Ratiometric fluorescence In3+ sensing via In3+-triggered tautomerization: Its applications to water samples, live cells and zebrafish

Article abstract of DOI:10.1016/j.dyepig.2020.108704

A novel ratiometric fluorescence sensor NCS ((E)-N-(furan-2-ylmethyl)-2-(2-hydroxybenzylidene)hydrazine-1-carbothioamide) was synthesized by a combination of furfuryl isothiocyanate bearing hydrazine and salicylaldehyde. Sensor NCS exhibited a ratiometric fluorescent response toward In³⁺ via thioamide tautomerization with blue-shifted emission from 484 to 444 nm in a near-perfect aqueous solution. NCS displayed a linear ratiometric relationship to micromolar concentrations (0–60 μM) of In³⁺ and the detection limit was found to be 2.68 μM. Moreover, sensor NCS exhibited an excellent selectivity for sensing In³⁺ in real samples as well as live cell and zebrafish. The sensing mechanism was demonstrated through UV–visible, fluorescent and ¹H NMR titrations, Job's plot, ESI-MS and theoretical calculations.

Full text of DOI:10.1016/j.dyepig.2020.108704

Dyes and Pigments 183 (2020) 108704
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: http://www.elsevier.com/locate/dyepig
Ratiometric fluorescence In3 sensing via In -triggered tautomerization:
+
3+
Its applications to water samples, live cells and zebrafish
a
a
a,
***
b
b,
**
c
Dongju Yun , Ju Byeong Chae , Haeri So
, Trinh N. Do , Ki-Tae Kim
, Yelim Yi ,
c
a,*
Mi Hee Lim , Cheal Kim
a
Department of Fine Chem., Seoul National Univ. of Science and Tech., Seoul, 139-740, Republic of Korea
Department of Environ. Engineering, Seoul National Univ. of Science and Tech., Seoul, 02811, Republic of Korea
Department of Chem, KAIST, Daejeon, 34241, Republic of Korea
b
c
A R T I C L E I N F O
A B S T R A C T
Keywords:
A novel ratiometric fluorescence sensor NCS ((E)-N-(furan-2-ylmethyl)-2-(2-hydroxybenzylidene)hydrazine-1-
Indium
carbothioamide) was synthesized by a combination of furfuryl isothiocyanate bearing hydrazine and salicy-
Ratiometric
3+
laldehyde. Sensor NCS exhibited a ratiometric fluorescent response toward In via thioamide tautomerization
Fluorescence chemosensor
Tautomerization
Calculations
with blue-shifted emission from 484 to 444 nm in a near-perfect aqueous solution. NCS displayed a linear
ratiometric relationship to micromolar concentrations (0–60
.68
μ
M) of In3 and the detection limit was found to be
+
3
+
2
μ
M. Moreover, sensor NCS exhibited an excellent selectivity for sensing In in real samples as well as live
Bioimaging
1
cell and zebrafish. The sensing mechanism was demonstrated through UV–visible, fluorescent and H NMR ti-
trations, Job’s plot, ESI-MS and theoretical calculations.
1
. Introduction
detection offers the possibility of monitoring analytes in living systems
[
25]. Nevertheless, there are no reports on fluorescence chemosensor for
3
+
Indium, a post-transition metal of group 13, is widely utilized in
In working at neutral pH in a near-perfect aqueous solution, to date. In
3
+
industrial products, semiconductors and solar cells [1,2]. Especially,
most of indium are consumed for the production of indium tin oxide
film, which in turn is employed for the production of LCD for electronic
gadgets like laptops, PC monitors, TV screens, and mobile phones [3–6].
On the other hand, recent reports suggest that compounds containing
indium are considered as carcinogenic, teratogenic and embryotoxic
materials to living organisms, though their biological functions are not
known to the human body [7,8]. Therefore, it is needed to develop in-
dium sensors, which are able to elucidate the biological role of indium in
living systems [9].
addition, no chemosensor can sense In in living organisms such as
zebrafish [7,9,17,21,26–30]. Therefore, it is highly demanding for the
development of fluorescent probes for indium ion in neutral aqueous
solution and living organisms such as zebrafish.
Among various fluorescence probes developed, ratiometric probes
are more attractive. Unlike the single-emission detection method,
ratiometric detection, which uses two different wavelengths, is less
affected by environmental factors like pH and temperature and can be
used efficiently in bioimaging studies. Thus, it helps to get more accurate
data not only in solution but also in living organisms. Therefore, it is
highly recommended to develop ratiometric probes for detecting ana-
lytes [31–37].
