Boronic acid functionalized boron dipyrromethene fluorescent probes: Preparation, characterization, and saccharides sensing applications

Article abstract of DOI:10.1021/ac301456s

Fluorescent probes based on boron dipyrromethene functionalized with a phenylboronic acid group (BODIPY-PBAs) were synthesized in high yield for the first time by Suzuki coupling of bis(pinacolato)diboron and 8-(4-bromophenyl)-1, 3,5,7-tetramethyl-4,4-dif

Full text of DOI:10.1021/ac301456s

Article
pubs.acs.org/ac
Boronic Acid Functionalized Boron Dipyrromethene Fluorescent
Probes: Preparation, Characterization, and Saccharides Sensing
Applications
Jingying Zhai,† Ting Pan,† Jingwei Zhu, Yanmei Xu, Juan Chen,‡ Yuanjie Xie, and Yu Qin*
State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering, Nanjing University,
Nanjing, China, 210093
S
* Supporting Information
ABSTRACT: Fluorescent probes based on boron dipyrrome-
thene functionalized with a phenylboronic acid group
(BODIPY−PBAs) were synthesized in high yield for the first
time by Suzuki coupling of bis(pinacolato)diboron and 8-(4-
bromophenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene (BODIPY). Wavelength tuning of the
fluorophores was achieved by attaching an auxochromic
substituent to the 5-position of the BODIPY core structure
through Knoevenagel condensation. The emission intensity of
fluorophores increases when binding to the analytes with diol
groups and forming boronic esters at fixed pH. These
compounds can detect monosaccharides in the concentration
range of 0.1−100 mM. Whereas glycogen was found to quench
the fluorescence of BODIPY−PBAs in an aqueous solution due to the self-quenching of the fluorophores after attaching in the
extensively branched and compact glucose polymer, further addition of D-fructose to the solution can release the fluorophores
from the polymer and the fluorescence regains. The BODIPY−PBA fluorophore has been applied in polymeric optodes
containing anion exchangers to perform repetitive measurement. Such sensors respond to different monosaccharides in the range
of 0.1−100 mM and demonstrate an improved selectivity toward D-fructose over other saccharides, compared to the results
obtained from homogeneous assay.
accharides, including monosaccharide, disaccharide, oligo-
group while the anionic form acts as an electron-donating
Ssaccharide, or polysaccharide, are part and parcel of living group.
In order to design an optical sensor for saccharide sensing
cells and a source of energy for animals so that the detection of
saccharides has attracted considerable interest in diagnostic
analysis, food technology, and biological science.1 One of the
most successful and historically significant electrochemical
approaches for monitoring saccharides is based on the
enzymatic electrodes which have been under development
since the 1960s,2 whereas chemosensors for sugar signaling
involving fluorescent dyes and chelator groups have gained
more and more attention in the last few decades.3,4 Especially,
the stable boronic acid based saccharide receptors have been
used to create saccharide sensors because boronic acids are
electron deficient Lewis acids having an sp2-hybridized boron
atom with a planar trigonal conformation under its neutral form
that can rapidly and reversibly react with 1,2 or 1,3 diols of
carbohydrates to form five- or six-membered cyclic esters in
nonaqueous or basic aqueous media.5,6 The complexation leads
to a decrease of the pKa value and induces the formation of the
anionic form of the boronic group at a specific pH. The anionic
form of the boron group is electron-rich and possesses an sp3-
hybridized boron atom with a tetrahedral conformation. When
the boronic acids are conjugated with fluorophores, the neutral
form of the boron group may act as an electron-withdrawing
with boronic acid, the photochemical properties of the dye
should be switched on or off upon interaction with the analyte.
