A water-soluble near-infrared fluorescent probe for specific Pd2+ detection

Article abstract of DOI:10.1016/j.bmc.2017.12.003

Palladium (Pd) is widely used in chemistry, biology, environmental science etc., and Pd²⁺ is the most plenitudinous oxidation state of the Pd that can exist under physiological conditions or in living cells, which could have adverse effects on both our health and environment. Thus, it is of great significance to monitor the changes of Pd²⁺. Hence, a novel near-infrared fluorescent probe M-PD has been developed for selective detection of Pd²⁺ based on naphthofluorescein in this work. The result demonstrated that M-PD exhibited favorable properties for sensing Pd²⁺ such as excellent water solubility, high selectivity and sensitivity. And the limit of detection was estimated as 10.8 nM, much lower than the threshold in drugs (5–10 ppm) specified by European Directorate for the Quality Control of Medicines. More importantly, detection and recovery experiments of Pd²⁺ in aspirin aqoeous solution and soil are satisfactory. In addition, M-PD has also been successfully used for near-infrared fluorescence imaging of Pd²⁺ in living cells, indicating that the probe has better feasibility and application potential in the determination of Pd²⁺.

Full text of DOI:10.1016/j.bmc.2017.12.003

Accepted Manuscript
2
+
A water-soluble near-infrared fluorescent probe for specific Pd detection
Jia Wen, Yinghua Lv, Pengyi Xia, Fengyu Liu, Yongqian Xu, Hongjuan Li, Su-
Shing Chen, Shiguo Sun
PII:
S0968-0896(17)32126-0
https://doi.org/10.1016/j.bmc.2017.12.003
BMC 14108
DOI:
Reference:
To appear in:
Bioorganic & Medicinal Chemistry
Received Date:
Revised Date:
Accepted Date:
31 October 2017
29 November 2017
1 December 2017
Please cite this article as: Wen, J., Lv, Y., Xia, P., Liu, F., Xu, Y., Li, H., Chen, S-S., Sun, S., A water-soluble near-
2
+
infrared fluorescent probe for specific Pd detection, Bioorganic & Medicinal Chemistry (2017), doi: https://doi.org/
0.1016/j.bmc.2017.12.003
1
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A water-soluble near-infrared fluorescent
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2
probe for specific Pd detection
+
a,1
b,1
a,1
c,d,*
a
a
Jia Wen , Yinghua Lv , Pengyi Xia , Fengyu Liu , Yongqian Xu , Hongjuan Li , Su-Shing Chen and
d,*
a,*
Shiguo Sun
a
Shaanxi Key Laboratory of Natural Products & Chemical Biology, College of Chemistry & Pharmacy,
Northwest A&F University, Yangling, Shaanxi 712100, China
b
College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, China
State Key Laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology, No.2 linggong
c
Road, Ganjingzi, District, Dalian 116023, China
d
Systems Biology Laboratory, Department of Computer Information Science and Engineering, University of
Florida, Gainesville, FL, United States

Bioorganic & Medicinal Chemistry
journal homepage: www.els evier.com
2
A water-soluble near-infrared fluorescent probe for specific Pd detection
+
a,1
Jia Wen , Yinghua Lv , Pengyi Xia , Fengyu Liu Yongqian Xu , Hongjuan Li , Su-Shing Chen
b,1
a,1
c,d*
a
a
d,*
a,*
and Shiguo Sun
a
Shaanxi Key Laboratory of Natural Products & Chemical Biology, College of Chemistry & Pharmacy, Northwest A&F University, Yangling, Shaanxi 712100,
China
b
College of Animal Science and Technology, Northwest A&F University, Yangling, Shaanxi 712100, China
c
State Key Laboratory of Fine Chemicals, School of Chemistry, Dalian University of Technology, No.2 linggong Road, Ganjingzi, District, Dalian 116023, China
d
Systems Biology Laboratory, Department of Computer Information Science and Engineering, University of Florida, Gainesville, FL, United States
ARTICLE INFO
ABSTRACT
2
+
Article history:
Received
Palladium (Pd) is widely used in chemistry, biology, environmental science etc., and Pd is the
