Mesoporous silica nanobeans dual-functionalized with AIEgens and leaning pillar[6]arene-based supramolecular switches for imaging and stimuli-responsive drug release

Article abstract of DOI:10.1039/c9cc07115f

A bean-shaped and dual-functionalized organic-inorganic hybrid supramolecular system with a GSH-dependent turn-on fluorescence enhancement property and stimuli-responsive drug delivery function endowed with leaning towerarene-based switches has been const

Full text of DOI:10.1039/c9cc07115f

Volume 55 Number 94 7 December 2019 Pages 14087–14224
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Lei Fang, Ying-Wei Yang et al.
Mesoporous silica nanobeans dual-functionalized with
AIEgens and leaning pillar[6]arene-based supramolecular
switches for imaging and stimuli-responsive drug release

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Mesoporous silica nanobeans dual-functionalized
with AIEgens and leaning pillar[6]arene-based
supramolecular switches for imaging and
stimuli-responsive drug release†
Cite this: Chem. Commun., 2019,
55, 14099
Received 12th September 2019,
Accepted 9th October 2019
a
Xiangshuai Li,‡ab Junyou Han,‡b Jianchun Qin,‡b Ming Sun,c Jiarui Wu,
DOI: 10.1039/c9cc07115f
a
Liancheng Lei,c Jing Li,a Lei Fang *d and Ying-Wei Yang
*
rsc.li/chemcomm
A bean-shaped and dual-functionalized organic–inorganic hybrid frameworks and thus satisfy the growing needs. To inhibit and cure
supramolecular system with a GSH-dependent turn-on fluorescence tumours more effectively, diagnosis and tracing cell uptake mechan-
enhancement property and stimuli-responsive drug delivery function isms of nanomedicine are critical. The AIE features permit strong
endowed with leaning towerarene-based switches has been con- emission of fluorophores even in highly aggregated states that will
structed for simultaneous tumor inhibition and imaging.
overcome the ACQ problems and enable the development of fluores-
cence ‘‘turn-on’’ probes for bio-imaging.18,19
Significant advances in the fabrication of porous solids with
Herein, we construct a bean-shaped mechanized MSN delivery
ordered structures and new morphologies have promoted and system, that is, a dual-functionalized mesoporous silica nanobean,
broadened the application of these functional materials in the denoted as DF-MSNB, which possesses large drug loading capa-
past couple of decades.1–3 Recent development in the control of city and the capability of simultaneously indicating tumour sites
the particle shapes of silica materials, anisotropic structures in and eliminating tumour cells (Scheme 1). Briefly, nanobean
particular, has boosted intriguing applications in catalysis, energy shaped MSNs with two different functional groups (–NH2 and
storage, drug delivery, and bioimaging.4,5 As one of the most popular –SH) have been prepared via a one-pot co-condensation method.
drug delivery platforms, mesoporous silica nanoparticles (MSNs) Then a TPE derivative was conjugated upon reaction with
attracted tremendous attention due to their large loading capacity, –NH2 on the MSNB to provide potential imaging function, and
good biocompatibility, well-ordered pore channels, and ease of
functionalization.6,7 Thus, many researchers have devoted themselves
to mediating the morphology, surface functionalities, loading capa-
city, and particle size of MSNs for biomedical applications.8–10 To
date, MSNs with interesting morphologies, including sphere,11 rod,12
bowl,13 pod,14 and star15 shapes, and unique functions have been
prepared and used in building drug delivery systems. However, usage
of the reported MSNs was greatly restricted because most of them
only have unique functional groups on their surfaces that could only
perform limited functions.16,17 It is imperative to synthesize new
shaped MSNs with multiple functions and enhanced properties
to broaden and strengthen the applications of mesoporous silica
a College of Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012,
China. E-mail: ywyang@jlu.edu.cn
b College of Plant Science, Jilin University, 5333 Xi’an Street, Changchun 130062,
China
c College of Veterinary Medicine, Jilin University, 5333 Xi’an Street,
Changchun 130062, China
d Department of Chemistry, Texas A&M University 3255 TAMU, College Station,
Scheme 1 Schematic illustration of MSNB preparation for application in
GSH/pH dual-stimuli responsive tumour theranostics with simultaneous
cell imaging. The construction of the DOX@DF-MSNB system has four
steps: (i) connection of TPE, (ii) conjunction of MBM, (iii) loading of DOX,
and (iv) capping with AWLP6.