Sandanayake and Shinkai reported the internal charge-transfer
(ICT) types of colorimetric sensors for saccharides based on
the intramolecular interaction between the tertiary amine and
the boronic acid group using a UV−vis absorption method in
1994.7 At the same time, fluorescence measurement became
one of the most sensitive and available detection methods for
saccharides based on molecular rigidification,8,9 photoinduced
electron transfer (PET),10,11 or excited-state charge transfer
(CT) mechanisms.12 Yoon and Czarnik first reported an
anthracene compound modified with a boronic acid as receptor
for saccharide sensing.10 Wulff recognized that a benzylic amine
at the ortho position of phenylboronic acid (PBA) allowed for
B−N bond formation.13 Cooper and James investigated factors
that influenced the B−N strength after saccharides bound to
boronic acids.14 More recently, Yang et al. used the influence of
Received: May 27, 2012
Accepted: November 9, 2012
Published: November 16, 2012
© 2012 American Chemical Society
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Figure 1. Schemes for the syntheses of 2b and 4b.
the B−N strength to develop a series of diboronic acid
compounds to label cells based on cell surface carbohydrate
structures.15 Shinkai’s and Wang’s groups have reported ICT
fluorescent sensors for saccharides.16,17 Another study based on
the disruption of an ion-pair interaction between poly-
(phenylene ethylene) and a boronic acid functionalized benzyl
viologen derivative has been reported by DiCesare et al. for
saccharide detection.18
dehyde, and other synthetic reagents and solvents were
purchased from Sigma-Aldrich (Switzerland). High molecular
weight poly(vinyl chloride) (PVC), anion-exchanger tridode-
cylmethylammonium chloride (TDMACl), bis (2-ethylhexyl)
sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), and
tetrahydrofuran (THF) were purchased from Fluka (Switzer-
land).
Sodium phosphate dibasic anhydrate, sodium phosphate
monobasic monohydrate, sodium hydroxide, D-glucose, D-
fructose, D-(+)-galactose, D-sorbitol, and glycogen were
obtained from Sangon (Shanghai, China). All aqueous solutions
were prepared by dissolving the appropriate salts or diluting
standard solutions as specified in nanopure-purified (18.2
MΩ·cm) deionized water.
One of the key requirements for establishing robust
fluorescence sensing systems is a strong, reversible, and
sufficiently rapid response over the concentration range of
interest. This requires the optimization of fluorophore
properties including large absorption coefficients, high quantum
yield (typically, QY > 0.1) upon binding of analytes, suitable
excitation and emission wavelengths to minimize the back-
ground signal, and good chemical and photostability. Various
chromophores and fluorophores have been conjugated with
boronic acid;3 however, dipyrromethene boron difluoride
(BODIPY)-based boronic acid probes are rarely seen.19
BODIPY dyes are well-known to be highly fluorescent, very
stable, having narrow emission bandwidths and amenable to
structure modification.20 At the same time, very few lipophilic
polymer membrane sensors have been reported21 for boronic
acid based saccharides detection, although such membranes
have been widely utilized for operative extraction of saccharides
from aqueous solutions.22 In this work, we developed the new
synthetic route to obtain BODIPY−PBA derivatives with
different emission wavelengths in high yield. Such probes
have been fully characterized and applied in homogeneous
assay and polymeric optical sensors for detection of
monosaccharides and glycogen.
Phosphate buffer solutions were prepared from 10−3
M
sodium phosphate dibasic, adjusted with 10−2 M NaOH to the
desired pH. All saccharides were dissolved in phosphate buffer
solution.
The preparation of BODIPY−PBA derivatives 2b and 4b is
depicted in Figure 1; the syntheses and characterizations have
been described in detail in the Supporting Information.
A Shimadzu RF-5301PC fluorescence spectrometer and
Thermo Scientific Varioskan Flash spectral scanning multimode
reader were used for fluorescence measurements in homoge-
neous assay and membrane phase. The pH was monitored with
a calibrated glass pH electrode (Sartorius PB-10).
