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Electrochemistry of Myoglobin with CoMoO4 Nanorods Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 475
http://dx.doi.org/10.5012/bkcs.2013.34.2.475
Direct Electrochemistry and Electrocatalysis of Myoglobin with CoMoO4
Nanorods Modified Carbon Ionic Liquid Electrode
Zengying Zhao, Lili Cao,† Anhui Hu,† Weili Zhang,† Xiaomei Ju,† Yuanyuan Zhang,† and Wei Sun†,*
School of Science, National Laboratory of Mineral Materials, China University of Geosciences, Beijing 100083, P.R. China†College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, P.R. China
*E-mail: sunwei@qust.edu.cn
Received October 19, 2012, Accepted November 19, 2012
By using ionic liquid 1-hexylpyridinium hexafluorophosphate (HPPF6) based carbon ionic liquid electrode
(CILE) as the substrate electrode, a CoMoO4 nanorods and myoglobin (Mb) composite was casted on the
surface of CILE with chitosan (CTS) as the film forming material to obtain the modified electrode (CTS/
CoMoO4-Mb/CILE). Spectroscopic results indicated that Mb retained its native structures without any
conformational changes after mixed with CoMoO4 nanorods and CTS. Electrochemical behaviors of Mb on the
electrode were carefully investigated by cyclic voltammetry with a pair of well-defined redox peaks from the
heme Fe(III)/Fe(II) redox center of Mb appeared, which indicated that direct electron transfer between Mb and
CILE was realized. Electrochemical parameters such as the electron transfer number (n), charge transfer
coefficient (α) and electron transfer rate constant (ks) were estimated by cyclic voltammetry with the results as
1.09, 0.53 and 1.16 s−1, respectively. The Mb modified electrode showed good electrocatalytic ability toward
the reduction of trichloroacetic acid in the concentration range from 0.1 to 32.0 mmol L−1 with the detection
limit as 0.036 mmol L−1 (3σ), and the reduction of H2O2 in the concentration range from 0.12 to 397.0 μmol L−1
with the detection limit as 0.0426 μmol L−1 (3σ).
Key Words : Carbon ionic liquid electrode, Electrochemistry, CoMoO4 nanorods, Myoglobin
Introduction
Direct electrochemistry of redox proteins and electrode is
currently attracting widespread attentions due to its impor-
tance to understand the structure and function of proteins.
The research can also provide the basic information for the
development of electrochemical biosensors. Myoglobin (Mb)
is an important oxygen transporting protein in the biological
system, which is consisted of a polypeptide chain and a
heme cofacter.1-3 However, due to the deep burying of electro-
active center in the complicated structure of protein and the
denaturation of proteins or the unfavorable orientation on the
electrode interface, direct electron transfer of proteins on the
bare electrode is difficult to be realized.4 Great efforts have
been made to increase the electron transfer kinetics of pro-
teins with electrodes by using mediators or promoters such
as polymer films,5 clay,6 nanoparticles7 and biomembranes.8
By using these functionalized materials direct electrochemistry
of proteins could be greatly enhanced on the modified elec-
trodes with a pair of redox peaks appeared.
