On–off Bodipy chemosensor for recognition of iron(III) ion based on the inner filter effect and its applications in cellular and bacterial imaging

Article abstract of DOI:10.1002/bio.3127

One strong fluorescent Bodipy-containing derivative was synthesized and characterized using ¹H NMR, electrospray ionization mass spectrometry and elemental analysis. Its electrochemical and photophysical properties were investigated. In additio

Full text of DOI:10.1002/bio.3127

Research article
Received: 28 January 2016,
Revised: 11 February 2016,
Accepted: 21 February 2016
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/bio.3127
On–off Bodipy chemosensor for recognition of
iron(III) ion based on the inner filter
effect and its applications in cellular
and bacterial imaging
Lingcan Kong,a* Keyu Lu,b Guangyuan Ma,a Yuyang Yao,a Xia Linga
and Wenwei Liua*
ABSTRACT: One strong fluorescent Bodipy-containing derivative was synthesized and characterized using 1H NMR, electrospray
ionization mass spectrometry and elemental analysis. Its electrochemical and photophysical properties were investigated. In ad-
dition, the Bodipy derivative could be used as an on–off fluorescent probe for the detection of Fe3+ ions based on the inner filter
effect because the absorption band of the Fe3+ ion overlaps the excitation band of Bodipy very well upon irradiation with UV
light. Furthermore, the Bodipy-based sensor has obvious advantages including simplicity, rapid response, high selectivity, sensi-
tivity and a detection limit of 1.2 μmol/L, and has been demonstrated in real water samples including tap water, mineral water
and water from Lake Tai. Moreover, the fluorescent probe could also be used as a probe for the determination of Fe3+ in cellular
and bacterial imaging. Copyright © 2016 John Wiley & Sons, Ltd.
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: Bodipy; fluorescent probe, iron(III); cellular imaging, bacterial imaging
target molecule or ions in the detection system (20–22). This
Introduction
method often shows enhanced sensitivity relative to other
During past decades, many industrial and anthropogenic pro-
methods because changes in the absorption of the sensors could
cesses have released heavy metal ions into the environment
(1–3). Iron is one of the most important of the transition
metals because of its crucial roles in many biochemical processes
transform into the exponential changes in the fluorescence inten-
sity (23). In fact, the choice of chemosensor via fluorescent IFE is
also crucial.
including oxygen uptake, electron transfer and the catalysis of
Relative to other organic dyes, Bodipys are an interesting class of
oxido-reductase reactions (4,5). Iron deficiency results in poor work
performance and decreased immunity (6). However, excessive iron
(III) ions are also hazardous to public health because of the associ-
ation of iron with the development of severe diseases including
materials possessing merits such as large molar absorption coeffi-
cients (ε), high quantum yields and other rich photophysical
properties (24–26). These properties enable Bodipy-containing
molecules to be used in the development of Bodipy-based fluores-
various cancers, organ dysfunction and hepatitis (7–9). Therefore,
cent sensors by designing molecules accordingly (27). To make the
the quantitative determination of iron(III) in environmental sam-
synthesis easy, an IFE-based mechanism is employed. To the best
of our knowledge, Bodipy-containing fluorescent sensors for Fe3+
ples is of great importance and intense research efforts have been
devoted to developing methods for iron(III) ion detection (10–12).
Compared with other techniques, fluorescent methods have a
ions based on IFE mechanism are very rare (28).
