A new rhodamine B-based ‘off-on’ colorimetric chemosensor for Pd2+ and its imaging in living cells

Article abstract of DOI:10.1016/j.ica.2018.05.032

A colorimetric rhodamine-based fluorescent probe RBPTA has been designed to detect Pd²⁺ under mild condition (pH > 4) in aquenous solution and living HeLa cells. The probe displays high sensitivity (DL 4.2 nM), selectivity and quick response (20 min) toward Pd²⁺, driven by a PET process.

Full text of DOI:10.1016/j.ica.2018.05.032

Accepted Manuscript
A new rhodamine B-based ‘off-on’ colorimetric chemosensor for Pd2+ and its
imaging in living cells
Huilian Chen, Xinxin Jin, Weixia zhang, Hongfei Lu, Wei Shen
PII:
S0020-1693(18)30493-6
https://doi.org/10.1016/j.ica.2018.05.032
ICA 18283
DOI:
Reference:
Inorganica Chimica Acta
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Revised Date:
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3 April 2018
21 May 2018
23 May 2018
Please cite this article as: H. Chen, X. Jin, W. zhang, H. Lu, W. Shen, A new rhodamine B-based ‘off-on’ colorimetric
chemosensor for Pd2+ and its imaging in living cells, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/
j.ica.2018.05.032
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A new rhodamine B-based ‘off-on’ colorimetric chemosensor
for Pd2+ and its imaging in living cells
Huilian Chen,a Xinxin Jin,a Weixia zhang,a Hongfei Lu, *a Wei Shen,*b
a School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, 212003
Zhenjiang, China.
E-mail:zjluhf1979@just.edu.cn
b Jiangsu Key Laboratory of Pesticide Science, Department of Science, Nanjing Agricultural University, 210095
Nanjing, China.
E-mail: swgdj@njau.edu.cn
ABSTRACT
A colorimetric rhodamine-based fluorescent probe RBPTA has been designed to detect Pd2+
under mild condition (pH>4) in aquenous solution and living HeLa cells. The probe displays high
sensitivity (DL 4.2 nM), selectivity and quick response (20 min) toward Pd2+, driven by a PET
process.
Keywords: Fluorescent probe; Rhodamine derivative; Palladium; cell imaging
1. Introduction
Palladium, one of the platinum group elements, has been widely used in various fields,
such as catalytic converters, fuel cells, electronics, medical instruments and jewelry [1-5].
Frequent use of palladium species has resulted in a high level of residual palladium ions in
water and soil [6]. Palladium may coordinate with thiols-containing amino acids, DNA,
RNA, proteins, vitamin B6 and further disturb several cellular processes. Excess palladium
accumulation would pose a great threat to human health as well [7-9]. Because of the
hazardous effects of palladium, European Agency for the Evaluation of Medicinal Products
had set the threshold limit of palladium found in drugs as 5-10 ppm, and suggested dietary
intake of palladium less than 1.5-15 μg per person per day [10, 11].
Some conventional methods and techniques, atomic absorption spectroscopy (AAS),
inductively coupled plasma atomic emission spectroscopy (ICP-AES), inductively coupled
plasma mass spectrometry (ICP-MS), solid phase micro extraction-high performance liquid
chromatography (SPME-HPLC), and X-ray fluorescence (XRF), have been used to detect
palladium [12-16]. Nevertheless, all these approaches require sophisticated and expensive
instruments, complicated sample preparation, rigorous experimental conditions, as well as
specialized and experienced operators. In contrast, fluorometric determination could avoid
the shortcoming of these convention methods in the term of trace analysis and detection,
meanwhile maintains the high selectivity and accuracy [18]. Owning to the nature of
1

