N, N ′-di-caboxy methyl perylene diimide (PDI) functionalized CuO nanocomposites with enhanced peroxidase-like activity and their application in visual biosensing of H2O2 and glucose

Article abstract of DOI:10.1039/c7ra04463a

Nanomaterial-based enzyme mimics (nanoenzymes) are a new forefront of chemical research at present. N,N′-Di-carboxy methyl perylene diimide (PDI) functionalized CuO nanobelts with pores (PDI-CuO nanobelts), which were prepared via a facile method and char

Full text of DOI:10.1039/c7ra04463a

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N,N0-di-caboxy methyl perylene diimide (PDI)
functionalized CuO nanocomposites with
enhanced peroxidase-like activity and their
application in visual biosensing of H2O2 and
glucose†
Cite this: RSC Adv., 2017, 7, 25220
a
a
a
a
a
b
*
Miaomiao Chen, Yanan Ding, Yan Gao, Xixi Zhu, Peng Wang, Zhiqiang Shi
a
*
and Qingyun Liu
Nanomaterial-based enzyme mimics (nanoenzymes) are a new forefront of chemical research at present.
N,N0-Di-carboxy methyl perylene diimide (PDI) functionalized CuO nanobelts with pores (PDI–CuO
nanobelts), which were prepared via a facile method and characterized using various analytical
techniques, were demonstrated for the first time to possess higher intrinsic peroxidase-like activity
towards classical colorimetric substrate 3,30,5,50-tetramethylbenzidine (TMB) in the presence of hydrogen
peroxide (H2O2), compared with that of pure CuO nanobelts without PDI modification. The underlying
reaction mechanism was elucidated by catalyzing the decomposition of H2O2 and generating hydroxyl
radicals (cOH). The improved catalytic activity of PDI–CuO nanobelts for colorimetric reactions could be
ascribed to the synergistic effects of CuO and PDI nanobelts. Moreover, the proposed PDI–CuO
biosensor platform exhibited a more sensitive response to H2O2 with a low limit of detection (LOD) of
2.38 mM. This convenient sensing platform was further extended to detect glucose in combination with
the specificity of glucose oxidase (GOx) for the oxidation of glucose and generation of H2O2. The linear
range for glucose detection was from 2 mM to 50 mM with a low detection limit of 0.65 mM. Therefore,
besides high sensitivity and selectivity, this colorimetric system also holds considerable potential for
biological process research.
Received 22nd April 2017
Accepted 28th April 2017
DOI: 10.1039/c7ra04463a
rsc.li/rsc-advances
focused on studying of nanomaterials as peroxidase-like
mimics, since Yan and co-workers found that Fe3O4 nano-
1. Introduction
particles possessed an intrinsic enzyme mimetic activity similar
to that of naturally occurring horseradish peroxidase (HRP).8
Thus, an incredible number of investigations on nanomaterials
possessing peroxidase-like activity have been reported, such as
carbon based nanomaterials (graphene oxide,9 carbon nano-
tubes,10 iron-based metal–organic framework nanomaterials,11
suldes (CuS,12 FeS13) etc.).
With the developing and widening of studies on peroxidase-
like mimics, more and more researchers have paid attention to
composites such as peroxidase-like mimics, which realize the
combination of the respective properties of each component or
to achieve cooperatively enhanced performances.14 Generally,
the composites can be variously classied into two kinds: one is
inorganic–inorganics and the other is organic–inorganics. For
example, as for inorganic–inorganics composites with the
peroxidase-like activity, scientists have studied bimetallic
nanoparticles as peroxidase-like mimics, such as Fe/Co,15 Au/
Pb,16 Pd–Ir core–shell nanocubes.17 Moreover, Au/CuS nano-
composites18 and Au–carbon nanotube nanocomplex19 have
been found to demonstrate highly peroxidase activity. In
Most natural enzymes are proteins that can catalyze various
biochemical reactions with excellent substrate specicity and
efficiency under mild conditions, which is of great signicance
in the aspects of environmental protection, biotechnology,
agriculture and clinical diagnosis.1–4 However, the disadvan-
tages of natural enzymes, such as easy denaturation, high cost
of preparation and purication, low stability under environ-
mental conditions and some other shortcomings, restrict their
further application in practice.5 To overcome the drawbacks of
natural enzymes,6 intensive efforts have been made to develop
enzyme mimics, due to their easier preparation, stability and
cost reduction.7 In recent years, more and more people have
aCollege of Chemical and Environmental Engineering, Shandong University of Science
and Technology, Qingdao 266510, P. R. China. E-mail: qyliu@sdust.edu.cn; Fax: +86
0532 80681197; Tel: +86 0532 86057757
bSchool of Chemistry, Chemical Engineering and Materials, Shandong Normal
University, Jinan 250013, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c7ra04463a
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addition, Wang and coworkers have prepared highly dispersed
CeO2 on TiO2 nanotube and found that the nanocomposites
showed superior peroxidase-like activity.20 Liu and coworkers
have comparatively studied composites of CeO2, CuS, Ag2S, ZnS
based on Montmorillonite as supports and found that these
composites possessed peroxidase-like activity and applied in
colorimetric detecting for H2O2.21–24
Fig. 1 The molecular structure of N,N0-di-carboxy methyl perylene
diimides (PDI).
