Electrodeposited MnO2/Au composite film with improved electrocatalytic activity for oxidation of glucose and hydrogen peroxide

Article abstract of DOI:10.1016/j.electacta.2010.01.095

The major drawback of currently used MnO₂ film sensor is the loss of electrical conductivity due to the formation of a poorly conductive MnO₂ layer. To overcome this problem, a coating in which the Au is alloyed with MnO₂ has been developed. The fabrication of the codeposited film electrode of Au and MnO₂ by using a cyclic voltammetric (CV) method was described, and systematic physical and electrochemical characterization was performed. This MnO₂/Au film electrode enhanced MnO₂ electrocatalytic activity. The oxidation process of glucose at the codeposited MnO₂/Au shows a well-defined peak at 0.27 V in alkaline aqueous solution. In contrast, the glucose oxidation at Au modified glassy carbon electrode (GCE) just shows a shoulder wave at 0.42 V. The experimental results indicate that the modification of MnO₂ on the surface of GCE significantly improved the electrocatalytic activity towards the oxidation of glucose. Further study shows that the MnO₂/Au could also effectively catalyze the oxidation of hydrogen peroxide in pH 7.0 phosphate buffer solution (PBS).

Full text of DOI:10.1016/j.electacta.2010.01.095

Electrochimica Acta 55 (2010) 3471–3476
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrodeposited MnO2/Au composite film with improved electrocatalytic
activity for oxidation of glucose and hydrogen peroxide
Yu Jun Yanga,b,c, Shengshui Hua,b,∗
a School of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China
b School of Chemistry and Chemical Engineering, Xuchang University, Xuchang 461000, China
c State Key Laboratory of Transducer Technology, Chinese Academy of Sciences, China
a r t i c l e i n f o
a b s t r a c t
Article history:
The major drawback of currently used MnO2 film sensor is the loss of electrical conductivity due to the
formation of a poorly conductive MnO2 layer. To overcome this problem, a coating in which the Au is
alloyed with MnO2 has been developed. The fabrication of the codeposited film electrode of Au and MnO2
by using a cyclic voltammetric (CV) method was described, and systematic physical and electrochemical
characterization was performed. This MnO2/Au film electrode enhanced MnO2 electrocatalytic activity.
The oxidation process of glucose at the codeposited MnO2/Au shows a well-defined peak at 0.27 V in
alkaline aqueous solution. In contrast, the glucose oxidation at Au modified glassy carbon electrode
(GCE) just shows a shoulder wave at 0.42 V. The experimental results indicate that the modification of
MnO2 on the surface of GCE significantly improved the electrocatalytic activity towards the oxidation of
glucose. Further study shows that the MnO2/Au could also effectively catalyze the oxidation of hydrogen
peroxide in pH 7.0 phosphate buffer solution (PBS).
Received 7 December 2009
Received in revised form 26 January 2010
Accepted 27 January 2010
Available online 2 February 2010
Keywords:
Electrocatalysis
Composite
Enzyme-free sensor
Electrodeposition
Glucose
© 2010 Elsevier Ltd. All rights reserved.
1. Introduction
and metallophthalocyanines [29–32] were widely used. It was also
reported that MnO2 with various crystalline structures are promis-
The electrocatalytic oxidation of glucose has been a focal sub-
ject of many investigations, because of the great importance of
glucose sensing in human blood and their potential use for fuel
cell applications [1–5]. Glucose oxidase as enzymatic catalyst has
been widely used for glucose biosensor fabrication [6–11]. Good
selectivity and high sensitivity have been achieved for glucose
detection by enzymatic glucose sensors. However, owing to the
nature of enzymes, the most common and serious problem with
enzymatic glucose sensors lies in their lack of long-term stability.
For instance, the activity of GODx can be easily affected by tem-
perature, pH value, humidity, and toxic chemicals [12–14]. Direct
electrocatalytic oxidation of glucose at an enzyme-free electrode
would exhibit conveniences and advantages to avoid the draw-
backs of the enzyme electrode. Early researches have focused on
the use of noble metal-based (containing Pt [15–17] and Au [18]),
and alloys-based (containing Pt, Ru, Pb, Au, and Cu [19–25]) elec-
trodes for developing enzyme-free sensors. Various attempts have
been made during recent years and modified electrodes made from
carbon nanotubes [26], CuO nanowire [27], CuO nanospheres [28]
ing electrode materials for electrocatalytical oxidation of glucose
[33,34].
