Hierarchical Cu/Cu(OH)2 nanorod arrays grown on Cu foam as a high-performance 3D self-supported electrode for enzyme-free glucose sensing

Article abstract of DOI:10.1039/c6ra19576h

Hierarchical Cu/Cu(OH)₂ nanorod arrays grown on commercially available Cu foam (Cu/Cu(OH)₂ NRA/CF) was prepared via a three-step strategy involving the wet chemical synthesis of Cu(OH)₂ NRA/CF, a chemical reduction reaction for conversion from Cu(OH)₂ NRA/CF to Cu NRA/CF, and finally galvanostatic anodization to grow Cu(OH)₂ nanoparticles on Cu NRA/CF. Hierarchical Cu/Cu(OH)₂ NRA/CF shows high catalytic activity towards glucose oxidation in an alkaline solution and can serve as a promising electrode material for enzyme-free glucose sensing. At an applied potential of +0.5 V, the sensor showed a broad detection range of 0.001-1.0 mM, a high sensitivity of 9.18 mA mM^-1 cm^-2, and a low detection limit of 0.45 μM (S/N = 3). Furthermore, the sensor exhibits excellent selectivity against common interferents and good reliability for glucose detection in human serum samples.

Full text of DOI:10.1039/c6ra19576h

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ARTICLE TYPE
Hierarchical Cu/Cu(OH) nanorod arrays grown on Cu foam as a highꢀ
2
performance 3D selfꢀsupported electrode for enzymeꢀfree glucose
sensing
Lili Bie, Xue Luo, Qingqing He, Daiping He, Yan Liu and Ping Jiang*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
Hierarchical Cu/Cu(OH)2 nanorod arrays grown on
ed from the surface poisoning effects, as well as high cost and
limited reserves. Therefore, tremendous efforts are focused on
commercially available Cu foam (Cu/Cu(OH) NRA/CF) was
2
prepared via a threeꢀstep strategy involving the wet chemical 50 fabricating highꢀperformance sensors using lowꢀcost and
1
2,13
14,15
earthꢀabundant metals, such as copper,
cobalt,
1
1
2
0
5
0
synthesis of Cu(OH) NRA/CF, chemical reduction reaction
2
1
6,17
nickel,
Hierarchical
and so on.
nanostructured
for conversion from Cu(OH) NRA/CF to Cu NRA/CF, and
2
1
8ꢀ20
architectures
selfꢀ
finally galvanostatic anodization to grow Cu(OH)2
nanoparticles on Cu NRA/CF. Hierarchical Cu/Cu(OH)2
NRA/CF shows highly catalytic activity towards glucose
oxidation in an alkaline solution and be served as a promising
electrode material for enzymeꢀfree glucose sensing. At an
applied potential of + 0.5 V, the sensor showed a broad
detection range of 0.001ꢀ1.0 mM, a high sensitivity of 9.18 mA
assembled from lowꢀdimensional nanostructured building
blocks have become a class of significant functional materials.
Due to their larger surface, good conductivity and
permeability, hierarchical nanomaterials arouse much interest
in many emerging research fields, especially environmental
remediation, sensor, and energy conversion. Various
5
6
6
5
0
5
hierarchical nanostructures such as hyperꢀbranched Cu@Cu O
−1
−2
2
mM cm , and a low detection limit of 0.45 ꢁM (S/N = 3).
Furthermore, the sensor exhibits excellent selectivity against
the common interferences and good reliability for glucose
detection in human serum samples.
21
coaxial nanowires,
hierarchical Ni/NiO coreꢀshells
and 3D hierarchical cobalt oxide
22
nanostructure
23
architecture, have been demonstrated as novel electrode
materials for glucose sensing with high sensitivity and good
selectivity. For electrochemical tests, however, it requires the
effective immobilization of these hierarchical nanomaterials
on electrode surfaces with the use of polymer binder (Nafion
or PTFE) as a filmꢀforming agent. The whole process is timeꢀ
consuming and such polymer binder may block the active
Introduction
Numerous efforts have been devoted to glucose detection
because of its wide application in biotechnology, clinical
2
3
3
5
0
5
1
,2
diagnostics, food industry and many other fields.
