Dual signaling of thallium(III) ions via oxidative cleavage of a sulfonhydrazide linkage

Article abstract of DOI:10.1016/j.jphotochem.2020.112471

The thallium is widely used in various research and industrial applications but is very toxic. In this work, we developed a novel reaction-based dual signaling probe for the selective and sensitive determination of Tl³⁺ via the oxidative cleavage of a rhodamine–dansylhydrazide conjugate. The designed probe showed pronounced colorimetric and fluorescence signaling behavior toward Tl³⁺ with a detection limit of 1.3 × 10^–7 M (0.027 ppm), as well as selectivity over other common metal ions, anions, and oxidants. The Tl³⁺ signaling process required less than 2 min and was not influenced by the solution pH within the range of 4.0–5.5; however, the signal diminished significantly above pH 6.0. To demonstrate the practical applicability of the designed probe, a simple and convenient colorimetric assay for the determination of Tl³⁺ in commercial reagents was established using an office scanner as a readily available signal capturing device.

Full text of DOI:10.1016/j.jphotochem.2020.112471

Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
Contents lists available at ScienceDirect
Journal of Photochemistry & Photobiology A: Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Dual signaling of thallium(III) ions via oxidative cleavage of a
sulfonhydrazide linkage
Yu Jeong Lee, Myung Gil Choi, Jae Hoon Yoo, Tae Jung Park, Sangdoo Ahn*, Suk-Kyu Chang*
Department of Chemistry, Chung-Ang University, Seoul, 06974, Republic of Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
The thallium is widely used in various research and industrial applications but is very toxic. In this work, we
developed a novel reaction-based dual signaling probe for the selective and sensitive determination of Tl3+ via
the oxidative cleavage of a rhodamine–dansylhydrazide conjugate. The designed probe showed pronounced
3+
Tl
sensing
Sulfonhydrazide
Dual signaling
Oxidative cleavage
Office scanner
3+
–7
colorimetric and fluorescence signaling behavior toward Tl
ppm), as well as selectivity over other common metal ions, anions, and oxidants. The Tl
with a detection limit of 1.3 × 10 M (0.027
3+
signaling process
required less than 2 min and was not influenced by the solution pH within the range of 4.0–5.5; however, the
signal diminished significantly above pH 6.0. To demonstrate the practical applicability of the designed probe, a
3
+
simple and convenient colorimetric assay for the determination of Tl in commercial reagents was established
using an office scanner as a readily available signal capturing device.
1. Introduction
has also recommended that thallium species at a concentration of 15
mg/m3 be considered an immediate threat to life and health [13].
The development of selective and sensitive detection methods for
Therefore, convenient and sensitive thallium-selective analytical
methods are urgently required.
toxic metal ions is crucial for the monitoring and remediation of ha-
zardous species toward environmental protection [1]. Thallium is of
particular relevance in this regard because it is used in various modern
industrial activities [2], including the manufacture of various electrical
and electronic components, optical lenses, semiconductor materials,
gamma radiation detection equipment, infrared detectors, and low-
temperature thermometers [3]. Thallium is also used in acid-resistant,
corrosion-resistant, antifriction alloys and in medicines, health pro-
ducts, and pigments for cosmetics [4]. These applications and the
subsequent release of thallium into the environment have led to an
increase in thallium levels in our ecosystems [5–7].
Determination of Tl3+ has been carried out using several instru-
mental methods, including atomic absorption spectroscopy [14,15],
inductively coupled plasma-mass spectrometry [16,17], and X-ray
fluorescence spectroscopy [18]. Electroanalytical methods [19–21]
such as potentiometry using a tetrachlorothallate(III)-PVC membrane
sensor [22], measurements using a solid-contact ion-selective electrode
with an electropolymerized transducer [23], and square-wave voltam-
metric stripping analysis using a poly(4-vinylpyridine)/mercury film
electrode [24] have also been used. However, optical methods that rely
on colorimetric or fluorescence signaling are much more advantageous
because of their selectivity, sensitivity, convenience, and potential for
miniaturization to satisfy the requirements of on-site measurements
[25,26].
Despite its widespread use, thallium is highly toxic to humans [8].