With the development of nanotechnology different kinds
of nanoparticles had been applied to direct electrochemistry
of protein. Nanostructure materials have exhibited unique
properties such as large surface area, exceptional chemical
stability, tunable porosity, good electrical conductivity, high
mechanical strength, biocompatibility and catalytic activities.9
The presence of nanomaterials on the electrode can provide
a novel way to enhance electron transfer rate between
proteins and electrode due to the quantum size effect and
surface effect.10 Different kinds of nanoparticles such as
carbon nanotube (CNT), graphene, metal, semiconductor
with various morphologies had been used in the protein
electrochemistry. For example, Wang et al.11 investigated the
direct electrochemistry and electrocatalysis of Mb adsorbed
in gold nanoshells. Ruan et al.12 studied the direct electro-
chemistry and electrocatalysis of Mb based on graphene-
ionic liquid (IL)-chitosan bionanocomposites. Sun et al.13
prepared graphene-TiO2-IL nanocomposite film modified
electrode and applied it to investigate the direct electro-
chemistry of hemoglobin (Hb). Ma et al.14 developed a
biocompatible nano-platform for immobilization of Hb
based on ZrO2 nanotubes-IL for the electrochemical sensing
of NaNO2. But there are seldom reports about the appli-
cation of molybdate compounds in the field of protein
electrochemistry. Metal molybdates are important inorganic
materials with many applications in photoluminescence,
electrochemistry and catalyst. As for CoMoO4, there are
three basic types existing under atmospheric pressure, that is
the low temperature α-CoMoO4, the high temperature β-
CoMoO4 and the hydrate CoMoO4·nH2O. Kichambare et al.15
applied CoMoO4 as a photo anode in the polycrystalline
pellet form for photovoltaic electrochemical cell. Rodriguez
et al.16 investigated the electronic properties and phase trans-
formations of CoMoO4 and NiMoO4 by X-ray absorption
near-edge spectroscopy and XRD studies. Pandey et al.17
studied the structural, optical, electrical and photovoltaic
electrochemical properties of CoMoO4 thin film. Peng et
al.18 proposed a large scale synthesis method of nanostruc-
476 Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 Zengying Zhao et al.
tured CoMoO4 by precipitation strategy. By decreasing the
dimensionality, nanostratured CoMoO4 exhibits many novel
properties such as high surface area, optical transparency,
good antibacterial activities, good biocompatibility, relative-
ly good conductivity, which are of great importance in
heterogeneous catalysis and industrial application. Ding et
al.19 synthesized molybdate hydrates nano/microcrystals by
a hydrothermal approach and investigated the magnetic,
photocatalytic and electrochemical properties. Pei et al.20
prepared nanostructured CoMoO4 catalysts supported on
mesoporous silica SBA-15 with different loadings and
investigated the catalytic activity of these catalysts in the
oxidative dehydrogenation of propane. Xiao et al.21 synthe-
sized a one-dimensional CoMoO4 nanorods by hydrothermal
methods and investigated the lithium storage capability. Mai
et al.22 fabricated asymmetric supercapacitor based on
hierarchical MnMoO4/CoMoO4 heterostructured nanowires,
which showed a specific capacitance and good reversibility.
Due to the specific electronic properties, CoMoO4 nano-
materials have the potential application to direct electro-
chemistry of redox proteins.
In recent years carbon ionic liquid electrode (CILE) has
been widely used in the field of electrochemical sensors.23
CILE was prepared by using IL as the binder and the
modifier in the traditional carbon paste electrode (CPE). ILs
are compounds consisted entirely of ions that exist in liquid
state around room temperature, which exhibit the properties
such as extraordinarily high chemical and thermal stability,
good conductivity, wide electrochemical windows and good
dissolving capability.24 Due to the present of IL in CPE,
CILE has been proven to exhibit excellent performances
such as resistivity towards electrode fouling, high rates of
electron transfer and the inherent catalytic activity. It has
been reported that CILE combines the advantages of carbon
electrode such as glassy carbon electrode (GCE), carbon
ceramic electrode and pyrolytic graphite electrode.25 So
CILE has been used as the working electrode in the field of
electrochemical sensors. Maleki et al.26 made a CILE with
noctylpyridinum hexafluorophosphate and carbon powder to
investigate the electrochemical behaviors of different electro-
active compounds. Sun et al.27,28 fabricated an N-butylpyri-
dinium hexafluorophasphate based CILE for the electro-
chemical applications. Safavi et al.29 fabricated a glucose
sensor based on nanoscale nickel hydroxide modified CILE.
