A nano-sized Cu-MOF with high peroxidase-like activity and its potential application in colorimetric detection of H2O2and glucose

Article abstract of DOI:10.1039/d1ra04877e

Peroxidase widely exists in nature and can be applied for the diagnosis and detection of H₂O₂, glucose, ascorbic acid and other aspects. However, the natural peroxidase has low stability and its catalytic efficiency is easily affected by external conditions. In this work, a copper-based metal-organic framework (Cu-MOF) was prepared by hydrothermal method, and characterized by means of XRD, SEM, FT-IR and EDS. The synthesized Cu-MOF material showed high peroxidase-like activity and could be utilized to catalyze the oxidation ofo-phenylenediamine (OPDA) and 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. The steady-state kinetics experiments of the oxidation of OPDA and TMB catalyzed by Cu-MOF were performed, and the kinetic parameters were obtained by linear least-squares fitting to Lineweaver-Burk plot. The results indicated that the affinity of Cu-MOF towards TMB and OPDA was close to that of the natural horseradish peroxidase (HRP). The as-prepared Cu-MOF can be applied for colorimetric detection of H₂O₂and glucose with wide linear ranges of 5 to 300 μM and 50 to 500 μM for H₂O₂and glucose, respectively. Furthermore, the specificity of detection of glucose was compared with other sugar species interference such as sucrose, lactose and maltose. In addition, the detection of ascorbic acid and sodium thiosulfate was also performed upon the inhibition of TMB oxidation. Based on the high catalytic activity, affinity and wide linear range, the as-prepared Cu-MOF may be used for artificial enzyme mimics in the fields of catalysis, biosensors, medicines and food industry.

Full text of DOI:10.1039/d1ra04877e

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A nano-sized Cu-MOF with high peroxidase-like
activity and its potential application in colorimetric
detection of H2O2 and glucose†
Cite this: RSC Adv., 2021, 11, 26963
a
a
a
a
b
*
Hao Yu, Hanliu Wu, Xuemei Tian, Yafen Zhou, Chunguang Ren
a
*
and Zhonghua Wang
Peroxidase widely exists in nature and can be applied for the diagnosis and detection of H2O2, glucose,
ascorbic acid and other aspects. However, the natural peroxidase has low stability and its catalytic
efficiency is easily affected by external conditions. In this work, a copper-based metal–organic
framework (Cu-MOF) was prepared by hydrothermal method, and characterized by means of XRD, SEM,
FT-IR and EDS. The synthesized Cu-MOF material showed high peroxidase-like activity and could be
utilized to catalyze the oxidation of o-phenylenediamine (OPDA) and 3,30,5,50-tetramethylbenzidine
(TMB) in the presence of H2O2. The steady-state kinetics experiments of the oxidation of OPDA and TMB
catalyzed by Cu-MOF were performed, and the kinetic parameters were obtained by linear least-squares
fitting to Lineweaver–Burk plot. The results indicated that the affinity of Cu-MOF towards TMB and
OPDA was close to that of the natural horseradish peroxidase (HRP). The as-prepared Cu-MOF can be
applied for colorimetric detection of H2O2 and glucose with wide linear ranges of 5 to 300 mM and 50 to
500 mM for H2O2 and glucose, respectively. Furthermore, the specificity of detection of glucose was
compared with other sugar species interference such as sucrose, lactose and maltose. In addition, the
detection of ascorbic acid and sodium thiosulfate was also performed upon the inhibition of TMB
oxidation. Based on the high catalytic activity, affinity and wide linear range, the as-prepared Cu-MOF
may be used for artificial enzyme mimics in the fields of catalysis, biosensors, medicines and food industry.