In fact, thallium is more toxic to mammals than mercury, lead, or
cadmium [9], and chronic exposure leads to changes in cell-cycle
progression and the nervous system [10]. Thallium exists in two oxi-
dation states, thallous (Tl+) and thallic (Tl ), with the latter being ∼4
orders of magnitude more toxic than the former to human beings and
domestic and wild animals [11,12]. Therefore, thallium is considered a
priority pollutant by the United States Environmental Protection
Agency. The maximum contaminant levels for thallium in drinking
water and wastewater effluent have been set at 0.002 and 0.14 mg/L,
respectively. The National Institute for Occupational Safety and Health
For this purpose, several spectrophotometric methods that employ
optical indicating materials, such as chloro-substituted hydroxamic acid
3+
extractants [27],
a
quinalizarin ion associate on
a
styr-
ene–divinylbenzene anion-exchange resin [28], an optode membrane
prepared from plasticized PVC using a complexing agent [29], and 3-
methyl-2-benzothiazolinone hydrazone in an oxidative coupling reac-
tion [30] have been reported. However, the selectivity and sensitivity of
the techniques they were involved in were not satisfactorily elucidated
⁎
Corresponding authors.
E-mail addresses: sangdoo@cau.ac.kr (S. Ahn), skchang@cau.ac.kr (S.-K. Chang).
https://doi.org/10.1016/j.jphotochem.2020.112471
Received 26 November 2019; Received in revised form 25 February 2020; Accepted 26 February 2020
Available online 05 March 2020
1010-6030/ © 2020 Elsevier B.V. All rights reserved.

Y.J. Lee, et al.
Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
the frequently encountered matrix effect in Tl3+ analysis so that such
methods could be applied in routine investigation of analytes origi-
nating from various sources (Table S1) [31–33].
In organic synthesis, thallium(III) salts have been widely employed
as versatile oxidants for many practical applications [34–36] such as
the oxidation of phenols, oxidative rearrangement of ketones to esters
or acids and olefins to aldehydes or ketones, electrophilic cyclization of
unsaturated substrates bearing an internal nucleophile, and phenolic
6.70 (s, 1 H), 6.42–6.27 (m, 2 H), 6.18 (dd, J = 9.1, 2.6 Hz, 2 H), 5.73
(s, 2 H), 3.30 (q, J =7.2 Hz, 8 H), 2.90 (s, 6 H), 1.17 (t, J =7.1 Hz, 12
H). 13C NMR (150 MHz, CDCl
) δ 168.3, 153.0, 152.3, 151.4, 148.6,
3
134.2, 133.7, 130.0, 129.5, 129.4, 129.3, 128.6, 128.3, 128.0, 127.4,
124.4, 123.5, 122.9, 119.7, 114.6, 107.7, 104.4, 97.6, 66.6, 45.6, 44.3,
+
+
+
12.8. HRMS: (FAB ); m/z calcd. for
C
40
H
44
N
5
O
4
S
[M+H] :
690.3114, found: 690.3109.
3
+
oxidative coupling [37]. In particular, Tl
has proven to be very ef-
2.3. Preparation of stock solutions
fective for the deprotection of some commonly employed protecting
groups. For instance, thallium(III) trifluoroacetate, a mild oxidant with
soft acid characteristics, was found to cleave various S-protecting
groups of cysteine with the spontaneous formation of cystine [38]. The
regeneration of aldehydes or ketones from their oximes [39,40], di-
thioacetals [41], toluene-p-sulfonylhydrazones [42], and semi-
carbazones [40] has also been successfully accomplished.
A stock solution of probe 1 (5.0 × 10 4 M) was prepared in spec-
–
troscopic-grade DMSO. A thallium(III) nitrate stock solution (1.0 ×
10 M) was prepared in a 0.1 N HCl solution. Stock solutions (1.0 ×
10 M) of other metal ions and anions were prepared by dissolving the
appropriate metal perchlorate salts or sodium salts of anions in distilled
water.
–
2
–
2
In this work, we developed a novel reaction-based probe for the
selective colorimetric and fluorescence signaling of toxic, en-
2.4. Investigation of Tl3+ signaling behavior
3
+
vironmentally important Tl ions. We found that the sulfonhydrazide
functionality, which has previously been used as a colorimetric and
fluorescence switch in a hypochlorite signaling probe based on the
rhodamine–dansyl dyad framework [43], is readily cleaved by oxida-
All signaling experiments were conducted under optimized condi-
tions using a mixture of pH 4.76 acetate buffer and DMSO (8:2, v/v).
