Rhodamine Diaminomaleonitrile Conjugate as a Novel Colorimetric Fluorescent Sensor for Recognition of Cd2+ Ion

Article abstract of DOI:10.1007/s10895-017-2046-x

Rhodamine diaminomaleonitrile linked probe (RD-1) shows highly sensitive colorimetric and selective turn-on fluorescent response to Cd²⁺ over other metal ions. The fluorescence intensity and absorbance of the probe RD-1 showed a good linearity, with very low detection limits of 18.5?nm. The probe RD-1 was preliminarily applied to the determination of Cd²⁺ ion in water samples from river and tap water with satisfying results. The live cell image confocal microscopy, HeLa cell demonstrated that RD-1 had low cytotoxicity with good membrane permeable property is successfully applied to fluorescence microscopic imaging for the detection of Cd²⁺ ions.

Full text of DOI:10.1007/s10895-017-2046-x

J Fluoresc
DOI 10.1007/s10895-017-2046-x
ORIGINAL ARTICLE
Rhodamine Diaminomaleonitrile Conjugate as a Novel
Colorimetric Fluorescent Sensor for Recognition of Cd Ion
2+
1
1
2
Perumal Sakthivel & Karuppannan Sekar & Gandhi Sivaraman
&
3
Subramanian Singaravadivel
Received: 10 December 2016 /Accepted: 9 February 2017
#
Springer Science+Business Media New York 2017
Abstract Rhodamine diaminomaleonitrile linked probe (RD-
) shows highly sensitive colorimetric and selective turn-on
Introduction
1
2+
fluorescent response to Cd over other metal ions. The fluo-
rescence intensity and absorbance of the probe RD-1 showed a
good linearity, with very low detection limits of 18.5 nm. The
probe RD-1 was preliminarily applied to the determination of
The development of luminescent chemical devices is an active
field of research in supramolecular chemistry [1–3]. An im-
portant area within this field is the development of lumines-
cent chemosensors [4–8]. Such sensors have the advantage of
possessing high sensitivity and selectivity, as well as provid-
ing on-line and real-time analysis that has revolutionized the
field of chemical analysis, particularly in critical care analysis
of blood and serum samples [9, 10].
Cadmium, an essential element in the earth, is widely used
in agriculture and industry. These sources of cadmium cause
excessive exposure to human society. Whereas Cd is also
known for its toxicity, which can induce serious health and
environmental problem, such as renal dysfunction, Calcium
metabolism disorders, prostate cancer, etc. [11, 12]. The EPA
2+
Cd ion in water samples from river and tap water with satis-
fying results. The live cell image confocal microscopy, HeLa
cell demonstrated that RD-1 had low cytotoxicity with good
membrane permeable property is successfully applied to fluo-
2+
rescence microscopic imaging for the detection of Cd ions.
2
+
.
.
.
Keywords Rhodamine Diaminomaleonitrile Cadmium
.
Sensor Fluorescence
(
United States Environmental Protection Agency) gives an
Highlights
2
+
enforceable drinking water standard for Cd of 5 ppb to pre-
vent kidney damage and other related diseases, while the
WHO (World Health Organization) provides a more strict
•
Rhodamine diaminomaleonitrile based probe for colorimetric and
fluorescent detection of Cd(II) was developed.
The detection limit of sensor is 18.5 nm.
•
•
The probe can be used to detect Cd(II) in live cells.
2+
guideline value for Cd of 3 ppb for drinking water [13].
Electronic supplementary material The online version of this article
doi:10.1007/s10895-017-2046-x) contains supplementary material,
which is available to authorized users.
Fluorescence is a powerful method to detect ions and neu-
tral molecules owing to its operational simplicity and high
sensitivity. The challenge in development of any fluorescent
sensor is the induced signal change when a target specifically
binds to the probe [14–17].
(
*
*
Karuppannan Sekar
karuppannansekar@gmail.com
2
+
Several sensors have been developed and utilized for Cd
imaging in living cells [18, 19]. In spite of their fascinating
Subramanian Singaravadivel
vesp1984@gmail.com
2
+
responses to Cd , these sensors still have some hang-ups, such
as simple response, UV excitation, and large spectral overlap
[20, 21]. To date, it is still a tremendous challenge to design
1
2
3
Department of Chemistry, Anna University - University College of
Engineering, Dindigul 624622, India
2
+
2+
Cd selective sensors for the accurate detection of Cd in
aqueous solutions and biological environments [22, 23].