Electrochemical methods have been widely investigated and 70 sites of the catalyst, inhibit the diffusion of analyte, and
utilized due to its remarkable features such as high sensitivity,
increase the series resistance of the device, leading to reduced
As a result, it is of significant
importance to prepare selfꢀsupported electrode by directly
3
24,25
super selectivity, simple instrumentation, and easy operation.
catalytic activity.
In past decades, enzymatic glucose electrochemical sensors
have attracted extensive attention for their high sensitivity and
growing
hierarchical
nanostructures
on
conductive
2
6ꢀ29
selectivity towards glucose oxidation. However, such sensors 75 substrate.
3
0,31
26,32
often suffer from high cost, timeꢀconsuming operation and
Metal foam such as Cu foam
and Ni foam
, as a
insufficient longꢀterm stability originating from the intrinsic
commercial available material with 3D porous structure and
excellent electrical conductivity, has been used extensively as
an efficient conductive substrate for constructing various selfꢀ
80 supported electrodes. Due to the unique pore structure and
large surface area, metal foam not only facilitates sufficient
transport of reactants and products in electrochemical process,
but also provides more catalyst loading and more active sites
exposure, leading to an improved catalytic activity.
3
,4
nature of enzymes.
Electrochemical enzymeꢀfree glucose
sensors based on the direct electrochemical oxidation of
5
,6
glucose triggered great interest and were widely exploited.
Noble metals and their composites
7
ꢀ9
10,11
were exploited as
electrode materials for enzymeꢀfree glucose sensing in the
early research studies, but most of them have distinct
problems including low sensitivity and poor selectivity resultꢀ
4
0
85
In this paper, we demonstrated the successful synthesis of
hierarchical Cu/Cu(OH)2 nanorod arrays supported on Cu
Key Laboratory of Green Synthesis and Applications, College of
Chemistry, Chongqing Normal University, Chongqing 401331, China.
Corresponding author, E-mail: jphdp868@126.com
foam (Cu/Cu(OH) NRA/CF) via a threeꢀstep strategy. Firstly,
Cu(OH)2 nanorod arrays grown on Cu foam (Cu(OH)2
NRA/CF) were fabricated by a simple wet chemical reaction.
2
4
5
†
Electronic Supplementary Information (SI) available: Experimental
section and Figures. See DOI:
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The Cu(OH)2 NRA/CF were subsequently converted to Cu
substrate.
nanorod arrays on Cu foam (Cu NRA/CF) by a NaBH4
reduction reaction. Finally, galvanostatic anodization of
Characterizations
corresponding Cu NRA/CF produces hierarchical Cu/Cu(OH)2
55
Powder XRD data were acquired on a RigakuD/MAX 2550
diffractometer with Cu Kα radiation (λ=1.5418 Å). SEM
measurements were carried out on a XL30 ESEM FEG
scanning electron microscope at an accelerating voltage of 20
kV. All electrochemical measurements were performed on a
Autolab PGSTAT 302 electrochemical workstation (Metrohm
Ltd, Switzerland). A typical threeꢀelectrode system was
employed with a saturated Ag/AgCl as reference electrode, a
Pt wire as counter electrode, and the Cu/Cu(OH)2 NRA/CF
5
0
5
0
NRA/CF. As a novel selfꢀsupported electrode for enzymeꢀfree
glucose sensing, the presented Cu/Cu(OH) NRA/CF exhibits
2
superior catalytic activity than other sensors including
Cu(OH) NRA grown on conductive substrate, commercial Cu
2
f
o
a
m
,
C
u
/
C
u
(
O
H
)
N
R
A
g
r
o
w
n
o
n
C
u
f
o
i
l
(
C
u
/
C
u
(
O
H
)
2
2
60
1
1
2
NRA/CFL), and various other hierarchical nanostructured
glucose sensors. The high performance of Cu/Cu(OH)2
NRA/CF can be attributed to the following reasons: (1) The
3
D CF used as conductive substrate with a large surface area
(
0.5 cm × 0.5 cm) as a working electrode. All electrochemical