Received 23rd June 2021
Accepted 30th July 2021
DOI: 10.1039/d1ra04877e
rsc.li/rsc-advances
oxidation.9 Furthermore, Muhammad Fiaz et al. synthesized
high efficient oxygen evolution reaction (OER) catalyst
1. Introduction
NiS@MOF-5, which can be coated on Ni-foam to form
NiS@MOF-5/NF and showed OER catalytic activity and excellent
stability.10 Besides, Nguyenet et al. found that Ni-MOF-74
possessed ultrahigh catalytic activity for the arylation of
azoles.11
Enzyme, also called biocatalyst, has the characteristics of
high efficiency, specicity and mild reaction conditions.12,13
Peroxidase is a kind of enzyme, which is widely existed in nature
and can participate in the metabolism of organisms,14 it can
also be used for the diagnosis and detection of H2O2, glucose,
ascorbic acid.15,16 However, natural enzymes usually have
drawbacks of the high cost of preparation and purication,
special storage conditions and low stability.15,17–20 The enzyme
activity can only be best performed under suitable conditions,
such as optimal temperature and acid-alkali conditions.13,21,22
Therefore, people begin to pay attention to the research of
articial mimic peroxidase.23–27
Metal–organic frameworks (MOFs) are crystalline porous
framework materials that are formed with organic ligands and
metal ions through coordination bonds with a periodic network
structure.1 MOFs have been widely used in catalysis,2 sensing,3
gas adsorption and separation,4 luminescence5 and other elds
due to their large specic surface area, unsaturated sites, and
structural and functional diversity.6–8 MOFs materials have been
shown to have great application prospects with more and more
kinds of MOFs and their composite materials having been
discovered. In the eld of catalysis, MOFs with high catalytic
efficiency have been reported. Qin et al. found that hollow
mesoporous MOF exhibited superior catalytic performance
when loading Pd nanoparticles toward benzyl alcohol
aChemical Synthesis and Pollution Control Key Laboratory of Sichuan Province,
College of Chemistry and Chemical Engineering, China West Normal University,
Nanchong 637002, Sichuan, P. R. China. E-mail: zhwangs@163.com; Fax: +86 817-
2445233; Tel: +86 817-2568081
It has been reported that Fe3O4 could catalyze the oxidation
of TMB and OPDA to generate blue and orange color reactions,
respectively.28 Since then, many researchers have carried out
research on the application of Fe3O4 mimic peroxidase in the
eld of glucose detection.29,30 Later, it has been discovered that
bYantai Institute of Materia Medica, Yantai 264000, Shandong, P. R. China. E-mail:
cgren@yimm.ac.cn
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d1ra04877e
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Co3O4 nanoparticles,31 V2O5 nanowires,32 CuO nanoparticles,33 transform infrared (FT-IR) spectrometer (Nicolet-6700) was
MnO2 microspheres34 and Ag2O,21 etc. also have intrinsic cata- applied to record FTIR spectroscopy. Scanning electron
lytic activity on classic peroxidase substrates in the presence of microscopy (SEM) image and energy dispersive X-ray spectros-
H2O2. At present, colorimetry is the most widely used method copy (EDS) image were taken by a Hitachi S4800 scanning
for glucose detection. The principle is that glucose oxidase electron microscope.
(GOX) catalyzes the oxidation of glucose and the reduction of O2
to H2O2, then the simulated peroxidase catalyzes H2O2 to 2.3. Cu-MOF preparation
produce hydroxyl free groups to oxidize substrates (TMB, DAB,
The Cu-MOF was prepared by using hydrothermal method.