The well-known fluorophore rhodamine exists in two
forms; one is the spirolactam and the other is the amide form.
Institute for Stem Cell Biology and Regenerative Medicine,
Bangalore 560065, India
Department of Chemistry, SSM Institute of Engineering and
Technology, Dindigul 624002, India

J Fluoresc
The spirolactam form does not exhibit absorption and emis-
sion, whereas the amide form exhibits absorption and emis-
sion in the visible region. When metal ions or analyte binds
with the rhodamine dye, the spirolactam ring can be readily
converted into the amide form. This has been utilized for the
development of chemosensors for metal ions [24–34].
standard. ESI-MS spectral analysis was performed in positive
ion mode on a liquid chromatography-ion trap mass spectrom-
eter (LCQ Fleet, Thermo Fisher Instruments Limited, US).
Fluorescence microscopic images were taken with a Nikon
fluorescence microscope using a filter.
Diaminomaleonitrile represents a class of π conjugated
compound with electronic donor and acceptor parts with high
electron affinity nature and interesting binding properties [35].
There are very few reports on cadmium sensing based on
rhodamine dyes through spirocyclic ring opening mechanism
Synthesis
Synthesis of 2-Amino-3″,6″-Bis(Diethylamino)
Spiro[Isoindoline-1,9″-Xanthen]-3-One 1:
[
36–38]. In this paper, we developed a rhodamine based probe
Rhodamine B hydrazide was synthesized for the following
reported procedure [39]. Rhodamine B 4 g (6.26 mmol) was
dissolved in 40 ml of methanol and added excess amount of
hydrazine hydrate drop wise to the solution. The reaction mix-
ture was refluxed until red colour disappeared. After comple-
tion of reaction, the reaction mixture was cooling to room
temperature and the solution was poured into 400 ml of dis-
tilled water for 6 h. Then the solid precipitate was filtered and
dried in vacuum to give compound 1 in pale pink solid. Yield:
(88%).
RD-1 linked to diaminomaleonitrile moiety (Scheme 1). This
2
+
could be used for the detection of Cd with high sensitivity
and selectivity, good linearity, and showed significant colori-
metric and fluorometric response in a short time. The low
cytotoxicity and cell-membrane penetrability of RD-1 were
confirmed by MTT assay and cell imaging, respectively.
Experimental
Materials and General Methods
Synthesis of (E)-2-((3″,6″-Bis(Diethylamino)
-3-Oxospiro[Isoindoline-1,9″-Xanthen]-2-Yl)Imino)
All reagents and solvents were used without purification.
Rhodamine B and diaminomaleonitrile were purchased from
Sigma Aldrich. Metal chloride salts procured from Merck
were used as the source for metal ions.
Absorption measurements were carried out using an
Antech (AN-UV-7000) UV-vis spectrophotometer.
Fluorescence spectra were recorded on F-4500 Hitachi fluo-
rescence spectrophotometer. The slit width was 5 nm for both
excitation and emission. NMR spectra were recorded on a
Bruker (Avance) 300 MHz instrument using TMS as internal
Acetaldehyde 2:
The compound 1 (700 mg, 1.54 mmol) was dissolved in 40 ml
of ethanol, an excess amount of 40% aqueous glyoxal was
added drop wise to the reaction mixture and stirred at room
temperature for 12 h. After the reaction is completed 50 ml of
saturated sodium chloride solution was added to obtain the
pale yellow precipitate. The precipitate was filtered and dried
in vacuum and purified by column chromatography in hexane/
ethyl acetate mixture (9:1) afforded 0.38 g of compound 2 in
6
8% yield.
1
H NMR (300 MHz, CDCl ), δ (ppm): 9.38–9.36 (d, 1H,
3
J = 7.5 Hz), 7.98–7.96 (d, 1H, J = 7.2 Hz), 7.48–7.41 (m, 4H),
.27 (d, 1H, J = 7.5 Hz), 7.05 (d, 1H, J = 6.83 Hz), 6.32–6.40
m, 2H), 6.15–6.19 (m, 2H), 3.21 (q, 8H, J = 6.9 Hz), 1.07 (t,
O
O
OH
7
(
a
N
NH2
Cl-
N
12H, J = 6.9 Hz).
