Electrodeposited spinel NiCo2O4 nanosheet arrays for glucose sensing application

Article abstract of DOI:10.1039/c5ra13833g

We report the growth of NiCo₂O₄ nanosheet arrays on a conducting substrate by a simple and highly reproducible electrodeposition method. Non-enzymatic glucose sensing properties of the as-prepared nanosheets are studied. NiCo₂O₄ nanosheets show a linear response with respect to the change in glucose concentration varying from 5 to 65 μM and exhibit a sensitivity value of 6.69 μA μM^-1 cm^-2 with a LOD value of 0.38 μM. It is proposed that nanosheets are advantageous for glucose sensing applications because of their large surface area with enormous active edges and superior electrochemical properties providing efficient transport pathways for both electrons and ions.

Full text of DOI:10.1039/c5ra13833g

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DOI: 10.1039/C5RA13833G
(A)
(b)
Adding
(a)
Oxidizes
Cathodic
Scan
ITO
Anodic
scan
GL+M*(II)
GE+M*(III)
M* (III)
NiCo2O4
M*(II)
M* (III)
NiCo2O4
M*(II)
Cathodic
M*(II)
Anodic
scan
M* = Ni,Co
Scan
(B)
CH2OH
CH2OH
O
H
C
O
H
OH
H
C
H
OXIDIZE
H
C
O
C
C
H
C
OH
C
OH
C
C
H
C
OH
OH
OH
H
OH
H
GLUCONO-
GLUCOSE
(C6H12O6)
LACETONE
(C6H10O6)
TOC: Nonꢀenzymatic glucose sensing properties of the NiCo2O4 nanosheets are studied. NiCo2O4
nanosheets show linear response with respect to the change in glucose concentration varying from 5 to
65 µM and exhibit the sensitivity value of 6.69 µAꢁMꢀ1cmꢀ2 with a LOD value of 0.38 µM.

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DOI: 10.1039/C5RA13833G
Electrodeposited Spinel NiCo2O4 Nanosheet Arrays
for Glucose Sensing Application
Kusha Kumar Naik, Suresh Kumar, Chandra Sekhar Rout *
School of Basic Sciences, Indian Institute of Technology, Bhubaneswar751013, Odisha
India
Abstract: We report the growth of NiCo2O4 nanosheet arrays on a conducting substrate by a
simple and highly reproducible electrodeposition method. Non-enzymatic glucose sensing
properties of the as-prepared nanosheets are studied. NiCo2O4 nanosheets show linear response
with respect to the change in glucose concentration varying from 5 to 65 µM and exhibit the
sensitivity value of 6.69 µAμM-1cm-2 with a LOD value of 0.38 µM. It is proposed that
nanosheets are advantageous for glucose sensing applications because of their large surface
area with enormous active edges and superior electrochemical properties providing efficient
transport pathways for both electrons and ions.
Keywords: Layered materials, Spinel, Nanosheet, Electrodeposition, Glucose sensor
∗Corresponding author. Tel.: +91674-2576092
E-mail address: csrout@iitbbs.ac.in (Dr. C.S. Rout)
1

