Hierarchical 3-dimensional nickel–iron nanosheet arrays on carbon fiber paper as a novel electrode for non-enzymatic glucose sensing

Nanoscale
PAPER
View Article Online
View Journal
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Cite this: DOI: 10.1039/c5nr06802a
Received 1st October 2015,
Accepted 26th October 2015
DOI: 10.1039/c5nr06802a
www.rsc.org/nanoscale
<strong>Hierarchical</strong> 3-<strong>dimensional</strong> <strong>nickel–iron</strong> <strong>nanosheet</strong>
<strong>arrays</strong> on carbon fiber paper as a novel electrode
for non-enzymatic glucose sensing†
Palanisamy Kannan, a,c Thandavarayan Maiyalagan, b Enrico Marsili,* c Srabanti Ghosh, d
Joanna Niedziolka-Jönsson* a and Martin Jönsson-Niedziolka* a
Three-<strong>dimensional</strong> <strong>nickel–iron</strong> (3-D/Ni–Fe) nanostructures are exciting candidates for various applications
because they produce more reaction-active sites than 1-D and 2-D nanostructured materials and
exhibit attractive optical, electrical and catalytic properties. In this work, freestanding 3-D/Ni–Fe interconnected
hierarchical <strong>nanosheet</strong>s, hierarchical nanospheres, and porous nanospheres are directly grown
on a flexible carbon fiber paper (CFP) substrate by a single-step hydrothermal process. Among the nanostructures,
3-D/Ni–Fe interconnected hierarchical <strong>nanosheet</strong>s show excellent electrochemical properties
because of its high conductivity, large specific active surface area, and mesopores on its walls (vide infra).
The 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array modified CFP substrate is further explored as a novel electrode
for electrochemical non-enzymatic glucose sensor application. The 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> exhibit significant catalytic activity towards the electrochemical oxidation of glucose, as
compared to the 3-D/Ni–Fe hierarchical nanospheres, and porous nanospheres. The 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> can access a large amount of glucose molecules on their surface (mesopore walls)
for an efficient electrocatalytic oxidation process. Moreover, 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong>
showed higher sensitivity (7.90 μA μM −1 cm −2 ) with wide linear glucose concentration ranging from
0.05 µM to 0.2 mM, and the low detection limit (LOD) of 0.031 µM (S/N = 3) is achieved by the amperometry
method. Further, the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array modified CFP electrode can be
demonstrated to have excellent selectivity towards the detection of glucose in the presence of 500-fold
excess of major important interferents. All these results indicate that 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>
<strong>arrays</strong> are promising candidates for non-enzymatic glucose sensing.
1. Introduction
<strong>Hierarchical</strong> nanostructures assembled by low-<strong>dimensional</strong>
building blocks including nanoparticles, 1,2 nanorods, 3,4 and
nanoplates 5,6 often exhibit significant morphology and/or size
dependent properties. 7–11 Considered as an important functional
nanomaterial, <strong>nickel–iron</strong> (Ni–Fe) nanostructures
exhibit extraordinary electrical, catalytic, and magnetic
a Institute of Physical Chemistry, Polish Academy of Sciences, 44/52 ul. Kasprzaka,
01-224 Warsaw, Poland. E-mail: joaniek@ichf.edu.pl, martinj@ichf.edu.pl;
Fax: +48223433333; Tel: +4822333433130
b School of Chemistry, University of East Anglia, Norwich NR4 7TJ, UK
c Singapore Centre on Environmental Life Sciences Engineering (SCELSE), Nanyang
Technological University, 60 Nanyang Drive, SBS-01N-27, Singapore.
E-mail: emarsili@ntu.edu.sg; Fax: +65-6515-6751; Tel: +65-6592-7895
d Department of Chemical, Biological and Macromolecular Sciences, S. N. Bose
National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata-700098,
India
†Electronic supplementary information (ESI) available. See DOI: 10.1039/
c5nr06802a
properties and have potential technological applications in
electromagnetic shielding, absorbing materials, catalysis, and
sensors. 10,12–14 Great attention has been focused on the
fabrication of Ni–Fe micro-/nanostructures by using various
physical and chemical methods. 10,15–18 For instance, low
<strong>dimensional</strong> Ni–Fe nanostructures including nanochains 10
and nanorods 15,19 have been synthesized by hydrothermal and
calcination methods. Three <strong>dimensional</strong> (3-D) Ni–Fe nanostructures
such as flowers, 18 dendrites, 20 and Ni–Fe layered
double hydroxide films 8 have also been reported. The 3-D Ni–
Fe hierarchical nanostructures are preferable for various technological
applications because they produce more reactionactive
sites than 1-D and 2-D nanostructured materials and
exhibit attractive optical, electronic, magnetic, and catalytic
properties. 7,18
The formation of hierarchical nanostructures is a selfassembly
process, in which the ordered superstructures are
formed by small building blocks, i.e., 0-D nanoparticles,
1-<strong>dimensional</strong> nanorods or nanowires, and 2-D nanoflakes.
21–23 Moreover, it is well known that templates and/or
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
shape modifiers and controllers are usually used to prepare
such hierarchical and complexed micro/nanostructures. 24,25 In
addition, hierarchically nanostructured materials have also
been fabricated by physically constrained crystal growth with
the assistance of templates, 26,27 which need to be completely
removed after synthesis. Template-free methods, including
solution phase reduction, 28 chemical vapour deposition, 29
thermal decomposition, 30 electrochemical deposition, 31 and
hydrothermal methods, 32 were widely explored to synthesize
hierarchical nanostructured materials. Among them, the
hydrothermal method has received huge attention because of
its simplicity, and suitability for large-scale production, which
offers abundant control parameters and can be used for electrode
modifications. Although different nanoarchitectures
have been successfully prepared by the hydrothermal method
(vide supra), we show that it is possible to directly grow 3-D
Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong>, hierarchical nanospheres,
and porous nanospheres through the hydrothermal process on
a flexible substrate.
To accurately detect glucose is of immense scientific technological
importance for clinical diagnostics in diabetes
control and analytical applications in biotechnology, environmental
pollution control, and the food industry. 33–37 Since
enzyme based amperometric sensors have significant drawbacks
in stability because of the intrinsic nature of
enzymes, 38–41 some methods have been developed to determine
the glucose concentration without using them. 42–46
However, because of the surface poisoning from the adsorbed
intermediates and chloride, most of the non-enzymatic
sensors have distinct problems with low sensitivity and poor
selectivity. 47–49 Interferential effects from endogenous species
including ascorbic acid, uric acid, and dopamine cannot be
totally eliminated. As a result, a major consideration in practical
non-enzymatic glucose sensing is focused on fabricating
high-performance devices using resourceful transition-metal
catalysts. 50–59 Now, diabetes mellitus is a public health
problem, and this metabolic disorder results from insulin
deficiency and hyperglycemia and is reflected by blood glucose
concentrations higher or lower than the normal range of
80–120 mg dL −1 (4.4–6.6 mM). Good glycemic control is the
cornerstone for proper diabetes management. Hence, it is pertinent
to explore and develop non-enzymatic sensors with a
high sensitivity and a low detection limit to achieve convincing
clinical measurements.