Furfuryl isothiocyanate bearing hydrazine could be used as both a
fluorescent signaling agent and a binding site for chelating metal ions
[38–43]. The salicylaldehyde group is water-soluble and has the ability
to strongly chelate with metal ions, displaying various optical responses
according to the type of metal ions [44,45]. Hence, we expected that a
To detect trace metal ions, several traditional methods have been
conventionally used, such as ICP-MS, electrochemistry, chromatography
and AAS [10–14]. However, the methods need expensive instruments,
sample pre-treatment and complicated procedures [15,16]. Compared
to these methods, fluorescence spectrometry is convenient for the
sensing of trace metal ions due to cheap instrumentation, easy usage,
fast response and low detection limit [17–24]. Moreover, fluorescence
*
Corresponding author.
*
*
* Corresponding author.
** Corresponding author.
E-mail addresses: ktkim@snut.ac.kr (K.-T. Kim), chealkim@snut.ac.kr (C. Kim).
https://doi.org/10.1016/j.dyepig.2020.108704
Received 2 May 2020; Received in revised form 7 July 2020; Accepted 8 July 2020
Available online 1 August 2020
0
143-7208/© 2020 Elsevier Ltd. All rights reserved.

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
novel sensor produced from the combination of furfuryl isothiocyanate
bearing hydrazine and salicylaldehyde may have a great water solubility
and induce unique optical changes to specific metal ions.
(
)
2
A
A
S
t
× F
t
n
t
Φ
Ft
=
​
Φ
FS
​
×
×
× F
S
n
S
Herein, we represent a ratiometric fluorescence probe NCS for
sensing In3 in aqueous media. Interestingly, NCS displayed a sensitive
+
Φ = fluorescence quantum yield
F
fluorescence response to In3 in real water samples and biological sys-
+
A = absorbance
tems. To date, NCS is the sole fluorescent sensor capable of monitoring
F = integrated fluorescence emission
n = refractive index of the solution
t = test sample
3
+
In in biological systems. The sensing mechanism for the detection of
3
+
In was demonstrated by the variant spectroscopic and theoretical
studies.
S = standard material
2
. Experimental
.1. Chemicals and instrument
All chemicals were obtained commercially. H and 13C NMR spectra
2
.6. pH effect
A series of buffers were provided by adding KOH and HCl in the bis-
2
tris buffer (pH 6 and 7) and the Tris-HCl buffer (pH 8 and 9), respec-
1
ꢀ 3
tively. 12.0
μ
L (5 × 10 M) of the stock NCS was added to 2.987 mL of
were provided on a Varian spectrometer (400/100 MHz). ESI-MS spectra
were produced on a Waters SQD quadrupole machine. UV–vis and
fluorescence spectra were provided with PerkinElmer (Lambda 2S) and
fluorescence (LS45) spectrometers, respectively.
3+
each buffer to give 20
μ
M 216
μ
L of the stock In was transferred to
each quartz cuvette prepared above. With the shaking of the solutions
for 3 s, their fluorescence spectra were collected.
2
.7. 1H NMR titrations
2
.2. Synthesis of NCS, (E)-N-(furan-2-ylmethyl)-2-(2-
ꢀ
3
hydroxybenzylidene)hydrazine-1-carbothioamide
Four NMR glass tubes containing NCS (1.5 × 10 mmol) dissolved
in deuterated-DMSO (500 L) were prepared. Various equivalents (0, 1,
3 and 7) of In(NO dissolved in deuterated-DMF were put into four
NMR tubes, respectively. Their H NMR spectra were obtained after 30 s.
μ
ꢀ 3
Hydrazine (1 × 10 mol) and 2-(isothiocyanatomethyl)furan (1 ×
3 3
)
ꢀ 3
1
1
0
mol) were dissolved to 5 mL of methanol and the mixture was
ꢀ 3
shaken for 5 h. Then, 2-hydroxybenzaldehyde (1 × 10 mol) was added
drop by drop to the above mixture. With stirring for 8 h, ivory precipi-
tation was produced. It was filtered and rinsed with hexane (yield: 84%,
2.8. Determination of In3
+
◦
1
3+
m.p.: 117–119 C). H NMR in deuterated-DMSO, ppm: δ 11.49 (s, 1H),
Fluorescence analysis toward In in real water samples was carried
2
9
7
7
2
1
1
.85 (s, 1H), 8.78z (t, J = 6.1 Hz, 1H), 8.40 (s, 1H), 7.90–7.92 (m, 1H),
.56–7.57 (m, 1H), 7.19–7.24 (m, 1H), 6.86–6.88 (m, 1H), 6.83 (t, J =
.2 Hz, 1H), 6.39–6.40 (m, 1H), 6.28–6.30 (m, 1H), 4.81 (d, J = 6.0 Hz,
out by adding 12
2
μL (0.5 mmol/L) of the stock NCS and 3 × 10 μL (1 ×
10 mmol/L) of buffer to 2.687 mL samples. With the shaking of the
solutions for 3 s, their fluorescent spectra were collected.