Homogeneous Measurements. Fluorescent boronic
acids 2a, 2b, 4b were dissolved in ethanol with all 1 μM
concentration for homogeneous fluorescence detection using a
Shimadzu RF-5301PC fluorescence spectrometer; the max-
imum excitation and maximum emission wavelengths of 2a, 2b,
and 4b are as follows: 2a λex = 490 nm, λem = 502 nm; 2b λex =
493 nm, λem = 510 nm; 4b λex = 564 nm, λem = 580 nm
(excitation slit width, 3 nm; emission slit width, 1.5 nm;
scanning speed, 3000 nm/min).
EXPERIMENTAL SECTION
■
Reagents and Instrumentation. 4-Bromobenzaldehyde,
2,4-dimethylpyrrole, bis(pinacolato)diboron, 4-methoxybenzal-
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For glycogen detection, 2b in ethanol (1.6 mM) was diluted
with pH 9.0 phosphate buffer solution to obtain 5 μM 2b
solutions. The different concentrations of glycogen buffer
solution (pH 9.0) were mixed with the above solution,
respectively. After 20 min, the mixture was transferred into a
quartz cuvette for fluorescence measurement using a Shimadzu
for acid catalysis, which led to a much reduced reaction time
(within 1 h) compared to the reaction catalyzed with acetic
acid.
Similar to other BODIPY fluorophores, compounds 2b and
4b exhibited high quantum yields and were relatively insensitive
to solvent polarity. The quantum yield of 2b in ethanol is 0.37
(using fluorescein as a standard), and the quantum yield of 4b
was calculated to be 0.25 (using rhodamine B in ethanol as a
standard). The emission wavelength of these compounds is
slightly red-shifted in less polar dichloromethane than in the
polar solvent acetonitrile. As shown in Figure 2, due to
RF-5301PC fluorescence spectrometer (λex = 450 nm, λem
510 nm; excitation slit width, 5 nm; emission slit width, 5 nm;
scanning speed, 3000 nm/min). For the pH response, 10−4
=
M
2b in ethanol was diluted by different pH values of phosphate
buffer solutions to obtain 1 μM BODIPY−PBA solution. For
the saccharides detection, 10−3 M 2b was dissolved in ethanol
and then diluted with different amounts of monosaccharides
which were prepared by pH 9.0 phosphate buffer solution to
obtain 2.3 × 10−6 M BODIPY−PBAs.
Preparation and Measurements of Polymeric Opto-
des. A total amount 100 mg of mixture containing 5 mmol/kg
BODIPY−PBA, 2.5 mmol/kg TDMACl, PVC, and the
plasticizer DOS or NPOE (1:2 by weight) was prepared and
dissolved in 1 mL of THF. After complete dissolution, these
cocktails were then uniformly dispensed (5 μL/well) into each
U-bottomed microwell of polypropylene plate. The plates were
air-dried in a dust-free vessel for at least 4 h prior to use. In all
measurements, the excitation wavelength was chosen at 450 nm
and the emission wavelength was at 536 nm. All membranes
inside the wells were conditioned with pH 9.0 buffer solution
until the polymer film-coated wells had stable fluorescence
intensities.
RESULTS AND DISCUSSION
■
Boron dipyrromethane dyes are usually produced from
commercially available pyrrole-based starting materials. The
target probe 2b can be synthesized from condensation of 2,4-
dimethyl-1H-pyrrole and 4-formylbenzeneboronic acid that is
obtained from 4-bromobenzaldehyde.23 However, the boronic
acid substituted benzaldehyde has low reactivity and boronic
acid groups tend to bind to silica gel, which makes the
separation extremely difficult. Alternatively, protected 4-
formylphenylboronic acid with less polarity was used to
simplify the separation step, but the reaction yield is
comparatively low due to the electron-donating property of
boronic ester.19 In this work, we first prepared 8-(4-
bromophenyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a,4a-
diaza-s-indacene 1 according to the literature,24 followed by
conversion of bromide to phenyl boronic ester through Suzuki
coupling in high yield (93%) as shown in Figure 1. It was found
that the hydrolysis of BODIPY−boronic acid ester using
conventional methods with only HCl was unsuccessful due to
the presence of the relatively large BODIPY structure. By
adding sodium periodate in HCl solution or using diethanol-
amine, the yield of hydrolysis reaction improved up to 90%.