In this work, three-<strong>dimensional</strong> <strong>nickel–iron</strong> (3-D/Ni–Fe)
interconnected hierarchical <strong>nanosheet</strong>s, hierarchical nanospheres,
and porous nanospheres are directly grown on flexible
carbon fiber paper (CFP) collectors by a single-step hydrothermal
process. Our approach utilizes small amounts of Fe
metal as a doping agent for growing various morphologies. It
is supposed that the ratio of urea and metal salts can assist
the formation of hierarchical nanostructures, which is confirmed
by the experimental results (vide infra). Further, we
study the enzyme-free electrochemical sensing of glucose as a
model system by using 3-D/Ni–Fe nanostructures. Interestingly,
3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> resulted in a remarkable
enhancement in the electrocatalytic activity of glucose oxidation,
reusability, and stability because of its high
conductivity, large specific surface area and mesopores on its
walls. The 3-D/Ni–Fe hierarchical nanospheres and porous
nanospheres were also tested under similar experimental conditions
used for comparing the electrochemical activity. The
3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> showed higher sensitivity
(7.90 μA μM −1 cm −2 ) with wide linear response of glucose
concentration ranging from 0.05 µM to 0.2 mM, and the low
detection limit (LOD) of 0.031 µM (S/N = 3) is achieved by the
amperometry method. These results show the potential of
these materials for use as electrodes for ultrasensitive electrochemical
experiments. We anticipate that they can be used in
many different systems in the future.
2. Experimental section
2.1. Materials
FeCl 2·4H 2 O and Ni(NO 3 ) 2·6H 2 O, NaOH were obtained from
Sigma-Aldrich Chemical Company. Urea (>99%) was received
from Merck Company. The nitric acid (HNO 3 ) solution was
obtained from Aldrich Company. All other chemicals used in
this investigation were of analytical grade. All the solutions
were prepared with Millipore water (18 mΩ) obtained from a
Millipore system. Argon (99.99%) was supplied by Multax
Company, Poland.
2.2. Pre-treatment of CFP
The CFP substrate was washed repeatedly with 0.1 M HNO 3
solution, and then subjected to 5 min ultra-sonication treatment
in solvents such as acetone, ethanol and water, respectively.
Next, the CFP substrate was rinsed with Millipore water,
followed by drying with a stream of argon gas. Finally, the
above pre-treated CFP substrate was used as collectors for preparing
various morphologies of 3-D/Ni–Fe nanostructures.
2.3. Synthesis of 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array
nanostructures
The typical synthesis of 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>
<strong>arrays</strong> on carbon fiber paper can be explained as follows (optimized
ratio as 2 : 1): 2 mM of FeCl 2·4H 2 O and 1 mM of
Ni(NO 3 ) 2·6H 2 O were added to 20 mL of Millipore water, and
then stirred for 15 min to obtain a homogeneous solution.
Thereafter, 25 mM of urea was added quickly to the reaction
mixture, and then the reaction mixture was stirred again for
10 minutes; next, the above reaction mixture was transferred to
a Teflon-lined stainless steel autoclave vessel. Finally, the pretreated
CFP substrate was placed in the reaction mixture, and
then continuously heated at 90° C for 6 h. After completion of
the reaction, the CFP was carefully removed from the reaction
vessel, and then thoroughly washed with Millipore water, followed
by drying at 40 °C for 8–12 h for further studies. The
other 3-D/Ni–Fe nanostructures such as hierarchical nanospheres
and porous nanospheres were obtained by repeating
the above procedure by changing the Ni–Fe ratio to 1 : 1, and
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
1 : 2, respectively. The mass loading for all samples of Ni–Fe
nanostructures on the CFP substrate was calculated as
∼0.42 mg cm −2 . The 3-D/Ni–Fe hierarchical nanostructures
grown over the CFP substrate can be used as a working
electrode for electrochemical non-enzymatic glucose sensor
experiments.
2.4. Instrumentation
The morphologies of Ni–Fe nanostructures were characterized
by field emission-scanning electron microscopy (FE-SEM JEOL
JSM-6700F). High-resolution transmission electron microscopy
(HRTEM) was carried out using a JEOL JEM 3010 instrument
with an acceleration voltage of 200 kV. The samples were
placed on a carbon-coated copper grid for morphology and
size analyses. The crystallographic information was obtained
by the powder X-ray diffraction technique (XRD, Shimadzu
XRD-6000, Ni filtered CuKα (λ = 1.54 Å) radiation operating at
30 kV/40 mA). The specific surface area of the nanostructures
was determined using the classic BET method (the Brunauer–
Emmett–Teller isotherm). The BET isotherm is the basis for
determining the extent of nitrogen adsorption on a given
surface. XPS analysis was performed on a VG ESCALAB MK II
with an Mg-Kα (1253.6 eV) achromatic X-ray source. Nitrogen
adsorption data were collected using a Quantachrome autosorb
automated gas sorption system. The electrochemical
measurements were performed with a two compartment cell
with a CFP (exposed geometric area = 0.16 cm 2 ), a Pt wire, and
Ag/AgCl (3 M KCl) as the working, auxiliary and reference
electrodes, respectively. Cyclic voltammograms were recorded
using a computer controlled Autolab PGSTAT30 (Metrohm
Autolab) electrochemical analyser. All electrochemical experiments
were carried out under an argon atmosphere.
3. Results and discussion
3.1 Synthesis and characterization of 3-D/Ni–Fe hierarchical
nanostructures on CFP
The 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> with high density
could be easily grown on CFP by a facile and one step hydrothermal
route. The CFP was chosen here because of its fine
groove-like skeleton and high porosity, which helped to
increase the active surface area of nanostructures. 60–62 The
morphology of as-synthesized 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong>/CFP was characterized by the FE-SEM technique,
as shown in Fig. 1. It can be seen that the smart 3-D/
Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> were quite uniform,
upright, outward, densely packed and well aligned, hierarchical
wall-like <strong>nanosheet</strong>s grown on the surface of the CFP substrate
and were ultrathin, which is favorable for the full
utilization of active materials (Fig. 1A–D) for technological
applications. Such hierarchical wall-like <strong>nanosheet</strong>s were composed
of several individual nano-walls with the lengths of 5–7
µm (Fig. 1A). Each wall appeared to grow from the same
origin/center of the CFP substrate. This indicates that the hierarchical
wall-like 3-D/Ni–Fe bimetallic <strong>nanosheet</strong>s were successfully
synthesized by the surfactant-free hydrothermal
reduction method. Interestingly, from the enlarged views
Fig. 1 FE-SEM images of interconnected hierarchical 3-D/Ni–Fe <strong>nanosheet</strong>s (A), and the corresponding different enlarged views (B, C), and close
up view of a single <strong>nanosheet</strong> array showing the interconnected nano “wall block” nanostructure (D).
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 2 FE-SEM images of extended views of interconnected 3-D hierarchical <strong>nanosheet</strong>s (A), and view of mesopores in the <strong>nanosheet</strong>s (B), and
photographs (C) of carbon fiber paper before (i) and after (ii) growing the Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong>.
(Fig. 1B and C), the <strong>nanosheet</strong>s are interconnected with each
other to form a wall-like nanostructure, which might possess
better mechanical strength and durability. Further, these crystalline
<strong>nanosheet</strong>s well-retained their hierarchical <strong>nanosheet</strong>
morphology without any calcination/annealing process. As
shown in the high-magnification FE-SEM image (Fig. 1D), the
interconnected <strong>nanosheet</strong>s form a highly open and mesoporous
structure. Thus, a large specific (active) surface of 3-D/
Ni–Fe hierarchical <strong>nanosheet</strong>s is highly accessible by the electrolyte/analyte
when it is employed as an electrode material for
electrochemical sensing.