N
O
N
O
1
N
Synthesis of (2-Amino-3-(((1E,2E)
Rhodamine B
-
-
2-((3″,6″-Bis(Diethylamino)
3-Oxospiro[Isoindoline-1,9″-Xanthen]-2-Yl)Imino)
b
H N
2
O
Ethylidene)Amino)Maleonitrile) RD-1:
O
CN
N
O
N
N
CN
N
c
N
The compound 2 (500 mg, 1.01 mmol) was dissolved in 30 ml
of ethanol and diamino maleonitrile (1.01 mmol) was added to
the solution and refluxed 70 °C for 6 h. After completion of
reaction the precipitate was filtered and washed with ethanol.
The crude product was purified by column chromatography
with hexane/ethyl acetate (8/2, v/v), brown solid was obtained
(0.38 g, 65%).
N
O
N
N
O
2
N
RD-1
Scheme 1 Synthesis of Probe RD-1 a Hydrazine-hydrate, MeOH,
reflux, 65 °C, 12 h. b Glyoxal, EtOH, rt. c 2,3-diaminomaleonitrile,
EtOH, 70 °C, 6 h

J Fluoresc
−
1
FT-IR (KBr, cm ): 699, 787, 1115, 1222, 1262, 1307,
Results and Discussion
Synthesis of RD-1
1
374, 1513, 1591, 1613, 1699, 2205 and 2967.
H NMR (300 MHz, CDCl ), δ (ppm): 8.41–8.38 (d, 1H,
1
3
J = 7.8 Hz), 8.01–7.97 (m, 2H), 7.54–7.46 (m, 3H, ArH), 7.13–
7
5
.10 (d, 1H, J = 7.8 Hz), 6.49–6.43(m, 3H), 6.28–6.25 (m, 2H),
.29 (s, 2H), 3.30 (q, 8H, J = 6.6 Hz), 1.15 (t, 12H, J = 6.9 Hz).
ESI-Ms.: m/z [M + H] : 586.28; found: 586.58.
Compound 2 (1 mmol) and diaminomaleonitrile (1 mmol)
were mixed with 20 mL ethanol and the mixture was stirred
under reflux condition for 6 h. The suspension was filtered,
and then the solid was dried in vacuum. The residue was
purified by column chromatography hexane/ethyl acetate
+
Stock Solution Preparation for Spectral Detection
(
8/2, v/v) as elutent to afford brown solid in a yield of 65%.
+
3+
2+
2+
2+
The chloride or nitrate salts of Ag , Al , Ba , Ca , Cd ,
RD-1 was characterized by FT-IR, NMR and Mass spectral
analysis (Fig. S1-S3).
2+
3+
2+
3+
2+
+
2+
2+
+
2+
Co , Cr , Cu , Fe , Hg , K , Mg , Mn , Na , Ni ,
2+
2+
Pb and Zn were prepared in acetonitrile-water (7:3) mix-
ture as stock solutions (1 mmol). The RD-1 stock solution
1 mmol) was prepared in acetonitrile-water (7:3) mixture.
The working solutions of RD-1 were freshly prepared by di-
luting the highly concentrated stock solution to the desired
concentration prior to spectroscopic measurements.
The absorption spectra of probe RD-1 (1:1) toward various
+
+
2+
2+
2+
2+
2+
metal ions such as Na , K , Ca , Cu , Cd , Zn , Cd ,
Hg , Pb , Fe , Cr , Ni , Al , Ag and Co were inves-
2
+
2+
2+
3+
2+
3+
+
2+
(
2
+
tigated (Fig. 1). Upon addition of Cd , an absorption peak
emerged at 530 nm. The development of the noticeable naked-
eye detection of the magenta colour in the probe upon addition
of Cd involves a metal-induced delactonization of rhoda-
mine. Upon complexation, colourless spirolactam form is con-
verted into its (colorless to pink) colored ring opened amide
form. The change in the color and absorbance wavelength
makes it feasible to distinguish Cd from other metal ions.
Upon addition of Cd ion the probe RD-1 leads to a linear
relationship of gradual enhancement of the intensity at 530 nm
2
+
UV-Vis and Fluorescence Titration Studies
The absorption and fluorescence responses of the probe RD-1
towards various metal ions was investigated by UV-vis spec-
troscopy and fluorescence spectroscopy respectively in
acetonitrile-water (7:3) mixture.