On the other hand, composites based on organic–inorganics
have been found to demonstrate peroxidase-like activity. For
example, Yu and co-workers have reported that PVP modied
MoS2 nanoparticles offer a sensing atform to achieve efficient
detection for H2O2 and glucose.25 Lv and coworkers have
prepared bovine serum albumin (BSA)-stabilized MnO2 nano-
particles (NPs) exhibiting highly peroxidase-like activities.26
Huang and coworkers have reported the peroxidase-like activity
of chitosan stabilized silver nanoparticles.27 Li and coworkers
have reported poly(styrene sulfonate) and Pt bifunctionalized
graphene nanosheets as an articial enzyme to construct
a colorimetric chemosensor.28 Nevertheless, in these previous
studies, the organics were all employed as powerful supports to
prepare inorganics in nanoscale, while not used as organic
functional molecules.
formamide (DMF), hydrogen peroxide (30 wt%, H2O2), glucose,
fructose, and lactose were purchased from Guangcheng
Reagent Co (Tianjin, China). Glucose oxidase (GOx, S 200 U
mgꢀ1) was purchased from Sigma-Aldrich and stored in
a refrigerator at ꢀ18 ꢁC. N,N0-Di-carboxy methyl perylene dii-
mides (PDI) was synthesized according to the previous reports.37
The molecular structure of PDI is shown in Fig. 1. The other
regents above were of analytical reagent grade and used without
further purication.
2.2 Preparation of CuO nanobelts and PDI–CuO
nanocomposites
Perylene tetracarboxyl diimides (PDI), a kind of organic
molecules with conjugated p-electron systems, is one of the
most popular visible light absorbing compounds. PDIs are
currently being investigated as photoactive materials for use in
a variety of elds, due to their excellent photochemical and
thermal stability, high luminescence efficiency, and novel
optoelectronic properties.29–36 However, to the best of our
knowledge, there is no report on studying PDI molecules
functionalized CuO nanobelts as enhanced peroxidase-like
mimics for the detection of H2O2 and glucose. With these
ideas in our mind, if PDI molecules combine with CuO nano-
belts to provide a nanocomposite, it will demonstrate a novel
peroxidase-like activity.
CuO nanobelts were synthesized by a facile hydrothermal
method combined with subsequent calcination.38 In a typical
procedure, CuCl2$2H2O (2 mmol, 0.341 g) and SDBS (0.696 g)
were dissolved in 20 mL distilled water to form a blue solution.
NaOH (20 mL, 5 M) aqueous solution was dropwise added to the
solution under stirring for 30 min, resulting in a light blue
solution. The obtained solution was further aging for 4 h, and
then transferred into a teon-lined stainless steel autoclave
reactor for 6 h at 100 ꢁC. Aer hydrothermal treatment, the
system was cooled at room temperature naturally. The precipi-
tate was washed with distilled water and ethanol for several
ꢁ
ꢁ
times and dried at 60 C for 2 h, and nally calcined at 350 C
for 3 h.
Herein, we report porous CuO nanobelts modied with N,N0-
di-carboxy methyl perylene diimides (PDI) molecules. It is the
rst time to demonstrate that the composites (PDI–CuO)
possess the enhanced intrinsic peroxidase-like activity,
compared to the pure CuO nanobelts without PDI modication.