1
3
H); C NMR in deuterated-DMSO, ppm: δ 177.1 (1C), 156.4 (1C),
52.3 (1C), 141.9 (1C), 139.5 (1C), 131.2 (1C), 126.7 (1C), 120.4 (1C),
2
.9. Imaging tests in live cells
19.2 (1C), 116.1 (1C), 110.5 (1C), 107.2 (1C), 40.3 (1C). ESI-MS: (NCS
+
+
H ): calcd, 276.08 (m/z); found, 276.00. Elemental analysis: calcd
HeLa cells grew under the previous conditions [47]. Then, the cells
(
%) for C13
H
13
3
N O
2
S: C, 56.71; H, 4.76; N, 15.26; S, 11.64; found (%): C,
ꢀ 6
rinsed with buffer (1 mL) were treated with NCS (5 × 10 M) and In
5
6.34; H, 4.78; N, 15.21; S, 11.60.
(
NO
3
)
3
(250 and 500 M). After incubation for 10 min, fluorescence
μ
imaging was conducted with a fluorescence microscope [λex = 357
(
±20) nm; λem = 447 (±28) nm].
2
.3. Fluorescent and UV–vis spectral experiments
+
ꢀ
2
2
.10. Visualization of In3 in zebrafish
All experiments were executed in bis-tris buffer (1 × 10 M, pH 7).
ꢀ 3
NCS stock solution (5 × 10 M) was prepared in dimethylsulfoxide and
ꢀ 2
For the fluorescence imaging in zebrafish, 6-day-old zebrafish were
In(NO
3
)
3
stock solution (2 × 10 M) was prepared in bis-tris buffer. The
M. Fluorescent and
incubated under the previous conditions [48]. In the control group, the
medium was replaced with prepared medium containing NCS (5 M)
concentrations of NCS were adjusted to be 20
μ
μ
UV–vis spectral changes were collected by adding the corresponding
concentrations of In3 to the NCS solution.
+
and the zebrafish were incubated for additional 15 min. After the
zebrafish were rinsed with E2 medium, fluorescence imaging was
collected. For the positive control group, the above NCS-treated zebra-
2
.4. Job’s plot
3+
ꢀ 5
ꢀ 5
fish were treated with In (1 × 10 and 2 × 10
μ
M) for 15 min in E2
medium. The zebrafish were rinsed with E2 medium and then subjected
to fluorescence imaging. All of them were anesthetized by
2
ꢀ 3
ꢀ
2
× 10
μ
L (5 × 10 M) of the stock NCS was diluted to 19.80 mL of
5
buffer to give 5 × 10
M. 300–2700
μ
L of the diluted NCS were
ꢀ 2
ethyl-3-aminobenzoate methanesulfonate (1 × 10 %) before fluores-
transferred to quartz cuvettes. To give the same concentration, 0.05 mL
cent imaging. Fluorescence images were provided on a microscope and
the mean fluorescence intensity was determined by using Icy software.
ꢀ 2
3+
(
2 × 10 M) of the stock In was diluted to 19.95 mL of bis-tris buffer.
+
3
00–2700
μ
L of the diluted In3 were added to each NCS. Each cuvette
was massed up to 3 mL. With the shaking of the solutions for 3 s, their
fluorescence spectra were collected.
2
.11. Cytotoxicity test of NCS
The cytotoxicity of NCS in zebrafish was evaluated by using acridine
2
.5. Quantum yields
orange (AO) staining which can detect apoptotic cells under a fluores-
cence microscope. The 6-day-old zebrafish were prepared and treated
Quantum yields of NCS and NCS-In3 were determined by using
quinine (Φ = 0.54 in 100 mM H SO solution) as a standard fluorophore
46]. Quantum yields were provided with the following equation [29].
