Accepted Manuscript Title: A turn-on fluorescent probe for selective and sensitive detection of hydrogen sulfide Author: Fang Ma Mingtai Sun Kui Zhang Huan Yu Zhenyang Wang Suhua Wang PII: DOI: Reference:
S0003-2670(15)00416-X http://dx.doi.org/doi:10.1016/j.aca.2015.03.040 ACA 233826
To appear in:
Analytica Chimica Acta
Received date: Revised date: Accepted date:
25-9-2014 24-1-2015 24-3-2015
Please cite this article as: Fang Ma, Mingtai Sun, Kui Zhang, Huan Yu, Zhenyang Wang, Suhua Wang, A turn-on fluorescent probe for selective and sensitive detection of hydrogen sulfide, Analytica Chimica Acta http://dx.doi.org/10.1016/j.aca.2015.03.040 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
A turn-on fluorescent probe for selective and sensitive
2
detection of hydrogen sulfide
3
Fang Maa,b,1 Mingtai Sun,b,1 Kui Zhang,b Huan Yu,b Zhenyang
4
Wang,b and Suhua Wanga,b,*
5
6
7
a
Department of Chemistry, University of Science & Technology of China, Hefei,
Anhui, China b
Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui, China
8
E-mail:
[email protected];
[email protected] 9
Graphical abstract
10 11
12
Highlights
13
1. Fluorescence turn-on detection of hydrogen sulfide based on
14
displacement method.
15
2. High sensitivity and selectivity for hydrogen sulfide detection.
16
3. Visual detection of hydrogen sulfide gas based on a simple and
17
portable fluorescent indicating paper.
18
1
1
ABSTRACT
2
Animidazolethione based turn-on fluorescent probe was synthesized for the detection
3
of hydrogen sulfide, a biologically relevant molecule and an important air pollutant.
4
The probe rapidly and selectively reacted with hydrogen sulfide to produce a strongly
5
fluorescent product, resulting in the fluorescence enhancement of the system. The
6
detection limit was determined to be 30 nM at the probe concentration of 1.0 μM. An
7
indicating paper for visual detection of hydrogen sulfide gas has been fabricated by
8
immobilizing the probe on a piece of appropriate paper substrate, and the detection
9
limit of the visual method reached as low as 0.7 ppm.Moreover, the fluorescence turn-
10
on/off of the system showed good reversibility when exposed alternately to hydrogen
11
sulfide and mercuric ion, which was utilized to make an INHIBIT logic circuit for the
12
presence of the two species.
13
Keywords:Fluorescence turn-on sensing; Chemosensor; Displacement; Hydrogen
14
sulfide
15
1. Introduction
16
The detection and monitoring of hydrogen sulfide (H2S) has attracted great
17
concerns due to its important biological functions at low concentration and toxicity at
18
high level [1]. H2Scan be formed by protonation of bisulfide(HS-) and sulfide anion
19
(S2-), which is widely employed in industrial processes for production of sulfur,
20
sulfuric acid, dyes and cosmetics, and etc. It can be also found in biosystems due to
21
microbial reduction of sulfate by anaerobic bacteria and formation from sulfur-
22
containing amino acids in meat proteins [2]. Exposure to high concentration of H2S
23
leads to severe impact on human health including personal distress, irritation of
24
mucous membranes, loss of consciousness and permanent brain damage [3]. In 2
1
addition, H2S is also an endogenous gasotransmitter following nitric oxide (NO) and
2
carbon monoxide (CO) [4-7]. Thus, the development of efficient and sensitive
3
approaches for H2S detection is of great importance for exploring its biological
4
functions and environment protection.