It can be observed from Fig. 2 that in situ growth of hierarchical
Ni–Fe <strong>nanosheet</strong> <strong>arrays</strong> resulted in 3-D interconnected
and oriented nanoarchitectures, the length is more than
∼60 µm (Fig. 2A), which can help overcome the problem of low
conductivity in conventional <strong>nanosheet</strong> <strong>arrays</strong>. Further, it has
already been pointed out that numerous 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong>s were grown uniformly on the CFP surface.
Importantly, wall-like 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong>
cannot be destroyed into discrete walls even under ultrasonication
for a long period of time (20 min), indicating that
the complexed nanostructures are actually integrated and not
made up of loosely grown nano-walls through magnetic dipole
interactions. The 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> were
synthesized using nickel nitrate and iron chloride as metal
sources and urea as the precipitant under hydrothermal conditions
at 90 °C (see the Experimental section). At this temperature,
urea was decomposed into ammonia, the reason for
creating an alkaline environment, and carbonate, which served
as an intercalated anion. Now, Ni 2+ and Fe 3+ cations released
from the reaction mixture are simultaneously reduced to
metallic atoms, and then spontaneously formed 3-D/Ni–Fe
bimetallic nanoparticle nuclei. The formed nuclei (Ni cations)
occupy the center of the octahedral arrangement to grow into
a small sheet-like structure, with OH − groups forming the vertices
of octahedra; then the octahedra share edges to form
two-<strong>dimensional</strong> sheets, which rely on the hydrogen bonding
between the hydroxyl groups of adjacent sheets. Next, the
sheets can further grow three-<strong>dimensional</strong> network-like sheets
by self-assembly and then reconstruction as well as a further
growth step process. The grown hierarchical Ni–Fe <strong>nanosheet</strong>s
characteristics will potentially exhibit superior performance in
the electrochemical non-enzymatic glucose sensor (see below).
During the reaction, the urea not only acts as the stabilizing or
complexing regent but also plays a key role in the formation of
the hierarchical morphology. Because of the urea, the
<strong>nanosheet</strong>s becomes flexible, 63 and can be wrinkled and bent,
which will help <strong>nanosheet</strong>s connect with each other and leads
to the formation of ordered <strong>arrays</strong> (Scheme 1-1).
The synergistic effect of Fe in the reaction mixture also
highly influences the formation of 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> under these conditions, i.e., Fe acted as a
nucleating agent inducing the reduction of Ni at this (90 °C)
reaction temperature and assists the formation of such hierarchical
3-D/Ni–Fe nanostructures. As a result, sheet-like Ni–Fe
hierarchical nanostructures formed, and simultaneously, rapid
release of water molecules during the conversion process
resulted in the generation of mesopores over the surface of
<strong>nanosheet</strong>s (Fig. 2B), which resulted in the growth (in situ) of
mesoporous 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>s on the CFP
surface (Scheme 1-1). The distance between <strong>nanosheet</strong>s was
∼250 nm and the film thickness was approximately 50–100 nm
(Fig. 2B). To conclude, a yellowish-brown film was coated on
the surface of CFP (Fig. 2C, ii), indicating the successful
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Scheme 1 Schematic representation of the formation of freestanding 3-D/Ni–Fe interconnected hierarchical <strong>nanosheet</strong>s (1), hierarchical nanospheres
(2), and porous nanospheres (3) on a flexible carbon fiber paper (CFP) substrate.
growth of 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong>. The masses
of all the Ni–Fe nanostructures were determined by cutting the
CFP with grown samples into smaller pieces with the diameter
of 15 mm. Then CFP with grown samples and CFP were
weighed with a high-precision analytical balance (Sartorius,
max. weight 5100 mg, d = 0.001 mg) from which the exact
mass of the samples was then determined. The loading
density of the 3-D/Ni–Fe active material is calculated to be
0.42 mg cm −2 (vide supra).
Next we used the Ni–Fe ratio of 1 : 1 for preparation; interestingly
we observed that 3-D/Ni–Fe has a hierarchical nanosphere
morphology. The FE-SEM image obviously shows that
the as prepared 3-D/Ni–Fe nanoparticles have a hierarchical
nanospheres (flower-like) morphology (Fig. 3A and B). The particles
are uniform in size, ∼400 nm (Fig. 3B). The inset of
Fig. 3B shows that the hierarchical nanospheres with a flowerlike
architecture are assembled by several interconnected tiny
sheet-like petals with a smooth surface and the thickness ca.
150 nm. Such hierarchical nanosphere architectures follow a
stepwise growth mechanism; at first, the generation of tiny
crystalline nanoparticle nuclei occurs in a reaction mixture
(vide infra) and subsequently, site-specific anisotropic growth
occurred due to a non-symmetrical assembly process
(Scheme 1-2). Then, the particles continue to grow as striking
hierarchical nanospheres (inset of Fig. 3B) with few nanoleaves
sharing their originating center through coarsening,
also known as Ostwald ripening (Scheme 1-2). 64,65
On the other hand, for the Ni–Fe ratio of 1 : 2, the nanoparticle
nuclei undergo random aggregation, followed by
growth of interconnected porous nanosphere particles (Fig. 3A
and B) due to nanoparticle-face attraction through van der
Waals forces (Scheme 1-3). Further, CO 2 decomposed from
CO(NH 2 ) 2 can also act as soft template to induce the verity of
3-D/Ni–Fe nanostructure morphologies, since no other surfactant,
templates and emulsions were used in this work (vide
supra). As can be seen from the enlarged view (Fig. 3B and
inset), the porous nanospheres were uniform with a size of
∼300 nm (Fig. 3B). Importantly, no calcination treatment
process was required in this work for preparing hierarchical Ni–
Fe nanostructures. It should be noted here that this procedure
establishes a universal protocol for the synthesis of 3-D/Ni–Fe
hierarchical nanostructures without adopting different strategies,
reaction conditions, or injection of foreign reagents
(vide supra). Changing the ratio of the stabilizer and the pre-
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 3 FE-SEM images of hierarchical 3-D/Ni–Fe nanospheres (A), porous 3-D/Ni–Fe nanospheres (C) and the corresponding enlarged views (B, D),
and insets showing the close up view of hierarchical nanosphere (B) and porous nanosphere (D) morphologies.
cursor or vice versa resulted in the formation of 3-D/Ni–Fe
nanostructures of different morphologies (Fig. S1 in the ESI†).