PDI–CuO nanocomposites can catalyze the oxidation of perox-
idase substrate, 3,30,5,50-tetramethylbenzidine (TMB), in the
presence of H2O2. Surprisingly, the colorimetric reaction can be
CuO nanobelts (20 mg) dispersed into DMF solution of PDI
(1 mg mLꢀ1) under stirring for 4 h. Aer that, separated by
centrifugation, washed with distilled water and ethanol for
several times and dried at 60 ꢁC for 4 h. The target product was
obtained for subsequent experiments.
2.3 Characterization
observed by the naked eye only in 40 s. The uorescent experi- The morphology and size distribution of the samples were
ment veried the rapid reaction mechanism was from the characterized by a transmission electron microscope and a high
decomposition of H2O2 and generating hydroxyl radicals (cOH) resolution TEM (HRTEM) at an accelerating voltage of 200 kV
by adding the PDI–CuO nanocomposites into the colorimetric (TEM JEM-2100, JEOL, Japan). The scan electron microscopy
reaction system (TMB/H2O2). Based on the experimental results, images were obtained by scanning electron microscopy (SEM,
we designed a facile visual colorimetric sensor using PDI–CuO JEOL, Japan). The crystalline phases of all catalysts were per-
nanocomposites as enzyme mimics for convenient detecting formed by using a D/Max2500PC-RA diffractometer with Cu Ka
ꢁ
˚
H2O2 and glucose, respectively.
(l ¼ 1.5406 A) radiation. The 2q values in the range of 10–90
were collected with a 0.021ꢁ step size. X-ray photoelectron
spectra (XPS) were recorded on a PHI Quantera SXM spec-
trometer with an Al Ka ¼ 280.00 eV excitation source, and
binding energies were calibrated by referencing the C 1s peak
2. Experimental section
2.1 Materials
Copper chloride (CuCl2$2H2O), sodium dodecylbenzene sulfo- (284.5 eV) to reduce the sample charge effect. The Brunauer–
nate (SDBS), sodium hydroxide (NaOH), ethanol, N,N-dimethyl Emmett–Teller (BET) surface area was measured by nitrogen
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adsorption–desorption at 77 K using a Micromeritics ASAP
2010M instrument.
Ultraviolet spectra were recorded on a UV-8000PC spectro-
photometer (Shanghai, China). Fluorometric measurement was
carried out by a Cary Eclipse spectro uorophotometer (Varian,
Inc, USA).
2.7 Selectivity for colorimetric detection of glucose
For specicity analysis, 5.0 mM fructose, 5.0 mM maltose,
5.0 mM lactose, and 5.0 mM sucrose instead of 1.0 mM glucose
were used as control experiences, respectively. The detection
process was similar to the standard glucose assay.
3. Results and discussion
3.1 Characterization of PDI–CuO nanocomposites
2.4 Kinetic study
The reaction kinetics for the catalytic oxidation of TMB was
measured in time course mode by monitoring the absorbance
variation at 652 nm with a 3 min interval. Unless otherwise
stated, a typical experience was carried out at 55 ꢁC by using 0.2
mL PDI–CuO (0.03 mg mLꢀ1) in 1.4 mL buffer (HAc–NaAc, pH ¼
4.0) with 0.2 mL H2O2 and 0.2 mL TMB as substrates, respec-
tively. In the experimental procedure, except for the xed
concentration of TMB (2 mM) and various concentration of
H2O2 (0.002–0.1 mM) as well as the xed concentration of H2O2
(0.25 M) and various concentration of TMB (0.02–0.10 mM). The
apparent kinetic parameters based on Lineweaver–Burk plots of
the double reciprocal of the Michaelis–Menten equation as
described below: 1/v ¼ Km/Vmax (1/[S] + 1/Km), where v is the
initial velocity, [S] is the concentration of the substrate, Km is
the Michaelis constant and Vm is the maximal reaction
velocity.14
The crystal phases of CuO, PDI–CuO nanocomposite were
characterized by X-ray diffraction (XRD), shown in Fig. 2. From
Fig. 2A, it can be seen that pure CuO crystal exhibited diffraction
peaks (2q) centered at ca. 32.5ꢁ, 35.4ꢁ, 35.5ꢁ, 38.7ꢁ, 38.8ꢁ and
48.7ꢁ, corresponding to (110), (002), (11ꢀ1), (111), (200) and
(202) planes, in accordance with the monoclinic crystal struc-
ture (JCPDS card no. 48-1548). Compared with the XRD data of
CuO, the weak XRD peaks of PDI functionalized CuO nanobelts
was found, as shown in Fig. 2B. This demonstrated that the PDI
functionalized CuO nanobelts has the same crystal phase as
that of the pure CuO, together with no destroying in structure,
except for a little weak diffraction peaks.39,40
The morphology of the PDI–CuO nanobelts was imaged by
SEM and TEM, respectively. From Fig. 3A and B, it can be seen
that the PDI–CuO nanocomposites show belt-like morphologies
with the average size of 1 mm in length and 100 nm in width.