most plenitudinous oxidation state of the Pd that can exist under physiological conditions or in
living cells, which could have adverse effects on both our health and environment. Thus, it is of
Received in revised form
Accepted
2
+
great significance to monitor the changes of Pd . Hence, a novel near-infrared fluorescent probe
2
M-PD has been developed for selective detection of Pd based on naphthofluorescein in this
+
Available online
2
+
work. The result demonstrated that M-PD exhibited favorable properties for sensing Pd such
as excellent water solubility, high selectivity and sensitivity. And the limit of detection was
estimated as 10.8 nM, much lower than the threshold in drugs (5-10 ppm) specified by European
Directorate for the Quality Control of Medicines. More importantly, detection and recovery
Keywords:
2
+
Pd detection
2+
experiments of Pd in aspirin aqoeous solution and soil are satisfactory. In addition, M-PD has
2+
Near-infrared fluorescence
Water solubility
Naphthofluorescein
Imaging
also been successfully used for near-infrared fluorescence imaging of Pd in living cells,
indicating that the probe has better feasibility and application potential in the determination of
2+
Pd .
2
009 Elsevier Ltd. All rights reserved.
1
. Introduction
of the Pd that can exist under physiological conditions or in
living cells. Hence, development of efficienct methods for
With the development of modern industry, heavy and
transition-metal ions have received intense attention in many
fields such as chemistry, biology, and environmental science.
Among them, palladium (Pd), a rare inner transition metal, is
enormously used as efficient catalysts in the fields of material
science, drug synthesis, organic catalytic reactions, automobile
exhaust disposing and fuel cells, etc. In addition, Pd is also
widely used to prepare jewellery, electric equipment and dental
3
materials. However, even after purification of the final products,
the residual Pd contaminates are still typically at a level of 300-
2
2+
detecting and imaging Pd is important for environment safe and
human health.
Up to now, there are many traditional methods reported for
2+ 8,9
the detection of Pd , such as atomic absorption/emission
1
2
spectrophotometry,
solid
phase
performance liquid chromatography, ion-coupled plasma
microextraction-high
2
10-12
emission-mass spectrometry, X-ray fluorescence and etc.
Unfortunately, they usually suffer from the expensive
instruments, time-consuming sample-pretreatment and require
well-trained individuals, which restricted their further practical
000 ppm, which is drastically higher than the specified
13,14
applications.
4
threshold in drugs (5-10 ppm). It is worthy note that, Pd species
can disturb many biological processes and lead to hard-to-ignore
health hazard through tightly binding to biomolecules such as
thiol-containing amino acids, protein, DNA, RNA and vitamins
In stark contrast, optical detection methods, particularly
fluorescence probes, show unique potential for the development
of highly sensitive and selective as well as relatively simple
analysis protocols. In recent years, a diverse kinds of fluorescent
5-7
2+
etc. In particular, Pd is the most plenitudinous oxidation state
2+
probes for Pd detection have been developed owing to their
high sensitivity and easy operation.
15-25
To date, there are four
main reaction mechanism to design and develop these probes,
including typical-metal binding, Pd-catalyzed fluorophore
———
∗ Corresponding author.
E-mail address: liufengyu@dlut.edu.cn (Fengyu Liu);
suchen@cise.ufl.edu (Su-Shing Chen);
sunsg@nwsuaf.edu.cn (Shiguo Sun)
2
6
formation,
Pd-catalysed Tsuji-Trost and Pd-catalysed
depropargylation. The probe based on metal binding mechanism
was usually difficult to achieve with high selectivity and
1
These authors contributed equally.
2+ 27-29
sensitivity for Pd .