5
Currently, several techniques such as electrochemistry [8-10], spectrophotometry
6
[11,12], chemiluminescence [13-15], chemical titration [16,17], fluorometry [18-20],
7
colorimetry[21-24], inductively coupled plasma atomic emission spectroscopy (ICP-
8
AES) [25,26],and chromatography [27-29] have been employed for detection of
9
hydrogen sulfide.Among these methods, fluorometry, in particular, has attracted much
10
attention due to its high sensitivity, simplicity and in-situ detection, as well as the
11
ability for temporal and spatial resolution [30]. However, fluorometry methods have
12
largely relied on the development of novel fluorescent probes, most of which are
13
mainly based on reaction-based methods and displacement methods [31-34].The
14
reaction-based methods generally require a relatively long reaction time which limits
15
their practical applications [35-37]. On the other hand, the displacement methods
16
utilizing the high affinity of H2Swith metal ion can rapidly reach reaction equilibrium,
17
hence allow for rapid and real-time detection of H2S.
18
To design such a displacement-based turn-on fluorescent probe for H2S, the
19
fluorescence background of the system should be very weak and the metal center can
20
bind strongly to H2S. It has been documented that Hg2+reacts rapidly with sulfide to
21
form amore stableproduct HgS with solubility product constant of Ksp=4×10-53 than
22
other organic ligands [38-40].We thus used Hg2+ and an imidazolethione compound,
23
2-(pyridin-2-ylmethyl)imidazo[1,5-a]pyridine-3(2H)-thione (PIPT), to synthesize a
24
novel turn-on fluorescent probe Hg(PIPT)2.H2Scould rapidly react withthe metal 3
1
center, mercuric ion, to release a strongfluorophore PIPT, leading to the fluorescence
2
recovery of the system.This method showed high selectivity andsensitivity for
3
hydrogen sulfide with a detection limit of 30 nM at the probe concentration of 1.0 μM.
4
2. Experimental section
5
2.1. Materials
6
2-picolylamine, pyridine-2-aldehyde, and tricarbonyldichlororuthenium(II) dimer
7
were purchased from Sigma-Aldrich and used as received. Carbon disulfide (CS2),
8
ammonium hydroxide (25%), sodium sulfide nonahydrate(Na2S·9H2O) and mercuric
9
nitrate(Hg(NO3)2) were purchased from Sinopharm Chemical Reagent Co., Ltd.
10
(Shanghai, China).Hydrogen peroxide (H2O2), tert-butyl hydroperoxide (TBHP),
11
sodium hypochlorite (NaClO) and potassium superoxide (KO2) were obtained from
12
AladdinReagent Co., Ltd.(Shanghai, China). All reagents and solvents were of
13
analytical-reagent grade and used as received without further purification.Ultrapure
14
water (18.2 MΩ·cm) was obtained from a Millipore water purification system.
15
2.2. Apparatus
16
1
H NMR spectra were recorded on Bruker AVANCE AV-400 spectrometer, in
17
DMSO-d6. Chemical shifts were reported in ppm with respect to residual solvent
18
protons, and coupling constants (J) were reported in Hz.Mass spectra were recordedon
19
a ProteomeX-LTQ mass spectrometer. UV-vis absorption spectra were collectedusing
20
a Shimadzu UV-2550 spectrometer. Fluorescent measurements were performed ona
21
Perkin-Elmer LS-55 fluorescence spectrometer, in 1 cm quartz cuvettes at room
22
temperature, with excitation and emission slit widths of 10 nm. Fluorescent photos
23
were taken using a Canon 350D digital camera under 365 nm irradiation. 4
1
2.3. Synthesis of PIPT and its Hg complex Hg(PIPT)2
2
The ligand 2-(pyridin-2-ylmethyl)imidazo[1,5-a]pyridine-3(2H)-thione (PIPT) was
3
synthesized using pyridine-2-aldehyde (54 mg) and 2-picolylamine (54 mg) as
4
starting compounds in methanol, followed by reducing with NaBH4under nitrogen
5
atmosphere. The intermediate product was purifiedby reduced pressure distillation
6
and redissolvedin dichloromethane/ethanol (1:1, V/V).Then the intermediate was
7
reacted with CS2 in the presence of NH3·H2O at ice bath for 10 hours.Theproduct
8
PIPT was obtained by chromatograph on silica gel column with ethyl
9
acetate/petroleum ether (5:8, V/V).ESI-MS (m/z): 242.10 (M + H+)(calcd 242.07).1H
10
NMR(DMSO-d6, 400 MHz)δ (ppm): 8.54 (d, J=5.2 Hz, 1H), 8.12 (dd, J=6.9 Hz,
11
J=1.2 Hz, 1H), 7.78 (td, J=7.0 Hz, J=1.6 Hz, 1H), 7.63 (s, 1H), 7.41 (q, J=9.2 Hz, 1H),
12
7.33 (d, J=5.6 Hz, 1H), 7.20 (d, J=7.6 Hz, 1H), 6.84 (q, J=7.2 Hz, 1H), 6.68 (td, J=6.4
13
Hz, J=1.2 Hz, 1H), 5.61 (s, 2H).
