A Highly Selective Fluorescent Chemosensor for Detecting Indium(III) with a Low Detection Limit and its Application

Article abstract of DOI:10.1007/s10895-018-2299-z

A highly selective chemosensor BHC ((E)-N-benzhydryl-2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine-1-carbothioamide) for detecting indium(III) was synthesized. Sensor BHC can detect In(III) by a fluorescence turn-on method. The detection limit was anal

Full text of DOI:10.1007/s10895-018-2299-z

Journal of Fluorescence
https://doi.org/10.1007/s10895-018-2299-z
ORIGINAL ARTICLE
A Highly Selective Fluorescent Chemosensor for Detecting Indium(III)
with a Low Detection Limit and its Application
1
1
Cheal Kim & Ju Byeong Chae
Received: 5 July 2018 /Accepted: 12 September 2018
Springer Science+Business Media, LLC, part of Springer Nature 2018
#
Abstract
A highly selective chemosensor BHC ((E)-N-benzhydryl-2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine-1-
carbothioamide) for detecting indium(III) was synthesized. Sensor BHC can detect In(III) by a fluorescence turn-on method.
The detection limit was analyzed to be 0.89 μM. Importantly, this value is the lowest among those previously known for
fluorescent turn-on In(III) chemosensors. Based on the analytical methods like ESI-mass, Job plot, and theoretical calculations,
the detection mechanism for In(III) was illustrated to be chelation-enhanced fluorescence (CHEF) effect. Additionally, sensor
BHC was successfully applied to test strips.
.
.
.
.
Keywords Fluorescence Chemosensor Indium Test strip Theoretical calculations
Introduction
are relatively high [12]. In contrast, chemosensors have been
noted for its easy usage, fast response and cost-effective ad-
Indium is one of the elements of group 13 and its consumption
has been gradually increased [1]. Most usage of indium is in
semiconductor-related applications [2]. Apart from these ap-
plications, the pollution from it can affect severe health prob-
lems [3]. Although it has no biological role in human body, its
effects have been reported to be toxic to humans, causing
kidney disease and interference towards iron metabolism [4].
Therefore, it is needed to develop efficient detecting strategies
for indium [5–7].
There are several analytical tools for the detection of a
broad range of metal ions like AAS, ICP-AES (inductively
coupled plasma atomic emission spectrometry), and other
electrochemical methods (Absence of Gradients and
Nernstian Equilibrium Stripping) [8–11]. However, they need
complex procedures and sample pre-treatment and the costs
vantages [13–17].
3
+
Owing to similar properties of the 13 group elements, Al
3
+
3+
and Ga , it is a challenge to distinguish In from them. Until
3
+
3+
now, many chemosensors for Al and Ga were developed,
3
+
3+
but a few for In [18–22]. Moreover, some of the In
3
+
chemosensors have difficulty in detecting In because they
are inhibited by Al and Ga or detected via quenching
response which is a less preferred method [2, 4, 5, 7]. Thus,
the chemosensor capable of sensing In without interferences
especially from Al and Ga with a turn-on response is
highly demanded.
The benzhydryl isothiocyanate with hydrazine moiety
could offer binding site to metal ions as well as act as a linker.
A naphthol moiety is widely used as a fluorophore because of
its unique photophysical property [23]. Therefore, we expect-
ed that the linkage of the two functional moieties can induce a
unique optical change towards a specific metal ion.
Herein, we present a highly selective and sensitive fluores-
3
+
3+
3
+
3
+
3+
Electronic supplementary material The online version of this article
(https://doi.org/10.1007/s10895-018-2299-z) contains supplementary
3
+
material, which is available to authorized users.
cence probe BHC, which can detect In via a fluorescence
3
+
turn-on. Importantly, it can distinguish In from the same
3
+
3+
*
Cheal Kim
group metals, Al and Ga , without interferences. In addi-
chealkim@seoultech.ac.kr
3+
tion, the binding mode and sensing mechanism for In were
explained, based on the spectroscopic studies and theoretical
calculations.
1
Department of Fine Chem, Seoul National University of Science and
Technology (SNUT), Seoul 138-743, South Korea