And Pd fluorescent sensor based on Pd-

catalyzed Tsuji-Trost reaction needed to add additional reducing
agent such as PPh , TFP (tri-2-furylphosphine) or TFP–NaBH
All reagents were purchased from commercial suppliers and
used without further purification. All the organic solvents were
analytical grade. Deionized water was used for all the
3
4
2+
0
2+ 30
for conversion of Pd to Pd in detection of Pd . To avoid
these problems, the Pd-catalysed depropargylation mechanism
31-33
1
13
measurements. H NMR and C NMR spectra were recorded on
a Bruker 500 AVANCE III spectrometer with chemical shifts
2
+
was more favored for the design of Pd fluorescent probes.
1
reported in ppm at room temperature (500 MHz for H NMR and
However, most of these probes work in a mixture of water and
organic solvent, which will somehow restrict their application in
the environmental and biological field. Thus, development of
1
3
125 MHz for C NMR, Germany). High resolution mass
spectrum (HRMS) was obtained with Thermo Fisher LCQ Fleet
mass spectrometer (USA).
3
4-36
probes with excellent water solubility is of great importance.
For example, in 2016, Wang et al. reported a fluorescent and
All spectrographic measurements were performed in 10 mM
phosphate buffered saline (PBS) (pH 7.4). The pH of the testing
systems was determined by a PHS-3C pH Meter (China).
Absorption spectra were measured with a Shimadzu UV-1750
UV-vis spectrometer (Japan). Luminescence spectra were
2
+
colorimetric probe containing oxime-ether for Pd in pure water
3
and living cells; Most recently, Hou’s group reported a
7
2
+
coumarin-based colorimetric and fluorescent dual probe for Pd
38
that can be used in live cells. While, these probes need the
ultraviolet or visible light to excite, which severely limits in
biological applications because the fluorescence imaging in the
visible region would be easily disturbed by auto-fluorescence of
collected by using
spectrometer (Japan). Cell culture was carried out in an incubator
with a humidified atmosphere of 5% CO at 37°C. Cell toxicity
a
Shimadzu RF-5301 fluorescence
2
3
9-41
living systems.
In comparison, near infrared (NIR)
tests were tested by microplate reader (KHB ST-360). The
confocal laser microscope data were acquired using a confocal
fluorescence microscope (Nikon A1R). Aspirin was purchased
from Northwest A&F University hospital and dissolved in PBS
for further use. Soil was obtained in Northwest A&F University.
And the soil was pretreated with acid before detection according
fluorescent probes, which own deeper tissue penetration and thus
can reduce auto-fluorescence efficiently. Therefore, a potential
approach is to develop NIR fluorescent probes for the detection
2
+ 42
of Pd . Recently, Wang's group has designed a NIR fluorescent
probe for Pd, which exhibits high sensitivity and selectivity
0
2+
toward both Pd and Pd . Unfortunately, this probe has a main
56-58
to the literatures.
drawback of poor water solubility, which is a disadvantage for
All of the experiments were performed in compliance with the
relevant laws and institutional guidelines, and were approved by
Northwest A&F University.
43
bio-imaging application. Zhang’s group reported a fluorescent
probe for Pd. Although this probe emits in the red light region, it
cannot be used for monitoring Pd in living cells owing to the
4
4
2.2. Synthetic procedures of probe (M-PD)
need of high proportion of organic solvents.
To solve these, we designed and synthesized a new
4
6
Synthesis of Compound M: According to the literature,
2
+
fluorescent Pd probe M-PD with emission in the NIR region.
