A selective fluoroionophore based On bODIPY-Functionalized magnetic silica nanoparticles: Removal of Pb2+ from human blood

Article abstract of DOI:10.1002/anie.200804714

Get the lead out: The title fluorescence receptor exhibits a high affinity and selectivity for Pb²⁺ over competing metal ions in water (see picture) with an overall emission change of approximately 8-fold at the emission maximum for Pb²⁺

Full text of DOI:10.1002/anie.200804714

Angewandte
Chemie
DOI: 10.1002/anie.200804714
Chemosensors
A Selective Fluoroionophore Based on BODIPY-functionalized
Magnetic Silica Nanoparticles: Removal of Pb2+ from Human Blood**
Hye Young Lee, Doo Ri Bae, Ji Chan Park, Hyunjoon Song, Won Seok Han,* and
Jong Hwa Jung*
Since heavy metal ions can cause severe risks for human
health and the environment, methods for the facile prepara-
tion of fluorescence receptors with high selectivity and
sensitivity for heavy metal ions have received much atten-
tion.[1] Among the known heavy metal ions, Pb2+ is one of the
most dangerous, causing adverse health effects from lead
exposure, particularly in children.[2] A variety of symptoms
have been attributed to lead poisoning, including abdominal
pain and vomiting. The accumulation of Pb2+ in the body
leads to many serious human afflictions, including muscle
paralysis, mental confusion, memory loss, and anemia,
suggesting that Pb2+ affects multiple targets in vivo.[3] Plau-
sible molecular targets of lead include calcium- and zinc-
binding proteins which control cell signaling and gene
expression, respectively.[4] Thus, it is important to develop a
safe and effective procedure to detect and remove lead from
the body after toxic lead contamination.[5]
In the last few years many approaches, including chemical
precipitation, membrane filtration, ion exchange, and liquid
extraction, have been employed for the removal or recovery
of heavy metal ions from aqueous phases. However, no
practical means for removal have yet been developed.
Despite its own limitation for in vivo use, the magnetically
assisted chemical separation process, which utilizes magnetic
nanoparticles functionalized with a fluorescence receptor,
offers a promising approach for simple and efficient recovery
of heavy metal ions for biological, toxicological, and environ-
mental use.[6] The magnetic nanoparticles having appended
receptors have some important advantages as a solid chemo-
sensor and adsorbent in heterogeneous solid-liquid phases.
First, such nanoparticles are readily synthesized by sol-gel
condensation, a versatile technique that allows chemical
functionalities. Second, the receptors immobilized on an
inorganic support can remove the guest molecules (toxic
metal ions and anions) from the pollutant solution. Third, the
magnetic nanoparticles can be easily isolated from pollutants
by using a small magnet and then repeatedly utilized with
suitable treatment. In particular, the magnetic nanoparticles
can also provide efficient binding to the guest molecules
because their high surface-to-volume ratio simply offers more
contact area.
Xu and co-workers recently reported the use of bisphos-
phate-modified magnetic nanoparticles to remove radioactive
metal toxins (e.g., UO22+) with high efficiency from blood.[6c]
In their study, they found that the designed magnetic nano-
particles can remove 69% of the initial 100 ppm UO22+ from
blood. They also suggested that these functionalized, bio-
compatible magnetic nanoparticles can act as useful and
effective agents for selective and rapid removal of radioactive
metal toxins in vivo. This result prompted us to carry out the
corresponding reactions because the fabrication of new
biocompatible magnetic nanoparticles might be possible by
introducing the modified fluorescence receptor for probing
metal toxins, as well as effective separation of metal toxins
from blood. In this work, a new 4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (BODIPY) derivative (2) was selected as a
signal-transducing unit because it absorbs and emits in the
visible region with high excitation coefficients, high fluores-
cent quantum yields, and high photostability.[7] When the
fluorescence receptor 2 is combined with the magnetic
property, the new class of BODIPY-functionalized magnetic
silica nanoparticles can therefore be an ideal candidate for the
removal or recovery of Pb2+ with high efficiency from water
or human blood.
