Enzyme-free glucose sensor based on au nanobouquet fabricated indium tin oxide electrode

Article abstract of DOI:10.1166/jnn.2014.9921

In this study, we demonstrated a simple, rapid and inexpensive fabrication method to develop a novel gold nanobouquet structure fabricated indium tin oxide (GNB/ITO) electrode based on electrochemical deposition of gold ions onto ITO substrate. The morphology of the fabricated electrode surface was characterized by scanning electron microscopy (SEM) to confirm the GNB formation. Enzyme-free detection of glucose using a GNB/ITO electrode was described with high sensitivity and selectivity based on cyclic voltammetry assay. The results demonstrate a linear relation within wide concentration range (500 nM to 10 mM) of glucose, with a correlation coefficient of 0.988.The interference effect of uric acid was effectively avoided for the detection of glucose (1 μM to10 mM). Moreover, the developed sensor was applied to determine the concentration of glucose in the presence of human serum to indicate the ability of GNB/ITO electrodes in real samples. Hence, newly developed GNB/ITO electrode has potential application in enzyme-free glucose sensor with highly sensitivity and selectivity.

Full text of DOI:10.1166/jnn.2014.9921

Article
Journal of
Nanoscience and Nanotechnology
Vol. 14, 8432–8438, 2014
Copyright © 2014 American Scientific Publishers
All rights reserved
www.aspbs.com/jnn
Printed in the United States of America
Enzyme-Free Glucose Sensor Based on Au Nanobouquet
Fabricated Indium Tin Oxide Electrode
Jin-Ho Lee1ꢀ2, Waleed Ahmed El-Said3, Byung-Keun Oh1ꢀ3, and Jeong-Woo Choi1ꢀ3ꢀ∗
1Department of Chemical and Biomolecular Engineering, Sogang University, 35 Baekbeom-Ro,
Mapo-Gu, Seoul 121-742, Republic of Korea
2Research Institute for Basic Science, Sogang University, 35 Baekbeom-Ro,
Mapo-Gu, Seoul 121-742, Republic of Korea
3Interdisciplinary Program of Integrated Biotechnology, Sogang University,
35 Baekbeom-Ro, Mapo-Gu, Seoul 121-742, Republic of Korea
In this study, we demonstrated a simple, rapid and inexpensive fabrication method to develop a
novel gold nanobouquet structure fabricated indium tin oxide (GNB/ITO) electrode based on elec-
trochemical deposition of gold ions onto ITO substrate. The morphology of the fabricated electrode
surface was characterized by scanning electron microscopy (SEM) to confirm the GNB formation.
Enzyme-free detection of glucose using a GNB/ITO electrode was described with high sensitivity
and selectivity based on cyclic voltammetry assay. The results demonstrate a linear relation within
wide concentration range (500 nM to 10 mM) of glucose, with a correlation coefficient of 0.988.
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The interference effect of uric acid was effectively avoided for the detection of glucose (1 ꢀM to
IP: 109.161.210.180 On: Sat, 05 Dec 2015 21:45:35
10 mM). Moreover, the developed sensor was applied to determine the concentration of glucose in
Copyright: American Scientific Publishers
the presence of human serum to indicate the ability of GNB/ITO electrodes in real samples. Hence,
newly developed GNB/ITO electrode has potential application in enzyme-free glucose sensor with
highly sensitivity and selectivity.
Keywords: Enzyme Free, Glucose, Nano–Pattern, Electrochemical Sensor, Nanobouquet.
