Sensitive and selective nonenzymatic glucose detection using functional NiO-Pt hybrid nanofibers

Article abstract of DOI:10.1016/j.electacta.2011.09.039

By calcining electrospun Ni(NO₃)₂-H ₂PtCl₆-PVP composite nanofibers, Pt-doped NiO nanofibers have been successfully fabricated. Their morphologies were characterized using scanning electron microscopy and transmission electron microscopy, and structures were analyzed by X-ray diffraction. Tiny Pt nanoparticles (<10 nm) were dispersed in NiO matrix and the whole nanofiber displayed a rough surface and porous structure. The as-prepared hybrid nanofibers were employed for nonenzymatic glucose detection in alkaline electrolyte and showed greatly improved electrocatalytic activity compared to those obtained with pure NiO nanofibers and Pt nanofibers, with higher sensitivity (180.80 μA mM ^-1 cm^-2), lower detection limit (313 nM), and good linear range (up to 3.67 mM). These results suggest that electrospun NiO-Pt hybrid nanofibers are a promising nanomaterial for design and fabrication of electrochemical devices for glucose detection.

Full text of DOI:10.1016/j.electacta.2011.09.039

Electrochimica Acta 58 (2011) 209–214
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Sensitive and selective nonenzymatic glucose detection using functional NiO–Pt
hybrid nanofibers
Yu Dinga, Yixin Liua, Lichun Zhangb, Ying Wanga, Michael Bellagambaa, Joseph Parisia, Chang Ming Lic,
Yu Leia,∗
a Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, CT 06269-3222, USA
b Institute of Material Science, University of Connecticut, Storrs, CT 06269-3222, USA
c School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 637457, Singapore
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 16 June 2011
Received in revised form 29 August 2011
Accepted 14 September 2011
Available online 24 September 2011
By calcining electrospun Ni(NO3)2–H2PtCl6–PVP composite nanofibers, Pt-doped NiO nanofibers have
been successfully fabricated. Their morphologies were characterized using scanning electron microscopy
and transmission electron microscopy, and structures were analyzed by X-ray diffraction. Tiny Pt
nanoparticles (<10 nm) were dispersed in NiO matrix and the whole nanofiber displayed a rough sur-
face and porous structure. The as-prepared hybrid nanofibers were employed for nonenzymatic glucose
detection in alkaline electrolyte and showed greatly improved electrocatalytic activity compared to those
obtained with pure NiO nanofibers and Pt nanofibers, with higher sensitivity (180.80 ␮A mM−1 cm−2),
lower detection limit (313 nM), and good linear range (up to 3.67 mM). These results suggest that electro-
spun NiO–Pt hybrid nanofibers are a promising nanomaterial for design and fabrication of electrochemical
devices for glucose detection.
Keywords:
NiO–Pt nanofibers
Glucose sensor
Electrospinning
Nonenzymatic
© 2011 Elsevier Ltd. All rights reserved.
1. Introduction
nanoporous Pt–Pb alloy networks [7], Pt–Pb alloy nanoparticles
deposited on carbon nanotubes [8] and Pt–WO3 composite wire
In recent years, considerable attention has been paid to develop
stable and sensitive enzyme-free electrodes to replace the enzyme
(glucose oxidase or glucose dehydrogenase) based glucose sensors
which usually suffer from stability problems due to the intrin-
sic features of proteins. Precious metals such as Pt and Au have
been extensively studied in the construction of nonenzymatic elec-
trochemical glucose sensors [1,2]. However, conventional Pt and
Au electrodes are easily poisoned by the adsorbed intermediates
and chloride, leading to low sensitivity. In addition, glucose detec-
tion at these electrodes is easily interfered by other electroactive
compounds such as ascorbic acid (AA) and uric acid (UA) [3]. Vari-
eties of nanostructured Pt has been synthesized to enhance the
sensing performance, such as mesoporous Pt [4], highly ordered
Pt-nanotubes arrays [5] and three dimensional ordered macrop-
orous Pt [6]. It has been reported that sensitivity, selectivity and
anti-fouling property may be improved by increasing the ratio of
nanoscopic surface area to the geometric surface area (roughness
factor) [4]. On the other hand, several Pt composites have also been
investigated to address the poisoning issue and improve sensitiv-
ity, including Pt nanoparticles supported on carbon nanotubes [1],
[9]. Earlier studies also indicate the modification of Pt surfaces by
other metals such as Tl, Bi, and Pb may alter the adsorption and oxi-
dation route, leading to improved electrocatalytic activity towards
glucose oxidation [7].
