A single-step emulsion approach to prepare fluorescent nanoscale coordination polymers for bioimaging

Article abstract of DOI:10.1039/c4ra00214h

A crystalline nanoscale coordination polymer (NCP) based on fluorene and Zr⁴⁺ was synthesized through a simple microemulsion method. The emulsion method is facile and convenient for NCP production, the nanoparticles are fluorescent and thermal-

Full text of DOI:10.1039/c4ra00214h

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A single-step emulsion approach to prepare
fluorescent nanoscale coordination polymers for
bioimaging†
Cite this: RSC Adv., 2014, 4, 14803
Received 9th January 2014
Accepted 13th March 2014
a
b
b
b
a
b
Zhiyong Sun, Yangxue Li, Xingang Guan, Tingting Sun, Li Chen,* Zhigang Xie*
b
and Xiabin Jing
DOI: 10.1039/c4ra00214h
www.rsc.org/advances
A crystalline nanoscale coordination polymer (NCP) based on fluorene the crystallization time, but required special power-consuming
4+
and Zr was synthesized through a simple microemulsion method. apparatus. It is highly desirable to develop new method to
The emulsion method is facile and convenient for NCP production, the prepare the CPs in simple and mild condition. Very recently,
nanoparticles are fluorescent and thermal-stable, and most impor- several groups have reported some new methods to make CPs,
22
23
tantly, they are in nanoscale thus making them applicable for like spray-dry strategy and microuidic approach.
bioimaging.
Microemulsion method (MEM) is usually used for the prep-
aration of polymeric nanoparticles. It is easy and convenient,
and the nanoparticles prepared by MEM usually have narrow
Luminescent nanomaterials have drawn great interest in
bioscience such as in bioimaging, as drug carriers, and for
disease detection. In luminescence bioimaging, luminescent
24
size distribution. Very recently, Eddaoudi et al. reported a
single-step emulsion-based technique to assembly of CPs into
1
25
3D hollow superstructures.
nanomaterials are used to label a molecule of interest and to
render luminescent signals. Many new luminescent nano-
materials, have been synthesized for bioimaging application
Polyuorenes are of interest and currently being investigated
to use in light-emitting diodes, eld-effect transistors and
26–28
plastic solar cells.
Fluorene-based materials have been
2
including semiconductor nanocrystals, upconversion nano-
studied in bioscience because of their stability and safety to
3
4
5–8
phosphors, quantum dots and other nanoparticles. Among
them, coordination polymers (CPs), also called metal–organic
frameworks, are attractive not only for their porous structures
and high surface areas, but also for the convenience of them to
be designed and incorporated with function groups which
29–31
living cells.
Some reports on the conjugated polymers based
on uorene for biomarkers and detection of proteins and DNA
32–35
were published in last several years.
Herein, we synthesized novel nanoscale coordination poly-
4+
mers (NCPs) with microemulsion method using Zr and uo-
9
–11
made CPs have potential applications in catalysis,
gas
rene derivatives. The NCPs were characterized by
thermogravimetric analysis (TGA), powder X-ray diffraction
PXRD), Fourier transform infrared spectroscopy (FT-IR), scan-
ning electron microscopy (SEM) and transmission electron
microscopy (TEM). Then the bioimaging experiment was
carried out for they are uorescent and in nanoscale which is
easy to endolysis by living cells.
12,13
14
15,16
storage,
separation and bioscience.
However, CPs
particles are usually in micrometer scale, which limit their
application. Recently, Lin's group reported the ability to scale
(
17
down the size of CPs to nanoscale, thus made the luminescent
18–21
CPs an excellent material for biological applications.
Conventionally, CPs are synthesized via time-consuming
hydrothermal or solvothermal methods, these methods require
several hours or days for crystallization and nanoparticles
formation. Other approaches involve alternative energy sources
such as microwave irradiation or ultrasound usually decreased
Scheme 1 shows the preparation of the ligand and NCPs.
0
The ligand (2,7-(4-carboxyl-benzene)-9,9 -dioctyl-9H-uorene) was
prepared through Suzuki coupling reaction and subsequent
1
hydrolysis reaction. The structures were conrmed by H-NMR
4
(Fig. S1, ESI†). Then the ligand and ZrCl were dissolved in DMF
with a small amount of triuoroacetic acid (TFA) and hydrochloric
acid (HCl) to modulate the crystallinity of the nanoparticles, then
the mixture was dropped into a heated silicon oil bath to get the
a
Department of Chemistry, Northeast Normal University, 5268 Renmin Street,
Changchun 130024, P. R. China. E-mail: chenl686@nenu.edu.cn
b
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin Street, Changchun NCPs. Silicon oil is immiscible with DMF and used to form
1
30022, P. R. China. E-mail: xiez@ciac.ac.cn; Tel: +86-431-85262779
emulsion drops, in which the particles were prepared aer