Briey, 0.45 g (2.14 mmol) H3BTC was dissolved in 48 mL
absolute ethanol and stirred for 10 min. Next, addition of 0.75 g
(3.1 mmol) of Cu(NO3)2$3H2O to the above solution and
continued stirring for 10 min. Then, transferred the mixed
solution into a Teon-lined stainless autoclave. Aer heated at
120 ꢀC for 12 h and cooled down to the room temperature,
OPDA, etc.) to produce color reaction.35
As a peroxidase mimetic enzyme, MOFs have substantive
applications in colorimetric detection of some substances such
as H2O2 and glucose. It has been reported that some iron-
containing MOFs, such as MIL-53(Fe),36 MIL-88(Fe)37 and MIL-
68(Fe)38 possess the properties of peroxidase mimics. In the
presence of H2O2, the hydrothermally synthesized MIL-53(Fe)
collected the Cu-MOF by centrifugation and washed 3 times
can catalyze the oxidation of TMB and OPDA, which has been
with absolute ethanol, then dried in a vacuum drying-oven for
applied to the detection of actual samples such as glucose and
serum with a good linear range and selectivity. Later, it was
found that precious metals such as Au and other metals,39 and
composite metals (such as bimetallic) also have the catalytic
activity of mimetic enzymes,40 which makes MOFs as a popular
new material in the simulation of peroxidase.
24 h at 60 C to obtain the target product.44
ꢀ
2.4. Peroxidase-like activity
The catalytic oxidation of TMB by H2O2 was performed in
100 mM acetate buffer (pH 4.0) in the presence of Cu-MOF
catalyst. Briey, 2.4 mL of 0.06 mg mLꢁ1 Cu-MOF (Cu-MOF
solid was dispersed in acetate buffer by ultrasonication), 300
mL TMB (0.3 mM, dissolve the DMF) and 300 mL H2O2 (0.6 mM)
were mixed and reacted for 20 min at 30 ꢀC. The maximum
absorption wavelength of TMB oxidized product (652 nm)45 was
measured with a UV-Vis spectrophotometer. For OPDA oxida-
tion, 1 mL of 0.06 mg mLꢁ1 Cu-MOF solution (Cu-MOF solid
was dispersed in deionized water), 1 mL OPDA (0.4 mM,
dissolve the deionized water) and 1 mL H2O2 (0.6 mM) were
reacted for 20 min at 30 ꢀC. The maximum absorption wave-
length of OPDA oxidized product (416 nm)15 was measured by
a UV-Vis spectrophotometer.
Several Cu-MOFs were reported previously that different
organic compounds were used as coordination ligands, such as
uric acid,41 2-aminoterephthalic acid42 and 1,10-phenanthroline-
2,9-dicarboxylic acid.43 In this work, we prepared a Cu-MOF by
using
a simple hydrothermal method with 1,3,5-benzene-
tricarboxylic acid (H3BTC) as ligand. The peroxidase-like activity of
the as-prepared Cu-MOF was investigated by the oxidation reaction
of TMB and OPDA with H2O2. The Cu-MOF showed high
peroxidase-like activity, which can be used for catalyzing OPDA
and TMB to generate colored products in the presence of H2O2. To
investigate the possible oxidation mechanism of the Cu-MOF,
typical Michaelis–Menten curves were obtained through steady-
state kinetic experiments. Furthermore, the color reaction of
TMB with H2O2 can be inhibited by some reductive substances.
2.5. Cu-MOF kinetics measurements
Based on these ndings, we obtained satised results with the Cu- First, 6 mg Cu-MOF solid was dispersed in 100 mL acetate buffer
MOF for colorimetric detection of H2O2, ascorbic acid, sodium (pH 4.0) to prepare 0.06 mg mLꢁ1 Cu-MOF solution. The
thiosulfate and glucose.
concentration of the TMB was xed at 0.2 mM and a series of
H2O2 with different concentrations (10 mM–90 mM) were
prepared. During the reaction, 2.6 mL Cu-MOF solution, 0.1 mL
H2O2 solutionꢀand 0.3 mL TMB were mixed with a total volume
of 3 mL at 30 C. The reaction product was sampled at regular
intervals and spectroscopically detected at 652 nm by using
a UV-Vis spectrophotometer. Similar experiments were per-
formed by varying the concentration of TMB (0.1 mM–0.9 mM)
with xed concentration of H2O2 (3.5 mM).