1. INTRODUCTION
sensing activity. Moreover, the activity of GOx is very
sensitive to sodium dodecyl sulfate (SDS) under acidic
conditions as well as to hexadecyltrimethylammonium bro-
mide (CTAB) under basic conditions. In addition to pH,
temperature, toxic chemicals for sterilization, and humid-
ity effects of enzyme, potentially causes significant harm
to the sensor activity in use as well as in storage.5 Another
limitation for the enzyme–based glucose sensor is the
severe interference that could be caused by endogenous
electro–activity in the whole blood samples. Instability
of GOx upon sterilization might limit the enzymatic glu-
cose sensors from being used for long term monitor-
ing in humans. Therefore, the need for electrochemical
enzyme–free glucose sensors has received considerable
interest. The main advantage of enzyme–free glucose sen-
sor includes high sensitivity and selectivity, in addition
to the prevention of fouling by adsorbed intermediates
and some anions, such as chloride ions. All of these
issues depend on the properties of the electrode materials
because the electro–catalytic activity is the main factor that
affects both the sensitivity and selectivity of the glucose
The determination of glucose has drawn much attention
in the field of biotechnology for clinical diagnosis, man-
agement of diabetes mellitus and in food industry. There-
fore, tremendous efforts have been made to develop a
glucose sensor with high sensitivity and selectivity.1ꢀ2
Early studies done by Clark and Lyons that have been
shown an enzymatic glucose sensor based on immobi-
lized glucose oxidase (GOx) enzyme were drawn much
attention.3 Although, these enzyme–based glucose sensors
have shown good selectivity and sensitivity; however, these
sensors have a lot of drawbacks such as loss of enzyme
activity, chemical and thermal instabilities originated from
the intrinsic nature of enzymes.4 Previous studies reported
that, the environmental conditions of enzyme–based glu-
cose sensors, including strong acidic conditions, basic con-
ꢀ
ditions, or high temperatures (above 40 C) could cause
fatal damage to GOx enzyme, which leads to loss of
∗Author to whom correspondence should be addressed.
8432
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doi:10.1166/jnn.2014.9921

Lee et al.
Enzyme-Free Glucose Sensor Based on Au Nanobouquet Fabricated Indium Tin Oxide Electrode
sensor. Therefore, numerous of studies have been devoted
in the investigation and preparation of glucose enzyme–
free sensors.6ꢀ7 It is reported that bare metal electrodes
(platinum or gold electrodes) can act as enzyme–free sen-
sors for the determination of glucose.8ꢀ9 However, these
electrodes suffer from low sensitivity, poor selectivity and
poisoning by intermediates and chloride.10
MO, USA). All other solutions were prepared with
distilled Millipore (Milli–Q) water. Other chemicals that
were used in this study were obtained commercially at
reagent grades.
2.2. Fabrication of Gold Nanobouquet
Pattern on ITO Electrode
Much efforts have been focused on developing enzyme-
free glucose sensors based on the direct detection
of the glucose redox behavior on various electrode
materials including nanotubular arrayed platinum (Pt),11
gold (Au) nanoparticles,12 copper nanoparticles,13ꢀ14 Pt
nanoparticles,15ꢀ16 nickel nanoparticles,17 carbon nanotubes
(CNTs),18ꢀ19 mesoporous Pt,20 macroporous Pt films,21
Pt–Pb nanowire arrayed electrodes,22 three–dimensional
Au films,23 and Pt–Ru nanoparticles24 to overcome the
disadvantages of the bulk electrodes.25ꢀ26 Among all
these materials, Au nanostructures are attracted much
attention for the use in a wide range of applications,
including biosensors, chemical-sensor, optical scattering,
diffraction, and other applications due to their higher
conductivity, inertness, biocompatibility and large surface
area.27 The enhancement of the electrochemical conduc-
tivity of the nanostructured modified electrodes compared
to that of the bare electrodes could be related to the
increase of the electrode’s active surface area. Conversely,
the immersion of a nanomaterial in an electrolyte could
ITO-coated glass substrates were cleaned by sonication
for 15 min in 1% Triton X–100, deionized water (DIW),
and ethanol. Then, they were treated with basic piranha
ꢀ
solution (1:1:5, H2O2:NH4OH:H2O) for 30 min at 80 C.
Finally, the ITO substrates were cleaned again with DIW
and dried under N2 stream to obtain a clean ITO surface.
GNB was electrochemically deposited onto ITO substrates
(2 cm × 1 cm) using a 1 mM HAuCl4 aqueous solution
containing 17 ꢁg/L of SDS as a surfactant. The potential
was maintained at −0.9 V (vs. Ag/AgCl). The active area
for the electrochemical deposition of GNB was 1 cm ×
1 cm. Moreover, to remove any surfactant traces, which
may be adsorbed onto the GNB surface, the substrates
were rinsed with DIW and sonicated for 5 min with iso-
propyl alcohol. The surface morphologies of the GNB
electrode were analyzed by a scanning electron micro-
scope (SEM) (ISI DS-130C, Akashi Co., Tokyo, Japan).
