Iwamoto M., Kwon Y.-S., Lee T. (Eds.) Nanoscale Interface for Organic Electronics
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Self-Assembled Viologen Derivative and Its Application 59
counter and reference electrode, respectively. We observed the charge
transfer properties of self-assembled viologen monolayers in 0.1 M
NaClO
4
electrolyte solution. The scan range was from 0 to -1.0 V and the
estimation of the peak current was based on the second cycle of the
cyclic voltammetry (CV) curve. In biosensor experiment, the stock
solutions were made by phosphate buffer solution (PBS, pH 7). HCl was
used to maintain pH.
4. Results and Discussions
4.1. Verification of Self-Assembly by Resonant Frequency Shift
The self-assembling of viologen onto the gold electrode of the QCM
was investigated by resonance properties. Figure 4 shows the time
dependence to resonance frequency and resonance resistance shift of
the QCM in ethanol-acetonitrile solution. In this case, the frequency
decreased rapidly at first, and then the rate of decrease slowed. The
assembling process was completely finished about 60 min. The measured
frequency shift was about 386 Hz. From this value, we calculated that
the adsorption mass was about 412 ng/cm
2
, according to the Sauerbrey
equation (Eq. (1)).
40-42
Fig. 4. Resonance properties during self-assembling process using QCM.
D.-Y. Lee et al. 60
4.2. Redox Reaction and Electrochemical QCM Response
After the adsorption of viologen onto the gold electrode of the QCM
was completed, the electrode was rinsed with ethanol:acetonitrile (1:1)
solution and determined the electrochemical behavior. Figure 5(a) shows
cyclic voltammograms of the self-assembled viologen mololayer onto
gold-electrode of the QCM at different scan rates (50, 100, 200, and
400 mV) in 0.1 M NaClO
4
. This is consequence of the first charge
reaction, V
2+
↔ V
•+
. A pair of well-defined redox peaks determined. All
curves indicated reversible broad redox reactions,
43
and the cathodic
potential (E
pc
) and anodic potential (E
pa
) peaks were centered at -0.51 V
and -0.47 V, respectively. In this case, the difference of E
pc
and E
pa
was below 59 mV (
│E
pc
– E
pa
│< 59/n mV). From this value, the redox
reaction was completely reversible reaction according to the Nernst
equation (5).
14
0 0
[ ] [ ]
ln 0.059ln
[ ] [ ]
RT ox ox
E E E
nF red red
= + = + (5)
where, E
0
is formal potential, R is the gas constant (8.314 J/mol), T is
absolute temperature, n is electron number in redox reaction and F is the
Faraday’s constant (96,520 C/mol).
(a) (b)
Fig. 5. Cyclic voltammograms reaction of self-assembled viologen monolayer at different
scan rate (a) and relationship of scan rate and peak current (b) in 0.1 M NaClO
4
electrolyte solution.
Self-Assembled Viologen Derivative and Its Application 61
Figure 5(b) shows the relationship between scan rates and peak
currents. When the scan rate was increased, the redox peak current also
increased linearly. This fact signified that the redox reaction was
reversible.
17
Peak currents were increased linearly with potential scan
rates with the square root of the scan rates, and the peaks were also
symmetrical.
44
Figure 6 shows the resonant frequency change which obtained during
the CV for this same monolayer in NaClO
4
electrolyte solution. In CV,
this was consequence of the first electron reaction, V
2+
+ e
-
⇔ V
•+
. The
frequency change was about 18.1 Hz. From the data, the transferred mass
was about 19.36 ng by Sauerbrey equation (1). Multiplying by Avogadro
number, the number of shifted ions were about 2.33 × 10
13
. We believe
that this mass change was caused by the anions present for charge
compensation of the viologen and some solvent. The EQCM frequency
data reveal that mass is lost during the reduction process and that mass
loss is reversed during the oxidation. These frequency changes have been
previously interpreted as indicative of anion loss (gain) from the
monolayer, which is consequent to the injection (removal) of electrons.
4.3. Electrochemistry of the Hb/Viologen-Modified Gold Electrode
Figure 7 shows the CVs recorded for the VC
8
SH/Au (solid line) and
Hb/VC
8
SH/Au (dashed line) in 0.1 M PBS (pH 6.0). It can be seen that
Fig. 6. Resonant frequency shift during the redox reaction in 0.1 M NaClO
4
electrolyte
solution. (Scan rate is 100 mV/s).
