Fast, sensitive, selective and reversible fluorescence monitoring of TATP in a vapor phase

Article abstract of DOI:10.1039/c8cc08399a

The development of sensors for the detection of triacetone triperoxide (TATP) has attracted great attention. Here, we constructed a low-cost, portable, reusable, visible paper-based fluorescent sensor for the sensitive detection of TATP via vapor sampling. Under optimized conditions, the fluorescent film showed a high sensitivity to TATP with a detection limit of lower than 0.5 μg mL^-1 in air. The linear range of the response is from 0.5 to 8.0 μg mL^-1. In addition, the paper-based sensor exhibited high selectivity to TATP. The presence of potential interferents showed little effect on sensing. Moreover, sensing is fully reversible. Fortunately, the test can also be conducted in a visualized way.

Full text of DOI:10.1039/c8cc08399a

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Fast, sensitive, selective and reversible
fluorescence monitoring of TATP
in a vapor phase†
Cite this: Chem. Commun., 2019,
5, 941
5
Received 23rd October 2018,
Accepted 14th December 2018
a
a
a
a
a
a
Yanqin An,‡ Xiaojie Xu,‡ Ke Liu, Xuan An, Congdi Shang, Gang Wang,
a
b
a
a
Taihong Liu,
Hong Li, Haonan Peng * and Yu Fang
*
DOI: 10.1039/c8cc08399a
rsc.li/chemcomm
The development of sensors for the detection of triacetone triperoxide casualties of the would-be bombers. Therefore, it is of pivotal
TATP) has attracted great attention. Here, we constructed a low-cost, importance to develop real-time, on-site and high-speed
(
portable, reusable, visible paper-based fluorescent sensor for the sensors for the detection of TATP. However, there are no nitro
sensitive detection of TATP via vapor sampling. Under optimized groups or aromatic moieties in the structure of TATP, and
conditions, the fluorescent film showed a high sensitivity to TATP with thereby it does not show any significant absorption in the
À1
a detection limit of lower than 0.5 lg mL in air. The linear range of the ultraviolet and visible regions, and moreover shows no distinct
À1
6–11
response is from 0.5 to 8.0 lg mL . In addition, the paper-based sensor fluorescence characteristics.
As a result, the conventional
exhibited high selectivity to TATP. The presence of potential interferents methods for explosive detection, even sniffer dogs, could not be
showed little effect on sensing. Moreover, sensing is fully reversible. used for the detection of TATP.
Fortunately, the test can also be conducted in a visualized way.
Nowadays, the frequently used strategies for TATP sensing
are based on indirect ways. Due to the easy decomposition
1
–3
Triacetone triperoxide (TATP),
also known as ‘‘mother of of TATP, scientists tried to construct chemical sensors for TATP
Satan’’, has been widely utilized by terrorists during the last few detection by monitoring one of its decomposition products,
1
2,13
decades. The destructive power of TATP is almost as strong as hydrogen peroxide or acetone.
TNT. A few grams of TATP can easily blow off the fingers, while quantum cascade laser photoacoustic spectroscopy to detect TATP
In 2007, Patel et al. employed
4
14
concentrated pounds of it are devastating. In 2016, a serious and its precursor acetone, which showed high sensitivity.
terrorist attack by using TATP killed at least 31 people in But this technique needs large and expensive equipment and
Brussels. Moreover, the starting materials of TATP – i.e. acetone, also complicated calculations. Compared to this method, the
hydrogen peroxide, and acid – are all commercially available in fluorescence technique possesses high sensitivity and selectivity
pharmacies and reagent companies, and the synthesis process towards the target analytes, which can detect a wide range of
5
of TATP is very simple and available on the internet. Due to the substances ranging from metal ions and anions to organic
possibility of TATP being prepared on board, airports have to neutral chemicals and biological molecules based on different
1
5–17
enforce strict limitations on the volume of carrying liquids in mechanisms.
