Author's Accepted Manuscript
Colorimetric detection of Hydrogen peroxide and glucose using the magnetic mesoporous silica nanoparticles Yonghong Wang, Bo Zhou, Shun Wu, Kemin Wang, Xiaoxiao He
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Received date: 3 October 2014 Revised date: 8 December 2014 Accepted date: 11 December 2014 Cite this article as: Yonghong Wang, Bo Zhou, Shun Wu, Kemin Wang, Xiaoxiao He, Colorimetric detection of Hydrogen peroxide and glucose using the magnetic mesoporous silica nanoparticles, Talanta, http://dx.doi.org/10.1016/ j.talanta.2014.12.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Colorimetric Detection of Hydrogen Peroxide and Glucose
2
Using the Magnetic Mesoporous Silica Nanoparticles
3
Yonghong Wanga,b, Bo Zhoua, Shun Wua, Kemin Wangb,*, Xiaoxiao Heb
4
a. College of Life Science and technology, Central South University of Forestry and Technology,
5
410004, Changsha, China. E-mail: [email protected]
6
b. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Biology, College of
7
Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P.R.China.
8 9
Abstract
10
In this work, we synthesized a type of magnetic mesoporous silica nanoparticle
11
(denoted as Fe3O4@MSN) with Fe3O4 as the core and mesoporous silica the shell.
12
The superparamagnetic Fe3O4-core provides high peroxidase-mimic activity and
13
makes the artificial enzymatic system easily recyclable. Furthermore, Fe3O4
14
nanoparticles are encapsulated in MSN shells to hinder the aggregation and keep them
15
stable even under harsh conditions. Meanwhile, small active molecules are allowed to
16
diffuse in and out of the MSN shells. Based on these functional units, the
17
Fe3O4@MSN as robust nanoreactors can catalyze a self-organized cascade reaction,
18
which includes oxidation of glucose by oxygen to yield gluconic acid and H2O2, and
19
the latter further oxidizes 3,3,5,5-tetramethylbenzidine (TMB) to produce a color
20
change. The Fe3O4@MSN, whose catalytic efficiency was not strongly dependent on
21
pH and temperature, was successfully used for the detection of glucose and showed
22
excellent sensitivity with a detection limit of 0.4×10-5 mol/L. Nevertheless, the assay
23
is also highly selective toward the glucose detection.
24 25
Keywords: Magnetic mesoporous nanoparticles; Peroxidase-mimic activity; Glucose;
26
Detection.
27 1
1
1. Introduction
2
Nanomaterials have received considerable attention over the past few decades
3
because of their unique size, shape, composition and structure-dependent properties.
4
There has been an explosive growth in the use of nanomaterials as catalysts involving
5
both homogeneous and heterogeneous catalysis. But the possibility of nanomaterials
6
as certain artificial enzymes, important subdivisions of catalysis, had long remained
7
unknown. Until the first nanoparticle-based artificial enzyme was reported, Fe3O4
8
nanoparticles were found to possess an intrinsic peroxidase-like activity
9
which time some other nanomaterials have been evaluated as peroxidase mimetics.
10
These studies show that the nanomaterial-based peroxidase mimetics enjoy
11
advantages of low cost, high stability and tunability in catalytic activities and can be
12
potentially used in bioassays and medical diagnostics.
[1]
, since
13
Various nanomaterials including Fe3O4 magnetic nanoparticles[2,3] , positively
14
charged gold nanoparticles[4], cupric oxide nanoparticles[5], CuS nanoparticles[6], ceria
15
nanoparticles[
16
nanoparticles[11], carbon nanodots[12] and folate-polyoxometalate hybrid spheres[13]
17
have been reported to possess peroxidase-like activity and used for the visual
18
detection of H2O2 and glucose. In recent years, mesoporous silica nanoparticles (MSN)
19
have gained great interests in many fields due to their unique advantages, including
20
good biocompatibility, large load capacity, tunable pore sizes, the ease of surface
21
functionalization, large surface area, and high thermal and mechanical stability
22
[14,15,16,17]
23
payloads such as mediators, enzymes, and antibodies owning to their high pore
24
volume and large surface area [18,19]. Moreover, the surface properties and composition
25
of MSN can be easily tailored by changing the organic components during the MSN
7 , 8 ]
, graphene oxide[
9 ]
, carbon nanotubes[
10 ]
, prussian blue
. More importantly, MSN can encapsulate or immobilize a large amount of
2
1
preparation process, which makes them considerably attractive for a wide arrange of
2
applications such as catalyst, drug release, sensors and separation [20,
21]
.
3
In this work, we synthesized a type of Fe3O4@MSN with Fe3O4 as the core and
4
mesoporous silica the shell. The superparamagnetic Fe3O4 core provides high
5
peroxidase-mimic activity and makes artificial enzymatic system easily recyclable.
6
Furthermore, Fe3O4 nanoparticles are encapsulated in MSN shells to hinder the
7
aggregation and keep them stable even under harsh conditions. Meanwhile, small
8
active molecules are allowed to diffuse in and out of the MSN shells. Serving as
9
robust nanoreactors, the Fe3O4@MSN can catalyze a self-organized cascade reaction
10
based on these functional units mentioned above, namely oxidation of glucose by
11
oxygen to yield gluconic acid and H2O2 in the first place, and sequently the H2O2
12
further oxidizes 3,3,5,5-tetramethylbenzidine (TMB) to produce a color change. It’s
13
known to all that Fe3O4@MSN was used successfully for hydrogen peroxide and
14
glucose detection for the first time. And the catalytic efficiency of Fe3O4@MSN was
15
not strongly dependent on pH and temperature. As a nanoreactor, Fe3O4@MSN can
16
catalyze a self-organized cascade reaction and simultaneously optimized the test with
17
a better sensitivity while MSN is comparatively conceivable to be modified in the
18
application of interface detection.
