A highly selective turn-on fluorescent chemodosimeter for Cr(vi) and its application in living cell imaging

Article abstract of DOI:10.1039/c3ra46543h

A BODIPY-based fluorescent probe, functionalized with an aminomaleonitrile was synthesized as a turn-on fluorescent chemodosimeter for Cr(vi) in aqueous solution based on the Cr(vi) promoted oxidation reaction. Moreover, it can fluorescently respond to Cr(vi) in living cells.

Full text of DOI:10.1039/c3ra46543h

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A highly selective turn-on fluorescent
chemodosimeter for Cr(VI) and its application
Cite this: RSC Adv., 2014, 4, 2989
in living cell imaging†
a
a
b
a
b
Received 10th November 2013
Accepted 27th November 2013
*
*
Jia-Hai Ye, Yixin Wang, Yang Bai, Wenchao Zhang and Weijiang He
DOI: 10.1039/c3ra46543h
www.rsc.org/advances
A BODIPY-based fluorescent probe, functionalized with an amino-
Among these methods, uorescent sensing appeared to be
maleonitrile was synthesized as a “turn-on” fluorescent chemo- the most attractive method for detecting Cr(VI) with the distinct
dosimeter for Cr(VI) in aqueous solution based on the Cr(VI) promoted advantages of high sensitivity, selectivity and easy operation.
oxidation reaction. Moreover, it can fluorescently respond to Cr(VI) in However, there have been only few uorescent probes for the
living cells.
facile detection of Cr(VI). Furthermore, most of the reported
uorescent Cr(VI) probes are based on a uorescence quenching
mechanism and suffer from at least one undesirable limitation,
such as limited selectivity, low sensitivity, poor water solubility,
use of harmful organic solvents, poor detection limit or narrow
useable pH range.1,11,12 In general, the uorescence turn-on
response for detecting metal ions is highly preferable in prac-
tical applications because the uorescent turn-off response can
experience interference by other external factors. Therefore, the
exploration of new uorescent turn-on probes for analyzing
Cr(VI) with appropriate sensitivity, high selectivity remains a
challenge. One alternative strategy to achieve uorescence turn
on involves the use of reaction-based indicator systems, che-
modosimeters, and has attracted a great deal of attention.28
Recently, more and more borondipyrromethene (BODIPY)
derivatives have been widely employed as chemoprobes for
detecting ions owing to their remarkable photophysical prop-
erties, such as high molar extinction coefficients, high uores-
cence quantum yields, excellent photostability, easy structural
modication and appropriate redox potential.29–32
Chromium(VI) is an environmental pollutant and is universally
known to promote some diseases such as damage exposed skin,
irritate mucous membranes, produce pulmonary sensitivity,
create dental erosion, cause loss of weight, induce renal
damage, and target the respiratory tract and skin due to its
highly carcinogenic and mutagenic properties.1 In addition,
experimental evidence links chromium(VI) with various types of
cancer.2 The increased hazardous status is attributed to the
high oxidation potential and the correlation between oxygen
consumption and single strand breakage (SSB) in DNA by Cr(VI)
suggests the participation of an active oxygen-coordinated
chromium species in this process.3 World Health Organisatin
(WHO) recommends chromium(VI) to be limited to 0.05 mg Lꢀ1
(0.17 mM) within groundwater and Cr(VI) is one of six materials
whose uses are regulated by the RoHS directive of European
Union.4,5 Therefore, the accurate determination of Cr(VI) at trace
level is important in the eld of environmental science and
industry. Up to date, there have been many detection methods
developed for Cr(VI) analysis, such as FAAS6 or ET-AAS,7
ICP-AES,8 ICP-MS,9 colorimetric method,10 uorescence,1,11,12
chemiluminesence,13 electrochemical method,14–25 SERS,26 X-ray
uorescence (XRF),27 etc.
In this communication, we demonstrated a novel BODIPY
based turn-on uorescent chemodosimeter integrated with
diaminomaleonitrile unit for the detection of Cr(VI) in aqueous
solution. It is known that de-diaminomaleonitrile reaction can
be proceeded by an oxidant (Scheme 1).33,34 Thus we hypothe-
sized that incorporation of formyl-BODIPY with dia-
minomaleonitrile can generate a new potential probe for an
oxidant.
aSchool of Chemical Engineering, Nanjing University of Science and Technology,
Nanjing, 210094, P. R. China. E-mail: yejiahai@njust.edu.cn; Fax: +86 25 8431
5857; Tel: +86 25 8430 3116
bState Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing, 210093, P. R. China. E-mail: heweij69@nju.
edu.cn; Fax: +86 25 8331 4502; Tel: +86 25 8359 7066
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3ra46543h
Scheme 1 De-diaminomaleonitrile leading to aldehyde by an oxidant.