The HRTEM images (Fig. 4; image A) show that the nanostructure
of Ni–Fe grown on CFP is composed of a well-defined
<strong>nanosheet</strong> morphology with the length of 1 μm; the Ni–Fe
<strong>nanosheet</strong> offers abundant catalytic sites, which contributes to
the high electrocatalytic activity of the composite material. The
HRTEM image of the Ni–Fe hierarchical <strong>nanosheet</strong> (image B)
shows mesoporous architectures. A large amount of well-distributed
pores (on the surface) can be clearly seen, which is
well-consistent with the results observed from FESEM. The
hierarchical Ni–Fe <strong>nanosheet</strong> together with the mesoporous
structure provides a large specific surface area, which was estimated
by the Brunauer–Emmett–Teller (BET) method 66 to be
337.9 m 2 g −1 , much higher than those for hierarchical Ni–Fe
nanospheres (211.3 m 2 g −1 ) and porous Ni–Fe nanospheres
(136.4 m 2 g −1 ), respectively (Fig. S2†). The improved surface
area allows for the rapid access of electrolyte ions, provides
abundant active sites for the electrocatalytic reactions, and
facilitates fast electron transport between the electrode
materials and the analytes. The close up view of the HRTEM
image (image C) clearly shows that the interplanar spacing of
0.14 nm corresponds to the (111) crystalline plane. Further, a
selected area electron diffraction (SAED) pattern analysis of
hierarchical 3-D Ni–Fe <strong>nanosheet</strong>s showed several well-defined
rings with discrete dots in the diffraction pattern illustrating
the crystalline nature of the sample (image D). This SAED
diffraction pattern was well aligned with the XRD spectra,
suggesting the crystalline nature of hierarchical Ni–Fe nanostructures.
Next, the Ni–Fe hierarchical nanospheres grown on
CFP were composed of ultrathin nanoflakelets with a dimension
of ∼400 nm (image E), and close assemblies of Ni–Fe
porous nanospheres (image F) with a size of ∼300 nm were
further confirmed by HRTEM analysis. The results obtained
from HRTEM were highly consistent with the FESEM analysis.
The phase structure and purity of the as-synthesized 3-D/
Ni–Fe samples were examined by the XRD method. Fig. 5
shows the XRD pattern of all Ni–Fe samples. It can be seen
from Fig. 5 that all of the diffraction peaks can be indexed to
pure nanocrystalline structures. The XRD profile of the 3-D/Ni–
Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> (Fig. 5A), hierarchical nanospheres
(Fig. 5B), and porous nanospheres (Fig. 5C) on the
CFP substrate shows that the peaks at 43.1, 53.3, 62.7, 76.4,
79.6, and 96.0 could be indexed as the (111), (200), (220),
(311), (222), and (400) crystalline planes of the fcc (face centered-cubic)
Ni phase (JCPDS No. 04-0850), respectively. 1,67–69
The peak corresponding to the (111) plane is more intense
than the other planes. The ratio between the intensities of the
(200) and (111) diffraction peaks is lower (0.51) than the usual
value (0.60), suggesting that the (111) plane is the predominant
orientation. Interestingly the ratios of the relative peak
intensities of the high index planes (311) and (222) are higher
(0.62 versus 0.42) and (0.67 versus 0.55) than the standard
values (dotted box in Fig. 5A). This observation reveals that the
3-D/Ni–Fe hierarchical <strong>nanosheet</strong>s were more abundant in
high index facets than 3-D/Ni–Fe hierarchical nanospheres
(Fig. 5B) and 3-D/Ni–Fe porous nanospheres (Fig. 5C). The
absence of NiO peaks mainly at 37.2 and 44.3 corresponds to
the (111) and (220) planes, indicating that no oxide product
was observed in the samples. Furthermore, the diffraction
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 4 High-resolution TEM images of hierarchical Ni–Fe <strong>nanosheet</strong>s with different magnifications (A–C), and the corresponding SAED pattern
(image D). Images E and F represent hierarchical Ni–Fe nanospheres and porous Ni–Fe nanospheres, respectively.
peaks at 35.4, 53.1 and 62.5 can be indexed as the (311), (511),
and (440) planes corresponding to the Fe component in all the
Ni–Fe nanostructures. 70 Their XRD patterns differ only in the
relative intensities of given crystalline planes. The intensity of
Fe peaks gets better (Fig. 5C) when the mole ratio 1 : 2 (Ni–Fe)
is used for the synthesis of 3-D/Ni–Fe porous nanospheres
rather than equal (Fig. 5B) or lower (Fig. 5A) mole ratios.
It has also been reported that the high concentration of the
Fe precursor (in the case of the 1 : 2 ratio) resulted in the formation
of oxide phases, 68 though in our synthetic protocol we
have not observed any oxide phases. Except for Ni–Fe phases,
the small broad diffraction peak observed at 26.5 in
Fig. 5(A–C) corresponds to the (002) plane of the graphitic
carbon of the CFP substrate. 71 No additional peaks apart from
the carbon fiber substrate were observed; this indicates that
high-purity 3-D/Ni–Fe nanostructures were obtained during
the synthesis. The strong, sharp peaks and very low backgrounds
reveal that the as-synthesized Ni–Fe bimetallic nanoparticles
had a high degree of crystallinity (vide supra). As we
discussed, Fe acted as a nucleating agent during the reaction
and assisted the formation of highly crystalline 3-D/Ni–Fe
nanostructures.
X-ray photoelectron spectroscopy (XPS) is a powerful tool to
identify the elements’ states in bulk material. 72 By the analysis
of binding energy (BE) values, we have confirmed the nature of
Ni and Fe metals in the 3-D/Ni–Fe hierarchical nanostructures.
Core-level high-resolution XPS spectra of Ni–Fe hierarchical
<strong>nanosheet</strong>s exhibit two peaks present at 855.4 and 873.1 eV
with a spin-energy separation of 17.7 eV, corresponding to
Ni 2p 3/2 and Ni 2p 1/2 , respectively (Fig. S3A†). 73 The binding
energy of the Ni 2p 3/2 peaks is different from that in other
reports of NiO (853.7 eV), NiS (853.1 eV) and Ni (852.6 eV), 74,75
which reveals that the Ni exist in the form of divalent. Next,
the high-resolution Fe 2p spectrum (Fig. S3B†) shows two distinct
peaks with binding energies of about 707.8 eV for
Fe 2p 3/2 and 722.4 eV for Fe 2p 1/2 . 76 The shakeup satellite peak
present at ∼860–870 eV and ∼712–720 eV is characteristic of
Ni 2+ and Fe 3+ ions, respectively, in hierarchical Ni–Fe nanostructures.
It also shows that the synthesized Ni–Fe nanostructures
contain both Fe 3+ and Fe 2+ ions, but it is obvious
that the amount of Fe 3+ is higher than the amount of the Fe 2+
ions. Generally, the Fe 3+ and Fe 2+ ions are found in its lattice
due to its inverse spinel structure. The XPS result confirms
that the Fe exists as Fe 2+ /Fe 3+ and Ni as Ni 2+ in the prepared
samples. The chemical composition (atomic percent) of the asprepared
3-D/Ni–Fe hierarchical <strong>nanosheet</strong>s was determined
by energy-dispersive X-ray (EDX) spectrometry as shown in
Fig. S3C.† The only detectable elements are iron, nickel,
carbon, and oxygen. While the carbon and oxygen should arise
from the carbon fiber paper, and oxidation from the surface of
the samples, the corresponding elementary analysis reveals
that the atomic ratio (%) of Ni to Fe is 63.3 : 31.2, which is very
close to the initial set ratio of Fe : Ni = 2 : 1. The atomic ratios
(%) of other morphologies such as 3-D/Ni–Fe hierarchical
nanospheres and 3-D/Ni–Fe porous nanospheres were
47.7 : 46.9% and 32.4 : 63.1%, respectively, which is consistent
with their ratios 1 : 1 and 1 : 2. The above EDS results matched
with the XRD pattern analysis, which revealed the crystallinity
of the as-prepared hierarchical Ni–Fe nanostructures.