Interestingly, many pores (ca. 5–10 nm) in PDI–CuO nanobelts
can be observed, shown in Fig. 3C. The fringe spacing is ca.
0.275 nm, corresponding to (110) crystal plane, shown in
Fig. 3D. Theoretically, the large number of nanoporous are able
to enlarge the specic surface area, and thus increase the
activity sites of materials.41
2.5 Reaction mechanism
We suspect that the peroxidase-like activities of the PDI–CuO
nanocomposites may due to the decomposition of H2O2 into
OH radicals or the mechanism of electron transfer. Thus,
a uorometric spectra method was employed to measure the
OH radicals with terephthalic acid as a probe under the optional
conditions. The typical experimental procedure is as follows:
terephthalic acid (0.5 mM), H2O2 (10 mM), and the PDI–CuO
nanocomposites with different concentrations were incubated
Then, the composition of PDI–CuO nanocomposites was
measured by the EDS mapping images, unambiguously
demonstrating the coexistence of C, N, O, Cu elements in the
product. Of the different elementary compositions, C and N are
from PDI molecules, shown in Fig. S1 (ESI†). Therefore, the EDS
mapping images further conrmed that PDI had been
successfully distributed on the surface of CuO nanobelts.
ꢁ
in acetate buffer (pH ¼ 4.0) at 55 C for 30 min. Immediately,
the solutions were studied for uorometric measurement.
2.6 Colorimetric detection of H2O2 and glucose
For detecting the H2O2 standard solution, PDI–CuO nanobelts
were carried out using different concentration of 200 mL H2O2
(0.002–0.1 mM), then mixed with 200 mL TMB of xed concen-
tration (2 mM) as the substrate in acetate buffer (1.4 mL, pH ¼
ꢁ
4.0). The resulting mixture was incubated at 55 C for 3 min.
Then, the absorbance of the treated nal mixtures were
measured at 652 nm.
For glucose assay, the catalytic oxidization of glucose by
glucose oxidase (GOx) (glucose + O2 / H2O2+ gluconic acid)
was coupled with colorimetric detection of H2O2. Briey,
glucose assay was performed as follows: 0.1 mL GOx (0.5 mg
mLꢀ1) and 0.5 mL glucose with different concentrations in PBS
ꢁ
buffer (pH ¼ 7) were kept for 30 min at 37 C in a dark condi-
tion. Then, 0.2 mL PDI–CuO, 0.2 mL TMB and 0.6 mL above
glucose reaction solution were added to 1.0 mL HAc buffer.
Aer 3 min (55 ꢁC) incubation, the UV-vis absorption spectra of
solution were recorded.
Fig. 2 The XRD patterns of pure CuO (A) and PDI–CuO nanobelts (B),
respectively.
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Based on the previous report, the large number of pores are
able to enlarge the specic surface area, and thus increase the
activity sites.44 The Brunauer–Emmett–Teller (BET) surface area
was measured by nitrogen adsorption–desorption at 77.35 K.
Before measurement, the samples were degassed at 60 ꢁC for 10
hours. Nitrogen adsorption–desorption isotherms of PDI–CuO
nanobelts was shown in Fig. S2 (ESI†). The large surface area
(12.947 m2 gꢀ1), pore volume (Vp ¼ 0.044 cc gꢀ1), and small pore
diameter (dp ¼ 1.653 nm) of PDI–CuO nanocomposites were
found.