A schematic diagram for the formation of Au nanobou-
quets on ITO surface by electrochemical deposition tech-
nique is depicted in Figure 1(a).
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induce charge on the surface regions of a material via an
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application of a potential across the electrolyte–material
interface. However, the development of a simple, rapid,
inexpensive method for fabrication of a highly sensitive
electrical nanostructured substrate is still in demand to
monitor the electrochemical characteristics of glucose in a
mixture with good selectivity.
Copyright: American Scientific Publishers
2.3. Electrochemical Measurements of
Glucose Determination
All electrochemical measurements as well as the elec-
trodes modification were performed using a potentiostat
(CHI–660A, CHI, USA) controlled with “general purpose
electrochemical system” software. An in–house three–
electrode system comprised of GNB/ITO electrode as the
working, a platinum wire as the counter, and Ag/AgCl as
reference electrodes were used at a scan rate of 50 mV/s.
In order to minimize the error, all the data are the mean
standard deviation of three different experiments. All the
measurement was performed in neutral pH at RT.
In this work, we present a simple, rapid, and inexpensive
method for fabricating a uniform Au nanobouquet (GNB)
modified ITO electrode. The highly sensitive GNB/ITO
electrode was used to investigate the interdependence of
the electrochemical signals on the oxidation of wide range
of glucose (500 nM to 10 mM) without enzymes using
the cyclic voltammetry (CV) technique. Furthermore, the
CV assay was used for the simultaneous determination of
glucose in the presence of high concentration (500 ꢁM) of
uric acid (UA) as interference. Further, the determination
of different concentrations of glucose (1 ꢁM to 10 mM)
in the presence of human serum was used to prove the
ability of GNB–modified ITO electrodes for detection in
real sample. These results indicate that low detection limits
for glucose were obtained due to the high electro-catalytic
properties of the GNB/ITO electrode.
3. RESULTS AND DISCUSSION
3.1. Surface Morphology and Current Transient of
Nanobouquet Structured Gold Film
Figure 1(b) illustrates the current density versus time curve
at a potential of −0.9 V (Ag/AgCl) for 30 s. The cur-
rent density increased drastically during the first two mil-
liseconds and gradually decreased to a stationary value
at approximately 20 ms. This gradual decrease was due
to limited AuCl−4 diffusion to the ITO surface, which
most likely resulted from nucleation and growth of the Au
nanostructures as indicated in the current transient profile,
which demonstrates the initial nucleation and growth pro-
cess during metal deposition.28 SDS as an ionic surfactant
was added to modify the interfacial properties of both the
2. EXPERIMENTAL DETAILS
2.1. Materials
Glucose, UA, human serum, SDS, and gold chloride
(99.9%+) were purchased from Sigma–Aldrich (St. Louis,
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Enzyme-Free Glucose Sensor Based on Au Nanobouquet Fabricated Indium Tin Oxide Electrode
Lee et al.
were observed to be in the range of 400 nm to 600 nm in
diameter.
3.2. Electrochemical Behavior of Glucose on
Bare ITO and GNB Electrodes
The general oxidation pathway for the glucose can be
explained: two hemiacetal–types of glucose (ꢂ– and
ꢃ–glucose) are converted to each other through acid–
catalyzed hydrolysis via aldehyde–type glucose. The ratio
of two hemiacetal–types of glucose would be ꢂ:ꢃ = 11:89,
if it were not for the influence of the anomeric effect.29
A schematic of the general reaction pathway is illustrated
in reaction Scheme 1 for ꢂ– and ꢃ–glucose, the hydrogen
atom tethered to carbon is activated due to the stronger
acidity of the hemiacetalic OH group (pKa = 12ꢄ3) com-
pare to alcoholic OH group (pKa = 16). Thus, the prod-
uct of electrochemical oxidation of ꢂ– and ꢃ–glucose is
glucono–ꢅ–lactone, which is the final stable product of
two–electron oxidation of glucose.30
Figure 2(a) shows the cyclic voltammogram behavior
of the direct oxidation of 1 ꢁM of glucose at bare ITO
electrode. From this result, no significant redox current
peaks could be observed, which may be related to slow
kinetic electron transfer at the bare ITO electrode in addi-
tion to surface fouling due to the adsorption of interme-
diates. On the other hand, large background was observed
for a GNB–modified ITO electrode in compare to that
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of the bare ITO electrode (Fig. 2(a)) indicates the higher
Copyright: American Scientific Publishers
background charging current. This could be related to the
larger surface area of the GNB–modified ITO electrode.