14
The complex Hg(PIPT)2 was readily synthesized from solutions of PIPT and
15
Hg(NO3)2with a molar ratio of 2:1in dimethylsulfoxide.The structure of the complex
16
was characterized by 1H NMR and mass spectrometry.ESI-MS (m/z): 342.00 ((M +
17
2H+)/2)(calcd 342.05). 1H NMR (DMSO-d6, 400 MHz)δ(ppm): 8.57 (d, J=6.0 Hz, 1H),
18
8.40 (dd, J=6.1 Hz, J=1.2 Hz, 1H), 8.24 (s, 1H), 7.96 (d, J=8.8 Hz, 1H), 7.81 (d, J=8.4
19
Hz, 1H), 7.60 (t, J=7.0 Hz, 1H), 7.48 (d, J=7.0 Hz,1H), 7.25 (t, J=6.0 Hz, 1H), 7.17 (t,
20
J=6.9 Hz, 1H), 5.91 (s, 2H).
21
2.4. Calculation of thebinding constant of the Hg(PIPT)2 complex
22
23
The binding constant K of the Hg(PIPT)2 complex was determined according to the Benesi-Hildebrand equation [41]:
5
1 1 1 = + ′ ′ F−F K(F − F )[Hg ] F − F ′
1
where F0 is the initial fluorescence intensity of free PIPT, F is the fluorescence
2
intensity of PIPT in the presence of Hg2+, F′ is the fluorescence intensity of PIPT after
3
addition of excess amount of Hg2+, and K is the binding constant of the Hg(PIPT)2
4
complex. For this system, the solution of PIPT with excess Hg2+is almost non-
5
fluorescent, hence F′≈0. Thus a linear relationship is obtained between F0/(F0-F) and
6
1/[Hg2+], and the K is equal to the value of the intercept/slope of the calibration plot.
7
2.5. The fluorescence response of the probeto H2S
8
For fluorescence experiments, 3.0 μL of Hg(PIPT)2probesolution (1.0 mM) was
9
first dilutedin 3.0 mL of EtOH/H2O (1:2, V/V). Then appropriate amount of H2Sstock
10
solution (0.1mM) was added into the probe solution and mixed thoroughly. The final
11
concentrations of H2Swere calculated to be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0,
12
1.1, 1.2, and 1.3 μM.The fluorescence spectra were recorded before and after the
13
addition of H2S.All the measurements were performed independently in triplicate and
14
averaged.
15
The fluorescence response of the probe toward H2S gas has also been examined.
