
typical TPE based AIE dyes, the optimal excitation wavelength
was also remarkable red shift.26 Based on the optical properties
of GluꢀTPE, we could draw a conclusion that indeed formation
of amphiphilic AIE active Glucan through formation of
dynamic bonds.
Fig. 2 The FT-IR spectra of Glucan and Glu-TPE FONs, which is used to evidence
successful preparation of Glu-TPE FONs. The incisive peak at 1690 cm-1 in the sample of
Glu-TPE FONs is first appeared, which indicates the formation of –CH=N- bond. The
peak at 1350 cm-1 is caused by stretching vibration of B-O bond, which is formed by the
dehydration reaction of Glucan and ABBA.
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Fig. 3 The representative fluorescence and UV-Vis spectra of Glu-TPE FONs. (A) UV-Vis
spectrum of Glu-TPE FONs. The absorption peak was located at 337 and 407 nm,
evidencing the formation of Schiff base between TPE-CHO and ABBA. The inset is the
water dispersion of Glu-TPE FONs. Good dispersibility and stability can be found,
indicating the amphiphilicity of Glu-TPE. (B) Fluorescent excitation and emission
spectra of Glu-TPE dispersed in aqueous solution. The excitation wavelength of Glu-TPE
is 417 nm, while the emission wavelength was located at 516 nm.
Fig. 4 (A) the representative fluorescent curves of Glu-TPE FONs dispersed in aqueous
solution before and after UV lamp irradiation. The results demonstrated the great
photostability of Glu-TPE FONs. (B) pH-responsive PL spectrum of Glu-TPE FONs
dispersed in water with different pH values, which is used to demonstrate that
existence of Schiff base (-CH=N-) in Glu-TPE FONs.
The great biocompatibility of fluorescent nanoparticles is of
great importance for their application prospect in biomedical
fields. Therefore, the cell viability of GluꢀTPE FONs was
detected to evaluate their potential biomedical application
prospects. As shown in Fig. S6, no obvious decrease of cell
viability could be observed after HeLa cells were incubated
with 10ꢀ100 µg mL ꢀ1 of GluꢀTPE FONs for different time. The
cell viability is still greater than 90% even the concentrations of
GluꢀTPE FONs were arrived to 100 µg mLꢀ1. The preliminary
results indicated that GluꢀTPE FONs possess desirable
cytocompatibility. On the other hand, cell uptake behavior of
GluꢀTPE FONs was determined using CLSM. As shown in Fig.
5A, the fluorescent signal can be clearly observed when cells
were irradiated with 405 nm laser. Furthermore, many dark
areas were surrounded by the areas with fluorescent signal.
Combined with the bright field image of cells, we could find
that the areas with fluorescent signal were overlapped with the
location of cells (Fig. 5C). The CLSM results clearly confirmed
that GluꢀTPE FONs can be internalized by cells. Moreover, the
dark areas at the center of cells should be the location of cell
nucleus. It is therefore we could conclude that GluꢀTPE FONs
are mainly distributed in the cytoplasm and cannot enter the cell
nucleus. Taken advantages of the good biocompatibility,
fluorescent properties and stimuli responsiveness, GluꢀTPE
FONs should be promising candidates for bioimaging,
biosensing and drug delivery applications.
The photostability of FONs play an important role for their
biomedical applications. It has been demonstrated that the
fluorescent nanoparitcles showed much better photostability as
compared with the organic dyes.49 Herein, the photostability of
GluꢀTPE FONs was examined via continuous irradiation water
suspension of GluꢀTPE for 1 h using UV lamp at 365 nm. And
the fluorescent spectra of the water suspension of GluꢀTPE
before and after irradiation were determined. As shown in Fig.
4A, it can be seen that the fluorescent intensity of GluꢀTPE was
decreased from 201 to 186 a.u., demonstrating excellent
photostability of GluꢀTPE FONs. As reported from previous
articles, pHꢀresponsive property of fluorescent nanomaterials
based on Schiffꢀbased bind has important potential for
biomedical application. For example, Liu et al described a
novel salicylaldehyde Schiffꢀbased sensor with aggregation
induced emission performance for detection of Cu2+ and Al3+.
The colorimetric and fluorescence variations of salicylaldehyde
Schiffꢀbased sensor were happened after addition of Cu2+ and
Al3+.50 On the other hand, Tang’s group synthesized a pHꢀ
responsive fluorogen consisting of tetraphenylethene (TPE) and
cyanine (Cy) units with AIE feature, which shows obvious pH
variation of strongꢀtoꢀmedium red emission at pH 5ꢀ7, weakꢀtoꢀ
nil red emission at pH 7ꢀ10 and nilꢀtoꢀstrong blue emission at
10ꢀ14. This unique pHꢀresponsive performance makes it
potential biomedical applications in cancer diagnosis and drug
screening.51 Therefore, the pH responsiveness of GluꢀTPE
FONs was also evaluated using fluorescent spectroscopy. As
shown in Fig. 4B, the emission peaks of GluꢀTPE FONs were
located at 513, 516, 500 and 501 nm when the pH values were
10.8, 7.4, 5.6 and 3.2. The blue shift of emission of GluꢀTPE
FONs is due to the decomposition of Schiff base. On the other
hand, significant decrease of fluorescent intensity of GluꢀTPE
FONs is likely ascribed to the precipitation of TPEꢀCHO during
measurement.
Fig. 5 CLSM images of HeLa cells incubated with 20 µg mL -1 of Glu-TPE FONs for 3 h.
(A) fluorescent image after excitation with 405 nm laser. (B) Bright field. (C) Merged
image. Scale bar = 20 µm
4. Conclusions
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13 13. A. P. Alivisatos, W. Gu and C. Larabell, Annu. Rev.
Biomed. Eng., 2005, , 55-76.
14 14. W. C. Chan, D. J. Maxwell, X. Gao, R. E. Bailey, M. Han
and S. Nie, Curr. Opin. Biotech., 2002, 13, 40-46.
15 15. F. Pinaud, X. Michalet, L. A. Bentolila, J. M. Tsay, S.
In summary, a facile and highꢀefficient method for the
fabrication of AIE active FONs with pH responsiveness has
been developed in a oneꢀpot strategy, which combined the
hydrophobic TPEꢀCHO and hydrophilic carbohydrate polymers
(Glucan) using ABBA as the bridge. The dynamic bonds (e. g.
Schiff base and phenyl borate) were contained in GluꢀTPE
FONs. It is therefore GluꢀTPE FONs can be potentially
responded to the pH and glucose. On the other hand, the Gluꢀ
TPE polymers can self assemble into water dispersible
nanoparticles because of their amphiphilicity. The hydrophobic
AIE dye (TPEꢀCHO) was encapsulated in the core of FONs,
which result in strong fluorescence emission for the AIE
properties of TPEꢀCHO. However, the hydrophilic Glucan was
covered on the surface of hydrophobic core, which leads to
good water dispersibility of GluꢀTPE FONs. As compared with
the FONs based on conventional organic dyes, GluꢀTPE FONs
should possess better optical properties because AIE active
dyes could effective overcome the ACQ effect. Furthermore,
the strategy described in this work is rather simple and
effective, which can occur under room temperature, air
atmosphere and absent of toxic metal catalysts. Finally, the
stimuli responsiveness of GluꢀTPE FONs makes them more
promising for various biomedical applications, such as pH
sensors and pH/ glucose controlled drug delivery.
7
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A one-pot strategy has been developed for preparation of stimuli responsive AIE active glucan
through formation of dynamic Schiff base and phenyl borate