A new ICT and CHEF based visible light excitable fluorescent probe easily detects in vivo Zn2+

Article abstract of DOI:10.1039/c5ra03353e

A new chelator and ICT donor based visible light excitable Zn²⁺ sensor was designed and developed by integrating quinoline and 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde. The probe is sensitive towards Zn²⁺ in absorbance as well as in fluorescence experiments in 90% aqueous medium. The sensor demonstrates Zn²⁺-specific emission enhancement due to the ICT and CHEF process with the LOD in the range of 10^-8 M. The fluorescence quantum yield of the chemosensor is only 0.02, and it increases almost 11-fold (0.22) after complexation with Zn²⁺. Interestingly, the introduction of other metal ions causes the fluorescence intensity to remain almost unchanged. Moreover, the ability of the probe (BQ) to sense Zn²⁺ in living cells has been explored.

Full text of DOI:10.1039/c5ra03353e

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A new ICT and CHEF based visible light excitable
2
+
fluorescent probe easily detects in vivo Zn †
Cite this: RSC Adv., 2015, 5, 31189
a
a
a
Krishnendu Aich, Shyamaprosad Goswami,* Sangita Das
b
and Chitrangada Das Mukhopadhyay
2+
A new chelator and ICT donor based visible light excitable Zn sensor was designed and developed by
integrating quinoline and 2-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde. The probe is sensitive
2+
towards Zn in absorbance as well as in fluorescence experiments in 90% aqueous medium. The sensor
2+
demonstrates Zn -specific emission enhancement due to the ICT and CHEF process with the LOD in
Received 23rd February 2015
Accepted 23rd March 2015
ꢀ8
the range of 10 M. The fluorescence quantum yield of the chemosensor is only 0.02, and it increases
2+
almost 11-fold (0.22) after complexation with Zn . Interestingly, the introduction of other metal ions
DOI: 10.1039/c5ra03353e
causes the fluorescence intensity to remain almost unchanged. Moreover, the ability of the probe (BQ)
2+
www.rsc.org/advances
to sense Zn in living cells has been explored.
3
normal growth and development. It also plays crucial role for
the key cellular processes such as DNA repair and apoptosis.
Introduction
4
5
Detection and imaging of biologically relevant target molecules A deciency of zinc causes an imbalanced metabolism, which in
through uorescence in living systems has emerged as an area turn can induce retarded growth in children, brain disorders,
6
of intense interest in the chemistry–biology interface owing to high blood cholesterol and can also be implicated in various
1
2+
its signicant biomedical implications. Zn has received neurodegenerative disorders such as Alzheimer's disease,
7
considerable attention as it is the second most abundant heavy epilepsy, ischemic stroke, and infantile diarrhea. Fluorescent
2
+
2+
metal ion aer iron present in the human body with a total Zn imaging with Zn sensors has demonstrated great success
2
+
content of 2–3 g in the whole body and a concentration as high in providing temporal-spatial information of Zn homeostasis
2
8
as 10 mM in serum. It is an essential nutrient required for in live cells. Therefore, nowadays there is a huge demand for
2
+
the development of Zn chemosensors. Fluorescence spec-
troscopy is a powerful method for sensing and imaging metal
9
cations at submicromolar concentrations. In recent times, a
number of selective and sensitive imaging tools capable of
2
+
10
rapidly monitoring Zn ions have been developed. Specially
development of sensitive sensors which can distinguish the
2
+
2+
metal ions with almost similar characteristic (like Zn /Cd ,
Pb /Hg pairs which may interfere in each other detection) are
in high demand.
2
+
2+
In the context of the above objectives and in continuation of
11
our work, in here, we have synthesized a highly sensitive and
selective hydroxyquinoline based new visual and uorescent
2
+
probe BQ for Zn . We have screened its potential applications
in cell imaging and studied its cytotoxic properties. Interest-
Scheme 1 Reagents and conditions: (i) ethylchloroacetate, K
2
CO
3
, dry
2+
ingly here, Cd is found to perturb the uorescence a slight but
acetone, reflux, 12 h. (ii) NH –NH , EtOH, reflux, 2 h, (iii) 2, EtOH, reflux,
2
2
2
+
the output is different from Zn .
6
h.