16
The H2S gas was prepared bya stoichiometric reaction between Na2S and diluted
17
H2SO4. Briefly, 0.4 mL of H2SO4(0.1 mmol) was slowly injected into a sealed flask
18
(350 mL) containing of Na2S·9H2O (0.05 mmol). Then different volume (3, 6, 9, 12,
19
15, 18 and 21 μL) of the gas was sucked by a micro syringe and injected into the
20
probe solution to collect the fluorescence spectra. The fluorescence changes of the
21
probe in the presence ofH2S were observed under a UV lamp (8 W, λex = 365 nm) and
22
the images were recorded by a digital camera. 6
1
2.6. Selectivity studies of the probe to H2S
2
The fluorescence responses of the Hg(PIPT)2 complex to various reactive species,
3
common anions and metal ionswere carefully examined by a similar procedure to that
4
of H2S. Typically, into each 3.0 mL of the as-prepared probe solutions(1.0 μM) were
5
respectively added these species.The reactive speciestestedwere hydrogen peroxide
6
(H2O2), tert-butyl hydroperoxide (TBHP), hydroxyl radical (·OH), sodium
7
hypochlorite (NaClO), potassium superoxide (KO2),sodium nitrite (NaNO2), cysteine
8
(Cys), and glutathione (GSH). Hydroxyl radicalwas generated in situ by adding
9
ferrous sulfate in the presence of 10 equivalents of H2O2 based on Fenton reaction.
10
Some gases,such as carbon monoxide (CO), carbon dioxide (CO2), nitric oxide (NO),
11
nitrogen dioxide (NO2), sulfur dioxide (SO2), and ammonia (NH3), have also been
12
studied to examine their effect on the probe.CO was prepared by dissolved
13
tricarbonyldichlororuthenium(II) dimer in dimethylsulfoxide.The fluorescence spectra
14
were recorded after the addition of these species.For interference experiments,the
15
fluorescence spectra were respectively collectedand compared after the addition of
16
H2S in the presence of the species.
17
2.7. Examination of the interaction between Hg(PIPT)2 complex and H2S
18
The interaction between Hg(PIPT)2 complex and H2S was carefully analyzed by
19
NMR and UV-vis absorption spectrometry.The NMR spectrum of PIPT was first
20
recorded by dissolving 10 mg of PIPT in 0.5 mL of DMSO-d6. The NMR spectrum of
21
Hg(PIPT)2was then obtained by adding and thoroughly mixing 10 mg of
22
Hg(NO3)2into the PIPT solution. Then the Hg(PIPT)2solution in DMSO-d6 was
23
injected with excessive H2S gasfor reaction. Themixture was filtered to remove the
24
precipitate of HgS and to regenerate the PIPT for NMRmeasurement. 1H NMR 7
1
(DMSO-d6, 400 MHz)δ (ppm): 8.55 (d, J=7.0 Hz, 1H), 8.12 (dd, J=7.0 Hz, J=1.2 Hz,
2
1H), 7.81 (td, J=7.9 Hz, J=1.2 Hz, 1H), 7.64 (s, 1H), 7.43 (q, J=9.1 Hz, 1H), 7.35 (d,
3
J=5.6 Hz, 1H), 7.22 (d, J=7.9 Hz, 1H), 6.84 (d, J=8.1 Hz, 1H), 6.69 (td, J=6.0 Hz,
4
J=1.2 Hz, 1H), 5.62 (s, 2H). For the UV-vis absorption experiments, the absorption of
5
free ligand PIPTand Hg(PIPT)2 complexwere first obtained. Various concentrations of
6
H2Swerethen gradually added into the probesolution to monitor the UV-vis spectral
7
changes.
8
2.8. Preparation of fluorescent indicating paper for visual detection of H2S gas
9
Cellulose acetate microporous membrane (10 mm × 35 mm) was used as the
10
substrate for immobilizing the probe. 2.0 μL of the probe solution (10 μM) was
11
carefully dropped onto a piece of the membrane. The fluorescence indicating paper
12
was then obtained after the solution was dried in air to form a spot about 8 mm in
13
diameter.Such a piece of indicating paper was placed in a clear glass container(350
14
mL in volume) for visual detection of H2S gas.Different amount of H2S gas sample
15
was injected into the container with the indicating paper. The fluorescence change of
16
the indicating paper was recorded by digital camera under a UV lamp. The empirical
17
detection limit of this visual method was determined as the least amount of H2S
18
capable of producing fluorescence on the indicating paper that could be clearly seen
19
bynaked eyes.