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1. Introduction
DOI: 10.1039/C5RA13833G
Over the past decade, development of non-enzymatic electrochemical glucose sensors
have risen at a considerable rate due to its easy fabrication, cost effective, high sensitivity, fast
and accurate measurements. Determination of glucose concentration are not only relevant for
use in blood sugar monitoring of many diseases like diabetes, cardiovascular disease and
endocrine metabolic disorder but also in the food industry, biotechnology, clinical laboratories
and bio-processing.1 The rising demand for glucose sensors with high sensitivity and reliability,
fast response and selectivity have driven tremendous research efforts for decades.2 To succeed
on the fabrication of a high performance glucose sensor, nanostructure metals, metal oxides,
chalcogenides and carbon nanomaterials with high surface to volume ratio have been
extensively used.3–6 Furthermore, thin film nanosheets nanomaterials can be used to
incorporate the activity of analyte within its local nano-to-micro-scale environment, thereby
enhancing the electron transfer between the analyte and the electrode with superior
electrochemical properties.
Mixed transition metal oxides (MTMOs), typically ternary metal oxides with two different
metal cations, have received an upsurge of interest in recent years due to their promising roles.
Spinel NiCo2O4 is a MTMOs, has received growing attention due to its technological
applications in the field of supercapacitor,7–9 lithium ion batteries,10 and electrocatalyst,11
arising from its superior electrochemical properties compared to its binary counterparts and
other transition metal oxides. NiCo2O4 exhibits an inverse spinal structure with Ni cations
occupying the octahedral sites while Co cations are evenly distributed to both octahedral and
tetrahedral sites.12 It possesses much better electronic conductivity which is beneficial for fast
electron transfer between electrode and electrolyte and the excellent performance can be
attributed due to high redox reactions of the cobalt and nickel ions.11,13,14 The NiCo2O4
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nanostructures greatly improve the performance in electrochemical applications bDyOoI: f10fe.10ri3n9/gC5aRA13833G
high specific surface area, short diffusion path for ions or electrons, and efficient channels for
mass transport.15
Biosensors based on different methods of fabrication have been reported in recent years.
Depending on the various properties and phenomena of the detector and techniques used
biosensors can be classified into optical biosensors, electrochemical biosensors, electrical
biosensors, vibrational biosensors and mechanical biosensors. Among the various biosensors,
electrochemical based biosensors involve simple fabrication processes and mechanisim, easier
operation, fast response time, low detection limit and posess high stability.16–18
Indium tin Oxide (ITO) is transparent and conductive substrates provides the way of
excellent electron transfer between the deposited nanostructure and ITO substrates and it
provide a reliable platform for the fabrication of biosensor. The glucose immobilized on ITO
surfaces are considered to be adsorptions, which contain the carboxylic acid groups or other
related functional groups form spontaneous linkages with the ITO surfaces to form stable
assemblies.19–21
Continuing with the glucose sensor report, Wang et al. reported nickel-cobalt
nanostructures (Ni-Co NSs) electrodeposited on reduced graphene oxide (RGO)-modified
glassy carbon electrode (GCE) for glucose sensor applications.22 Similarly Dong et al. reported
glucose sensing properties of Co3O4 nanowires on three-dimensional graphene foam grown
by chemical vapour deposition .23 Li et al. reported uniform growth of large-area 3D β-Ni(OH)2
and NiO nanowalls on a variety of rigid and flexible substrates for electrochemical glucose
sensor applications.24
Herein, we report the growth of NiCo2O4 nanosheet arrays on indium tin oxide (ITO)
coated glass substrate by electrodeposition method. The electrochemical sensing behaviour of
the nanosheets towards glucose molecule is studied. The developed NiCo2O4 nanosheets based
3