Hydrogen peroxide is an intermediate or a product in biochem-
ical reactions catalyzed by oxidase. Thus, the monitoring of H2O2
with a reliable, rapid and economic method is of great significance
[35]. The catalytic effect of MnO2 towards the oxidation of H2O2
was also reported [36–38].
In this article, a new type of catalyst, MnO2/Au, with enhanced
sensing properties of glucose and hydrogen peroxide by taking
advantages of MnO2 [33,34] and Au [18], was prepared by a CV
deposition process. This MnO2/Au film exhibited excellent electro-
catalytic activity. It is highly tolerant to chloride ions and generates
more stable, reproducible and larger current responses compared
with other enzyme-free electrodes. Additionally, electro-oxidation
of glucose on such MnO2/Au surfaces took place at remarkably
more negative potentials and, thus, interference could be effec-
tively avoided by detecting glucose at a low potential.
2. Experimental
All chemical reagents used in this experiment were of analytical
grade. All solutions were prepared with doubly distilled water. Thin
film of MnO2/Au film was codeposited on GCE by cycling in 2 mM
HAuCl4, 10 mM KMnO4 and 0.04 M H2SO4 aqueous solution from
∗
Corresponding author at: College of Chemistry & Molecular Sciences, Wuhan
University, Wuhan 430072, China.
E-mail addresses: sshu@whu.edu.cn, cghu@whu.edu.cn,
yangyujun418@gmail.com (S. Hu).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.01.095

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Y.J. Yang, S. Hu / Electrochimica Acta 55 (2010) 3471–3476
Fig. 1. Scanning electron micrographs of gold (a), MnO2 (b) and MnO2/Au (c) electrodeposited on GCE.
−
0.3 V to −0.5 V at the scan rate of 2 mV s−1 for 2 cycles. Au modified
GCE (Au/GCE) was prepared by CV in 2 mM HAuCl4, 0.04 M H2SO4
solution (from 0.3 V to −0.5 V at the scan rate of 2 mV s−1) for 2
cycles. MnO2 modified GCE (MnO2/GCE) was prepared by CV in
6 mM KMnO4, 0.04 M H2SO4 solution (from 0.3 V to −0.5 V at the
scan rate of 2 mV s−1) for 2 cycles.
of MnO4 species and precipitation of manganese dioxide are in
agreement with the Pourbaix diagram for Mn [39]. However, only
limited information is available in literature related to the com-
plex chemistry of the reduction of MnO4−. The kinetic pathway of
reducing Mn7+ to Mn4+ depends on electrode potential, pH, concen-
−
tration of MnO4 and other species in the solutions [40]. In acidic
aqueous solutions the following reaction can result in the reduction
A three-electrode electrolytic cell was employed for electrode-
position and electrochemical tests. A GCE (5 mm diameter) was
used as the cathode. A platinum wire was used as an anode. The sat-
urated calomel electrode (SCE) was used as a reference electrode.
Morphology study of the films on the GCE surface was carried out
with a Quanta 200 scanning electron microscope (SEM; FEI Com-
pany, Holland). The electrochemical tests were carried out with a
CHI 830 potentiostat (Chen Hua Company, China).
3. Results and discussion
Fig. 1 shows the SEM micrographs of the Au, MnO2 and MnO2/Au
thin films electrodeposited on GCE. The pure Au sample (Fig. 1a)
consists of nanoparticles with the average diameter of about
200 nm. The pure MnO2 sample (Fig. 1b) shows a surface morphol-
ogy resembling that of the GC substrate, indicating the presence
of a continuous MnO2 film on top of the substrate rather than iso-
lated particles. Fig. 1c corresponding to the codeposited MnO2/Au
catalyst indicates the presence of MnO2/Au microspheres with the
diameter ranging between 200 nm and 1.2 ␮m.
The deposition mechanism can be attributed to the diffusion
and cathodic reduction of anionic MnO4 species. The reduction
−
Fig. 2. XRD pattern of the MnO2 film electrodeposited on GCE.