Although a few dual signaling and remediation systems
for detection and adsorption of metal ions from water or
common solvents are now known, to best of our knowledge,
only one case of a fluorescence receptor immobilized on
magnetic nanoparticles for the removal of a metal toxin from
blood has been reported by Xu and co-workers.[6c] Further-
more, there have been no reports of a fluorescence receptor
being immobilized on magnetic nanoparticles for the removal
of Pb2+ from blood. Herein, we report the synthesis of 1 and
its uses for the detection and removal of Pb2+ in both water
and human blood.
[*] H. Y. Lee, D. R. Bae, Dr. W. S. Han, Prof. J. H. Jung
Department of Chemistry and Research Institute of Natural
Sciences and Environmental Biotechnology National Core Research
Center, Gyeongsang National University, Jinju 660-701 (Korea)
Fax: (+82)55-758-6027
E-mail: wshan@gnu.ac.kr
jonghwa@gnu.ac.kr
J. C. Park, Prof. H. Song
Department of Chemistry and School of Molecular Science
Korea Advanced Institute of Science and Technology
Daejeon 305-701 (Korea)
Compound 3 was synthesized as described previously.[8]
Nickel nanoparticles were prepared by a modified polyol
process.[9] The particles were then coated with silica shells by
using the Stꢀber method using tetraethyl orthosilicate
(TEOS) as a silica source in water to yield Ni@SiO2 core/
shell particles,[10] as detailed in the Supporting Information.
[**] This work was supported by a grant from the EB-NCRC (grant no.
R15-2003-012-01001-0) and (grant no. R01-2007-000-20299-0) sup-
ported by the KSEF/MOST of Korea. BODIPY=4,4-difluoro-4-bora-
3a,4a-diaza-s-indacene.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.200804714.
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Receptor 2 was easily prepared by treating 3 with 3-
(Figure 1b). For additional proof of the new bond formation,
we took IR and TOF-SIMS spectra of 1. In the IR spectrum of
1, the bands attributed to the Ni@SiO2 core/shell particles
themselves were observed, as well as strong new bands at
1608, 1541, 1402, 1301, and 1186 cmÀ1 appeared, which
originated from the receptor 2, indicating that 2 resided on
the Ni@SiO2 core/shell particles (see the Supporting Infor-
mation, Figure S1). The TOF-SIMS spectrum of 1 displayed
the fragments of 2 (m/z = 396, 427, 582), giving us firm
evidence that 2 was covalently anchored onto the surface of
the Ni@SiO2 core/shell particles (see the Supporting Infor-
mation, Figure S2).
(triethoxysilyl)propyl isocyanate in the presence of triethyl-
amine (Scheme 1). The Ni@SiO2 core/shell particles were
then reacted with 2 in toluene under vigorous stirring
Spectroscopic measurements with 1 were performed in
0.2m 3-(N-morpholine)propanesulfonic acid (MOPS), buffer
pH 7. The absorption spectrum of free 1 showed a single
visible absorption band at 505 nm (e = 6.50 ꢁ 104 mÀ1 cmÀ1) and
a corresponding emission maximum at 510 nm. As expected, 1
is virtually nonfluorescent in its apo state (F < 0.003), which
resulted from the efficient photoinduced electron transfer
(PET)[11] quenching of the fluorophore by the lone pair of
electrons on the nitrogen atom in the benzoyl moiety. Upon
the addition of increasing amounts of Pb2+, 1 showed a large
CHEF (chelation-enhanced fluorescence) effect in the emis-
sion spectra, resulting from the blocking of the PET process.
An overall emission change of approximately 8-fold (F =
0.019, Figure 2) at the emission maximum (lem = 510 nm)
was observed for Pb2+. The absorption spectrum of Pb2+-
bound 1 showed a single visible absorption band at 505 nm
(e = 6.27 ꢁ 104 mÀ1 cmÀ1). Interestingly, the increase in the
fluorescence intensity of 1 upon exposure to Pb2+ was
reversible with the addition of a strong base (0.01n NaOH)
to the acidic solution (0.01n HCl) (Figure 3). In addition, the
fluorescence change was reproducible over several cycles of
detection/separation. The Jobꢂs plot using the fluorescence
changes indicated 1:1 binding for 1 with Pb2+ (see the
Supporting Information, Figure S3). From the fluorescence
Scheme 1. Synthesis of BODIPY-functionalized magnetic silica nano-
particles 1.
overnight to covalently link 2 to the surface of the Ni
nanoparticles by the sol-gel reaction. The synthetic 1 was well
characterized by transmission electron microscopy (TEM),
confocal laser scanning microscopy (CLSM), FTIR spectros-
copy, time-of-flight second ion mass spectroscopy (TOF-
SIMS), and fluorophotometry methods.