Thanks to these advantages, scientists have
hand luggage and execute careful monitoring of luggage and designed several fluorescent sensors to realize the sensitive
1
8–31
people. In fact, TATP is presently recognized as one of the detection of hydrogen peroxide from TATP decomposition.
substances having a great impact on the daily lives of millions Unfortunately, all of these methods based on chemical reactions
of people who have probably never heard about it. In addition, are one-time use methods and cannot be used in continuous real
unlike TNT, TATP is unstable, and it can be ignited by heat, time detection. Hence, it is of urgent importance to develop
friction, static, and even movement, which could cause mass costless, portable, reusable, and easy-to-use fluorescent sensors
for the detection of TATP.
a
Herein, we developed a fluorescent compound based test
paper, which could monitor TATP and its decomposition
product of acetone in the gas phase with high sensitivity, short
Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of
Education, School of Chemistry and Chemical Engineering, Shaanxi Normal
University, Xi’an 710062, China. E-mail: phn@snnu.edu.cn, yfang@snnu.edu.cn;
Tel: +86 29 81530786
response time and full reversibility. The azetidine derivative of
b
College of Chemistry and Chemical Engineering, Xi’an Shiyou University,
Xi’an 710065, China
32,33
naphthalene diimides (NDI)
named as DNNDI was synthe-
sized (Fig. 1), where the azetidine group could not only improve
the fluorescence quantum yields of classical fluorophores
†
Electronic supplementary information (ESI) available: Experimental details and
supplemental figures. See DOI: 10.1039/c8cc08399a
These authors contributed equally to this work.
3
4–37
‡
NDI, but also enhance their photochemical stability.
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state of the compound was calculated using time-dependent
density functional theory (TDDFT) at the CAM-B3LYP/6-31G(d,p)
43
level in a suite of Gaussian 09 programs. From the calculated
results, S ’ S occurs between the highest occupied molecular
1
0
orbital (HOMO) and the lowest unoccupied molecular orbital
LUMO).
As shown in Fig. S3 (ESI†), the electron density distribution
(
Fig. 1 (a) The chemical structure of TATP; (b) schematic illustration for
of the LUMO is mainly located on the NDI core, whereas the
electrons of the HOMO are extensively delocalized around the
NDI core and azetidine moiety. Comparing the electronic
structures of the HOMO and LUMO, it is found that DNNDI
possesses intra-molecular charge transfer (ICT) character in the
excited states, which could result in the red-shift of the maxi-
mum emission position and the lowering of the fluorescence
intensity when increasing the polarity of the used solvents.
In other words, if the polarity of the surrounded micro-
environment of the fluorophore, DNNDI, is changed, the fluores-
cence properties must be correspondingly varied. These features
of the specially synthesized compound afford the possibility of
sensing the volatile organic compounds, such as acetone.
the synthesis route of DNNDI.
Interestingly, DNNDI-based sensing papers showed a remark-
able response to the vapor of acetone and TATP, and non-
contact visualization detection of TATP could also be realized.
To have a better understanding of the electronic structures
of DNNDI in the ground and excited states, their UV-vis
absorption and fluorescence emission spectra in solvents of
different polarities were examined at a concentration of
À6
À1
5
.0 Â 10 mol L . The results are depicted in Fig. 2. Clearly,
the UV-vis spectra consisted of three absorption bands, appear-
ing at around 345 nm, 360 nm, and 590 nm, respectively
Filter papers were chosen as the matrix to study the sensing
behavior of DNNDI, where 20 mL of the DNNDI solution
(Fig. 2a). The absorption peaks between 330 and 400 nm could
be attributed to the p–p* transitions of the NDI core. The strong
and broad absorption band centered at 590 nm is characteristic
of n–p* transitions, which may arise from the donation of
electron density from the lone pairs on the N atoms to the NDI
À4
À1
(1 Â 10
mol L , toluene : MeOH = 2 : 1) was dropped.