3.2 Peroxidase-like activity of PDI–CuO nanocomposites
The peroxidase-like activity of PDI–CuO was investigated using
the peroxidase substrate 3,30,5,50-tetramethylbenzidine (TMB)
in the presence of H2O2. TMB is a kind of common chromogenic
substrate and is usually used for practical analytical applica-
tion. Clearly, from Fig. 5A, it can be seen that the absorbance of
the reaction system (PDI–CuO + H2O2 + TMB) was much higher
than that of the system (CuO + H2O2 + TMB) at 652 nm (curve
Fig. 3 SEM (A), TEM (B and C) and HR-TEM (D) images of PDI–CuO
nanobelts.
To further determine the interaction between PDI and CuO
nanobelts, the XPS spectra of PDI–CuO nanocomposites were
used to analyze the chemical composition and surface elec-
tronic state of the as-prepared PDI–CuO nanocomposites,42
shown in Fig. 4. As shown in Fig. 4A, all peaks could be
contributed to Cu, O, N, C elements. The peaks in Fig. 4B with
binding energies at 933.9 and 953.6 eV are from Cu2 + (CuO) due
to Cu 2p2/3 and Cu 2p1/2, respectively. C 1s spectrum (Fig. 4C)
can be deconvoluted into three peaks at 284.3 eV (C sp2),
285.0 eV (C sp3) and 289.0 eV (O–C]O) with the C sp2 compo-
nent being dominant.43 As a result, all elements of the PDI–CuO
nanocomposites can be found in the XPS data, suggesting that
CuO are successfully modied by PDI.
Fig. 5 (A) Typical absorbance curves of different reaction systems for
3 min in HAC–NaAc (pH ¼ 3.8) buffer: (a) PDI–CuO + H2O2 + TMB; (b)
CuO + H2O2 + TMB; (c) PDI–CuO + TMB; (d) H2O2 + TMB; (e) TMB,
respectively. (B) Time-dependency of peroxidase-like activity of PDI–
CuO nanocomposites. The absorbance of the reaction system (TMB:
Fig. 4 XPS spectra of PDI–CuO (A), Cu 2p (B), C 1s (C) and N 1s (D), 2 mM; H2O2: 0.25 M; PDI–CuO: 0.3 mg mLꢀ1) was monitored in time
respectively.
scan mode. The inset is the corresponding colorimetric photograph.
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a and b), indicating the enhanced catalytic activity of PDI–CuO
nanocomposites than that of pure CuO nanobelts for the cata-
lytic oxidation of TMB. Surprisingly, we also found that the color
of the reaction system containing TMB, H2O2 and PDI–CuO
nanocomposites has rapidly been changed from colorless to
blue within 40 s. On visual observation, the reaction system of
TMB + H2O2 in absence of PDI–CuO nanobelts (Fig. 5A, curve d)
or the TMB + PDI–CuO without H2O2 (Fig. 5A, curve e) shows
negligible color change, suggesting that both H2O2 and PDI–
CuO were necessary for the catalytic oxidation of TMB.
Furthermore, it can be also found that the catalytic activity of
PDI–CuO nanocomposites with pores is higher than that of
PDI–CuO without pores, shown in Fig. S3 (ESI†).
Moreover, the experiment results show that the catalytic
activity of PDI–CuO nanocomposites was time dependent,
shown in Fig. 5B. In addition, the colorimetric reaction of the
system is generally required to be incubated for some “time
interval” before the corresponding absorption spectra are
recognized as a valid measurement.45 We have summarized the
required “time interval” for different types of nanomaterials for
the detection of H2O2 in this study together with other reported
materials as peroxidase mimics, listed in Table 1. Obviously,
PDI–CuO nanocomposites could oxidize the substrate TMB with
visualized the color change in short time, exhibiting the higher
catalytic activity of the nanocomposites, compared with other
materials listed in Table 1. In other words, the response time of
reaction system containing PDI–CuO nanocomposites observed
by the naked eye is shorter than that of other articial
peroxidase-like mimics, such as CuS–MMT,22 PtPd–Fe3O4,46
Fe3O4 NPs,8 Au NPs47 and TCPP–NiO nanomaterials.48
Fig.