fluorometric detection, for instance simple operation, fast response, in situ analysis, low
cost, even naked-eye observation without instruments[19, 20], quite a number of efforts
have been done to develop fluorescent probes for palladium.
A series of fluorescent probes for palladium detection have been synthesized based on
various fluorophores, oxime derivatives [21], rhodamine dyes [22-24], triazole [25],
cyanines [26], boron dipyrroethane dyes [27], benzothiazole [28], chromen [29],
Naphtalimide [30]. yet companying with some defects in their nature, for example the
changes of fluorescence signature can’t be observed by eyes, high detection limit, long
response time and harsh pH condition [31-35].
Rhodamine fluorophore has a special photoluminescent property, its spirolactam form (no
fluorescence) ring-open form (fluorescence) would be triggered by a specific analyte
[36-37]. On this basis, we developed a new rhodamine based fluorescence RBPTA from
pyridine and thiophene moiety with remarkable nature of colorimetric, naked-eye, ‘off-on’
sensing system for the detection of Pd2+ (Scheme 1). To our delight, RBPTA exhibited a
desired high selectivity and sensitivity for the detection of Pd2+. The sensing process of
RBPTA for palladium is based on induced opening of spirolactam ring with a brilliant
pink colortion and fluorescence emitted (Scheme 2).
Scheme 1. Synthesis of RBPTA
2. Experimental
2.1 Materials and methods
2-Aminomethylpyridin, 2-Thenaldehyde, methyl acrylate, sodium borohydride,
Rhodamine B, ethanediamine, EDC·HCl and DIPEA were purchased from Energy
Chemical, metal ions AgNO3, CdCl2, Cs2CO3, CuCl, FeCl3, SnCl2·2H2O, HgCl2, CaCl2,
FeCl2·4H2O, NiCl2·6H2O, CuCl2·2H2O,MgCl2·6H2O, CoCl2·6H2O, ZnCl2, Pb(NO3)2,
PdCl2, NaCl, AlCl3,MnCl2 were purchased from Sinopharm Chemical Chemical Co., Ltd.,
and reagents of analytical reagent grade. All solvernts purchased from Shanghai Wohua
Chemical Co., Ltd., and double-distilled water was used in all experiments. All reagents
and organic solvents used were used without further purification. Thin-layer
chromatography was performed on a HAIYANG silica gel F254 Plate, and Column
chromatography was performed on HAIYANG silica gel (type: 200-300 mesh, 300-400
mesh).
2

1H NMR and 13C NMR spectra were collected on Bruker-Avance DPX 400MHz, the
chemical shifts in parts-per-million (ppm) for NMR spectra were referenced relative to
tetramethylsilane (TMS, 0.00 ppm) as the internal reference. Mass spectra were obtained
from mass spectrometer (Agilent-6110). Fluorescent spectra were measured on
Spectofluorometer FS5. UV-vis spectra were obtained on U3010-vis spectrophotometer.
The pH levels were measured using FE20.
2.2 Sythesis
2.2.1. Compound 3: 1-(pyridin-2-yl)-N-(thiophen-2-ylmetheyl) methanamine:
2-Aminomethylpyridin (1 g, 9.25 mmol) was added to a solution of 2-Thenaldehyde
(1.036 g, 9.25 mmol) in methanol (15 ml) with nitrogen atmosphere. The mixture was
stirred at room temperature overnight, before sodium borohydride (1.05 g, 27.75 mmol)
was slowly added to the mixture at 0
℃, and the mixture was stirred for 8 hours. The
reaction mixture was quenched by water, after methanol was evaporated under reduced
pressure, then extracted with dichloromethane (20 mL×3). The organic phases were
combined and then washed with saturated brine, dried with Na2SO4, then filtered. Removal
of the solvents under reduced pressure gave a crude product, which was purified by silica
1
gel chromatography (eluent: EA:PE 1:5) to produce a yellow oily liquid (1.06g, 56%). H
NMR (CDCl3, 400 MHz): δ 8.58 (ddd, J = 4.9, 1.8, 0.9 Hz, 1H), 7.67 (td, J = 7.6, 1.8 Hz,
1H), 7.34 (d, J = 7.7 Hz, 1H), 7.27 – 7.21 (m, 1H), 7.19 (ddd, J = 7.5, 4.9, 1.1 Hz, 1H),
6.97 (d, J = 3.4 Hz, 2H), 4.07 (s, 2H), 3.98 (s, 2H), 2.44 (s, 1H). ESI-MS: calcd. for
[M+H]+, 205.07; found, 205.0.
2.2.2. Compound 4: Methyl-3-((pyridine-2-ylmethyl) (thiophen-2-ylmethyl) amino)
propanoate:
A mixture of compound 3 (0.82 g, 4 mmol) and methyl acrylate (0.69 g, 8 mmol) in dry
methanol (10 mL) was refluxed for 5 hours, then methyl acrylate and methanol was
evaporated under reduced pressure and the crude compound was purified by silica gel
1
chromatography (eluent: EA:PE 1:5) to produce a yellow oily liquid (0.86 g, 74 %). H
NMR (CDCl3, 400 MHz) δ 8.53 (ddd, J = 4.9, 1.9, 1.0 Hz, 1H), 7.70 (td, J = 7.6, 1.8 Hz,
1H), 7.57 (dt, J = 7.9, 1.1 Hz, 1H), 7.27 – 7.21 (m, 1H), 7.18 (ddd, J = 7.5, 4.9, 1.3 Hz,
1H), 6.98 – 6.91 (m, 2H), 3.90 (s, 2H), 3.83 (s, 2H), 3.67 (s, 3H), 2.92 (t, J = 7.2 Hz, 2H),
2.57 (t, J = 7.2 Hz, 2H). ESI-MS: calcd. for [M+H]+, 291.11; found,290.9.
2.2.3. Compound 1: 3-((pyridine-2-ylmethyl)(thiophen-2-ylmethyl)amino)-propanoic
acid
A solution of compound 4 (1 g, 3.5 mmol) in 10mL methanol was added NaOH (0.42 g,
10.5 mmol), then the mixture was refluxed for 3 hours, then the reaction mixture was
cooled to 0
℃, and neutralized with dilute HCl, the solvent was evaporated, the residue
was purified silica gel chromatography (eluent: MeOH:DCM 1:50) to produce a light
3