2
+
2
+
(Fig. S4).
MTT Assay
Fluorescence Titration and Selectivity
The cell viability of the probe RD-1 were tested against HeLa
cell lines using the 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl
tetrazolium bromide (MTT) assay. The cells were seeded into a
Changes of fluorescence emission spectra of the probe RD-1
in the presence of various cations were studied in HEPES
buffer (10 μM, pH 7.54). Fluorescence titration was used to
further investigate the binding capability of RD-1 for Cd .
The probe RD-1 weak fluorescence upon excitation at 530 nm
4
well plate at a density of 1.5 × 10 cells per well and incubated
2
+
in medium containing RD-1 at concentrations ranging from 0
to 50 μM for 30 min. To each well, 100 μL of MTT was added
and the plates were incubated at 37 °C for 1 h to allow MTT to
form formazan crystals by reacting with metabolically active
cells. The medium with MTT was removed from the wells.
Intracellular formazan crystals were dissolved by adding
1
00 μL of DMSO to each well and the plates were shaken
for 10 min. The absorbance was recorded using Plate reader.
Cell Culture and Fluorescence Imaging
HeLa cells were grown in modified Eagle^s medium supple-
mented with 10% FBS (fetal bovine serum) at 37 °C. The
HeLa cells were incubated with the probe RD-1 (10 μM in
DMSO/H O (7:3, v/v) buffered with HEPES buffer) and im-
2
aged through fluorescence microscope. The cells were washed
with HEPES three times to remove the excess of the probe
RD-1 in the extra cellular parts and growth medium. Again
the probe treated cells were further incubated with Cd(NO3)2
(
10 μM) for 10 min at 37 °C and imaged with Nikon fluores-
Fig. 1 UV-vis absorption spectra of probe RD-1 (10 μM) upon addition
of various metal ions in 10 μM HEPES buffer solution
cence microscope.

J Fluoresc
Fig. 4 Fluorescence response of 10 μM RD-1 to various metal ions.
Black bars represent the addition of metal ion to RD-1. Red bars
represent the change of the emission upon the subsequent addition of
Fig. 2 Fluorescence spectra of probe RD-1 (10 μM) upon addition of
various metal ions in 10 μM HEPES buffer, λex = 530 nm
2+
Cd to the above solution
because of its spirocyclic structure did not open upon the free
RD-1 (Fig. 2). Upon gradual addition of Cd develops a
maximum absorbance when the molar fraction of 0.5, indicat-
ing a 1:1 stoichiometry. ESI mass spectrometric analysis pro-
vided further support for the formation of the 1:1 complexes
2
+
significantly strong emission band at 553 nm (Fig. 3).
2
+
2+
The addition of Cd (0–20 μM) increased the fluorescence
intensity by approximately 200-fold. The fluorescence inten-
sity remained constant following the addition of greater than
RD-1+ Cd . A signal at 701.1776 corresponded to RD-1+
2
+
+
2+
Cd +H were observed when Cd was added to RD-1 in
methanol (Fig. S5 and S6).
2
+
5
0 μM (excess) Cd . The enhancement in fluorescence in-
On the basis of the 1:1 stoichiometry and UV–Vis titration
2
+
tensity was likely due to the Cd -triggered rhodamine
spiroring opening reaction [40].
data, the association constants (K ) of the probe RD-1 with
a
2
+
Cd were calculated using the Benesi–Hildebrand eq. [41]
These results show that the probe RD-1 is very selective
and sensitive towards Cd over other metal ions (Fig. 4).