Results and discussion
a
Department of Chemistry, Indian Institute of Engineering Science and Technology,
Shibpur, Howrah-711 103, India. E-mail: spgoswamical@yahoo.com
Synthesis of BQ is accomplished by reaction of the compounds
b
Centre for Healthcare Science & Technology, Indian Institute of Engineering Science
2
and 1 in ethanol under reuxing condition for 6 h (Scheme 1).
and Technology, Shibpur, Howrah-711 103, India
Compounds 1 and 2 were prepared from according to previously
reported procedure. The yield of the nal imine functionalized
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c5ra03353e
12
1
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compound obtained to be 65%. The probe (BQ) was character-
ized by NMR and HRMS studies (Fig. S9–S11, ESI†).
Sensing studies
In order to investigate the metal-binding behavior of the probe
(BQ) towards different cations, we have monitored both the
UV-visible absorption and uorescence study of BQ with
+
+
2+
2+
2+
2+
3+
2+
different cations (Na , K , Mg , Cu , Mn , Fe , Fe , Co ,
2
+
2+
2+
2+
2+
Ni , Cd , Ca , Zn and Hg as their chloride salts). All of the
titration studies of BQ were carried out in CH OH–H O (1/9, v/v, Fig. 2 Emission spectra of BQ (10 mM) in (MeOH–H O, 1/9, v/v,
3
2
2
2
+
1
mM HEPES buffer at pH ¼ 7.4) solution. The electronic pH ¼ 7.4) in presence of (a) Zn (0–1.5 equivalents) and (b) different
analytes (4 equivalents). Inset: emission colour change of BQ upon
addition of 2 equivalents of Zn after illumination under UV light.
absorption spectral behavior of BQ (10 mM) exhibited two sharp
2
+
bands at 360 and 282 nm (Fig. 1a). Upon gradual addition of
aqueous solution of Zn (0–1.5 equiv.), the bands at 360 and
lex ¼ 400 nm.
2
+
2
4
82 nm gradually decreased along with a new peak appeared at
05 nm, which readily increased with Zn concentration. This
2
+
2
+
(
I
475) exhibited a beautiful linear relationship with Zn
new peak is being attributed to internal charge transfer (ICT) of
BQ aer interaction with Zn . This spectral behavior consec-
utively showed three well-dened isosbestic points centred at
2
concentration (0 to 9 mM, Fig. S1b, ESI†) with a R value of
2
+
0
.9807.
This overall spectral behavior of uorescence enhancement
3
80 nm, 340 nm and 305 nm.
2
+
of the probe BQ aer being induced by Zn may be due to the
contribution of two mechanisms, namely ICT and CHEF
mechanism. BPQ itself exhibited a weak uorescence intensity
at 435 nm, which may be due to the occurrence of ꢀE, ꢀZ
isomerism for free rotation of the imine (–C]N) segment.
Now the introduction of Zn , this kind of (E-, Z-) isomerism
may stop and CHEF mechanism may came into play, which
ultimately formed a stable chelate complex between the cation
Zn ) and the probe BQ. The addition of Zn eventually made
the system more rigid (Scheme 2) and revealed a fabulous
increment in emission prole. The formation of 1 : 1 complex-
ation with Zn was conrmed by Job's plot (Fig. S6†) and HRMS
data, it shows peaks at m/z 451.0923, which may be due to the
Furthermore, BQ exhibits a good linear relationship of
2
+
absorbance ratio (A405/A282) with added Zn concentration (0 to
9
further supported by the association constant determined from
Benesi–Hildebrand plot by using UV-vis data and it was found
2
+
mM, Fig. S2, ESI†). The strong binding of Zn with BQ was
13
2
+
5
ꢀ1
to be 5.77 ꢁ 10 M (Fig. S4, ESI†). Notably, the addition of
other metal cations did not perturb the initial absorption
2
+
spectrum of the chemosensor signicantly (except Cu , in here
a slight change was noticed). From these UV-vis spectral studies,
it is obvious that the probe BQ revealed a very high affinity
towards Zn in the ground state.
The uorescence spectrum of the probe BQ (10 mM) exhibi-
ted a weak emission band centered at 435 nm in CH OH–H O
2
+
2+
(
2
+
2
+
3
2
2+
formation of BQ–Zn complex species.
solution (1/9, v/v, 1 mM HEPES buffer at pH ¼ 7.4) upon exci-
Now selectivity and specicity are the two very important
factors in order to evaluate the efficiency of any probe. So to
prove the selectivity of the probe BQ toward Zn ions, we
carried out the uorescence titration experiment of BQ in
presence of other above mentioned cations. It was found that
the probe was prone to Zn only (selective enhancement of
emission at 475 nm) and this affinity was very much prominent
even in the presence of other guest metal ions (Fig. S7, ESI†).