20
3. Results and discussion
21
3.1. Characterizations
22
Fig.1 outlinesthe synthetic routes for the ligand PIPT and its mercuric complex
23
Hg(PIPT)2. 1H NMR and mass spectroscopy studies have confirmed their structures 8
1
(Fig. S1, S2 and S3).The binding constant of the complex was determined to be
2
K=5.6×105 based on the Benesi-Hildebrand method (Fig. S4).Before reaction with
3
Hg2+, the free PIPT displays a maximum emission at 505 nm with a high fluorescence
4
quantum yield ofФ = 63.9% (Fig. S5, S6).However, the fluorescence is greatly
5
quenchedafter addition of Hg2+ andthe fluorescence quantum yield decreases to 3.43%
6
(Table S1).
7
8
Fig. 1
3.2. Sensitive fluorescence turn-on response of the probe toH2S
9
Upon exposure to H2S,the fluorescence of the probe gradually increaseswith the
10
H2S concentration,following a dose-response manner (Fig. 2). The immediate
11
fluorescence turn-on response reaches equilibrium within 30 seconds and the
12
fluorescence intensity keeps constant within 10 minutes (Fig. S7).One equivalent of
13
H2S can enhance the fluorescence intensity by ~ 13-foldand the fluorescence
14
quantum yield increases to 61.7%. More H2Scannot further increase the
15
fluorescence, suggestinga 1:1 stoichiometric reaction between the probe and
16
H2S.The inset in Fig. 2 shows the plot of fluorescence increment (I/I0) against the
17
concentration of H2S. Clearly, the plot fits linearly with a correlation coefficient of
18
0.997 in the concentration range from 0.1 μM to 1.0 μM, andreaches a platform
19
when the concentration of H2Sis higher than 1.0 μM.The detection limit (3σ)is
20
estimated to be about 30 nM.The comparison with other methods reported in
21
literatures shows the relatively high sensitivity of the current method (Table 1).
22
Furthermore, the Hg(PIPT)2 probe also shows turn-on response to H2S gas (Fig. S8).
23
Fig. 2
24
Table 1 9
1
3.3. Effects of the probe concentration on the sensitivity
2
The effect of probe concentration on the analytical performance was carefully
3
examined to optimize the detection condition. As can be seen in Fig. 3, relatively low
4
probe concentrations,such as 1.0 μM and 3.0 μM, result in two identicalcalibration
5
curves except for different linear ranges. When the probe concentration is increased
6
higher to 5.0μM, however,the slope of the fitted line slightlydecreases, suggesting a
7
drop of the sensitivity at higher probe concentration. The drop of sensitivity may be
8
due to the self-quenching of the probe or higher background fluorescence of the probe
9
before the addition of H2S. The results show thata probe concentration of 3.0μM
10
11
12
could be the optimized concentration for further detection. Fig. 3
3.4. Selectivity of Hg(PIPT)2 probe forH2S
13
To examine the selectivity of the probe toward H2S, the fluorescence responseof the
14
probe to other species including H2O2, TBHP,·OH, ClO-, O2-, NO3-, NO2-,GSH, Cys,
15
Cl-, CO32-, HCO3-, SO42-, SO32-, F-, Br-,OAc-, and OH- were studied following the
16
same conditions as that of H2S. As presented in Fig. 4,the fluorescence of the probe is
17
greatly enhanced by H2S, whereas other species show no obvious enhancement on the
18
fluorescence(Fig. S9). It’s noted that GSH and Cys also exhibitturn-on effect on the
19
fluorescence of the probe, which is due to the affinity between Hg2+ and thiol group of
20
GSH and Cys (Fig. S10). Fortunately, their interferences can be easily eliminated by a
21
simple pretreatment with DMSO, which can oxidize the thiol group to disulfide.The
22
disulfide has less affinity to Hg2+and thus has a negligible effect on the fluorescence
23
of the probe. The fluorescence responses can also be easily observed under a UV lamp
24
(365 nm)(Fig. 4A).Upon addition of H2S, a bright green fluorescence is observed, 10
1
while no fluorescence can be observed for other species. The selective fluorescence
2
turn on by H2S alsoexhibits high anti-interference against other relevant species.
