Communication
doi.org/10.1002/chem.202102094
Chemistry—A European Journal
presence of DMMP vapors can be monitored by using a simple
smartphone, and a quantification of DMMP vapors can be
obtained by image straightforward processing.
(ɛ=2085) and 530 nm (ɛ=21300), respectively. After excitation
at 500 nm, emission spectrum shows a strong emission band at
538 nm, typical of the BODIPY chromophores (see the Support-
[30]
BDPy-NH was designed for an easy optical detection of
ing Information).
Recognition properties in solution were
2
NAs. For this reason, we introduced a BODIPY scaffold as
chromophore, and an ortho-diamine aryl moiety, to recognize
DMMP via hydrogen bonds.
evaluated monitoring this emission band. In particular, Figure 1
À 6
shows the emission spectra of BDPy-NH (1×10 M in CHCl )
2
3
[20]
À 4
after progressive additions of a DMMP solution (1×10 M in
Synthesis was performed by a modified literature protocol:
starting from 4-acetamidobenzaldehyde, which after reaction
with HNO leads to 3-NO -4-acetamidobenzaldehyde 1. Depro-
CHCl ), calculating a binding constant value of log 6.60 for the
1:1 sensor/DMMP stoichiometry, supported by the ESI-MS
spectrum (see the Supporting Information).
3
3
2
tection of the amino group was performed by using HCl,
Notably, calculated limit of detection is 9.47 ppt, many
orders of magnitude lower than the IDLH (concentration of
toxin in air that is immediately dangerous to life and health)
obtaining the 3-NO -4-aminobenzaldehyde 2, which, in the
2
presence of kryptopyrrole, TFA in catalytic amount, DDQ and
[31]
BF (OEt) , affords the nitro-amino-BODIPY 3. The reduction of
values of the common CWAs (2–30 ppb).
3
2
the À NO group with H /Pd leads to the final sensor BDPy-NH
Selectivity is a crucial parameter for a real sensor. In order to
test the selectivity towards DMMP respect to other common
2
2
2
[28,29]
(
see details in the Supporting Information).
UV-Vis spectrum
of BDPy-NH in CHCl shows two main bands, centered at 390
interfering analytes, we exposed BDPy-NH to air for 5 minutes,
2
3
2
and then the emission spectrum was recorded. As shown in
Figure 2, no change of emission intensity was detected, proving
the selectivity of the sensor to DMMP also in the presence of
the common analytes in the air (24000 ppm of water, 400 ppm
of CO , 5 ppm of NO, and 10 ppm of CO). We also tested the
2
selectivity in competition with triethyl-phosphite (Et P), phos-
3
phocholine (Pho-Ch, used as phosphocholine chloride calcium
salt tetrahydrate simulant of V series), triphenylphosphine
(
PPh ) and methanol: in particular, we exposed BDPy-NH to a
3
2
large excess of these substances (50 equiv), and then 1 equiv-
alent of DMMP was added. As shown in Figure 2, BDPy-NH2
recognizes DMMP also in the presence of a large excess of the
competitors. We note that BDPy-NH recognizes phosphocho-
2
line with lower affinity respect to DMMP, suggesting a
selectivity of the sensor for G series CWAs. Probably, the
presence of the cationic aliphatic chain in the phosphocholine
[32]
scaffold leads to a lower response of the probe.
À 6
Figure 1. Emission spectra of BDPy-NH
2
(1×10 M in CHCl
3
, λex =500 nm)
In order to obtain a real-world sensor device, we developed
a prototypal solid-supported test strip. We tested the sensing
properties of BDPy-NH2 under realistic conditions: in air, by
exposing to CWA vapors. Test strip was performed by dropping
upon the addition of DMMP. Inset: intensity changes upon the progressive
addition of DMMP equivalents.
2
μL of the sensor solution (0.1 mM in CH Cl ) onto neutral
2 2
alumina substrate and exposing it to progressive amounts of
DMMP vapors into a closed vial for 1 h at 50°C. Although
DMMP sensing by BDPy-NH is instantaneous (as demonstrated
2
by the measurements in solution), we attempted this time to
lead the DMMP evaporation. Control tests were performed by
spotting fluorescent carbon nanoparticles onto same strip and
exposed it to the same amounts of the simulant.
Figure 3a shows the effect of the interaction of the sensitive
probe as the amount of simulant increases. The image reveals
an increase in fluorescence intensity as the analyte concen-
tration rises. Thanks to the emission in the visible range when
illuminated in the ultraviolet, it was possible to acquire images
of the test strips by means of a standard smartphone. A simple
image processing allowed us to perform a cross section analysis
of the pixel intensity expressed in grayscale.
À 6
Figure 2. Normalized fluorescence responses of BDPy-NH
CHCl
50 equiv of triethyl-phosphite, phosphocholine, triphenylphosphine and
2
(1×10 M in
3
, λex =500 nm) to air (bubbled for 5 min), other competitive guests
The figure shows that the control spots (on the left of each
test strip) are not affected (constant fluorescence intensity) by
increasing the concentration of nerve gas simulant, whereas the
(
methanol), and DMMP (1 equiv). Bars represent the initial over the final
emission intensity at 530 nm.
Chem. Eur. J. 2021, 27, 1–5
2
© 2021 The Authors. Published by Wiley-VCH GmbH
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