19
2. Experimental Section
20
2.1. Chemicals and Materials
21
Tetraethylorthosilicate (TEOS), cetyltrimethylammonium bromide (CTAB),
22
glucose oxidase (GOx), horseradish peroxidase (HRP), 3, 3, 5, 5-tetramethylbenzidine
23
(TMB) were purchased from Sigma-Aldrich. Glucose, fructose, maltose and lactose
24
were obtained from Shanghai Sangon Biological Engineering Technology and Service
25
Co. Ltd, China. FeCl3•6H2O, sodium acetate, ethylene glycol, ethylenediamine and 3
1
30% hydrogen peroxide (H2O2) were purchased from Beijing Chemical Reagent
2
Company (Beijing, China). Other reagents and chemicals were at least analytical
3
reagent grade. All materials were purchased and used as received without further
4
treatment. The water used throughout all experiments was purified by a Milli-Q
5
system (18.2 MΩ-cm, Millipore System Inc.).
6
2.2. Synthesis of Magnetite Core The spherical magnetic Fe3O4 particles were prepared according to the literature
7 8
[22,23]
9
into a mixed solution of ethylene glycol (10 mL) and ethylenediamine (5 mL). After
10
vigorously stirring for 30 min, the obtained solution was transferred to a Teflon-lined
11
stainless-steel autoclave and heated at 200 ℃ for 24 h. The autoclave was then cooled
12
to room temperature naturally. The obtained black magnetite particles were washed
13
with ethanol and deionized water in sequence, and dried in hot air oven at 80 ℃ for 24
14
h.
15
2.3. Synthesis of Fe3O4@MSN Nanocomposites
. Typically, FeCl3•6H2O (0.5 g) and sodium acetate (1.5 g) were quickly added
16
The core-shell structured Fe3O4@ MSN nanocomposites were prepared by a
17
modified Stöber sol-gel method [24]. In a typical procedure, as-prepared Fe3O4 (0.10 g)
18
nanoparticles were treated with ethanol by ultrasonication for 30 min. Subsequently,
19
the treated nanoparticles were separated by centrifugation, and then well dispersed in
20
a mixture of ethanol (80 mL), deionized water (20 mL), and concentrated ammonia
21
aqueous solution (28 wt %, 1.0 mL). TEOS (30 µL) was then added dropwise to the
22
solution. After stirring for 6 h, the products were separated by a magnet and washed
23
with ethanol and water, and then redispersed in a mixed solution containing CTAB
24
(0.3 g), deionized water (80 mL), concentrated ammonia aqueous solution (28 wt %,
25
1.5 mL), and ethanol (60 mL). The resulting solution was vigorously stirred for 30 4
1
min. TEOS (400 µL) was then added dropwise to the solution with stirring. After
2
another stirring for 6 h, the products were collected and separated with a magnet,
3
washed with ethanol and water several times to remove the unreacted species, and
4
dried in vacuum at 60 ℃ for 24 h. Finally, the CTAB-removed product was dried in
5
vacuum at 60 ℃ for 12 h and denoted as Fe3O4@MSN nanocomposites.
6
2.4. Characterization of Fe3O4@MSN Nanocomposites
7
UV-vis absorption spectra were measured on a Beckman DU-800 UV–vis The
morphology
and
microstructure
of
Fe3O4@MSN
8
spectrophotometer.
9
nanocomposites were characterized by using JEM-3010 transmission electron
10
microscopy (TEM) and JSM-6700F scanning electron microscopy (SEM). TEM
11
sample was prepared by applying diluted particle suspensions to formvar film-coated
12
copper grids followed by drying preparations at
13
adsorption-desorption isotherms were obtained at -196 ℃ on a Micromeritics ASAP
14
2010 sorptometer by static adsorption procedures. Specific surface areas were
15
calculated from the adsorption data in the low-pressure range using the
16
Brunauer-Emmett-Teller (BET) model. Pore size was calculated by using the
17
Barrett-Joyner-Halenda (BJH) model on the adsorption branch of the isotherm.
18
2.5. H2O2 Detection Using Fe3O4@MSN as Peroxidase Mimetics
room temperature. N2
19
To investigate the peroxidase-like activity of the as-prepared Fe3O4@MSN, the
20
catalytic oxidation of the peroxidase substrate TMB in the presence of H2O2 was
21
tested. In a typical experiment, 30 μL of 60 mM TMB, 25 μL of the Fe3O4@MSN
22
stock solution, and 30 μL of 100 mM H2O2 were added into 115 μL of 0.2 M acetate
23
buffer, the mixed solution was incubated for 20 min. The Fe3O4@MSN was then
24
removed from the reaction solution by an external magnetic field. 100 μL of the
25
resulting reaction solution was used for absorption spectroscopy measurement. To 5
1
examine the influence of reaction buffer pH on the Fe3O4@MSN activity, 0.1 M
2
acetate buffer solutions from pH 2.0 to 12.0 were investigated. To examine the
3
influence of incubation temperature on the Fe3O4@MSN activity, catalytic reactions
4
incubated in different temperature water baths from 20 to 80 ℃ were investigated. As
5
control experiments, 10 μL of water was used instead of 10 mL of Fe3O4@MSN.
6
2.6. Glucose Detection Using Fe3O4@MSN
7
Glucose detection was realized as follows: (1) 20 μL of 20 mg/mL GOx and 80
8
μL of glucose of different concentrations in 10 mM phosphate buffered saline (PBS,
9
pH 7.4) were incubated for 20 min; (2) 30 μL of 60 mM TMB, 25 μL of the
10
Fe3O4@MSN stock solution, and 845 μL of 0.2 M acetate buffer (pH 5.5) were added
11
into the above 100 μL glucose reaction solution; (3) the mixed solution was incubated
12
in a 40 °C water bath for 20 min, and the Fe3O4@MSN were then removed from the
13
reaction solution by an external magnetic field; (4) the final reaction solution was
14
used to perform the absorption spectroscopy measurement. In control experiments, 5
15
mM maltose, 5 mM lactose, and 5 mM fructose were used instead of glucose.
16
3. Results and discussion
17
3.1 Characterization of Fe3O4@MSN
18
The SEM and TEM were used to characterize the synthesized Fe3O4@MSN
19
nanoparticles. The SEM and TEM micrograph of Fe3O4@MSN are displayed in
20
Figure 1. One can see that the size distribution of Fe3O4@MSN with an average
21
diameter and length of ~100 nm. The magnetic core inside the mesoporous silica
22
matrix is loose clusters composed of nanocrystals. As can be seen from Figure 2A,
23
the black solution was Fe3O4@MSN nanocomposites (photo a), and precipitate could
24
be observed in the aqueous medium and the supernatant of the aqueous medium
25
became transparent after magnetic treatment (photo b). Additionally, the N2 6
1
adsorption-desorption isotherms of Fe3O4@MSN showed a typical MCM-41 structure
2
(type IV) with a BET surface area of 506.18 m2 g-1. The BJH curve showed narrow
3
pore size distribution of Fe3O4@MSN with an average pore diameter of 2.4 nm and
4
pore volume of 0.86 cm3g-1 (Figure 2B). These findings provided immediate evidence
5
for the fact that Fe3O4@MSN nanocomposites were synthesized.