Therefore, the GNB–modified ITO electrode displays an
advantage for providing better electron-transfer kinetics as
compared with the bare ITO electrode.
The CV for the glucose (1 ꢁM) at the GNB–modified
ITO electrodes in the potential range from +0.9 to −0.2 V
(versus Ag/AgCl) at scan rate 50 mV/s (Fig. 2(a)) shows
an anodic and cathodic current peak at potential 510 mV
Figure 1. Fabrication of GNB–modified ITO electrode surface.
(A) Schematic diagram for fabrication of GNB structures modified ITO
electrode based on electrochemical deposition technique. (B) Current–
versus–time profile for Au electrochemical deposition onto ITO electrode
at a potential of −0.9 V (vs. Ag/AgCl) for 30 s at 25 ꢀC. (C) SEM image
of GNB–modified ITO electrode surface, scale bar 500 nm.
particles and the electrode to control the morphology of
the aggregates. The SEM image of electrodeposited GNB
nanostructures on an ITO surface at 30 s is shown in
Figure 1(c), which clearly demonstrates that these electro-
chemical deposition conditions including concentration of
Au3+ (1 mM), concentration of surfactant (17 ꢁg/L), and
ꢀ
temperature (25 C), time (30 s) and voltage (−0.9 V, vs.
Scheme 1. Reaction scheme for different glucose forms: Schematic dia-
gram of the equilibrium between ꢂ–glucose and ꢃ–glucose forms in an
aqueous solution and the oxidation pathway of ꢂ–and ꢃ–glucose into
glucose lactone.
Ag/AgCl) of the deposition are results in the formation
of uniformed distributed Au bouquet nanostructures over
a large electrode surface area. The nanobouquet structures
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Lee et al.
Enzyme-Free Glucose Sensor Based on Au Nanobouquet Fabricated Indium Tin Oxide Electrode
advantages related to providing better electron–transfer
kinetics than that of bare ITO electrodes, and the catalytic
properties of Au nanoparticles might advance the oxida-
tion of glucose at the GNB/ITO electrode. These results
demonstrate the sensitivity of the GNB/ITO electrode.
Moreover, the effect of pH was determined using dif-
ferent solutions with pH in the range of 4 to 9. In the
acidic pH or basic pH solutions, glucose was converted
to another anomer (mannose or fructose) via the anomer-
ization process, which shifts the oxidation peak potential
of glucose (Fig. 2(b)). In addition, the effect of temper-
ature also was determined by studying glucose oxidation
ꢀ
ꢀ
behavior at different temperatures (10 C–37 C). As tem-
perature changes, the oxidation peak potential changes its
signal (Fig. 2(c)). Based on these results, we selected neu-
tral solution and RT as the optimized conditions for further
experiments.
3.3. Cyclic Voltammetry for Detection of
Different Concentrations of Glucose
on GNB–Modified ITO Electrodes
Figure 3(a) shows the cyclic voltammograms for different
concentrations of glucose (from 500 nM to 10 mM) at the
GNB/ITO electrode. Upon addition of glucose, the anodic
current peak increased with increasing concentration of
glucose. The lowest concentration measured in this system
is 500 nM, which is lower than that obtained by previ-
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32ꢀ33
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ous approaches, such as CNT composite electrodes,
Copyright: American Scientific Publishe12rs
Au nanoparticles, etc. (Table I). The anodic current peaks
found to be linearly increased with the glucose concen-
trations. However, no change in anodic peak current was
observed when the concentration of glucose was more than
10 mM which could be related to the saturated GNB/ITO
electrode. The calibration plot for glucose determination
shows a linear relation in a wide range from 500 nM to
1 mM with a correlation coefficient of 0.984 (Fig. 3(b)).
These results suggest that the GNB/ITO electrode could be
used to develop a highly sensitive biosensor for determina-
tion of low glucose concentrations. This indicates that the
GNB/ITO electrode exhibited good electrocatalytic perfor-
mance for oxidation of glucose.