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Chemoprobe 1 was readily obtained in two steps (Scheme 2).
The intermediate, 2-formyl-BODIPY 3, was prepared on the
basis of a known procedure using the classical Vilsmeier reac-
tion.35 Reaction of intermediate 3 with diaminomaleonitrile
afforded compound 1 in 56% yield. The structure of the nal
product 1 was conrmed by NMR, and HRMS analysis
(See ESI†).
The sensing behaviour of 1 was investigated by uorescence
measurements with different anions i.e., Fꢀ, Clꢀ, Brꢀ, Iꢀ, OAcꢀ,
C2O42ꢀ, NO3ꢀ, CO3ꢀ, HCO3ꢀ, PO43ꢀ, SO42ꢀ, HSO4ꢀ, ClOꢀ,
2ꢀ
ClO4ꢀ, S2ꢀ, OHꢀ, Cr2O72ꢀ, SO3 and different cations i.e., Li+,
Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Pb2+, Fe3+, Co2+, Ni2+, Cu2+, Cr3+,
Ag+, Cd2+, Hg2+, and the oxidants such as Mn7+, Ce4+ and H2O2
(Fig. 1). Considering that probe 1 is not completely water
soluble we screened various organic solvents and the combi-
nations of DMF–H2O. A combination of DMF–H2O (3 : 7, v/v)
proved to be highly efficient for the uorescent sensing process.
As shown in Fig 1, probe 1 displayed a rather week uorescent
emission at 507 nm. However, it became strongly uorescent
upon addition of Cr(VI). The compound 1 behaves as a “turn-on”
type of uorescence probe towards Cr(VI). Whereas other ions
did not induce any discernible spectral changes. Next, the
uorescence titration of probe 1 with Cr(VI) was conducted in
2ꢀ
Fig. 2 The fluorescence spectra of 1 (10 mM) upon addition of Cr2O7
(0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.2, 1.5, 2.0, 2.5, 3.0, 3.5,
4.0, 4.5, 5.0 equiv., K2Cr2O7) in H2O : DMF ¼ 3 : 7. Inset: the linear
relationship of fluorescence titration.
DMF–H2O (3 : 7, v/v, Fig. 2). Upon incremental addition of Cr(VI)
to 1 solution, the uorescence intensity increased remarkably
and a uorescence enhancement factor of more than 4-fold at
507 nm aer reaching the titration equilibrium (5 equiv.) was
estimated within 5 min, displaying a quick response to Cr(VI).
For practical applicability, the proper uorescence titrations at
different pH conditions (pH 4.0–10.0) were also carried out
(Fig. S8, ESI†). Experimental results show that both free probe 1
and uorescence enhancement responses to Cr(VI) are stable in
the range of pH from 6.0 to 10.0. This property of probe 1
Scheme 2 Design and synthesis of chemodosimeter 1.
Fig. 3 (a) Fluorescence responses of probe 1 (10 mM) to various
anions: Cr2O7 only, C2O42ꢀ, ClO4ꢀ, SO32ꢀ, ClOꢀ, Fꢀ, Brꢀ, HSO4
,
2ꢀ
ꢀ
NO3ꢀ, Clꢀ, HCO3ꢀ, CO32ꢀ, S2ꢀ, NO2ꢀ, Iꢀ, SO42ꢀ, PO43ꢀ, OAcꢀ in
H2O : DMF (3 : 7, v/v), black bars represent addition of different anions
Fig. 1 (a) Changes in the fluorescence spectra of probe 1 (1 mM) upon (5 equiv.) to the solution. Blue bars represent the change of the
addition of various anions (1 equiv.) (K2Cr2O7, Na2C2O4, Mg(ClO4)2, emission that occurs upon the subsequent addition of Cr(VI) (5 equiv.)
Na2SO3, NaClO, NaF, NaBr, NaHSO4, AgNO3, NaCl, NaHCO3, Na2CO3, to the above solutions. Wait for 30 s each test, lex ¼ 470 nm. (b)
Na2S, NaNO2, NaI, Na2SO4, K3PO4, NaOAc, 1 mM) in PBS/DMF (3 : 7, Fluorescence responses of probe 1 (10 mM) to various cations: K2Cr2O7
v/v, pH ¼ 6.8). (b) Changes in the fluorescence spectra of probe 1 (1 only, Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Al3+, Pb2+, KMnO4, Fe3+, Co2+
,
mM) upon addition of various cations and H2O2 (K2Cr2O7, LiCl, NaCl, Ni2+, Cu2+, Cr3+, Ag+, Zn2+, Cd2+, Hg2+, (NH4)2Ce(NO3)6, and H2O2, in
KCl, MgSO4, CaCl2, Ba(NO3)2, Al(NO3)3, Pb(NO3)2, KMnO4, FeCl3, H2O : DMF (3 : 7, v/v), black bars represent addition of different cations
Co(NO3)2, Ni(NO3)2, CuCl2, Cr2(SO4)3, AgNO3, Zn(OAc)2, CdCl2, HgCl2, (5 equiv.) to the solution. Blue bars represent the change of the
(NH4)2Ce(NO3)6, and H2O2, 1 mM) in PBS/DMF (3 : 7, v/v, pH ¼ 6.8). emission that occurs upon the subsequent addition of Cr(VI) (5 equiv.)