6 7
Figure 1.
8
Figure 2.
9 10
3.2. The Fe3O4@MSN as Peroxidase Mimetics and Their Use in H2O2 Detection It is well known that peroxidase can catalyze the oxidation of peroxidase [25]
11
substrate by hydrogen peroxide to produce a color change
12
peroxidase-like activity of the as-prepared Fe3O4@MSN, the catalytic oxidation of
13
peroxidase substrate TMB in the presence of H2O2 was tested (equation 1). Because
14
the amount of the colored oxidized TMB product is proportional to the concentration
15
of H2O2 present in the solution, the concentration of H2O2 can be determined by
16
recording the absorbance of the solution according to the Beer’s law. As seen in
17
Figure 3A, upon the addition of Fe3O4@MSN to the peroxidase substrate TMB in the
18
presence of H2O2, a blue color product can be formed. And the blue color of the
19
solution results from the product formed by the oxidation of TMB. The resulting
20
solution shows a maximum absorbance at 655 nm in the UV-Vis spectrum originates
21
from the oxidation of TMB (Figure 3B), indicating that Fe3O4@MSN has
22
peroxidase-like catalytic activity in the absence of any other catalysts [26
23 24 25
Figure 3. 7
. To investigate the
27]
.
1
Similar to peroxidase, the catalytic activity of Fe3O4 dependent on solution pH [1]
, but the pH and temperature-dependent
2
and reaction temperature has been reported
3
activity of Fe3O4@MSN remains unknown, which was therefore also investigated in
4
this study. And the result indicates that the activity of Fe3O4@MSN is not strongly
5
dependent on solution pH and reaction temperature. In view of the stability and
6
catalytic activity of the Fe3O4@MSN, 40 ℃ was taken as the optimal reaction
7
temperature and pH 5.5 was set as the optimal pH value. Because the catalytic activity
8
of the Fe3O4@MSN is H2O2 concentration-dependent, the system discussed above
9
could be used to detect H2O2. Under the optimal conditions, the developed method
10
was used for H2O2 detection. Figure 4A shows a typical H2O2 concentration response
11
curve. The calibration graph of the absorbance at 655 nm to H2O2 concentration was
12
linear in the range from 1.0×10-6 to 1.0 ×10-4 mol/L where as low as 1.0×10-6 mol/L
13
H2O2 could be detected under the optimal experimental conditions (Figure 4B). The
14
regression equation was y=0.0287x+0.2685 (y is the absorption values, x is H2O2
15
concentration) and the correlation coefficient was 0.9852.
16 17 18
Figure 4. 3.3. The stability of Fe3O4@MSN catalytic activity
19
In general, the activity of natural enzyme is lost after exposure to extremes of pH
20
and high temperature. As for horseradish peroxidase, after treatment at temperatures 40 ℃ for only 2 h, the enzyme activity dramatically declined. In
22
contrast, Fe3O4@MSN is expected to be more stable because it is an inorganic
23
material. To verify this, the catalytic activity of Fe3O4@MSN was measured after
24
incubation at a range of temperatures and pH values. The experimental results show
25
that the Fe3O4@MSN are indeed stable over a wide range of pH from 2.0 to 12.0, and 8
1
temperature from 40 to 90 ℃. The study on the Fe3O4@MSN catalytic activity
2
suggests that the reproducibility of Fe3O4@MSN samples prepared at different times
3
is satisfactory (the relative catalytic activity of the Fe3O4@MSN could retain more
4
than its 95% original value after used for 5 times.) (Figure 5). The robustness of
5
Fe3O4@MSN makes them suitable for a broad range of applications in the
6
biomedicine and environmental chemistry fields.
7
Figure 5.
8 9
3.4. Glucose Detection Using GOx and the Fe3O4@MSN
10
H2O2 is the main product of glucose oxidase-catalyzed reaction. When the
11
peroxidase-like activity of the Fe3O4@MSN is coupled with the glucose catalytic
12
reaction by GOx, colorimetric determination of glucose could be realized. The GOx
13
oxidizes glucose to form gluconic acid and H2O2 quantitatively, and the H2O2
14
produced is then utilized by Fe3O4@MSN to oxidize TMB to produce a blue colored
15
solution (equation 2). Therefore, colorimetric detection of glucose could be easily
16
realized using the colorimetric method. By this methodology, the calibration graph of
17
the absorbance at 655 nm to concentration of glucose was found to be linear in the
18
range 1.0×10-5 to 5.0×10-4 mol/L with a correlation coefficient of 0.9958 (Figure. 6)
19
The regression equation was y=0.0273x+0.2452 (y is the absorption value, x is the
20
glucose concentration). The detection limit (LOD) was 0.4 ×10-5 mol/L calculated
21
according to the signal which is equivalent to 3 times the standard deviation of the
22
blanks.
23 24 25
Figure. 6 9
1
Most of the Fe3O4@MSN catalysts are anchored inside the pore channels that
2
give accesses to small molecules such as H2O2 and TMB while obstruct large
3
molecules like glucose oxidase. As a result, multistep reactions occur at two different
4
parts of the material, namely generation of H2O2 from glucose using Fe3O4@MSN
5
occurring outside the pore channels while the oxidation of TMB by the Fe3O4@MSN
6
inside the pore channels. This allows two different catalytic reactions to proceed
7
simultaneously at two parts of the material without interfering with each other.
8
3.5. Study of Interference and Selectivity
9
In order to test whether the detection of glucose is specific or not, control
10
experiments were taken using fructose, lactose, and maltose respectively. Before it,
11
however, the selectivity is very important in the real application. For glucose
12
detection, the selectivity experiments were carried out using buffer solution, 5 mM
13
maltose, 5 mM fructose, and 5 mM lactose in place of glucose (5 mM). The results
14
demonstrated that the intensity of these glucose analogues was negligible compared
15
with that of glucose even at concentrations as high as 5 mM (Figure 7). Thus the
16
method developed here showed high selectivity toward glucose detection. This
17
indicates that this biosensing system has high selectivity for glucose, which could be
18
attributed to the high affinity of glucose oxidase for glucose detection.