leads to a significant increase in the catalyst loading and more
active site exposure. (2) Hierarchical structure of Cu/Cu(OH)2
65
experiments were performed at room temperature and all the
potentials are reported against the saturated Ag/AgCl
reference electrode. For amperometric detection, all
measurements were performed by applying an appropriate
potential to the working electrode and allowing the transient
background current to decay to a steadyꢀstate value before the
addition of the analyte. The solution was stirred to provide
convective transport.
NRA owns large specific surface area, facilitating more active
site exposure. (3) The direct growth of Cu/Cu(OH) NRA on
2
CF enables intimate contact, good adhesion and excellent
3
3
electrical connection between them. Moreover, the absence
70
2
4
of a polymer binder avoids the blocking of active site and
2
5
the inhibition of diffusion.
Experimental section
Materials
Results and discussion
Scheme
1 represents the formation of the hierarchical
CF was purchased from Aladdin Ltd. (Shanghai, China).
Ethanol, acetone, HCl, (NH ) S O , NaOH, NaBH and KOH
75
Cu/Cu(OH) NRA/CF and its application for glucose sensing. As
2
25
4
2
2
8
4
is shown, threeꢀstep synthesis process was involved in the
preparation of hierarchical nanostructures. According to the
were bought from Chengdu Chemical Reagent Factory
Chengdu, China). Ascorbic acid (AA), uric acid (UA),
(
34
previous reports, Cu(OH)2 NRA/CF was firstly prepared by
dopamine (DA) and dꢀ(+)ꢀglucose were supplied by J&k
Chemical Ltd. (China). Human serum was supplied by
Chongqing Emergency Medical Central. All aqueous solutions
were prepared with deionized water.
simply immersing CF in an aqueous solution containing NaOH
and (NH ) S O . Then, the resulted Cu(OH) NRA/CF was
80
4
2
2
8
2
30
reduced to metallic Cu NRA/CF with putting Cu(OH) NRA/CF
2
into 1 M NaBH aqueous solution for at least 20 min. After being
4
washed with deionized water and dried in a vacuum oven at 80℃
for 2 h, the Cu NRA/CF was subsequently put in an alkaline
Preparation of Cu(OH) NRA/CF
2
Prior to wet chemical reaction, a piece of CF (2 cm × 2 cm) 85 solution for galvanostatic anodization, with the current density
2
was washed with ethanol, acetone, 3 M HCl and water
respectively to remove the surface impurities and dried in air.
The cleaned CF was then immersed in an aqueous solution
including 2 M NaOH and 1 M (NH ) S O (mole ratio is 20:1)
kept at 10 mA/cm . After that, the Cu/Cu(OH) NRA/CF with
2
35
hierarchical structure was obtained.
Fig. 1 shows the Xꢀray diffraction (XRD) patterns for Cu(OH)2
NRA/CF (curve a), Cu NRA/CF (curve b) and Cu/Cu(OH)2
NRA/CF (curve c), respectively. Curve a shows diffraction peaks
indexed to orthorhombic phase Cu(OH) (JCPDS No.72ꢀ0140)
and that of metallic copper (JCPDS No. 04ꢀ0836) originated
4
2
2
8
for 1 h at room temperature. The resulted Cu(OH) NRA/CF
2
90
was removed from the solution and washed with water several
times, then dried in air.
34
2
40
35
from CF, suggesting successfully synthesis of Cu(OH)2 NRA
Preparation of Cu NRA/CF
grown on Cu foam by wet chemical method. After chemical
Cu NRA/CF were prepared by immersing the corresponding 95 reduction with NaBH solution, only the diffraction peaks (curve
4
Cu(OH) NRA/CF in 1 M NaBH aqueous solution for at least
2
4
b) of the copper are observed at 43.3°, 50.4° and 74.1°, which are
well indexed to (111), (200) and (220) planes of metallic Cu
2
0 min, then was washed with water and dried in a vacuum
4
5
over at 80 ℃ for 2 h.
(
JCPDS No. 04ꢀ0836), implying the complete reduction of
Cu(OH)2 NRA. Following galvanostatic anodization, the
100 diffraction peaks (curve c) indexed to Cu(OH) (JCPDS No.72ꢀ
0140) appears again, indicating that galvanostatic anodization