In this work, CoMoO4 nanorods were synthesized and
used for the investigation on the direct electrochemistry of
Mb with CILE as the substrate electrode. Mb modified
electrode was fabricated with the addition of CoMoO4
nanorods and chitosan (CTS) was used as the film to fix the
composite on the electrode surface, which could increase the
stability of the modified electrode. Direct electrochemistry
of Mb was realized and enhanced with a pair of well-defined
redox peaks appeared, which could be attributed to the
specific properties of CoMoO4 nanorods. Electrochemical
behaviors of Mb were carefully investigated with the electro-
chemical parameters calculated. The modified electrode
exhibited excellent catalytic activity to the electrochemical
reduction of trichloroacetic acid (TCA) and hydrogen per-
oxide (H2O2) with wider linear range and lower detection
limit.
Experimental
Reagents. Myoglobin (Mb, MW. 17800, Sigma), 1-hexyl-
pyridinium hexafluorophosphate (HPPF6, Lanzhou Green-
chem ILS. LICP. CAS., China), chitosan (CTS, minimum
95% deacetylated, Dalian Xindie Chemical Reagents Ltd.
Co., China), graphite powder (average particle size 30 µm,
Shanghai Colloid Chemical Plant, China), trichloroacetic
acid (TCA, Tianjin Kemiou Chemical Ltd. Co., China) and
hydrogen peroxide (H2O2, Tianjin Bodi Chemical Holding
Ltd. Co., China) were used as received. CoMoO4 nanorods
(nano-CoMoO4) were synthesized based on the reported
procedure.21 0.1 mol L−1 phosphate buffer solutions (PBS)
with various pH values were prepared and used as the sup-
porting electrolyte. All the other chemicals were of analy-
tical reagent grade and doubly distilled water was used to
prepare all solutions.
Apparatus. All the electrochemical measurements were
executed on a CHI 750 B electrochemical workstation
(Shanghai CH Instrument, China) with a conventional three-
electrode system, which was composed of a modified CILE
as working electrode, a saturated calomel electrode (SCE) as
reference electrode and a platinum wire as counter electrode.
UV-Visible absorption spectrum and FT-IR spectrum were
operated with a Cary 50 probe spectrophotometer (Varian
Company, Australia) and a Tensor 27 FT-IR spectrophoto-
meter (Bruker, Germany), respectively. Scanning electron
microscopy (SEM) was conducted on a JSM-6700F scann-
ing electron microscope (Japan Electron Company, Japan).
Electrode Preparation. CILE was prepared with the
following procedure: 0.8 g of HPPF6 and 1.6 g of graphite
powder were ground carefully in a mortar to get an IL modi-
fied carbon paste. Then a portion of homogeneous paste was
packed firmly into a glass tube (Φ = 4.2 mm) with the elec-
trical contact established through a copper wire to the end of
the paste. Before use the surface of CILE was polished on a
weighing paper to get a mirror-like interface for the further
modification.
The modifier was prepared by mixing Mb and nano-
CoMoO4 homogeneously to obtain a suspension solution
with the final concentrations of 15.0 mg mL−1 and 0.3 mg
mL−1, respectively. Then 8 μL of mixture was evenly spread
onto the CILE surface and the electrode was left in the air to
allow the water evaporated gradually. Finally, 5.0 µL of 1.0
mg mL−1 CTS (in 1.0% HAC) solution was dropped on the
electrode surface and dried to get a uniform film. The fabri-
cated electrode was denoted as CTS/CoMoO4-Mb/CILE and
kept at 4 oC refrigerator when not use. Other modified elec-
trodes such as CTS/CILE, CTS/Mb/CILE etc. were fabri-
cated with the similar procedures for comparison.
Electrochemical Measurement. The three-electrode system
was immersed in a 10 mL cell containing 0.1 mol L−1 pH 3.0
PBS and scanned in the potential range from 0.2 to –0.6 V
Electrochemistry of Myoglobin with CoMoO4 Nanorods Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 477
(vs SCE) at the scan rate of 100 mV s−1. Before the measure-
ment the buffer solutions were deoxygenated by bubbling
high pure nitrogen thoroughly for 30 min and the nitrogen
atmosphere environment was kept in the electrochemical
cell during the procedure.