Y.J. Yang, S. Hu / Electrochimica Acta 55 (2010) 3471–3476
3473
Fig. 4. The CV behaviors of the bare GCE (curve a), MnO2 modified GCE (curve b),
gold modified GCE (curve c) and MnO2/Au modified GCE (curve d) in 10 mM glucose,
0.1 M NaOH solution at 100 mV s−1, scan range: −0.5 V to 0.7 V, initial potential:
−0.5 V.
Fig. 3. The CV behaviors of the MnO2/Au modified GCE in the absence (a) and pres-
ence (b) of 10 mM glucose in 0.10 M NaOH solution at 100 mV s−1, scan range: −0.5 V
to 0.7 V, initial potential: −0.5 V.
−
of MnO4 species:
(XPS), Raman spectroscopy (RS) and electrochemically modulated
infrared spectroscopy (EMIRS). Their experimental results indicate
that, in borate solutions at pH 9.2, during the MnO2 reduction,
MnO2 is reduced to Mn(III)OOH while in the reversal positive scan,
Mn(III)OOH was oxidized to MnO2:
MnO4− + 4H+ + 3e− → MnO2 + 2H2O
(1)
Fig. 2 shows a typical XRD pattern of the as-synthesized pure MnO2
sample. All the reflection peaks can be readily indexed to pure
body-centered tetragonal ␣-MnO2 phase, with lattice constants of
a = 9.816 Å, c = 2.857 Å; which are in agreement with the standard
values (JCPDS 44-0141, a = 9.784 Å, c = 2.863 Å). No other phase was
detected in the final products.
MnO2 + H2O + e = MnOOH + OH−
MnOOH + OH− − e = MnO2 + H2O
(2)
(3)
The electrocatalytic performance of the MnO2/Au towards the
oxidation of glucose was investigated by CV. Fig. 3 shows the CV
behaviors of the MnO2/Au in the absence (a) and presence (b) of
10 mM glucose in 0.10 M NaOH solution. CV of the MnO2/Au mod-
ified GCE in 0.1 M NaOH aqueous solution showed two pairs of
redox peaks (curve a). The thin MnO2 electrodeposited on gold
has been studied [41,42] using X-ray photoelectron spectroscopy
Without the addition of glucose, there is a pair of redox peaks
for the MnO2/Au modified electrode in alkaline solution (Fig. 3a). In
the negative scan, MnO2 was reduced to MnOOH, which was subse-
quently oxidized to MnO2 in reversal scan. Two anodic peaks (peak
Ia and IIa) can be assigned to the oxidation of MnOOH to Mn(IV), and
gold to gold oxide, respectively. Two cathodic peaks (peaks Ic and
IIc) can be taken to represent the generation of MnOOH from Mn(IV)
Fig. 5. (a) CVs of MnO2/Au modified GCE in 0.10 M NaOH solution containing 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1.0 mM glucose at 100 mV s−1; (b) CVs of MnO2/Au
modified GCE in 0.10 M NaOH solution containing 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 and 10.0 mM glucose at 100 mV s−1; (c) the plot of the oxidation peak current with the
concentration of glucose.

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Y.J. Yang, S. Hu / Electrochimica Acta 55 (2010) 3471–3476
Fig. 6. CVs of MnO2/Au modified GCEs in 0.10 M NaOH, 0.10 M KCl solution containing 6.0 mM glucose at 100 mV s−1. The MnO2/Au modified GCEs were prepared in 5 mL
deposition bath containing 2 mM HAuCl4, 10 mM KMnO4 and 0.04 M H2SO4, scan range: 0.3 V to −0.5 V, initial potential: 0.3 V, (a) at scan rate of 1, 2, and 4 mV s−1 for 1, 2,
and 4 cycles, respectively and (b) at 2 mV s−1 for 1, 2, and 3 cycles.
[43], and gold oxide to gold, respectively [18]. In the presence of
glucose, two strong anodic peaks (peak IIIa and IVa) were observed
at 0.271 V and 0.076 V (curve b) during the anodic scan and the
reverse cathodic scan, respectively while the peak current of peak
IIa increased significantly with the addition of glucose. The peak IIIa
at 0.271 V presents the oxidation process of glucose. Above a poten-
tial of +0.3 V, the decrease of current occurs due to the formation of
gold oxide, which competes for surface adsorption sites with glu-
cose, also inhibiting the direct electro-oxidation of glucose. In the
reverse cathodic scan, with the reduction of the surface gold oxide,
enough surface active sites are available for the direct oxidation of
glucose, resulting in large peak at around 0.076 V.