For thallium(III) signaling experiments, the probe 1 stock solution (30
3
+
–4
3+
tion using Tl
ions under mild conditions at room temperature [42].
μL, 5.0 × 10 M), analyte stock solution (Tl , oxidant, metal ion, or
–2
By exploiting this facile reaction, we designed an optical probe for the
anion; 15 μL; 1.0 × 10 M), and pH 4.76 acetate buffer (450 μL, 0.20
M) were added to a vial and subsequently diluting the mixture with
distilled water and DMSO (3.0 mL, 8:2 (v/v) mixture of acetate buffer
and DMSO). The final probe 1, analyte, and buffer concentrations were
3
+
colorimetric and fluorescence sensing of Tl
species. The probe con-
sisted of conjugated rhodamine and dansyl dyes with an oxidatively
cleavable sulfonhydrazide linkage as a signal trigger. The designed
system showed pronounced colorimetric and fluorescence responses
–
6
–5
–2
5.0 × 10 , 5.0 × 10 , and 3.0 × 10 M, respectively.
3
+
toward Tl
with high selectivity over other metal ions, anions, and
some representative oxidants. Furthermore, the signaling behavior
2.5. Determination of detection limit for Tl3+
could be evaluated with the aid of an easy-to-use office scanner.
The limit of detection (LOD) for Tl3+ was estimated according to the
IUPAC guidelines using the equation LOD = 3sbl/m, where sbl is the
standard deviation of the responses of probe 1 alone (number of mea-
surements = 10) and m is the slope of the titration curve [45].
2. Experimental section
2.1. General
Thallium(III) nitrate, rhodamine B base, dansyl chloride, phos-
2.6. Confirmation of the Tl3+ signaling process of probe 1
phorus oxychloride, and hydrazine monohydrate were purchased from
Aldrich Chemical Co. All other reagents and solvents were obtained
The Tl3+-assisted conversion of probe 1 to rhodamine B base and
1
1
from commercial sources and used as received. H NMR (300 and 600
dansyl acid was confirmed by H NMR spectral measurements. A sig-
1
3
3+
MHz) and C NMR (150 MHz) spectra were recorded using a Varian
Gemini 2000 or VNS NMR spectrometer and referenced against the
residual solvent signal. UV–vis and fluorescence spectra were acquired
using a Scinco S-3100 spectrophotometer and a FluoroMate FS-2
fluorescence spectrophotometer, respectively. Mass spectra were col-
lected using a Micromass Autospec mass spectrometer. Dansylhydrazine
was prepared by reacting dansyl chloride with hydrazine according to a
previously reported procedure [44].
naling mixture of probe 1 and Tl
was prepared by slowly adding
thallium(III) nitrate trihydrate (8.9 mg, 0.02 mmol) to a solution of
1
probe 1 (6.9 mg, 0.01 mmol) in 1.0 mL of DMSO-d
spectrum was obtained in situ. The 1H NMR spectra of probe 1 alone,
rhodamine B base, and dansyl acid in DMSO-d were also obtained.
6
, and the H NMR
6
2.7. Determination of Tl3+ in commercial reagents using an office scanner
The concentration of Tl3+ in commercial reagents was assayed
using an office scanner as a readily available color determination de-
vice. All signaling measurements were carried out under the optimized
conditions using a mixture of pH 4.76 acetate buffer and DMSO (8:2, v/
v).