In order to explore the sensing performances of the as fabri-
cated sensing papers, their fluorescence properties were first
examined. As shown in Fig. S4 (ESI†), the steady-state emission
spectra of DNNDI were recorded under the excitation of absorp-
tion maximum wavelengths (360 nm and 590 nm) according
to the excitation spectrum. The emission maximum of the
3
8,39
core.
These results indicate that the introduction of an
azetidine moiety does not have a significant effect on the
electron structure of the NDI core. However, the intensities of
the fluorescence emissions change significantly upon solvent
variation, and in particular, for the solvents of acetone and
DMF, the fluorescence intensities are obviously lower compared
with other solvents (Fig. 2b). To be clear, the fluorescence quantum
3
CHCl solution of DNNDI is centered at 638 nm, while the
film fluorescence shifted incrementally to 656 nm, suggesting
aggregation of the fluorophore in the film state. In addition, the
strong emission displayed by the DNNDI dyed paper would be
favorable for further sensing applications.
yields (F ) of DNNDI in the solvents tested were determined, and
f
the results are shown in Table S1 (ESI†).
Furthermore, the photochemical stability of the DNNDI-based
fluorescent film was investigated in the dry state. The results are
presented in Fig. S5a (ESI†). It can be seen that there is almost no
decrease in the emission intensity even after 9 h of continuous
illumination, demonstrating the excellent stability of the
as-prepared film.
A sensor device was constructed to study the sensing
performance of the as prepared fluorescent film. The structure
of the device is shown in Fig. 3. In short, the sensor device
mainly consists of three parts: a sensor unit, a sampling system,
and a display system. The sensor unit contains a sampling
It can be seen that the F values of DNNDI in the solvents
f
and even in the film state are all greater than 14%, demonstrating
that DNNDI is an efficient fluorophore owing to the introduction
40
of the azetidine moiety. The relatively low quantum yields in
acetone and DMF are consistent with their intensities in fluores-
cence spectra. The strong dependence of F
endows DNNDI with an opportunity to sense acetone.
f
on organic solvents
41,42
To further understand the solvent variation dependent fluores-
cence properties, the electron density distribution in the excited
Fig. 2 Solvent effect and concentration effect. UV-vis spectra (a) and
fluorescence spectra (b) of DNNDI in different solvents at a concentration
of 5.0 Â 10À6 mol L (lex = 360 nm).
Fig. 3 (a) Schematic representation of the DNNDI based fluorescent
sensor device; (b) the fluorescence film-based home-made non-contact
sensing platform.
À1
942 | Chem. Commun., 2019, 55, 941--944
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chamber, an optical system, and an electronic system. There is
no doubt that the sensor unit is the key component of the
device. The main function of the sampling system, consisting
of a stationary gas supply system, air pump, and the micro-
controller system, is to make the vapor steady in the sampling
chamber. The display system converts electrical signals into
visual images through computer software. Thus, the following
sensing tests in this work were all conducted by using this
device.
Fig. 4 (a) The film response to different concentrations of TATP vapor.
Inset: A plot of the differences in the response intensities against the
concentration of TATP vapor. Note: the TATP powder (2 mg) was sealed in
a 250 mL bottle for more than 0.5 h, and then the powder decomposed
Firstly, the DNNDI-based sensing paper was used to monitor
acetone vapor. As shown in Fig. S5b (EIS), the sensing paper
presents a significant response to the saturated acetone vapor, totally. We sampled the TATP vapor with an injector and the vapor was
diluted with air; (b) fluorescence intensity of the DNNDI film monitored at
and the fluorescence quenching efficiency can reach around
6
50 nm (lex = 360 nm) in response to saturated acetone vapor, TATP
77%. The response process is almost instantaneous, and the
vapor and potential interferences.
response time is less than 1 s. Moreover, the sensing test is fully
reversible. The film could be reused at least 30 times without
any attenuation of the fluorescence quenching efficiency, the sensor to TATP vapor was fully reversible during 3 times
demonstrating the excellent reusability of the film. of repetition, which was never achieved before and was very
Furthermore, the sensing performance of the DNNDI-based favorable for practical uses.