yellow powder (0.54 g, 56 %). 1H NMR (CDCl3, 400 MHz) δ 9.46 (s, 1H), 8.58 (d, J = 5.0
Hz, 1H), 7.69 (t, J = 7.7 Hz, 1H), 7.35 (d, J = 7.8 Hz, 1H), 7.24 (dd, J = 11.1, 6.4 Hz, 2H),
6.97 (p, J = 3.4 Hz, 2H), 3.99 (s, 2H), 3.88 (s, 2H), 2.96 (t, J = 6.4 Hz, 2H), 2.58 (t, J = 6.4
Hz, 2H). ESI-MS: calcd. for [M+H]+ 277.35; found, 276.2.
2.2.4. Compound 2 2-(2-aminoethyl)-3’, 6’-bis (diethylamino) spiro [isoindoline- 1,9’-
xant-hen]-3-one
A solution of Rhodamine B (2 g, 4.499 mmol) in ethyl alcohol (30 mL) was heated for 20
minutes, then ethanediamine (3.0 ml, 44.98 mmol), the mixture was refluxed for 12 hours.
The mixture was evaporated in reduced pressure, the distilled water was added to the
residue, and the mixture was extracted with dichloromethane (50 mL×3), then the organic
phase was combined, washed with saturated brine, and dried with Na2SO4, then filtered,
Removal of the solvents under reduced pressure gave a crude product, which was purified
by silica gel chromatography (eluent: MeOH:DCM 1:50) to produce a light yellow powder
(1.81 g, 83 %).1H NMR (CDCl3, 400 MHz) δ 7.97 – 7.87 (m, 1H), 7.51 – 7.44 (m, 2H),
7.16 – 7.07 (m, 1H), 6.45 (d, J = 8.8 Hz, 2H), 6.39 (d, J = 2.6 Hz, 2H), 6.29 (dd, J = 8.9,
2.6 Hz, 2H), 3.35 (q, J = 7.1 Hz, 8H), 3.21 (t, J = 6.6 Hz, 2H), 2.45 (t, J = 6.6 Hz, 2H), 1.65
(s, 2H), 1.18 (t, J = 7.0 Hz, 12H). ESI-MS: calcd. for [M+H]+ 485.28; found, 485.3.
2.2.5. Compound RBPTA
Compound 1 (0.5g, 1.81mmol), EDC (0.38g, 2mmol), DIPEA (0.78g, 6mmol) were
stirred in dichloromethane for 0.5 hour. Compound 2 (0.88g, 1.8 1mmol) was added the
mixture was stirred in room temperature for 8 hours. The mixture was evaporated under
reduced pressure, the residue was dissolve by dichloromethane, the solution was washed
by diluted citric acid, saturated sodium bicarbonate, and saturated brine, the mixture was
dried with Na2SO4, then filtered, Removal of the solvents under reduced pressure gave a
crude product, which was purified by silica gel chromatography (eluent: MeOH:DCM
1
1:50) to produce a pink powder (1.05g, 78%). H NMR (CDCl3, 400 MHz) δ 8.49 (dd, J =
5.0, 1.7 Hz, 1H), 7.96 – 7.88 (m, 1H), 7.62 (td, J = 7.7, 1.8 Hz, 1H), 7.47 (tt, J = 7.5, 3.4
Hz, 3H), 7.39 (t, J = 4.8 Hz, 1H), 7.18 (dd, J = 5.0, 1.3 Hz, 1H), 7.16 – 7.05 (m, 2H), 6.97
– 6.87 (m, 2H), 6.48 – 6.35 (m, 4H), 6.26 (dd, J = 8.9, 2.6 Hz, 2H), 3.88 (s, 2H), 3.80 (s,
2H), 3.33 (p, J = 6.7 Hz, 10H), 3.06 (q, J = 5.5 Hz, 2H), 2.84 (t, J = 6.9 Hz, 2H), 2.37 (t, J
13
= 6.8 Hz, 2H), 1.17 (t, J = 7.0 Hz, 12H). C NMR (CDCl3, 101 MHz) δ 171.52 , 169.47 ,
159.22 , 153.87 , 153.29 , 148.96 , 148.86 , 141.85 , 136.50 , 132.63 , 130.61 , 128.52 ,
128.08 , 126.46 , 126.17 , 124.99 , 123.88 , 122.97 , 122.79 , 122.02 , 108.20 , 105.03 ,
97.83 , 65.46 , 59.33 , 52.45 , 49.66 , 44.33 , 40.02 , 39.81 , 34.22 , 12.63 . ESI-MS: calcd.
for [M+H]+ 743.37; found, 743.3 Elemental analysis (%): calcd. for RBPTA C 71.13, N
11.31, H 6.78; found, C 71.21, N 11.45, H 6.79.
4