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glucose sensor shows linear response towards varying glucose concentration in a rDaOnIg: 1e0.f10ro39m/C55RA13833G
to 65 μM with a sensitivity value of 6.69 AμM-1cm-2 , LOD (Limit of Detection) value of 0.38
µM and LOQ (liquid of quantification) is 1.27 μM. It has been proposed that the NiCo2O4
nanosheets are advantageous for glucose sensing applications because of its efficient transport
pathways for both electrons and ions.25,26
2. Experimental Section
2.1 Material Preparation
The electrodeposition of NiCo2O4 has been carried out by electrochemical chrono-
amperometric technique in a glass cell with three electrodes configuration. In the first step,
0.01 M nickel nitrate hexahydrate and 0.02 M cobalt nitrate hexahydrate were dissolved in 10
ml of de-ionized water (DI). After complete dissolution, 0.01 M of Potassium chloride (KCl)
was mixed as supporting electrolyte. The three electrodes of the electrodeposition set-up
consist of Pt as counter electrode, Ag/AgCl as reference electrode and ITO/glass as working
electrode. The portion of the working electrode where the NiCo2O4 needs to be deposited was
dipped in to the solution and rest part of the ITO was kept in air. In the second step, -1.1 V
potential was applied to the electrode for 180 s and the temperature of the solution was
maintained at 70 ºC by a hot plate with continuous magnetic stirring. At high temperature with
applied potential, the dissolved Ni and Co ions attract to each other by a driving force and
nucleate to form NiCo2O4 seed layers and further growth during the electrodeposition process
lead to the formation of nanosheet arrays. In the next step, the as-prepared NiCo2O4 nanosheet
arrays on ITO/glass was dried at room temperature overnight followed by calcination at 500
ºC for 6 hour. At 500 ºC, formation of black coloured and pure phase of NiCo2O4 nanosheets
took place.
2.2. Material Characterization
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The crystallinity of the as-synthesized material was characterized by X-ray diffraction
DOI: 10.1039/C5RA13833G
(XRD) patterns of Bruker D8 Advanced diffractometer using Cu-Kα radiation (λ = 1.54184
Å). Morphology and composition of the as-prepared samples were examined by FESEM
((MERLIN Compact with GEMINI I electron column, Zeiss Pvt. Ltd., Germany) equipped
with energy dispersive X-ray spectroscopy (EDAX).
2.3. Electrochemical Glucose sensing Measurements
Cyclic voltammetery (CV) and Chrono-amperometry (CA) experiments were
performed by using a PG262A potentiostat/galvanostat (Technoscience Ltd., Bangalore,
India). All the electrochemical experiments were performed in a three electrode glass cell
containing 0.1 M NaOH aqueous solution as the electrolyte. The NiCo2O4 nanosheet arrays
grown on ITO/glasswere usedas the working electrode; Ag/AgCl and platinum wire were used
as reference and counter electrode respectively. For CV measurements, all the electrodes were
dipped in 6 ml of NaOH solution and the potential window in the range of -0.3 to 0.9 V was
selected to observe the oxidation and reduction peak positions. Similarly, for CA
measurements, a potential value of 0.4 V was applied in a glass cell containg 140 ml of NaOH
aquous solution and change in current with respect to the glucose concentrations have been
measured after an interval of time of 100 s.
3. Results and discussion
Morphology of the as-synthesized NiCo2O4 nanosheets was observed by FESEM
depicted in Fig. 1a and b. The electrodeposited nanosheets are homogeneous, uniform and well
populated though out the surface of ITO which can be clearly seen in the low magnification
FESEM image as shown in Fig. 1a. The lateral length of the nanosheets were 2-3 μm range
and a thickness ~30-50 nm.
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The crystalline phase of the annealed black thin film samples were identifiDeOdI:b10y.10X39R/CD5R.A13833G
As shown in Fig. 1c, all the characteristic diffraction peaks, (111), (220), (311), (222), (400),
(422), (511) and (440) can be indexed to cubic NiCo2O4 crystal structure (JCPDS card No. 20-
0781) having lattice parameter a=b=c= 8.11 Ǻ. No other impurity peaks were observed
suggesting that the synthesized material is of high purity with good crystalline.27 The surface
compositions of NiCo2O4 nanosheets were determined by EDAX, confirming the presence of
Ni, Co, and O atoms Fig. 1d. The elemental mapping of the NiCo2O4 nanosheets indicated the
uniform distribution of the individual atoms (Ni, Co, and O) throughout the as-grown sample
Fig. 2. Atomic ratio of Ni, Co and O was estimated to be nearly 1:2:4 confirming the formation
of pure NiCo2O4 phase.
The electrocatalytic property of the NiCo2O4 film was first asserted by CV
measurements taking a potential range from -0.3 to 0.9 V in 0.1 M NaOH solution at a scan
rate of 40 mVs-1. The CVs of NiCo2O4 nanosheets without glucose and in different
concentrations of glucose solution (From 100-1000 μM with successive increase in
concentration by 100 μM) are depicted in Fig. 3a. In anodic scan, a broad oxidation peak in the