J Fluoresc
Scheme 1 Synthesis of compound BHC
Experimental Section
128.55 (4C), 128.14 (1C), 127.61 (1C), 127.37 (4C), 127.23
(2C), 123.47 (1C), 122.84 (1C), 118.42 (1C), 110,11 (1C),
General Information
60.70 (1C). Positive-ion ESI-MS: m/z calcd, for [2·BHC +
+
+
+
Na ] , C H N O S + Na , 845.27; found, 845.18.
5
0 42 6 2 2
Chemicals were provided commercially. Stock solutions of
the cations (Cd , Al , K , Ga , Ca , In , Zn , Na ,
2
+
3+
+
3+
2+
3+
2+
+
3+
Fluorescence and UV-vis Titrations of BHC with In
2
+
2+
3+
2+
2+
2+
3+
2+
2+
Cu , Ni , Fe , Co , Hg , Mg , Cr , Pb , Mn and
+
Ag ) were prepared using nitrate salts in dimethylsulfoxide
A stock solution of BHC was prepared in dimethylsulfoxide
2
+
−
2
(
20 mM). Perchlorate salt was used for the Fe stock solution.
NMR data were measured using a Varian spectrometer
400 MHz). A Perkin Elmer spectrometer (Lambda 2S UV/
(DMSO, 1 × 10 M). 3 μL of it was diluted to 3 mL of
−
2
DMSO for 10 μM concentration. A stock solution (2 × 10
M) of In(NO ) was prepared in DMSO. For the fluorescence
(
3
3
3
+
Vis) was used for absorption spectra. ESI-mass data were
gained on a Thermo Finnigan LCQTM instrument. A
Perkin-Elmer spectrometer (LS45) was used for fluorescence
data, and the slit width for excitation and emission was 10 nm.
titration, 1.5–37.5 μL of the In solution was taken and
3
+
mixed with BHC. 1.5–19.5 μL of the In solution was added
to the solution of BHC for UV-vis titration. Both fluorescence
and UV-vis spectra were measured.
3
+
Synthesis and Characterization of BHT
Quantum Yield of BHC and BHC-In
(1-benzhydrylthiourea)
Quantum yield (Ф) was calculated by using fluorescein (Ф =
F
Benzhydryl isothiocyanate (1.12 g, 5.0 mmol) and hydrazine
monohydrate (334 μL, 5.5 mmol) were dissolved in 10 mL of
absolute ethanol and stirred for 6 h until white precipitate
0.92 in basic ethanol) as a standard fluorophore [24]. The
equation of quantum yield is as follows [25]:
formed. It was filtered and washed with chilly ethanol and
2
1
Φ
¼ ΦFðSÞ ðAS FX =AX FSÞ ðnX =nSÞ
diethylether. Yield: 0.87 g (60%). H NMR (DMSO-d ,
FðXÞ
6
4
6
00 MHz, ppm): δ 8.96 (s, 1H), 8.37 (s, 1H), 7.28 (m, 10H),
.76 (s, 1H), 4.64 (s, 2H).
Synthesis and Characterization of BHC ((E)
N-benzhydryl-2-((2-hydroxynaphthalen-1-yl)
-
methylene)hydrazine-1-carbothioamide)
BHT (480 mg, 2.0 mmol) and 2-hydroxy-1-naphthaldehyde
(
360 mg, 2.1 mmol) were dissolved in 5 mL of absolute eth-
anol and stirred for 1 day until pale yellow powder formed. It
was filtered and washed with chilly ethanol and diethylether.
1
Yield: 0.46 g (56%). H NMR (CDCl , 400 MHz, ppm): δ
3
1
7
7
0.62 (s, 1H), 10.23 (s, 1H), 9.00 (s, 1H), 7.92 (d, J = 8.4, 1H),
.83 (d, J = 9.2 Hz, 1H), 7.79 (d, J = 8.4 Hz, 1H), 7.54 (t, J =
.8 Hz, 1H), 7.4 (t, J = 7.6 Hz, 1H), 7.32 (m, 11H), 7.17 (d,
1
3
J = 8.8 Hz, 1H), 6.92 (d, J = 8.4 Hz, 1H), C NMR (DMSO-
d6, 100 MHz, ppm): δ = 176.73 (1C), 156.70 (1C), 142.51
Fig. 1 Fluorescence spectra of BHC (10 μM) with various metal ions (23
(
1C), 141.90 (2C), 132.50 (1C), 131.40 (1C), 128.82 (1C),
equiv). Excitation wavelength: 416 nm