Recently, Bodipy derivatives have been successfully used in the
lot of advantages, such as high sensitivity and convenience (13).
fluorescent detection of metal ions based on the strong interaction
As a result, many fluorescent chemosensors have been employed
for the detection of iron(III) ion by monitoring changes in their
fluorescent intensity (14–16). Different photophysical processes,
such as photoinduced electron transfer, intramolecular charge
between Bodipy derivatives and metal ions (29–31). By contrast,
corresponding studies on the determination of metal ions using
IFE, which has relative weak interaction between Bodipy deriva-
tives and metal ions, were very rare. Furthermore, investigations
transfer, fluorescence resonance energy transfer and metal–ligand
charge transfer, are constantly employed in fluorescent sensors
(17–19). In general, the above sensing mechanism often involves
the intermolecular interaction between the chemosensor and
* Correspondence to: L. Kong and W. Liu, Wuxi Center for Disease Control
and Prevention, Wuxi 214023, People’s Republic of China. E-mail:
the target molecule. It works well only when there is proper
geometry and distance. Thus, these methods are complicated
and time-consuming, leading to restricted applications. An
alternative way to design fluorescent chemosensors is based
on the inner filter effect (IFE), which is known to result from
the absorption of excited light and emission induced by the
konglingcan2010@163.com; liuwwcdc@126.com
a
Wuxi Center for Disease Control and Prevention, Wuxi 214023, People’s Re-
public of China
b
State Key Laboratory of Food Science and Technology, Jiangnan University,
Wuxi 214122, People’s Republic of China
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L. Kong et al.
on cellular and bacterial imaging are also scarce. To the best of our
knowledge, this work represents the first study on the detection of
metal ions in cells and bacteria based on the IFE mechanism. Here,
we present a novel Bodipy-containing fluorescent sensor 1 for Fe3+
ion determination in acetonitrile/water media (9:1 v/v) including
real water such as tap water, mineral water and water from Lake
Tai. This method is highly reproducible and the prepared com-
pound 1 exhibits strong fluorescence in the absence of Fe3+. Inter-
estingly, the fluorescence is greatly quenched upon addition of
Fe3+. More importantly, the fluorescent sensor shows good sensi-
tivity and selectivity in the presence of other metal ions, such as
Mn2+, Zn2+, Pb2+, Cr3+, Er3+, Yb3+ and Tb3+. These advantages
suggest that the resultant sensor 1 is a promising fluorescent
probe for the detection of heavy metal ions in the environment.
Moreover, compound 1 could be used as a probe for the detection
of Fe3+ ions in cells and bacteria.
OCH2CH2CH2-), 1.43 (s, 6H; -CH3 of Bodipy at 1,7-position), 1.33 (m,
8H; -CH2-), 0.89 (t, J = 7.0 Hz, 3H; -CH3). ESI-MS: m/z 453.2 [M+H]+.
Anal. calcd (%) for C27H35BF2N2O: C, 71.68; H, 7.80; N, 6.19. Found:
C, 71.42; H, 7.83; N, 6.31.
Application as a Fe(III) probe
A stock solution of FeCl3 with a concentration of 9 mmol/L was
prepared and various Fe3+ concentrations were obtained by serial
dilution. To check the sensitivity of compound 1, other ions includ-
ing Na+, K+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+, Mg2+, Mn2+,
Zn2+, Pb2+, Cr3+, Er3+, Yb3+, Tb3+ and Eu3+ were used. All the exper-
iments were similar to the one used for the detection of Fe(III) ions.
Cellular and bacterial imaging
Hep-2 cells were cultured in Dulbecco’s modified Eagle’s me-
dium supplemented with 10% fetal bovine serum and 1%
penicillin/streptomycin (DMEM) using a 96-well plate. Suspen-
sions (30 μg/mL) of compound 1 from the stock solution
were prepared with Dulbecco’s phosphate buffer saline and
DMSO mixed solution (DPBS/DMSO = 1:1 v/v). After sonica-
tion for 10 min to ensure complete dispersion, an aliquot
(typically 0.01 mL) of the suspension was added to the well
of a chamber slide, then incubated at 37°C in a 5% CO2 incu-
bator for 24 h. Prior to fixation of the Hep-2 cells on the slide
for inspection with confocal fluorescence microscopy, the ex-
cess compound 1 was removed by washing three times with
a warm DPBS and DMSO mixed solution (1:1 v/v).