0.4-0.9 V range was observed and the amplitude of the oxidation peak increased and reduction
peak decreased with each addition of glucose concentration in the solution as shown in Fig.
3a. This change in the peak current sucessively suggested that the electrodeposited NiCo2O4
nanosheet is a stable and good electro catalytic material suitable for glucose sensing
applications.23,28–31
The mechanism of increase in peak current is shown in Fig. 4(A), and it can be
understood as follows:
NiCo2O4+ OH¯+ H2O ↔ NiOOH+ 2CoOOH+ e¯-----------------------------------------------(1)
CoOOH + OH ¯ ↔ CoO2 + H2O + e¯ -------------------------------------------------------------(2)
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Ni (II) + Co (II) → Ni (III) + Co (III) + 2e¯-------------------------------------------------------V(i3ew)Article Online
DOI: 10.1039/C5RA13833G
Glucose (C6H12O6) → Gluconolactone (C6H10O6) + 2H++ 2e¯---------------------------------(4)
During the anodic scan, Ni (II) and Co (II) species present in the dissolved NiOOH and
CoOOH compounds oxidise to Ni (III) and Co (III) species in the appied potential range by
releasing two electrons, (Eq. 3). when we droped the glucose molecules , the glucose molecule
(GL) dissociate and converted to gluconolactone (GE) by giving up two electrones into the
solution, (Eq. 4, Fig. 4b). The oxidation of Ni and Co ions and glucose molecules occure
simultaneouly in the same potential range but the rate of oxidations of Ni and Co ions present
on the electrode surface determine the rate of detection of glucose molecules. Thus the
detection of glucose molecule is the intrinsic electrochemical activity of the material and the
rate of detection can be enhanced by the engineering the morphology of the materials and
controling the other parameters like pH,.molarity of aquous solution and the substrate.28,32–34
In cathodic scan, the oxidised Ni (III) , Co (III) species reduce to Ni (II) and Co (II)
ions by accepting the electrons and returns to its original state (Eq. 5).27,35–37 Thus oxidation
and reduction are observed in each addition of glucose molecules in the elctrolyte. The anodic
peak current increases periodically by increasing glucose concentration due to release of more
number of electrons. Again the high affinity of glucose to glucanolactone can be attributed to
NiCo2O4 due to its biocompatibility, large surface area, active edges and high electron
38–41
communication capability.
Fig. 3b shows linear response of oxidation peak with
correlation co-efficient R2=0.99. This means that the NiCo2O4 nanosheets prepared by us
exhibit uniform response of glucose molecules and show good electro catalytic behaviour.
Fig. 3c shows CVs of NiCo2O4 nanosheets electrode at different scan rates in the
presence of 100 μM glucose concentration in the solution. The obtained result showed that both
the oxidation and reduction peak current increase linearly with increasing scan rates because
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by increasing scan rate, electrons transfer between the surface of the electrode and electrolyte
DOI: 10.1039/C5RA13833G
increases. A graph of the anodic and cathodic peak current against the square root of the scan
rate is shown in Fig. 3d. It exhibits a linear relation demonstrating that the oxidation of glucose
at the electrode surface is a diffusion controlled process.42,43 It can be found that the peak
current is proportional to the square root of scan rate, showing a typical diffusion controlled
electrochemical behaviour. But the CV remained unchanged at different scan rates which
confirmed that the NiCo2O4 nanosheets are a stable material for glucose sensing.
Amperometric measurement was recorded to estimate the detection limit and the sensitivity
value of NiCo2O4 nanosheet electrode at different glucose concentrations. The measurements
have been carried out at 0.4 V potential under the vigorous stirring of the solution at 1100 rpm.
When 5 μM of glucose molecules added into the 140 ml of NaOH aqueous solution the current
rose steeply to reach a stable value with a response time of 26 s. The current value increased
successively by periodic addition of 5 μM of glucose molecules into the solution with a time
interval of 100 s (Fig. 5a). The sensitivity and linear range of detection can be found by taking
the consideration of calibration graph which observed that NiCo2O4 nanosheets show linear
response value from 5 to 65 μM glucose concentrations with the sensitivity value of 6.69
AμM-1cm-2. The limit of detection (LOD) and limit of quantification (LOQ) of the
amperometric glucose sensor were estimated using the formula in eqn 6 & 744
3 s
b
LOD =
-------------------------------------------------------------------------------(5)
m
10s
b
LOQ =
---- --------------------------------------------------------------------------------------(6)
m
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where sb is the standard deviation obtained from five measurements of the blank signal
DOI: 10.1039/C5RA13833G
(0.00057 mA) and m is the slope value extracted from the calibration plot (0.00446 mA M-1).