the measured fluorescence intensity [1/(F − F )] at 553 nm
0
2
+
2+
showed a linear relationship with 1/[Cd ], where F and F
0
Job^s Plot analysis was used to find the stoichiometry for
RD-1/Cd complex. Job^s Plots exhibited the same
are respectively the fluorescence intensities of the blank and
2
+
2+
2+
sample solution containing RD-1 and Cd , and [Cd ] are the
2
+
concentrations of Cd in the sample solutions. The associa-
2
+
5
−1
tion constant between RD-1 and Cd was 2.33 × 10 M
Fig. 3 Concentration-dependent fluorescence enhancement of RD-1
2
+
(
1
10 μM) on the addition of various amounts of Cd (0–1.5 equiv) in
Fig. 5 Plot of change of fluorescence intensity at λEmm = 553 Vs
concentration of Cadmium ions added to the probe RD-1
0 μM HEPES buffer solution (pH 7.54), λex = 530 nm

J Fluoresc
Fig. 6 a Brightfield images of
HeLa cells incubated with RD-1
(10 μM) for 30 min at 37 °C. b
Fluorescence microscopic images
of HeLa cells incubated with RD-
1
(10 μM). c Merged images of a
and b. d Brightfield images RD-1
pretreated HeLa cells and again
treated with 10 μM Cd(NO
3 2
) for
1
0 min. e Fluorescence
microscopic images HeLa cells
incubated with Probe RD-1 and
1
3 2
0 μM Cd(NO ) for 10 min. f
Merged images of d and e
determined from fluorometric titration data [42]. Also, the
To further explore the complexation mode, FT-IR spec-
2
+
detection limit of Cd was determined from the absorbance
titration profile as 18.5 nm based on 3σ/slope. The perfect
linearity relationship between fluorescence intensity and the
trometry was used to investigate the free ligand RD-1 and
2
+
their Cd - complex (Fig. S8). We observed a shift of the
stretching vibration frequency of the C = N bands from
2
+
−7
−1
−1
concentration of Cd in the range of 1.0 * 10 to 1.0
1613 cm and 1513 cm (free RD-1), to slightly changes
−5
−1
2
2+
−1
*
10 mol L with a correlation coefficient of R = 0.9908
RD-1+ Cd complex the C = N bands 1591 cm and
2
+
−1
was observed (Fig. 5). The LOD for Cd detection by the
probe RD-1 is sufficient to detect Cadmium ions in living cells
and biological systems.
1374 cm , the stretch vibration of the carbonyl group of
−1
2+
RD-1 is 1699 cm almost disappeared in the (RD-1+ Cd )
complex, these data indicate that the carbonyl and imines
2
+
The pH changes were investigated after the addition of
bond take part in coordination with Cd complex.
2
+
different amounts of Cd ion results indicated that the fluo-
2
+
rescence enhancement is due to the coordination of Cd ,
which induced the formation of a strongly fluorescent ring
Application in Living Cells
2
+
opened RD-1-Cd complex. The pH study clearly elaborates
We next evaluated RD-1 with HeLa cells to investigate the
potential biological application of RD-1 for fluorescence im-
aging. The cytotoxicity was evaluated by standard MTT
2
+
the applicability of the probe for sensing Cd in the physio-
logical pH range (Fig. S7).
Fig. 7 Frontier molecular
orbitals of RD-1 and RD-1 +
2
+
Cd obtained from the DFT
calculations using Gaussian 09
program

J Fluoresc
2+
Table 1 Quantification of Cd in water samples with RD-1
to the probe RD-1 (10 μM), there is no change in the emission
2
+
Sample Cd added (μgL−1) Cd found (μgL−1) Recovery (%)
2+
2+
intensity whereas Cd salts treated water samples showed a
good linear dependences of fluorescence intensity enhance-
2
+
Drinking water
ment. This result indicated that RD-1 could detect Cd in
A
0
-
-
solutions thereby confirming its potential application for
a
b
2+
B
50
100
50.01 ± 0.02
100.02
99.97
Cd analysis in water. The recovery and RSD values for the
a
b
2+
C
100.03 ± 0.03
-
addition of different concentrations of Cd ions in water sam-
Tap water
ples are given in Table 1.
A
B
C
0
-
a
b
50
100
50.04 ± 0.03
99.89
99.56
a
b
100.00 ± 0.06
-
Conclusions
River water
In conclusion, herein we report the synthesis of a new probe
RD-1 based on rhodamine dye, conjugated with
diaminomaleonitrile moiety, the colorimetric and fluorescent
A
B
C
0
-
a
b
50
50.06 ± 0.05
99.78
99.8
a
b
100
100.04 ± 0.06
2
+
recognition of Cd by RD-1 were free from the interference
of other metal ions. The chemosensor worked in aqueous so-
lution at physiological pH ions with a very low detection limit
of 18.5 nm. Further the non-toxicity of the probe makes it
a
Average of 3 measurements
Standard deviation
b
2
+
(
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
useful as an imaging agent for the detection of Cd in living
cells under physiological conditions.
mide) assay. The results indicate that the RD-1 was non-
toxic to the cells under the experimental conditions. The cells
were incubated with a 10 μM solution of RD-1 for 30 min at
7 °C in growth medium, and a very weak fluorescence was
observed (Fig. 6b). In succession, the cells were added with
Acknowledgements The Authors P.S. and K.S. great fully thanks to
financial support from University Grant Commission, New Delhi. (UGC-
MRP No. 43-186/2014 (SR)).
