Selective glucose sensing utilizing complexation with fluorescent boronic acid on polycation

Article abstract of DOI:10.1246/cl.2005.196

A novel sensing system for selective glucose detection has been established based on the 1:2 complex formation between glucose and fluorescent boronic acid in the presence of polycation which results in the emergence of excimer emission. Copyright

Full text of DOI:10.1246/cl.2005.196

196
Chemistry Letters Vol.34, No.2 (2005)
Selective Glucose Sensing Utilizing Complexation with Fluorescent Boronic Acid on Polycation
Yasumasa Kanekiyo and Hiroaki Taoꢀ
National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba 305-8569
(Received October 19, 2004; CL-041234)
A novel sensing system for selective glucose detection has
been established based on the 1:2 complex formation between
glucose and fluorescent boronic acid in the presence of polyca-
tion which results in the emergence of excimer emission.
1
a
0.8
0.6
0.4
There is a great demand for sensitive and selective glucose
sensing systems. Typically, glucose oxidase-based sensors have
b
0.2
0
been used for medical diagnostics and bioprocessing. It is well
recognized, however, that the enzyme-based systems have many
problems such as instability, expensiveness, complexity, etc.1
Alternatively, sensors based on the boronic acid–glucose inter-
action have been extensively studied by Shinkai et al.2 The
unique characteristic of glucose is its tendency to form 1:2 com-
plexes in which two boronic acids are bound by one glucose.3,4
By utilizing this characteristic, various types of diboronic acid
receptors have been developed and shown that these receptors
posses higher binding affinity toward glucose than for other sac-
charides.5 Nevertheless, it seems to us that the sensing specificity
of diboronic acid receptors are not satisfactory especially when
saccharide concentration is high. Since the detection selectivity
of diboronic acids are governed by the difference in binding con-
stants for saccharides, non-selective response against saccha-
rides having low binding affinities is inevitable when the saccha-
rides concentrations are high enough to shift the equilibrium to-
ward the complex formation side.
350
400
450
500
550
600
Wavelength / nm
Figure 1. Fluorescence spectra of 1 ([1] = 1 mM) excited at
342 nm in aq solution containing 10 mM glucose buffered with
10 mM of NH3 (pH ¼ 10:2) in the absence (a) and presence
(b) of 2 ([2] = 310 mM).8
0.6
0.5
0.4
0.3
0.2
0.1
0
Monomer
emission
Excimer
emission
0
2.48
12.4
62
[2] /
310 1550 7750
HO
HO
OH
OH
M
µ
Figure 2. Effect of the concentration of 2 on the intensity ratio
between excimer (482 nm) and monomer (376 nm) emissions in
the presence ( ) and absence ( ) of glucose. Excitation wave-
length, concentrations of 1 and NH3 are the same as those in
Figure 1.
Glucose
OH
B
B
HO
O
O
O
O
OH
OH
B
HO
emissions in the range of 360–430 nm having maxima at 377
and 396 nm, and no excimer emission was observed (Figure 1,
spectrum a). The spectrum was drastically changed by adding
commercially available polycation (2)7 in the solution
(Figure 1, spectrum b): a broad excimer emission arose in the
range of 430–600 nm. The observed spectral change indicates
that the 1:2 complex between glucose and 1 was formed only
in the presence of polycation. We then checked the effect of
the concentration of 2 on the spectral behavior (Figure 2). In
the presence of glucose, the excimer emission from 1 was inten-
sified with increasing concentration of 2, while excess addition
of 2 resulted in a decrease of the excimer emission. It must be
noted that the excimer emission was somewhat increased by
the addition of 2 even in the absence of glucose. Since 1 exists
as a univalent anion, this observation suggests that an electrostat-
ic interaction exists between uncomplexed 1 and 2.
Scheme 1. Generation of excimer emission due to 1:2 complex
formation between glucose and fluorescent boronic acid.
(CH2)3
C
O
N
H
N
Cl
2
B(OH)2
n
1
We here report a novel fluorometric detection strategy for
the selective detection of glucose. As illustrated in Scheme 1,
a 1:2 complex formation between glucose and fluorescent boron-
ic acid (1)6 is utilized to bring two pyrenyl moieties nearby and
to create excimer emission. Since saccharides such as fructose
and galactose have low tendency to form 1:2 complexes, the de-
tection can be made selectively toward glucose.
In an aqueous glucose solution, 1 showed only monomer