3
Results indicate that the presence of Cl-, NO3 -, SO42-, SO32-, H2O2 and TBHP at 100
4
times higher concentration than H2Sdo not interferethe fluorescence responses of the
5
probe to the latter. The presence of OH-, ClO- and O2-at 10 times concentration of H2S
6
can slightlyenhance the fluorescence, which could be attributed to the decomposition
7
of the probe in strong alkaline condition. However, these interference increments are
8
negligible when compared with that of H2S. It can be seen that Br- at 10 times
9
concentration of H2S exhibits an enhancement on the fluorescence of the probe, which
10
maybe due to the formation of HgBr42- (lgK=21.00). However,Br-has much lower
11
reactivity with Hg2+ than H2S, and its presence shows a little effect on H2S
12
detection(Fig. 4B).In addition, the fluorescence responses of the probe toward various
13
common metal ions such as K+, Ba2+, Ca2+, Mg2+, Ba2+, Cd2+, Ni2+, Co2+, Cu2+, Fe3+
14
and Zn2+, and gases such as CO, CO2, NO, NO2, SO2 and NH3, have also been studied.
15
Results show that none of the metal ions or the gases exhibit apparent turn-on effect
16
on the fluorescence of the probe (Fig. S11, S12).Although a slight decreasing of the
17
fluorescence are observed in the presence of Zn2+, Cu2+ and Fe3+ when their
18
concentrations were 10 times of H2S which could be due to that the three metal ions
19
competitively react to H2S with the probe, they do not affect the probe itself. These
20
results indicate the high selectivityof the probe toward H2S.
21
Fig. 4
22
3.5. Mechanism of fluorescence turn-on by H2S
23
The fluorescence recovery of the probe with H2S is due to the release of the
24
fluorescent ligand PIPT from the mercuric complex after H2S reacted with the metal 11
1
center, as illustrated in Fig. 5. This is rational when considering that the binding
2
constant of HgSis much higher than that of the Hg(PIPT)2complex.To better
3
understand the reaction mechanism of Hg(PIPT)2 probe with H2S,NMR and UV-vis
4
spectra of Hg(PIPT)2complex in the absence and presence of H2S were thoroughly
5
examined. As shown in Fig. S1, the productof Hg(PIPT)2after reaction with H2S
6
possesses the same characteristic resonance peaksto that of the free ligand PIPT,
7
suggesting the liberation of PIPT by H2S.The UV-vis spectral changes of the probe
8
before and after addition of H2S were also examined (Fig. 5 and S13). It is observed
9
that the Hg(PIPT)2 probe solution has an initial broad band centered at 325 nm. Upon
10
additionof H2S, the absorption band gradually decreases, accompanied by appearance
11
of two new bands at 300 nm and 365 nm. The absorption spectra after treated with
12
H2Shave nearlyidentical characteristicswith that of the ligand PIPT, further
13
confirming this displacement mechanism.