In this work, we fabricated a novel hybrid nanofiber consisting of
Pt and NiO by the facile electrospinning technique followed by cal-
cination. Electrospinning is a relatively simple and versatile method
for fabricating nanofibers, which is originally applied to pure
organic polymers [10]. Recently this technique has been extended
to produce metal oxide or noble metal nanofibers by calcination of
polymer composite nanofibers containing the corresponding metal
salts. A series of metal oxide nanofibers, such as CuO [3,11], ZnO
[12], Co3O4 [13,14], NiO [15] and TiO2 [10,16], and noble metal
nanofibers such as Ag [17], Au [18] and Pt [19] have been devel-
oped following this two-step procedure. NiO has been reported as
a good catalyst for glucose electrooxidation in alkaline medium,
which has negligible intermediates- or chloride-associated poison-
ing issue [3,15]. To prepare Pt-doped NiO nanofibers, Ni(NO3)2 and
H2PtCl6 were co-dissolved in poly(vinyl pyrrolidone) (PVP) solu-
tion and electrospun to generate precursory composite nanofibers.
After calcination in air at 500 ◦C for 3 h, the polymer matrix was
completely degraded and Ni(NO3)2 was decomposed to NiO while
H2PtCl6 was converted to Pt, since noble metal tends to stay in a
zero oxidation state. Pt nanoparticles were well distributed in/on
∗
Corresponding author. Tel.: +1 860 486 4554; fax: +1 860 486 2959.
E-mail address: ylei@engr.uconn.edu (Y. Lei).
0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2011.09.039

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Y. Ding et al. / Electrochimica Acta 58 (2011) 209–214
Fig. 1. SEM images of (A) Ni(NO3)2–H2PtCl6–PVP nanofibers electrospun from PVP sol–gel in ethanol–water containing Ni(NO3)2 and H2PtCl6; (B) NiO–Pt nanofibers; inset
shows a SEM image with higher magnification.
the NiO nanofibers. The as-prepared hybrid nanofibers were then
employed for glucose detection in alkaline electrolyte and the com-
bination of NiO and Pt was expected to offer a synergistic effect
between individual components: on one hand, the NiO matrix can
prevent the adsorption of poisoning species on the Pt surfaces; on
the other hand, the Pt dopants may provide more opportunities for
electron transfer due to its good electron conductivity.
2.3. Apparatus and electrochemical measurements
A JEOL 6335F field-emission scanning electron microscope
(SEM) was employed to examine the morphology and the size
of the as-electrospun nanofibers before and after calcination.
More detailed morphology and selected area electron diffraction
(SAED) patterns were studied using a Tecnai T12 transmission elec-
tron microscope (TEM) operated at 120 kV. High resolution TEM
images were obtained at a JEOL 2010 FasTEM. XRD patterns of
the as-prepared samples were obtained with an Oxford diffrac-
tion XcaliburTM PX Ultra with ONYX detector. Cyclic voltammetry
(CV) measurements were performed on a Model CHI 601C Electro-
chemical Workstation (CH Instruments, USA). All electrochemical
experiments were conducted using a three-electrode electrochem-
ical cell (a working volume of 5 mL) with a working electrode, an
Ag/AgCl (3 M KCl) reference electrode, and a platinum wire counter
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 steady-state value, before the addition of the analyte. A stirred
solution was employed to provide convective transport.