Scheme 2. RBPTA and Pd2+ sensing process
2.3. Stock solution
Ionic stock solution(10-3 M) of chloride salts of Cd2+, Cu+, Fe3+, Sn2+, Hg2+, Ca2+, Fe2+, Ni2+,
Cu2+, Mg2+, Co2+, K+, Zn2+, Pb2+, Na+, Al3+, Mn2+, Pd2+, Pt2+ and Cs2CO3, AgNO3, Ba(NO3)2 were
prepared in EtOH/H2O (3:2, v/v, pH 7.4, HEPES buffer, 0.5 mM). And probe’s stock solution (1
mM) of RBPTA was prepared in EtOH/H2O (3:2, v/v, pH 7.4, HEPES buffer 0.5 mM).
2.4. General method of UV-vis and fluorescence
The UV-vis and fluorescent methods were carried out to evaluate the nature of RBPTA.
Test samples were prepared by free stock solution (EtOH/H2O 3:2 v/v, pH 7.4, HEPES
buffer, 0.1 mM), and the UV-vis absorption spectra fluorescent spectra were measure in 25
℃
.And in fluorescence measurement fluorescence intensity at λex = 566 nm, λem = 584 nm.
2.5. Cells studies of RBPTA
2.5.1. Cytotoxicity of RBPTA
RBPTA was dissolved in DMSO as a stock solution, then RBPTA concentrations in cell-culture
medium were controlled from 0 to 15 μM, then HeLa cells were incubated with the solutions
above. Last MTT assay was executed to evaluate the cytotoxicity of RBPTA.
2.5.2. fluorescent imaging in living cells
Control group: HeLa cells was incubated with RBPTA (10 μM). After 30 min, cell-culture
medium was removed, and fresh medium was added. Then fluorescence imaging experiment was
taken (λex=566 nm, λem=586 nm).
Experimental group: HeLa cells was incubated with RBPTA (10 μM) for 30 min, then with
PdCl2 (10 μM) for 30 min. Cell-culture medium was removed, and fresh medium was added. Last
fluorescence imaging experiment was taken (λex=566 nm, λem=586 nm).
2.6. Preparation of paper test
Filter papers was dipped in the stock solution of RBPTA (1 mM), then test papers were dried in
air to measure different concentrations of Pd2+.
3. Results and discussion
3.1. pH response of RBPTA
5