14
15
Fig. 5
3.6. Logic gate usage of the Hg(PIPT)2 probe
16
The fluorescence of the probeafter exposure toH2Scan be quenchedbyadding one
17
equivalent ofHg2+and restored again by the addition ofanother one equivalent of
18
H2S.This system could keep almost the same emission intensity even after 13 times of
19
alternate addition of H2S and Hg2+ (Fig. S14).Such a fluorescence “on-off” cycle
20
could be applied for a logic gate on the basis of the fluorescence signal operated by
21
two inputs, In(H2S) and In(Hg2+) (Fig. 6). This kind of logic gateshave recently been
22
widely studied, such asAND [42], OR [43], YES [44], NOT [45], NOR [46],XOR
23
[47], and INHIBIT[48].The two inputs have been set as 0 and 1, respectively,for
24
itsabsence and presence. The addition of H2S leads to fluorescence enhancement and 12
1
the output is read out as 1.When treated with Hg2+ again, the fluorescence is quenched
2
and the output is read out as 0. When both of the two inputs are 0 or 1, the
3
fluorescence is quenched and the output is 0, suggesting a INHIBIT logic gate. Fig. 6
4
5
3.7. Fluorescent indicating paper for visual detection of H2Sgas
6
We further applied the fluorescence turn-on probe to fabricate fluorescent
7
indicating paper for H2Sgas because convenient and portable sensors are in high
8
demand for instant and on-site detection[49-52]. Fig. 7 presents the fluorescence
9
images of the indicating paper after exposure to H2S gasfor 1 minuteunder a UV
10
lamp.Clearly, the fluorescence intensities of the spots gradually increase as the
11
concentrations of H2S increasingfrom 0.7 to 4.0 ppm, following a dose-dependent
12
manner.The least amount of H2S generating obvious fluorescent spots is estimated to
13
be 0.7 ppm (Right panel in Fig. 7).The indicating spots become fully fluorescent at the
14
concentration of 4.0 ppm H2S. The fluorescence responses of the indicating paper
15
have also been examined in the presence of other common gases such as CO, CO2,
16
NO, NO2, SO2, and NH3(Fig. S15).Results show that only H2S gas greatly lightens the
17
fluorescence of the indicating paper while other gases exhibit no enhancement on the
18
fluorescence, demonstrating the high selectivity for H2S gas. Such an indicating paper
19
can serve as a potential tool for the instant, sensitive, and convenient detection of H2S
20
gas.
21
22
Fig. 7
3.8. Spike and recovery test of H2Sin real water samples
13
1
The spike and recovery test was conducted in tap water and real lake water to
2
validate the method for H2S detection. The tap water was used directly without further
3
purification and the real lake water collected from a local lake was first filtered
4
through polyvinylidene fluoride (PVDF) microporous filter(0.45 μm)to remove any
5
particulate suspension. The recovery studies were carried out in the mixture of water
6
and ethanol (2:1, V/V) spiked with H2Sat three different concentrations (0.2, 0.5, and
7
1.0 μM). Each concentration was done in triplicate and the average was presented
8
with standard deviation. Table 2 shows the results with and without spiked H2S. The
9
contents of H2S in both tap water and lake water without spiked H2S are below the
10
detection limit of this method, so the values are not considered in the calculation of
11
recovery. It can be seen that the recovery of H2S for the two samples was statistically
12
close to 100% (ranging from 94.6% to 107%), indicating the validation of the
13
detection of H2S in real samples. Table 2
14
15
4. Conclusions
16
In summary, we have synthesized a novel turn-on fluorescence probe for H2S. The
17
probe showed a rapid, selective and sensitivefluorescence turn-on responsetoward
18
H2S. The probe was also successfully applied for the detection of H2S in real water
19
samples. Moreover, a simple and portable paper-based sensor has been fabricated by
20
immobilizing the probe on cellulose acetate papers for the visual detection of H2S gas.
21
This rapid, convenient and effective method has the potential for the real-time
22
detection of H2Sgas and is expected to extend to the visual detection of other gas.
23
Acknowledgement
14
1
We are grateful for the financial support from the National Natural Science
2
Foundation of China (Nos. 21475134, 21302187,91439101).
3
Notes
4
1
These two authors contributed equally to this work.
5
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8
Fig. 1.Scheme represents for the synthesis procedures for PIPTand Hg(PIPT)2 complex.