For OPDA oxidation, 6 mg Cu-MOF solid was dispersed in
100 mL 0.1 M PBS buffer (pH 7.4) to prepare 0.06 mg mLꢁ1 Cu-
MOF solution. The concentration of OPDA was xed at 0.4 mM
with a series of concentration of H2O2 solutions (0.02 mM–0.6
mM). During the reaction, 1 mL Cu-MOF solution, 1 mL H2O2
and 1 mL OPDA were mixed with a total volume of 3 mL at 30 ꢀC.
The reaction product was sampled at regular intervals and
spectroscopically detected at 416 nm by a UV-vis spectropho-
2. Experimental
2.1. Materials
1,3,5-Benzenetricarboxylic acid (H3BTC) and TMB were obtained
from Shanghai Titan Scientic Co, Ltd (Shanghai, China). OPDA,
hydrogen peroxide (H2O2, 30%), copper nitrate trihydrate
(Cu(NO3)2$3H2O), sodium acetate (NaAc), acetic acid (HAc),
ethanol absolute, phosphate buffered saline (PBS), sodium
hydroxide (NaOH), hydrochloric acid (HCl), GOX, glucose, maltose,
lactose, sucrose were obtained from Chendu Kelong Chemical
Reagent Company. All the reagents were of analytical reagent grade
and all the aqueous solutions were prepared with deionized water.
2.2. Characterizations
X-ray powder diffraction (XRD) spectroscopy was performed on tometer. Similar measurements were carried out by varying the
Rigaku Dmax/Ultima LV X-ray powder diffractometer. Fourier concentration of OPDA (0.05 mM–1 mM) with xed
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data presented in this work were the averages of at least two
measurements with an error less than 5% unless otherwise
stated.
3. Results and discussions
3.1. Characterizations
The XRD pattern of the Cu-MOF is shown in Fig. 1. The char-
acteristic peaks at 2q ¼ 6.7ꢀ, 9.5ꢀ, 11.6ꢀ, 13.4ꢀ, 14.9ꢀ, 17.5ꢀ,
19.1ꢀ, 25.9ꢀ and 39.1ꢀ correspond to the (200), (220), (222), (400),
(420), (511), (440), (731) and (882) crystal planes.48–50 The narrow
and sharp peaks and the main peaks are coincided well with the
simulated peaks, which prove that the synthesized material is
the target product. The SEM image shows that the Cu-MOF
sample is mainly composed of polyhedron, and some irreg-
ular particles can also be seen on the surface of the sample
(Fig. 2). The FTIR spectrum of Cu-MOF is shown in Fig. S1,† the
Fig. 1 The XRD pattern of Cu-MOF.
concentration of H2O2 (0.6 mM). By monitoring the absorbance peaks at 1370 cmꢁ1 can be attributed to the aromatic ring
ꢁ1
at 652 nm and 416 nm for TMB and OPDA oxidation, the steady- extension. 690–900 cm
were assigned to the out-of-plane
state reaction rates were obtained with the Lambert Beer's law: A bending vibration of aromatic hydrocarbons C–H.51 The
¼ 3 ꢂ b ꢂ C. A is absorbance which can be measured; 3 is the absorption bands at 600–800 cmꢁ1 are due to lattice vibrations
molar extinction coefficient of OPDA oxidation product (3 ¼ 16.7
of Cu–O, Cu–O–Cu and O–Cu–O. The stretching vibration of
mMꢁ1 cmꢁ1
)
and TMB oxidation product (3
¼
39
benzene ring is at 1579 cmꢁ1, whereas the peak at 3404 cmꢁ1
can be ascribed to water molecules and hydroxyl groups on the
46
mMꢁ1 cmꢁ1),47 b is the path length of light (b ¼ 1 cm). The rate V
can be calculated by the change of concentration with time: V ¼ surface of the sample.51–55 The energy dispersive spectrum (EDS)
Dc/Dt. Michaelis–Menten equation, V ¼ Vmax[S]/(Km + [S]), was and element mapping indicate that Cu, O and C elements are
used to obtain the apparent kinetic parameters by nonlinear coexisted and distributed evenly in the sample (Fig. S2†).