The probe is composed of naphthofluorescein as the fluorophore
and the terminal propargyl moiety which has been demonstrated
to be favorable for selective palladium recognization45 as the
recognition unit (Scheme 1). In the absence of any analyte, the
probe M-PD has almost no fluorescence due to the protection of
hydroxyl group of naphthofluorescein by propargyl group. Upon
phthalic anhydride (0.890 g, 6.0 mmol) and 1,6-
dihydroxynaphthalene (2.40 g ， 15 mmol) were added in a
round-bottom flask. After adding methanesulfonic acid (15 mL),
the mixture was refluxed for 12 h at 135
. Next, the mixture was
poured into ice-water and filtered. The crude product was
purified by silica gel column chromatography (CH
1
2 2 3
Cl /CH OH =
25:1) to give compound M as a aubergine solid. Yield: 0.983 g
1
2
+
the addition of Pd , the depropargylation reaction occurs and
thus the protected hydroxyl group of M-PD is liberated,45 which
lead to the significant enhancement of fluorescence. In detection
(
(
37.8%). H NMR (500 MHz, DMSO-d
d, J = 9.1 Hz, 2H), 8.09 (m, 1H), 7.76 (m, 2H), 7.46 (d, J = 8.8
6
) δ 10.17 (s, 2H), 8.70
Hz, 2H), 7.37 (dd, J = 9.1, 2.4 Hz, 2H), 7.30 (d, J = 6.7 Hz, 1H),
7
2
+
of Pd , M-PD displays high selectivity, sensitivity and excellent
water solubility. Most importantly, detection and recovery
.21 (d, J = 2.4 Hz, 2H), 6.71 (d, J = 8.8 Hz, 2H).
Synthesis of Compound M-PD: According to the literature,
4
7
2+
experiments of Pd in aspirin aqoeous solution and soil are
satisfactory. In addition, M-PD could also be used to monitor
Pd in living cells (human hepatocellular carcinoma cell HepG-2
was chosen as an example). All of these performances make M-
PD appropriate for potential application in environment or living
systems.
M (0.432 g，1.0 mmol) and potassium carbonate (0.207 g，1.5
mmol) were added in a round-bottom flask. After adding
anhydrous acetonitrile (15 mL), the mixture was stirred for 1 h at
50
. Next, 3-bromopropyne (83 µL，1.1 mmol) was added and
the mixture was refluxed for 6 h and then extracted with
2+
dichloromethane. The crude product was purified by silica gel
2 2 3 2 5
column chromatography (CH Cl / CH COOC H = 150:1) to
give compound M-PD as a light yellow solid. Yield: 0.263 g
1
(
(
1
(
55.9%). H NMR (500 MHz, DMSO-d
d, J = 9.1 Hz, 1H), 8.71 (d, J = 9.1 Hz, 1H), 8.10 (dd, J = 6.2,
.9 Hz, 1H), 7.81 – 7.73 (m, 3H), 7.59 (d, J = 9.0 Hz, 1H), 7.51
d, J = 2.4 Hz, 1H), 7.49 – 7.45 (m, 3H), 7.37 (dd, J = 9.0, 2.4
Hz, 1H), 7.31 (dd, J = 6.2, 1.5 Hz, 1H), 7.21 (d, J = 2.4 Hz, 1H),
.81 (d, J = 8.7 Hz, 1H), 6.72 (d, J = 8.7 Hz, 1H), 4.99 (d, J = 2.3
6
) δ 10.17 (s, 1H), 8.77
6
13
Hz, 2H), 3.64 (t, J = 2.3 Hz, 1H). C NMR (125 MHz, DMSO-
d
1
1
1
6
) δ 168.83, 157.40, 156.86, 153.22, 146.02, 145.93, 135.97,
35.83, 135.41, 130.33, 125.71, 124.80, 124.49, 124.20, 123.90,
23.80, 123.21, 122.75, 119.35, 119.30, 118.50, 117.27, 110.70,
2
Scheme 1. Recognition mechanism of M-PD toward Pd .
+
09.44, 109.37, 108.32, 82.99, 78.88, 78.60, 55.73. HRMS:
+
[
M+H] , calculated for [C31
H O
18 5
]: 471.1227; found: 471.12286.
