A new chromo-fluorogenic probe based on BODIPY for NO2 detection in air

Article abstract of DOI:10.1039/c4cc08654f

A novel colorimetric probe for the selective and sensitive detection of NO₂ in solution and in air based on a BODIPY core containing an oxime group has been prepared.

Full text of DOI:10.1039/c4cc08654f

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A new chromo-fluorogenic probe based on BODIPY
for NO detection in air
2
Cite this: DOI: 10.1039/x0xx00000x
a,b
a,b
a,b
a,b
L. Alberto Juárez, Ana M, Costero, * Margarita Parra, Salvador Gil , Félix Sancenón
a,c,d
and R. Martínez-Máñez
*
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
A novel colorimetric probe for the selective and sensitive because they require of very inexpensive instrumentation. Moreover,
detection of NO in solution and in air based in a BODIPY in certain circumstances colour modulation can even be observed to
2
core containing an oxime group has been prepared.
the naked eye making chromo-fluorogenic approaches highly
attractive for certain applications. However, despite the inherent
advantages of optical probes the number of publications related to
The selective and sensitive detection of toxic gases is one of the
most promising applications of optical probes and the search of new
sensing systems has been investigated with increasing intensity in
the design of molecular chemodosimeters for NO detection is very
2
1
0
scarce.
last years. In this context nitrogen dioxide (NO ) is one of the most
2
prevalent and dangerous gases. There are several sources of this
pollutant which are mainly related with un-vented gas stoves and
1
heaters in addition to tobacco smoke. Nitrogen dioxide is a highly
[
H NOH]HCl
2
N OH
reactive oxidant and corrosive and it acts mainly as an irritant
Na CO
2
3
2
CHO
affecting the mucosa of eyes, nose, throat, and respiratory tract.
N
F
N
F
N
F
N
F
B
NO
2
B
Moreover extremely high-dose exposure to NO2 may result in
pulmonary edema and diffuse lung injury, whereas continued
1
2
exposure to high NO levels can contribute to the development of
2
acute or chronic bronchitis. Even low level NO exposure may cause
2
Scheme 1. Structure of the BODIPY derivatives 1 and 2.
increased bronchial reactivity in some asthmatics, decreased lung
function in patients with chronic obstructive pulmonary disease and
increased risk of respiratory infections, especially in young
Following our interest in the development of chromo-fluorogenic
probes for toxic gases, we show herein a new chemosensor able to
3
children. No standards have been agreed upon for nitrogen oxides in
detect selectively the presence of NO both in solution and in air (see
2
indoor air, moreover ASHRAE and the US EPA National Ambient
Air Quality Standards list 0.053 ppm as the average 24-hour limit for
Scheme 1). The design of the probe is based in the ability of NO to
2
4
react with oximes and give the corresponding carbonyl group under
NO in outdoor air. However NO levels in certain cities and at
2
2
1
1
very soft conditions. Moreover we have used as dye a BODIPY
core which are a class of well-known fluorophores with widespread
applications as fluorescent probes due to their valuable
characteristics, such as high molar absorption coefficients and high
quantum yields leading to intense absorption and fluorescence
certain hours can reach much higher values of near 100 ppm.
Traditionally electrochemical sensors are usually used for
detection of NO in real labor environments, however interference
2
from coexisting gases have been reported to be a problem in these
devices. Moreover recent alternative approaches for detecting NO
2
1
2
5
bands.
Probe 2 was easily prepared from the corresponding aldehyde 2-
formyl-8-phenyl-1,3,5,7-tetramethylboron-dipyrromethene (1).
Moreover compound 1 was readily prepared 8-phenyl-1,3,5,7-
such as laser-based photoacoustic spectroscopy, surface acoustic
6
7
wave (SAW), transition metal oxide devices carbon quantum dot-
8
functionalized aerogels, or ozone treated graphene have been
reported. In fact there is an interest in the design of new sensors
9
1
3
tetramethylboton-dipyrromethene by oxidation with DMF and
capable of selectively detect NO . In this context chromo-
2
1
4
POCl3. Probe 2 was then obtained by reaction of 1 with
fluorogenic probes are highly appealing for real-time monitoring and
hydroxylamine hydrochloride under mild basic conditions in
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1
5
1
ethanol:water. Compound 2 was fully characterized by H NMR, relative to Fluorescein at pH=8.06 (λexc =490 nm)). This was clearly
1
3
1
C NMR and MS (see Supporting Information for details). The demonstrated via a simple comparison between H NMR and UV
oxime in 2 is electronically connected to the BODIPY core and it spectra of the reaction product between 2 and NO and these of
2
was expected that its transformation to the corresponding aldehyde aldehyde 1. From additional titration experiments of 2 with NO2
in the presence of NO would result in a significant optical change.
limits of detection (LOD) of 0.56 ppm (from UV-vis) and 0.46 ppm
2
(from fluorescence) were determined.
Despite this interesting optical response of probe 2 in solution,
0
.3
.25
.2
.15
.1
Probe 2 + 2 ppm NO2
Probe 2
the detection of NO2 in gas phase is of greater importance.
Therefore, and encouraged by the sensitive response observed with 2
in acetonitrile, in an attempt to extend the application of 2 to real-
time monitoring, we decided to take a further step and developed test
strips for the colorimetric detection of NO2 in air. To this end,
hydrophobic polyethylene oxide films containing probe 2 were
prepared. Sensing films were readily obtained by mixing 2 and
polyethylene oxide (Mw 400,000 Dalton) in dichloromethane. The
mixture was then poured into a glass plate and kept in a dry
atmosphere for at least 24 h (see Supporting Information). In a
typical assay, films were placed into a container holding air and NO2
0
0
0
0
0
.05