least square tting the absorbance data. The Vmax is the reaction
velocity of an enzyme with saturated substrate. Km is so called
Michaelis constant, which represents the substrate concentra-
3.2. Peroxidase activity
The peroxidase-like activity of the Cu-MOF was evaluated by the
catalytic reaction of OPDA and TMB with H2O2. Fig. 3A shows
that the Cu-MOF can catalyze H2O2 to oxidize OPDA at 30 C,
tion when enzymatic reaction velocity V reaches the half of the
Vmax. Usually, the Vmax and Km values can be determined by
Lineweaver–Burk double reciprocal model (1/V ¼ (Km/Vmax)$(1/
[S]) + 1/Vmax). A straight line is formed by plotting 1/V as
a function of 1/[S], and the intercept of this line on X axis
ꢀ
which produce a color product since the solution become yellow
aer the reaction (Fig. 3A, inset). The oxidation product of
OPDA shows an absorption band at wavelength of 416 nm in the
visible region (Fig. 3A). Besides, the Cu-MOF can also catalyze
the oxidation of TMB by H2O2, and the oxidation product of
TMB exhibited a broad absorption band at 652 nm in the visible
region and a peak at 371 nm in the UV region (Fig. 3B). The color
of the TMB solution changed to blue aer oxidation by H2O2
(Fig. 3B, inset). The absorption peaks at 416 nm and 652 nm for
represents ꢁ1/Km, and Y axis represents 1/Vmax
.
The experimental procedures of the effects of pH, catalyst
concentration and reaction temperature on the peroxidase-like
activity of Cu-MOF, and the detection of H2O2, ascorbic acid,
sodium thiosulfate and glucose were similar to the above-
mentioned experimental process (see ESI† for details). The
Fig. 2 The SEM images of Cu-MOF with different magnifications.
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Fig. 3 The UV-Vis spectra of OPDA (A) and TMB (B) (insets: photographs of OPDA and TMB oxidized with H2O2) with and without Cu-MOF
material. (C and D) Are the corresponding reaction equations for Cu-MOF catalyzed OPDA and TMB, respectively.
OPDA and TMB solutions, respectively, were not observed in the concentration were investigated for the peroxidase activity.
UV-Vis spectra without addition of Cu-MOF (Fig. 3A and B), and First, we explored the effect of pH. For the OPDA, the reaction
the corresponding solutions were still colorless (the little glass activity increased from pH 3.0 to pH 4.5, while decreased with
bottles on the right of the insets in Fig. 3A and B, respectively). further pH increase up to 9.0 (Fig. 4A), which similar to that of
These results proved that the colored products generated by the the peroxidase activity of HRP effected by pH. While for the
reaction of OPDA and TMB with H2O2 were indeed catalyzed by TMB, the reaction activity increased from pH 3.0 to pH 4.0,
the Cu-MOF material.
while decreased with further increasing of the pH (Fig. 4B). We
Fig. 3C and D show the corresponding reaction equations for further investigated the effect of temperature on the peroxidase-
Cu-MOF catalyzed OPDA and TMB oxidation, respectively. In like activity of Cu-MOF. It can be seen that the catalytic activity
the presence of Cu-MOF as catalysts, OPDA and TMB are of Cu-MOF increased from 25 ꢀC to 70 ꢀC when oxidation of
oxidized by H2O2, producing a yellow-colored dimer product OPDA with H2O2 (Fig. 4C) and the activity of the enzyme was not
(2,3-diaminophenazine) (Fig. 3C) and a blue oxidized product lose even up to 70 ꢀC. While the highest activity was at 30 ꢀC for
complex (Fig. 3D), and H2O2 is reduced to H2O simultaneously. TMB oxidation, and the color of the oxidation product faded
The 371 and 652 nm bands in the absorption spectrum of TMB marvelously at 45 ꢀC (Fig. 4D), which indicated that the enzyme
oxidation product are a charge transfer complex consisting of had been inactivated. Finally, we studied the catalyst concen-
the diamine (TMB) as a donor and the diimine dication (TMB2+
as an acceptor.56,57
)
tration effect and the results are shown in the Fig. 4E and F. The
activity of OPDA oxidation increased linearly with the increase
of catalyst between 0.03 and 0.06 mg mLꢁ1, which reached
maximum at 0.06 mg mLꢁ1 and then tends to be at. However,
the concentration of catalyst had little effect on the activity for
the oxidation of TMB with the activity higher than 70% between
3.3. Experimental condition optimization
Natural enzymes are easily inactivated under extreme condi-
tions such as strong acid, strong base and high temperature.