Every drop of ion interval is 30 s. lex ¼ 470 nm.
to the above solutions. Wait for 30 s each test, lex ¼ 470 nm.
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suggests that no buffer solutions are required for the detection
of Cr(VI), which is convenient for the practical application.
To further examine the effective applications of the chemo-
dosimeter, the uorescence responses of 1 to Cr(VI) in the
presence of typical competing anions, cations and several
oxidants such as KMnO4, CAN, and H2O2 were studied. As
shown in Fig. 3, most of competing ions only exhibited
minimum interference in the detection of Cr(VI). The observa-
tion that upon treatment of Cr(VI) in the presence of different
competing ions probe 1 displayed green uorescence further
supports that probe 1 is useful for selectively sensing Cr(VI) even
under competition from other related ions. Moreover, as shown
in Fig. 4, no observable both of color and uorescence changes
were caused for the anions and cations except for Cr(VI). This
results further demonstrated the high selectivity of probe 1 for
visual detection of Cr(VI) (Fig. 4, Fig. S12, ESI†).
Fig. 5 Proposed sensing mechanism and partial 1H NMR spectra of 1
2ꢀ
(5 mM) in DMSO-d6 upon addition of (a) 0, (b) 1 equiv. of Cr2O7
.
The plausible sensing mechanism of probe 1 towards Cr(VI)
can be ascribed to the de-diaminomaleonitrile reaction of the
aldehyde group by Cr(VI) under mild conditions which is similar
to the specic deprotection reaction promoted hypochlorite.33,34
Furthermore, 1H NMR spectroscopy was employed to provide
direct evidence to conrm the assumed sensing mechanism. As
formyl-BODIPY also appeared. at 6.4 ppm which was shied
downeld from the signal corresponding to the pyrrole proton
on 1 at 6.3 ppm slightly.35 All these results clearly indicated that
the de-diaminomaleonitrile reaction occurred with the addition
of Cr(VI) into the aqueous solution of 1.
We next evaluated the potential utility of probe 1 for the
uorescence imaging of Cr(VI) in living cells. Hela cells treated
with 10 mM probe 1 alone exhibited very weak background
uorescence, Fig. 6(1a–c). Whereas Hela cells treated with probe
1 and then further incubated with Cr(VI) displayed enhanced
green uorescence, Fig. 6(2a–c). These data indicate that probe
1 is cell membrane permeable and capable of uorescent
imaging of Cr(VI) in living cells.
1
shown in Fig. 5, upon treatment with Cr(VI) ion, the H NMR
spectrum of 1 solution changed. The characteristic signal cor-
responding to the aldehyde group proton (–CHO) emerged at
9.9 ppm and the characteristic signal corresponding to the –N]
CH (Ha in Fig. 5) proton disappeared gradually. At the same
time, the singlet signal corresponding to the pyrrole proton on
In summary, on the basis of a specic de-diaminomaleoni-
trile reaction, we have demonstrated a novel strategy in
designing uorescent probes for the highly selective detection
of Cr(VI). The probe 1, which features high selectivity and
pH-independency, was successfully utilized in detecting Cr(VI)
in aqueous media and living cells. We hope the results present
Fig. 6 Confocal fluorescence images of living Hela cells: (1a) cells
Fig. 4 (a) Color and (b) fluorescence (365 nm lamp) change of 1 loaded with 10 mM probe at 25 ꢁC for 1 h (lex ¼ 488 nm; band path,
(10 mM) to various cations and H2O2 (only 1, LiCl, NaCl, KCl, MgSO4, 490–650 nm); (1b) bright field images; (1c) overlaid images of panels 1a
CaCl2, Ba(NO3)2, Al(NO3)3, Pb(NO3)2, Cr2(SO4)3, KMnO4, K2Cr2O7, and 1b; (2a) probe 1-loaded cells with 10 mM Cr(VI) at 25 ꢁC for 4 h (lex
FeCl3, Co(NO3)2, Ni(NO3)2, CuCl2, AgNO3, Zn(OAc)2, CdCl2, HgCl2, 488 nm; band path, 490–650 nm); (2b) bright field images; (2c)
¼
(NH4)2Ce(NO3)6, and H2O2, 10 mM) in H2O : DMF (3 : 7, v/v) solution.
overlaid images of panels 2a and 2b.
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2992 | RSC Adv., 2014, 4, 2989–2992
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