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BULLETIN OF THE
ISSN (Print) 0253-2964 | (Online) 1229-5949
KOREAN CHEMICAL SOCIETY
Tokyo, Japan). Photophysical response to each analyte was
estimated by adding each analyte (sodium salt, 2 equiv of
cyanide; 20 equiv. of other analytes) into each aliquot of
the solution of 1 (5 μM in DMSO). A competing experi-
ment was performed by adding 2 equiv of cyanide into the
mixture of all analytes (each 20 equiv) in 1 (5 μM in
DMSO). The fluorescence experiment was performed by
excitation at 400 nm (slit width: 5 × 5 nm).
Scheme 1. Cyanide probing concept of 1.
Paper-based Sensor. A dumbbell-shaped hydrophilic pat-
tern was tailored using Microsoft PowerPoint software
(Figure S3). The cross-linking channel on the paper was
approximately 1.6 cm in length and 0.2 cm in width. A
large circle with a diameter of 0.7 cm and a small circle
with a diameter of 0.5 cm were drawn at the top and bot-
tom of the cross-linking channel, respectively. The tailored
dumbbell shape was printed with wax-based solid ink on
Whatman chromatography paper using a Xerox 8570DN
inkjet printer. After the paper was heated by placing it on a
thus, probe 1 can be utilized for detecting cyanide in paper-
based sensors. We fabricated a dumbbell-shaped, simple
paper device that allows the two-point referencing detection
of cyanide. The rapid, quantitative determination of cyanide
in the linear range of 0–25 mM was achieved on the inter-
nally referenced test strip in a simple and cost-effective
manner.
Experimental
ꢀ
hot plate with the wax side up for 15 s at 120 C and then
cooled to RT, the dumbbell-shaped hydrophilic pattern was
completely separated from the wax printed hydrophobic
Synthesis Procedure for ((6-(dimethylamino)-1,3-Ben-
zothiazol-2-yl)methylene)malononitrile (1). Probe 1 was
prepared following a previously reported synthesis proce-
18
site. A solution of probe 1 in acetonitrile (1.2 μL, 5 mM)
was dropped onto a detection site (large circle; (a) in
Figure S3) and dried for 5 min. Then, 10 μL of various
NaCN solutions in water (0–100 mM) was introduced onto
the sample loading site (small circle; (c) in Figure S3). The
sample droplet reached the detection site through the cross-
linking channel, and then, the paper device was dried for
1
6
dure (Scheme S1, Supporting Information). To a solution
of 6-(dimethylamino)-1,3-benzothiazole-2-carbaldehyde
2) (160 mg, 0.78 mmol) in 2-propanol (9.75 mL), malo-
1
6
(
nonitrile (77.3 mg, 1.17 mmol), and pyridine (0.16 mL)
ꢀ
were added. The mixture was stirred for 1.5 h at 90 C. The
reaction mixture was cooled to room temperature (RT), and
H O was subsequently poured into the mixture to quench
2
1
h. The fluorescence intensity changes on the paper were
measured by irradiation at 365 nm (6 W) using a hand-
held UV lamp (ENF-260C; Spectroline, Westbury, New
York, USA). The paper strip was irradiated with UV light
and photographed. The image was then imported to the
Adobe Photoshop CS6 software to digitize the changes in
fluorescence. The images were then transformed to gray
scale, and the mean fluorescence intensity was determined
from the image histogram. To compensate for measure-
ment errors caused by various light sources, an internal
standard was introduced by measuring the intensity on
the sample loading circle because both circles (i.e., the
the reaction. The mixture was extracted three times with
CHCl , and the combined organic layer was dried over
3
Na SO . All volatiles were evaporated under reduced pres-
2
4
sure. The resulting crude product was purified by flash col-
umn chromatography with dichloromethane:methanol
1
(
20:1) as an eluent to give a violet solid (89% yield); H
NMR (300 MHz, DMSO-d ): δ 8.61 (s, 1H), 7.97 (d,
6
J = 9.2 Hz, 1H), 7.37 (d, J = 2.4 Hz, 1H), 7.2 (dd, J = 9.2,
1
3
2
.4 Hz, 1H), 3.07 (s, 6H); C NMR (75 MHz, DMSO-d6):
δ 151.2, 151.1, 151.0, 145.3, 141.4, 125.9, 116.4, 114.8,
+
1
13.9, 101.7, 80.4; HRMS (FAB , m-NBA): m/z calcd for
detection and sample loading sites) will be equally
C H N S: 255.0704, observed: 255.0705.
1
3
11
4
19,20
affected by the light source.
Thus, all data were inter-
Photophysical Property Measurements. A 10-mM stock
solution of 1 was prepared in DMSO; however, the solution
appeared to be unstable even on exposure to ambient light
because of the labile nature of the vinyl linker. Thus, all
the experiments were performed with the solution carefully
wrapped in aluminum foil to protect the solution from
ambient light. The solution was diluted to 5 μM in DMSO
just before photophysical measurements. The cyanide titra-
tion experiment was performed by adding increasing
amounts of tetrabutylammonium cyanide (TBAC,
nally referenced by measuring the ratio of intensity at the
detection site to the intensity at the sample loading site.
−
To test the selectivity of the paper strips, 30 mM of CN ,
1
7
−
2−
−
−
3
−
−
−
SH , HPO4 , OAc , N , F , Cl , and Br solutions
(sodium salt) were prepared in 100 mM PBS buffer. Each
analyte solution (10 μL) was loaded onto the sample load-
ing site, and the results were determined using the afore-
mentioned method.
Results and Discussion
0–25 μM) to the solution of 1 (5 μM in DMSO). Each mix-
ture was measured using Beckman DU 800 spectrophotom-
eter (Beckman Coulter, Ramsey, Minnesota, USA) and FP-
Design Concept of Probe. Our probe was designed to
have an electron push–pull conjugated structure consisting
of electron donor and acceptor moieties. Malononitrile
6500 Spectrofluorometer (JASCO International Co. Ltd.,
Bull. Korean Chem. Soc. 2016, Vol. 37, 1320–1325
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