BODIPY dyes with absorption and emission in the visible or
near-infrared range are more favorable.20 The methods to tune
the fluorescence emission of the dye to longer wavelength
include the attachment of strong electron-donating groups to
the core structure,25 rigidifying the core structure of the dye
molecules26, and extending conjugation of the system.27 Here
compound 3 was synthesized by adding an auxochromic
substituent to the 5-position of the BODIPY core structure
through Knoevenagel condensation as shown in Figure 1. We
used a microwave reactor instead of the traditional Soxhlet
extractor to provide a more efficient dehydration condition. At
the same time, 4-methylbenzenesulfonic acid (TsOH) was used
Figure 2. Fluorescence spectra of 1 μM 2a, 2b, and 4b in ethanol; the
maximum excitation and maximum emission wavelengths of 2a, 2b,
and 4b are 2a λex = 490 nm, λem = 502 nm; 2b λex = 493 nm, λem = 510
nm; 4b λex = 564 nm, λem = 580 nm.
conjugation extending of the BODIPY core the fluorescence
excitation and emission wavelengths of 4b are red-shifted
compared with 2b in ethanol. The maximum excitation and
emission wavelengths of 4b are 564 and 580 nm, respectively,
while compound 2b has been excited and emits at 493 and 510
nm in the same solvent.
Figure 3 shows the pH response of 2b; the fluorescence
intensity increases when the sample becomes more basic. The
pKa values of 2b and 4b determined from the pH calibration
curves are 10.1 0.15 (Figure 3) and 10.4 0.03 (Supporting
Information Figure S1). The values are higher than the ones of
unsubstituted phenyl boronic acid, which is mainly due to the
attachment of the BODIPY structure.28 In the BODIPY−PBA
structure, appending the phenyl boronic acid at the meso
position of the BODIPY fluorophores decouples the two
subunits because of the almost perpendicular arrangement
between the fluorophores and phenyl ring. Trisubstituted
boron atom has an sp2 trigonal planar geometry with an empty
p orbital that makes the boronic acid an electron acceptor.
Obviously, the electron-withdrawing capability of the phenyl
boronic acid is moderate, since both 2b and 4b demonstrate
relatively high quantum yields. The fluorescence lifetime of 2b
was measured to be 3.27 ns in ethanol (Supporting Information
Figure S17), and the lifetime of the BODIPY core is 5.45 ns in
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Figure 3. pH response of 2b (1 μM in ethanol−H2O): λex = 450 nm,
λem = 510 nm; error bars indicate standard deviation (n = 5).
Figure 4. Fluorescence emission spectra of 2b (2.3 μM) with different
concentrations of D-fructose at pH 9.0; λex = 450 nm, λem = 510 nm.
ethanol.29 It has been reported that the PET process leads to
the decrease of fluorescence lifetime.30 Furthermore, the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) energy of the phenyl-
boronic acid and BODIPY core (Supporting Information
Figure S16) calculated from the cycle voltammogram were
EHOMO (phenylboronic acid) = −8.31 eV, ELUMO (phenyl-
boronic acid) = −3.88 eV, EHOMO (BODIPY) = −5.82 eV,
ELUMO (BODIPY) = −2.97 eV. The results showed that the
LUMO energy level of phenyl boronic acid is slightly lower
than the LUMO energy level of the BODIPY, which leads to an
indistinct PET process. When OH− attaches to boron, the
boronic acid begins a transition to its corresponding anionic
tetrahedral species, which makes the subunit electron-rich. The
change increases the LUMO energy level of the phenyl boronic
acid and further suppresses the PET process from BODIPY to
the chelator so that the fluorescence enhancement has been
observed.