2.2. Preparation of rhodamine–dansylhydrazide 1
Rhodamine–dansylhydrazide 1 was prepared by reacting rhodamine
B base with dansylhydrazine following a reported procedure [43]. A
solution of rhodamine B base (0.44 g, 1.0 mmol) in 15 mL of POCl was
3
stirred under reflux for 6 h. After removing the volatiles under reduced
pressure, the residue was dissolved in dichloromethane. The resulting
solution was added dropwise to a mixture of dansylhydrazine (0.27 g,
2.7.1. Preparation of calibration curve for Tl3+
Calibration was carried out using a Tl3+ solution standardized by
iodometry [46]. The solutions used to construct the Tl3 calibration
+
–
4
1.0 mmol) and triethylamine (1 mL) in dichloromethane (20 mL), and
curve were prepared by mixing probe 1 (120 μL, 5.0 × 10 M), a
standardized Tl3+ solution (6.0, 12.0, 18.0, 24.0, or 30.0 μL, 1.0 × 10
M), and pH 4.76 acetate buffer (450 μL, 0.20 M) in a vial and subse-
quently diluting the mixture with distilled water and DMSO (3.0 mL,
–3
the reaction mixture was stirred for 12 h. Then, the reaction mixture
was washed with distilled water three times. The organic phase was
separated and evaporated under reduced pressure, and the residue was
3
+
purified by column chromatography (silica gel, CH
2
Cl
2
/CH
3
OH = 29:1,
8:2 (v/v) mixture of acetate buffer and DMSO). The final probe 1, Tl
,
,
–
5
–6
v/v) to yield rhodamine–dansylhydrazide 1 (0.32 g, 46%) as a pale
and acetate buffer concentrations were 2.0 × 10 , 2.0–10.0 × 10
1
–2
white powder. H NMR (600 MHz, CDCl
7
3
) δ 8.34 (d, J =8.4 Hz, 1 H),
and 3.0 × 10 M, respectively. The green channel level of the solutions
was obtained for the images captured by an Epson Perfection V550
office scanner in transmittance mode. The calibration curve for the
.99–7.84 (m, 2 H), 7.67–7.60 (m, 1 H), 7.45–7.41 (m, 2 H), 7.31 (t, J
=8.0 Hz, 1 H), 7.11 (t, J =7.9 Hz, 2 H), 6.94 (dd, J = 6.2, 2.1 Hz, 1 H),
2

Y.J. Lee, et al.
Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
standardized Tl3+ reagent was plotted using the ΔGreen value (255 –
green channel level), and the slope of the plot was then determined.
+
2
.7.2. Tl3 assay of commercial reagents
3
+
The Tl
samples containing different amounts of Tl . The samples were pre-
assay of commercial reagents was conducted using five
3
+
–
4
3+
pared by adding probe 1 (120 μL, 5.0 × 10 M), the Tl
solution
–
3
under analysis (6.0, 12.0, 18.0, 24.0, and 30.0 μL; 1.0 × 10 M), and
pH 4.76 acetate buffer (450 μL, 0.20 M) to a vial and diluting the
mixture with distilled water and DMSO to obtain a 8:2 (v/v) mixture of
the acetate buffer and DMSO (3.0 mL). A calibration curve for the Tl3+
reagent was constructed by plotting the ΔGreen value as a function of
3
+
[
Tl ], and the slope of the plot was estimated. The Tl3+ content of
reagent was calculated using the equation given below.
Fig. 1. Tl3+-selective signaling behavior of probe 1 as expressed by the ab-
(
Slope of calibration curve for reagent)
sorbance change (A/A
0
) at 556 nm. Inset: UV–vis spectra of probe 1 in the
Tl3 content of reagent (%) =
+
–6
3+
n
3
+
absence and presence of various metal ions. [1] = 5.0 × 10 M, [Tl ] = [M
(
Slope of calibration curve for standard Tl
)
+
–5
–2
]
= 5.0 × 10 M, [buffer] = 3.0 × 10 M in a mixture of acetate buffer (pH
4.76) and DMSO (8:2, v/v).
×
100%
=
satisfactory solubility of the probe. The response of the probe in aqu-
eous DMSO became enhanced with the increases in water content up to
50% and then remained constant (Fig. S3).
3
. Results and discussion
Reaction-based Tl3+-selective probe 1 was prepared in moderate
yield (46%) by treating rhodamine B base with POCl to obtain rho-
damine acyl chloride, which was subsequently reacted with dansylhy-
drazine (triethylamine/CH Cl , rt) (Scheme 1) [43]. The probe was
designed to include a sulfonhydrazide linkage between the rhodamine
and dansyl fluorophores as an oxidatively cleavable group that can act
as a signaling trigger for the analyte.
The signaling properties of the probe toward metal ions were in-
vestigated by UV–vis and fluorescence spectroscopy. The signaling
conditions were optimized based on a systematic survey of the effects of
pH and solvent composition. Probe 1 was nearly colorless and showed a
broad absorption band of moderate intensity at 320 nm. Upon treat-
Under these conditions (acetate buffer solution (pH 4.76) containing
3
20% DMSO), the probe solution exhibited weak light-blue fluorescence,
with a weak emission band centered at 498 nm. The colorimetric re-
sponses of the probe toward common metal ions and anions were as-
sessed by UV–vis spectroscopy. Upon treatment with 10 equiv of re-
presentative metal ions, a strong absorption band at 556 nm was
observed exclusively in the presence of Tl3+ ions (Fig. 1 and Fig. S4),
and the solution color changed from nearly colorless to pink. The ab-
2
2
sorbance enhancement induced by Tl3+ at 556 nm (A/A
than 95-fold, whereas the other tested metal ions and anions caused no
measurable response.