The pH response of RBPTA in EtOH/H2O (3:2, v/v, pH 7.4, HE-PES buffer, 0.5 mM) solution,
acid base titration was taken (pH=1.00, 2.06, 3.03, 4.08, 5.14, 6.03, 7.0 6, 8.06, 8.9 2, 10.05, 11.04,
12.03), and the fluorescent intensities of RBPTA at 566 nm were recorded (Figure 1). It showed
that RBPTA did not emit fluorescence (λex=566 nm) at pH>5, it means that the spirolactam of
RBPTA would be kept in pH 5-12. And the fluorescence intensity (λex=566 nm) tended to be
stable at pH<3, for the ring-opening of the spirolactam. These results suggested that RBPTA
recognized palladium with pretty low background fluorescence at pH from 5 to 12. Herein, further
UV-vis and fluorescence studies were carried out in EtOH /H2O (3:2, v/v, PH 7.40, HEPES buffer,
0.5 mM) solution.
Figure 1 The fluorescent intensity of RBPTA (10 μM) show effect of ph in EtOH/H2O (3:2 V/ V) at 25 ℃. λex=566 nm, λem=586 nm.
3.2. Response time
Response time of probe of RBPTA was investigated by fluorescence method (Figure 2). Test sample
was prepared by placing 10 μΜ RBPTA and 5 equiv of Pd2+ in 3 mL free stock solution (EtOH/H2O 3:2
v/v, pH 7.4, HEPES buffer, 0.1mM), and the sample was tested immediately, until the fluorescence
intensity of sample reached the maximum value(0-28 min).
Figure 2. Fluorescence intensity of RBPTA ((10 μM)) with Pd2+ (5 eq) over a period of 28 min, λex= 566 nm. Inset: Plot of the fluorescence
intensities at 584 nm over a period of 28 min.
3.3. Job’s plot of RBPTA and Pd2+
6

The solutions of Pd2+ and RBPTA were prepared with a total concentration of 50 μM, and the
mole fraction of Pd2+ to RBPTA from ranged from 0 to 1. A job’s plot (Figure. 3) was generated to
revealed that RBPTA and palladium complex is 1:1 stoichiometry.
Figure 3. Job’s plot of RBPTA complexing with Pd2+, λex=566 nm, λem=586 nm.
3.4. Fluorescence titration
The cation binding properties of RBPTA are studied by using the chloride salts of Cd2+, Cs3+,
Cu+, Fe3+, Sn2+, Hg2+, Ca2+, Fe2+, Ni2+, Cu2+, Mg2+, Co2+, K+, Zn2+, Pb2+, Na+, Al3+, Mn2+, Pd2+,
Pt2+ and AgNO3, Ba(NO3)2 in EtOH/H2O (3:2, v/v, pH 7.4, HEPES buffer, 0.5 mM) solution.
Upon addition of cations to a colorless solution of RBPTA (0.2 equiv. 10 μM), only Pd2+ could
urge the mixture to emit fluorescence and become pink (Figure 4a), whereas others cannot. It
suggested that RBPTA can function as a highly selective chemosensor for Pd2+. Then, the
fluorescence titration experiment (Figure 4b) was taken to further demonstrated high sensitivity of
RBPTA to detect Pd2+.
Figure 4. a) RBPTA (10 μM) and cations (50 μM) in EtOH/H2O (3:2, v/v, pH 7.4, HEPES buffer, 0.5 nM) solution, after 4 hours’ standing at
25 ℃. The excitation and emission wavelengths were 566 nm and 584 nm, respectively. b) fluorescence spectra of addition of different amounts of
Pd2+ in EtOH/H2O (3:2, v/v, pH 7.4, HEPES buffer, 0.5 nM) solution, after 4 hours’standing at 25 ℃. λex=566 nm, λem=586 nm.
3.5. Binding association constant
7