Results and Discussion
SEM Images. SEM was used to record the image of the
synthesized CoMoO4 nanomaterial with the results shown in
Figure 1 and the inset was the enlarged magnitude of the
image. It can be seen that CoMoO4 appeared as rodlike
nanostructures with the average diameter of 200 nm. Also
some of the nanorods aggregated together to form bundles
like structure. The disorder distribution of CoMoO4 nano-
rods can form a porous structure on the electrode surface
with the increase of the effective area, which is suitable for
the immobilization of Mb molecules.
FT-IR and UV-Vis Absorption Spectroscopy. FT-IR spectro-
scopy is a sensitive tool for studying the secondary structure
of heme proteins. The characteristic amide I (1700-1600
cm−1) and amide II (1620-1500 cm−1) bands of proteins can
provide the detailed information on the secondary structure
of polypeptide chain. The amide I band is caused by the
C=O stretching vibration of peptide linkages in the back-
bone of the protein, and the amide II band is assigned to a
combination of N-H bending and C-N stretching vibrations.30
FT-IR spectroscopy was recorded with the results shown in
Figure 2(A). It can be seen that the amide I and II bands of
native Mb were located at 1651 and 1528 cm−1 (curve a).
While the mixture of CTS, CoMoO4 and Mb also gave the
similar positions with the amide I and II bands at 1649 and
1525 cm−1 (curve b). The almost same position of the wave-
number in FT-IR spectra indicated that Mb still retained its
original structure after immobilized with CTS and CoMoO4
nanorods.
The secondary structure of proteins in the composite can
be further confirmed by UV-Vis absorption spectroscopy. In
UV-Vis absorption spectrum the Soret absorption band from
the four iron heme groups of heme proteins is sensitive to
the variation of the microenvironment around the heme
group and the band shift may provide the information about
the denaturation on the tertiary structure in heme proteins.31
Figure 2(B) presented the typical UV-Vis absorption spectro-
scopy of Mb in the composite material. It can be seen that
the native Mb gave a Soret absorption band at 409 nm in pH
3.0 PBS (curve a). While the mixture solution of CTS-
CoMoO4-Mb also had the Soret band at 409 nm without
changes (curve b), suggested that the secondary structure of
proteins did not change after mixing with CTS and CoMoO4
nanorods. CTS is a biodegradable and nontoxic natural
biopolymer originated from the exoskeleton of crustaceans,
which has been widely reported as an immobilization matrix
for the preparation of biosensor and bioreactor with ex-
cellent film-forming ability.32,33 So the results indicated that
CoMoO4 nanorods were also biocompatible nanomaterials
without the change of Mb structure.
Direct Electrochemistry of Mb Modified Electrode.
Cyclic voltammograms of different modified electrodes in
pH 3.0 PBS at the scan rate of 100 mV s−1 were recorded and
demonstrated in Figure 3. It was observed that no voltam-
metric responses appeared on both CILE (curve a) and CTS/
CILE (curve b), indicating no electroactive substance present
on the electrode. On CTS/Mb/CILE (curve c) a pair of un-
symmetric redox peaks appeared on cyclic voltammogram
with the cathodic peak current (Ipc) as 6.709 μA and the
anodic peak current (Ipa) as 6.057 μA. The redox peak
potential was got with the values of Epc as −0.284 V and
Epa as −0.171 V, and the peak-to-peak separation (ΔEp) as
113 mV. The results indicated that direct electron transfer
between Mb and CILE was realized with slow electron
Figure 1. SEM images of CoMoO4 nanorods. Inset is the highmagnication of SEM image.