The observed signal is due to the oxidative cleavage of the sulfon-
hydrazide linkage in the probe by Tl3+. Upon reaction with Tl , probe
1 is converted to its two constituent dyes: pink-colored rhodamine 2,
which exhibits orange fluorescence, and colorless dansyl acid 3, which
exhibits blue fluorescence (Scheme 2). The postulated transformation
was confirmed by the 1H NMR and mass spectra of the signaling pro-
0
) was greater
3
+
ment with Tl ions, a new absorption band at 556 nm was evolved and
the response was maximized in a mixture of acetate buffer (pH 4.76)
and DMSO (8:2, v/v) (Fig. 1). The Tl signal of the probe was found to
be strongly dependent on the pH of the medium, as shown in Fig. S1.
3+
3
+
3
+
Strong Tl
signals were observed between pH 4.0 and 5.5, but the
signal diminished significantly above pH 6.0. Furthermore, we con-
1
3
+
ducts. As shown in Fig. 2, the H NMR spectrum of the signaling pro-
firmed that the pH-sensitive Tl
ions [47] are stable in acetate-buf-
duct (1 + Tl3+) was similar to the sum of the spectra of the expected
signaling products rhodamine B base and dansyl acid. In addition, the
TLC behavior of the 1 + Tl3+ signaling system (Fig. S5) confirmed that
rhodamine B base and dansyl acid were produced from probe 1 during
the Tl3+ signaling process. Furthermore, the mass spectrum of the
fered solutions at pH 4.0–5.6 based on the turbidity profiles of the so-
lution under illumination by laser light (Fig. S2). Therefore, the
signaling experiments were carried out in an acetate buffer solution at
pH 4.76.
In acetate buffered (pH 4.76) solution, further optimization of the
organic solvent composition for the efficient Tl
ducted. Among common organic solvents, DMSO acting as a scavenger
for the hypochlorous acid was selected. Although 2% DMSO is sufficient
for this scavenging purpose, 20% DMSO was employed to ensure
3
+
3
+
signaling product obtained from probe 1 in the presence of Tl
showed a diagnostic peak at m/z 442.3, in agreement with the expected
ions
signaling was con-
+
signaling product, rhodamine B base (calcd. for [C28
42.2) (Fig. S6).
30 2 3
H N O ] , m/z
4
Scheme 1. Preparation of Tl3+-signaling probe 1, which functions via oxidative cleavage of the sulfonhydrazide linkage.
3

Y.J. Lee, et al.
Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
Scheme 2. Tl3+ signaling via oxidative cleavage of sulfonhydrazide-based probe 1.
As the Tl3+ sensing mechanism is based on the oxidative cleavage of
the probe, we investigated potential interference from other common
oxidants. As shown in Fig. S7, no measurable responses were observed
in the presence of the tested oxidants, including H
2 2
O , peracetic acid
(
PAA), hypochlorous acid (HOCl), and ammonium persulfate (APS).
Note that the same molecule, rhodamine–dansyl conjugate 1, has been
reported to show a significant response toward HOCl [43]. However, as
described earlier, the HOCl signal was suppressed under the present
measurement conditions by the introduction of DMSO, which acts as a
scavenger for HOCl, into the signaling medium [48].
Next, the competitive signaling behavior of probe 1 toward Tl3+ in
the presence of other common metal ions and anions was elucidated. As
3
+
shown in Figs. 3 and S8, the Tl signaling response of probe 1 was not
substantially influenced by the presence of most of the surveyed metal
ions and anions. A competitive experiment with iodide ions was not
Fig. 3. Tl3+-selective signaling of probe 1 in the presence of background metal
ions as expressed by the absorbance ratio AMetal+Tl(III)/ATl(III) at 556 nm. [1] =
5
3
+
conducted because Tl
is routinely standardized by iodometric titra-
.0 × 10– M, [Tl ] = [M ] = 5.0 × 10 M, [buffer] = 3.0 × 10 M in a
6
3+
n+
–5
–2
tion using the reaction with iodide ions.