cause the growth of Cu(OH) on Cu NRA/CF.
Preparation of Cu/Cu(OH) NRA/CF
Cu/Cu(OH)2 NRA/CF were obtained by galvanostatic
anodization of the resulted Cu NRA/CF in an alkaline solution
2
2
2
2
(
3 M KOH) for 200 s, with current density kept at 10 mA/cm .
Fig. 2a shows SEM images of Cu(OH)2 NRA/CF in lowꢀ
magnification, indicating they are 1D structures about several
105 micrometers in length. The highꢀmagnification SEM image (see
Fig. 2b) further reveals that they have diameters ranging from
100 nm to 200 nm with smooth surface. After chemical reduction
50
Preparation of Cu/Cu(OH) NRA/CFL
2
Cu/Cu(OH) NRA/CFL were prepared with the same method
2
except that a piece of Cu foil was used as a conductive
2
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with NaBH solution, such Cu(OH) NRA were found converted
The electrocatalytic activity of Cu/Cu(OH) NRA/CF towards
4
2
2
to Cu NRA with diameter less than 100 nm, rough surface and
decreased length (Fig 2c and 2d). The development of such
glucose oxidation in an alkaline solution was also investigated.
Fig. 4a shows the CVs of Cu/Cu(OH) NRA/CF electrode in the
2
morphology is associated with hydrogen release and conversion 60 absence (black curve) and presence (red curve) of 1.0 mM
5
from Cu(OH) to metallic Cu. Galvanostatic anodizing Cu NRA
glucose in 0.1 M NaOH solution. No obvious oxidation peak was
observed in absence of glucose. However, a gradual increase in
anodic current was observed at + 0.5 V when the glucose was
added, followed a slight decrease in cathodic current, indicative
2
in an alkaline solution for 200 s produces a large quantity of
uniform nanoparticles with diameter around 50 nm grown on its
surface (Fig. 2e and 2f), constructing a hierarchical structure
consisted by oneꢀdimensional nanorods and zeroꢀdimensional 65 of an irreversible electroꢀoxidation reaction that occurred at
3
1
1
0
nanoparticles. XRD patterns in Fig. 1 confirmed the composition
of these nanostructures. All results suggests the successful
approximately + 0.5 V during scanning. According to the
previous research, the enhanced anodic current is attributed to the
electrochemical oxidation of glucose with the participation of
fabrication of hierarchical structure of Cu/Cu(OH) NRA/CF.
2
39,40
Cu(III).
The possible mechanism of the electrocatalytic
process of glucose can be expressed as followings:
Nitrogen adsorptionꢀdesorption isotherm measurement (Fig
S1) was conducted to investigate the surface areas of the as
38
70
−
−
1
5
prepared Cu/Cu(OH) NRA scratched down from the Cu foil. The
Cu(II) + OH → Cu(III) + e
2
BrunauerꢀEmmettꢀTeller (BET) specific surface area (SSA) of
Cu(III) + glu cos e → Cu(II)
+
gluconolactone
2
Cu/Cu(OH) NRA was calculated to be 27.60 m /g, much larger
2
2
Fig. 4b shows the CVs curves of Cu/Cu(OH) NRA/CF in 0.1
than that of Cu NRA (12.25 m /g), which can be attributed to its
2
M NaOH solution including 0.1 mM glucose at different scan
rates. The anodic peak current of oxidation of glucose (the
corresponding voltage is at + 0.5 V) was found proportional to
the scan rate. As indicated in the inset of Fig 4b, a good linearity
between scan rate and perk current within the range of 1ꢀ50 mV/s
was observed, indicating a surfaceꢀcontrolled electrochemical
hierarchical structure.
7
5
2
2
3
3
0
5
0
5
Electrochemical impedance spectrum (EIS) is an effective
way to measure the electron transfer resistance. Fig. 3a shows the
typical EIS of the CF, Cu(OH) NRA/CF, Cu NRA/CF, and Cu/
2
Cu(OH) NRA/CF. As for bare Cu foam, a small semicircular
2
portion at high frequency is observed, illustrating low transfer
resistance and good conductivity of the CF. After being covered
with Cu(OH)2 NRA, the semicircle diameter was observed
increases from a value close to 30 ohm up to 110 ohm, implying