paper at different concentrations of acetone (from 750 to 3.0 Â For practical applications, potential interferents, for
0 ppm) was tested under optimal conditions. Remarkably, the instance personal care products typically found in travelers’
5
1
intensity variation of the fluorescence emission decreases with baggage, can be highly problematic in the detection of TATP.
increasing concentrations of acetone vapor, just as shown in In order to assess the selectivity of the sensing papers, an
Fig. S6 (ESI†). The calibration plots show a good linear relation- interference study was performed using lotion, liquid soap,
ship between the response intensities and the values of the shampoo, body wash, dishwashing liquid, cola, and commonly
4
analyte concentrations in the range from 750 to 7.5 Â 10 ppm found liquids, in particular volatile organic compounds (VOCs),
(
Note: I and I represent the fluorescence intensities of the film such as hexane, HCHO, CHCl , toluene, HOAc, aniline, as well
0
3
in the presence and absence of the corresponding analyte as other peroxide compounds HMTD and H O . Fig. 4b shows
2
2
vapor). The correlation coefficient is 0.9984 and the linear the linear graphs of (I/I
0
À 1) for acetone, TATP vapor and
À4
regression equation is RI = 0.0347 À 6.941 Â 10
A
C (ppm). common interferents. It was found that personal care products
In addition, 750 ppm of the analyte, which corresponds and common VOCs have little effect on the fluorescence emission
to 400 times dilution of saturated acetone vapor at room of the sensor. And in the case of hexane and toluene, which
temperature, could result in a significant response of the enhanced the fluorescence emission, one probable explanation
sensing device, suggesting that the detection limit of the is that the solvent vapor disrupted the interaction between
analyte should be lower than this value.
solid molecules to a significant extent, which weakened the
Having low chemical stability, TATP can easily decompose aggregation-caused quenching effect. Overall, the sensor exhibited
and release acetone at room temperature. Based on this point, high selectivity to TATP in the vapor phase.
the as-prepared sensing papers were used to monitor TATP
Visualization monitoring, as a convenient analytical
vapor without any pretreatment. The sensitivity of the proposed method, has offered an attractive alternative due to the easy
method was investigated by detecting TATP vapor at different recognition of color and brightness changes without the need for
À1
À1
À1
À1
concentrations (0.5 mg mL , 1.0 mg mL , 2.0 mg mL
4
,
any external sophisticated instruments and trained technicians.
À1
.0 mg mL , and 8.0 mg mL ) and each test was repeated Thus, the TATP visualization test was tried with the as-prepared
3
times. As depicted in Fig. 4a, the fluorescence signal of the sensing papers. It was found that once the TATP vapor is injected
film-based sensor was recorded upon introduction of different onto the surface of the fluorescent paper, its emission was
concentrations of TATP vapor. It can be seen that a gradual quenched immediately with the color changing from pink to
increase of response intensity was clearly observed with an purple under UV light, as shown in Fig. 5c and Video S1 (ESI†).
increase in the concentration of TATP vapor. The sensor Therefore, the DNNDI-based fluorescent paper could be
presents high sensitivity to TATP vapor as evidenced by the produced in a portable and low-cost test-kit (Fig. 5), which should
À1
significant response to a low concentration of TATP (0.5 mg mL ), be applicable for visualization monitoring of TATP in the
which is below the risk threshold of TATP for the safety of the vapor phase.
1
public and people’s lives. The inset of Fig. 4b shows that the
In conclusion, we described a new paper-based fluorescent
response intensity exhibits a good linear relationship with sensor with an azetidine derivative of naphthyldiimide, DNNDI,
the concentration of TATP vapor, and the calibration equation as a sensing fluorophore. Based on the developed fluorescent
2
is RI = 26.09c À 5.33 with a correlation coefficient R of 0.9972 paper, a sensitive and selective detection method for TATP
(
where RI is the response intensity and c is the concentration of in the vapor phase was established. The response intensity of
À1
TATP vapor in mg mL ). Moreover, the fluorescent response of the sensing papers exhibits a good linear relationship with the
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