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especially, for low concentration detection of
Well-designed and synthesized facile receptors or ensembles are
crucial for highly sensitive sensing -glucose [14].
Besides many reported one-component fluorescent probes for
glucose, two-component probe is another promising sensing
ensemble for -glucose, which is proposed and developed by Singa-
D
-glucose [12,13].
mixture ensemble of Na2HPO4 (0.2 M, 61.0 mL) and NaH2PO4
(0.2 M, 39.0 mL)) buffer solution. The stock solution (5.0 ꢂ 10ꢃ3 M)
of NAHBDS was diluted in 100 mL volumetric flask with pH 7.4 buf-
fer solution to afford the working solution (5.0 ꢂ 10ꢃ5 M). The stock
solutions of BBVs all were 0.04 M. The stock solutions of monosac-
charides all were 1.0 M in 10 mL measuring flask. The standard stock
solutions of lower concentration were prepared by suitable dilution
of the stock solutions with pH 7.4 buffer solution. All spectra detec-
tions were carried out at pH = 7.4 buffer solution and the working
solutions were placed in a quartz cuvette with 1 cm path. The total
volume of working solution was 2 mL. The added volume of all titra-
tion experiments did not exceed 3% of the total. Fluorescence spectra
were monitored with a Perkin–Elmer LS50B luminescence spec-
trometer, the excitation and emission slit widths were 15 nm and
20 nm respectively. The Uv–vis absorption spectra were recorded
on a Varian Cary 300 absorption spectrometer. All of the experi-
ments were performed at room temperature.
D
D
-
D
ram and co-workers [15–23]. In the probe, anionic fluorescent dye
is an optic signal reported section and its fluorescence is modulated
by electron transfer from dye to BBVs. Cationic viologen BBV acts as
quenchers and receptors. It is reasonably believed that the two-
component approach to molecular sensing can provide consider-
able flexibility in choosing the quencher/receptor and luminophor
components depending on the particular requirements of the
sensing application. Three boronic acid substituted viologens BBVs
(o-BBV, m-BBV and p-BBV) are firstly used in sensing monosaccha-
ride ensembles as quenchers/receptors [15,16]. In order to expand
and obtain high sensitivity and selectivity ensembles for monosac-
charides, our group [24–29] also developed some two-component
ensembles for monosaccharide by using polyelectrolyte or fluores-
cent quantum dots as optic signal reported section, and polymer
BBV, different boric acid substituted BBVs, different charge BBVs
as quenchers/receptors. Despite the progress has been made great
efforts, the sensing ensembles based on BBVs quenchers/receptors
Synthesis of NAHBDS, o-BBV, m-BBV and p-BBV
NAHBDS and BBVs were synthesized according to previously re-
ported methods [29,19]. The structures were showed in Fig. 1. The
detailed synthetic procedures can be seen supplementary data.
with high sensitivity for low concentration
is poor. In the paper, our aim is to realize highly sensitive detection
for -glucose in water solution based on BBVs quenchers/receptors.
D-glucose (<10.0 mM)
Results and discussion
D
The design idea lies in employing simple ensemble and easy
preparation method to obtain highly efficient probes. Azo dye,
2,7-naphthalenedisulfonic acid-5-amino-4-hydroxy-3-[p-sodium
benzenesulfonate)-diazenyl]-sodium salt (NAHBDS), is long wave-
length emission fluorescence material, which can avoid the inter-
The formation of preliminary quenching ensembles
Based on the sensing way to
of BBVs to NAHBDS dye is crucial for obtaining highly selective
-glucose detection. Firstly, the Uv–vis and fluorescent emission
D-glucose, the quenching efficiency
D
ference of D-glucose and other species in blood samples. In the
spectra of dye NAHBDS were determined in pH 7.4 buffer solutions
(Fig. 2). It can be seen from Fig. 2, the maximum wavelengths of
Uv–vis and fluorescent emission spectra of NAHBDS are 526 nm
and 590 nm, respectively. The longer wavelength of NAHBDS
ensembles, cationic viologen BBVs are both quenchers and recep-
tors. Anionic fluorescent dye NAHBDS is an optic signal reported
section. The efficient interactions of NAHBDS and BBVs through
forming neutral hole-complex can give an appropriate microenvi-
ronment and provide multidimensional reactive groups to catch
(590 nm) is desired for
D-glucose detection because it can avoid
the interference of -glucose itself absorption in 400–500 nm. Next,
D
D-glucose molecule.
the interactions of NAHBDS and BBVs were observed by titration
experiments in pH 7.4 buffer solution (Figs. 3, S1 and S2). The re-
sults indicate that the fluorescence of NAHBDS all is quenched by
three BBVs quenchers and form stable ground-state complexes.
The fluorescent intensities of NAHBDS are reduced and new long
wavelength emission peaks can be observed in Figs. 4 and S3. The
quenching order of three BBVs to NAHBDS is m-BBV > o-BBV > p-
BBV at different pH buffer solutions. The quenching actions of NAH-
BDS and BBVs in pH 7.4 buffer solution are stronger than that in pH
2.6 and 10.0. The results may come from the lower efficiency of
charge transfer from dye to quencher in pH 2.6 and 10.0 than that
of pH 7.4. The charge transfer of the ensembles may be restrained
by relative excess ions (H+ or OHꢃ) in pH 2.6 and 10.0.
Experimental
Materials and instruments
Solvents used were purified and dried by standard methods
prior to use. Unless otherwise stated, all chemical reagents were
obtained from commercial suppliers and used without further
purification. 4-Aminobenzenesulfonic acid and 5-amino-4-hydro-
xy-7-sulfonaphthalene-2-sulfonate were purchased from Aohe
Finechem (Beijing, China). o-(Bromomethyl)-phenylboronic acid,
m-(bromomethyl)-phenylboronic acid, p-(bromomethyl)-phenyl-
boronic acid and 4,40-dipyridyl were obtained by from Aldrich
(Steinheim, Germany). 1H NMR and 13C NMR were measured on
a Bruker ARX400 spectrometer with chemical shifts reported as
ppm (TMS as an internal standard). pH measurements were carried
out on a Mettler Toledo MP 220 pH meter. 11B NMR spectra were
recorded on a Bruker at 80 MHz and were reported in ppm with re-
spect to BF3ꢁOEt2 (d = 0). High-resolution mass spectra (HRMS)
were acquired on an Agilent 6510 Q-TOF LC/MS instrument (Agi-
lent Technologies, Palo Alto, CA) equipped with an electrospray
ionization (ESI) source.
The sensing processes of three sensing ensembles to D-glucose
The sensing processes of the sensing ensembles to
were investigated by fluorescent spectra in pH 7.4 buffer solutions
(Figs. 4 and S3). Upon introducing -glucose to the NAHBDS/m-BBV
D-glucose
D
sensing ensemble (fluorescent ‘‘on–off’’ state), an apparent recov-
ery of the NAHBDS fluorescence (590 nm) is observed by forming
negatively charged borate ester between m-BBV and
The recovery extent of NAHBDS fluorescence is dependent on the
-glucose concentration. The 7.5-fold recovery of NAHBDS/m-BBV
fluorescent intensity ‘‘off-state’’ is observed only in the present of
10.0 mM -glucose (Fig. 5). Compared with previously reported
-glucose sensing probes, the ensemble has higher sensitivity for
-glucose. It is worth notice that the relative fluorescent intensities
D-glucose.
D
Solution preparation and fluorescence measurements
D
All experiments of water were redistilled water. All of the work-
ing solutions were buffered at pH 7.4 0.1 using a phosphate (the
D
D