19
Figure 7.
20 21
4. Conclusion
22
In summary, Fe3O4@MSN were prepared and investigated as peroxidase
23
mimetics. The catalytic oxidation of peroxidase substrate TMB with H2O2 using the
24
Fe3O4@MSN was realized. The Fe3O4@MSN as peroxidase mimetic provides a
25
colorimetric assay for H2O2. The colorimetric method showed good response toward 10
1
H2O2 detection with a linear range from 1×10-6 to 1×10-4 mol/L. More importantly, a
2
sensitive and selective analytical platform for glucose detection was fabricated using
3
GOx and the as-prepared Fe3O4@MSN. The analytical platform developed exhibited
4
sensitive and selective detection of glucose with the linear range from 1×10-5 to
5
5×10-4 mol/L. Because the Fe3O4@MSN can rival natural enzymes due to their easy
6
preparation, robustness, and stability in rough conditions, the analytical platform for
7
the detection of H2O2 and glucose developed here not only confirms that the
8
Fe3O4@MSN possesses an intrinsic peroxidase-like activity but also shows great
9
potential applications in varieties of simple, cost-effective, and easy-to-make
10
biosensors in the future.
11
Acknowledgments
12
This work was supported in part by the National Natural Science Foundation of
13
China (21305164), State Key Laboratory of Chemo/Biosensing and Chemometrics,
14
Hunan University (2013019), Scientific Research Fund of Hunan Provincial
15
Education Department (13C1138).
16 17
Figure captions
18
Figure 1. Characterization of synthesized Fe3O4@MSN. (A) TEM image of
19
Fe3O4@MSN; (B) SEM image of Fe3O4@MSN.
20
Figure 2. (A) Photographs of Fe3O4@MSN in pH 5.5 buffers without (a) and with (b)
21
magnetic treatment; (B) Nitrogen adsorption-desorption isotherms and pore size
22
distribution of Fe3O4@MSN (inset).
23
Figure 3. (A) Typical photographs of TMB catalytically oxidized by the Fe3O4@MSN
24
in the absence (left) and in the presence of H2O2 (right). (B) Absorption curves of
25
TMB reaction solutions catalytically oxidized by the as-prepared Fe3O4@MSN in the 11
1
presence of H2O2 incubated at 40 ℃ in pH 5.5 buffers (line a. TMB + Fe3O4@MSN +
2
H2O2, line b. TMB + H2O2, line c. Fe3O4@MSN + H2O2).
3
Figure 4. (A) A dose response curve for H2O2 detection using the as-prepared
4
Fe3O4@MSN as artificial enzymes and (B) the Linear calibration plot between the
5
absorbance at 655 nm and concentration of H2O2 (0.01 mM to 1 mM ). The error bars
6
represent the standard deviation of three measurements. The insert shows the
7
dependence of the absorbance at 655 nm on the concentration of H2O2 in the range 1
8
μM to 10 μM.
9
Figure 5. (A) A dose response curve for glucose detection using the as-prepared
10
Fe3O4@MSN as artificial enzymes and (B) the Linear calibration plot between the
11
absorbance at 655 nm and concentration of glucose (10 μM to 500 μM ). The error
12
bars represent the standard deviation of three measurements. The insert shows the
13
dependence of the absorbance at 655 nm on the concentration of glucose in the range
14
10 μM to 100 μM
15
Figure 6. The relative catalytic activity of Fe3O4@MSN after 5 cycles.
16
Figure 7. Determination of the selectivity of glucose detection with 5 mM lactose, 5
17
mM fructose, 5 mM maltose, and 1 mM glucose using GOD and Fe3O4@MSN. The
18
error bars represent the standard deviation of three measurements.
19 20
References
21
12
1 2 3 4 5 6 7 8 9 10
Highlights 1. A magnetic mesoporous silica nanoparticle was synthesized used for H2O2 and glucose detection. 2. The magnetic mesoporous silica nanoparticles provide high peroxidase-mimic activity. 3. The magnetic mesoporous silica nanoparticles can rival natural enzyme. 4. This is a competitive analytical platform for the detection of H2O2 and glucose.
13
1
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15
*Graphical Abstract (for review)
Fig 1
Figure
Fig 1
Figure
Fig 2
(A)
Volume Adsorbed (cm3/g)
300 250 200
Pore Volume (cm3/g)
350
150
1.0 .8 .6 .4 .2 0.0 1
2 3 4 5 6 7 Pore Diameter (nm)
100 50 0 0.0
.2
.4
.6 P/P0
(B)
.8
1.0
Figure
Fig 3
B .8 a
Abs
.6
.4 b .2 c 0.0
300
400
500
600
Wavelength/nm
700
800
Figure
Fig 4
.9
.8
.8
100 μM .7
.6 Abs
Abs
.6
1 μM
.60 .55
.5
.4
.50
Abs
.45 .40
.4
.35 .30
.2
.3 .25 0
2
4
6
8
10
12
H2O2[1X10-5mol]
.2
500
550
600
650
700
Wavelength/nm
(A)
750
800
0
20
40
60
H2O2[1¡Á10-6mol]
(B)
80
100
120
Figure
Fig 5
.8
.8
500 μM
.7
.6
10 μM
Abs
.4
.60
.5
.55 .50 .45
.4
Abs
Abs
.6
.40 .35 .30
.2
.3
.25 .20 0
2
4
6
8
10
12
glucose[1x10-4mol]
.2
500
550
600
650
700
Wavelength/nm
(A)
750
800
0
20
40
glucose [1¡Á10-5mol]
(B)
60
Figure
Fig 6
Relative catalytic activity [%]
100
95
90
85
80 0
1
2
3 Times
4
5
6
Figure
Fig 7
1.0
.8
Abs
.6
.4
.2
0.0 buffer
glucose
maltose
lactose
fructose
Colorimetric detection of Hydrogen peroxide and glucose using the magnetic mesoporous silica nanoparticles Yonghong Wang, Bo Zhou, Shun Wu, Kemin Wang, Xiaoxiao He
www.elsevier.com/locate/talanta
PII: DOI: Reference:
S0039-9140(14)00995-3 http://dx.doi.org/10.1016/j.talanta.2014.12.013 TAL15285
To appear in:
Talanta
Received date: 3 October 2014 Revised date: 8 December 2014 Accepted date: 11 December 2014 Cite this article as: Yonghong Wang, Bo Zhou, Shun Wu, Kemin Wang, Xiaoxiao He, Colorimetric detection of Hydrogen peroxide and glucose using the magnetic mesoporous silica nanoparticles, Talanta, http://dx.doi.org/10.1016/ j.talanta.2014.12.013 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1
Colorimetric Detection of Hydrogen Peroxide and Glucose
2
Using the Magnetic Mesoporous Silica Nanoparticles
3
Yonghong Wanga,b, Bo Zhoua, Shun Wua, Kemin Wangb,*, Xiaoxiao Heb
4
a. College of Life Science and technology, Central South University of Forestry and Technology,
5
410004, Changsha, China. E-mail: [email protected]
6
b. State Key Laboratory of Chemo/Biosensing and Chemometrics, College of Biology, College of
7
Chemistry and Chemical Engineering, Hunan University, Changsha 410082, P.R.China.