2. Experimental
2.1. Reagents
Nickel nitrate hexahydrate (Ni(NO3)2·6H2O), hydrogen
hexachloroplatinate(IV) hexahydrate (H2PtCl6·6H2O) and d-(+)-
glucose were purchased from Acros Organics. Sodium hydroxide
(NaOH) was supplied by Fisher Scientific. Poly(vinyl pyrrolidone)
(PVP, MW = 1,300,000) and Nafion® perfluorinated resin solution
(20 wt% in lower aliphatic alcohols and water, containing 34%
water) were obtained from Sigma–Aldrich. All aqueous solutions
were prepared with deionized water (18.2 Mꢀ cm) generated by a
Barnstead water system.
3. Results and discussion
2.2. Preparation of NiO–Pt nanofibers modified electrode
3.1. Characterization of the nanofibers before and after
calcination
0.4 g Ni(NO3)2·6H2O and 0.1 g H2PtCl6·6H2O were dissolved in
1.6 g water and then mixed with a 2.8 g solution consisting of
0.4 g PVP and 2.4 g ethanol. The Ni(NO3)2–H2PtCl6–PVP compos-
ite nanofibers were prepared using a 23-gauge needle with a flow
rate of 0.3 mL/h at an applied voltage of 20 kV over a gap distance of
15 cm and were collected on aluminum foil. The precursor was then
calcined under air atmosphere at 500 ◦C for 3 h in order to remove
the polymer matrix and generate NiO–Pt nanofibers. In order to
prepare stable H2PtCl6–PVP sol–gel and produce Pt nanofibers
with good morphology, 0.3864 g H2PtCl6·6H2O and 0.3864 g PVP
were dissolved in 4.5 mL DMF/H2O (3 mL DMF plus 0.5 mL H2O).
To prepare 5 mg/mL NiO–Pt nanofibers suspension, 5 mg NiO–Pt
nanofibers was first suspended in 1 mL ethanol and sonicated for
1 h, and then a 5 ␮L suspension was dropped onto the surface of
glassy carbon electrode (GCE). After drying in air, an aliquot of 5 ␮L
Nafion solution (1 wt% in ethanol) was cast on the layer of NiO–Pt
nanofibers in order to entrap NiO–Pt nanofibers. The as-prepared
electrode (denoted as NiO–Pt NFs/GCE) was immersed in water for
1 h to wet the Nafion layer thoroughly before use. Similar proce-
dure was also applied to prepare NiO or Pt nanofibers modified
GCEs (NiO NFs/GCE and Pt NFs/GCE).
Fig. 1A shows the SEM image of Ni(NO3)2–H2PtCl6–PVP compos-
ite nanofibers electrospun from PVP sol–gel containing Ni(NO3)2
and H2PtCl6 using ethanol–water as the solvent. Each nanofiber was
uniform with an average diameter of 464 27 nm. The formation
of this type of quasi-one dimensional structure may be attributed
to the high concentration of metal salts contained in sol–gel, which
may lead to the incomplete drying of the inner part of ejected fibers
before reaching the collector; while the skin on the surface easily
became dry due to the rapid evaporation of solvent. The collapse of
the skin caused the fibers to have a flat shape [20,21]. The SEM mor-
phology of the calcined sample is presented in Fig. 1B, indicating
the continuous and flat nanofiber structure is still kept, while the
surfaces become rough (clearly shown in the inset) and the average
diameter decreases to 214 77 nm.