2
. Experimental sections
.1. Reagents and apparatus
2
.3. Analytical procedure
2

All experiments were performed in an absolute PBS solution
pH 7.4, 10 mM). In the selectivity experiments, the test samples
were prepared by adding an appropriate amount of the metal ions
3. Results and discussion
(
3
.1. Synthesis of probe M-PD
2+
stock solution (50 µM Pd and 100 µM other metal ions) to a 3
mL solution of M-PD (10 µM). In the titration experiment, a
solution of M-PD (10 µM) was prepared at room temperature
The detailed synthetic routine of probe M-PD is outlined in
Scheme S1 in the Supporting Information. By two simple steps,
phthalic anhydride and 1,6-dihydroxynaphthalene in the solution
of methanesulfonic acid were refluxed for 12 h giving compound
M. Then, compound M-PD was obtained by the reaction of
compound M with potassium carbonate and 3-bromopropyne in
with the addition of appropriate amount of PdCl
was added to the quartz cuvette using
2
solution, which
micropipette.
a
Spectroscopic data were recorded upon the addition of analytes at
room temperature. Spectroscopic data were recorded 30 min after
the addition of the metal ions. And the fluorescence emission
spectra of the result solutions were recorded at an excitation
wavelength of 610 nm (unless otherwise noted, all spectral were
measured according to this method).
1
13
C
anhydrous acetonitrile, which was confirmed by H NMR,
NMR and HRMS (Fig. S1-S4).
3.2. Spectral properties of M-PD
The spectroscopic properties of M-PD were assessed in an
absolute PBS at pH 7.4. M-PD (10 µM) displayed one major
absorption band centered at 578 nm. This band was increased and
The detection limit was calculated based on the fluorescence
4
titration according to the literature. In the absence and presence
8
2
+
of Pd , the fluorescence emission spectra of M-PD were
measured three times for each point and the standard deviation of
blank measurement was achieved. To gain the slop, the
fluorescence intensity at 668 nm was plotted to the concentration
2
+
had a silght red-shifted after the addition of 7 equiv of Pd (Fig.
2
+
S7). In the absence of Pd , with 610 nm excitation, the M-PD in
PBS solution emitted weak fluorescence, which was mainly
because the propargyl group in M-PD trammeled the hydroxyl
2
+
of Pd . So the detection limit was calculated with the following
equation:
2
+
group of naphthofluorescein. While with the addition of Pd ions
0-7 equiv), the fluorescence intensity at 668 nm gradually
(
Detection limit = 3σ/k
enhanced, attributing to the disappearance of propargyl group
and the liberation of protected hydroxyl group (Fig. 1a).
Moreover, Fig. 1b showed that the fluorescence intensity
Wherein σ is the standard deviation of blank measurement, k
is the slop between the fluorescence intensity versus Pd
2
+
concentration.
In real sample analysis, according to the literatures,
2
+
6
2-64
increased linearly with the increasing Pd concentration from 0.0
2
to 70 µM (R = 0.998), and the detection limit was measured to
10 g of
surface soil was added to polytetrafluoroethylene (PTFE) beakers
containing 50 mL aqua regia. The mixture was heated to near
dryness, re-dissolved into ultrapure water, filtrated to remove
suspended matters, sealed and stored in 50 mL PTFE bottles for
use. Aspirin aqoeous solution was prepared by dissolving
different amount of aspirin in ultrapure water. Then, different
2
+
be 10.8 nM. Compared with previous probes for Pd detection
based on Pd-catalysed depropargylation mechanism (Table 1),
2
7,35,49-61
M-PD not only can work well in an absolute PBS
solution (Fig. S8) but also exhibit low detection limit and NIR
emission, indicating that M-PD could be used as an effective tool
2
+
2
+
for the sensing of Pd in environmental and biological fields.
amount of Pd was added into soil or aspirin samples for further
use. A solution of M-PD (10 µM) was prepared at room
temperature with the addition of appropriate amount of pretreated
Pd samples, which was added to the quartz cuvette using a
micropipette. Spectroscopic data were recorded upon the addition
of analytes at room temperature.