8 9
Abstract
10
In this work, we synthesized a type of magnetic mesoporous silica nanoparticle
11
(denoted as Fe3O4@MSN) with Fe3O4 as the core and mesoporous silica the shell.
12
The superparamagnetic Fe3O4-core provides high peroxidase-mimic activity and
13
makes the artificial enzymatic system easily recyclable. Furthermore, Fe3O4
14
nanoparticles are encapsulated in MSN shells to hinder the aggregation and keep them
15
stable even under harsh conditions. Meanwhile, small active molecules are allowed to
16
diffuse in and out of the MSN shells. Based on these functional units, the
17
Fe3O4@MSN as robust nanoreactors can catalyze a self-organized cascade reaction,
18
which includes oxidation of glucose by oxygen to yield gluconic acid and H2O2, and
19
the latter further oxidizes 3,3,5,5-tetramethylbenzidine (TMB) to produce a color
20
change. The Fe3O4@MSN, whose catalytic efficiency was not strongly dependent on
21
pH and temperature, was successfully used for the detection of glucose and showed
22
excellent sensitivity with a detection limit of 0.4×10-5 mol/L. Nevertheless, the assay
23
is also highly selective toward the glucose detection.
24 25
Keywords: Magnetic mesoporous nanoparticles; Peroxidase-mimic activity; Glucose;
26
Detection.
27 1
1
1. Introduction
2
Nanomaterials have received considerable attention over the past few decades
3
because of their unique size, shape, composition and structure-dependent properties.
4
There has been an explosive growth in the use of nanomaterials as catalysts involving
5
both homogeneous and heterogeneous catalysis. But the possibility of nanomaterials
6
as certain artificial enzymes, important subdivisions of catalysis, had long remained
7
unknown. Until the first nanoparticle-based artificial enzyme was reported, Fe3O4
8
nanoparticles were found to possess an intrinsic peroxidase-like activity
9
which time some other nanomaterials have been evaluated as peroxidase mimetics.
10
These studies show that the nanomaterial-based peroxidase mimetics enjoy
11
advantages of low cost, high stability and tunability in catalytic activities and can be
12
potentially used in bioassays and medical diagnostics.
[1]
, since
13
Various nanomaterials including Fe3O4 magnetic nanoparticles[2,3] , positively
14
charged gold nanoparticles[4], cupric oxide nanoparticles[5], CuS nanoparticles[6], ceria
15
nanoparticles[
16
nanoparticles[11], carbon nanodots[12] and folate-polyoxometalate hybrid spheres[13]
17
have been reported to possess peroxidase-like activity and used for the visual
18
detection of H2O2 and glucose. In recent years, mesoporous silica nanoparticles (MSN)
19
have gained great interests in many fields due to their unique advantages, including
20
good biocompatibility, large load capacity, tunable pore sizes, the ease of surface
21
functionalization, large surface area, and high thermal and mechanical stability
22
[14,15,16,17]
23
payloads such as mediators, enzymes, and antibodies owning to their high pore
24
volume and large surface area [18,19]. Moreover, the surface properties and composition
25
of MSN can be easily tailored by changing the organic components during the MSN
7 , 8 ]
, graphene oxide[
9 ]
, carbon nanotubes[
10 ]
, prussian blue
. More importantly, MSN can encapsulate or immobilize a large amount of
2
1
preparation process, which makes them considerably attractive for a wide arrange of
2
applications such as catalyst, drug release, sensors and separation [20,
21]
.
3
In this work, we synthesized a type of Fe3O4@MSN with Fe3O4 as the core and
4
mesoporous silica the shell. The superparamagnetic Fe3O4 core provides high
5
peroxidase-mimic activity and makes artificial enzymatic system easily recyclable.
6
Furthermore, Fe3O4 nanoparticles are encapsulated in MSN shells to hinder the
7
aggregation and keep them stable even under harsh conditions. Meanwhile, small
8
active molecules are allowed to diffuse in and out of the MSN shells. Serving as
9
robust nanoreactors, the Fe3O4@MSN can catalyze a self-organized cascade reaction
10
based on these functional units mentioned above, namely oxidation of glucose by
11
oxygen to yield gluconic acid and H2O2 in the first place, and sequently the H2O2
12
further oxidizes 3,3,5,5-tetramethylbenzidine (TMB) to produce a color change. It’s
13
known to all that Fe3O4@MSN was used successfully for hydrogen peroxide and
14
glucose detection for the first time. And the catalytic efficiency of Fe3O4@MSN was
15
not strongly dependent on pH and temperature. As a nanoreactor, Fe3O4@MSN can
16
catalyze a self-organized cascade reaction and simultaneously optimized the test with
17
a better sensitivity while MSN is comparatively conceivable to be modified in the
18
application of interface detection.