Moreover, association constant value of Pd2+ with RBPTA (Figure 5), based on
fluorescence titration, has been calculated by emission intensity date following the
modified Benesi-Hildenbrand equation, F – F0 = ΔF = [Pd2+](Fmax – F0)/(1/Ka + [Pd2+]).
Here F is fluorescence intensity at λex = 566 nm, λem = 584nm, F0 is fluorescence intensity
of RBPTA at λex = 566 nm, λem = 584 nm, Fmax is saturated fluorescence intensity at λex =
566 nm, λem = 584nm at λex = 566 nm, λem = 584nm of RBPTA-Pd complex, and Ka is
association constant. Ka was evaluated to be 4.88 × 104 M-1.
Figure 5. Fluorescence intensity of RBPTA (10 μM) at 584 nm upon addition of Pd2+ (3 μM, 4 μM, 7 μM, 9 μM, 11 μM, 12 μM).
3.6. Detection limit
The detection limit of RBPTA, based on fluorescence titration as well, was calculated by
the equation: Detection limit = 3SD/S. The fluorescence emission spectrum of RBPTA was
measured 10 times, then the standard deviation (SD) was calculated (supporting materials).
Meanwhile, the slop (S) was obtained by plotted the fluorescence intensity at 584 nm with
various concentrations of Pd2+ (Figure 6). Thus the detection limit was evaluated to be 4.22
nM
.
Figure 6. Fluorescence intensity of RBPTA ((10 μM)) at 584 nm with different concentration of Pd2+
.
3.7. Competition expriments
Competition experiments, to further explore the selectivity of RBPTA for palladium,
were performed in the presence of Pd2+ (5 equiv, 50μM) mixed with others cations (5
8

equiv, 50 μM): Ag+, Cd2+, Cs3+, Cu+, Fe3+, Sn2+, Hg2+, Ca2+, Fe2+, Ni2+, Cu2+, Mg2+, Co2+,
K+, Zn2+, Pb2+, Na+, Al3+, Mn2+, Ba2+and Pt2+, respectively, bound to RBPTA (1 equiv.
10 μM), the fluorescence studied (Figure 7) showed those free cations would have little
interference the sensing of palladium by RBPTA
.
Figure 7. Pd2+ (5 equiv, 50 μM) ,free cations (5 equiv, 50 μM), and RBPTA (1 equiv 10 μM). after 4 hours’ standing at 25 ℃. λex=566 nm, λem=586
nm.
3.8. MS spectra study
The MS spectra Figure 8 shown that the peak appeared at m/z 743.3 before complexing it is
corresponds to [RBPTA + H]+, while the peak appeared at 849.3 m/z after complexing, it assigned
to the complex [RBPTA2- + Pd2+ + H+]+. It further confirms that the coordination mode of
RBPTA and palladium is 1:1 stoichiometry.
Figure 8. The MS spectrum of RBPTA-Pd2+ complex
3.10. Density functional theory (DFT) calculation
The spatial distributions and obital energies of the HOMO and LUMO of RBPTA and
RBTPA-Pd were generated using DFT calaulations with the B3LYP method using 6-31+G
(d, p) as the basis set(Figure 10). It shown that the energy gaps between the HOMO and
LUMO in the RBPTA and RBTPA-Pd were calculated to be 378.3 kJ/mol and 200.3
kJ/mol, respectively, the results exhibited that the binding of palladium to RBPTA lowered
the HOMO-LUMO energy gap of the complex and stabilized the system
9

Figure 9. HOMO and LUMO orbitals of RBPTA and the RBPTA-Pd complex.
3.11. Cell studies
Moreover, cytotoxicity assays were taken to evaluate the cytotoxicity of RBPTA. An
MTT assay was taken with different RBPTA concentrations from 0 to 15 μM in HeLa
cells. As shown in Figure 10, the probe showed no toxicity to HeLa cells, the results
suggested that the probe could be used to detect Pd2+ in biological samples.
Figure 10 Cytotoxicity of RBPTA in HeLa
Encouraged by the promising properties of RBPTA, the imaging applications in living
cells was investigated to search whether RBPTA could realize the detection of Pd2+ in
living cells. As shown in Figure 11, HeLa cells which were incubated with RBPTA (10
μM) showed no fluorescence (Figure 11c), while it display strong green fluorescence after
being treated with PdCl2 (Figure 11g).The result indicate that RBPTA is capable of
fluorescence imaging of palladium in living cells.
10

Figure 11. Bright-field and fluorescence image of HeLa cells: (a-d)HeLa cells only incubated with the probe (10 μM) for 0.5 h in 37℃: (a)
bright-field image; (b) fluorescence image from blue channel; (c) fluorescence image from green channel; (d) merge image of (b) and (c); further
treated with PdCl2 for 0.5 h in 37 ℃: (e) bright-field image; (f) fluorescence image from blue channel; (g) fluoresceence image from green channel;
(h) merge image of (f) and (g). scale bar 2 μm.
3.12. Test papers
What is more, practical application, test papers, was conducted. Filter paper was dipped in stock
solution with RBPTA (1 mM), then was exposed to different concentration of Pd2+. Last test paper
was observed under 356 nm UV light (Figure12). It shown that the RBPTA can be made as a test
paper to ration detect for Pd2+.
Figure 12. Test paper, treated with different concentrations of Pd2+, taken under 356 nm UV light.
3. 13. Comparison of Pd2+ probes
Table 1 comparison of Pd2+ probes
Detection
Probe
Chemical structure
Ex/Em
Solvent system
Application
Test paper
limit/mol·L-1
Ethanol/Water
(1:1)
Ref. 18
530/580
1.85×10-7
11