All Escherichia coli bacteria were grown overnight at 37°C in
Luria–Bertani medium. After overnight growth, a colony from each
bacteria was placed into a 10 mL falcon tube. The bacteria were
centrifuged for 5 min at 12000 g, washed twice with sterilized
PBS (pH 7.4), and the cell pellet was resuspended in 1 mL of a
PBS/DMSO mixed solution (1:1 v/v) of compound 1 (15 μg/mL,
pH 7.4) under gentle vortexing. The bacteria with compound 1
were kept at 37°C for 24 h with gentle shaking. After incubation,
the mixture was centrifuged to pellet the compound 1-labeled bac-
teria, the supernatant was discarded and the pellet was suspended
in a PBS/DMSO mixed solution. The process was repeated three
times using PBS/DMSO mixed solution (1:1 v/v) to remove all
unbound compound 1. Finally, the pellet was again suspended in
1 mL of a PBS/DMSO mixed solution (1:1 v/v) and fixed on a slide
for inspection using confocal fluorescence microscopy.
Experimental
Materials
2,4-Dimethylpyrrole was purchased from Energy Chemical
(Shanghai, China). 4-Hydroxybenzaldehyde, tetrachloro-p-ben-
zoquinone and trifluoroacetic acid were purchased from
Aladdin Chemical (Shanghai, China). All other reagents were
used as received without further purification. Deionized water
was used in all experiments.
Preparation of a strong fluorescent
Bodipy-containing derivative
The Bodipy derivative was prepared as previously reported with
slight modification (32). A mixture of 4-hydroxybenzaldehyde
(0.61 g, 5.0 mmol) and 1-bromooctane (1.06 g, 5.5 mmol) in the
presence of potassium carbonate (0.83 g, 6.0 mmol) in acetone
was heated to reflux for 2 days with stirring under nitrogen. The
mixture was cooled to room temperature, and the solvent was
removed under reduced pressure. The obtained crude intermedi-
ate product was purified by column chromatography on silica
gel with petroleum ether/ethyl acetate (20:1 v/v) as the eluent to
give the benzaldehyde intermediate product (compound 2).
Yield: 0.82 g, 80%. The prepared benzaldehyde product (0.70 g,
3.4 mmol) and 2,4-dimethylpyrrole (0.65 g, 6.8 mmol) were dis-
solved in dichloromethane and degassed. After addition of two
drops of trifluoroacetic acid to the above solution, the mixture
was further stirred for 5 h. The solvent was removed under re-
duced pressure and purified by column chromatography on silica
gel with petroleum ether/ethyl acetate (10:1 v/v) as the eluent to
give another intermediate product. The obtained product was
dissolved in dichloromethane, tetrachloro-p-benzoquinone
was added to oxidize the above product and the mixture
was stirred for 1 h. Triethylamine (3.1 mL) and boron fluo-
ride ethyl ether (3.2 mL) were then added to the above solution.
After stirring for 2 h, the solvent was removed under reduced pres-
sure and the crude product was purified by column chromato-
graphy on silica gel with petroleum ether/ethyl acetate (10:1
v/v) as the eluent to give the target molecule (compound 1). Yield:
568 mg, 37%. 1H NMR (500 Hz, CDCl3, 298 K, relative to Me4Si)/ppm:
δ = 7.15 (d, J = 8.5 Hz, 2H; Bodipy protons at 8-o-Ar-position), 6.99 (d,
J = 8.5 Hz, 2H; Bodipy protons at 8-m-Ar-position), 5.97 (s, 2H; pyrrole
protons at 2,6-position), 4.00 (t, J = 6.5 Hz, 2H; -OCH2-), 2.55 (s, 6H; -
CH3 of Bodipy at 3,5-position), 1.82 (m, 2H; -OCH2CH2-), 1.49 (m, 2H; -
Characterization methods
1H NMR was recorded on a Bruker DRX 500 (500 MHz) spectrome-
ter (Shanghai, China) with chemical shifts reported relative to
tetramethylsilane (Me4Si). All positive ion ESI-MS were recorded
on QTRAP 2000 mass spectrometer (Shanghai, China). Elemental
analysis of compound 1 was performed on a Flash EA 1112 ele-
mental analyzer (Shanghai, China). UV–vis absorbance spectra
were recorded on a Cary 50 scan spectrophotometer at room tem-
perature. The fluorescence spectra were recorded using a
Shimadzu RF-5301 spectrophotometer (Shanghai, China). Cyclic
voltammetric measurements were performed by using a CH
Instruments Inc. model CHI 660C electrochemical analyzer
(Shanghai, China). Electrochemical measurements were per-
formed in dichloromethane solution with 0.1 mol/d3 nBu4NPF6 as
the supporting electrolyte at room temperature. The reference
electrolyte was an Ag/AgNO3 (0.1 mol/d3 in acetonitrile) electrode
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Bodipy recognition of iron(III) ion and cellular and bacterial imaging
Scheme 1. Synthetic route of compound 1.