TX 77843-3255, USA. E-mail: fang@chem.tamu.edu
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c9cc07115f
‡ These authors contributed equally to this work.
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1,3-dimethyl-benzoimidazolium (MBM) stalks were installed via
disulfide bond formation. Taking advantage of the flexible
structure, superior cavity adaptability, and guest selectivity of
leaning towerarenes we recently discovered,20 we further synthe-
sized a water-soluble version of leaning pillar[6]arene (AWLP6)21
to thread onto the MBM stalks on the MSNB, leading to the
formation of MBMCAWLP6 pseudorotaxane-based supramole-
cular nanovalves to prevent premature drug leakage from the
pores and regulate the on-command release of drugs. Notably,
MBM can efficiently quench TPE fluorescence (OFF) via donor–
acceptor type electron transfer (ET), resulting in a relatively
weaker system emission.22 Upon encountering GSH, disulfide
bond-connected MBM on the surface can be cut off, and as a
result, system fluorescence can be greatly enhanced (ON),
enabling the DF-MSNB to probe tumour cell sites of a high level
of GSH. Benefiting from the supramolecular nanovalves based
on MBMCAWLP6 and dynamic disulfide bonds, the DF-MSNB
system can regulate drug release in response to certain conditions
Fig. 1 (A) SEM image, (B) TEM image, (C) XRD pattern, and (D) N2
adsorption–desorption isotherms and pore size distribution of the MSNB.
such as a tumour microenvironment (TME) that is acidic and modified with more fantastic functionalities, endowing this nano-
contains high concentration of GSH.23,24 Experimental results platform with more potential applications. Two main functionalities,
suggest that the DOX-loaded DF-MSNB (DOX@DF-MSNB) could i.e., TPE as a widely used AIEgen that can provide monitoring
kill tumour cells and simultaneously serve as a ‘‘turn-on’’ probe function, and MBMCAWLP6-based supramolecular nanovalves cap-
for tumour cell imaging.
able of reducing cargo leakage and regulating the release of drugs,
The synthetic strategy for the MSNB follows a specific have been introduced into the MSNB delivery system via covalent
addition order change of precursors, addition order of organo- bonds (Fig. S3–S5, ESI†). The TPE-functionalized MSNB (MSNB-TPE)
silanes is critical for nanobean formation. Deprotonated showed strong fluorescence and a quantum yield of 5.08% due to
MPTMS under high pH conditions will hinder the bending of the restriction of the intramolecular motion of TPE resulting from
negatively charged silica-surfactant cylinder micelle walls due the covalent bonding between TPE and the MSNB (Fig. S6 and S7,
to the charge repulsion between the deprotonated MPTMS and ESI†). A model guest, 1,2,3-trimethylbenzimidazolium iodide (MBM-
the silica-surfactant cylinder micelle walls, thus resulting in the CH3), was prepared to bind with AWLP6 to prove the host–guest
vertical growth. However, when the silica source is TEOS and/or interaction of MBM and AWLP6. From 1H NMR titration, the
APTMS, the growth of the silica-surfactant cylinder micelle host–guest binding constant (Ka) was calculated to be (2.7 Æ 0.5)
walls will not be affected and they will be gradually curved to  103 MÀ1 (Fig. S8 and S9, ESI†). Detailed synthetic information
be sphere-shaped (Fig. S1, ESI†). In these cases, TEOS, MPTMS, is provided in the ESI† (Fig. S10–S17).
and APTMS were mixed together to be a homogenous silica
The DF-MSNB system possesses good GSH-induced fluores-
source solution according to the order: 1st TEOS, 2nd MPTMS, cence enhancement property (Fig. 2A), and its TEM image (Fig. 2B)
and 3rd APTMS (the adding interval is ca. 30 seconds). After a also proved its bean-shaped morphology. Upon increasing the
co-condensation procedure, the MSN morphology observed GSH concentration, the fluorescence intensity of the DF-MSNB
using a scanning electron microscope (SEM) and a transmis- obviously increased (Fig. 2C and Fig. S18, ESI†). To use the
sion electron microscope (TEM) can be concisely controlled to fluorescent drug delivery system, the stimuli-responsive optical
be bean-shape (Fig. 1A and B). The existence of APTMS relieves properties of the DF-MSNB were examined under TME mimic
charge repulsion of the deprotonated MPTMS and silica- conditions (pH = 5.0 and [GSH] = 20 mM). Obviously, the DF-MSNB
surfactant cylinder micelle walls, leading to the formation of also exhibited GSH-dependent fluorescence enhancement
a partially curved bean-like MSNB.