Herein, the effect of pH, temperature, and catalyst
0.03 and 0.09 mg mLꢁ1
.
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Fig. 4 The effect of pH for oxidation of OPDA (A) and TMB (B), temperature effect for oxidation of OPDA (C) and TMB (D), and the effect of
catalyst concentration for oxidation of OPDA (E) and TMB (F).
rate of Cu-MOF peroxidase gradually increases with the increase
of OPDA (Fig. 5B). However, when the concentration of OPDA
increases to a certain extent, the reaction rate also gradually
slows down. The tting parameters (Km and Vmax) could be
obtained through hyperbola curve tting, which were shown in
the Fig. 5C and D.
The steady-state kinetics of TMB oxidation by H2O2 catalyzed
with Cu-MOF is shown in Fig. 6A. The reaction rate of TMB
oxidation gradually increased with the increasing of H2O2 when
xing TMB. While when the H2O2 increases to a certain extent,
the increasing of the reaction rate becomes slower and gradu-
ally attens out. Secondly, when the concentration of H2O2 is
xed, the reaction rate of Cu-MOF peroxidase gradually
3.4. Steady-state kinetics study
Steady-state kinetics assays were carried out to explore the
mechanism of the peroxidase-like activity of the synthesized Cu-
MOF. The kinetic data were measured by xing concentration of
H2O2 and varying the OPDA (or TMB) concentration or vice versa
with Cu-MOF. The formation rates of the OPDA and TMB
oxidized products were monitored from the increasing of the
absorbance at 416 nm and 652 nm, respectively. The Fig. 5A
showed the reaction rate of Cu-MOF peroxidase gradually
increased with the increase of H2O2 when xing OPDA. While
when the H2O2 increases to a certain extent, the increasing rate
of the reaction rate becomes slower and gradually attens out.
Secondly, when the concentration of H2O2 is xed, the reaction
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Fig. 5 Steady-state kinetics for the reaction of OPDA with H2O2 in the present of Cu-MOF. (A and C) Fixed OPDA concentration (0.4 mM) and
varied H2O2 concentration (0.02 mM–0.6 mM); (B and D) fixed H2O2 concentration (0.6 mM) and varied OPDA concentration (0.05 mM–1 mM).
The curves in panels A and B were obtained by nonlinear least square fitting to Michaelis–Menten equation, V ¼ Vmax$[S]/(Km + [S]), and the lines
in panels C and D were obtained by linear least square fitting to Lineweaver–Burk double reciprocal model, 1/V ¼ (Km/Vmax)$(1/[S]) + 1/Vmax
.
increases with the increase of TMB (Fig. 6B). However, when the
concentration of TMB increases to a certain extent, the reaction
rate also gradually slows down. By using the Lineweave–Burk
double-reciprocal model to t the data in the Michaelis curve,
the straight lines can be obtained as shown in the Fig. 6C and D.
The kinetic parameters Km and Vmax for the catalyst of Cu-
MOF were calculated through the intercept and slope in the
straight line. Tables S1 and S2† list the Km and Vmax values of
several catalysts for substrates OPDA, TMB and H2O2. Km value
is one of the characteristic constant of enzymes, which indicates
the affinity between enzyme and substrate. The higher the Km
value, the smaller the affinity between enzyme and substrate.