and the working electrode was a glassy carbon electrode (CH In-
struments) with a platinum wire as the counter electrode. The
working electrode surface was first polished with 1 μm alumina
slurry, then rinsed with ultrapure deionized water and sonicated
for 5 min in a beaker containing ultrapure water. The polishing
and sonication steps were repeated twice and the working
electrode was finally rinsed under a stream of ultrapure deionized
water. A ferrocenium/ferrocene couple (FeCp+2/0) was used as the
internal reference. All solutions for use in the electrochemical
studies were deaerated with prepurified argon gas prior to
measurement.
whereas one quasi-reversible reduction wave at –1.17 V vs. SCE is
observed in the reductive scan (Fig. S1). The oxidation and reduction
waves are assigned to the oxidation and reduction of Bodipy, re-
spectively, which is consistent with previous studies on Bodipy (33).
Photophysical properties and optical responses
of compound 1 to Fe3+ ions
The electronic absorption spectrum of compound 1 in a mixed
solution of acetonitrile and water (9:1 v/v) shows intense absorp-
tion with molar extinction coefficient in the order of 104 dm3/
mol/cm at ~ 340–370 nm, which is tentatively assigned to the S0
→ S2 transition of Bodipy, consistent with previous reports on
the Bodipy system (34). In addition, compound 1 also shows an-
other intense band at 480–510 nm in the electronic absorption
spectra. A molar extinction coefficient in the order of 104 dm3/
mol/cm, which is assigned to the S0 → S1 transition of Bodipy, is
commonly observed in other Bodipy systems (35). Upon addition
of Fe3+ ions, the absorption spectrum over the range 300–400
nm shows an obvious increase due to the effect of the absorption
of Fe3+, but the color of the solution shows no obvious change
(Fig. 1).
General procedure for fluorescence titration
The fluorescence titration of compound 1 with Fe3+ was performed
as follows: 2 mL of compound 1 (2.5 μmol/L) in a mixed solution of
acetonitrile and water (9:1 v/v) was placed in a cuvette, and certain
equivalents of Fe3+ in water were added to the solution of com-
pound 1 using a micro-injector. Because very small amounts of
Fe3+ were added, the final volume of the solution was almost
unchanged (2 mL). The mixed solution was incubated within 1
min and the corresponding spectra were subsequently measured.
Upon excitation at λ = 360 nm, compound 1 shows green emis-
sion at about 510 nm in a mixture of acetonitrile and water (9:1 v/v)
at room temperature, which is assigned to Bodipy-centered emis-
sion. The quantum yield of compound 1 reaches 79% using
Rhodamine 6G as a standard. It is interesting that the fluorescent
Results and discussion
Synthesis of Bodipy-containing derivative compound 1
The synthetic route for compound 1 used in this study is shown in
Scheme 1. Compound 2 was synthesized by the substitution reac-
tion of p-hydroxybenzaldehyde with 1-bromooctane in acetone in
the presence of potassium carbonate. Compound 1 was prepared
by several steps, involving the condensation of compound 2 with
2,4-dimethylpyrrole, oxidation with tetrachloro-p-benzoquinone,
followed by reaction with boron fluoride ethyl ether. The
introduction of an alkyl chain was used to increase the solu-
bility of Bodipy in organic solvent. All the intermediates were
characterized using 1H NMR spectroscopy. The final product
1
was characterized by H NMR spectroscopy, ESI-MS, and gave
satisfactory elemental analysis.