3
+
mixture of acetate buffer (pH = 4.76) and DMSO (8:2, v/v).
To quantify the analytical behavior of the probe for Tl
determi-
3
+
nation, the absorbance at 556 nm was measured as a function of [Tl
]
3
+
fluorescence signaling of Tl3+. In the aqueous acetate buffer solution
(pH = 4.76) containing 20% DMSO, probe 1 exhibited a broad emis-
sion band of moderate intensity centered at 498 nm. Upon treatment
with Tl3+, a strong emission band appeared at 583 nm, resulting in a
change in the fluorescence color from green to orange. No measurable
responses were discernible for other tested metal ions (Fig. 5) and an-
ions (Fig. S12). Furthermore, the Tl3+ fluorescence signaling behavior
of probe 1 did not seem to be affected by the presence of common metal
ions and anions in the background (Fig. S13). However, the signaling
selectivity determined by ratiometry using the fluorescence intensities
at 583 and 498 nm was not satisfactory owing to the relatively weak
fluorescence of the dansyl moiety at 498 nm (Fig. S14). For this reason,
we analyzed the fluorescence signaling behavior of probe 1 using the
(
7
Fig. 4). The calibration plot was linear up to a Tl
concentration of
–6
.0 × 10 M. From the linear part of the plot, the LOD of the probe for
3
+
was estimated to be 1.9 × 10–7 M (0.039 ppm) according to the
Tl
IUPAC guidelines (3sbl/m) [45]. In addition, the UV–vis and fluores-
3
+
–5
cence spectra of 1 + Tl (1.0 × 10 M) and rhodamine B base alone
Figs. S9 and S10) indicated that the absorbance and fluorescence in-
tensities reach saturation when the concentration is further increased to
(
–5
3+
1
.0 × 10 M. The colorimetric signaling of Tl
was fast, and a sa-
turated response was achieved within 2 min of sample preparation.
Furthermore, the probe was stable under the measurement conditions,
and there was no detectable deterioration of the response over several
hours (Fig. S11).
We also investigated the possibility of applying probe 1 for
Fig. 2. Partial 1H NMR spectra of probe 1, probe 1 treated
with Tl (1 + Tl3+), rhodamine B base, and dansyl acid. [1]
3
+
–
2
=
DMSO-d
[rhodamine B base] = [dansyl acid] = 1.0 × 10 M in
3
+
6
. The spectrum of 1 + Tl
was recorded in situ
using the signaling solution obtained by mixing probe 1 (1.0
–
2
3+
–2
×
10 M) and Tl
(2.0 × 10 M).
4

Y.J. Lee, et al.
Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
3
+
Fig. 4. Concentration-dependent absorbance changes at 556 nm for the Tl
Fig. 6. Colorimetric signaling behavior of probe 1 as expressed by the change in
–
6
3+
–6
3+
signaling behavior of probe 1. [1] = 5.0 × 10 M, [Tl ] = 0–6.0 × 10 M,
buffer] = 3.0 × 10 M in a mixture of acetate buffer (pH = 4.76) and DMSO
the ΔGreen value (255 – green channel level) as a function of [Tl ]. [1] = 2.0
–
2
–5
3+
–5
–2
[
× 10 M, [Tl ] = 0 – 1.0 × 10 M, [buffer] = 3.0 × 10 M in a mixture of
acetate buffer (pH = 4.76) and DMSO (8:2, v/v). The inset images were ob-
tained with a scanner and analyzed using the Photoshop CS6 software.
(8:2, v/v).
obtained using the green channel was linear up to a Tl3+ concentration
2
of 10 μM (R = 0.9923). Thus, this approach is suitable for the
straightforward determination of Tl3+ levels in various practical ap-
plications. From the concentration-dependent signaling response, the
3+
LOD of probe 1 for Tl using the scanner-based method was estimated
–
7
as 1.3 × 10 M (0.027 ppm) according to the IUPAC guidelines [45].
Finally, this scanner-based method was applied to assay commercial
thallium(III) reagents (thallium(III) nitrate trihydrate) (Table 1). The
results of the colorimetric signaling-based assay of Tl3+ ions performed
using probe 1 were in good agreement with those of the standard io-
dometric titration method [46] (relative error = –0.8% to 0.2%).