Ethanol/Water
(1:1)
Ref. 4
550/562
420/590
Not mentioned
Not mentioned
Not mentioned
Mice imaging
Ethanol/Water
(1:1)
Ref. 29
Ethanol/Water
(1:1)
Ref. 34
505/552
566/586
5.0×10-9
Test paper
This
Ethanol/Water
(3:2)
Cells imaging
Test paper
4.2×10-9
work
4. Conclusion
In conclusion, a new rhodamine fluorescent probe for palladium species with high
sensitivity and selectivity and quick response was developed. Additionally, RBPTA can be
applied to detect Pd2+ in both water sample, and living cells. RBPTA could be made as test
paper to detect Pd2+ with quantitation as well.
Acknowledgements
The authors acknowledge the financial support of the National Natural Science Foundation of
China (No. 21402067)
Notes and references
1
2
3
Janet Kielhorn, Christine Melber, Detlef Keller, Inge Mangelsdorf. Int. J. Hyg. Environ. Health. 205
(2002) 417-432.
Stephanie MacQuarrie, J. Hugh Horton, Jack Barnes, Kevin McEleney, Hans-Peter Loock, Cathleen
M. Crudden. Angew. Chem. Int. Ed. 47 (2008) 3279-3282.
Tetsuo Iwasawa, Makoto Tokunaga, Yasushi Obora, Yasushi Tsuji. J. Am. Chem. Soc. 126 (2004)
6554-6555.
12