Electrochemical property of compound 1
Compound 1 shows one quasi-reversible oxidation wave at +1.15 V
vs. Saturated Calomel Electrode (SCE) in the oxidative scan of its cy-
clic voltammogram in dichloromethane (0.1 mol/dm3 nBu4NPF6),
Figure 1. UV–vis absorption spectral changes of compound 1 upon addition of
different amounts of Fe3+ ion (0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 μmol/L).
(Inset) Photograph of compound 1 without and with Fe3+ ion (100 μmol/L).
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L. Kong et al.
Figure 2. Emission spectral changes of compound 1 upon addition different amounts of Fe3+ ion (0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100 μmol/L) by excitation at 360 nm (a)
and excitation at 460 nm (b). (Inset) Photograph of compound 1 without and with Fe3+ ion (100 μmol/L).
intensity gradually decreases with increasing concentrations of
Fe3+ from 10 to 100 μmol/L (Fig. 2). By contrast, the fluorescent
intensity does not show any obvious change on the addition of
Fe3+ ions upon excitation at λ = 460 nm (Fig. 2). In view of the good
spectral overlap between the absorption of Fe3+ and the excitation
spectrum of compound 1 over the range 300–400 nm (Fig. S2), the
mechanism of fluorescent quenching of compound 1 is proposed
to be due to absorption of Fe3+. The mechanism is further sup-
ported by excitation spectral changes upon addition of different
amounts of Fe3+ ions measured at an emission of 511 nm (Fig. S3),
which shows the lack of fluorescent quenching in the region
without the absorption of Fe3+. The emission intensity gradually
decreases in the region with the absorption of Fe3+ ion with
increasing concentrations of Fe3+.
almost no change in the fluorescence intensity at 512 nm within
the investigated response time window of 0.5–15 min. Thus, a
reaction time of 0.5 min may be used for this system and the data
show that compound 1 has a reasonable response time.
For practical purposes, the pH titration of compound 1 was
performed to investigate the suitable pH range for iron(III) ion
sensing between pH 2.0 and pH 10.0. In the presence of iron(III)
ions, the fluorescence intensity is stable over this wide pH range
(Fig. 5), which shows the good stability of compound 1 and iron
(III) ions within the investigated pH window. Thus, compound 1
could detect iron(III) ions over a wide pH range (2–10).
1
To confirm the proposed mechanism, H NMR experiments are
1
performed and H NMR spectra of compound 1 before and after
the addition of 30 eq. of Fe3+ ions are recorded in chloroform (Fig. 3).
As expected, there is no obvious change upon addition of Fe3+,
which suggests that there is very weak interaction between com-
pound 1 and Fe3+, and fluorescence quenching is the result of the
IFE of Fe3+. The results of UV–vis absorbance, photoluminescence
and photoluminescence excitation spectra, as well as 1H NMR spec-
tra, confirm that fluorescence quenching arises from the absorbance
of Fe3+, ensuring that the IFE occurs in an efficient way.
Response time is a crucial factor in many fluorescent chemo-
sensors. Therefore, the effect of reaction time upon addition of
50 eq. of iron(III) ions was investigated (Fig. 4). Changes in the fluo-
rescence intensity of compound 1 at 512 nm were studied for
response times of 0.5–15 min. Figure 4 shows that there is
Figure 4. Fluorescence intensity changes on addition of iron(III) (50 eq.) to compound
1 (1 × 10–5 mol/L) in a mixed solution of acetonitrile and water (9:1 v/v) from 1 to 15
min. λem: 512 nm.
Figure 5. Variation in fluorescence intensity with the pH of compound 1 (1 × 10–5
mol/L) in the presence of iron(III) (50 eq.). λem: 512 nm.