J Fluoresc
Fig. 2 Changes in fluorescence
3
+
emission spectra when In was
added into sensor BHC (10 μM).
Inset: fluorescence intensity at
4
90 nm (0–25 equiv). Excitation
wavelength: 416 nm. Error bars
represent standard deviations
from three repeated experiments
3
+
Where the meaning of each abbreviation is
Job Plot Measurement of BHC with In
1
60 μL of a BHC stock solution (DMSO, 1 × 10− M) was
2
ФF fluorescence quantum yield
diluted to 39.84 mL DMSO for 40 μM concentration. 80 μL
A
F
n
s
Absorbance
3
+
−2
of an In stock solution (DMSO, 2 × 10 M) was diluted to
9.92 mL DMSO for 40 μM concentration. Both solutions
The area of fluorescence emission curve
Refractive index of the solvent
standard
3
were mixed from the molar fractions of 0.1 to 0.9 while main-
taining a constant overall concentration (40 μM). The emis-
sion spectrum of each solution was measured.
x
unknown
Fig. 3 Changes in UV-vis spectra
3+
when In was added into sensor
BHC solution (10 μM)

J Fluoresc
Fig. 4 Positive-ion ESI-MS
3+
spectrum of BHC-In (100 μM,
3+
1
equiv. of In )
Competition Experiment
4.5 μL of various metal-ion stock solutions dissolved in
visible detection limit. The test kit prepared above was also
2
+
3+
+
applied to 20 μM of various metal solutions (Cd , Al , K ,
3
+
2+
3+
2+
+
2+
2+
3+
2+
2+
3
Ga , Ca , In , Zn , Na , Cu , Ni , Fe , Co , Hg ,
2
+
3+
+
3+
2+
3+
2+
+
2+
2+
3+
2+
2+
+
DMSO (Cd , Al , K , Ga , Ca , In , Zn , Na , Cu ,
Mg , Cr , Pb , Mn and Ag ).
2
+
3+
2+
2+
2+
3+
2+
2+
+
Ni , Fe , Co , Hg , Mg , Cr , Pb , Mn and Ag ,
0 mM) were diluted to 3 mL of DMSO (23 equiv). The same
2
3
+
Theoretical Studies
amount of an In stock solution was added to each solution.
A stock solution of BHC (10 mM, 3 μL) was added to them
and mixed. The emission spectrum of each solution was
measured.
3
+
Energy-optimized structures of BHC and BHC-In complex
were calculated by density functional theory (DFT) using
Gaussian 09 W program [26]. The hybrid functional was
Becke, 3-parameter, Lee-Yang-Parr (B3LYP) and the basis
3
+
Fluorescence Test Kit
set was 6-31G(d,p) [27–30]. All atoms except In were ap-
plied to 6-31G(d,p) while LANL2DZ basis set was used as
3
+
Filter papers were immersed to 700 mM of BHC solution
effective core potential (ECP) for In [31–33]. Since imagi-
nary frequency was not found in optimized structures of BHC
(
1 mL, DMSO). After they were dried in the oven, various
3
+
3+
amounts (10, 20, 50, 100, and 200 μM) of an In stock
and BHC-In , their geometries represented local minima.
solution were applied to them for determining the lowest
CPCM was used for considering solvent effect of DMSO
3+
Scheme 2 Fluorescence turn-on mechanism and proposed binding structure of BHC-In