D.-Y. Lee et al. 62
only viologen-modified electrode gives a well-defined redox peaks. The
peaks are located at -530 mV and -620 mV. But it is noteworthy, after
the immersion of the VC
8
SH/Au into the solution containing Hb, there is
a new pair of peak appears at lower negative potential. For this new
redox peaks, the formal potential E
0
, was determined to be -135 mV form
the average value of the cathodic and anodic peaks which are centered at
-30 mV and -240 mV, respectively. This formal potential (-130 mV) is
slightly negative compared with standard potential of Hb at gold colloid-
thiol-modified gold electrode.
45
Therefore, it can be stated that new
redox peaks arise from heme groups of Hb that immobilized onto the
viologen-modified electrode. Normally only hemoglobin does not show
any electrochemical characteristics as mentioned above. So, in case of
this, redox-active viologen derivative is playing an important role to
exchange electrons between Hb and electrode.
4.4. Catalytic Properties of the Sensor Towards H
2
O
2
Figure 8 shows the CVs obtained from the Hb/VC
8
SH-modified gold
electrode in presence (dashed line) and absence (solid line) of H
2
O
2
in
0.1 M PBS at pH 6.0. As shown in Fig. 5, when 1
× 10
-4
M H
2
O
2
was
added into the electrolyte solution, an obvious increase of the cathodic
peak current and the disappearance of the anodic peak current were
observed. Therefore, it can be said that upon addition of H
2
O
2
increased
Fig. 7. CVs of VC
8
SH/Au and Hb/VC
8
SH/Au electrode in 0.1 M PBS (pH 6.0). (Scan
rate: 200 mV/s).
Self-Assembled Viologen Derivative and Its Application 63
reduction current at the electrode, indicated the electrocatalytic reduction
property of H
2
O
2
.
However, this obvious increase in the cathodic current
indicated that the Hb keeps its natural structure after immobilizing
onto the viologen SAM-modified electrode. The generic reaction for
reduction of H
2
O
2
by Hb could be as follows.
Heme - Fe
2+
+ 2H
2
O
2
→ Heme - Fe
3+
+ 2H
2
O + O
2
Heme - Fe
2+
→ Heme - Fe
3+
+ e
-
4.5. Optimum Conditions of the Biosensor for Detecting H
2
O
2
The pH value is one of the most important factors for working with
biosensor that affect the response of the electrode to H
2
O
2
. So we
investigated the pH effect on the sensor response in presence of H
2
O
2
.
Figure 9 shows the cathodic current response of the sensor at different
pH in presence of 1
× 10
-4
M H
2
O
2
. According to this figure, it can be
seen that the peak current which attains the maximum level at pH 6.0.
When the pH was more than 6.0, the peak current started to decrease
slowly. In the pH range 3.0 ~ 6.0, the peak current increases steeply.
Especially for pH value < 4.0, the current response is very low. At these
pH values, the low response may be due to the denaturation of Hb.
Therefore, pH 6.0 was chosen to be used for working media solution to
determine H
2
O
2
of this sensor.
Fig. 8. Cyclic voltammograms Hb/VC
8
SH/Au electrode in the presence of 1 × 10
-4
M
H
2
O
2
and absence of H
2
O
2
.
D.-Y. Lee et al. 64
Influence of applied potential on amperometric response of the
biosensor also is an important parameter. We studied the influence of
applied potential on current response of the biosensor to H
2
O
2
. Figure 10
displays the attributed current at different applied potential in presence of
2.5
× 10
-5
M H
2
O
2
. The resulting data shows that the steady-state current
increases gradually as voltage increases from -100 mV to -300 mV.
According to this experiment, the maximum current was achieved at
-300 mV. Therefore, we have chosen applied potential -300 mV as the
working potential for this sensor.
Fig. 9. Effect of pH in the presence of 1 × 10
-4
M H
2
O
2
.
Fig. 10. Influence of applied potential on the amperometric response of the sensor in the
presence of 2.5 × 10
-5
M H
2
O
2
.
Self-Assembled Viologen Derivative and Its Application 65
4.6. Amperometric Response of the Biosensor
Figure 11 illustrates the amperometric response of the Hb/VC
8
SH-
modified gold electrode using the chronoamperometric technique that
consists of successive additions 1
× 10
-5
M H
2
O
2
in the PBS (pH 6.0) as
recorded at operating potential of -300 mV. It can be observed that as
soon as adding H
2
O
2
,
the background current was changed and the
reduction current rises steeply to reach value. Figure 12 displays
calibration plot obtained for the Hb/VC
8
SH-modified gold electrode
using optimum experimental conditions. Under the optimized experimental
Fig. 11. Typical steady-state current-time response of the sensor with successive
additions of 1 × 10
-5
M H
2
O
2
to the 0.1 M PBS (pH 6.0).