Figure 3. 1H NMR changes in compound 1 in chloroform before (a) and after (b)
addition of 30 eq. of Fe3+ ion.
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Bodipy recognition of iron(III) ion and cellular and bacterial imaging
To examine the sensitivity and selectivity of compound 1, the ef-
fect of different types of metal ions (Na+, K+, Ba2+, Ca2+, Cd2+, Co2+,
Cu2+, Fe2+, Hg2+, Mg2+, Mn2+, Zn2+, Pb2+, Cr3+, Er3+, Yb3+, Tb3+ and
Eu3+) on the fluorescence was investigated. These ions were stud-
ied under the same conditions as Fe3+. Figure 2 shows that the
fluorescence intensity of compound 1 was gradually quenched
with increasing concentrations of Fe3+. Moreover, a linear propor-
tionality between the logarithm of the fluorescent intensity and
the concentration of Fe3+ is observed over the range 10–100
μmol/L (Fig. 6). Furthermore, the limit of detection is estimated
to be 1.2 μmol/L in terms of a signal-to-noise ratio of 3. By contrast,
the fluorescence intensity of compound 1 shows no obvious
change upon addition of other metal ions, as shown in Fig. 7.
These results indicate that the coexistence of other metal ions
does not interfere with the measurement of Fe3+
.
To further assess its application in real water samples, compound
1 was applied to the detection of Fe3+ in samples including tap wa-
ter, mineral water and Tai lake water containing different amounts
of Fe3+. Real water samples were first filtered to remove any solid
suspension. Studies were performed with 11 concentrations (0, 10,
20, 30, 40, 50, 60, 70, 80, 90 and 100 μmol/L) for each water. It was
clear that fluorescent intensity gradually decreases with the increase
in the concentration of Fe3+, and a linear relationship between the
logarithm of fluorescent intensity of compound 1 and the concen-
tration of Fe3+ was observed over the range from 10 to 100 μmol/
L (Figs S4–S6). These results indicate that the sensor system is highly
sensitive towards Fe3+ in real water samples. Furthermore, re-
covery tests (Table 1) were performed using the three types
of water with a fixed amount of Fe3+ (10.5, 40.4 and 80.9
μmol/L), and the relative standard deviations (RSD) of the
water samples were close to 100% (from 95–105%), which
suggests that the fluorescent method performs well for the
detection of Fe3+ in real water.
Cellular and bacterial applications of compound 1
With a strong red fluorescence, the as-prepared compound
1 showed great potential for use in biological imaging. The
cell internalization and intracellular distribution of com-
pound 1 were evaluated using confocal laser fluorescence
microscopy. In this study, MTT and an apoptosis assay were
used to evaluate the cytotoxicity of compound 1. As indi-
cated in Fig. 8, the viability of Hep-2 cells remained > 80%
after incubation with compound 1, even after 30 h at a con-
centration of 60 μg/mL. The results indicate that compound
1 has low acute toxicity. In addition, Fig. 9 reveals the bright
field, confocal fluorescence and overlaid imaging of Hep-2
cells incubated with compound 1 for 24 h. As indicated in
bright field, Hep-2 cells incubated with compound 1 main-
tain their normal morphology, suggesting good biocompati-
bility at this dose and incubation time. Fluorescence images
irradiated at 405 nm show green fluorescence within the
Hep-2 cells and reveal the uptake behavior of Hep-2 cells.
It could also be seen that the fluorescence signal is mostly
distributed in the cytoplasm. The results show that com-
pound 1 could be used as a probe for cellular imaging. In-
terestingly, the fluorescence intensity irradiated with 405
nm is greatly decreased upon addition of Fe3+ (10 μM),
whereas the fluorescence intensity of compound 1 lacking
Fe3+ shows a strong green fluorescence (Fig. 10). The results
suggest that compound 1 could be used as a probe for
measuring Fe3+ in cells.