3.2 Electrochemical behaviour of the 3-D/Ni–Fe hierarchical
nanostructures on CFP electrode
To take advantage of its (3-D/Ni–Fe hierarchical <strong>nanosheet</strong>
<strong>arrays</strong>) mesopores and large specific (active) surface area
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 5 XRD patterns of as-synthesized 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> (A), hierarchical Ni–Fe nanosphere (B), and porous Ni–Fe nanosphere (C)
morphologies.
(Fig. S2†), we decided to study enzyme-free electrochemical
sensing of glucose as a model system. The electrocatalytic behavior
of 3-D/Ni–Fe hierarchical nanostructures towards
glucose oxidation was studied by cyclic voltammetry (CV) in
0.1 M NaOH solution. As shown in Fig. 6A, a couple of sensitive
redox peaks for the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array
CFP electrode is observed at potentials of 0.43 and 0.58 V
(Fig. 6A, curve a), which could be mainly attributed to the
Ni(II)/Ni(III) redox couple in alkaline medium. 77,78 It has been
known that when nickel is immersed in alkaline solutions,
spontaneous dissolution of the metal occurs followed by the
formation of Ni(OH) 2 and finally NiOOH (eqn (1) and (2)). 79
Ni þ 2OH
Ni þ 2OH
! NiO þ H 2 O þ 2e ðorÞ
! NiðOHÞ 2
þ 2e
NiO þ OH ! NiOOH þ e ðorÞ
ð2Þ
NiðOHÞ 2
þ OH $ NiOOH þ H 2 O þ e
Furthermore, the electrochemical signal of the 3-D/Ni–Fe
hierarchical <strong>nanosheet</strong> array CFP electrode is much larger
than that of the bare CFP electrode (Fig. 6A, curve b),
suggesting that the former electrode is highly suitable for electrochemical
detection. Next, on the injection of 0.25 mM
glucose, the sharp anodic peak current recorded from the
3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode is significantly
higher than that from the same electrode without
ð1Þ
glucose. In addition, the behaviour of the cathodic peak
current is slightly increased due to the glucose oxidation
(Fig. 6A, curve c). These experimental results suggest the excellent
electrocatalytic properties of 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> toward the oxidation of glucose. The oxidation
of glucose at the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array
CFP electrode was electrocatalyzed by the NiO(OH)/Ni(OH) 2
redox couple, according to the following reactions (eqn (3)
and (4)): 80 NiðOHÞ 2
þ OH $ NiOOH þ H 2 O þ e ð3Þ
NiOOH þ glucose ! NiðOHÞ 2
þ glucolactone
The significant increase of the anodic peak current contributes
to the excellent electrocatalytic activity of Ni(OH) 2 in the
3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> on glucose oxidation,
which is accompanied by the oxidation of Ni 2+ to Ni 3+ ,asin
eqn (3). In addition, because of the absorption of glucose and
the oxidized intermediates on the active sites in mesopores of
the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array based electrode,
the anodic peak potential shifts to a little positive direction. 81
It is also ascribed to the diffusion limitation of glucose at the
electrode surface; 67 these results are consistent with the previous
Ni based literature. 67,80,81
Further, Fe acted as a synergistic catalyst to enhance the
electrocatalytic oxidation of glucose in the bimetallic Ni–Fe
ð4Þ
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 6 (A) CVs of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode in 0.1 M NaOH solution with (a) and without (b) 0.25 mM glucose. The
CVs obtained for the bare CFP electrode in 0.1 M NaOH containing 0.25 mM glucose for comparison (c). (B) CVs of the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array CFP electrode in a 0.1 M NaOH solution containing different concentrations of glucose. The scan rate of 50 mV s −1 is used for the
above (A) and (B) experiments. (C) CVs of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode in 0.25 mM glucose at various scan rates, and
the inset shows plots of peak currents versus the square root of the scan rate. (D) CVs of 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP (a), 3-D/Ni–Fe
hierarchical nanosphere CFP (b), and 3-D/Ni–Fe porous nanosphere CFP (c) electrodes in 0.1 M NaOH solution containing 0.25 mM glucose.
based nanoparticle system. 1,2,8 Importantly, the increased concentration
of Fe content in the bimetallic system has increased
the overall electrocatalytic reaction to some extent; 1,2,8 however
in our case the morphology of Ni–Fe nanostructures has also
played an important role. We further conducted chronoamperometric
measurements to evaluate the catalytic rate constant
(k cat ); when the oxidation current is dominated by the
rate of the electrocatalytic reaction, the catalytic current (I cat )
can be written as eqn (5).
I cat =I L ¼ π 1=2 ðk cat C 0 tÞ 1=2
where I cat and I L are the currents in the presence and absence
of glucose, respectively; k cat is the catalytic rate constant
(M −1 s −1 ), C 0 the bulk concentration (M) of glucose, and t the
ð5Þ
elapsed time (s). Based on the slope of I cat /I L vs. t 1/2 , the k cat
value is calculated to be 1.80 × 10 3 M −1 s −1 taking the glucose
concentration C 0 = 0.25 mM into account for the 3-D/Ni–Fe
hierarchical <strong>nanosheet</strong> array CFP electrode, while the k cat
obtained on the bare CFP electrode is calculated to be 0.31 ×
10 3 M −1 s −1 . Fig. 6B displays the CVs of the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array CFP electrode in 0.1 M NaOH containing
different concentrations of glucose (from 0.05 to 0.5 mM) at a
scan rate of 50 mV s −1 . Upon successive additions of glucose, a
remarkable current and potential increase of the anodic peak
is obviously observed; this indicates that the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array CFP electrode has good sensitivity.
Fig. 6C shows the effect of the scan rate on glucose oxidation
at the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode in
0.1 M NaOH containing 0.25 mM glucose. It can be seen that
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
the anodic peak shows a slightly positive shift, and the cathodic
peak shifts negatively with the increase in scan rate. These
results indicate that the redox reaction of Ni(OH) 2 on the
surface of carbon fiber is rapid and reversible. Moreover, the
anodic peak potential shifts positively, suggesting that there is
a kinetic limitation in the reaction of glucose oxidation. 44 The
inset of Fig. 6C shows that both anodic and cathodic peak currents
from the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP
electrode linearly scale with the square root of the scan rate,
indicating that the redox reaction of Ni(OH) 2 at the CFP
surface is a typical diffusion-controlled electrochemical
process. 82 To compare the electrochemical performance of the
3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array based CFP electrode,
CVs of the 3-D/Ni–Fe hierarchical nanosphere CFP and 3-D/Ni–
Fe porous nanosphere CFP electrodes were measured in 0.1 M
NaOH electrolyte containing 0.25 mM glucose at a scan rate of
50 mV s −1 , and the corresponding CV is shown in Fig. 6D. The
CV analysis shows three peaks at 0.57, 0.60, and 0.62 V for 3-D/
Ni–Fe interconnected hierarchical <strong>nanosheet</strong>s, Ni–Fe nanospheres
and porous Ni–Fe nanospheres, respectively. The 3-D/
Ni–Fe interconnected hierarchical <strong>nanosheet</strong>s show the lowest
overpotential and the highest oxidation current, 310 µA vs. 260
and 230 µA for Ni–Fe nanospheres and porous Ni–Fe nanospheres,
respectively. It can be seen that the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array CFP electrode (Fig. 6D, curve a)
showed enhanced electrocatalytic response towards the oxidation
of glucose in contrast to the 3-D/Ni–Fe hierarchical
nanosphere CFP (Fig. 6D, curve b), and 3-D/Ni–Fe porous
nanosphere CFP (Fig. 6D, curve c) electrodes due to a large
specific (active) surface area, and the interconnected wall-like
configuration of <strong>nanosheet</strong>s provided an ideal platform for
accessing a large amount of glucose molecules. Overall, the
observed higher electrocatalytic activity of 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> can be explained as: (i) the nanostructure
of 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> offers a large
specific (active) surface area; (ii) the interconnected wall-like
configuration and good electronic conductivity of 3-D/Ni–Fe
<strong>nanosheet</strong>s could support and provide reliable electrical connections
towards the glucose molecules; (iii) their compatibility,
i.e. 3-D/Ni–Fe <strong>nanosheet</strong>s can be directly grown on the
current collector (CFP), makes them self-supporting nanostructures,
(iv) 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>s as active
materials possess high electrochemical activity and contribute
considerably compared to the other morphologies.