Figure 2. (A) FT-IR spectra of (a) Mb film; (b) CTS/CoMoO4-Mb composite film; (B) UV-Vis absorption spectra of native Mb (curve a)and CTS-CoMoO4-Mb mixture (curve b) solution with pH 3.0 PBS, respectively.
478 Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 Zengying Zhao et al.
transfer rate, which was in accordance with the former
reported result.34 CILE has been proven to exhibit some
specific characteristics such as good conductivity, high rates
of electron transfer and the inherent catalytic activity. Also a
layer of IL film is present on the electrode surface, which
could provide a specific interface for the immobilization of
Mb and the realization of the electron transfer. With the
addition of CoMoO4 nanorods on the electrode surface, a
pair of well-defined and quasi-reversible redox peaks ap-
peared with the increase of redox peak currents (curve d),
indicating the presence of CoMoO4 nanorods enhanced the
electron transfer between Mb and CILE. The redox peak
current was obtained as 18.92 μA (Ipc) and 17.08 μA (Ipa),
respectively, which was about 2.8 times higher than that of
CTS/Mb/CILE. The peak potentials were located at −0.179
V (Epa) and −0.260 V (Epc), respectively, with the ΔEp
value of 81 mV. The increase of the redox peak currents and
the decrease of the ΔEp value indicated that the presence of
CoMoO4 nanorods on the electrode surface exhibited ex-
cellent electrocatalytic ability and improved the electron
exchange rate. The formal potential, which was calculated
from the midpoint of Epa and Epc, was obtained as −0.220
V (vs. SCE), and the result was the typical characteristics of
heme Fe(III)/Fe(II) redox couples. So Mb molecules on the
electrode underwent a quasi-reversible electrochemical reac-
tion due to the presence of CoMoO4 nanorods on the CILE
surface.
Effect of Scan Rate. To further investigate electrochemical
characteristics of the immobilized Mb on the electrode
surface, the effect of scan rate on the cyclic voltammetric
response was investigated in the scan rate range from 80 to
800 mV s−1. As shown in Figure 4, the cathodic and anodic
peak currents of Mb increased gradually with the increase of
scan rate. Two linear regression equations between the redox
peak current and scan rate were calculated as Ipc(μA) =
104.2 ν(V s-1) + 8.221 (γ = 0.997) and Ipa(μA) = −101.6 ν
(V s−1) − 6.454 (γ = 0.993), respectively. The results indicat-
ed that the electron transfer process of Mb in CTS/CoMoO4/
CILE was a typical surface-confined electrochemical behavior.
The surface concentration (Γ*) of the electroactive Mb on
the electrode can be further calculated by integration of the
cyclic voltammetric reduction peaks based on the formula
of Q = nFAΓ*,35 where Q is the integration charge of the
reduction peak, n is the electrons transfer number, F is the
Faraday constant, A is the area of the modified electrode.
The charge value (Q) was nearly constant at different scan
rates and the average value of Γ* was obtained as 7.13 ×
10−9 mol cm−2. While the theoretical monolayer concentration
of protein on the electrode surface was 2.0 × 10−11 mol cm−2,
so multilayers of Mb on the electrode surface took place the
electrochemical reaction. Also the total surface concent-
ration of Mb in the composite film on the electrode surface
was calculated as 5.36 × 10−8 mol cm−2, then 13.28% of the
immobilized Mb molecules took part in the reaction. The
results could be attributed to the presence of CoMoO4
nanorods resulted in a porous structure with higher surface
area. The interaction of CoMoO4 nanorods with Mb also
happened in the film, then the several layers of Mb mole-
cules near the electrode surface underwent the electron
transfer with the help of CoMoO4 nanorods.
From Figure 4 it can also be seen that the redox peak
potentials moved gradually with the increase of scan rate.