0
400
450
500
550
600
(
1 ppm). Immediately a clear color modulation from pink to pale
yellow was observed (see Figure 2). From additional experiments
wavelength (nm)
using the polyethylene oxide membrane containing 2 and different
4
3
3
2
2
1
1
00
50
00
50
00
50
00
amounts of NO in air a visual limit of detection of 0.1 ppm was
determined after ten minutes exposure. Moreover Figure 2 also show
2
Probe 2 + 2 ppm NO2
Probe 2
a
photograph of the emission changes (excitation using a
conventional UV lamp) of the sensing polyethylene oxide membrane
in the absence and presence of NO also at a concentration of 1 ppm.
2
Using emission changes a visual LOD of 0.1 was determined for the
detection of NO in air after ten minutes exposure. These LOD are
2
3
lower than the alarm threshold of 400 µg/m (ca. 0.2 ppm)
established by the European Community for nitrogen dioxide.
50
0
495
545
wavelength (nm)
595
A
B
Figure 1. a) UV (a) fluorescence (b) spectra and spectra of probe 2
-5
2
(acetonitrile, 10 M) alone and after bubbling air containing NO at a
concentration of 2 ppm. Insets display the visual changes both in color and
fluorescence.
Figure 2. Sensing polyethylene oxide membranes containing probe 2. A)
Colour modulation of the sensing film in absence (left) and presence (right)
of NO
2
(1 ppm) in air. B) Emission of the sensing film (excitation at 254 nm)
(1 ppm) in air.
Acetonitrile solutions of probe 2 showed a visible absorption
band at 515 nm (log ε = 4.2). Moreover the probe was weakly
fluorescent due to C=N isomerization with an emission band
in absence (left) and presence (right) of NO
2
1
5
One important issue in relation to the design of probes for
pollutant gases is the role played by potential interferents or false-
positive outcomes produced by other species. Bearing this concept in
mind, the reactivity of probe 2 with other hazardous gases (i.e. NO,
CO , H S, SO ) was also studied. Moreover the probe was also
centered at 560 nm (λexc = 500 nm) and a quantum yield of only 0.19
(relative to Rhodamine B in EtOH (λexc = 500 nm) ). Bubbling of air
containing NO at a concentration of 2 ppm to acetonitrile solutions
2
of probe 2 immediately resulted in clear optical response. In
particular a hypsochromic shift of the absorption band from 515 nm
to 492 nm (log ε = 4.4) was observed (see Figure 1a). Moreover a
remarkable emission change was also found (see Figure 1b); in the
2
2
2
tested in the presence vapours of acetone, hexane, chloroform,
acetonitrile and toluene. Polyethylene oxide films containing probe 2
were prepared and the films were placed into a container holding the
corresponding gas. In all cases probe 2 displayed a remarkably
selective response for NO2 in air. In particular no reaction was
detected in the presence of NO, CO , H S and SO at very high
presence of NO the weak emission at 560 nm disappeared and a
2
new highly emissive band at 515 nm (λexc = 485 nm, φ = 0.77)
evolved. This remarkable chromo-fluorogenic response was visible
to the naked eye (see also Figures 1 and 2). Optical changes were
2
2
2
concentrations (up to 100 ppm). Moreover, no colour or emission
changes were observed in the presence of the volatile organic
attributed to the transformation of the oxime
corresponding aldehyde 1 that is strongly fluoresecent (φ = 0.77
2 into the
1
4
2
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compounds such as acetone, hexane, chloroform, acetonitrile and
toluene (up to 100 ppm in air). In addition it was also observed that
no colour changes of the probe were observed in the presence of
water vapour. Such behaviour indicated that there was no reaction
between 2 and these gases tested, thus rendering 2 a suitable
4
5
U.S. Environmental Protection Agency (EPA). Office of
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selective probe for the detection of NO . In a final experiment the
2
membrane containing 2 was introduced into a container with all the
studied vapours for 24 h yet no change in the colour of the probe was
observed. In contrast, when the same experiment was carried with
the additional presence of NO2 the expected colour change took
place.
6
7
Venema, A., Nieuwkoop E., Vellekoop M.J., Nieuwenhuizen M.S.,
Barendsz A.W., Sensors and Actuators, 1986, 10, 47-64.
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In summary, we reported herein a simple probe based on a
BODIPY derivative that was able to chromo-fluorogenically detect
the presence of NO both in solution and in air. In particular, the
2
reaction of probe 2 with NO induced in the transformation of the
2
oxime to an aldehyde. The conversion of 2 in 1 resulted in a
hypsochromic shift of the absorption band concomitantly with a
colour change from pink to orange. In addition a strong enhancement
of the fluorescence emission together with a blue shift of the band
was also observed rendering 2 a fluorimetric off-on sensing method
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2
incorporated onto polyethylene oxide membranes, which allowed the
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development of simple test strips for the chromo-fluorogenic sensing 11 Mokhari J., Naimi-Jamal M. R., Hamzehal H.. 11th international
of NO in air with a limit of detection of ca. 0.1 ppm. In addition,
probe 2 was highly selective and allowed the optical detection of
Electronic Conference on Synthetic Organic Chemistry (ECSOC-11)
1-30 November 2007
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We thank the Spanish Government (MAT2012-38429-C04) and
Generalitat Valenciana (PROMETEOII/2014/047) for support.
SCSIE (Universidad de Valencia) is gratefully acknowledged for all
the equipment employed.
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ana.costero@uv.es
c
Departamento de Química, Universidad Politécnica de Valencia, Camino de
Vera s/n, 46022, Valencia, Spain. E-mail: rmaez@qim.upv.es
d
CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-
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