+
with 0 and 5
zebrafish were rinsed with E2 medium then followed by incubation in
10 g/mL AO for 1 h. They were rinsed with E2 medium three times and
μ
M of NCS in E2 medium for 15 min, respectively. The
2
4
[
μ
2

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
fluorescence images were taken by using a fluorescence microscope.
2
.12. Calculations
DFT/TD-DFT studies were conducted for establishing the ground-
state forms of NCS and NCS-In3 and their sensing mechanism was
studied by using Gaussian 09 software [49]. B3LYP [50,51] was selected
as hybrid functional and the basis set was 6–31G(d,p) [52,53]. The
+
optimized forms of NCS and NCS-In3 showed local minima since no
imaginary frequencies were shown. The solvent effect for water was
considered with the polarization continuum model (CPCM) [54,55]. The
electronic properties of all structures were studied by using TD-DFT with
considering the thirty lowest singlet states.
+
3
. Results and discussion
Probe NCS was easily synthesized from the combination of furfuryl
isothiocyanate bearing hydrazine and salicylaldehyde (Scheme 1). The
structure of NCS was confirmed by 1H and C NMR, ESI-MS (Fig. S1)
and elemental analysis.
13
ꢀ 5
Fig. 1. Fluorescent variations of NCS (2 × 10
(72 equiv.).
M) with diverse cations
3
.1. Spectroscopic studies of NCS to In3
+
For the purpose of evaluating selectivity of sensor NCS to In3 , the
+
fluorescence spectral change of NCS upon addition of competing cations
3
+
2+
3+
+
2+
+
2+
3+
2+
2+
2+
3+
2+
like In , Zn , Al , Cu , Ca , Cr , Mg , Cd , Ni , Fe , Fe ,
2
+
3+
2+
2+
Mn , Ga , Co , K , Na and Pb was investigated (Fig. 1; λex = 345
nm). NCS exhibited cyan fluorescence at 484 nm. A highly selective
fluorescent ratiometric response was observed on the addition of In3
+
,
while most of the other cations showed no significant changes. With the
addition of In3 , the fluorescence emission of NCS shifted from 484 to
+
4
44 nm with significant intensity increase in a few seconds, and the
2
+
2+
3+
2+
fluorescence color changed from cyan to blue. Fe , Cu
,
Fe , Ni
and Co2 induced turn-off in fluorescence, and Zn did a slight blue
shift from 484 to 444 nm. In addition, NCS showed no fluorescent
response to a variety of anions (Fig. S2). These results demonstrated that
+
2+
NCS can operate as a highly effective ratiometric probe for In3 . In
particular, NCS is the first chemosensor that can selectively detect In3
+
+
at neutral pH in a near-perfect aqueous media (Table S1). Importantly,
3
+
3+
3+
NCS can distinguish In from Al and Ga even though it is a huge
ꢀ
5
3+
challenge to distinguish them due to their similar properties.
Fig. 2. Fluorescent variations of NCS (2 × 10 M) with In (0–76 equiv.).
444 484
3
+
To investigate the photophysical properties of NCS and In3 , fluo-
+
Inset: Plot of the emission ratios (I /I ) with respect to In equivalence.
rescence and UV–vis spectral changes were examined. On addition of
3
+
3+
In (0–76 equiv.) to NCS, the fluorescence intensity gradually dimin-
I
444/I484, which indicates that NCS-In complex has a 1:1 stoichiom-
ished at 484 nm and increased at 444 nm in a ratiometric manner
etry. To provide further evidence for the 1:1 binding mechanism, ESI-MS
analysis was performed (Fig. S4). The mass spectrum indicated that the
peaks of 544.13 and 622.15 (m/z) can be assigned as NCS-
(
Fig. 2). The emission intensity ratio (I444/I484) increased progressively
3
+
as the concentration of In increased. Quantum yields of NCS and NCS-
3
+
+
3+
+
3+
In turned out to be 0.075 and 0.41, respectively. The UV–vis spectral
changes exhibited that the absorbance band around 270–350 nm grad-
ually diminished and the band at 400 nm increased, upon addition of
2H +In +2DMSO [calcd, m/z = 543.99] and NCS-2H +In +3DMSO
1
[calcd, m/z = 622.00]. H NMR titrations were performed to further
support the binding process of NCS with In3 (Fig. 4). Hydroxyl proton,
+
3
+
In (0–50 equiv.) (Fig. 3). One isosbestic point was observed at 356 nm,
suggesting the production of a species from the combination of NCS and
1 7
H (9.9 ppm) and amide proton, H (11.5 ppm) gradually disappeared
3
+
upon the addition of In . On the other hand, the rest protons of H
2
to H
9
3
+
3+
In
.
showed interesting changes. As the amount of In increased, the peaks
were gradually reduced and simultaneously appeared at different ppm.