80
kinetic process of Cu/Cu(OH) NRA/CF in alkaline solution.
2
The optimal operating potential for electrochemical detecting
glucose with Cu/Cu(OH) NRA/CF was further studied. Fig. 5
2
shows the amperometric responses towards dropwise addition of
inferior conductivity of Cu(OH) . However, it returns to a value
2
0
.01 mM glucose into 0.1 M NaOH solution at different
about 25 ohm after the complete conversion from Cu(OH)2
NRA/CF to Cu NRA/CF. Compared with the bare CF, Cu
NRA/CF shows lower transfer resistance which can be attributed
to the superior conductivity of Cu nanostructure. After the growth
of Cu(OH)2 nanoparticles on the surface of Cu NRA, the
semicircle diameter has a slight increase but still keeps smaller
85
potentials. A wellꢀdefined, stable and rapid change in current can
be observed with the successive additions of 0.01 mM glucose
under detection potentials from 0.40 V to 0.55 V in 0.05 V
increments. The Cu/Cu(OH)2 NRA/CF exhibits sensitive and
rapid current response to the glucose addition, achieving steady
state current in less than 5 s. The sensitivity is enhanced steadily
in the range from 0.40 to 0.50 V. However, a slight decrease is
observed when the potential beyond 0.55 V. Therefore, the
followed amperometric detection of glucose was performed under
the potential of 0.50 V.
90
than that of Cu(OH) NRA/CF, implying superior conductivity
2
and faster electron transfer of the hierarchical Cu/Cu(OH)2
NRA/CF.
The electrochemical behavior of Cu/Cu(OH) NRA/CF was
examined in 0.1 M NaOH solution (Fig. 3b). For comparison, CF
2
95
Fig. 6a shows an amperometric response of Cu/Cu(OH)2
4
4
5
5
0
5
0
5
and Cu/Cu(OH) NRA/CFL were also examined. Like any other
2
3
1,36,37
NRA/CF with successive addition of the glucose solution with
Cu based nanomaterials,
the oxidative current of Cu(II) to
different concentrations into 0.1 M NaOH solution, at an
applied potential of 0.50 V. The addition of glucose was
incremented at the rate of 1, 5, 10, 50, 100 and 500 ꢁM,
Cu(III) in the potential range +0.4 V to + 0.7 V was not clear.
However, the cathodic peak at about + 0.57 V, corresponding to
the reduction of Cu(III) to Cu(II), was observed on reversing the
scan, clearly indicating the presence of Cu(III). . Here, we
compared the cyclic voltammograms (CVs) behaviors of three
kinds of Cu based electrodes. As is shown, bare CF exhibits
3
8
100 respectively. As shown in Fig 6b, the Cu/Cu(OH) NRA/CF
2
gives a linear dependence range from 1ꢁM to 1 mM of
2
glucose with a correlation coefficient (R ) of 0.991 and a
ꢀ
1
ꢀ2
remarkably high sensitivity of 9.18 mA mM cm . Such
lower current response while Cu/Cu(OH) NRA grown on both
2
ꢀ
1
ꢀ2
sensitivity is better than those of 418 ꢁA mM cm at
CF and CFL show higher amperometric responses, which should
be attributed to the larger specific surface area of the Cu/Cu(OH)2
NRA originated from its hierarchical nanostructure. Due to the
pore structure, CF owns larger specific surface and benefits more
Cu/Cu(OH)2 NRA loading and more active sites exposure.
Consequently, Cu/Cu(OH)2 NRA/CF exhibits larger current
responses than that of Cu/Cu(OH)2 NRA/CFL in the same
conditions.
3
8
ꢀ
1
05 Cu(OH) nanotube arrays on copper foils, and 5.85 mA mM
2
1
ꢀ2
41
cm at commercial Cu foam. Moreover, compared with
other copperꢀbased enzymeꢀfree glucose sensors with
hierarchical nanostructure (Tab S2), the sensitivity is still
ꢀ
1
ꢀ2
better than those of 1.321 mA mM cm
at CuO/TiO2
4
2
ꢀ1
ꢀ2
1
10 nanocomposites, 2.657 mA mM cm at hierarchical CuO
4
3
ꢀ1
ꢀ2
nanoflowers,
1.42 mA mM cm
at hyperꢀbranched
2
1
ꢀ1
ꢀ2
Cu@Cu O coaxial nanowires, 0.408 mA mM cm at
2
4
4
CuO/ZnO hybrid hierarchical nanostructures, 3.252 mA
Journal Name, [year], [vol], 00–00 |
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3