The TEM image of Pb2+-bound 1 revealed a spherical
structure with a narrow size distribution (30–40 nm) which
remained as crystalline nanocrystals (Figure 1a). The spheres
of Pb2+-bound 1 were also directly observed in solution state
by CLSM methods, which showed slight aggregation as the
result of surface modification by the attachment of 2 in
comparison to the as-prepared Ni@SiO2 core/shell particles
Figure 2. Fluorescence titrations of 1 (5.2ꢀ10À6 m) upon addition of
increasing amounts of Pb2+ (0, 0.1, 0.2, 0.3, 1, 2, 3, 4, 5, 7, 10, 15, 20,
30, 50, 70, and 100 equiv) in water. The pH value was adjusted by
using 0.2m MOPS, buffer pH 7. Excitation was at 505 nm, and
emission was monitored at 510 nm.
Figure 1. a) TEM and b) CLSM images (lex =505 nm) of Pb2+-bound 1
prepared in water.
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Figure 3. Fluorescence spectra of 1 without (a) and with (b) Pb2+, and
after treatment with HCl/NaOH in water (c). The inset is a photograph
of 1 without (left) and with (right) Pb2+ in water. The pH value was
adjusted by using 0.2m MOPS, buffer pH 7.
titrations, the association constant (K) for Pb2+ coordination
to 1 was calculated to be 1.05 ꢁ 105 mÀ1 (logK = 5.02).[12] The
addition of 15 ppb Pb2+, which is the maximum limit
(provided by the United States Environmental Protection
Agency) for the allowable level of lead in drinking water, to a
0.1 mm solution of 1 resulted in a 10.5% increase in the
fluorescence intensity (see the Supporting Information,
Figure S4).[5a] Spectroscopic measurements using 2 were
performed in an acetonitrile solution to provide a compar-
ison. Receptor 2 also showed a single visible absorption band
at 497 nm (e = 8.30 ꢁ 104 mÀ1 cmÀ1) and a corresponding emis-
sion maximum at 510 nm (F = 0.067). Upon the addition of
Pb2+, the fluorescence intensity of 2 increased by approx-
imately 3-fold (F = 0.189, see the Supporting Information,
Figure S5) with the same absorption maximum (labs = 497 nm,
e = 8.06 ꢁ 104 mÀ1 cmÀ1) and emission maximum (lem
=
510 nm) as the apo form. It should be mentioned that Yoon
and co-workers reported compound 3 as a fluorescence
chemosensor for Pb2+.[8] From the fluorescence titrations, the
association constant for 3 with Pb2+ was observed to be 8.8 ꢁ
103 mÀ1. The selectivity of 1 for Pb2+ is approximately 12-fold
higher than that for 3, because of the preorganization of 2 on
the surface of the nanoparticle.[6e] In general, the preorgani-
zation of receptors on the surface reduces their conforma-
tional flexibility and increases their effective concentration.
In this organic-inorganic hybrid material 1, chemical detec-
tion of Pb2+ is facilitated by the synergistic effects of multiple
noncovalent interactions.
To additionally evaluate the utility of 1 as an ion-selective
fluorescence probe for Pb2+, the competition-based fluores-
cence emission changes of 1, upon addition of various
biologically and environmentally relevant metal ions such as
Li+, Na+, Mg2+, K+, Ca2+, Cu2+, Zn2+, Ag+, Cd2+, and Hg2+,
were investigated in aqueous solution (Figure 4). Compound
1 displayed a large CHEF effect only with Pb2+. Minimal or no
changes were observed with the other metal ions, even though
there was a relatively small quenching effect with Cu2+
Figure 4. a) Fluorescence responses of 1 (3.9ꢀ10À5 m) upon addition
of Li+, Na+, Mg2+, K+, Ca2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+
(20 equiv) in water. b) Fluorescence responses of 1 (8.9ꢀ10À5 m) upon
addition of Li+, Na+, Mg2+, K+, Ca2+, Cu2+, Zn2+, Ag+, Cd2+, and Hg2+
(20 equiv), and subsequent addition of Pb2+ (20 equiv) in water.
c) Visual fluorescence changes for the same samples used in (a). For
all measurements, the pH value was adjusted by using 0.2m MOPS,
buffer pH 7. Excitation is at 505 nm, and emission is monitored at
510 nm.