3
Cd(NO ) (10 μM) for 10 min at 37 °C. After the cells were
3
2
washed with 3 × 1 mL of PBS three times, an obvious fluo-
rescence response from the intracellular region was observed.
The bright field image confirmed that the cells were viable
throughout the imaging experiments and the probe RD-1
had good cell-membrane permeability, which could be used
References
1
.
.
Gunnlaugsson T, Clive Lee T, Parkesh R (2003) Cd(II) sensing in
water using novel aromatic Iminodiacetate based fluorescent
chemosensors. Org Lett 5:4065–4068
2
+
for detecting intracellular Cd (Fig. 6, Fig. S9 and Fig. S10).
2
Hutchinson TC, Meema KM (1987) Lead, mercury, Cadmium and
arsenic in the environment. Wiley, New York, pp 69–88
Density Functional Theory Studies
3. Zhang Y, Zhang Z, Yin D, Li J, Xie R, Yang W (2013) High-affinity
binding of cadmium ions by mouse Metallothionein prompting the
Design of a Reversed-Displacement Protein-Based Fluorescence
Biosensor for cadmium detection. ACS Appl Mater Interfaces 5:
To get an insight into the electronic structure and the photo
2
+
physical properties of RD-1 and RD-1+ Cd adduct, density
functional theory (DFT) calculations was carried out with the
Gaussian 09 program [43] with the B3LYP/6-311G and
LANL2DZ for cadmium ions respectively. From the opti-
mized geometries the DFT calculations were carried out using
above mentioned sets. Frontier molecular orbital’s derived
from the optimized geometries, the HOMO and LUMO of
RD-1 is localized over the whole xanthenyl ring and
diaminomaleonitrile unit, respectively, whereas in RD-1 +
9
709–9713
4. Li X, Gao X, Shi W, Ma H (2014) Design strategies for water-
soluble small molecular chromogenic and fluorogenic probes.
Chem Rev 114:590–659
5
.
De Silva AP, McCaughan B, McKinney BOF, Querol M (2003)
Newer optical-based molecular devices from older coordination
chemistry. Dalton Trans 10:1902–1913
6. Balzani V (2003) Photochemical molecular devices. Photochem
Photobiol Sci 2:459–476
7.
8.
9.
Kim HN, Ren WX, Kim JS, Yoon J (2012) Fluorescent and color-
imetric sensors for detection of lead, cadmium, and mercury ions.
Chem Soc Rev 41:3210–3244
Guo Z, Park S, Yoon J, Shin I (2014) Recent progress in the devel-
opment of near-infrared fluorescent probes for bioimaging applica-
tions. Chem Soc Rev 43:16–29
2
+
Cd the xanthenyl unit has HOMO character and the
diaminomaleonitrile unit with reasonable contribution from
2
+
Cd has LUMO character (Fig. 7 and Fig. S11).
Spichiger-Keller. U. S. (1998) Chemical sensors and biosensors for
medical and biological applications. Wiley-VCH, Weinheim
Practical Application
1
0. Zhou X, Su F, Tian Y, Youngbull C, Johnson RH, Meldrum DR
2
+
The potential utilities of RD-1 for Cd analysis in environ-
+
(2011) A new highly selective fluorescent K sensor. J Am Chem
mental water were performed. On the addition of water sample
Soc 133:18530–18533

J Fluoresc
1
1. McElroy JA, Shafer MM, Dietz AT, Hampton JM, Newcomb PA
2006) Cadmium exposure and breast cancer risk. J Natl Cancer Inst
8:869–873
2. Violaine V, Dominique L, Philippe HJ (2003) Cadmium, lung and
prostate cancer: a systematic review of recent epidemiological data.