(Fig. 2D). The fluorescence behavior of MSNB-TPE-MBM against
The MSNB exhibits highly ordered 2D meso-channels according GSH follows a linear relationship, and KSV was calculated to be
to the result of sharp 100 crystal planes in its X-ray diffraction (XRD) ca. À1.3 Â 102 (Fig. S19, ESI†). In the case of MBM, upon
pattern (Fig. 1C). N2 adsorption–desorption analysis of the MSNB excitation, electrons can easily transfer from the conduction
illustrates its large surface area of 872.0 m2 gÀ1, and pore volume of band (CB) of TPE to the LUMO of MBM, leading to fluorescence
0.54 mL gÀ1, and its pore size is 2.2 nm (Fig. 1D). Compared with quenching due to the ET process (Fig. 2A).22 Cyclic voltammetry
spherical and rod shaped MSNs (MSNS and MSNR), the newly (CV) was performed to further certify the ET identity. As in Fig. S20
obtained MSNB shows more regular channels and large surface (ESI†), since a disulfide bond-linked electron-deficient molecule
areas based on the results of XRD patterns and BET analysis (Fig. S2, MBM or MBMCAWLP6 can be cut off by GSH, upon treatment
ESI†). Meanwhile, although the surface areas of the MSNR and with 20 mM GSH, MSNB-TPE-MBM and DF-MSNB all exhibited
MSNB are comparable, the relatively large size of the MSNR greatly a decreased reduction potential from À0.83 to À0.99 V and À0.84
hinders the in vivo application.25 Notably, possessing two different to À0.99 V, respectively. The less negative reduction potentials
reactive groups (–NH2 and –SH), the MSNB was permitted to be indicated that MBM has a high reduction potential and it is easier
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Fig. 3 (A) Schematic presentation of drug release behaviour of the
DOX@DF-MSNB by GSH and/or under acidic conditions. Time-dependent
DOX release profiles from 0.5 mg of the DOX@DF-MSNB platform (B) at
different concentrations of GSH (the inset shows the digital photos of final
solutions with different concentrations of GSH for 22 h: from left to right,
10 mM, 5 mM and 0 mM, respectively), (C) in the PBS solutions of different pH
values (the inset shows the digital photos taken after the DOX@DF-MSNB was
placed in PBS solutions of different pH for 72 h: from left to right, pH 5 and 7.4).
(D) Premature release of the DOX@DF-MSNB in deionized water for
different periods of time (the inset shows the absorbance spectra of the
released DOX after placing the material in deionized water for 0.5, 1 and
33 days, respectively).
Fig. 2 (A) Schematic illustration of the GSH-induced fluorescence
enhancement phenomenon of MSNB-TPE-MBM and DF-MSNB. TEM
image of (B) DF-MSNB. GSH-dependent fluorescence enhancement
of the DF-MSNB in (C) deionized water and (D) TME mimic conditions
(0.25 mg mLÀ1; lex = 317 nm, lem = 475 nm, slit widths: ex = 5 nm, em = 3 nm).
for MBM to accept electrons from the photo-excited state of TPE, in solutions containing 5 mM or 10 mM of GSH for 22 hours,
serving as an acceptor in the system.22
the cumulative release percentage of DOX reached 63.0 Æ 2.5%
On the other hand, the fluorescence lifetime of the DF-MSNB or 92.7 Æ 1.8%, respectively, which was also confirmed by the
was increased from 2.6 ns to 3.2 ns after treatment with 20 mM solution color changes. Meanwhile, the DOX@DF-MSNB was
GSH, which is ascribed to the inhibition of ET resulting from the incubated in PBS solution of pH 5 and 7.4, respectively, to
removal of MBM entities (Fig. S21, ESI†). If the positively charged investigate its pH-responsive ability. Under neutral conditions,
MBM unit of the system was replaced with a similar neutral drugs were kept tightly in the pores of the MSNB, showing
molecule (BM), the fluorescence intensity of MSNB-TPE-BM negligible release, however, the release rate and amount of DOX
becomes much higher than that of MSNB-TPE-MBM at the same greatly increased in the acidic solution of pH 5 (Fig. 3C). When
concentration (Fig. S22A, ESI†), indicating that no fluorescence the DOX@DF-MSNB was placed in water without the activation
quenching occurs in the absence of MBM. After that, TPE-Br was of any stimulus, only a small amount of DOX (4.0 Æ 0.7% and
mixed with a model electron-withdrawing molecule (MBM-CH3) 9.9 Æ 0.4%) was released after standing for 12 hours and 3 days,
in water to test fluorescence changes. As in Fig. S22B (ESI†), with respectively. Notably, even for prolonged monitoring of drug
a constant concentration of TPE-Br, and upon increasing the leakage from the DOX@DF-MSNB for over a month (33 days
amount of MBM-CH3, the fluorescence of TPE-Br solution gra- herein), only 10.5 Æ 1.2% of drug was released, indicating the
dually decreased.