The oxidation peak shifted to the positive direction and the
reduction peak shifted to the negative direction with the
peak-to-peak separation (ΔEp) increased, indicating a quasi-
reversible process. The relationship of redox peak potentials
and the natural logarithm of scan rate (ln ν) were calculated,
which was linearly dependant in the range from 80 to 800
mV s−1 with the linear regression equations as Epc(V) =
−0.0445 lnν − 0.285 (γ = 0.993) and Epa(V) = 0.0509 lnν −
0.128 (γ = 0.996), respectively. Then the electrochemical
parameters of Mb in the composite film could be calculated
based on the Laviron's equations:36,37
log ks=αlog(1−α)+(1−α)logα−log −
Epc = E0′
−RT
αnF----------lnν
Epa = E0′
+ RT
1 α–( )nF----------------------lnν
RTnFν---------- 1 α–( )αnFΔ Ep
2.3RT--------------------------------------
Figure 3. Cyclic voltammograms of (a) CILE, (b) CTS/CILE, (c)CTS/Mb/CILE and (d) CTS/CoMoO4-Mb/CILE in pH 3.0 PBS atthe scan rate of 100 mV s−1.
Figure 4. Cyclic voltammograms of CTS/CoMoO4-Mb/CILE inpH 3.0 PBS with different scan rates (a-k: 80, 100, 160, 200, 280,340, 400, 500, 600, 700, 800 mV s−1).
Electrochemistry of Myoglobin with CoMoO4 Nanorods Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 479
where α is the electron transfer coefficient, n is the number
of electron transferred, ν is the scan rate, and E0' is the
formal potential, ks is the electron transfer rate constant and
ΔEp is the peak-to-peak potential separation, R, T and F
have their conventional meanings. Based on these equations
the value of n was estimated as 1.09, suggesting that totally
one electron was involved in the electrode reaction. The
values of α and ks were further calculated as 0.53 and 1.16 s−1.
The value of ks is bigger than that of 0.34 s−1 on Mb/NiO/
GCE38 and 0.41 s−1 on Mb-HSG-SN-CNTs/GCE,39 indicating
that CoMoO4 nanorod acted as an excellent promoter to the
direct electron transfer between Mb and the electrode.
It is well-known that most of the heme proteins exhibit a
pH-dependent conformational equilibrium and the pH value
of the buffer solution influences the electrochemical reaction
of the heme proteins. The effect of buffer pH on the response
of CTS/CoMoO4-Mb/CILE was investigated in the pH range
from 1.0 to 7.0. The increase of buffer pH led to a negative
shift of both reduction and oxidation peak potentials, which
indicated that protons involved in the electrode reaction. The
maximum redox peak currents were obtained at pH 3.0
buffer solution, which was selected for the furthur investi-
gation.
Electrocatalysis of CTS/CoMoO4-Mb/CILE. Because
of the presence of similar active center of Mb with per-
oxidase, Mb exhibits intrinsic peroxidase activity in the cata-
lytic reaction. Due to the presence of Mb on the electrode
surface, the modified electrodes often showed good electro-
catalytic ability toward the reduction of different substrates
with a large decrease of activation energy. The electro-
catalytic activity of CTS/CoMoO4-Mb/CILE to TCA and
H2O2 was investigated to probe its potential applications.
Figure 5 showed the cyclic voltammograms of the modified
electrode with different concentrations of TCA. It can be
seen that a new reduction peak appeared at −0.258 V (vs
SCE) with the addition of TCA, and the reduction peak
currents increased gradually with the disappearance of the
oxidation peak current, which was a typical electrocatalytic
reduction process. The linear relationship of the electro-
catalytic reduction peak current and TCA concentration was
constructed in the range from 0.1 to 32.0 mmol L−1 with the
linear regression equation as Iss (μA) =8.443C (mmol L−1) +
34.30 (n = 17, γ = 0.998). The detection limit, which was
calculated based on a signal-to-noise ratio of 3, was got as
0.036 mmol L−1 (3σ). When the TCA concentration was
more than 32.0 mmol L−1 the catalytic reduction peak currents
began to level off with a plateau appeared, which was a
typical Michaelis-Menten kinetic mechanism. So the apparent
Michaelis-Menten constant (KMapp), which gives an indi-
cation of the enzyme-substrate kinetics, can be obtained
from the following Lineweaver-Burk equation:40
where c is the bulk concentration of the substrate, Iss is the
steady current after the addition of substrate, and Imax is the
maximum current measured under saturated substrate condi-
tion. Then the KMap value was calculated as 0.547 mmol L−1
with the above equation. So the Mb molecules immobilized
on the electrode surface exhibited a high affinity for TCA. In
order to compare the electrochemical performance of Mb
modified electrodes, the electrochemical data were sum-
marized in Table 1. It can be seen that the CTS/CoMoO4-
Mb/CILE exhibited wider linear range and lower detection
limits for TCA detection.