Figure 6. Linear relationship between the logarithm of fluorescent intensity and the
concentration of Fe3+ ion in a mixed solution of acetonitrile and water (9:1 v/v).
Figure 7. Relative emission intensity (I0 — I)/I0 of compound 1 upon addition
of 7 × 10–5 mol/L of different metal ions. I0 and I represent the maximum emission
intensity of compound 1 before and after addition of metal ions.
Table 1. Recoveries of iron(III) ion spiked in tap water, mineral water and Tai lake water by compound 1 in a mixed solution of
acetonitrile and water (9:1 v/v) using six measuring times of repetition.
Tap water
Mineral water
Tai lake water
Added Fe3+ Found Fe3+ Recovery (%) RSD (%) Found Fe3+ Recovery (%) RSD (%) Found Fe3+ Recovery (%) RSD (%)
(μM)
(μM)
(μM)
11.1
40.1
79.5
(μM)
10.5
40.4
80.9
10.7
39.8
81.4
101.9
98.5
100.6
6.1
5.2
3.5
105.7
99.2
98.3
5.2
3.1
2.2
11.1
40.9
81.3
105.7
101.2
100.5
4.6
3.4
4.3
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L. Kong et al.
In addition, fluorescence imaging could also be used in E.
coli. Figure 11 reveals the bright field, confocal fluorescence
and overlaid imaging of E. coli incubated with compound 1
for 24 h. From the bright field imaging of E. coli, we can see
that bacteria incubated with compound 1 maintain their
normal morphology and exhibit good biocompatibility with
compound 1. As indicated in Fig. 11(b), the bacteria incu-
bated with compound 1 exhibit green fluorescence, sug-
gesting the uptake behavior of E. coli. Figure 11(c)
demonstrates that the fluorescence signal is distributed
over almost the whole bacterium. The results confirm that
compound 1 could be used as a probes for bacterial imag-
ing. As expected, upon addition of Fe3+, the fluorescence
intensity on irradiation at 405 nm is greatly quenched rela-
tive to that free of the Fe3+ ion (Fig. 12). The results confirm
Figure 8. Viability of Hep-2 cells after 24 h incubation with different concentrations
of compound 1 in the cell medium, as determined by a MTT assay.
Figure 9. (a) Bright field, (b) confocal fluorescence and (c) overlaid imaging of Hep-2 cell imaging captured by laser scanning confocal microscopy.
Figure 10. (a) Bright field, (b) confocal fluorescence and (c) overlaid imaging of Hep-2 cell imaging with Fe3+ ions (10–5 mol/L) captured by laser scanning confocal microscopy.
Figure 11. (a) Bright field, (b) confocal fluorescence and (c) overlaid imaging of E. coli bacteria imaging captured by laser scanning confocal microscopy.
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Bodipy recognition of iron(III) ion and cellular and bacterial imaging
Figure 12. (a) Bright field, (b) confocal fluorescence and (c) overlaid imaging of E. coli bacterial imaging with Fe3+ ions (10–5 mol/L) captured by laser scanning
confocal microscopy.
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In summary, we have demonstrated a simple, convenient, rapid
response, and economical on–off fluorescent method for the
detection of Fe3+ using Bodipy-containing derivative compound
1 as a fluorescent sensor based on the IFE. The probe appears to
have high sensitivity and selectivity relative to conventional
methods, with a detection limit of 1.2 μmol/L, and has been dem-
onstrated in real water including tap water, mineral water and Tai
lake water. The results suggest that the novel probe has great
potential in the detection of Fe3+ in environmental samples. In
addition, compound 1 could be used as a probe for the detection
of iron(III) ions in cells and bacteria. It is anticipated that our
method will provide a new perspective on ion detection in
environmental and biological samples.
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This work was supported by the Health Bureau Foundation of Wuxi
City, China (MS201524) and Science and Technology Development
Foundation Project of Wuxi City, China (CSE31N1429). We also
acknowledge support from Wuxi Center for Disease Control and
Prevention, China.
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