The electrocatalytic performance of the bare GCE, Au/GCE,
MnO2/GCE and MnO2/Au modified GCE (MnO2/Au/GCE) towards
the oxidation of glucose was investigated by CV. Fig. 4 illus-
trates the CV behaviors of the bare GCE, MnO2/GCE, Au/GCE, and
MnO2/Au/GCE in 0.10 M NaOH solution containing 10 mM glucose.
No current response is observed at the bare GCE (cure a). Because of
the loss of electrical conductivity due to the formation of a poorly
conductive MnO2 layer, it is not a surprise to find out that no
peak occurs on MnO2/GCE (curve b). A barely observable anodic
peak is obtained at 0.42 V during the anodic scan at the Au/GCE
(curve c). In the case of the MnO2/Au/GCE, three strong anodic
peaks are observed at 0.271 V, 0.076 V and 0.45 V (curve d). Like
MnO2/Au/GCE electrode, there is an anodic peak at ∼0.2 V during
the cathodic scan for Au/GCE electrode too (curve c). The anodic
peak at 0.16 V for Au/GCE electrode is also due to the oxidation of
glucose [44].
current response after it was stored at room temperature for 30
days, indicating the excellent stability of the sensor. These results
demonstrate that the MnO2/Au electrode is very efficient for the
determination of glucose.
As shown in Fig. 4, MnO2 in the MnO2/Au plays a crucial role for
the oxidation of glucose. The catalytic effect of MnO2 towards the
oxidation of glucose is probably due to a parallel catalytic reaction.
As soon as MnO2 is reduced to lower valence states by glucose,
it is electro-oxidized back to MnO2 at the electrode surface. The
catalytic mechanism of gold towards the oxidation of glucose in
alkaline solution may be described as following [18]:
Au + OH− = AuOH + e
(4)
−
OH
AuOH + CHO(CHOH)4CH2OH−→ COOH(CHOH)4CH2OH
+Au + H2O + e
(5)
Therefore, MnO2 and gold act not only as the electron mediate but
as catalyst as well [33]. Studies on the SEM of MnO2/Au/GCE (Fig. 1c)
and Au (Fig. 1b) further confirm our assumption that the improve-
ment in catalytic activity is attributed to catalytic effects of MnO2
and gold rather than any physical effects (such as increase in surface
area).
The effects of scan rate and number of scan cycles during the
CV deposition process on the catalytic oxidation of glucose were
also investigated. As shown in Fig. 6a, the oxidation peak shifted
positively as the scan rate is increased from 1 to 2 and 4 mV s−1
The CVs of the MnO2/Au electrode in different concentrations of
glucose were also measured. Fig. 5a and b shows the standard addi-
tions of 100 ␮M and 1 mM of glucose, respectively, and after each
addition the voltammetric response was recorded. These results
clearly indicate that, as the concentration of glucose increased, the
peak currents of three anodic peaks at 0.271 V, 0.076 V and 0.45 V
also increased. The variation of the peak current at 0.271 V vs. glu-
cose concentration is linear in the glucose concentration range of
100 ␮M to 20 mM with a sensitivity and correlation coefficient of
18.9 ␮A mM−1 and 0.9988, respectively. This linear concentration
range of 0.1–20 mM is of advantage as the likely glucose level in
normal and diabetic person usually varies from 0.2 to 20 mM [45].
The anodic peak at 0.076 V is assigned to the oxidation of glucose.
Thus, it is not surprising to find out that the peak current at 0.076 V
is also linear with the glucose concentration. The fabrication repro-
ducibility of six biosensors, prepared under the same conditions,
showed an acceptable reproducibility with a R.S.D. of 3.2% for the
peak current obtained in the glucose concentration of 1.0 mM. The
results indicate that the MnO2/Au electrode has a good operational
stability. The activity of the electrode retained almost its initial
Fig. 7. (a) CVs of MnO2/Au modified GCE in 0.10 M NaOH, 0.10 M KCl solution con-
taining 6.0 mM glucose at 100 mV s−1 and (b) CVs of MnO2/Au modified GCE in
0.10 M NaOH solution containing 6.0 mM glucose at 100 mV s−1
.