Thus all these experiments established that the probe BQ
2
+
tation at 400 nm. On incremental addition of Zn (0–1.5 equiv.)
to the solution of the probe BQ, the uorescence emission
exhibited an enhancement along with a red shi from 435 nm
to 475 nm. This dramatic red shi (ꢂ40 nm) of the uorescence
2
+
2
+
of BQ aer introduction of Zn was attributed to the internal
2
+
charge transfer (ICT). In addition, the emission band at 475 nm
2
+
signicantly enhanced aer incremental addition of Zn
Fig. 2a). During the course of titration the intensity at 475 nm
(
2
+
showed a major response only towards Zn and it can detect
exclusively Zn at 475 nm without any noticeable interference.
2
+
In the uorescence titration experiment of BQ, a different
3 2
Fig. 1 UV-vis spectra of BQ (10 mM) in CH OH–H O solution (1/9, v/v,
2+
pH ¼ 7.4) in presence of (a) Zn (0–1.5 equivalents) and (b) different
2+
analytes (3 equivalents).
Scheme 2 Probable binding mode of BQ with Zn .
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2
+
interference was noticed with Cd , it showed a slight change in
emission at 465 nm but no interference at 475 nm. From this

uorescence experiment it was demonstrated that, the probe
BQ was capable to detect back to back two of very similar cations
2
+
with two different outputs (for Zn it is a strong peak at 475 nm
2
+
and for Cd a weak peak at 465 nm). To determine the limit of
2
+
detection i.e. how lower concentration of Zn can be deter-
mined by the probe (BQ), we recorded the uorescence data
3 2
using 10 mM solution (CH OH–H O, 1/9, v/v, 1 mM HEPES
buffer, pH ¼ 7.4) of BQ (Fig. S1b, ESI†). The detection limit of
2
+
ꢀ8
BQ for Zn was determined to be 2.35 ꢁ 10 M, using the
equation DL ¼ K ꢁ Sb /S, where K ¼ 3, Sb is the standard
1
1
deviation of the blank solution and S is the slope of the cali-
bration curve (Fig. S1, ESI†).
14
pH study
In order to examine the pH sensitivity of our probe BQ, we
examined the acid–base titration experiment. From the titration
Fig. 3 It represents % cell viability of HCT cells treated with different
concentrations (10 mM to 50 mM) of BQ for 12 h determined by MTT
study it was observed that BQ does not undergo any noticeable assay. Results are expressed as mean of three independent
experiments.
change in the uorescence prole within the pH range from
2–8. But in strong basic conditions (pH > 9), deprotonation of
the phenolic group causes the coloration along with strong
green uorescence (Fig. S8a, ESI†). Thus BQ can be employed either probe compound (10 mM) or ZnCl
(20 mM) alone (Fig. 4,
2
2
+
for the detection of Zn in near-neutral pH range (pH ¼ 7.4). panel a & b).
2
+
The pH sensitivity of BQ in presence of Zn was also studied.
The results revealed that in strong acidic pH (<3) and in strong striking green uorescence was observed inside RAW cells,
2
Upon incubation with ZnCl followed by probe compound a
2
+
2+
basic pH (>10) detection of Zn was a little bit hampered. But in which indicated the formation of probe–Zn complex, as
the pH range of 3 to 9, BQ can detect Zn with no such inter- observed earlier in solution studies. Further, an intense green
2
+
ference (Fig. S8b, ESI†).
uorescence was conspicuous in the perinuclear region of RAW
cells (Fig. 4, panel b) which indicates that the probe can pene-
2
+
trate cell membrane easily and can be used to detect Zn in
cells. The uorescence microscopic analysis strongly suggested
that probe could readily cross the membrane barrier, permeate
Live-cell imaging study
Cell viability assay. Considerations of the practical applica-
tion of thermodynamic favourable binding properties of BQ
2
+
with Zn led to the further examination of the ability of the
2
+
probe (BQ) to sense Zn in the living cells. In order to full this
objective it is important to determine the cytotoxic effect of BQ
2
+
and Zn and the complex on live cells. The well-established
MTT assay, which is based on mitochondrial dehydrogenase
activity of viable cells, was adopted to study cytotoxicity of above
mentioned compounds at varying concentrations mentioned in
method section. Fig. 3 shows that probe compound did not
exert any adverse effect on cell viability; same is the case when
2
cells were treated with varying concentrations of ZnCl .