2
.4. Cell cultures, cytotoxicity assay and fluorescence imaging
HepG-2 cells were cultured in 1640 medium containing 10%
FBS, 1% penicillin/streptomycin (complete 1640) in 5% CO
3
2
at
7 °C. For cell viability study, HepG-2 cells were seeded in 96-
5
Fig. 1. Fluorescence titration studies of M-PD. (a) Fluorescence spectra of
2+
well microplates at a density of 1×10 cells/mL in 100 µL
complete 1640 medium. After 24 h of cell attachment, plates
were washed with 100 µL/well PBS and then cells were cultured
in medium with various concentrations (2.5-20 µM) of M-PD for
M-PD (10 µM) upon addition of Pd (1-70 µM) in PBS buffer; (b) The linear
2+
relationship between the fluorescence intensity and the concentration of Pd .
2
All data were collected at 30 min after the addition of Pd (n=3).
+
2
3.3. Selectivity for Pd detection
+
2
4 h. 10 µL of MTT (5 mg/mL) prepared in PBS was added to
each well and the plates were incubated at 37°C for 4 h in a 5%
CO humidified incubator. The medium was then carefully
For a new fluorescent probe, it is very important to own
highly selective response to the target species over other
potentially competing species, which is necessary for potential
application in complex biological and environmental samples.
Therefore, the selectivity studies of M-PD toward various metal
ions were investigated and the results are shown in Fig. 2. There
was no notably fluorescence change in the presence of the
2
removed, and the purple products were lysed in 100 µL dimethyl
sulfoxide (DMSO). The plate was shaken for 10 min and the
absorbance was measured at 490 nm using a microplate reader
(
KHB ST-360).
For fluorescence imaging, HepG-2 cells were seeded in 35-
mm dishes and allowed to adhere for 24 h. Then the cells were
treated with 10 µM M-PD and incubated at 37°C for 1 h. After
removing the culture medium and washing twice with PBS,
fluorescence images of cells were captured. Complete 1640 were
added to the cell culture, which was then treated with a 20 µM
+
+
2+
2+
2+
2+
2+
common cations, such as Ag , Al , Ba , Ca , Cd , Co , Cu ,
2+
3+
2+
+
+
2+
Fe , Fe , Hg , K , Li , Mg , Mn , Ni , Pb , Zn . However,
2+
2+
2+
2+
a much larger fluorescence enhancement was observed for M-PD
2
+
upon addition of Pd . These results clearly demonstrate that M-
2
+
2
+
PD is a highly selective fluorescent probe for Pd , and also
2+ 45
verify that the depropargylation is specific toward Pd .
Pd and incubated at 37°C for an additional 30 min. After
washing twice with PBS, fluorescence images of the cells were
captured.

DMSO : H2O
95 : 5, v/v)
8
8 µM
466 nm
570 nm
47
48
(
CH3CN–H2O
156 nM
Fig. 2. Competitive experiments for selectivity. (a) Fluorescence responses of
2
EtOH : H2O
(1 : 1, v/v)
2
1 nM
569 nm
49
+
M-PD (10 µM) to Pd (50 µM) and other cations (100 µM for each) in PBS
10 mM, pH 7.4). (b)Fluorescence intensity changes of M-PD (10 µM) upon
(
+
3+
2+
the addition of various metal ions (100 µM): 1. Blank, 2. Ag , 3. Al , 4. Ba ,
2
+
2+
2+
2+
2+
3+
. Ca , 6. Cd , 7. Co , 8. Cu , 9. Fe , 10. Fe , 11. Hg , 12. K , 13. Li ,
2+
+
+
5
1
PBS containing
50% EtOH
2
+
2+
2+
2+
2+
4. Mg , 15. Mn , 16. Ni , 17. Pb , 18. Zn , in the presence of Pd (50
2+
93 nM
542 nm
457 nm
530 nm
50
51
52
µM) in PBS. The black bars represent the fluorescence response of M-PD and
2
+
competing ions. The red bars represent the subsequent addition of 50 µM Pd
to the above solutions. All data were measured after 30 min.