These results showed that the Km values of the Cu-MOF for
OPDA and TMB were 0.54 mM and 0.456 mM, respectively. And
the Km values of natural HRP for OPDA and TMB were 0.59 mM
and 0.434 mM, respectively.28,58 Therefore, the affinity of Cu-
MOF was similar to that of natural HRP, indicating it can be
used as an articial peroxidase. Through further comparison,
we found that the affinity of Cu-MOF for OPDA and TMB is
better than some of the published peroxidase mimetic mate-
rials, such as the affinity of Fe3O4@Cu@Cu2O to OPDA and the
affinity of Cu NCs or MoO2 to TMB (Tables S1 and S2†).
3.5. Colorimetric detection of H2O2, ascorbic acid and
sodium thiosulfate
The oxidation of TMB by H2O2 via the catalysis of Cu-MOF to
generate a blue product, and the reaction rate was proportional
to the concentration of H2O2. Based on this principle, a colori-
metric method to detect H2O2 was established. As shown in
Fig. 7A, the absorbance at 652 nm increased with the concen-
tration increasing of H2O2 from 5 mM to 400 mM. A well linear
relationship can be achieved between the absorbance intensity
and H2O2 concentration from 5 mM to 300 mM (Fig. 7B). The
detection limit was 4.6 mM and the correlation coefficient was
0.997. The detection limit was determined by LOD ¼ KS0/S. K is
the numerical factor chosen on the basis of the condence level
desired. S0 is the standard deviation59 of the blank measure-
ments (n ¼ 11, K ¼ 3), while S is the slope of the calibration
curve. Table S3† list several peroxidase mimics for colorimetric
detection of H2O2. According to the Table S3,† the linear range
of the as-prepared Cu-MOF is wider than some of the published
peroxidase mimics such as CuS-GNS,60 and the detect limitation
is also lower than some reported peroxidase mimics such as
MnO2,58 indicated that Cu-MOF is suitable for the colorimetric
detection of H2O2.
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Fig. 6 Steady-state kinetics for the reaction of TMB with H2O2 in the present of Cu-MOF. (A and C) Fixed TMB concentration (0.2 mM) and varied
H2O2 concentration (10 mM–90 mM); (B and D) fixed H2O2 concentration (3.5 mM) and varied TMB concentration (0.1 mM–0.9 mM). The curves
in panels A and B and the lines in panels C and D were obtained as stated in Fig. 5.
Moreover, it was found that the color reaction of TMB with
H2O2 could be inhibited by ascorbic acid (AA) and sodium
thiosulfate (Na2S2O3). Accordingly, a colorimetric detection
method of AA and Na2S2O3 was also developed based on the
color reaction inhibition (ESI, Fig. S3 and S4†). It should be
pointed out that the detection of AA and Na2S2O3 is not specic,
for other reductive substance such as Na2SO3 can also inhibit
the color reaction of TMB with H2O2.21,61
3.6. Glucose detection
GOX is a typical oxidoreductase that can be used to catalyze the
oxidation of glucose to produce glucono-d-lactone and H2O2.62 It
can be used in clinical diagnosis, rapid and accurate determi-
nation of glucose content in body uid, which provides reliable
data for doctors to accurately judge the patient's condi-
tion.37,63,64 As shown in the Fig. 8A and B, the absorbance at
652 nm for TMB oxidation increased with the glucose
Fig. 7 Colorimetric detection of H2O2. Dose–response curve (A) and linear calibration plot (B) for the detection of H2O2 with Cu-MOF.