Boronic acids can form compounds with 1,2 or 1,3 diols to
produce five- or six-membered cyclic esters in nonaqueous or
basic aqueous media, and the cyclic esters dissociate when the
medium is changed to acidic pH. The complexation of boronic
acids with diol groups is usually more preferred in basic
solution. In this work, pH 9.0 buffer solutions were used due to
the better sensitivity of 2b toward diols at pH 9.0 than at pH
7.4 (Supporting Information Figure S5). When the concen-
tration of D-fructose changed from 0.1 to 100 mM in pH 9.0
buffer solution containing 2b, the fluorescence intensity
increased accordingly as shown in Figure 4. Similar results
were observed for other monosaccharides including D-sorbitol,
D-(+)-galactose, and D-glucose, as demonstrated in Figure 5.
It has been reported that, upon formation of boronic ester,
the fluorescence intensity decay remains monoexponential for
the complex, but with a longer fluorescence lifetime.19 At the
same time, the process of boronic acid changing to cyclic
boronic ester decreases the pKa value and induces the
equilibrium to the direction of formation of anionic cyclic
boronic ester that is electron-rich. When the phenylboronic
acid is conjugated with a BODIPY, the neutral form of the
Figure 5. Fluorescence intensity changes of 2b (2.3 μM) as a function
of different saccharide concentrations in 0.001 M phosphate buffer
◆
●
solution at pH 9.0; λex = 450 nm, λem = 510 nm: ( ) D-fructose; ( )
■
▲
D-sorbitol; (
) D-(+)-galactose; ( ) D-glucose; error bars indicate
standard deviation (n = 5).
boron group acts as an electron-withdrawing group, while the
anionic form acts as an electron-donating group.31 Similar to
the pH response, by increasing the concentration of the
monosaccharides, more anionic cyclic boronic ester will be
produced, and therefore the fluorescence intensity is enhanced.
The association constants orders for phenylboronic acid with
different monosaccharides are D-sorbitol > D-fructose > D-
(+)-galactose > D-glucose.32 The larger the association
constant, the more stable the anionic boronic ester. Sorbitol
and fructose are both capable of binding with boronic acid to
form a tridentate compound, which gives higher affinity than
other saccharides.33 The sequence of the association constants
of 2b with different monosaccharides are D-fructose (297 M−1)
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> D-sorbitol (262 M−1) > D-(+)-galactose (31 M−1) > D-glucose
(29 M−1) in solution at pH 9.0. BODIPY−PBA derivatives
exhibited fructose selectivity over other monosaccharides.
Similarly, the probe 4b responded to D-fructose and D-sorbitol
in the range of 1−100 mM and showed almost no response to
D-(+)-galactose and D-glucose in homogeneous solutions
(Supporting Information Figure S3). Both 2b and 4b showed
selective response to fructose in the presence of interfering
monosaccharides (glucose, galactose, and sorbitol) as shown in
Supporting Information Figures S9 and S11. The relatively
narrower response range of 4b might be due to its weaker
complexation with monosaccharides as shown in Supporting
Information Table S1. Considering its higher affinity to diols,
2b was chosen for the following experiments.