Figure 2. (A) Electrochemical behavior of glucose at bare ITO and
GNB–modified ITO electrode: (a) Cyclic voltammograms of glucose on
a bare ITO, (b) background signal of a GNB–modified ITO electrode,
and (c) CV of glucose on a GNB–modified ITO electrode. (B) Elec-
trochemical behavior of glucose at different pH range from (a) 4 to
(b) 9. (C) Electrochemical behavior of glucose at different temperatures
(a)10 ꢀC, (b) 24 ꢀC and (c) 37 ꢀC, respectively.
and 200 mV, respectively. The separation between the
potential peaks ꢁEpc − Epaꢁ exceeded 59 mV, which was
indicative of a distinct quasi-reversible character of the
glucose at GNB/ITO electrode process. The enhancement
factor for the electrochemical activity at GNB/ITO elec-
trode is mainly due to its larger surface to volume area
ratio derived by three dimensional gold nanobouquet struc-
tures. Moreover, these results might be related to moderate
electrocatalytic activity of the GNB/ITO electrode, which
is obtained by modifying poorly electrocatalytic elec-
trode (ITO) with a highly electrocatalytic material “Au.”
This might enable the electrode to obtain high signal–
to–background ratios compared to those of Au and Pt
electrodes.31 Therefore, the GNB/ITO electrode displays
3.4. Cyclic Voltammetry for the Detection of
Glucose in a Mixture with UA on
GNB–Modified ITO Electrodes
A major challenge in the electrochemical determination of
glucose is the coexistence of interfering materials, such as
uric acid (UA), which are commonly found in the human
blood. The presence of UA in physiological solutions
causes the greatest interference for direct electrochemi-
cal oxidation of glucose on various electrodes, especially
enzyme–free sensors.24 Therefore, the ability of the GNB–
modified ITO electrode to monitor different concentrations
of glucose in the presence of high concentration of UA
was investigated.
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Enzyme-Free Glucose Sensor Based on Au Nanobouquet Fabricated Indium Tin Oxide Electrode
Lee et al.
Figure 3. (A) Cyclic voltammograms of varying glucose concentrations (a) 500 nM, (b) 1 ꢁM, (c) 10 ꢁM, (d) 100 ꢁM, (e) 1 mM, (f) 10 mM
at GNB–modified ITO electrode. (B) Linear plot of anodic current peak as a function of glucose concentration (−IpꢆXꢇ = ꢆ0ꢄ14237 0ꢄ01154ꢇX +
ꢆ1ꢄ49989 0ꢄ05265ꢇ, R = 0ꢄ984). (C) Cyclic voltammograms of varying concentrations of UA (a) 100 ꢁM, (b) 200 ꢁM, (c) 300 ꢁM, (d) 400 ꢁM,
(e) 500 ꢁM on a GNB–modified ITO electrode. (D) Linear plot of anodic current peak as a function of UA concentration (−IpꢆXꢇ = ꢆ4ꢄ94046
0ꢄ11392ꢇX +ꢆ−5ꢄ14671 0ꢄ46856ꢇ, R = 0ꢄ996).
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Figure 3(c) shows the cyclic voltammetric behavior of
anodic current peak with an increasing concentration of
UA (Fig. 3(c)), and this increase was almost linear as
shown in Figure 3(d). The calibration plot for glucose
determination shows a linear relation over range from
100 ꢁM to 500 ꢁM with a correlation coefficient of 0.996
(Fig. 3(d)).
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UA on the GNB–modified ITO electrode, which shows
an irreversible behavior with an anodic current peak at
approximately 720 mV. Cyclic voltammograms for vari-
ous concentrations of UA (100 ꢁM to 500 ꢁM) on the
GNB–modified ITO electrode demonstrate an increase of
Copyright: American Scientific Publishers
UA was used as an interference agent and its effect
on the determination of glucose was examined and pre-
sented in Figure 4. The cyclic voltammograms for differ-
ent concentrations of glucose (1 ꢁM to 10 mM) in the
presence of UA (500 ꢁM) were shown in Figure 4(a).