Using these data, LOD and LOQ were calculated to be 0.38 M and 1.27 M respectively .
One of the most important analytical factors for an amperometric biosensor is the
selectivity of the sensor to target analyte. It is well-known that Ascorbic acid (AA) ,uric acid
(UA), Lactic acid (LA) and dopamine (DA) are common interfering species during catalytic
oxidation of glucose. The interference study has been carried out at 0.4 V potential under the
same experimental condition in the glass cell by adding the 5 μM of UA, DA,LA and AA
contineously into the solution in the separation of 100 s, Fig. 5c. The present electrode can
successfully avoid interferences from UA, DA, LA and AA . Furthermore, we performed the
interference test to demonstrate the ability of our sensor to differentiate glucose from fructose,
which is isomeric with glucose. To investigate the reproducibility of the NiCo2O4 nanosheets
electrode, seven independently fabricated electrodes were tested for glucose sensing and it
showed an acceptable reproducibility with a relative standard deviation of 3.1% for the current
determined at a glucose concentration of 5 µM. The stability of the electrode by monitoring the
remaining amount of current response after successive cycling of the electrode for 100 circles
was examined. It was found that the peak current for glucose oxidation retains 90 % of its initial
value. Again, we observed CA experiment in the presence of 100 µM of glucose concentration
at 0.4 V potential for 3000 s. The NiCo2O4 nanosheets showed linear characteristic up to 3000
s Fig. 5e. The synthesized non-enzymatic glucose sensor possesses a low LOD of 0.38 µM and
a linear range from 5-65 µM which are excellent for glucose sensors. To check the advantages
of NiCo2O4 nanosheets compared to its binary oxides such as NiO and Cobalt oxide we carried
out the glucose sensing performance of the binary oxides prepared by following same
electrodeposition method. It is observed that NiO was insensitive to glucose under the same
measurement condition used for NiCo2O4 nanosheets. The glucose sensing performance of
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cobalt oxide is shown in Fig. S1. and S2. † Cobalt oxide showed a sensitivity of ~D3O.I:510μ.1A03µ9/MC5RA13833G
1cm-2 with LOD 0.38 µM which is low compared to NiCo2O4 nanosheets.
We have also prepared NiCo2O4 nanosheet arrays on other conductive substrates such
as Ni foam and Ni strip and their glucose sensing properties were studied (See Fig. S4, S5, S6,
S7). † Table 1 shows the comparison of the glucose sensing performance of the NiCo2O4
nanosheet arrays prepared on different substrates. The obtained sensitivity are 0.046 mAμM-
1cm-2 and 0.018 mAμM-1cm-2 for the NiCo2O4 nanosheets grown on Ni foam and Ni strip
respectively with the response time in the similar range of the NiCo2O4 nanosheets grown on
ITO/glass substrates. Further, the glucose sensing performance of NiCo2O4 nanosheets are
compared with the previous reports on Ni-Co-oxides for glucose sensing applications and our
results are comparable to the literature (Table 2).
4. Conclusion
In conclusion, NiCo2O4 nanosheets were grown on ITO/glass substrate by a simple
electrodeposition method. The NiCo2O4 nanosheets can be readily obtained by making the
seed layer and tuning the deposition time with enhanced electrocatalic activity suitable for
electrochemical glucose sensing applications. The NiCo2O4 nanosheets-based glucose sensor
exhibited extremely high sensitivity to glucose (6.69 μAµM-1cm-2), a low detection limit of
0.38 µM and good linear range response from 5- 65 µM. Hence the present electrodeposition
method for NiCo2O4 nanosheets growth paves the way for fabricating glucose sensors with low
cost, high sensitivity and good detection limit with great potential for industrial mass
production.
Acknowledgements
Dr. C.S. Rout would like to thank DST (Government of India) for the Ramanujan fellowship.
This work was supported by the DST-SERB Fast-track Young scientist (Grant No. SB/FTP/PS-
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065/2013), UGC-UKIERI thematic awards (Grant No. UGC-2013-14/005) and BRNS-DAE,
DOI: 10.1039/C5RA13833G
(Grant No. 37(3)/14/48/2014-BRNS/1502).
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Nur, and Magnus Willander Sensors (Basel). 2014 , 14, 5415–5425
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RSC Advances
Electrode
Sensitivity
Linear range
LOD
RespoVniesweArticle Online
DOI: 10.1039/C5RA13833G
time
26 s
21s
NiCo2O4/ITO
NiCo2O4/Ni
foam
NiCo2O4/Ni
strip
6.69 μAµM-1cm-2
5-65 µM
0.38 µM
8.5 µM
0.046 mAµM-1cm-2 5-50 µM
0.018 mAµM-1cm-2 5-65 µM
4.6 µM
27 s
Table-1 Comparision of glucose sensing performance of NiCo2O4 nanosheets prepared on
different electrodes.
Electrode
Sensitivity
Linear
range
0.005-15
mM
LOD Respon Reference
se time
NiCo2O4
nanoneedles on
Ni
91.34 mV/decade
—
10 s
45
foam(Enzymatic)
22
CNT-NiCo-oxide 66.15 μAµM-1cm-2 0.02-12.12
5 µM
—
mM
6-65 µM
NiCo2O4
nanosheets/ITO
6.69 μAµM-1cm-2
0.38
µM
26 s
Present work
Table-2 Comparision of glucose sensing performance of NiCo2O4 nanosheets with reported
literature.
14