6
The optimization of pH (A) and temperature (B) for the
peroxidase-like activity of the PDI–CuO nanocomposites. Experi-
ments were conducted by using 3 mg mLꢀ1 PDI–CuO in 2 mL of 1.4
mL buffer solution with 0.2 mL of 0.25 M H2O2 and 0.2 mL of 2 mM
TMB as substrates. In each curve, the relative activity was defined as
the ratio of catalytic activity of the maximum catalytic activity.
3.3 Optimization of experimental conditions
Similar to natural peroxidase, horseradish peroxidase (HRP)
and other articial peroxidase-like mimics based on nano- activity of PDI–CuO nanocomposites were declined at either
materials, the catalytic activity of the PDI–CuO nanocomposites lower pH or higher pH values, the relative activity was more
were dependent on pH and temperature, respectively.21,22,48 than 55% in a wide range of pH. Thus, the result reveals the
Likewise, the catalytic activity of PDI–CuO nanocomposites was PDI–CuO nanocomposites displayed an excellent stability than
optimized under a wide scope of experimental conditions, that of HRP in a wide pH scope.8 Fig. 6B shows the temperature-
including pH value and temperature. The effect of pH on the dependant on the peroxidase-like activity of PDI–CuO nano-
peroxidase-like activity of PDI–CuO nanocomposites was composites over a wide range from 20 to 65 ꢁC (20, 25, 30, 35, 40,
measured by varying pH from 2.2 to 8.0 (2.2, 3, 3.8, 4, 5, 6, 7, 8), 45, 50, 55, 60, 65). Generally, the catalytic activity of PDI–CuO
shown in Fig. 6A. Clearly, from Fig. 6A, it can be seen that the nanocomposites was up to the maximum at 55 ꢁC, while the
ꢁ
optimal pH was 4.0, similar to Ce NPs, PVP–MoS2 NPs reported enzymatic activity of HRP sharply decreased over 40 C due to
in previous publications.25,49 Interestingly, though catalytic the denaturalization of the enzyme under high temperature.8
Table 1 Comparison of typical nanomaterials for H2O2 detection
Peroxidase
substrates
Incubation
time (s)
Detection
limit (mm)
Nanomaterials
pH
Ref
CuS–MMT
PtPd–Fe3O4
Fe3O4 NPs
Au NPs
TCPP–NiO
PDI–CuO
TMB
TMB
DAB, OPD
TMB
TMB
300
300
600
600
1200
180
3.8
5.2
3.5
4.0
3.8
4
24.7
2
22
46
8
47
48
This
work
0.5
8
2.38
TMB
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Thus, pH 4.0 and the temperature of 55 ꢁC was selected for the
subsequent assays.
3.4 Steady-state kinetic of nanoparticles
To understand the catalytic performance of the PDI–CuO
nanocomposites, the steady-state kinetics was investigated
using TMB and H2O2 as substrates under the optimal condi-
tions (pH ¼ 4.0, 55 ꢁC). Fig. 7A and 7B show the typical
Michaelis–Menten curves of TMB and H2O2 by plotting the
initial reaction rate against concentration. Furthermore, the
apparent kinetic parameters (Km and Vm) were calculated
according to Lineweaver–Burk double reciprocal plots (Fig. 7C
and D). It is well-known that Km represents the affinity of
a enzyme toward substrates: the smaller the value of Km, the
stronger the affinity between the enzyme (catalysts) and the
substrate. As illustrated in Table 2, the Km value for PDI–CuO
with TMB as substrate was much lower than horseradish
peroxidase (HRP) and peroxides nanomimetics reported previ-
ously, indicating that PDI–CuO had a higher affinity towards
TMB than HRP and other nanomaterials. However, the Km value
of PDI–CuO with H2O2 substrate was 35.74, revealing that
a higher concentration of H2O2 was required to obtain
maximum catalytic activity.
3.5 Mechanism of the peroxidase-like activity of PDI–CuO
nanocomposites
Generally, the catalytic mechanism of peroxidase-like activity of
articial peroxidases can be divided into two kinds. One is the
generation of reactive hydroxyl radicals (cOH), and the other is
the electron transfer process.53 In order to shed light on the
catalytic mechanism of PDI–CuO nanocomposites, the uores-
cent probe, terephthalic acid (TA), was used as a typical cOH
radical capture reagent in the PDI–CuO + H2O2+TMB system.