19
2. Experimental Section
20
2.1. Chemicals and Materials
21
Tetraethylorthosilicate (TEOS), cetyltrimethylammonium bromide (CTAB),
22
glucose oxidase (GOx), horseradish peroxidase (HRP), 3, 3, 5, 5-tetramethylbenzidine
23
(TMB) were purchased from Sigma-Aldrich. Glucose, fructose, maltose and lactose
24
were obtained from Shanghai Sangon Biological Engineering Technology and Service
25
Co. Ltd, China. FeCl3•6H2O, sodium acetate, ethylene glycol, ethylenediamine and 3
1
30% hydrogen peroxide (H2O2) were purchased from Beijing Chemical Reagent
2
Company (Beijing, China). Other reagents and chemicals were at least analytical
3
reagent grade. All materials were purchased and used as received without further
4
treatment. The water used throughout all experiments was purified by a Milli-Q
5
system (18.2 MΩ-cm, Millipore System Inc.).
6
2.2. Synthesis of Magnetite Core The spherical magnetic Fe3O4 particles were prepared according to the literature
7 8
[22,23]
9
into a mixed solution of ethylene glycol (10 mL) and ethylenediamine (5 mL). After
10
vigorously stirring for 30 min, the obtained solution was transferred to a Teflon-lined
11
stainless-steel autoclave and heated at 200 ℃ for 24 h. The autoclave was then cooled
12
to room temperature naturally. The obtained black magnetite particles were washed
13
with ethanol and deionized water in sequence, and dried in hot air oven at 80 ℃ for 24
14
h.
15
2.3. Synthesis of Fe3O4@MSN Nanocomposites
. Typically, FeCl3•6H2O (0.5 g) and sodium acetate (1.5 g) were quickly added
16
The core-shell structured Fe3O4@ MSN nanocomposites were prepared by a
17
modified Stöber sol-gel method [24]. In a typical procedure, as-prepared Fe3O4 (0.10 g)
18
nanoparticles were treated with ethanol by ultrasonication for 30 min. Subsequently,
19
the treated nanoparticles were separated by centrifugation, and then well dispersed in
20
a mixture of ethanol (80 mL), deionized water (20 mL), and concentrated ammonia
21
aqueous solution (28 wt %, 1.0 mL). TEOS (30 µL) was then added dropwise to the
22
solution. After stirring for 6 h, the products were separated by a magnet and washed
23
with ethanol and water, and then redispersed in a mixed solution containing CTAB
24
(0.3 g), deionized water (80 mL), concentrated ammonia aqueous solution (28 wt %,
25
1.5 mL), and ethanol (60 mL). The resulting solution was vigorously stirred for 30 4
1
min. TEOS (400 µL) was then added dropwise to the solution with stirring. After
2
another stirring for 6 h, the products were collected and separated with a magnet,
3
washed with ethanol and water several times to remove the unreacted species, and
4
dried in vacuum at 60 ℃ for 24 h. Finally, the CTAB-removed product was dried in
5
vacuum at 60 ℃ for 12 h and denoted as Fe3O4@MSN nanocomposites.
6
2.4. Characterization of Fe3O4@MSN Nanocomposites
7
UV-vis absorption spectra were measured on a Beckman DU-800 UV–vis The
morphology
and
microstructure
of
Fe3O4@MSN
8
spectrophotometer.
9
nanocomposites were characterized by using JEM-3010 transmission electron
10
microscopy (TEM) and JSM-6700F scanning electron microscopy (SEM). TEM
11
sample was prepared by applying diluted particle suspensions to formvar film-coated
12
copper grids followed by drying preparations at
13
adsorption-desorption isotherms were obtained at -196 ℃ on a Micromeritics ASAP
14
2010 sorptometer by static adsorption procedures. Specific surface areas were
15
calculated from the adsorption data in the low-pressure range using the
16
Brunauer-Emmett-Teller (BET) model. Pore size was calculated by using the
17
Barrett-Joyner-Halenda (BJH) model on the adsorption branch of the isotherm.
18
2.5. H2O2 Detection Using Fe3O4@MSN as Peroxidase Mimetics
room temperature. N2
19
To investigate the peroxidase-like activity of the as-prepared Fe3O4@MSN, the
20
catalytic oxidation of the peroxidase substrate TMB in the presence of H2O2 was
21
tested. In a typical experiment, 30 μL of 60 mM TMB, 25 μL of the Fe3O4@MSN
22
stock solution, and 30 μL of 100 mM H2O2 were added into 115 μL of 0.2 M acetate
23
buffer, the mixed solution was incubated for 20 min. The Fe3O4@MSN was then
24
removed from the reaction solution by an external magnetic field. 100 μL of the
25
resulting reaction solution was used for absorption spectroscopy measurement. To 5
1
examine the influence of reaction buffer pH on the Fe3O4@MSN activity, 0.1 M
2
acetate buffer solutions from pH 2.0 to 12.0 were investigated. To examine the
3
influence of incubation temperature on the Fe3O4@MSN activity, catalytic reactions
4
incubated in different temperature water baths from 20 to 80 ℃ were investigated. As
5
control experiments, 10 μL of water was used instead of 10 mL of Fe3O4@MSN.
6
2.6. Glucose Detection Using Fe3O4@MSN
7
Glucose detection was realized as follows: (1) 20 μL of 20 mg/mL GOx and 80
8
μL of glucose of different concentrations in 10 mM phosphate buffered saline (PBS,
9
pH 7.4) were incubated for 20 min; (2) 30 μL of 60 mM TMB, 25 μL of the
10
Fe3O4@MSN stock solution, and 845 μL of 0.2 M acetate buffer (pH 5.5) were added
11
into the above 100 μL glucose reaction solution; (3) the mixed solution was incubated
12
in a 40 °C water bath for 20 min, and the Fe3O4@MSN were then removed from the
13
reaction solution by an external magnetic field; (4) the final reaction solution was
14
used to perform the absorption spectroscopy measurement. In control experiments, 5
15
mM maltose, 5 mM lactose, and 5 mM fructose were used instead of glucose.