2
+
However, exposure of HCT cells to probe–Zn complex resulted
in a decline in cell viability above 20 mM concentration.
The effect was more pronounced in higher concentration
and showed an adverse cytotoxic effect in a dose-dependent
manner. The viability of HCT cells was not inuenced by the
solvent (DMSO) as evidenced in Fig. 3, leading to the conclusion
that the observed cytotoxic effect could be attributed to probe–
2
+
Zn complex. The results obtained in the in vitro cytotoxic assay Fig. 4 Confocal microscopic images of probe in RAW 264.7 cells
ꢀ
5
pretreated with ZnCl
2
: (a) ZnCl
2
treatment only at 2.0 ꢁ 10
M
suggested that, in order to pursue uorescence imaging studies
ꢀ
1
2
+
concentration, nuclei counterstained with DAPI (1 mg mL ),
of probe–Zn complex in live cells, it would be prudent to
choose a working concentration of 10 mM for probe compound.
Imaging of cells. Fluorescence microscopic studies revealed
ꢀ
5
(
(
b) treatment a followed by probe BQ at concentration 1.0 ꢁ 10 M,
c) bright field image of the cells after treatment (d) overlay image in
dark field. All images were acquired with a 60ꢁ objective lens with a
a lack of uorescence for RAW cells when treated with scale bar of 10 mm. lex ¼ 400 nm.
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2
+
into RAW cells, and rapidly sense intracellular Zn . It is where, x & s indicate the unknown and standard solutions
signicant to mention here that bright eld images of treated respectively, F is the quantum yield, I is the integrated area
cells did not reveal any gross morphological changes, which under the uorescence spectra, A is the absorbance and n is the
suggested that RAW cells were viable. These ndings open up refractive index of the solvent.
the avenue for future in vivo biomedical applications of the
probe to image intracellular Zn .
Synthetic method for the preparation of the probe. To the
stirred solution of compound 2 (0.25 g, 1.15 mmol) in ethanol,
2
+
2
1
6
-hydroxy-3-(hydroxymethyl)-5-methylbenzaldehyde (0.2 g,
.20 mmol) was added and the reaction mixture was reuxed for
hours. Aer ensuring that the reactants were fully consumed,
Experimental
General
by checking TLC, the reaction mixture was allowed to cool to
room temperature. A white precipitate appeared which was
Unless otherwise mentioned, materials were obtained from
commercial suppliers and were used without further purica-
tion. Thin layer chromatography (TLC) was carried out using
Merck 60 F254 plates with a thickness of 0.25 mm. Melting
points were determined on a hot-plate melting point apparatus

ltered, washed with cold ethanol (1 mL ꢁ 2) and dried in air.
Yield ¼ (0.27 g) 65%.
1
6
H NMR (400 MHz, d -DMSO): d 2.24 (s, 3H), 4.52 (s, 2H),
4
.59 (s, 2H), 7.14 (s, 1H), 7.21 (t, J ¼ 7.8 Hz, 1H), 7.30 (d, J ¼ 8 Hz,
1
1H), 7.56 (m, 3H), 8.38 (dd, 1H), 8.46 (s, 1H), 8.96 (dd, 1H), 11.44
(s, 1H), 12.33 (s, 1H).
in an open-mouth capillary and are uncorrected. H and
1
3
C NMR spectra were recorded on JEOL 400 MHz and 125 MHz
1
3
6
C NMR (125 MHz, d
16.6, 121.3, 122.0, 127.2, 127.5, 128.9, 129.2, 129.4, 130.1,
131.9, 135.4, 148.5, 150.2, 152.4, 152.8, 164.0.
6
-DMSO): d 20.0, 57.5, 68.7, 112.9,
instruments respectively. For NMR spectra, CDCl
DMSO were used as solvents using TMS as an internal standard.
3
and d -
1
1
1
1
Chemical shis are expressed in d units and H– H and H–C
coupling constants in Hz. UV-vis spectra were recorded on a
JASCO V-630 spectrometer. Fluorescence spectra were recorded
on a Perkin Elmer LS 55 uorescence spectrometer. IR spectra
were recorded on a JASCO FT/IR-460 plus spectrometer, using
KBr discs. For the titration experiment, we use the cations viz.
+
HRMS (ESI, positive): calcd. for C20
H
19
N
3
NaO
4
[M + Na]
(
m/z): 388.1273; found: 388.1275.