aggregation, nucleus and crystallization (see the ESI† for detail).
†
Electronic supplementary information (ESI) available: Experimental procedures,
36
characterization data. See DOI: 10.1039/c4ra00214h
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Fig. 1d shows the FT-IR of the ligand and the nanoparticles.
ꢀ
1
The peaks at 2900 cm are due to C–H stretching vibration of
the C H chain of the uorene for both the ligand and the
8
17
particles. Compared with the ligand, the missing of the peak at
ꢀ1
1
691 cm of the NCPs is responsible for the coordination bond
formation in coordination polymers. Instead, the appearance of
ꢀ
1
ꢀ1
two new peaks at 1602 cm and 1420 cm are responsible for
antisymmetric and symmetric carboxylate stretching vibrations,
ꢀ
1
ꢀ1
the value between 1602 cm and 1420 cm is less than 200
cm , this indicates the ligand is connected to Zr through
bidentate coordination state.
ꢀ
1
4+
37–40
Since the NCPs are crystalline, as indicated by the PXRD
shown in Fig. 2a, we decided to study the structure of our NCPs.
From Fig. 2a, we can see the PXRD pattern of our NCPs t well
but a little blue shied compared to that of UiO-66, so we
concluded our NCPs would share the same structure with UiO-
41
6
6, which is consistent with the analysis of FT-IR. And we
simulated the structure of our NCPs as seen in Fig. 2c. The
possible reason of the slight difference is that the unit cell
volume of our NCPs is larger than UiO-66, the diffraction angles
shi to the small angles. We assumed there are two reasons for
this: (1) the ligand is different; our ligand is much longer
compared to terephthalic acid, which is the ligand of UiO-66,
and the octane chains of our ligand could increase the cell
volume. (2) We added TFA and HCl as modulation to control the
4+
42
crystallization, and the TFA could coordinate to Zr , then le
aer activated, thus would affect the PXRD pattern.
Scheme 1 Preparation of ligand and NCPs.
We also studied the TGA of the nanoparticles, the result is
shown in Fig. 2b. The weight loss of the material is steady
The SEM (a and b) and TEM (c) of the NCPs were presented
in Fig. 1. The images show the particles were in good disper-
sion, and in nanoscale with diameter of about 50 nm, which is
easy to endocytosis by living cells for bioimaging application.
We can see that the particles are in nearly the same sphere
morphous from the SEM pictures.
ꢁ
decreased from room temperature to about 300 C due to the
ꢁ
solvent loss. The weight loss from 300 to 500 C is because of the
ꢁ
ligand decomposing. And from 500 to 630 C, the rate of weight
loss decreased and the nally get to a steady state. This is
because that the nal substance is the very stable zirconium
oxide. The TGA result shows our NCPs are as stable as
Fig. 2 (a) PXRD of as synthesized NCPs (red) and UiO-66 (black). (b)
TGA. (c) Simulated structure of NCPs, the green parts represent the
Fig. 1 SEM (a and b) and TEM (c) of the NCPs. FT-IR Spectroscopy (d) ligand, colors of atoms O (red), Zr (light blue); MTT (d) of HeLa cells
of the ligand (red) and the particles (black). after NCPs endocytosis.
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Fig. 3 Microscopic images of the cells. The scale bars are 500 mm and
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UiO-66.
Moreover, the amount of the Zr calculated from
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The particles remain uorescence when dispersed in water
(as shown in Fig. S2 and S3, ESI†) and common organic
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As shown in Fig. 2d, no obvious cytotoxicity to
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ꢀ1
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which indicated by Lin's and Petoud's groups.
The signal of
the nanoparticles is high under microscopic with irritation. To
further conrm the NCPs remain intact within HeLa cells, we
carried out the control experiment with the ligand as the bio-
imaging agent, the pictures are presented in Fig. S4 (ESI).†
Because the ligand is not soluble in water environment so it
aggregates into large particles, which is different with the NCPs.
We can also see that the cells were in good shape and condition
under different resolutions.
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In summary, we have synthesized a nanoscale coordination
polymer material through
a convenient microemulsion
method. The nanoparticles were characterized through FIRT
and PXRD, which indicated the NCPs formed through coordi-
nation bond and were crystalline. SEM and TEM pictures
conrmed the size of the particles were in good distribution and
in nanoscale which made them possible for endocytosis by
living cells. The uorescence of the NCPs in HeLa cells aer
endocytosis for bioimaging conrmed our idea for the possible
application on bioscience of the NCPs.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (project no. 91227118 and 21104075).
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