Y.J. Yang, S. Hu / Electrochimica Acta 55 (2010) 3471–3476
3475
Fig. 8. (a) CVs of H2O2 on MnO2/Au/GCE in PBS (pH 7.0) in the absence (curve a) and presence of 10 mM H2O2 (curve b). Scan rate: 100 mV s−1; (b) dynamic current responses
of MnO2/Au/GCE to successive addition of H2O2 at pH 7.0. Inject 20 ␮L 5 × 10−2 M H2O2 solution into 10 mL PBS (pH 7.0) with a microsyringe. The concentration change of
H2O2 is 10 ␮M per addition. Applied potential: 0.70 V; (c) calibration curve of H2O2 amperometric biosensor based on MnO2/Au/GCE in PBS buffer (pH 7.0). Applied potential
0.70 V.
while the highest peak current is obtained at 2 mV s−1. At 2 mV s−1
,
cant oxidative current at potentials between 0.5 V and 1.0 V (curve
b). The current for the oxidation of Mn(II,III) to MnO2 significantly
increases with increasing H2O2 concentration. The characteristic
shape of the CV in this potential region indicates that the signal
is probably due to a parallel catalytic reaction. As soon as MnO2
is reduced to lower states by H2O2, it is electro-oxidized back to
MnO2 at the electrode surface [36]:
the oxidation current is increased significantly with increasing the
number of scan cycles from 2 to 3 cycles (Fig. 6b). However the
obtained film will be too thick and easy to crack when the GCE was
scanned for 3 cycles in the plating bath. Thus, the number of scan
adopted in this experiment is 2 cycles.
To evaluate the selectivity of the proposed biosensor, three pos-
sible interfering biomolecules, ascorbic acid (AA), dopamine (DA),
and uric acid (UA), which normally coexist with glucose in real
samples (human blood) were examined [46]. Considering that the
concentrationof glucose in thehumanbloodis about30times ofAA,
DA or UA, the voltammetric response of the MnO2/Au towards the
addition of 1 mM glucose and 0.1 mM AA, DA, and UA was examined
in 0.10 M NaOH solution and the iglucose+interferent/iglucose is 103%,
99% and 98%, respectively. To sum up, the selectivity was improved
so much on this enzyme-free biosensor that the three common
interfering biomolecules, AA, DA, and UA caused negligible inter-
ference to the response of glucose at the MnO2/Au electrode.
Electrodes based on metals [15,17] or alloys [18,24] towards the
oxidation of glucose usually lose their activity due to the poisoning
of chloride ions [19]. In order to understand whether chloride ions
will poison the MnO2/Au electrode, the CV was measured in the
solution with high concentration of chloride ions (i.e., replacing
0.10 M NaOH with 0.10 M KCl + 0.10 M NaOH as the electrolyte).
The current response of MnO2/Au/GCE towards glucose oxidation
remains almost unchanged (Fig. 7), implying that the MnO2/Au/GCE
is also highly resistant to poisoning by chloride ions and can be used
as a glucose sensor even in the presence of high concentration of
chloride ions.
MnO2 + H2O2 → MnO (or Mn2O3) + O2 + H2O
MnO (or Mn2O3) → MnO2 + 2e
(6)
(7)
Since the above two reactions are fast, the parallel current is much
higher than the oxidation current of MnO2 on the electrode sur-
face without H2O2. Effect of applied potential on the amperometric
response of 10 ␮M H2O2 in phosphate buffer solution was studied.
Although at 0.80 V the signal is highest, we choose 0.70 V as the
operating potential because above 0.70 V there is increased noise,
which is a disadvantage for measuring low H2O2 concentrations.