16
3. Results and discussion
17
3.1 Characterization of Fe3O4@MSN
18
The SEM and TEM were used to characterize the synthesized Fe3O4@MSN
19
nanoparticles. The SEM and TEM micrograph of Fe3O4@MSN are displayed in
20
Figure 1. One can see that the size distribution of Fe3O4@MSN with an average
21
diameter and length of ~100 nm. The magnetic core inside the mesoporous silica
22
matrix is loose clusters composed of nanocrystals. As can be seen from Figure 2A,
23
the black solution was Fe3O4@MSN nanocomposites (photo a), and precipitate could
24
be observed in the aqueous medium and the supernatant of the aqueous medium
25
became transparent after magnetic treatment (photo b). Additionally, the N2 6
1
adsorption-desorption isotherms of Fe3O4@MSN showed a typical MCM-41 structure
2
(type IV) with a BET surface area of 506.18 m2 g-1. The BJH curve showed narrow
3
pore size distribution of Fe3O4@MSN with an average pore diameter of 2.4 nm and
4
pore volume of 0.86 cm3g-1 (Figure 2B). These findings provided immediate evidence
5
for the fact that Fe3O4@MSN nanocomposites were synthesized.
6 7
Figure 1.
8
Figure 2.
9 10
3.2. The Fe3O4@MSN as Peroxidase Mimetics and Their Use in H2O2 Detection It is well known that peroxidase can catalyze the oxidation of peroxidase [25]
11
substrate by hydrogen peroxide to produce a color change
12
peroxidase-like activity of the as-prepared Fe3O4@MSN, the catalytic oxidation of
13
peroxidase substrate TMB in the presence of H2O2 was tested (equation 1). Because
14
the amount of the colored oxidized TMB product is proportional to the concentration
15
of H2O2 present in the solution, the concentration of H2O2 can be determined by
16
recording the absorbance of the solution according to the Beer’s law. As seen in
17
Figure 3A, upon the addition of Fe3O4@MSN to the peroxidase substrate TMB in the
18
presence of H2O2, a blue color product can be formed. And the blue color of the
19
solution results from the product formed by the oxidation of TMB. The resulting
20
solution shows a maximum absorbance at 655 nm in the UV-Vis spectrum originates
21
from the oxidation of TMB (Figure 3B), indicating that Fe3O4@MSN has
22
peroxidase-like catalytic activity in the absence of any other catalysts [26
23 24 25
Figure 3. 7
. To investigate the
27]
.
1
Similar to peroxidase, the catalytic activity of Fe3O4 dependent on solution pH [1]
, but the pH and temperature-dependent
2
and reaction temperature has been reported
3
activity of Fe3O4@MSN remains unknown, which was therefore also investigated in
4
this study. And the result indicates that the activity of Fe3O4@MSN is not strongly
5
dependent on solution pH and reaction temperature. In view of the stability and
6
catalytic activity of the Fe3O4@MSN, 40 ℃ was taken as the optimal reaction
7
temperature and pH 5.5 was set as the optimal pH value. Because the catalytic activity
8
of the Fe3O4@MSN is H2O2 concentration-dependent, the system discussed above
9
could be used to detect H2O2. Under the optimal conditions, the developed method
10
was used for H2O2 detection. Figure 4A shows a typical H2O2 concentration response
11
curve. The calibration graph of the absorbance at 655 nm to H2O2 concentration was
12
linear in the range from 1.0×10-6 to 1.0 ×10-4 mol/L where as low as 1.0×10-6 mol/L
13
H2O2 could be detected under the optimal experimental conditions (Figure 4B). The
14
regression equation was y=0.0287x+0.2685 (y is the absorption values, x is H2O2
15
concentration) and the correlation coefficient was 0.9852.
16 17 18
Figure 4. 3.3. The stability of Fe3O4@MSN catalytic activity
19
In general, the activity of natural enzyme is lost after exposure to extremes of pH
20
and high temperature. As for horseradish peroxidase, after treatment at temperatures 40 ℃ for only 2 h, the enzyme activity dramatically declined. In
22
contrast, Fe3O4@MSN is expected to be more stable because it is an inorganic
23
material. To verify this, the catalytic activity of Fe3O4@MSN was measured after
24
incubation at a range of temperatures and pH values. The experimental results show
25
that the Fe3O4@MSN are indeed stable over a wide range of pH from 2.0 to 12.0, and 8
1
temperature from 40 to 90 ℃. The study on the Fe3O4@MSN catalytic activity
2
suggests that the reproducibility of Fe3O4@MSN samples prepared at different times
3
is satisfactory (the relative catalytic activity of the Fe3O4@MSN could retain more
4
than its 95% original value after used for 5 times.) (Figure 5). The robustness of
5
Fe3O4@MSN makes them suitable for a broad range of applications in the
6
biomedicine and environmental chemistry fields.
7
Figure 5.
8 9
3.4. Glucose Detection Using GOx and the Fe3O4@MSN
10
H2O2 is the main product of glucose oxidase-catalyzed reaction. When the
11
peroxidase-like activity of the Fe3O4@MSN is coupled with the glucose catalytic
12
reaction by GOx, colorimetric determination of glucose could be realized. The GOx
13
oxidizes glucose to form gluconic acid and H2O2 quantitatively, and the H2O2
14
produced is then utilized by Fe3O4@MSN to oxidize TMB to produce a blue colored
15
solution (equation 2). Therefore, colorimetric detection of glucose could be easily
16
realized using the colorimetric method. By this methodology, the calibration graph of
17
the absorbance at 655 nm to concentration of glucose was found to be linear in the
18
range 1.0×10-5 to 5.0×10-4 mol/L with a correlation coefficient of 0.9958 (Figure. 6)
19
The regression equation was y=0.0273x+0.2452 (y is the absorption value, x is the
20
glucose concentration). The detection limit (LOD) was 0.4 ×10-5 mol/L calculated
21
according to the signal which is equivalent to 3 times the standard deviation of the
22
blanks.
23 24 25
Figure. 6 9
1
Most of the Fe3O4@MSN catalysts are anchored inside the pore channels that
2
give accesses to small molecules such as H2O2 and TMB while obstruct large
3
molecules like glucose oxidase. As a result, multistep reactions occur at two different
4
parts of the material, namely generation of H2O2 from glucose using Fe3O4@MSN
5
occurring outside the pore channels while the oxidation of TMB by the Fe3O4@MSN
6
inside the pore channels. This allows two different catalytic reactions to proceed
7
simultaneously at two parts of the material without interfering with each other.