Glycogen is an extensively branched and compact glucose
polymer that serves as the secondary long-term energy storage
in animal and fungal cells, with the primary energy stores being
held in adipose tissue. The routine approach for glycogen
detection is to use the periodic-acid-Schiff (PAS) reaction
which is originally described by MacManus in 1948.34,35 Other
methods such as incorporation of radioisotopes,36,37 immuno-
cytochemistry,38 or quantification of glucose after the
hydrolysis of glycogen39 are widely used for analyses of
glycogen. Nevertheless, few fluorescent approaches were
reported to directly measure the glycogen. In this work, when
adding glycogen into 2b solution, we observed fluorescence
quenching in the glycogen concentration range from 0.39 to
6.60 mg/mL, which is completely opposite to the response
toward monosaccharides, as shown in Figure 6. Due to the
Utilization of polymer-based optical sensors offers several
advantages over homogeneous assay, especially for noninvasive
continuous monitoring. In this work, BODIPY−PBAs were
constructed into a bulk film to form an optical sensor for
detecting various monosaccharides. The sensing film contains
fluorescent probe 2b, TDMACl as anion exchanger, PVC and
plasticizer as the membrane solvent. Polar plasticizer NPOE
rather than nonpolar DOS results in a better response to
saccharides, because the polar plasticizer can facilitate trans-
porting saccharides from the aqueous phase to membrane
phase.22 Due to the higher concentration of the probes and the
hydrophobic nature of the membrane, the fluorescence of the
membrane is stronger than in the homogeneous assay. It is
expected that the saccharides extracted into the membrane
phase form the anionic BODIPY−PBA−diol complexes that
are ion-paired with TDMA+ in the membrane (Scheme 1). A
Scheme 1. Complexation of Diols with BODIPY−PBA
Formed Ion Pair with TDMA+
severe leaching of the dye was observed when the lipophilic
membranes containing only BODIPY−PBA, but without
cationic sites, were immersed in basic or high-concentration
saccharide solution. Similar to homogeneous assay, the
response of the polymeric sensor toward different mono-
saccharides was studied in pH 9.0 buffer solution due to the
better sensitivity at pH 9.0 than at pH 7.4 (Supporting
Information Figure S6). The fluorescence enhancement was
observed in monosaccharide solutions from 0.1 to 100 mM as
shown in Figure 7. The proposed sensor exhibited selective
response to fructose in pH 9.0 buffer solution. The detection
limit of 2 × 10−4 M for fructose was obtained from the cross
section of the two extrapolated linear calibration curves in
Supporting Information Figure S6.41 It was found that the
response of the membrane sensor exhibited an unusual
fluorescence decrease at 10−4 to 10−3 M for some
monosaccharides. When the concentration was higher than
10−3 M, the fluorescence intensity gradually increased, and
similar results were also observed for 4b-based film (Supporting
Information Figure S4). It is possible that, after soaking the
membrane containing neutral dye (1) and anion exchanger
TDMACl in pH 9 buffer solutions, the OH− was exchanged by
Cl− into the membrane and attached to boron (1 → 3 in
Scheme 1); some portion of boronic acid dyes became anionic
tetrahedral species 3 which are ion-paired with TDMA+. The
boronic acid subunit is electron-rich in anionic tetrahedral
structure, which increases the LUMO energy level of the phenyl
boronic acid and suppresses the PET process from BODIPY to
the chelator so that the fluorescence enhancement of 3
compared to 1 has been observed as shown in Figure 3. The
fluorescence of the membrane increased after conditioning in
Figure 6. Fluorescence emission spectra of 2b (5 μM) in different
concentrations of glycogen buffer solution at pH 9.0, and the effect of
D-fructose addition on the fluorescence spectrum of 2b−glycogen
solution; λex = 450 nm, λem = 510 nm.
large amount of binding sites in glycogen and its extensively
branched and compact structure, BODIPY−PBAs bound to
glycogen in close proximity could be self-quenched.40 When D-
fructose was added into 5 μM 2b solution containing 0.98 mg/
mL glycogen, the fluorescence regained, because fructose
competes with glycogen and releases BODIPY−PBA into the
solution.
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The sensors also showed excellent reversibility, reproduci-
bility, and relatively fast response within 20 min by switching
fructose concentration between 10−2 and 10−1 M and
monitoring the fluorescence intensity at 536 nm as shown in
Figure 8. These results confirmed that no BODIPY−PBA was
Figure 7. Selectivity of the PVC−NPOE film containing 5 mmol/kg
2b and 2.5 mmol/kg TDMACl toward different saccharides in 10−3 M
◆
phosphate buffer solution at pH 9.0; λex = 450 nm, λem = 536 nm: (
)
■
●
▲
D-fructose; ( ) D-sorbitol; ( ) D-(+)-galactose; ( ) D-glucose; error
bars indicate standard deviation (n = 5).