3.3 Application of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array
CFP electrode in non-enzymatic glucose sensing
The simple fabrication procedure makes the as-prepared electrode
an effective platform for the amperometric determination
of glucose. Considering that the applied potential can
strongly affect the amperometric response of biosensors, we
have systemically investigated the impact of applied potential
on the amperometric response at the hierarchical 3-D/Ni–Fe
<strong>nanosheet</strong> array CFP electrode to glucose. The results indicate
that with the applied potential shifting from 0.60 to 0.70 V (in
0.05 V steps), the steady-state current increases and reaches a
maximum at 0.65 V; at the same time, applied potentials of
0.60 and 0.70 V can also cause a notable enhancement of the
current response per addition of glucose. Importantly, the
smaller background current and lower noise observed at an
optimized applied potential due to the glucose oxidation
process was efficiently completed at this potential, and thus
the applied potential of 0.65 V was selected for glucose detection.
Fig. 7A shows the amperometric response of the 3-D/Ni–
Fe hierarchical <strong>nanosheet</strong> array CFP electrode towards the successive
stepwise additions of glucose to a homogeneously
stirred 0.1 M NaOH solution at a working potential of
0.65 V. A steep increase in current responses was obtained
after each addition of 0.5 μM glucose solution, and a steadystate
current was achieved within 2 s, indicating that the 3-D/
Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode exhibits
extremely sensitive and rapid response characteristics. This
might be due to the fact that 3-D interconnected mesopores in
the walls provide low resistance and promote electron transfer
to reduce the response time. 67 The corresponding calibration
curve presented in Fig. 7B is linear over a concentration range
from 0.5 μM to 10.5 μM glucose with a correlation coefficient
of 0.9981. The sensitivity of the hierarchical 3-D/Ni–Fe
<strong>nanosheet</strong> array CFP electrode is calculated to be
7.90 μA μM −1 cm −2 . It was further noted that the current
response increases accordingly when the concentration of
glucose continuously increases up to 200 μM (Fig. 7C) with a
correlation coefficient of 0.9902 (Fig. 7D), indicating that all
active sites of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP
electrode were highly sensitive at higher concentration of
glucose. Based on a signal-to-noise ratio of 3 (S/N = 3), the
detection limit (LOD) was 0.031 μM calculated from the standard
deviation of amperometric baseline currents, suggesting
the very good sensitivity of the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array CFP electrode.
In order to evaluate the performance of the sensor, a comparison
of 3-D/Ni–Fe hierarchical nanosphere CFP and 3-D/
Ni–Fe porous nanosphere CFP electrodes towards the nonenzymatic
glucose sensor is shown in ESI Fig. S4A.† It can be
observed that the sensitivities of 3-D/Ni–Fe hierarchical nanosphere
CFP (curve a) and 3-D/Ni–Fe porous nanosphere
(curve b) CFP electrodes were 3.10, and 2.60 μA μM −1 cm −2 ,
respectively. We consider that the excellent electrocatalytic
activity of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode
should be attributed to the fact that the 3-D interconnected
wall-like nanostructures with abundant mesopores
and holes expanding from the surface to the bottom not only
facilitate transport of glucose molecules through the electrolyte/electrode
interface, but also allow them to come into
contact with more active surfaces (vide supra). Table S1† summarizes
the non-enzymatic glucose detection performance
with different Ni- or Fe-based electrodes reported so far. It can
be concluded that our 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array
CFP electrode possesses a higher sensitivity and a larger linear
range toward glucose detection. These superiorities were
attributed to the fact that the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>
<strong>arrays</strong> combined the synergistic effects from Fe, which results
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
Fig. 7 Amperometric response of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode at an applied potential of 0.65 V in 0.1 M NaOH with
the dropwise addition of 0.5 μM glucose (A), and the corresponding calibration plot of the obtained current response vs. glucose concentration (B).
Typical amperometric response of the 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array CFP electrode at 0.65 V with the successive additions of glucose up
to 200 μM in 0.1 M NaOH (C) and the corresponding calibration plot of the obtained current response vs. glucose concentration (D).
in high electrocatalytic activity and the electrical network
formed directly on the CFP surface. Moreover, well dispersed
Ni–Fe <strong>nanosheet</strong>s on the surface of CFP can favour the easy
access of glucose to <strong>nanosheet</strong>s, which significantly enhanced
the electrochemical response towards glucose oxidation. We
recorded the amperometric responses of 0.5 μM glucose (steps
a, b, g, k, l, and m), 250 μM of ascorbic acid (AA, step c), dopamine
(DA, step d), uric acid (UA, step e), acetaminophen (AP,
step f), fructose (step h), galactose (step i), and lactose (step j)
in homogeneously stirred 0.1 M NaOH solution, as shown in
Fig. S4B.† It was found that 3-D/Ni–Fe hierarchical <strong>nanosheet</strong>
<strong>arrays</strong> provide remarkable responses only for glucose
oxidation, and there is no obvious amperometric current
response for interfering species as compared to glucose, agreeing
well with the Ni based electrodes. 53,83
In order to verify the reliability of the non-enzymatic
glucose sensor for routine analysis, the sensor was employed
to determine glucose in blood serum samples. A commercial
One-Touch Ultra glucometer (Johnson & Johnson Medical, Ltd)
was used as the standard tool to check the reliability in hospitals.
In the current clinical practice, plasma rather than whole
blood was used to determine the concentration of glucose. The
levels of glucose in plasma are usually 10–15% higher than
glucose in the whole blood. In other words, [glucose] blood =
[glucose] plasma /1.14. 84 Through conversion, the results are
listed in Tables S2 and S3.† It can be found that the values
of glucose in human whole blood with the proposed sensing
electrode compared favourably to results obtained from the
hospital. In general, the proposed method provided decreased
analysis volume and an inexpensive and portable detection
platform. More importantly, it has been shown to offer an
accurate determination of glucose in real samples without any
separation procedure.
4. Conclusions
We demonstrated the direct growth of 3-D/Ni–Fe interconnected
hierarchical <strong>nanosheet</strong>s, hierarchical nanospheres, and
porous nanospheres on a flexible CFP substrate by a singlestep
hydrothermal process. Among the nanostructures, 3-D/
Ni–Fe interconnected hierarchical <strong>nanosheet</strong>s showed excellent
electrochemical properties because of their high conductivity,
large specific surface area and mesopores on their walls.