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ꢀ
1
ꢀ2
36
mM cm at chrysanthemumꢀlike CuO hierarchical film,
serum samples obtained by the Cu/Cu(OH) NRA/CF sensor
and those measured by the hospital. The relative standard
2
ꢀ
1
ꢀ2
36
4
5
.078 mA mM cm at candockꢀlike CuO hierarchical film,
.368 mA mM cm at dandelionꢀlike CuO hierarchical 60 deviations (RSD) and bias are less than 3% and 0.15 mM,
film,
decorated porous graphene foam (Cu(OH)2 /PGF). The
superior sensitivity for Cu/Cu(OH)2 NRA/CF can be
attributed to the following three reasons: (1) The porous
feature for CF not only favors more catalyst loading and more
active sites exposure, but allows more easy diffusion of
electrolyte and faster electron transfer in process of
electrochemistry. (2) The hierarchical structure of
Cu/Cu(OH) NRA also facilitates the exposure of more active
sites during the electrocatalytic process. (3) The direct growth
of Cu/Cu(OH) NRA on CF avoids the use of polymer binder,
thus effectively decreases the contact electrical resistance
between them and benefits more active site exposure.
ꢀ
1
ꢀ2
3
6
ꢀ1
ꢀ2
and 3.36 mA mM cm at Cu(OH)2 nanorods
respectively. Obviously, the Cu/Cu(OH) NRA/CF is suitable
2
4
5
5
0
5
for glucose detection in human serum.
For practical applications, the sensors should have the
advantage of good reproducibility and longꢀterm stability.
Therefore, we further probed the reproducibility and stability
6
5
of the Cu/Cu(OH) NRA/CF sensor in our experiments with
2
1
the amperometric method. The reproducibility was evaluated
by the measurements of the response currents towards 0.2 mM
2
glucose in 0.1 M NaOH solution at the Cu/Cu(OH) NRA/CF
2
70
sensor. The results of five parallel experiments show that the
2
Cu/Cu(OH) NRA/CF sensor has good reproducibility (RSD =
2
1
2
.72 %, n = 5). Moreover, the aboveꢀmentioned results
obtained from human samples (Table 1) also confirm the good
reproducibility of present sensor.
The response time was found less than 5 s to reach 95% of
steadyꢀstate current from the enlarged segment of the
amperometric response curve (inset in Fig. 6a) and the limit of
detection (LOD) was found to be 0.45 ꢁM based on signalꢀtoꢀ
noise ratio of 3. The detection limit of the asꢀprepared
75
The longꢀterm stability of the Cu/Cu(OH) NRA/CF sensor
2
was examined by measuring the amperometric response
currents towards 0.01 mM glucose in 0.1 M NaOH solution.
As shown in Fig S2, the current response was found
20
Cu/Cu(OH) NRA/CF is relatively low among other hierarchical
maintained 80% of the original value after a month
2
Cu based nanostructures (Tab S1), implying high performance 80 conservation at room temperature, suggesting the good longꢀ
term stability of the Cu/Cu(OH) NRA/CF sensor.
towards glucose sensing.
2
25
30
35
40
45
It is well known that some easily oxidative species such as
dopamine (DA), ascorbic acid (AA), and uric acid (UA), usually
coꢀexist with glucose in biological sample and consequently
interfere with the detection of glucose. Therefore, antiꢀ
interference property is another important parameter for the
practical use of glucose sensors. Herein, the interference test was
also investigated using Cu/Cu(OH)2 NRA/CF to evaluate the
possible application in glucose detection in human serum. Since
the normal physiological level of glucose (3ꢀ8 mM) is more than
Conclusions
Hierarchical Cu/Cu(OH) NRA/CF was fabricated via a threeꢀ
2
step strategy involving the wet chemical synthesis, chemical
reduction and galvanostatic anodization. Benefiting from the
porous substrate, hierarchical nanostructures, and selfꢀ
8
5
supported property, the present Cu/Cu(OH) NRA/CF shows
2
remarkable catalytic activity towards glucose sensing with a
high sensitivity and low detection limit. Moreover, the sensor
shows high selectivity, good reproducibility and longꢀterm
stability, and good reliability for glucose detection in human
samples. All these make Cu/Cu(OH)2 NRA/CF a good
candidate for the construction of enzymeꢀfree glucose sensor
with highꢀperformance.
90
1
0 times higher higher than those of the other three interfering
46
species, the molar ratio of 10:1 was used for AA, UA, and DA
to estimate their interference effects in the glucose sensing. Fig.
7
a shows the amperometric response of the Cu/Cu(OH) NRA/CF
2
for 0.1 mM glucose at 0.5 V, followed by the additions of 0.01
mM UA, 0.01 mM DA and 0.01 mM AA in a 0.1 M NaOH
solution. Obviously, almost no current response for such
electroactive interfering species was detected in comparison to
that of glucose, indicating the high selectivity of our present
Cu/Cu(OH)2 NRA/CF based sensor for glucose detection in
comparison to the normally coꢀexisting electroactive interfering
species.
95
Acknowledgements
This work was supported by the Natural Science Foundation
of China (21601022), the Foundation and Cuttingꢀedge
Research
cstc2016shmszx20004), Project of International Science and
00 Technology Cooperation Base Construction in Chongqing
Plan
of Chongqing
(cstc2015jcyjA90002,
1
(
(
cstc2014gjhz20002), and Chongqing Education Commission
KJ110604, KJ130642).
We further evaluated the reliability of the Cu/Cu(OH)2
NRA/CF sensor by detecting the concentration of glucose in
human serum samples. All serum samples were supplied by
Chongqing Emergency Medical Central. Fig. 7b shows the
amperometric responses of the Cu/Cu(OH)2 NRA/CF sensor
upon addition of 5 ꢁM glucose and three human serum
samples at an applied potential of 0.5 V in 0.1 M NaOH
solution. The determination of each sample was done three
times to verify the reproducibility of the values. The
concentration of glucose was determined by comparing the
amperometric response of 5 ꢁM glucose and that of human
serum sample. Table 1. lists the glucose concentrations in
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Journal Name, [year], [vol], 00–00 | 5