PBS containing
53 nM
1.0% EtOH
3
.4. Proposed mechanism
The recognition mechanism of M-PD to Pd could be
2+
2+
reasonably explained by the catalytic mechanism of Pd with the
propargyl group (Scheme 1). The HNMR spectroscopic analysis
provided the evidence for the binding pattern between M-PD and
EtOH : H O
2
(1 : 1, v/v)
1
191 nM
2+
Pd . The propargyl group of M-PD trammeled the hydroxyl
group of M-PD, hence the probe had weak fluorescence. After
pure water
containing 1
mM Triton X-
2+
the addition of Pd , the propargyl group of the M-PD in the
upfield disappeared (Fig. S5). Furthermore, another hydroxyl
0.9 µM
526 nm
53
100
1
group was formed in the downfield compared to the HNMR
spectroscopic of M-PD (Fig. S2). These results were ascribed to
the formation of compound M, following with fluorescence
changed from colorless to red. To further explore the mechanism,
EtOH : HB,
10 : 90, v/v)
9
.3 ppM
517 nm
423 nm
54
55
(
2+
addition of Pd to M-PD was subsequently analyzed by MS. As
shown in Fig. S6, a peak at m/z 433.15 corresponding to M was
observed, demonstrating the depropargylation reaction of M-PD
EtOH : Hepes
1 : 2000, v/v)
0.47 µM
(
2
+
catalyzed by Pd occurred.
Table 1. Comparisons of the proposed probe with previous
reports.
This
work
PBS
10.8 nm
668 nm
Detection
Limit
Emission
Wavelength
Structure of probe
Solvent
Ref.
21
3.5. Analysis of real samples and recovery test
To validate the feasibility of the method when applied to real
water
containing 10%
CH3CN
2+
samples, determination of Pd in aspirin aqoeous solution and
soil were conducted based on the aforementioned procedures.
30 nM
70 nM
520 nm
2
+
Fig. 3 showed that no Pd was found in aspirin aqoeous solution
or soil samples. Taking these two samples as substrates, standard
addition and recovery tests were further conducted. Known
amounts (2, 6, 10 µM, which were all lower than the
specification in drugs stated by European Directorate for the
PBS
553 nm
517 nm
43
44
4
2+
Quality Control of Medicines ) of Pd were spiked into samples
prior to pretreatment (in a simplified pretreatment, we need only
CH3CN : H2O
1 : 4, v/v)
8
7 nM
(
6
2-64
to extract soil samples with acid and filter it)
and recovery
results were conducted. The results indicate that M-PD offer
ideal sufficient sensitivity and accuracy, which is satisfactory for
real sample analysis.
PBS containing
10% (v:v)
-
492 nm
472 nm
45
29
CH3CN
H2O : CH3CN
1 : 1, v/v)
4
0 nM
(
CH3CN : H2O
1 : 1, v/v)
-
574 nm
46
(

degree under guidance of Prof. Shiguo Sun in the College of
Chemistry & Pharmacy, Northwest A&F University. Her
research interest is mainly focused on the fabrication and
modification of carbon/silicon based nanomaterials and their
applications for drug delivery and bioimaging.
1
00
aspirin solution
soil
8
0
6
0
Yinghua Lv, received her Ph.D in the College of Animal
Science and Technology, Northwest A&F University. She is a
postdoctoral at Prof. Wenxian Zeng’s Lab, in the College of
Animal Science and Technology, Northwest A&F University.
Her research interest is mainly focused on the mechanisms of
chemoresistance in cancer cells.
4
0
20
0
0
2
6
10
2+
Added concentration of Pd (µM)
Pengyi Xia received his master degree under the guidance of
Prof. Shiguo Sun in college of Chemistry & Pharmacy,
Northwest A&F University in 2017. His research interests focus
on metal ion probe for ion detection and disease diagnosis.