J Fluoresc
Compound BHC was obtained from the condensation reac-
tion of BHT and 2-hydroxy-1-naphthalaldehyde (Scheme 1).
1
13
It was fully characterized through H and C NMR and ESI-
MS analyses (Figs. S1-S3).
In order to study the sensing ability of compound BHC
towards various metals, fluorescence spectra were measured
with the excitation wavelength of 416 nm (Fig. 1). Most
metals did not show critical fluorescence change. In contrast,
3
+
only In displayed a remarkable increase of the fluorescence
emission at 490 nm. This obvious change indicated that sensor
3
+
BHC could detect In by fluorescence turn-on. For investi-
gating the counter-anion effect, we also used In (SO ) instead
2
4 3
of indium nitrate. Indium sulfate also showed nearly identical
fluorescence enhancement as done with indium nitrate.
To investigate binding properties, fluorescence titration
3
+
3
+
Fig. 5 Detection limit of BHC toward In based on 3σ/slope. Error bars
was achieved (Fig. 2). As the amount of In increased, fluo-
rescence emission at 490 nm was constantly increased.
represent standard deviations from three repeated experiments
3
+
Quantum yields (Ф) of BHC and BHC-In were calculated
[
34, 35]. According to energy-optimized structures of sensor
to be 0.0563 and 0.147. The binding interaction between
3
+
BHC and BHC-In complex, the UV-vis transition studies
were confirmed using TD-DFT (time-dependent DFT) meth-
od with thirty lowest singlet states.
3+
BHC and In was further studied with UV-vis titration
3+
(
Fig. 3). The increase of In induced absorption spectral
changes with two defined isosbestic points at 300 nm and
92 nm, and it implies that only one species is present at the
3
isosbestic point.
Results and Discussion
For the determination of binding stoichiometry of sensor
3
+
BHC and In , Job plot experiment was achieved (Fig. S4).
The highest fluorescence intensity appeared at the point where
the mole fraction was 0.5. It indicated that sensor BHC and
By the nucleophilic addition reaction of benzhydryl isothio-
cyanate and hydrazine, compound BHT was synthesized.
3
+
Fig. 6 Photographs of the test strips coated with sensor BHC. a Sensor BHC-test strips immersed in various concentrations of In (0–200 μM). b
Sensor BHC-test strips immersed in 20 μM of various metal ion solutions

J Fluoresc
3+
Fig. 7 Energy-optimized structure of (a) sensor BHC and (b) BHC-In complex
3
+
In were combined in a 1 to 1 ratio. To support the binding
Moreover, sensor BHC was applied to test strips. As
3
+
interaction between BHC and In , positive-ion ESI-MS ex-
periment was executed (Fig. 4). The peak of m/z = 679.99 was
suggestive of BHC-2H +In (calcd, m/z = 680.05). Its iso-
tope pattern was well matched with the calculated value,
supporting the 1: 1 binding stoichiometry of BHC and In .
shown in Fig. 6a, the obvious fluorescent emission appeared
3
+
above 20 μM of In . On the contrary, the same concentration
of other cations did not show fluorescence emission (Fig. 6b).
Therefore, it demonstrated that sensor BHC could be also
+
3+
3
+
3+
used for detecting In in the test strip.
Job plot and ESI-MS analyses drove us to propose the plau-
sible binding mode of BHC-In in Scheme 2.
To comprehend the detection mechanism of BHC towards
3
+
3+
In , theoretical calculations were achieved. Based on the 1 to
3
+
With the result of fluorescence titration, detection limit
1 binding stoichiometry between BHC and In , energy-
2
using 3σ/slope was analyzed to be 0.89 μM (R = 0.9996)
optimized structures and molecular orbital contributions of
3
+
(
Fig. 5) [36]. Significantly, the detection limit is the lowest
BHC and BHC-In complex were calculated. As shown in
Fig. 7a, sensor BHC displayed a bent form with the dihedral
angle 33.384° for 1 N, 2 N, 3C, and 4O. Upon chelating to
value among those previously known for fluorescent turn-on
3
+
In chemosensors, to date. (Table S1). Also, the association
3
+
constant (K) based on Benesi-Hildebrand equation was turned
In , its structure was flattened to 0.125° (Fig. 7b).
3
−1
out to be 4.3 × 10 M (Fig. S5) [37].
Based on these structures, molecular orbitals and transition
energies were obtained by using TD-DFT calculation with the
For the practical application, the selectivity of compound
3
+
3+
BHC for In was tested in the existence of other cations (Fig.
singlet excited states of BHC and BHC-In . Thirty singlet
2
+
2+
S6). Hg and Cu inhibited the fluorescence of sensor BHC,
states having non-zero oscillator strength were considered as
allowed-transition. For BHC, the main absorption band was
originated from the HOMO → LUMO transition (382.26 nm,
Fig. S7), indicating ICT (intramolecular charge transfer)
3
+
2+
and Fe and Fe displayed about half reduction of the fluo-
3
+
3+
rescence. Nevertheless, group 13 metals, Al and Ga ,
didn’t show any fluorescence interferences.