Fig. 12. Calibration curve of the biosensor.
D.-Y. Lee et al. 66
parameters, this sensor shows the linear response within the range
between 1
× 10
-5
to 1.6 × 10
-4
M concentrations of H
2
O
2
with a correlation
coefficient of 0.996 (n = 12). The detection limit was determined to be
3.0
× 10
-7
M (based on the S/N = 3).
45
This detection limit is lower than
the other biosensor.
4.7. Stability of the Biosensor
The repeatability of the sensor for current response was examined. It
was found relative standard deviation (RSD) 3.75% for ten successive
determinations at a H
2
O
2
concentration of 20 µM. The long-term stability
of this biosensor also was investigated over 30 days period. When the
Hb/VC
8
SH-modified gold electrode was not in use, it was stored in
PBS (pH 7). To examine this, the response of the Hb/VC
8
SH-modified
electrode to the H
2
O
2
was tested. It retained 90% of its initial current
response after 30 days.
5. Conclusions
We have demonstrated a self-assembled method to prepare well-defined
of a viologen derivative. The self-assembled process was determined
by resonant frequency shift. The electrochemical property of viologen
derivative was characterized in 0.1 M NaClO
4
, Na
2
SO
4
and Na
3
PO
4
and
electrolyte solutions using cyclic voltammetry. The modified electrode
showed reversible electrochemical properties and high stability. The
EQCM response was simultaneously determined by resonant frequency
during cyclic voltammetry. From the result, the immersed viologen can
act as an electron transfer mediator to access to the electrode surface
because the mass change for SAMs was not only governed by the
mobility of the ion in the viologen but also by the valence of the ion in
the electrolyte solution. We know the viologen molecules have their
own properties without regard to the influence of electrolyte solutions.
Furthermore, we expect that the ability to contact metal nanoparticles
electronically via redox-active molecules can form a basis for a range of
nanoscale electronic switches.
46
We have also demonstrated a simple
method for designing a H
2
O
2
biosensor using Hb. It has proved that
Self-Assembled Viologen Derivative and Its Application 67
thiol-viologen provided a suitable biocompatible microenvironment for
Hb. The catalytic properties of the designed sensor proved that Hb has
been kept its natural structure and can retain its biological activity. The
designed biosensor shows fast amperometric response, excellent linearity
and low detection limit. In addition, it shows very high sensitivity, good
reproducibility and stability.
Acknowledgment
This study was supported by research funds from Dong-A University.
References
1. N. Nakamura, H. X. Huang, D. J. Qian and J. Miyake, Langmuir 18, 5804 (2002).
2. A. Ulman, Academic Press, San Diego, Chap. 3 (1991).
3. R. Z. Nuzzo and D. L. Allara, J. Am. Chem. Soc. 105, 4481 (1983).
4. R. Maoz and J. Sagiv, Langmuir 3, 1034 (1987).
5. M. R. Deakin and D. A. Buttry, Anal. Chem. 61, 1147A (1989).
6. D. Y. Lee, S. H. Park, H. K. Shin, D. J. Qian and Y. S. Kwon, Mol. Cryst. Liq. Cryst.
445, 439 (2006).
7. J. Y. Ock, H. K. Shin, S. H. Song, S. M. Chang, D. J. Qian, J. Miyake and Y. S.
Kwon, Mol. Cryst. Liq. Cryst. 407, 525 (2003).
8. J. Y. Ock, H. K. Shin, D. J. Qian, J. Miyake and Y. S. Kwon, Jpn. J. Appl. Phys. 43,
2376 (2004).
9. H.-X. Huang, D.-J. Qian, N. Nakamura, C. Nakamura, T. Wakayama and J. Miyake,
Electrochim. Acta 49, 1491 (2004).
10. H. W. Kang, J. M. Kim, H. K. Shin and Y. S. Kwon, J. Kor. Phys. Soc. 32, 1750
(1998).