excellent drug storage ability and high stability of this DF-MSNB
The DOX loading capacity of the MSNB was calculated to be system (Fig. 3D).
222 mg gÀ1 (DOX/DOX@DF-MSNB, m/m) which is 2–3 times higher
The cytotoxicity of the DF-MSNB was tested using a MTT
than those of most traditional MSNs, and the details of the in vitro assay on a human normal hepatic cell line (L02). From Fig. 4A,
release experiment are provided in the ESI† (Fig. S23).26,27 Since the incubation of even 200 mg mLÀ1 of the DF-MSNB with L02 cells
MBM entities were covalently connected to the MSNB through for 24 hours showed a negligible effect on the cells, indicating
disulfide bonds, MBMCAWLP6 pseudorotaxanes would be cleaved the non-cytotoxicity of the DF-MSNB. After incubation with a
off by GSH to release DOX. The host–guest complexation of the high concentration of DF-MSNB of up to 200 mg mLÀ1 for 24 h,
negatively charged AWLP6 with the positively charged MBM stalks the DF-MSNB without DOX has a negligible effect on HepG2
mainly relies on electrostatic interactions. However, under acidic tumour cells (Fig. 4B). From Fig. 4C and D, free DOX and
conditions, the carboxylate (COOÀ) groups of AWLP6 will turn into DOX@DF-MSNB show an obvious effect in tumour cell killing,
COOH groups, losing the electrostatic attractions with MBM thus where the viability of the HepG2 cells was decreased obviously
leading to nanovalve opening and drug release (Fig. 3A).
with increasing concentrations of DOX and DOX@DF-MSNB,
As in Fig. 3B, without any stimuli, a negligible amount of respectively. That is to say, the main active anticancer compo-
DOX (5.3 Æ 0.9%) was released from the DOX@DF-MSNB after nent of the DOX@DF-MSNB is DOX with a loading ratio of
being dispersed in deionized water for 22 hours. As expected, 22.2% (m/m). Finally, the intracellular tumour monitoring
with an increasing concentration of GSH, the DOX release rate function was tested. As in Fig. 4E, upon increasing the incuba-
increases gradually. When the DOX@DF-MSNB was incubated tion time with the DF-MSNB (100 mg mLÀ1), blue fluorescence
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In conclusion, a mechanized bean-shaped DF-MSNB system
with large loading capacity and nearly zero premature release of
drugs was constructed, which showed not only GSH and pH dual-
responsive drug release but also GSH-dependent ‘‘turn-on’’ fluores-
cence enhancement suitable for cell imaging. Proof-of-concept
intracellular studies demonstrated that the DOX@DF-MSNB
system could be efficiently used for tumour inhibition, and the
tumour cells were able to emit blue fluorescence upon inter-
action with the DF-MSNB system.
This work was supported by the National Natural Science
Foundation of China (51673084 and 21871108).
Conflicts of interest
There are no conflicts to declare.
Notes and references
1 M. E. Davis, Nature, 2002, 417, 813.
2 Y. Lu, Y. Yang, A. Sellinger, M. Lu, J. Huang, H. Fan, R. Haddad,
G. Lopez, A. R. Burns, D. Y. Sasaki, J. Shelnutt and C. J. Brinker, Nature,
2001, 410, 913.
3 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka and G. D. Stucky, Science, 1998, 279, 548.
4 S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunieda,
O. Terasaki and T. Tatsumi, Nat. Mater., 2003, 2, 801.
5 Q. Xi, M. A. Alibakhshi, S. Jiao, Z. Xu, M. Hempel, J. Kong, H. G. Park
and C. Duan, Nat. Nanotechnol., 2018, 13, 238.