J Toxicol Environ Health Part B 6:227–256
imaging reagent for cellular uptake in Hct 116 cells. Chem
Commun 51:3649–3652
(
9
30. Goswami S, Das S, Aich K, Sarkar D, Mondal TK, Quah CK, Fun
H-K (2013) A single colorimetric sensor for multiple target ions: the
1
2
+
2+
simultaneous detection of Fe and Cu in aqueous media. Dalton
Trans:15113–15119
1
3. WHO, Avenue Appia 20, 1211 Geneva 27, Swizerland, http://www.
who.int/water_sanitation_health/dwq/chemicals/cadmium/en/
4. Rastogi SK, Pal P, Aston DE, Bitterwolf TE, Branen AL (2011) 8-
Aminoquinoline functionalized silica nanoparticles: a fluorescent
nanosensor for detection of divalent zinc in aqueous and in yeast
cell suspension. ACS Appl Mater Interfaces 3:1731–1739
31. Hu F, Zheng B, Wang D, Liu M, Du J, Xiao D (2014) A novel dual-
switch fluorescent probe for Cr(III) ion based on PET–FRET pro-
cesses. Analyst 139:3607–3613
1
3
2. Xuan W, Cao Y, Zhou J, Wang W (2013) A FRET-based ratiometric
fluorescent and colorimetric probe for the facile detection of
organophosphonate nerve agent mimics DCP. Chem Commun 49:
1
0474–10476
1
1
1
5. Vengaian KM, Britto CD, Sivaraman G, Sekar K, Singaravadivel S
3
3. Chereddy NR, Thennarasu S, Mandal AB (2013) A highly selective
and efficient single molecular FRET based sensor for ratiometric
(
2015) Phenothiazine based sensor for naked-eye detection and
−
bioimaging of Hg (II) and F ions. RSC Adv 5:94903–94908
3
+
detection of Fe ions. Analyst 138:1334–1337
34. Kumar N, Bhalla V, Kumar M (2014) Resonance energy transfer-
6. Ponnuvel K, Kumar M, Padmini V (2016) A new quinoline-based
2+
chemosensor for Zn ions and their application in living cell im-
aging. Sensors Actuators B Chem 234:34–45
2
+
2+
2+
3+
based fluorescent probes for Hg , Cu and Fe /Fe ions.
Analyst 139:543–558
7. Vengaian KM, Britto CD, Sivaraman G, Sekar K, Singaravadivel S
3
5. Park GJ, Jo HY, Ryu KY, Kim C (2014) A new coumarin-based
(
2016) Phenothiazine-diaminomalenonitrile based colorimetric and
3+
2
+
2−
chromogenic chemosensor for the detection of dual analytes Al
fluorescence Bturn-off-on^ sensing of Hg and S . Sensors
Actuators B Chem 235:232–240
−
and F . RSC Adv 4:63882–63890
3
6. Aich K, Goswami S, Das S, Mukhopadhyay CD, Quah CK, Fun H
2015) Cd2+ Triggered the FRET BON^ A new molecular switch
1
1
2
8. Xu Y, Zhang S, Zhu W, Qian X, Duan L (2008) A highly sensitive
and selective OFF-ON fluorescent sensor for cadmium in aqueous
solution and living cell. J Am Chem Soc 130:16160–16161
9. Varnes AW, Dodson RB, Wehry EL (1972) Interactions of
transition-metal ions with photoexcited states of flavines.