The detailed morphology of the as-prepared NiO–Pt nanofibers
was further characterized by TEM. Fig. 2A reveals that the
nanofibers consist of numerous nanoparticles which possess large
surface area and minimize transport hindrance for subsequent cat-
alytic reactions [3]. The rings displayed in selected area electron

Y. Ding et al. / Electrochimica Acta 58 (2011) 209–214
211
Fig. 2. (A) TEM image of single NiO–Pt nanofiber; insets indicate the EDX mapping of Ni and Pt element, respectively. (B) SAED pattern of the NiO–Pt nanofibers. (C) EDX
analysis of the NiO–Pt nanofibers; Cu and C peaks come from the TEM grid.
diffraction (SAED) pattern indicate the polycrystalline structure of
the hybrid nanofibers. X-ray energy dispersive spectroscopy (EDX)
was carried to analyze the compositions of the calcined sample and
the results shown in Fig. 2C imply the presence of Ni, O and Pt (Cu
and C peaks are attributed to the TEM grid). The distribution of NiO
and Pt was further characterized by EDX mapping. The two insets
in Fig. 2A display the heterogeneous and discontinuous distribu-
tion of Pt, while the distribution of NiO as the matrix is relatively
uniform and continuous. It is notable that the Pt is dispersed as tiny
dots with very small particle size (<10 nm). A high resolution TEM
(HRTEM) lattice image of the NiO–Pt nanofiber is shown in Fig. 3,
indicating the doping of tiny Pt crystallites in the NiO matrix.
The electrospinning cannot smoothly generate nanofibers
when the PVP sol–gel only containing H2PtCl6 was prepared in
ethanol/H2O as the solvent. Therefore we used a DMF/H2O system
as the solvent to dissolve PVP and H2PtCl6. Uniformly distributed,
continuous and smooth H2PtCl6–PVP composite nanofibers with
an average diameter of 190 19 nm were fabricated (Fig. 4A). After
calcination, the size of nanofibers was greatly shrunk to 39 6 nm
(Fig. 4B) and the calcined Pt nanofibers consisted of elongated Pt
nanoparticles and displayed a necklace-like structure (Fig. 4C).
In order to confirm the structure and composition of both NiO–Pt
nanofibers and Pt nanofibers, X-ray diffraction (XRD) was per-
formed. As shown in Fig. 5, the XRD spectrum of NiO–Pt composites
matches the combination of the spectra of NiO (JCPDS 04-0835)
and Pt (JCPDS 04-0802). The formation of face-centered cubic crys-
talline NiO is revealed by the diffraction peaks at 2ꢁ values of 37.28◦,
43.30◦, 62.92◦ corresponding to (1 1 1), (2 0 0) and (2 2 0) main crys-
tal planes, respectively; while the diffraction peaks at 2ꢁ values
of 39.76◦, 46.24◦, 67.45◦, which correspond to (1 1 1), (2 0 0), and
(2 2 0) crystal planes respectively, indicates the formation of cubic
crystalline Pt.
3.2. Electrochemistry behavior of NiO–Pt NFs, NiO NFs, and Pt NFs
modified GCEs
Electrooxidation of glucose at Pt nanofibers in 0.1 M NaOH
(pH = 13) was examined in the range of −0.3 V to 0.7 V. The lowest
applied potential was set at −0.3 V in order to prevent the reduc-
tion of dissolved oxygen in the solution. As shown in Fig. 6A, a
current increase (or a shoulder peak) at ca. −0.25 V is observed
Fig. 3. HRTEM lattice image of NiO–Pt nanofiber.

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Y. Ding et al. / Electrochimica Acta 58 (2011) 209–214
Fig. 4. SEM images of (A) H2PtCl6–PVP nanofibers electrospun from PVP sol–gel in DMF/H2O containing H2PtCl6; (B) Pt nanofibers. (C) TEM image of a single Pt nanofiber.
a), both CVs show a pair of well-defined redox peaks assigned
to Ni2+/Ni3+ redox couple (NiO + OH−–e− → NiO(OH)). When using
NiO–Pt hybrid nanofibers as the sensing material, the oxidation cur-
rent upon the addition of glucose obtained at potentials less than
+0.3 V was insignificant; while at the potentials above +0.3 V, the
response was rapidly increased with the applied potential, showing
similar trend with that obtained at the NiO NFs/GCE, but with much
higher current signal, which may be attributed to the excellent
electron transfer properties of the doped Pt.