J Fluoresc
7.
8.
9.
Kim H, Kim KB, Song EJ, Hwang IH, Noh JY, Kim PG, Jeong KD,
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ions. Inorg Chem Commun 36:72–76
Acar O, Türker AR, Kılıç Z (1998) Determination of bismuth,
indium and lead in geological samples by electrothermal AAS.
Fresenius J Anal Chem 360:645–649
Gęca I, Korolczuk M (2017) Sensitive anodic stripping
Voltammetric determination of indium(III) traces following double
deposition and stripping steps. J Electrochem Soc 164:H183–H187
transition from the naphthol group to the thiocyanate. In case
3
+
of BHC-In , the main absorption band was originated from
the HOMO-1 → LUMO+1 and HOMO → LUMO+1 transi-
tions (414.62 nm, Fig. S8). The electrons of both HOMO and
HOMO-1 were mainly localized in the dibenzene ring, where-
as those of LUMO+1 were localized in the naphthol moiety
(
Fig. S9). Their transitions indicated ICT and LMCT (ligand-
to-metal charge-transfer). The decrease of the energy gap be-
tween HOMO and LUMO corresponded to red shift of the
experimental UV-vis spectra.
1
0. Adya VC, Kumar M, Sengupta A, Natarajan V (2015) Inductively
coupled plasma atomic emission spectrometric determination of
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From these results, the sensing mechanism of BHC to-
11. Tehrani MH, Companys E, Dago A, Puy J, Galceran J (2018) Free
3
+
wards In maybe due to chelation-enhanced fluorescence
indium concentration determined with AGNES. Sci Total Environ
612:269–275
3
+
(
CHEF) effect. As In bound to BHC, the rotation of imine
1
1
1
2. Lee JJ, Park GJ, Kim YS, Lee SY, Lee JH, Noh I, Kim C (2015) A
(
-C=N) was inhibited [38]. Therefore, the rigid structure and
water-soluble carboxylic-functionalized chemosensor for detecting
inhibited non-radiative transition could induce fluorescence
enhancement.
3
+
Al in aqueous media and living cells: experimental and theoretical
studies. Biosens Bioelectron 69:226–229
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4. Park GJ, Lee JJ, You GR, Nguyen L, Noh I, Kim C (2016) A dual
2+
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chemosensor for Zn and Co in aqueous media and living cells:
experimental and theoretical studies. Sensors Actuators B Chem
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In conclusion, we synthesized a fluorescence chemosensor
BHC for detecting In by a fluorescence turn-on method. It
can obviously discriminate In from the same group metals,
Al and Ga , with no interferences. The detection limit for
3
+
3
+
15. Wu D, Sedgwick AC, Gunnlaugsson T, Akkaya EU, Yoon J, James
TD (2017) Fluorescent chemosensors: the past, present and future.
Chem Soc Rev 46:7105–7123
3
+
3+
3
+
In was 0.89 μM, which is the lowest among those previous-
1
6. Ghosh P, Banerjee P (2017) Small molecular probe as selective
3
+
3+
−
ly known for fluorescent turn-on In chemosensors, to date.
Sensor BHC was also successfully applied to test strips.
Moreover, fluorescence turn-on mechanism was proposed as
chelation-enhanced fluorescence (CHEF) effect using DFT/
TD-DFT calculation.
tritopic sensor of Al , F and TNP: fabrication of portable proto-
type for onsite detection of explosive TNP. Anal Chim Acta 965:
111–122
1
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Acknowledgements The National Research Foundation of Korea (NRF)
18. Lim C, An M, Seo H, Huh JH, Pandith A, Helal A, Kim HS (2017)
3+
(NRF-2018R1A2B6001686) is thankfully acknowledged.
Fluorescent probe for sequential recognition of Ga and pyrophos-
phate anions. Sensors Actuators B Chem 241:789–799
1
2
2
9. Kim DH, Im YS, Kim H, Kim C (2014) Solvent-dependent selec-
3+
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tive fluorescence sensing of Al and Zn using a single Schiff
base. Inorg Chem Commun 45:15–19
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