The result is different from the previously reported sensors which
Job’s plot analysis was conducted for studying the complexation
ratio of NCS with In3 (Fig. S3). It exhibited the highest value at 0.5 of
+
Scheme 1. Synthesis of NCS.
3

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
3
+
2+
2+
3+
affect the fluorescent response of NCS to In except Cu , Fe , Fe
and Cr3 . The four metal ions interfered 20–35% of the fluorescent
emission, but the fluorescence was still discernible. These results
+
implied that NCS could selectively detect In3 by a ratiometric fluo-
rescence response with diverse cations. We also tested the sensing ability
of NCS in the various pH values. In Fig. S5 is showed the emission in-
tensity ratios of NCS and NCS-In3 as a function of pH (6–9). These
+
+
results indicated that NCS can detect In3 in a ratiometric manner at pH
+
6
and 7.
3
.2. Practical applications
For application in real water samples, a calibration graph was made
for In3 , which shows a linear relationship (In = 0–60
+
3+
μ
M) (Fig. S6).
/K (Fig. 6). Asso-
with the equation of
Benesi-Hildebrand (Fig. S7) [56]. To inspect the practical capability of
Detection limit was found to be 2.68
μ
M by using 3
σ
3
ꢀ 1
M
ciation constant was analyzed as 8.47 × 10
NCS for In3 in real water samples, tap and drinking water were used
Table 1). Reasonable recoveries and R.S.D. values were given. The
outcomes signified that NCS can be a useful tool for the quantification of
+
Fig. 3. Absorption variations of NCS (2 × 10ꢀ 5 M) with In (0–50 equiv.).
3+
(
showed peaks to be shifted by binding with metal ions [29,48]. Thus, we
would argue the occurrence of thioamide tautomerization of NCS
3
+
(
Schemes 2 and 3). All these results led us to suggest that In might
bind with the oxygen, sulfur, and nitrogen atoms in thiol-tautomerized
1
NCS. With these data obtained from ESI-mass, Job’s plot, H NMR,
fluorescence and UV–vis titrations, the plausible sensing mechanism
between NCS and In3 was proposed (Scheme 3).
+
Inhibition test was conducted to confirm whether NCS could selec-
tively recognize In3 in the presence of diverse cations (Fig. 5). The
+
fluorescence intensity values (I444/I484) were measured by adding NCS
into the mixture of In3+ and each metal ion. Most metal ions did not
Scheme 2. Thioamide tautomerization.
1
3+
Fig. 4. H NMR titrations of NCS with In (0, 1, 3 and 7 equiv.).
4

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
3
+
.
Scheme 3. Proposed structure of NCS-In
Table 1
3
+ a
.
Analysis of In
3
+
3+
Sample
In added
M)
0.0
In found
M)
Recovery
R.S.D. (n = 3)
(
μ
(
μ
0.0
(%)
–
(%)
–
Tap water
1
0.0
9.83
0.0
98.3
–
1.36
–
Drinking
water
0.0
10.0
10.03
100.3
0.73
a
Condition: [NCS] = 2 × 10ꢀ 5 M in buffer (pH 7).
organism zebrafish [57]. For imaging, zebrafish incubated with 5
μ
M of
M)
NCS were treated with various concentrations of In3 (0, 10 and 20
+
μ
(
Fig. 8). The zebrafish incubated with only NCS exhibited no fluores-
3
+
cence. With the presence of In (10 and 20 M), the strong fluorescence
μ
emission was observed in zebrafish swim bladder and eyes. The mean
fluorescence intensity in the swim bladder was measured by Icy software
(
Fig. S8). With the quantification data, detection limit turned out to be
.97 M. The cytotoxicity of NCS was evaluated by AO staining (Fig. S9).
2
μ
No difference in the bright spots of zebrafish was observed, indicating
Fig. 5. Emission intensity ratios (I444/I484) of competitive selectivity of NCS (2
that NCS did not show the cytotoxicity. These bioimaging studies
ꢀ 5
3+
×
10 M) to In (72 equiv.) with other cations (72 equiv.).
3+
demonstrated that NCS had a great ability to detect In in the live cells
and zebrafish. Importantly, NCS is the first chemosensor that is able to
monitor In3 in live cells and zebrafish (Table S1).