In order to determine the optimum applied potential for real-
time detection, hydrodynamic voltammogram (HDV) was further
conducted by measuring the amperometric responses to 200 ␮M
glucose at different applied potentials from 0 V to 0.6 V. As
expected, the HDV of NiO–Pt showed similar shape with that of NiO,
but current responses were greatly enhanced (Fig. 7A). Oxidation
current of glucose can also be obtained in the potential range from
0.1 V to 0.3 V, illustrating the function of Pt in decreasing the onset
potential and improving the electrocatalytic sensitivity. Since the
response to glucose increased with the applied potential and too
high potential may also favor the oxidation of interference, +0.6 V
Fig. 5. XRD patterns for NiO–Pt, NiO and Pt nanofibers.
was adopted as the optimal potential for real-time detection.
Fig. 7B compares the amperometric responses of the NiO–Pt,
NiO and Pt nanofibers modified electrodes at +0.6 V with succes-
sive additions of glucose. In these three cases, current signals all
increase rapidly after each addition of glucose to the stirred solu-
tion, achieving 95% steady-state current within 4.1 s (NiO–Pt), 5.2 s
(NiO) and 5.7 s (Pt), respectively. Their sensitivity, detection limit
(S/N = 3), and linear range (obtained from calibration curves shown
in Fig. 7C) are listed and compared in Table 1. The sensitivity of
the NiO–Pt NFs/GCE is 5.5-fold greater than that obtained at the
NiO NFs/GCE and 28.8-fold of the Pt NFs/GCE. Moreover, the linear
range and the limit of detection have also been greatly improved.
The analytical parameters of the NiO–Pt NFs/GCE for nonenzymatic
in the presence of glucose, which may be attributed to the oxi-
dation of adsorbed intermediates by Pt–OH species [22,23]. This
oxidation process eliminated the adsorbed intermediates derived
from the electrochemical adsorption of glucose at lower potential
and thus released active catalytic sites for the direct oxidization of
glucose, leading to another oxidation peak at ca. +0.126 V. Further
increase of the applied potential led to the formation of platinum
oxide, which sacrificed the active sites and thus decreased the oxi-
dation current [1]. As a comparison, the CV of the NiO–Pt NFs/GCE
(Fig. 6B, trace c) was quite different from that of the Pt NFs/GCE
(Fig. 6A) but similar with that of the NiO NFs/GCE (Fig. 6B, trace
Fig. 6. (A) CVs of Pt NFs/GCE in the absence (a) and presence of 4 mM glucose (b) in 0.1 M NaOH. (B) CVs of NiO NFs/GCE (a and b) and NiO–Pt NFs/GCE (c and d) in the absence
(a and c) and presence of 4 mM glucose (b and d) in 0.1 M NaOH. The scan rate is 100 mV/s.

Y. Ding et al. / Electrochimica Acta 58 (2011) 209–214
213
Fig. 7. (A) Hydrodynamic voltammograms of 200 ␮M glucose at the NiO–Pt, NiO and Pt nanofibers modified electrodes in 0.1 M NaOH solution with a stirring rate of 300 rpm.
(B) Amperometric response of NiO–Pt NFs/GCE, NiO NFs/GCE and Pt NFs/GCE to successive additions of glucose to 0.1 M NaOH solution with a stirring rate of 300 rpm at an
applied potential of +0.6 V, respectively. (C) The calibration curves with corresponding Langmuir fitting curves.