The 3-D/Ni–Fe hierarchical <strong>nanosheet</strong> array modified CFP substrate
was successfully explored as a novel electrode for electrochemical
non-enzymatic glucose sensor application. The 3-D/
Ni–Fe hierarchical <strong>nanosheet</strong> <strong>arrays</strong> exhibit significant
improvement in the electrochemical oxidation of glucose,
as compared to the 3-D/Ni–Fe hierarchical nanospheres, and
porous nanospheres. Moreover, 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> possessed wide linear glucose concentration
ranging from 0.05 µM to 200 µM, higher sensitivity
This journal is © The Royal Society of Chemistry 2015
Nanoscale

View Article Online
Paper
Nanoscale
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
(7.90 μA μM −1 cm −2 ) and the lowest detection limit (LOD) of
0.031 µM (S/N = 3). Further, the 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> array modified CFP electrode can be demonstrated
to have excellent selectivity towards the detection of glucose in
the presence of 500-fold excess of major important interferents.
All these results indicate that 3-D/Ni–Fe hierarchical
<strong>nanosheet</strong> <strong>arrays</strong> are a promising candidate for non-enzymatic
glucose sensing.
Acknowledgements
Palanisamy Kannan thanks the NanOtechnology Biomaterials
and aLternative Energy Source for ERA Integration [FP7-
REGPOT-CT-2011-285949-NOBLESSE] project for financial
support.
References
1 J. Li, W. Tang, H. Yang, Z. Dong, J. Huang, S. Li, J. Wang,
J. Jin and J. Ma, RSC Adv., 2014, 4, 1988–1995.
2 H. Yang, X. Zhong, Z. Dong, J. Wang, J. Jin and J. Ma, RSC
Adv., 2012, 2, 5038–5040.
3 B. Nikoobakht, Z. L. Wang and M. A. El-Sayed, J. Phys.
Chem. B, 2000, 104, 8635–8640.
4 Z. Liu, S. W. Tay and X. Li, Chem. Commun., 2011, 47,
12473–12475.
5 F.-z. Mou, J.-g. Guan, Z.-g. Sun, X.-a. Fan and G.-x. Tong,
J. Solid State Chem., 2010, 183, 736–743.
6 Y. Leng, Y. Li, X. Li and S. Takahashi, J. Phys. Chem. C,
2007, 111, 6630–6633.
7 K.-L. Wu, R. Yu and X.-W. Wei, CrystEngComm, 2012, 14,
7626–7632.
8 Z. Lu, W. Xu, W. Zhu, Q. Yang, X. Lei, J. Liu, Y. Li, X. Sun
and X. Duan, Chem. Commun., 2014, 50, 6479–6482.
9 G. Tong, J. Guan, Z. Xiao, F. Mou, W. Wang and G. Yan,
Chem. Mater., 2008, 20, 3535–3539.
10 J. Jia, J. C. Yu, Y.-X. J. Wang and K. M. Chan, ACS Appl.
Mater. Interfaces, 2010, 2, 2579–2584.
11 R. Ding, J. Liu, J. Jiang, J. Zhu and X. Huang, Anal.
Methods, 2012, 4, 4003–4008.
12 W. Zhou, L. He, R. Cheng, L. Guo, C. Chen and J. Wang,
J. Phys. Chem. C, 2009, 113, 17355–17358.
13 J. Li, W. Tang, J. Huang, J. Jin and J. Ma, Catal. Sci.
Technol., 2013, 3, 3155–3162.
14 H. Ma, Y. Huang, M. Shen, D. Hu, H. Yang, M. Zhu,
S. Yang and X. Shi, RSC Adv., 2013, 3, 6455–6465.
15 R. Suresh, K. Giribabu, R. Manigandan, A. Stephen and
V. Narayanan, RSC Adv., 2014, 4, 17146–17155.
16 N. Wang, M. Wen and Q. Wu, Colloids Surf., B, 2013, 111,
726–731.
17 J. Wang, Z. Dong, J. Huang, J. Li, X. Jin, J. Niu, J. Sun, J. Jin
and J. Ma, Appl. Surf. Sci., 2013, 270, 128–132.
18 L. Liu, J. Guan, W. Shi, Z. Sun and J. Zhao, J. Phys. Chem. C,
2010, 114, 13565–13570.
19 B. Singh, C.-L. Ho, Y.-C. Tseng and C.-T. Lo, J. Nanopart.
Res., 2012, 14, 1–12.
20 X.-M. Zhou and X.-W. Wei, Cryst. Growth Des., 2008, 9,
7–12.
21 H. Wang and A. L. Rogach, Chem. Mater., 2013, 26, 123–
133.
22 M. De Volder and A. J. Hart, Angew. Chem., Int. Ed., 2013,
52, 2412–2425.
23 Z. Ren, Y. Guo, C.-H. Liu and P.-X. Gao, Front. Chem., 2013,
1(18), 1–22.
24 P. Gao, M. Zhang, H. Hou and Q. Xiao, Mater. Res. Bull.,
2008, 43, 531–538.
25 J. P. Xiao, Y. Xie, R. Tang, M. Chen and X. B. Tian, Adv.
Mater., 2001, 13, 1887–1891.
26 Q. Yang, T. Li, Z. Lu, X. Sun and J. Liu, Nanoscale, 2014, 6,
11789.
27 S. Cai, D. Zhang, L. Shi, J. Xu, L. Zhang, L. Huang, H. Li
and J. Zhang, Nanoscale, 2014, 6, 7346–7353.
28 X.-W. Wei, G.-X. Zhu, J.-H. Zhou and H.-Q. Sun, Mater.
Chem. Phys., 2006, 100, 481–485.
29 Z. W. Pan, Z. R. Dai and Z. L. Wang, Science, 2001, 291,
1947–1949.
30 D. Banerjee, J. Y. Lao, D. Z. Wang, J. Y. Huang, D. Steeves,
B. Kimball and Z. F. Ren, Nanotechnol, 2004, 15, 404–
409.
31 B. Yang, Y. Wu, B. Zong and Z. Shen, Nano Lett., 2002, 2,
751–754.
32 X. Zhang, A. Gu, G. Wang, Y. Huang, H. Ji and B. Fang,
Analyst, 2011, 136, 5175–5180.
33 J. Wang, Chem. Rev., 2007, 108, 814–825.
34 A. Heller and B. Feldman, Chem. Rev., 2008, 108, 2482–
2505.
35 N. Mitro, P. A. Mak, L. Vargas, C. Godio, E. Hampton,
V. Molteni, A. Kreusch and E. Saez, Nature, 2007, 445, 219–
223.
36 J. Shi, H. Zhang, A. Snyder, M.-x. Wang, J. Xie, D. Marshall
Porterfield and L. A. Stanciu, Biosens. Bioelectron., 2012, 38,
314–320.
37 Y. Huang, X. Dong, Y. Shi, C. M. Li, L.-J. Li and P. Chen,
Nanoscale, 2010, 2, 1485–1488.
38 G. Rocchitta, O. Secchi, M. D. Alvau, D. Farina, G. Bazzu,
G. Calia, R. Migheli, M. S. Desole, R. D. O’Neill and
P. A. Serra, Anal. Chem., 2013, 85, 10282–10288.
39 Y. Song, K. Qu, C. Zhao, J. Ren and X. Qu, Adv. Mater.,
2010, 22, 2206–2210.
40 E. S. Forzani, H. Zhang, L. A. Nagahara, I. Amlani, R. Tsui
and N. Tao, Nano Lett., 2004, 4, 1785–1788.