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2
Scheme. 1 Three-step synthesis process for hierarchical Cu/Cu(OH) NRA/CF and its application
for glucose sensing.

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2 2
Fig. 1 XRD patterns of Cu(OH) NRA/CF (curve a), Cu NRA/CF (curve b) and Cu/Cu(OH)
NRA/CF (curve c).

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2
Fig. 2 Low and high-magnification SEM images of Cu(OH) NRA/CF (a, b), Cu NRA/CF (c, d),
2
and Cu/Cu(OH) NRA/CF (e, f).

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Fig. 3 (a). EIS results of CF, Cu(OH)
2
NRA/CF, Cu NRA/CF, and Cu/Cu(OH)
3
2
NRA/CF in 0.10
-/4-
M KCl with the presence of 0.01 M equimolar [Fe(CN)
6
]
. (b). CVs of the CF, Cu/Cu(OH)
2
NRA/CF and Cu/Cu(OH)
2
NRA/CFL in 0.1 M NaOH solution with a scan rate of 20 mV/s.

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Fig 4. (a) CVs of Cu/Cu(OH)
glucose. (b) CVs of Cu/Cu(OH)
0 mV/s with the glucose concentration of 0.1 mM. Inset: the plot of the anodic response at 0.5 V
vs. the scan rate.
2
NRA/CF in the absence (black curve) and presence (red curve) of
2
NRA/CF in 0.1 M NaOH at various scan rates of 1, 5, 10, 20, 30,
5

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Fig. 5 Amperometric response with successive addition of 0.01 mM glucose at different detection
potentials.

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Fig. 6 (a) Amperometric response of Cu/Cu(OH)
glucose solution of different concentrations into 0.1 M NaOH solution. Inset: enlarged
amperometric response curve of the Cu/Cu(OH) NRA/CF on addition of 1 µM glucose into
NaOH solution. (b) Calibration curve for current vs. concentration of glucose.
2
NRA/CF with successive addition of the
2

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Fig. 7 (a). Amperometric response upon addition of 0.1 mM glucose, 0.01 mM UA, 0.01 mM DA
and 0.01 mM AA at an applied potential of 0.5 V in 0.1 M NaOH solution. (b) Amperometric
response upon addition of 5 µM glucose and three serum samples at an applied potential of 0.5 V
in 0.1 M NaOH solution.

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Table. 1 Glucose concentration in human serum samples that obtained in the hospital and
those obtained by the Cu/Cu(OH) NRA/CF sensor.
2
Glucose
Glucose
concentra-tion
obtained from the
present sensor
(mM)
concentr-ation
obtained from
the hospital
RSD
%)
Bias
Sample
(
(mM)
(mM)
1
2
3
6.26
5.75
4.73
6.19
1.06
2.29
2.45
-0.07
0.12
0.10
5.87
4.83