The relationship between the oxidation current and the concentra-
tion of H2O2 was examined in a PBS solution (pH 7.0). The solution
was stirred to ensure uniform distribution of H2O2 in the cell. Fig. 8b
displays the amperometric response for the H2O2. When the same
amount of H2O2 was injected into the cell, the concentration change
of H2O2 in the cell is 10 ␮M per addition and the current was
recorded instantly. Calibration curves for H2O2 measurement are
also presented in Fig. 8c. The current is linear for concentrations of
H2O2 from 5 × 10−6 to 1 × 10−2 M. The upper limit of linearity range
(10−2 M) was attained by examining the relationship between the
oxidation current and the concentration of H2O2 after injecting
same amount of H2O2 (concentration change: 5 × 10−4 M/addition)
into the cell. The sensitivity of the sensor to H2O2 was calculated
to be 1.49 × 104 ␮A M−1. The detection limit was estimated to be
1 × 10−6 M (signal/noise = 3).
Fig. 8a shows the CVs for hydrogen peroxide with the prepared
MnO2/Au modified GCE. In the absence of hydrogen peroxide, there
is a pair of very broad but barely observable waves between 0.2 V
and 0.8 V (curve a) in PBS solution. It may be assigned to the reduc-
tion of MnO2 to Mn(II,III) and the reoxidation of Mn(II,III) back to
MnO2 [36]. In the presence of H2O2, the CV displays a very signifi-

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Y.J. Yang, S. Hu / Electrochimica Acta 55 (2010) 3471–3476
[16] A.N. Gracea, K. Pandian, J. Phys. Chem. Solids 68 (2007) 2278.
4. Conclusion
[17] X.H. Kang, Z.B. Mai, X.Y. Zou, P.X. Cai, J.Y. Mo, Talanta 74 (2008) 879.
[18] M. Tominaga, T. Shimazoe, M. Nagashima, H. Kusuda, A. Kubo, Y. Kuwahara, I.
Taniguchi, J. Electroanal. Chem. 590 (2006) 37.
[19] Y.P. Sun, H. Buck, T.E. Mallouk, Anal. Chem. 73 (2001) 1599.
[20] R. Qiu, X.L. Zhang, R. Qiao, Y. Li, Y.I. Kim, Y.S. Kang, Chem. Mater. 19 (2007) 4174.
[21] S.B. Aoun, Z. Dursun, T. Koga, G.S. Bang, J. Electroanal. Chem. 567 (2004) 175.
[22] H.F. Cui, J.S. Ye, X. Liu, W.D. Zhang, F.S. Sheu, Nanotechnology 17 (2006) 2334.
[23] C.C. Jin, Z.D. Chen, Synth. Met. 157 (2007) 592.
[24] J.P. Wang, D.F. Thomas, A.C. Chen, Anal. Chem. 80 (2008) 997.
[25] Y. Bai, Y.Y. Sun, C.Q. Sun, Biosens. Bioelectron. 24 (2008) 579.
[26] J.S. Ye, Y. Wen, W.D. Zhang, L.M. Gan, G.Q. Xu, F.S. Sheu, Electrochem. Commun.
6 (2004) 66.
In this work we have been able to synthesize MnO2/Au on the
surface of GCE via a simple CV codeposition method. The size and
morphology of the sample was investigated through the use of FE-
SEM showing the sample to consist of MnO2/Au nanoclusters. These
MnO2/Au modified GCEs can be used in the catalytic oxidation of
glucose and hydrogen peroxide. This novel MnO2/Au composite
film is a potential candidate for application in terms of fuel cells
and enzyme-free sensors.
[27] Z.J. Zhuang, X.D. Su, H.Y. Yuan, Q. Sun, D. Xiao, M.M.F. Choi, Analyst 33 (2008)
126.
[28] E. Reitz, W.Z. Jia, M. Gentile, Y. Wang, Y. Lei, Electroanalysis 20 (2008) 2482.
[29] C. Barrera, I. Zhukov, E. Villagra, F. Bedioui, M.A. Paez, J. Costamagna, J.H. Zagal,
J. Electroanal. Chem. 589 (2006) 212.
[30] K.I. Ozoemena, T. Nyokong, Electrochim. Acta 51 (2006) 5131.
[31] P.N. Mashazi, K.I. Ozoemena, T. Nyokong, Electrochim. Acta 52 (2006) 177.
[32] L. Ozcan, Y. Sahin, H. Turk, Biosens. Bioelectron. 24 (2008) 512.