(Figures 4a and c). When Cu2+ binds tightly to the host
compound, intracomplex quenching has been reported (via
energy or electron transfer).[13] Also, the fluorescence inten-
sities of Pb2+-bound 1 are unchanged in the presence of Li+,
Na+, Mg2+, K+, Ca2+, Cu2+, Zn2+, Ag+, Cd2+, and Hg2+,
indicating that 1 is very promising as a selective adsorbent for
the separation of Pb2+ in vivo (Figure 2 and Figure 4b). We
also probed the binding abilities of 2 for metal ions on the
basis of fluorescence changes upon the addition of Li+, Na+,
Mg2+, K+, Ca2+, Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+ in an
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acetonitrile solution (see the Supporting Information, Fig-
Pb2+. Additionally, we also tested the removal of Pb2+ from
water using 1. By using the ICP-MS measurements, we found
that 1 (0.1 mm) can remove 97% of the initial 15 ppb Pb2+
from water. Thus, receptor 1 can be a potentially useful and
effective for the selective separation and rapid removal of
Pb2+ in vivo.
ure S6). As expected, the selectivity of 2 for metal ions was
almost the same as that of 1. In the case of 2+Pb2+, the
fluorescence change is ascribed to the complexation of a Pb2+
ion which induces a conformational change of two carbonyl
2+
=
groups, giving a C O···Pb coordination mode, resulting in
an enhanced emission intensity (see the Supporting Informa-
tion, Figure S7).[14] To understand the selective binding
property of 2 in the presence of Pb2+, we measured IR
spectra of 2 upon the addition of Li+, Na+, Mg2+, K+, Ca2+,
Cu2+, Zn2+, Ag+, Cd2+, Hg2+, and Pb2+. The characteristic
In summary, we have readily prepared BODIPY-func-
tionalized magnetic silica nanoparticles 1, a new type of
synthetic fluorescence receptor for probing Pb2+ in vivo. The
fluorescence receptor 1 exhibited a high affinity and high
selectivity for Pb2+ over other competing metal ions in water,
and successfully removed Pb2+ from human blood. These
findings may lead to the development of a new type of tailor
made biocompatible system built by immobilizing the appro-
priate fluorescence receptors onto the surface of novel
magnetic nanomaterials for the detection, recovery, and
removal of other heavy metal toxins from the human body.
peak of the C O groups in 2 at 1693 cmÀ1 shifted to 1678 cmÀ1
=
when it formed a complex with Pb2+, whereas no shifts in IR
spectra were observed with the other metal ions, giving us
firm evidence that Pb2+ was coordinated to the oxygen atoms
in the carbonyl groups (see the Supporting Information,
Figure S8). Meanwhile, Yoon and co-workers probed the
binding abilities of 3 upon addition of various metal ions in an
acetonitrile solution.[8] Compound 3 also displayed a large
CHEF effect with Pb2+, whereas it showed a small CHEF Experimental Section
effect with Zn+ and Cu2+. This difference suggests that the
carbonyl groups of 2 play an important role in the selectivity
for Pb2+ over other competing metal ions.
Experimental details are provided in the Supporting Information.
Received: September 26, 2008
Revised: December 10, 2008
Published online: January 7, 2009
The above results encouraged us to test the removal of
Pb2+ from human blood. The overall procedure for using 1 to
remove Pb2+ from human blood is illustrated in Figure 5a.
Keywords: blood · chemosensors · fluorescence · lead ·
.
nanoparticles
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b) Photograph of a magnet attracting Pb2+-bound 1 in water.
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Pb2+-bound 1 from the human blood (Figure 5b). To deter-
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4% residual Pb2+ remained in human blood, suggesting that
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