8
3.5. Study of Interference and Selectivity
9
In order to test whether the detection of glucose is specific or not, control
10
experiments were taken using fructose, lactose, and maltose respectively. Before it,
11
however, the selectivity is very important in the real application. For glucose
12
detection, the selectivity experiments were carried out using buffer solution, 5 mM
13
maltose, 5 mM fructose, and 5 mM lactose in place of glucose (5 mM). The results
14
demonstrated that the intensity of these glucose analogues was negligible compared
15
with that of glucose even at concentrations as high as 5 mM (Figure 7). Thus the
16
method developed here showed high selectivity toward glucose detection. This
17
indicates that this biosensing system has high selectivity for glucose, which could be
18
attributed to the high affinity of glucose oxidase for glucose detection.
19
Figure 7.
20 21
4. Conclusion
22
In summary, Fe3O4@MSN were prepared and investigated as peroxidase
23
mimetics. The catalytic oxidation of peroxidase substrate TMB with H2O2 using the
24
Fe3O4@MSN was realized. The Fe3O4@MSN as peroxidase mimetic provides a
25
colorimetric assay for H2O2. The colorimetric method showed good response toward 10
1
H2O2 detection with a linear range from 1×10-6 to 1×10-4 mol/L. More importantly, a
2
sensitive and selective analytical platform for glucose detection was fabricated using
3
GOx and the as-prepared Fe3O4@MSN. The analytical platform developed exhibited
4
sensitive and selective detection of glucose with the linear range from 1×10-5 to
5
5×10-4 mol/L. Because the Fe3O4@MSN can rival natural enzymes due to their easy
6
preparation, robustness, and stability in rough conditions, the analytical platform for
7
the detection of H2O2 and glucose developed here not only confirms that the
8
Fe3O4@MSN possesses an intrinsic peroxidase-like activity but also shows great
9
potential applications in varieties of simple, cost-effective, and easy-to-make
10
biosensors in the future.
11
Acknowledgments
12
This work was supported in part by the National Natural Science Foundation of
13
China (21305164), State Key Laboratory of Chemo/Biosensing and Chemometrics,
14
Hunan University (2013019), Scientific Research Fund of Hunan Provincial
15
Education Department (13C1138).
16 17
Figure captions
18
Figure 1. Characterization of synthesized Fe3O4@MSN. (A) TEM image of
19
Fe3O4@MSN; (B) SEM image of Fe3O4@MSN.
20
Figure 2. (A) Photographs of Fe3O4@MSN in pH 5.5 buffers without (a) and with (b)
21
magnetic treatment; (B) Nitrogen adsorption-desorption isotherms and pore size
22
distribution of Fe3O4@MSN (inset).
23
Figure 3. (A) Typical photographs of TMB catalytically oxidized by the Fe3O4@MSN
24
in the absence (left) and in the presence of H2O2 (right). (B) Absorption curves of
25
TMB reaction solutions catalytically oxidized by the as-prepared Fe3O4@MSN in the 11
1
presence of H2O2 incubated at 40 ℃ in pH 5.5 buffers (line a. TMB + Fe3O4@MSN +
2
H2O2, line b. TMB + H2O2, line c. Fe3O4@MSN + H2O2).
3
Figure 4. (A) A dose response curve for H2O2 detection using the as-prepared
4
Fe3O4@MSN as artificial enzymes and (B) the Linear calibration plot between the
5
absorbance at 655 nm and concentration of H2O2 (0.01 mM to 1 mM ). The error bars
6
represent the standard deviation of three measurements. The insert shows the
7
dependence of the absorbance at 655 nm on the concentration of H2O2 in the range 1
8
μM to 10 μM.
9
Figure 5. (A) A dose response curve for glucose detection using the as-prepared
10
Fe3O4@MSN as artificial enzymes and (B) the Linear calibration plot between the
11
absorbance at 655 nm and concentration of glucose (10 μM to 500 μM ). The error
12
bars represent the standard deviation of three measurements. The insert shows the
13
dependence of the absorbance at 655 nm on the concentration of glucose in the range
14
10 μM to 100 μM
15
Figure 6. The relative catalytic activity of Fe3O4@MSN after 5 cycles.
16
Figure 7. Determination of the selectivity of glucose detection with 5 mM lactose, 5
17
mM fructose, 5 mM maltose, and 1 mM glucose using GOD and Fe3O4@MSN. The
18
error bars represent the standard deviation of three measurements.
19 20
References
21
12
1 2 3 4 5 6 7 8 9 10
Highlights 1. A magnetic mesoporous silica nanoparticle was synthesized used for H2O2 and glucose detection. 2. The magnetic mesoporous silica nanoparticles provide high peroxidase-mimic activity. 3. The magnetic mesoporous silica nanoparticles can rival natural enzyme. 4. This is a competitive analytical platform for the detection of H2O2 and glucose.
13
1
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15
*Graphical Abstract (for review)
Fig 1
Figure
Fig 1
Figure
Fig 2
(A)
Volume Adsorbed (cm3/g)
300 250 200
Pore Volume (cm3/g)
350
150
1.0 .8 .6 .4 .2 0.0 1
2 3 4 5 6 7 Pore Diameter (nm)
100 50 0 0.0
.2
.4
.6 P/P0
(B)
.8
1.0
Figure
Fig 3
B .8 a
Abs
.6
.4 b .2 c 0.0
300
400
500
600
Wavelength/nm
700
800
Figure
Fig 4
.9
.8
.8
100 μM .7
.6 Abs
Abs
.6
1 μM
.60 .55
.5
.4
.50
Abs
.45 .40
.4
.35 .30
.2
.3 .25 0
2
4
6
8
10
12
H2O2[1X10-5mol]
.2
500
550
600
650
700
Wavelength/nm
(A)
750
800
0
20
40
60
H2O2[1¡Á10-6mol]
(B)
80
100
120
Figure
Fig 5
.8
.8
500 μM
.7
.6
10 μM
Abs
.4
.60
.5
.55 .50 .45
.4
Abs
Abs
.6
.40 .35 .30
.2
.3
.25 .20 0
2
4
6
8
10
12
glucose[1x10-4mol]
.2
500
550
600
650
700
Wavelength/nm
(A)
750
800
0
20
40
glucose [1¡Á10-5mol]
(B)
60
Figure
Fig 6
Relative catalytic activity [%]
100
95
90
85
80 0
1
2
3 Times
4
5
6
Figure
Fig 7
1.0
.8
Abs
.6
.4
.2
0.0 buffer
glucose
maltose
lactose
fructose