glucose detection are among the best reported values in the liter-
ature [4,24–29]. In order to apply the developed sensor for real
samples, where commonly found glucose concentrations are in the
range of 4–7 mM, Langmuir isothermal theory is used to fit the cali-
bration curves because electrochemical oxidation of glucose on the
electrode is a surface catalytic reaction, following Langmuir isother-
mal theory [14]. The corresponding fitting equations for NiO–Pt
NFs/GCE, NiO/GCE, and Pt NFs/GCE are presented as follows:
For NiO–Pt NFs/GCE (R2 = 0.99973),
15.48Cglucose
I =
1 + 0.09548Cglucose
For NiO NFs/GCE (R2 = 0.99646),
Fig. 8. Current responses obtained at Pt NFs/GCE and NiO–Pt NFs/GCE towards 4 mM
glucose, 4 mM glucose with 0.125 mM AA, and 4 mM glucose with 0.33 mM UA in
2.970Cglucose
I =
0.1 M NaOH solution with a stirring rate of 300 rpm at an applied potential of +0.6 V.
1 + 0.1486Cglucose
For Pt NFs/GCE (R2 = 0.9981),
that the charge-exclusion property of Nafion is not the major factor
to minimize the interference in our non-enzymatic glucose detec-
tion at +0.6 V vs. Ag/AgCl (3 M KCl). The excellent selectivity of the
0.5658Cglucose
I =
1 + 0.1114Cglucose
hybrid nanofibers may be attributed to the enhanced oxidation of
glucose as well as the repelling effect of the negative surface of NiO
In this way, the developed NiO–Pt NFs/GCE can be applied to very
towards the negatively charged AA and UA in alkaline electrolyte
broad range of glucose concentration.
[15].
To evaluate the selectivity of the proposed biosensor, two inter-
The inter-electrode reproducibility of the NiO–Pt nanofibers
fering compounds, ascorbic acid (AA) and uric acid (UA), which
based sensor was further evaluated using 6 electrodes, which were
usually coexist with glucose in real samples are examined. Tak-
prepared following the same protocol. A small relative standard
ing into account the concentrations of glucose (4–7 mM), AA
deviation (R.S.D.) of 7.4% in the detections of 200 ␮M glucose
(0.125 mM) and UA (0.33 mM) in human blood [22,30], amperomet-
at +0.6 V demonstrated that the preparation method was highly
ric responses to 4 mM glucose and the same amount of glucose with
reproducible. 8 successive measurements of 200 ␮M glucose at one
0.125 mM AA or 0.33 mM UA were compared. As shown in Fig. 8,
NiO–Pt NFs/GCE yielded a R.S.D. of 6.7%, indicating excellent intra-
the presence of 0.125 mM AA and 0.33 mM UA induces 36.6% and
electrode reproducibility and stability under continuous detection.
38.7% current increase at Pt NFs/GCE, respectively; while such cur-
rent increase drops dramatically at NiO–Pt NFs/GCE (1.42% for AA
and 3.62% for UA). In order to elaborate the role of Nafion and NiO in
such good selectivity, further selectivity study was conducted using
4. Conclusions
high concentration of UA and AA (1 mM UA and 1 mM AA) as well
We have successfully fabricated NiO–Pt nanofibers using a two-
as 4 mM glucose and the result is presented in Fig. S1. One can see
step method. Pt is dispersed as tiny dots along a NiO matrix. The
effect of Pt in glucose sensing was illustrated by a comparison study
between NiO–Pt, NiO and Pt nanofibers. Results showed that the
presence of Pt nanoparticles in NiO–Pt nanofibers could greatly
improve the sensitivity of glucose detection at +0.6 V. Excellent
selectivity and reproducibility were also demonstrated. These fea-
tures indicate that the NiO–Pt hybrid nanofiber is a novel and
promising candidate for nonenzymatic glucose sensors.
Table 1
Analytical characteristics of NiO–Pt, NiO and Pt NFs/GCE at +0.6 V vs. Ag/AgCl.
NiO–Pt NFs/GCE NiO NFs/GCE Pt NFs/GCE
Linear range up to/mmol l−1
3.67
1.94
1.28
2.63
4.02
6.27
Detection limit/␮mol l−1
0.313
Sensitivity/␮A (mmol l−1
)
−1 cm−2 180.80
32.91

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Y. Ding et al. / Electrochimica Acta 58 (2011) 209–214
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
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