Electrocatalysis of CTS/CoMoO4-Mb/CILE towards the
reduction of H2O2 was further investigated with the cyclic
voltammograms shown in Figure 6. With the addition of
different amounts of H2O2 into PBS, a new reduction peak
appeared at −0.255 V, indicating the electrocatalytic reduc-
tion. So the electrocatalytic reduction of H2O2 by Mb on the
modified electrode can be explained with the following
1
Iss
----- = 1
Imax
-------- + KM
app
Imaxc-----------
Figure 5. Cyclic voltammograms of CTS/CoMoO4-Mb/CILE inthe presence of 2.0, 4.0, 6.0, 8.0, 10.0, 12.0, 16.0, 22.0, 26.0, 30.0mmol L−1 TCA (a-j) in pH 3.0 PBS at the scan rate of 100 mV s−1.
Table 1. Electrochemical data of different Mb modified electrodes towards the reduction of TCA
Modified ElectrodesLinear Range
(mmol L−1)
Detection Limit
(mmol L−1)
Sensitivity
(µA mM−1)
KMapp
(mmol L−1)Refs
Mb/DNA/CILE 0.5-40.0 0.083 10.6 0.82 41
Nafion/Mb/Co/CILE 0.4-12.0 0.2 – 4.11 42
Nafion–BMIMPF6/Mb/CPE 0.2-11.0 0.016 48 – 43
Mb/ZrPNS/GCE 0.1-2.2 0.025 – – 44
Nafion/Mb/MWCNTs/CILE 1.57-12.0 0.1 58.2 3.396 45
CTS/CoMoO4-Mb/CILE 0.1-32.0 0.036 8.443 0.547 This work
BMIMPF6: 1-Butyl-3-methylimidazolium hexafluorophosphate; ZrPNS: zirconium phosphate nanosheets; MWCNTs: multi-walled carbon nanotubes
480 Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 Zengying Zhao et al.
equations:
Mb heme Fe(III) + H+ + e− → Mb heme Fe(II)
2 Mb heme Fe(II) + H2O2 + 2H+ → 2 Mb heme Fe(III) + 2H2O
The reduction peak current increased linearly with H2O2
concentration in the range from 0.12 to 397.0 μmol L−1 with
the linear regression equation as Iss(μA) = 0.0686C (μmol
L−1) + 16.62 (n = 19, γ = 0.998) and the detection limit was
calculated as 0.0426 μmol L−1 (3σ).
Based on the same method the apparent Michaelis-Menten
constant (KMapp) was further calculated as 0.016 mmol L−1.
A comparison of the results for the determination of H2O2
with different modified electrodes was also summarized
with the results listed in Table 2. Compared with other H2O2
biosensors, the fabricated CTS/CoMoO4-Mb/CILE had
wider linear range, lower detection limit, higher sensitivity
and smaller KMapp.
Interference. The influence of some possible interferents
on the voltammetric responses of 4.0 μmol/L H2O2 was
investigated by using the tolerable limit with the relative
deviation of ± 5%. No obvious interferences could be
observed with 1000 fold concentrations of K+, NH4+, Zn2+,
Mg2+, SO42−, Cl−, and 500 fold of ascorbate, uric acid,
acetaminophenol. The results indicated that this modified
electrode exhibited good selectivity.