2
+
2+
Synthesis of Zn complex (BQ–Zn ) of receptor. The
receptor, BQ (40 mg) and ZnCl (10 mg) were mixed together
2
and dissolved in 5 mL of methanol. Aer reux for 12 hours the
reaction mixture was cooled to room temperature. A reddish-
yellow coloured precipitate appeared which was ltered and
dried in vacuum.
+
+
2+
2+
2+
2+
3+
2+
2+
2+
2+
[
Na , K , Mg , Cu , Mn , Fe , Fe , Co , Ni , Ca , Cd ,
2
+
2+
Zn and Hg as their chloride salts.
2
+
HRMS (ESI, positive): calcd. for C20
Na + H ] (m/z): 451.0476; found: 451.0923.
H
18ZnN
3
NaO
4
[M + Zn
+
+
+ +
General method of UV-vis and uorescence titration
UV-vis method. For UV-vis titrations, stock solution of the
receptor (10 mM) was prepared in [(CH OH–water), 1/9, v/v]
3
Details of live-cell imaging
ꢃ
(at 25 C) using 1 mM HEPES buffered pH 7.4 solution. The
Materials methods. Frozen Human colorectal carcinoma cell
lines HCT 116 (ATCC: CCL-247) were obtained from the Amer-
ican Type Culture Collection (Rockville, MD, USA) and main-
tained in Dulbecco's modied Eagle's medium (DMEM, Sigma
Chemical Co., St. Louis, MO, USA) supplemented with 10% fetal
solutions of the guest cations using their chloride salts in the
ꢀ
5
order of 1 ꢁ 10 M, were prepared in deionized water using
HEPES buffer at pH ¼ 7.4. Solutions of various concentrations
containing the sensor and increasing concentrations of cations
were prepared separately. The spectra of these solutions were
recorded by means of UV-vis method.
ꢀ
1
bovine serum (Invitrogen), penicillin (100 mg mL ), and
ꢀ
1
streptomycin (100 mg mL ). The RAW 264.7 macrophages were
Fluorescence method. For uorescence titrations, stock
solution of the sensor (10 mM) used was the same as that used
for UV-vis titration. The solutions of the guest cations using
obtained from NCCS, Pune, India and maintained in DMEM
containing 10% (v/v) fetal calf serum and antibiotics in a CO
2
2
ꢀ5
incubator. Cells were initially propagated in 25 cm tissue
their chloride salts in the order of 1 ꢁ 10 M, were prepared
same as stated in UV-vis experiment. Solutions of various
concentrations containing sensor and increasing concentra-
tions of cations were prepared separately. The spectra of these
solutions were recorded by means of uorescence method.
Determination of uorescence quantum yield. To determine
ꢃ
culture ask in an atmosphere of 5% CO
humidied air till 70–80% conuency.
2
and 95% air at 37 C
Fluorescent imaging studies. For uorescent imaging
3
studies, RAW cells, 7.5 ꢁ 10 cells in 150 mL media were seeded
on sterile 12 mm diameter poly-l-lysine coated cover-slip and
2
+
kept in a sterile 35 mm covered Petri dish and incubated at
the quantum yields of BQ and BQ–Zn , we recorded their
absorbance in methanol solution. The emission spectra were
recorded using the maximal excitation wavelengths, and the
integrated areas of the uorescence-corrected spectra were
measured. The quantum yields were then calculated by
ꢃ
37
C in a CO
2
incubator for 24–30 h. Next day cells were
washed three times with phosphate buffered saline (pH 7.4)
and xed using 4% paraformaldehyde in PBS (pH 7.4) for
10 minutes at room temperature washed with PBS followed by
permeabilization using 0.1% saponin for 10 minutes. Then the
comparison with uorescein (F
reference using the following equation:
s
¼ 0.97 in basic ethanol) as
ꢀ
5
cells were incubated with 2.0 ꢁ 10 M ZnCl2 dissolved in
ꢃ
1
00 mL DMEM at 37 C for 1 h in a CO
2
incubator and observed
2
)
F
x
¼ F
s
ꢁ (I
x
/I
s
) ꢁ (A
s
/A
x
) ꢁ (n /n
x s
under 60ꢁ magnication of Andor spinning disc confocal
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microscope. The cells were again washed thrice with PBS
Acknowledgements
(
pH 7.4) to remove any free metal and incubated in DMEM
ꢀ5
containing probe (BQ) to a nal concentration of 1.0 ꢁ 10
M
Authors thank the CSIR and DST, Govt. of India for nancial
followed by washing with PBS (pH 7.4) three times to remove supports. K.A and S.D acknowledge CSIR for providing them
excess probe outside the cells. Again, images were acquired. fellowships.