9
10
Fig.2. Fluorescence enhancement of the Hg(PIPT) 2 probe solution (1.0 μM) upon the addition of
11
H2S(0-1.3 μM). Inset: The plot of fluorescence increment of the probe as a function of the H2S
12
concentration. I0 and I represent the fluorescence intensity of the probe in the absence and
13
presence of different concentrations of H2S, respectively. 20
1
Table 1.Comparison of the analytical features of different methods for the determination of H2S. Linear range
Limit of detection
(μM)
(μM)
Electrochemistry
20-165
7.5
[9]
Spectrophotometry
6.25-62.5
2.81
[12]
ICP-AES
0.156-781
0.156
[25]
Colorimetry
5-15
3
[24]
Chemiluminescence
6.0×10-4-0.01
2.0×10-4
[13]
0.5-8
0.28
[32]
0.5-4
0.021
[40]
0.1-1.0
0.03
This work
Method
Reference
Flurometry
This method 2
3
4
Fig. 3. Fluorescence enhancement curves of the Hg(PIPT)2 probe at three concentrations by H2Sin
5
EtOH/H2O (1:2, V/V). The fluorescence intensities were recorded 2 minutes after the addition of
6
H2S.
21
1 2
Fig. 4. Selectivity of the Hg(PIPT)2 probe toward H2Sover other selected analytes. Bars represent
3
the final fluorescence emission intensity (I) over the initial emission intensity (I0). (A) The
4
fluorescence response of Hg(PIPT)2 probe (1.0 μM) in the presence of 1.0 μM of H2Sand other
5
various selected analytes. Inset: The corresponding fluorescent images of the Hg(PIPT)2(1.0 μM)
6
probe upon the addition of one equivalent of H2S and the other selected analytes. The images were
7
taken by a digital camera under a 365 nm UV lamp irradiation. (B) The gray bars represent the
8
addition of selected species (100 μM for NaCl, Na2SO4, Na2SO3, NaNO3, H2O2, TBHP, and 10
9
μM for all other species) to a 1.0 μM Hg(PIPT)2 probe solution. The black bars represent the
10
subsequent addition of 1.0 μM of H2S to the solution. The emission intensities were recorded at 2
11
minutes after the analytes addition.
12
22
1
Fig.5. UV-vis titration curves of Hg(PIPT)2 probe (30 μM) with various concentrations of H2S.
2
Inset: Graphic representationforthe proposed mechanism of the detection of H2S by Hg(PIPT)2
3
probe.
A
H2S
H2S
Hg 2+
C
H2 S
Hg 2+
Inputs
H2S
Hg 2+
Output
In(H2S)
In(Hg 2+)
(505 nm)
0 0 1 1
0 1 0 1
0 (Low, Flu) 0 (Low, Flu) 1 (High, Flu) 0 (Low, Flu)
4 5
Fig. 6. Reversible fluorescence turn-on/off cycles for the detection ofH2S. (A) Fluorescence
6
images of the probe Hg(PIPT)2 upon the addition of H2S and Hg2+ sequentially. The images were
7
taken under a 365 nm UV lamp. (B) Fluorescence intensity of Hg(PIPT) 2 (1.0 μM) obtained upon
8
the alternate addition of H2S and Hg2+ in EtOH/H2O (1:2, V/V). A = [Hg(PIPT) 2]; B = [A+H2S]; C
9
= [B+Hg2+]; D = [C+H2S]; E = [D+Hg2+]; F = [E+H2S]; G = [F+Hg2+]; H = [G+H2S]. The
10
concentrations of Hg2+ and H2S for each titration were 1.0 μM. (C) The INHIBIT logic gate table.
23
1
control
0.7 ppm
2.1 ppm 4.0 ppm 2 3
Fig. 7.Paper-based visual detection of H2S gas at different concentrations of 0.7, 2.1, and 4.0 ppm.
4
The images on the left were takenunder regular laboratory light. The correspondingfluorescence
5
images under illumination of 365 nm UV lamp were shown on the right.
6
Table 2. Recovery test of H2S spiked in tap water and real lake water Tap water/ethanol
Lake water/ethanol
Found/μMRecovery(%)
Found/μM Recovery(%)
Spiked concentration (μM)
0.2 0.5 1.0
0.208
104 ± 2.7
0.511 102.2 ± 1.9 0.977
0.214
107 ± 3.6
0.487
97.4 ± 2.1
97.7 ± 1.5
0.946
7
24
94.6 ± 2.9