[33] D. Das, P.K. Sen, K. Das, J. Electroanal. Chem. 611 (2007) 19.
[34] J. Chen, W.D. Zhang, J.S. Ye, Electrochem. Commun. 10 (2008) 1268.
[35] K. Schachl, H. Alemu, K. Kalcher, I. Svancara, K. Vytras, Analyst 122 (1997) 985.
[36] S.J. Yao, S. Yuan, J.H. Xu, Y. Wang, J.L. Luo, S.S. Hu, Appl. Clay Sci. 33 (2006) 35.
[37] X.W. Zheng, Z.H. Guo, Talanta 50 (2000) 1157.
[38] K. Schachl, H. Alemu, K. Kalcher, H. Moderegger, I. Svancara, K. Vytras, Fresenius
J. Anal. Chem. 362 (1998) 194.
[39] A. Moussard, J. Brenet, F. Jolas, M. Pourbaix, J. van Muylder, in: M. Pourbaix (Ed.),
Atlas of Electrochemical Equilibria in Aqueous Solutions, National Association
of Corrosion Engineers, Pergamon Press, Oxford, 1974.
[40] J. Wei, I. Zhitomirsky, Surf. Eng. 24 (2008) 45.
[41] B.A. Lopez de Mishima, T. Ohtsuka, K. Konno, N. Sato, Electrochim. Acta 36
(1991) 1458.
Acknowledgement
The authors acknowledge financial support by the National
Nature Science Foundation of China (Nos. 30770549, 20805035 and
90817103).
References
[1] J.L.C. Clark, C. Lyons, A.N.Y. Aead, Science 102 (1962) 29.
[2] G. Reach, G.S. Wilson, Anal. Chem. 64 (1992) 381A.
[3] A.P.F. Turner, B. Chen, A.P. Sergey, Clin. Chem. 45 (1999) 1596.
[4] E. Katz, I. Willner, A.B. Kotlyar, J. Electroanal. Chem. 479 (1999) 64.
[5] N. Mano, F. Mao, A. Heller, J. Am. Chem. Soc. 125 (2003) 6588.
[6] X.H. Kang, Z.B. Mai, X.Y. Zou, P.X. Cai, J.Y. Mo, Anal. Biochem. 369 (2007) 71.
[7] S.G. Wang, Q. Zhang, R.L. Wang, S.F. Yoon, J. Ahn, D.J. Yang, Electrochem. Com-
mun. 5 (2003) 800.
[8] H. Tang, J.H. Chen, S.Z. Yao, L.H. Nie, G.H. Deng, Y.F. Kuang, Anal. Biochem. 331
(2004) 89.
[42] B.A. Lopez de Mishima, T. Ohtsuka, N. Sato, Electrochim. Acta 38 (1993) 341.
[43] C. Batchelor-McAuley, L. Shao, G.G. Wildgoose, M.L.H. Green, R.G. Compton,
New J. Chem. 32 (2008) 1195.
[44] M.P. Bui, S. Lee, K.N. Han, X.H. Pham, C.A. Li, J. Choo, G.H. Seong, Chem. Commun.
(2009) 5549.
[9] X. Chu, D.X. Duan, G.L. Shen, R.Q. Yu, Talanta 71 (2007) 2040.
[10] Y.J. Zou, C.L. Xiang, L.X. Sun, F. Xu, Biosens. Bioelectron. 23 (2008) 1010.
[11] Y.C. Tsai, S.C. Li, J.M. Chen, Langmuir 21 (2005) 3653.
[12] R. Wilson, A.P.F. Turner, Biosens. Bioelectron. 7 (1992) 165.
[13] F. Shoji, M.S. Freund, J. Am. Chem. Soc. 123 (2001) 3383.
[14] S.J. Park, H.K. Boo, T.D. Chung, Anal. Chim. Acta 556 (2006) 46.
[15] B. Beden, F. Largeaud, K.B. Kokoh, C. Lamy, Electrochim. Acta 41 (1996) 701.
[45] B.R. Eggins, Chemical Sensors and Biosensors, John Wiley & Sons, UK, 2003.
[46] B.H. Liu, R.Q. Hu, J.Q. Deng, Anal. Chem. 69 (1997) 2343.