Fengyu Liu received her Ph.D. in 2006 from the Dalian
University of Technology. She is currently an associate professor
in the state key laboratory of Fine Chemicals at the Dalian
University of Technology. Her research is focused on the
following two fields: (1) the quantitative detection of DNA
oxidative damage based on electrochemiluminescence; (2) the
fluorescent dye-based probes and their biological applications.
Yongqian Xu received his Ph.D. in Applied Chemistry from
the Dalian University of Technology (China) in 2007. In 2008, he
worked as a postdoctoral fellow at the University of Akron
(USA). He is currently a professor and doctoral supervisor at the
college of Chemistry & Pharmacy, Northwest A&F University,
China. His current research interests mainly focus on fluorescent
chemosensors.
2
Fig. 3. Detection and recovery of Pd in aspirin solution and soil (n = 3).
+
3
.6. Cellular imaging
Before the application of M-PD in cell imaging, the
cytotoxicity of M-PD was examined by standard MTT assay. As
shown in Fig. S9, the cell viability was still over 78% after 24 h
even when the concentration of M-PD reached up to 20 µM,
which demonstrates the low cytotoxicity of the probe. Then in
order to evaluate the cell permeability of M-PD and capability of
2
+
M-PD for the detection of Pd , living cells imaging was carried
out (Fig. 4). HepG-2 cells were incubated with 10 µM of M-PD
2
for 1 h, and then treated with 20 µM of Pd for 30 min. The
+
fluorescence images of HepG-2 cells were recorded before and
after addition of Pd . As shown in Fig. 4a, in the absence of Pd ,
free M-PD showed weak fluorescence signals in living cells.
2
+
2+
2
+
Whereas, after incubation with Pd , obvious enhanced red
fluorescence was observed in living cells (Fig. 4b). These data
demonstrate that M-PD has good cell-membrane permeability
Hongjuan Li obtained her Ph.D. from Shaanxi Normal
University (China) in 2010. She is currently an associate
professor at the college of Chemistry & Pharmacy, Northwest
A&F University, China. Her current research interests mainly
focus on the development of functional nanocomposites and
fluorescent chemosensor based on layered double hydroxide
materials.
2+
and could also be used to monitor the changes of Pd level in
living cells.
Su-Shing Chen obtained his Ph.D. degree from the University
of Maryland, College Park in 1970 and is currently a professor
and doctoral supervisor in the department of Computer
Information Science & Engineering, University of Florida-
Gainesville, USA. His current research interests mainly focus on
bioinformatics and computational biology.
Shiguo Sun obtained his Ph.D. degree in 2003 from Dalian
University of Technology and is currently a professor and
doctoral supervisor in the college of Chemistry & Pharmacy,
Northwest A&F University, China. His research interests include
functional molecules with special light or electrochemistry
properties, self-assembly chemistry of carbon nanotube/graphene
material for DNA and protein sensing, drug delivery and
fluorescence tracing, and electrochemiluminescence and
luminescence sensors.
Fig. 4. CLSM images of HepG-2 cells incubated with M-PD (10 µM) for 1 h
2
+
(
a), followed by incubation with 20 µM Pd for 30 min (b). Scale bar: 20 µm.
4
. Conclusions
In summary, a naphthofluorescein-based NIR fluorescent
2+
probe M-PD was developed for selective recognition of Pd .
The results demonstrate that M-PD exhibits excellent water
Acknowledgments
2
+
solubility and a high sensitivity for Pd detection with the
detection limit of 10.8 nM, which is much lower than the
threshold in drugs (5-10 ppm) stated by European Directorate for
the Quality Control of Medicines. M-PD has been successfully
This work was financially supported by the National Natural
Science Foundation of China (No. 21272030, 21472016,
2
1306019, 21576042).
2
+
used for NIR fluorescence detection of Pd in aspirin aqoeous
2
+
solution and soil, imaging of Pd in living cells, providing a
References and notes
2+
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