To assess the sensing selectivity of this system, we conduct-
Copyright ꢀ 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.2 (2005)
197
1
0.8
0.6
0.4
0.2
0
0.6
0.5
0.4
0.3
0.2
0.1
0
10 mM
1 mM
1 µM
0.01
0.1
1
10
100
0.01
0.1
1
10
100
[Glucose] / mM
[Saccharide] / mM
Figure 4. Calculated mole fractions of 1:2 complex formed be-
tween glucose and phenylboronic acid plotted against glucose
concentrations at various total boronic acid concentrations.
Figure 3. Dependence of I482=I377 on the concentration of sac-
charides ( : glucose, : fructose, ꢂ: galactose, : ribose) in the
presence of 2 ([2] = 310 mM). Excitation wavelength, concentra-
tions of 1 and NH3 are the same as those in Figure 1.
cent sensing system. The interaction between glucose and a
fluorescent boronic acid to form 1:2 complex has been utilized.
It has been found that the enrichment of fluorescent boronic
acids along a polycation promotes the 1:2 complex formation
that results in the creation of excimer emission. The present
system provides an alternative strategy for the selective sensing
of glucose without necessity of complicated and costly organic
synthesis.
ed a series of fluorescence studies against saccharides. As shown
in Figure 3, the excimer emission intensity showed the maxi-
mum value when glucose concentration was 10 mM. In contrast,
other saccharides induced quite week excimer emissions. The
observed sensing selectivity can be attributed to the difference
in the tendency to form 1:2 complexes: glucose binds two mole-
cules of 1 so that two pyrenyl moieties are brought close together
and thus the strong excimer emission is observed, whereas sac-
charides having low tendency to form 1:2 complexes cannot
gather two pyrenyl moieties.
This research was supported by Grant-in-Aid for JSPS
Fellows from the Ministry of Education, Culture, Sports, Science
and Technology of Japan.
Now, why polycation is necessary for the generation of ex-
cimer emission? As mentioned above, 1 is supposed to be en-
riched along the polycation chain via electrostatic interaction.
If the local concentration of 1 becomes higher, the formation
of 1:2 complex with glucose would be thermodynamically more
favorable. This hypothesis is supported by the fact that the exci-
mer emission is decreased when a large excess of 2 is added (see
Figure 2), because it should lower the local concentration of 1.
To further confirm the validity of the hypothesis, we made a
model calculation for the equilibrium mole fraction of 1:2 com-
plex (X value9 in Figure 4) using the stability constants for glu-
cose–phenylboronic acid complexes.3 When the total boronic
acid concentration is 1 mM, which is the same condition for
the fluorescence measurements, formation of 1:2 complex is
negligibly small. The formation of 1:2 complex becomes signif-
icant when the total boronic acid concentration is increased three
or four orders of magnitude. This result clearly supports the
above mentioned hypothesis that the increase in the local con-
centration of 1 is the key factor for the formation of 1:2 complex
and hence for the creation of excimer emission. In all the cases,
formation of 1:2 complex is maximal when glucose concentra-
tion is around 9 mM, which is in accord with the experimental
observations shown in Figure 3. This is explained by the fact that
1:1 complex becomes dominant over 1:2 complex in the pres-
ence of large excess of glucose. The importance of the electro-
static enrichment of 1 was additionally confirmed by the obser-
vation that the excimer emission was totally disappeared by add-
ing 10 mM of NaCl into the solution (data not shown). We ex-
pect that the sensing behavior would be affected by changing
the properties of polycation, namely charge density, conforma-
tional flexibility, etc. The investigation on that aspect is currently
underway in our laboratory.
References and Notes
1
2
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1 was synthesized by reacting 3-aminophenylboronic acid with
1-pyrenebutyric acid N-hydroxysuccinimide ester in DMF at
80 ꢁC for 24 h.
6
7
8
9
2: Polydiallyldimethylammonium chloride (Aldrich), Mw
400000{500000.
Concentration of 2 is defined as the concentration of cationic
unit.
¼
In conclusion, we have developed a glucose-specific fluores-
X = 2 ꢂ [1:2 complex]/{[1:1 complex] + [free boronate]}
Published on the web (Advance View) January 15, 2005; DOI 10.1246/cl.2005.196