Stability and Reproducibility. The stability and repro-
ducibility of CTS/CoMoO4-Mb/CILE was also studied. The
electrode was stored at room temperature when not in use, it
could remain 97.8% and 94.1% of its initial responses after
storage of 14 days and 30 days, respectively, which indicated
that the Mb modified electrode had good stability. Four
modified electrodes were fabricated with the same proce-
dure and further applied to the detection of 20.0 mmol L−1
TCA with a relative standard deviation (RSD) value of
2.37%. The results indicated that CTS/CoMoO4-Mb/CILE
exhibited good stability and reproducibility in the electro-
chemical application.
Conclusion
CoMoO4 nanorods were incorporated with Mb and further
modified on the CILE surface to get the Mb modified
electrode. The presence of CoMoO4 nanorods acted as an
efficient promoter to accelerate the direct electron transfer of
Mb with CILE, which may be due to the specific properties
of nanostructured CoMoO4. A pair of well-defined redox
peaks appeared on CTS/CoMoO4-Mb/CILE, which was
attributed to the direct electron transfer of Fe(III)/Fe(II) in
the redox protein. The electrocatalysis of Mb in the modified
electrode to the reduction of TCA and H2O2 was further
investigated with wider linear range and lower detection
limit. The CTS/CoMoO4-Mb/CILE electrode exhibited the
advantages such as long-term stability, high electrocatalytic
ability, good reproducibility and simply preparation proce-
dure. The results indicated the CoMoO4 nanorods had
potential applications in the field of the electrochemical
enzyme biosensor.
Acknowledgments. This work was supported by “the
Fundamental Research Funds for the Central Universities of
China, No. 2010ZY38” and the Laboratory Open Funds of
China University of Geosciences (Beijing).
Figure 6. Cyclic voltammograms of CTS/CoMoO4-Mb/CILE inthe presence of 0.0, 30.0, 100.0, 180.0, 280.0 µmol L−1 H2O2 (a-e)in pH 3.0 PBS at the scan rate of 100 mV s−1.
Table 2. Electrochemical data of different Mb modified electrodes towards the detection of H2O2
Modified ElectrodesLinear Range
(mmol L−1)
Detection Limit
(µmol L−1)
Sensitivity
(µA mM−1)
KMapp
(mmol L−1)Refs
Mb-HSG-SN-CNTs/GCE 2.0-1200 0.36 – 1.62 39
Mb/ZrPNS/GCE 0.8-12.8 0.14 – 0.034 44
{SG-Al2O3/Mb}9/PGE 1.0-125 0.6 0.265 – 46
Mb/ZrO2/MWCNT/GCE 1.0-116.0 0.53 17 0.085 47
Mb/HMS/GCE 4.0-124 0.062 424 0.065 ± 0.005 48
Mb/clay-IL/GCE 3.9-259 0.733 – 0.0173 49
Mb–TiO2/MWCNT/GCE 1-160 0.41 16.4 0.0831 50
PDDA/{ZrO2}3-Mb/PGE 0.02-3.0 0.01 2970 – 51
CTS/CoMoO4-Mb/CILE 0.12-397.0 0.0426 68.6 0.016 This work
PDDA: poly(diallyldimethylammonium); PGE: pyrolytic graphite electrode; GCE: glassy carbon electrode; SG: sol-gel; MWCNT: multi-walled carbonnanotube; HMS: hexago-nal mesoporous silica; IL: ionic liquid; HSG: hybrid silica sol-gel; SN-CNTs: Ag nanoparticle doped carbon nano-tubs;ZrPNS: zirconium phosphate nanosheets.
Electrochemistry of Myoglobin with CoMoO4 Nanorods Bull. Korean Chem. Soc. 2013, Vol. 34, No. 2 481
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