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Fig. 8 The colorimetric detection of glucose. Dose–response curve (A) and linear calibration plot (B) for glucose detection with Cu-MOF. (C)
Determination of the selectivity detection for glucose with 300 mM glucose, 2 mM sucrose, 2 mM lactose, and 2 mM maltose. (D) A proposed
reaction mechanism for detection of glucose.
concentration from 5 mM to 500 mM. A well linear relationship
The reaction mechanism for glucose detection is illustrated
can be obtained between the intensity of absorbance and the in Fig. 8D. First, GOX catalyzed the oxidation of glucose to
glucose concentration from 5 mM to 500 mM. The detection limit gluconic acid and O2 dissolved in the solution was reduced to
is 4.7 mM and the correlation coefficient is 0.993.
H2O2. Then the produced H2O2 oxidized TMB to a blue-colored
To explore the selectivity of glucose detection, we performed oxidation product (TMBox) via the catalysis of Cu-MOF. The
the colorimetric reaction by replacing glucose with other sugar production of TMBox is proportional to the amount of H2O2,
species, such as sucrose, lactose or maltose. The results show and the yield of H2O2 is proportional to the amount of glucose.
that the absorbance increase at 652 nm is very low for the Therefore, the production of TMBox is proportional to the
selected sugar species instead of glucose (Fig. 8C). Therefore, amount of glucose and glucose can be detected by measuring
the developed colorimetric detection method has high selec- the amount of TMBox. It also can be seen from the reaction
tivity for the detection of glucose.
mechanism that the detection of glucose is achieved by
measuring the content of H2O2, thus the selectivity of glucose
26970 | RSC Adv., 2021, 11, 26963–26973
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detection depends on the selectivity of GOX to glucose, but not
on the catalysis of Cu-MOF.
porous metal–organic frameworks, Chem. Mater., 2013, 25,
2767–2776.
´
Table S4† listed several peroxidase mimic catalysts for the
colorimetric detection of glucose. According to the Table S4,†
the linear range of the as-prepared Cu-MOF is wider than that of
NiFe2O4 MNPs and Ch-Ag NPs.65,66 The detection limit is rela-
tively large, which indicated that Cu-MOF has better linear
range and detection limit to detect glucose. These results
demonstrated that this colorimetric method may has potential
application for determine glucose concentration.
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4. Conclusion
In conclusion, we prepared Cu-MOF with high peroxidase-like
activity by a simple hydrothermal method. In the presence of
H2O2, Cu-MOF can catalyze the oxidation of OPDA and TMB.
Kinetics studies suggested that the affinity of Cu-MOF to TMB 10 M. Fiaz, M. Kashif, M. Fatima, S. R. Batool, M. A. Asghar,
and OPDA is close to that of HRP. Based on the color reaction of
TMB with H2O2, colorimetric methods for the detection of H2O2
and glucose were established. Moreover, the detection of
M. Shakeel and M. Athar, Synthesis of Efficient
TMS@MOF-5 Catalysts for Oxygen Evolution Reaction,
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the inhibition of TMB oxidation. These results indicate that Cu-
MOF based peroxidase-like activity may be applied in the elds
of catalysis, biosensor, food detection and environmental
monitoring.
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Conflicts of interest
There are no conicts to declare.
13 P. V. Iyer and L. Ananthanarayan, Enzyme stability and
stabilization—aqueous and non-aqueous environment,
Process Biochem., 2008, 43, 1019–1032.
Acknowledgements
This study was funded by the Open Project of Chemical
Synthesis and Pollution Control Key Laboratory of Sichuan 14 M. Yuan, H. Zhao, Q. Huang, X. Liu, Y. Zhou, X. Diao and
Province (CSPC2016-3-2), and the Opening Project of Key
Laboratory of Green Chemistry of Sichuan Institutes of Higher
Education (LZJ2002).
Q. X. Li, Comparison of three palm tree peroxidases
expressed by Escherichia coli: Uniqueness of African oil
palm peroxidase, Protein Expression Purif., 2020, 179, 105806.
15 Z. Wang, M. Chen, J. Shu and Y. Li, One-step solvothermal
synthesis of Fe3O4@Cu@Cu2O nanocomposite as
magnetically recyclable mimetic peroxidase, J. Alloys
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