Compared to pure glucose solution, the addition of UA
to glucose solution reduce the cathodic current peaks,
while the oxidation current peak for glucose in a mix-
ture was observed at nearly the same potential (approx-
imately 510 mV). Moreover, different concentrations of
glucose (1 ꢁM to 10 mM) were detected in the pres-
ence of a constant concentration of UA (500 ꢁM) at
GNB/ITO electrode. The oxidation current peaks of glu-
cose in a UA mixture showed a linear relation to the con-
centrations of glucose with a correlation coefficient of 0.98
(Fig. 4(b)). Moreover, it was observed that, the presence
of UA (500 ꢁM) did not affect the detection of glucose
at the GNB–modified electrode within the concentrations
ranging from 1 ꢁM to 10 mM. These results indicate that
this GNB–modified ITO electrode could be used for selec-
tively detecting various concentrations of glucose in the
presence of an interfering material (high concentrated UA:
500 ꢁM).34
Table I. Comparison of different electrode matrix for linear range and
real sample detection of enzyme free glucose sensors along with those
reported in literature.
Electrode matrix [Ref.]
Linear range (mM)
Pt-nanotube arrays11
2–14
0–8
Au nanoparticle12
Copper/MWCNT13
0.7–3.5∗
0.001–5∗
1–26.5
Cu nanoparticles14
Pt nanoparticles/CNT15
PtPbNP/MWCNT16
Up to 11
0.5–5∗
0.002–11
1–11
Ni powder17
MWCNT18
Multiple-branching CNT forest19
Mesoporous Pt20
0–10
Macroporouse Pt film21
Pt-Pb nanowire array22
3-D Au film23
0.001–10
0.008–11
0.005–10
1–15
0.05–0.3
Up to 28∗
0.0005–10∗
CNT supported PtRu nanoparticles24
Boron-doped CNT33
MnO2/MWNTs nanocomposite34
GNB modified ITO electrode (Present work)
Note: ∗Real sample (Blood serum) tested.
8436
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Lee et al.
Enzyme-Free Glucose Sensor Based on Au Nanobouquet Fabricated Indium Tin Oxide Electrode
4. CONCLUSIONS
Here, a free–enzymatic glucose sensor based on GNB
array modified ITO electrode was developed that demon-
strated several advantages, such as good analytical per-
formance and simple preparation process. It exhibited
high sensitivity with good potentiometric response, a low
detection limits and a wide linear range. The GNB array
was prepared by using electrochemical deposition method.
Electrochemical results showed that the GNB–modified
ITO electrode had large active surface, a good electron
transfer rate, larger current response and high electro–
catalytic activity for glucose oxidation in neutral solu-
tions than a bare ITO electrode, with a detection limit of
500 nM glucose. Moreover, GNB–modified ITO electrode
demonstrated an efficient determination of glucose in the
presence of UA (500 ꢁM) with good selectivity and with
sensitivity up to 1 ꢁM. In addition, the sensor has potential
applications in glucose concentrations detection in human
serum samples without interferences; therefore, it could
be suitable for the determination of glucose in real sam-
ples. It is expected that with such electronic and structural
properties, the GNB–modified ITO electrode could be a
promising electrode in electro–analytical and biosensing
applications. High sensitivity and selectivity and surface
renewal make this sensor ideal for detection of glucose in
real samples.
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Acknowledgments: This work was supported by the
Copyright: American Scientific Publishers
Leading Foreign Research Institute Recruitment Program
through the National Research Foundation of Korea(NRF)
funded by the Ministry of Science, ICT and Future
Planning(MSIP) (2013K1A4A3055268), by a National
Research Foundation of Korea (NRF) grant funded by
the Korea government (MEST) (2009-0080860) and by
the Sogang University Research Grant of 2013 (SRF-
201314003.01).
Figure 4. (A) Cyclic voltammograms of varying concentrations of glu-
cose (a) 1 ꢁM, (b) 10 ꢁM, (c) 100 ꢁM, (d) 1 mM, (e) 10 mM on
a GNB–modified ITO electrode in presence of fixed UA concentration
(500 ꢁM). (B) Linear plot of anodic current peak as a function of glu-
cose concentration and fixed UA concentration (500 ꢁM) (−IpꢆXꢇ =
ꢆ2ꢄ4496 0ꢄ27948ꢇX+ꢆ31ꢄ53788 1ꢄ39076ꢇ, R = 0ꢄ98). (C) Anodic cur-
rent peak corresponding to oxidation of varying concentrations of glucose
(1 ꢁM to 10 mM) in both (ꢀ) distilled water and (ꢁ) human blood
serum.
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Received: 29 March 2013. Accepted: 15 January 2014.
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J. Nanosci. Nanotechnol. 14, 8432–8438, 2014