4
Honglin Li, Jiangli Fan, Jianjun Du, Kexin Guo, Shiguo Sun, Xiaojian Liu Xiaojun Peng, 46 (2010)
1079-1081.
5
6
Thomas W. Lyons, Melanie S. Sanford. Chem. Rev. 110 (2010) 1147-1169.
Wei Liu, Jie Jiang, Chunyang Chen, Xiaoliang Tang, Jinmin, Peng Zhang, Kaiming Zhang, Zhiqi Li,
Wei Dou, Lizi Yang, Weisheng Liu. Inorg. Chem. 53 (2014) 12590-12594.
Clare L. S, Wiseman, Fathi Zereini. Science of the Total Environment. 407 (2009) 2493-2500.
Christopher D. Spicer, Therese Triemer, Benjamin G. Davis. J. Am. Chem. Soc. 134 (2012) 800-803.
Rahimi M. Yusop, Asier Unciti-Broceta, Emma M. V. Johansson, Rosario M. Sánchez-Martín, Mark
Bradley. Nature Chemistry. 3 (2011) 239-243.
7
8
9
10 Christine E. Garrett, Kapa Prasad. Adv. Synth. Catal. 346 (2004) 889-900.
11 John S. Carey, David Laffan, Colin Thomson, Mike T. Williams. Org. Biomol. Chem. 4 (2006)
2337-2347.
12 Clinio Locatelli, Dora Melucci, Giancarlo Torsi. Anal. Bioanal. Chem. 382 (2005) 1567-1573.
13 Karleen Van Meel, Anne Smekens, Marc Behets, Paul Kazandjian, René Van Grieken. Anal. Chem.
79 (2007) 6383-6389.
14 Boryana Dimitrova, Karma Benkhedda, Elisavea Ivanova, Freddy Adamas. J. Anal. At. Spectrom. 19
(2004) 1394-1396.
15 Honglin Li, Jiangli Fan, Xiaojun Peng. Chem. Soc. Rev. 42 (2013) 7943-7962.
16 Hua Chen, Weiying Lin, Lin Yuan. Org. Biomol. Chem. 11 (2013) 1938-1941.
17 Yu Chen, Bo Chen, Yifeng Han. Sensor and Actuators B. 237 (2016) 1-7.
18 Shyamaprosad Goswami, Debabrata Sen, Nirmal Kumar Das, Hoong-Kun Fun, Ching Kheng Quah,
Chem. Commun. 47 (2011) 9101-9103.
19 Mi Eun Jun, Kyo Han Ahn. Org. Lett. 12 (2010) 2790-2793.
20 Mian Wang, Yanglei Yuan, Hongmei Wang, Zhaohai Qin. Analyst. 141 (2016) 832-835.
21 Shyamaprosad Goswami, Debarata Sen, Nirmal Kumar Das, Hoong-Kun Fun, Ching Kheng Quan.
Chem. Commun. 47 (2011) 9101-9103.
22 Upendar Reddy G, Firoj Ali, Nandaraj Taye, Samit Chattopadhyay, Amitava Das. Chem. Commun. 51
(2015) 3649-3652.
23 Fei Liu, Juan Du, Meiying Xu, Guoping Sun. Chem. Asian. J. 11 (2016) 43-48.
24 Ji-Ting Hou, Kun Li, Kang-Kang Yu, Mei-Zhao Ao, Xin Wang, Xiao-Qi Yu. Analyst. 138 (2013)
6632-6638.
25 Xiaohang Wang, Zhiqian Guo, Shiqin Zhu, He Tian, Weihong Zhu. Chem. Commun. 50 (2014)
13525-13528.
26 Dongho Keum, Sungwoo Kim, Youngmi Kim. Chem. Commun. 50 (2014) 1268-1270.
27 Tiantian Chen, Tingwen Wei, Zhijie Zhang, Yahui, Jian Qiang, Fang Wang, Xiaoqiang Chen. Dyes
and Pigments. 140 (2017) 392-398.
28 Bin Liu, Weijian Chen, Dong Liu, Taisheng Wang, Chengjun Pan, Danqing Liu, Lei Wang, Ruke Bai.
Sensor and Actuators B: Chemical. 237 (2016) 899-904.
29 Shiguo Sun, Bo Qian, Na Jiang, Jitao Wang, Si Zhang, Xiaojun Peng, Org. Lett. 16 (2014) 1132-1135.
30 Huangmei Huang, Kemin Wang, Weihong Tan, Delie An, Xiaohai Yang, Shasheng Huang, Qiuge Zhai,
Leiji Zhou, Yan Jin. Angew. Chem. Int. Ed. 43 (2004) 5635-5638.
31 Prahpreet Singh, Lalit singh Mittal, Vanita Vanita, Kapil Kumar, Amandeep Walia, Gaurav Bhargava,
Subodh Kumar. J. Mater. Chem. B. 4 (2016) 3750-3759.
32 Yu Chen, Bo Chen, Daijun Luo,Yiyu Cai, Yaning Wei, Yifeng Han. Tetrahedron Letters. 57 (2016)
1192-1195.
33 Jie Jiang, Huie Jiang, Wei Liu Xianliang Tang, Xi Zhou, Weisheng Liu, Ruiting Liu. Organic Letters.
13 (2011) 4922-4925.
34 Honglin Li, Jiangli Fan, Mingming Hu, Guanghui Cheng, Danhong Zhou, Tong Wu, Febgkubg Song,
Shiguo Sun, Chunying Duan, Xiaojun Peng, Chem. Eur. J. 18 (2012) 12242-12250.
35 Virginie Dujols, Francis Ford, Anthony W. Czarnik, J. Am. Chem. Soc. 119 (1997) 7386-7387.
36 Jie Cui, Dong-Peng Li, Shi-Li Shen, Jin-Ting Liu, Bao-Xiang Zhao, RSC Adv. 5 (2015) 3875-3880.
37 Meipan Yang, Yinjuan Bai, Wenfei Meng. Zhao Cheng, Na Su, Bingqin Yang. Inorg. Chem. Commun.
46 (2014) 310-314.
13

Some of the important highlights of this work are following.
1. RBPTAis used as a chemosensor for selective and quantitative detection of palladium with a
quite low limitation as 4.22 nM.
2. RBPTAis highly selective to palladium without interference from other cations.
3. RBPTAdetects palladium under mild condition (pH>4) in aquenous solution.
4. RBPTAdisplays quick response (20 min)toward palladium.
5. RBPTAcan be utilized as a fluorescent probe for the detection of palladium in living cells
(HeLa cells).
6. RBPTA can be made as a test paper to ration detect for palladium.
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