The reason is that non-luminescent TA could capture cOH and
generate remarkable uorescent product, 2-hydroxyterephthalic
acid (HTA), at 425 nm (Fig. 8a).54 From Fig. 8b, it can be seen
clearly that photoluminescence (PL) intensity gradually
increased with increasing of amount of PDI–CuO nano-
composites. In addition, no PL intensity was observed in the
absence of H2O2 (Fig. 8b). This uorescent results revealed that
PDI–CuO nanocomposites could catalytically activate H2O2
decomposition to generate cOH radicals that subsequently
oxidized TMB to form a blue TMB oxide.55 The experience
further suggests more cOH radicals can be produced with the
increase of the amount of PDI–CuO. In other words, the
stronger the photoluminescence intensity, the more the
generated cOH. Therefore, based on the above results, the
peroxidase mimic catalytic mechanism of PDI–CuO nanobelts
was proposed, shown in Scheme 1.
Fig. 7 Apparent steady-state kinetic study of PDI–CuO (A–D). The
reaction velocity (v) was measured using 3 mg mLꢀ1 PDI–CuO in 1.4
mL of HAc–NaAc buffer (pH ¼ 4.0) at 55 ꢁC. (A): The concentration of
TMB was 2 mM while the H2O2 concentration was varied, (B): the
concentration of H2O2 was 0.25 M while the TMB concentration was
varied, and the double-reciprocal plots of peroxidase-like activity of
PDI–CuO with a fixed concentration of one substrate relative to
varying concentration of the other substrate for TMB and H2O2 (C and
D). The error bars represent the standard deviation of three
measurements.
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Table 2 Comparison of the apparent Michaelis constant (Km) and
maximum reaction rate (Vm)
Vmax
Km [mM]
[10ꢀ8 M sꢀ1
]
Catalyst
TMB
H2O2
TMB
H2O2
Ref.
PDI–CuO
HRP
Fe3O4
Fe/CeO2
C60[C(COOH)2]2
AuNPs/PVP–GNs
0.018
0.434
0.098
0.176
0.233
2.63
35.74
3.7
154
47.6
24.58
104
80.81
10
3.44
8.6
3.47
13.04
0.53
8.71
9.78
16.6
4.01
11.98
This work
8
8
50
51
52
Scheme 1 Schematic illustration of colorimetric sensor for H2O2 and
glucose detection using PDI–CuO nanobelts as catalysts.
3.6 Colorimetric detection of H2O2 and glucose
with a detection limit of 2.38 ꢂ 10ꢀ6 M, which was 19 times lower
than that of reported H2O2 sensors based on Au@Pt core–shell
nanorods (4.5 ꢂ 10ꢀ5 M).56 It suggested that PDI–CuO nano-
composites can offer a facile and sensitive method to detect H2O2
Considering the fact that PDI–CuO possesses the intrinsic
peroxidase-like activity, a simple colorimetric method was per-
formed to quantitatively detect H2O2 and glucose, respectively.
Fig. 9A shows the typical absorbance at 625 nm with the addition
of various concentrations of H2O2 under the optimal conditions
(pH 4.0, 55 ꢁC). Obviously, the absorbance of oxidized TMB
gradually increased with increasing of concentration H2O2. The
homologous linear calibration plot range is from 3 mM to 30 mM
Fig. 8 (a) The reaction of TA with cOH. (b) Fluorescent spectra of Fig. 9 (A) A dose–response curve for H2O2 detection using PDI–CuO
acetate buffer solution (pH ¼ 4) containing only TA and PDI–CuO (A) under the optimum conditions. Inset: the linear calibration plot for
or with H2O2 (0.25 M), TA (0.5 mM) and the PDI–CuO nanocomposites H2O2 detection (B) A dose–response curve for glucose detection
with different concentration ((B) 0, (C) 20, (D) 80, (E) 200, (F) 250, (G) using PDI–CuO as catalysts. Inset shows the linear response of the
300 mg mLꢀ1) were incubated at 55 ꢁC for 30 min. The FL excitation detection system to glucose. Error bars stand for the standard devia-
wavelength was fixed at 315 nm.
tions based on three repeated measurements.
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Acknowledgements
This work was nancially supported by the National Natural
Science Foundation of China (Grant No. 21271119) and Inno-
vation Fund of Science & Technology of Graduate Students
(SDUST).
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