+
3
.3. Theoretical studies
1
With UV–vis titrations, ESI-MS, Job’s plot and H NMR titration re-
3
+
sults, we calculated energy-optimized structures of NCS and NCS-In
for explaining the sensing mechanism. As shown in Fig. 9, NCS had a flat
binding site with the distorted furan moiety and the dihedral angle was
◦
3+
1
S, 2 N, 3C, 4O = 8.819 . NCS-In complex formed a distorted trigonal
bipyramidal structure with one nitrate.
According to the optimized structures of NCS and NCS-In3 , we
calculated possible transition states by using TD-DFT. The major tran-
sition of NCS was showed at 322.04 nm with intramolecular charge
+
transfer (ICT) and
occurred from the sulfur atom to the nitrogen one while
tion occurred in the salicylic aldehyde moiety. On the contrary, as In
bound to NCS, the ICT process decreased while * transition still
π→π
* character. (Figs. S10 and S11). The ICT
π
→ π
* transi-
3
+
π
→ π
maintained (Figs. S11 and S12). Considering these observations, the
sensing mechanism would be chelation-enhanced fluorescence (CHEF)
ꢀ
5
Fig. 6. Detection limit based on the change in the ratio of NCS (2 × 10 M)
effect [58,59]. Chelating with In3 might prevent non-radiative transi-
tion including ICT process from NCS ligand and led excitation energy to
be transferred to radiative transition [60]. Therefore, the complexation
+
3
+
.
with In
In3 in environmental as well as chemical applications.
+
3+
of NCS with In might cause increased fluorescent emission and help to
For the practical application of NCS toward In3 in biological sys-
+
1
get a higher quantum yield. With the outcomes of ESI-MS, Job’s plot, H
tems, we applied NCS to the live cells and zebrafish. For cell imaging,
NMR titrations and calculations, we proposed the plausible binding
mode in Scheme 3.
HeLa cells incubated with NCS were subsequently incubated with
various concentrations of In3 (0, 250 and 500
+
μ
M) (Fig. 7). The HeLa
cells treated with only NCS exhibited no fluorescence. However, after
the additional treatment with In3 (250 and 500
+
μ
M), the cells gradually
4. Conclusion
exhibited the obvious blue fluorescence. We then applied NCS to higher
We demonstrated a ratiometric fluorescent sensor NCS, which
5

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
ꢀ 6
Fig. 7. Fluorescent imaging of HeLa cells incubated with NCS and In(III). Cells were incubated with NCS and In(III) for 10 min. Conditions: [NCS] = 5 × 10 M; [In
III)] = 2.5 × 10ꢀ and 5 × 10 M; 37 C; 5% CO
. [λex = 357 (±20) nm; λem = 447 (±28) nm].
4
ꢀ 4
◦
(
2
ꢀ
6
3+
3+
ꢀ 6
Fig. 8. Fluorescence images of live zebrafish treated with 5 × 10 M of NCS without/with In . (a
1
-a
3
) Zebrafish were incubated with NCS (5 × 10 M) for 15 min;
3
+
ꢀ 5
ꢀ 5
(
b
1
-b
3
) subsequent treatment with In (1 × 10 M); (c
-c
1 3
) subsequent treatment with In (2 × 10 M). [λex = 350 (±25) nm; λem = 460 (±25) nm].
6

D. Yun et al.
Dyes and Pigments 183 (2020) 108704
3
+
.
Fig. 9. Energy-optimized forms of (a) NCS and (b) NCS-In
3
+
displayed a highly selective response for In among diverse cations
Appendix A. Supplementary data
containing Al3 and Ga at neutral pH in aqueous media. To date, there
+
3+
3
+
was no chemosensor for In working at neutral pH in a near-perfect
Supplementary data to this article can be found online at https://doi.
org/10.1016/j.dyepig.2020.108704.
aqueous media. In particular, sensor NCS is the first applicable ratio-
metric fluorescent chemosensor for the sensing of In3 not only in real
water samples but also in living organisms such as live cells and
zebrafish. The detection limit was calculated in both buffer solution
+
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3
+
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μ
3
+
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spectroscopic studies and DFT calculations.
[
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Investigation, Validation. Ki-Tae Kim: Writing - review & editing, Su-
pervision. Yelim Yi: Investigation, Validation, Writing - original draft,
Supervision. Mi Hee Lim: Writing - review & editing, Supervision.
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