Before uorescent imaging all the solutions were aspirated out
and cover slips containing cells were mounted on slides in a
Notes and references
0
mounting medium containing DAPI, (4 ,6-diamidino-2-
ꢀ1
phenylindole) in 1 mg mL concentration. DAPI is a popular
nuclear counterstain used in multicolor uorescent imaging of
cells. It preferentially stains dsDNA and its blue uorescence
stands out in contrast to green, yellow, or red uorescent
probes of other structures with little or no cytoplasmic label-
ling. Finally the slides were stored in dark before microscopic
images are acquired.
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Cytotoxicity assay. The cytotoxic effects of probe, ZnCl
2
and
probe–ZnCl complex were determined by an MTT assay
2
following the manufacturer's instruction (MTT 2003, Sigma-
4 (a) E. Ho and B. N. Ames, Proc. Natl. Acad. Sci. U. S. A., 2002,
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4
(
approximately 10 cells per well) for 24 h. Next day media was
removed and various concentrations of probe, ZnCl
2
and probe–
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2
were added to the cells and incubated for 24 h. Solvent control
samples (cells treated with DMSO in DMEM), no cells and cells
in DMEM without any treatment were also included in the
study. Following incubation, the growth media were removed,
and fresh DMEM containing MTT solution was added. The plate
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G. Sivaraman, A. Mahesh and D. Chellappa, Anal. Chim.
Acta, 2015, 853, 596; (f) G. Sivaraman, B. Vidya and
D. Chellappa, RSC Adv., 2014, 4, 30828; (g) L. E. Santos-
Figueroa, M. E. Moragues, E. Climent, A. Agostini,
R. Mart ´ı nez-M ´a n˜ ez and F. Sancen ´o n, Chem. Soc. Rev., 2013,
42, 3489; (h) S. Lee, K. K. Y. Yuen, K. A. Jolliffe and J. Yoon,
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P. Koutnik, T. Minami, L. Mosca, V. M. Lynch,
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ꢃ
was incubated for 3–4 h at 37 C. Subsequently, the supernatant
was removed, the insoluble colored formazan product was
solubilized in DMSO, and its absorbance was measured in a
microtiter plate reader (Perkin-Elmer) at 570 nm. The assay was
performed in triplicate for each concentration of probe, ZnCl
and probe–CdCl complex. The OD value of wells containing
2
2
only DMEM medium was subtracted from all readings to get rid
of the background inuence. Data analysis and calculation of
standard deviation were performed with Microso Excel 2007
(Microso Corporation).
Conclusions
In summary, a new quinoline based probe BQ was synthe-
sized, which is an excellent uorescent sensor for detection of
2
+
Zn . This phenomenon was observed due to the ICT-CHEF
2
+
mechanism only aer introduction of Zn in BQ solution.
2
+
Zn exhibits a tremendous increment in uorescence inten-
2
+
sity at 475 nm only aer introduction of Zn in BQ solution.
The photophysical study shows that the probe forms 1 : 1
2
+
complex with Zn . It produces a remarkably high selectivity
2
+
+
toward Zn ion over other competitive cations, such as Na ,
+
2+
2+
2+
2+
3+
2+
2+
2+
K , Mg , Cu , Mn , Fe , Fe , Co , Ni and Hg . The twist
is in the uorescence spectra with Cd which shows uores-
2
+
cence intensity at 465 nm. Most importantly, a discrimination
2
+
2+
of two metal ions (Zn and Cd ) of almost similar charac- 10 (a) K. R. Gee, Z. L. Zhou, W. J. Qian and R. Kennedy, J. Am.
teristic can be achieved by the probe in hand. The detection
Chem. Soc., 2002, 124, 776; (b) E. J. Song, J. Kang,
G. R. You, G. J. Park, Y. Kim, S.-J. Kim, C. Kim and
R. G. Harrison, Dalton Trans., 2013, 42, 15514; (c)
G. K. Tsikalas, P. Lazarou, E. Klontzas, S. A. Pergantis,
ꢀ8
limit was found to be in 10 M range. Moreover the probe BQ
2
+
could be a suitable platform for Zn imaging in biological
system.
This journal is © The Royal Society of Chemistry 2015
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