RSC Advances
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DOI: 10.1039/C5RA13833G
(a)
(b)
100 nm
(e)
200 nm
(c)
(d)
JCPDS-20-0781
ITO
20 25 30 35 40 45 50 55 60 65 70 75 80
2 Theta (Degree)
Fig. 1. (a) and ( b) Low and high magnification FESEM images of NiCo2O4 nanosheet arrays
grown on ITO coated glass. (c) XRD pattern, (d) EDX spectrograph and (e) photograph of the
as-prepared NiCo2O4 sample.
15

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RSC Advances
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DOI: 10.1039/C5RA13833G
(a)
(b)
Co
Ni
Element Weight Atomic
(c)
%
%
Ni
Co
O
22.51
12.87
28.11
59.03
49.35
28.14
O
Fig. 2. Elemental mapping of the NiCo2O4 nanosheet arrays: (a) Ni, (b) Co ,and (c) O.
Comparative table showing percentage of the elements
16

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DOI: 10.1039/C5RA13833G
7
6
2
R =0.99
4.0
3.5
3.0
2.5
5
j
4
3
2
a
1
0
-1
-2
-3
(a)
(b)
0
200
400
600
800
1000
-0.4 -0.2
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
Concentration
(
M
)
6
4
4
scan 8 mv/s
R2= 0.99
10 mv/s
20 mv/s
40 mv/s
80 mv/s
100 mv/s
2
0
2
Anodic
Cathodic
0
-2
-4
-2
-4
(d)
(c)
0
40
100
60 1/280
20(Scan rate)
-0.4 -0.2
0.0
0.2
0.4
0.6
0.8
1.0
Voltage (V)
Fig. 3. (a) CVs of NiCo2O4 electrode at different glucose concentrations: black colour solid
line shows the CV without glucose and in (a) 100 μM to (j) 1000 µM glucose in 0.1 M of
NaOH. (b) Variation of oxidation peak current at different glucose concentration, (c) CVs in
presence of 100 µM glucose at different scan rate, (d) Variation of oxidation and reduction
peak current at different scan rate for 100 µM glucose.
17

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DOI: 10.1039/C5RA13833G
(A)
(b)
Adding
(a)
Oxidizes
Cathodic
Scan
ITO
Anodic
scan
GL+M*(II)
GE+M*(III)
M* (III)
NiCo2O4
M*(II)
M* (III)
NiCo2O4
M*(II)
Cathodic
M*(II)
Anodic
scan
M* = Ni,Co
Scan
(B)
CH2OH
CH2OH
O
H
C
O
H
OH
H
C
H
OXIDIZE
H
C
O
C
C
H
C
OH
C
OH
C
C
H
C
OH
OH
OH
H
OH
H
GLUCONO-
GLUCOSE
(C6H12O6)
LACETONE
(C6H10O6)
Fig. 4.(A) Mechanism of glucose sensing of the NiCo2O4 nanosheets: (a) Without glucose and
(b) in presence of glucose.(B) shematic diagram of glucose and gluconolactone.
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DOI: 10.1039/C5RA13833G
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
0.30
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
2
R =0.99792
(a)
(b)
200 400 600 800 1000 1200 1400
0
10
20
30
40
50
60
70
Time (s)
Concentration (M)
0.14
0.12
0.10
0.08
0.06
0.04
0.050
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
AA
LA
(c)
(d)
UA DE
GL
AA
LA
UA DE
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
(e)
GL
0
500 1000150020002500300035004000
Time (s)
180 200 220 2T40i2m60e28(0s3)00 320 340 360 380
200 400 600 800 1000 1200 1400
Time (s)
Fig. 5. (a) Current versus time measurement at 0.4 V with successive addition of 5 μM of
glucose in 100 s time interval. (b) Dependence on current with respect to the glucose
concentration, (c) Interference study, (d) Response time of the sensor to achieve steady-state
current, and (e) inset showing stability graph in presence of 100 µM glucose concentration in
0.1 M of NaOH.
19