41 M. D. Gouda, S. A. Singh, A. G. A. Rao, M. S. Thakur and
N. G. Karanth, J. Biol. Chem., 2003, 278, 24324–24333.
42 P. Subramanian, J. Niedziolka-Jonsson, A. Lesniewski,
Q. Wang, M. Li, R. Boukherroub and S. Szunerits, J. Mater.
Chem. A, 2014, 2, 5525–5533.
43 C. Guo, H. Huo, X. Han, C. Xu and H. Li, Anal. Chem.,
2013, 86, 876–883.
44 X. Niu, M. Lan, H. Zhao and C. Chen, Anal. Chem., 2013,
85, 3561–3569.
Nanoscale This journal is © The Royal Society of Chemistry 2015

View Article Online
Nanoscale
Paper
Published on 18 November 2015. Downloaded by New York University on 21/11/2015 05:38:08.
45 X.-C. Dong, H. Xu, X.-W. Wang, Y.-X. Huang, M. B. Chan-
Park, H. Zhang, L.-H. Wang, W. Huang and P. Chen, ACS
Nano, 2012, 6, 3206–3213.
46 H. Pang, Q. Lu, J. Wang, Y. Li and F. Gao, Chem. Commun.,
2010, 46, 2010–2012.
47 M. Shamsipur, M. Najafi and M.-R. M. Hosseini, Bioelectrochemistry,
2010, 77, 120–124.
48 J. Wang, D. F. Thomas and A. Chen, Anal. Chem., 2008, 80,
997–1004.
49 C. Li, Y. Liu, L. Li, Z. Du, S. Xu, M. Zhang, X. Yin and
T. Wang, Talanta, 2008, 77, 455–459.
50 Q. Chen, J. Wang, G. Rayson, B. Tian and Y. Lin, Anal.
Chem., 1993, 65, 251–254.
51 T. You, O. Niwa, Z. Chen, K. Hayashi, M. Tomita and
S. Hirono, Anal. Chem., 2003, 75, 5191–5196.
52 J. Chen, W.-D. Zhang and J.-S. Ye, Electrochem. Commun.,
2008, 10, 1268–1271.
53 L.-M. Lu, L. Zhang, F.-L. Qu, H.-X. Lu, X.-B. Zhang,
Z.-S. Wu, S.-Y. Huan, Q.-A. Wang, G.-L. Shen and R.-Q. Yu,
Biosens. Bioelectron., 2009, 25, 218–223.
54 C. Li, Y. Su, S. Zhang, X. Lv, H. Xia and Y. Wang, Biosens.
Bioelectron., 2010, 26, 903–907.
55 Y. Liu, Y. Zhang, T. Wang, P. Qin, Q. Guo and H. Pang, RSC
Adv., 2014, 4, 33514–33519.
56 B. Zhan, C. Liu, H. Chen, H. Shi, L. Wang, P. Chen,
W. Huang and X. Dong, Nanoscale, 2014, 6, 7424–7429.
57 H. Liu, X. Lu, D. Xiao, M. Zhou, D. Xu, L. Sun and Y. Song,
Anal. Methods, 2013, 5, 6360–6367.
58 C. Guo, X. Zhang, H. Huo, C. Xu and X. Han, Analyst, 2013,
138, 6727–6731.
59 D. Xiang, L. Yin, J. Ma, E. Guo, Q. Li, Z. Li and K. Liu,
Analyst, 2015, 140, 644–653.
60 D. Kong, H. Wang, Z. Lu and Y. Cui, J. Am. Chem. Soc.,
2014, 136, 4897–4900.
61 J. Xiao, L. Wan, S. Yang, F. Xiao and S. Wang, Nano Lett.,
2014, 14, 831–838.
62 L. Huang, D. Chen, Y. Ding, S. Feng, Z. L. Wang and
M. Liu, Nano Lett., 2013, 13, 3135–3139.
63 J. T. Sampanthar and H. C. Zeng, J. Am. Chem. Soc., 2002,
124, 6668–6675.
64 L.-P. Zhu, H.-M. Xiao, W.-D. Zhang, Y. Yang and S.-Y. Fu,
Cryst. Growth Des., 2008, 8, 1113–1118.
65 H. G. Yang and H. C. Zeng, J. Phys. Chem. B, 2004, 108,
3492–3495.
66 L. Seymour, E. S. Joan, A. T. Martin and T. Matthias,
Characterization of Porous Solids and Powders: Surface Area,
Pore Size and Density, Particle Technology Series, Springer,
Netherlands, 2004, 16, 1–350.
67 H. Nie, Z. Yao, X. Zhou, Z. Yang and S. Huang, Biosens.
Bioelectron., 2011, 30, 28–34.
68 Y. Chen, X. Luo, G.-H. Yue, X. Luo and D.-L. Peng, Mater.
Chem. Phys., 2009, 113, 412–416.
69 M. N. Islam, M. Abbas and C. Kim, Curr. Appl. Phys., 2013,
13, 2010–2013.
70 X. Teng and H. Yang, J. Mater. Chem., 2004, 14, 774–
779.
71 P. Kannan, T. Maiyalagan, N. G. Sahoo and M. Opallo,
J. Mater. Chem. B, 2013, 1, 4655–4666.
72 D. Yang, A. Velamakanni, G. Bozoklu, S. Park, M. Stoller,
R. D. Piner, S. Stankovich, I. Jung, D. A. Field,
C. A. Ventrice Jr. and R. S. Ruoff, Carbon, 2009, 47, 145–
152.
73 H. Yan, J. Bai, J. Wang, X. Zhang, B. Wang,
Q. Liu and L. Liu, CrystEngComm, 2013, 15, 10007–
10015.
74 J. W. Lee, T. Ahn, D. Soundararajan, J. M. Ko and J.-D. Kim,
Chem. Commun., 2011, 47, 6305–6307.
75 H. W. Nesbitt, D. Legrand and G. M. Bancroft, Phys. Chem.
Miner., 2000, 27, 357–366.
76 N. Wang, M. Wen and Q. Wu, Colloids Surf., B, 2013, 111,
726–731.
77 Y. Zhang, F. Xu, Y. Sun, Y. Shi, Z. Wen and Z. Li, J. Mater.
Chem., 2011, 21, 16949–16954.
78 Y. Liu, H. Teng, H. Hou and T. You, Biosens. Bioelectron.,
2009, 24, 3329–3334.
79 M. Giovanni, A. Ambrosi and M. Pumera, Chem. – Asian J.,
2012, 7, 702–706.
80 Y. Jiang, S. Yu, J. Li, L. Jia and C. Wang, Carbon, 2013, 63,
367–375.
81 L. Zheng, J.-q. Zhang and J.-f. Song, Electrochim. Acta, 2009,
54, 4559–4565.
82 M. Tyagi, M. Tomar and V. Gupta, Biosens. Bioelectron.,
2014, 52, 196–201.
83 S. Yu, X. Peng, G. Cao, M. Zhou, L. Qiao, J. Yao and H. He,
Electrochim. Acta, 2012, 76, 512–517.
84 R. Haeckel, U. Brinck, D. Colic, H.-U. Janka, I. Püntmann,
J. Schneider and C. Viebrock, Clin. Chem., 2002, 48, 936–
939.
This journal is © The Royal Society of Chemistry 2015
Nanoscale