11. D. A. Buttry and M. D. Ward, Chem. Rev. 92, 1355 (1992).
12. S. Chen and F. Deng, Langmuir 18, 8942 (2002).
13. J.-Y. Ock, H.-K. Shin, Y.-S. Kwon and J. Miyake, Coll. Surf. A 257-258, 351 (2005).
14. A. J. Bard and L. R. Faulkner, J. Wiley, New York, Chap. 12 (1980).
15. K. Takada and H. D. Abruna, J. Phys. Chem. 100, 17909 (1996).
16. D.-Y. Lee, A. K. M. Kafi, S.-H. Park, D.-J. Qian and Y.-S. Kwon, Jpn. J. Appl. Phys.
45, 3772 (2006).
17. D.-Y. Lee, A. K. M. Kafi, S.-H. Park and Y.-S. Kwon, J. Nanosci. Nanotechnol.
6, 3657 (2006).
18. L. C. Clark and C. Lyons, Ann. N. Y. Acad. Sci. 102, 29 (1962).
19. X. Han, W. Huang, J. Jia, S. Dong and E. Wang, Biosens. Bioelect. 17, 741 (2002).
20. Y. Zhang, P. He and N. Hu, Electrochim. Acta 49, 1981 (2004).
D.-Y. Lee et al. 68
21. J.-P. Guilla, Electroanalysis 3, 741 (1991).
22. Q. Deng and S. Dong, J. Electroanal. Chem. 377, 191 (1994).
23. H. Wang, R. Guan, C. Fan, D. Zhu and G. Li, Sens. Actuators B 84, 214 (2002).
24. S. Liu, Z. Dai, H. Chen and H. Ju, Biosens. Bioelect. 19, 963 (2004).
25. Y.-D. Zhao, Y.-H. Bi, W.-D. Zhang and Q.-M. Luo, Talanta 65, 489 (2005).
26. A. K. M. Kafi, F. Yin, H.-K. Shin and Y.-S. Kwon, Thin Solid Films 499, 420
(2006).
27. W. Schuhmann, T. J. Ohara, H.-L. Schmidt and A. Heller, J. Am. Chem. Soc. 113,
1394 (1991).
28. I. Willner, A. Riklin and N. Lapidot, J. Am. Chem. Soc. 112, 6438 (1990).
29. F. Yin, H.-K. Shin and Y.-S. Kwon, Biosens. Bioelect. 21, 21 (2005).
30. P. N. Bartlett and J. M. Cooper, J. Electroanal. Chem. 362, 1 (1993).
31. W. H. Scouten, J. H. T. Luong and R. S. Brown, Trends Biotechnol. 13, 178 (1995).
32. T. Wink, S. J. VanZuilen, A. Bult and W. P. VanBennekom, Analyst 122, 43 (1997).
33. S. Dong and J. Li, Bioelectrochem. Bioenerg. 42, 7 (1997).
34. W. K. Paik, S. Eu, K. Lee, S. Chon and M. Kim, Langmuir 16, 10198 (2000).
35. K. K. Kanazawa and J. G. Gordon, Anal. Chim. Acta 175, 99 (1985).
36. H. Muramatsu, E. Tamiya and I. Karube, Anal. Chem. 60, 2142 (1988).
37. H. W. Kang and H. Muramatsu, Biosens. Bioelect. 24, 1318 (2009).
38. H. W. Kang, K. Ida, Y. Yamamoto and H. Muramatsu, Anal. Chim. Acta 624, 154
(2008).
39. V. E. Bottom, Introduction to Quartz Crystal Unit Design (Van Nostrand, New
York, 1982).
40. G. Sauerbey, Z. Phys. Chem. 155, 206 (1959).
41. A. Janshoff, C. Steinem, M. Sieber, A. el Bayâ, M. A. Schmidt and H.-J. Galla,
Eur. Biophys. J. 26, 261 (1997).
42. D.-Y. Lee, S.-H. Park, H.-K. Shin, D.-J. Qian and Y.-S. Kwon, Mol. Cryst. Liq.
Cryst. 445, 439 (2006).
43. H. Tatsumi, K. Takagi, M. Fujita, K. Kano and T. Ikeda, Anal. Chem. 71, 1753
(1999).
44. A. N. Khramov and M. M. Collinson, Anal. Chem. 72, 2943 (2000).
45. A. K. M. Kafi, D.-Y. Lee, S.-H. Park and Y.-S. Kwon, Microchem. J. 85, 308
(2007).
46. D. I. Gittins, D. Bethell, D. J. Schiffrin and R. J. Nichols, Nature 408, 67 (2000).
47. H. Muramatsu, A. Egawa and T. Ataka, J. Electroanal. Chem. 388, 89 (1995).