Figure 8. Response time curve of the PVC−NPOE film in the
alteration of the 10−2 M D-fructose and 10−1 M D-fructose in pH 9.0
phosphate buffer solution; λex = 450 nm, λem = 536 nm.
buffer. In the 10−4 M saccharides solution, the small amount of
diols extracted into the membrane react preferably with anionic
boronic acid 3 rather than with neutral dye 1 because of the
larger reaction constant (K2 > K1),32 and then form ester 4. The
electron density in the boronic acid subunit of the ester 4 is less
than 3 due to the distribution of electron over the carbon
atoms, which results in slight decrease of fluorescence emission.
At relatively high concentration the diols react with neutral dyes
and form esters, increasing the fluorescence. Due to the larger
apparent association constant, we did not observe the
fluorescence decrease for fructose at 10−4 M.
Compared to the homogeneous assay, the selectivity of the
optical membrane toward fructose was improved. In solution
the association constants of 2b with D-sorbitol (K = 262 M−1)
and D-fructose (K = 297 M−1) were quite close, and response
difference between the two analytes was limited. In the optode,
the apparent association constant of 2b with D-fructose (K = 88
M−1) is over 4 times the values for D-sorbitol (K = 20 M−1), D-
(+)-galactose (K = 23 M−1), and D-glucose (K = 8 M−1),
although the complexation in membrane phase is generally
weaker than in the solution (Supporting Information Table
S1). It was found that the 4b-based optode exhibited responses
to different monosaccharides in the range of 1−100 mM as
shown in Supporting Information Figure S4, which corre-
sponded well to the apparent association constants determined
in Supporting Information Table S1. Our results suggest that
the discrimination of different monosaccharides not only
depends on the binding constant of the receptor with
saccharides but also relates to the distribution constant of
various analytes between the organic phase and aqueous phase.
Consequently, the selectivity pattern of the polymeric optodes
is different from the one of homogeneous assay. Such optodes
can perform reliable measurements of fructose in the presence
of interfering monosaccharides (Supporting Information
Figures S10 and S12).
leaching from the membrane to the aqueous phase since the
quaternary ammonium was the lipophilic countercation that
can stabilize anionic BODIPY−PBA in the membrane phase
and suppress the leaching process.
CONCLUSIONS
■
In summary, we have developed a new synthetic route to
prepare boronic acid functionalized boron dipyrromethene
fluorescent probes with tunable wavelength in high yield. The
optical responses of BODIPY−PBAs to pH and monosacchar-
ides have been studied in detail. Such probes have been used to
directly monitor 0.39−6.60 mg/mL concentration of glycogen
in the homogeneous phase for the first time. Furthermore,
reusable polymeric optodes based on BODIPY−PBA probes
have been fabricated to perform monosaccharide measurements
in the linear range of 0.1−100 mM with 2 × 10−4 M detection
limit for fructose. The proposed sensors exhibited good
reproducibility and photostability with less than 1% signal
change after three measurement cycles in solutions of different
fructose concentrations and a relatively fast response time of
within 20 min.
ASSOCIATED CONTENT
* Supporting Information
Additional information as noted in text. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
*E-mail: qinyu75@nju.edu.cn. Phone: +86(25) 83592562. Fax:
+86(25) 83592562.
■
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Present Address
‡PharmaBlock (Nanjing) R&D Co., Ltd., 10 Xuefu Road,
Nanjing Hi-Tech Zone, Nanjing, China, 210061.
Author Contributions
†These authors contributed equally to this work.
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (Nos. 21135002, 21075062, and
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