4
. Conclusion
Fig. 5. Tl3+-selective fluorescence signaling of probe 1 over other common
metal ions as expressed by the fluorescence intensity at 583 nm. Inset: fluor-
escence spectra of probe 1 in the presence and absence of various metal ions.
A novel colorimetric and fluorescence reaction-based probe showed
3+
excellent selectivity for Tl
and anions. Signaling was realized by the Tl -assisted oxidative
cleavage of the sulfonhydrazide linkage in the probe to yield the con-
over other relevant oxidants, metal ions,
1] = 5.0 × 10– M, [Tl ] = [M ] = 5.0 × 10 M, [buffer] = 3.0 × 10
6
3+
n+
–5
–2
[
3+
M in a mixture of acetate buffer (pH = 4.76) and DMSO (8:2, v/v). λex =400
nm.
3
+
stituent dyes, rhodamine B base and dansyl acid. The Tl
signaling
process was not considerably affected by pH in the range of 4.0–5.5. To
demonstrate the practical applicability of the designed probe, we de-
veloped a method involving the use of an office scanner for the con-
fluorescence intensity at 583 nm alone, which originated from the
rhodamine fluorophore. As shown in Fig. S15, the Tl3+ fluorescence
signaling behavior was unaffected by the presence of common metal
ions and anions. These observations suggest that probe 1 can be used
3+
venient and sensitive analysis of Tl with a detection limit of 0.13 μM
3+
(
0.027 ppm). Our method was successfully applied to assay the Tl
3
+
for the selective and sensitive determination of Tl
by both colori-
contents of laboratory reagents.
metric and fluorescence measurements.
Subsequently, probe 1 was applied for the colorimetric determina-
CRediT authorship contribution statement
3
+
tion of Tl
using a readily available office scanner. Several reports
have described the use of a scanner as a portable device for the con-
venient chemical analysis of biologically and environmentally im-
portant chemical species [49–52]. We believe that the present system is
particularly suited to this approach because the pronounced colori-
metric and fluorescent responses of the probe to Tl3 is discernible to
the naked eye. To develop this method, we chose colorimetric signaling
rather than fluorescence signaling owing to the simplicity for routine
Yu Jeong Lee: Investigation, Writing - original draft, Formal ana-
lysis. Myung Gil Choi: Investigation, Writing - review & editing,
Visualization. Jae Hoon Yoo: Investigation, Formal analysis. Tae Jung
Park: Investigation, Writing - review & editing, Funding acquisition.
Sangdoo Ahn: Writing - review & editing, Supervision. Suk-Kyu
Chang: Conceptualization, Writing - review & editing, Supervision,
Funding acquisition.
+
3
+
applications and superior Tl selectivity under competitive conditions
of the former approach. Solutions with different concentrations of Tl3+
were prepared under the same signaling conditions and transferred to a
microwell. The microwell was imaged using a scanner in transmission
mode, and the obtained images were analyzed by a color analysis
program (Photoshop CS6, Adobe Systems). As can be seen in Fig. 6, the
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
3
+
colorimetric response of the probe toward Tl is readily perceived by
the naked eye. The plots of the red, green, and blue channel values as a
3
+
function of [Tl ] demonstrated that the most pronounced change was
observed using the green channel value (Fig. S16). The calibration plot
Acknowledgments
This study was supported by the National Research Foundation of
5

Y.J. Lee, et al.
Journal of Photochemistry & Photobiology A: Chemistry 394 (2020) 112471
Table 1
3 3
Assay of Tl(NO ) reagents using the scanner-based method with probe 1 and iodometric titration.
Sample
Tl3+ content determined using probe 1a
Tl3+ content determined by iodometric titrationa
Relative error
Tl3 reagent #1
+
b
96.6% ± 0.6%
97.2% ± 0.3%
96.8% ± 0.3%
96.4% ± 0.3%
0.2%
–0.8%
3+
b
Tl
reagent #2
a
b
Reported values are given as mean ± standard deviation (n = 3).
3+
Tl
reagents #1 and #2 were obtained from Aldrich Chemical Co. as thallium(III) nitrate trihydrate.
Korea (NRF) grant funded by the Korean Government (NRF-
018R1D1A1A09081790) and the Ministry of Science and ICT (MSI)
NRF-2019R1A2C208406511).
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