Fluorescence quenching studies. J Am Chem Soc 94:946–950
0. Li P, Zhou X, Huang R, Yang L, Tang X, Dou W, Zhao Q, Liu W
(
for the ratiometric detection of Cd2+ with live-cell imaging and
bound X-ray structure. Inorg Chem 54:7309–7315
3
7. Xu L, Xu Y, Zhu W, Sun X, Xu Z, Qian X (2012) Modulating the
selectivity by switching sensing media: a bifunctional chemosensor
2
+
2+
selectivity for Cd and Pb in different aqueous solutions. RSC
2
+
Adv 2:6323–6328
(
2014) A highly fluorescent chemosensor for Zn and the recog-
2
+
2+
38. Goswami S, Aich DS, Das AK, Mannaa A, Halder S (2013) A
highly selective and sensitive probe for colorimetric and
nition research on distinguishing Zn from Cd . Dalton Trans:
06–713
7
2+
fluorogenic detection of Cd in aqueous media. Analyst 138:
2
1. Zhao Q, Li R, Xing S, Liu X, Hu T, Bu X (2011) A highly selective
on/off fluorescence sensor for cadmium (II). Inorg Chem 50:
1
903–1907
3
9. Park J, Rao BA, Son Y (2015) Bturn-on^ fluorescent and colori-
1
0041–10046
2+
metric determination of Cu ions in aqueous media based on a
2
2. Sil A, Maity A, Giri D, Patra SK (2016) A phenylene–vinylene
rhodamine-N-phenyl Semicarbazide derivative. Fibers Polym 16:
2
+
terpyridine conjugate fluorescent probe for distinguishing Cd
9
53–960
2+
from Zn with high sensitivity and selectivity. Sensors Actuators
B Chem 226:403–411
4
4
0. Shortreed M, Kopelman R, Kuhn M, Hoyland B (1996) Fluorescent
fiber-opticcalcium sensor for physiological measurements. Anal
Chem 68:1414–1418
1. Yang BX, Ge J-F, Xu Y-J, Xu Q-F, Liang J, Lu J-M (2011)
Benzo[a]phenoxazinium-based red-emitting chemosensor for zinc
ions in biological media. Org Lett 13:2710–2713
2
2
2
2
2
3. Sivaraman G, Chellappa D (2013) Rhodamine based sensor for
naked-eye detection and live cell imaging of fluoride ions. J
Mater Chem B 1:5768–5772
4. Tharmaraj V, Pitchumani K (2013) A highly selective ratiometric
fluorescent chemosensor for Cu (II) based on dansyl-functionalized
thiol stabilized silver nanoparticles. J Mater Chem B 1:1962–1967
5. Fan J, Hu M, Zhan P, Peng X (2013) Energy transfer cassettes based
on organic fluorophores: construction and applications in
ratiometric sensing. Chem Soc Rev 42:29–43
4
4
2. Valeur B (2002) Molecular Fluorescence. Principles and
Applications. Wiley-VCH, Weinheim, p 339
3. Risch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA,
Cheeseman JR, Scalmani G, Barone V, Mennucci B, Petersson
GA, Nakatsuji H, Caricato M, Li X, Hratchian HP, Izmaylov AF,
Bloino J, Zheng G, Sonnenberg JL, Hada M, Ehara M, Toyota K,
Fukuda R, Hasegawa J, Ishida M, Nakajima T, Honda Y, Kitao O,
Nakai H, Vreven T, Montgomery JA Jr, Peralta JE, Ogliaro F,
Bearpark M, Heyd JJ, Brothers E, Kudin KN, Staroverov VN,
Kobayashi R, Normand J, Raghavachari K, Rendell A, Burant
JC, Iyengar SS, Tomasi J, Cossi M, Rega N, Millam JM, Klene
M, Knox JE, Cross JB, Bakken V, Adamo C, Jaramillo J, Gomperts
R, Stratmann RE, Yazyev O, Austin AJ, Cammi R, Pomelli C,
Ochterski JW, Martin RL, Morokuma K, Zakrzewski VG, Voth
GA, Salvador P, Dannenberg JJ, Dapprich S, Daniels AD, Farkas
O, Foresman JB, Ortiz JV, Cioslowski J, Fox DJ (2009) Gaussian
09, revision a 02. Gaussian Inc, Wallingford CT
6. Sunnapu O, Kotla NG, Maddiboyina B, Singaravadivel S,
Sivaraman G (2015) A rhodamine based Bturn-on^ fluorescent
probe for Pb (II) and live cell imaging. RSC Adv 6:656–660
7. Zhou L, Zhang X, Wang Q, Lv Y, Mao G, Luo A, Wu Y, Wu Y,
Zhang J, Tan W (2014) Molecular engineering of a TBET-based
two-photon fluorescent probe for ratiometric imaging of living cells
and tissues. J Am Chem Soc 136:9838–9841
2
8. Sun S, Qiao B, Jiang N, Wang J, Zhang S, Peng X (2014)
Naphthylamine–rhodamine-based ratiometric fluorescent probe
2+
for the determination of Pd ions. Org Lett 16:1132–1135
2
9. Reddy GU, Ali F, Taye N, Chattopadhyay S, Das A (2015) A
2
+
new turn on Pd -specific fluorescence probe and its use as an