6 N. K. Mal, M. Fujiwara and Y. Tanaka, Nature, 2003, 421, 350.
7 S. Mura, J. Nicolas and P. Couvreur, Nat. Mater., 2013, 12, 991.
8 Y. Zhao, B. G. Trewyn, I. I. Slowing and V. S.-Y. Lin, J. Am. Chem. Soc.,
2009, 131, 8398.
¨
9 H.-Y. Chiu, D. Goßl, L. Haddick, H. Engelke and T. Bein, Chem.
Mater., 2018, 30, 644.
10 H. Djojoputro, X. F. Zhou, S. Z. Qiao, L. Z. Wang, C. Z. Yu and
G. Q. Lu, J. Am. Chem. Soc., 2006, 128, 6320.
11 R. Jin, Z. Liu, Y. Bai, Y. Zhou, J. J. Gooding and X. Chen, Adv. Funct.
Mater., 2018, 28, 1801961.
12 Y. You, L. He, B. Ma and T. Chen, Adv. Funct. Mater., 2017, 27, 1703313.
13 H. Sun, D. Liu and J. Du, Chem. Sci., 2019, 10, 657.
14 S. Yang, X. Zhou, P. Yuan, M. Yu, S. Xie, J. Zou, G. Q. Lu and C. Yu,
Angew. Chem., Int. Ed., 2007, 46, 8579.
15 R. Wang, N. Zhao and F.-J. Xu, Adv. Funct. Mater., 2017, 27, 1700256.
16 S. Giri, B. G. Trewyn, M. P. Stellmaker and V. S. Y. Lin, Angew. Chem.,
Int. Ed., 2005, 44, 5038.
17 R. A. Perez, R. K. Singh, T. H. Kim and H. W. Kim, Mater. Horiz.,
2017, 4, 772.
18 J. Mei, Y. Hong, J. W. Lam, A. Qin, Y. Tang and B. Z. Tang, Adv.
Mater., 2014, 26, 5429.
Fig. 4 Cytotoxicity of the DF-MSNB on (A) L02 and (B) HepG2 cells.
Inhibition effect of (C) DOX and (D) DOX@DF-MSNB on HepG2 cells. (E)
Fluorescence microscopy images of HepG2 cells after treatment with 100
mg mLÀ1 DF-MSNB for 1 h, 2 h, and 4 h separately, scale bar = 40 mm.
(F) Flow cytometric analysis of HepG2 cells incubated with the DF-MSNB 19 X. Wei, M. J. Zhu, Z. Cheng, M. Lee, H. Yan, C. Lu and J. J. Xu, Angew.
(100 mg mLÀ1), DOX (6 mg mLÀ1) and DOX@DF-MSNB (30 mg mLÀ1) for 24 h.
Chem., Int. Ed., 2019, 58, 3162.
20 J.-R. Wu, A. Mu, B. Li, C.-Y. Wang, L. Fang and Y.-W. Yang, Angew.
Chem., Int. Ed., 2018, 57, 9853.
21 X. Wang, J.-R. Wu, F. Liang and Y.-W. Yang, Org. Lett., 2019, 21, 5215.
22 S. Pramanik, C. Zheng, X. Zhang, T. J. Emge and J. Li, J. Am. Chem.
Soc., 2011, 133, 4153.
23 M.-X. Wu and Y.-W. Yang, Adv. Mater., 2017, 29, 1606134.
24 Y.-W. Yang, Y.-L. Sun and N. Song, Acc. Chem. Res., 2014, 47, 1950.
25 Y. Liu, P. Bhattarai, Z. Dai and X. Chen, Chem. Soc. Rev., 2019,
48, 2053.
26 Q.-L. Li, D. Wang, Y. Cui, Z. Fan, L. Ren, D. Li and J. Yu, ACS Appl.
Mater. Interfaces, 2018, 10, 12155.
27 X. Li, J. Han, X. Wang, Y. Zhang, C. Jia, J. Qin, C. Wang, J.-R. Wu,
W. Fang and Y.-W. Yang, Mater. Chem. Front., 2019, 3, 103.
in the HepG2 cells became stronger and stronger. Therefore,
the DF-MSNB system was proven to be capable of imaging
tumour cells. Cell apoptosis studies were further performed by
the Annexin V-FITC/PI dual-staining method. The pure material
DF-MSNB shows nearly no influence on HepG2 cells while the
apoptosis rate of 54.3% and 63.56% of HepG2 cells induced by
DOX and DOX@DF-MSNB strongly indicated their efficient
therapeutic effects on tumour cells (Fig. 4F).
14102 | Chem. Commun., 2019, 55, 14099--14102
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