Anal. Chem. 2007, 79, 5328-5335
Electrochemical Behavior of L-Cysteine and Its
Detection at Ordered Mesoporous Carbon-Modified
Glassy Carbon Electrode
Ming Zhou, Jie Ding, Li-ping Guo,* and Qing-kun Shang
Faculty of Chemistry, Northeast Normal University, Changchun, 130024, People’s Republic of China
electrochemical responses could be observed.13,14 It has been
realized that the method to solve this problem may be to utilize
new materials as electrodes; at such an electrode surface, the
electrochemical responses could be simply obtained directly.5-23
Over the past decades, several carbon-based materials, including
fullerene15 and boron-doped diamond, have been explored for the
electrochemical oxidation and detection of CySH.6 Recently, due
to their unique electronic, chemical, and mechanical properties,
carbon nanotubes (CNTs) as a new class of carbon nanomaterials
have been exploited for the electrochemical oxidation of CySH.7,22
The high electrocatalytic activity observed at CNTs is attributed
to the presence of the oxygen-containing functional groups on the
surface of CNTs and a large number of edge plane graphite sites
within the walls and at the ends of CNTs.7,24,25
In this paper, the electrochemical behavior of L-cysteine
(CySH) was investigated thoroughly at an ordered meso-
porous carbon-modified glassy carbon (OMC/GC) elec-
trode. The voltammetric studies showed there were three
anodic peaks for the electrooxidation of CySH in the pH
range of 2.00-5.00; however, one peak disappeared
above pH 5.00. This behavior has never been reported
before. Through the studies of the effect of pH on the
distribution fractions (δ) of the four chemical species of
CySH, we conclude only CySH2+ (H3A+) and CyS- (HA-)
are the electroactive substances and should be respon-
sible for the electrooxidation of CySH. And for the first
time, we successfully established the exact and systemic
mechanisms based on the electroactive species to explain
CySH oxidation at different pH values. On the other hand,
a sensitive CySH sensor was developed based on an
OMC/GC electrode, which shows a large determination
range (18-2500 µmol L-1), a high sensitivity (23.6 µA
mmol L-1), and a remarkably low detection limit (2.0
nmol L-1, which is the lowest value ever reported for
direct CySH determination on the electrodes) at pH 2.00.
At pH 7.00, the modified electrode can be still used to
readily detect CySH in the range of the physiological
levels. These make OMC/GC electrode a promising
candidate for efficient electrochemical sensors for the
detection of CySH.
Besides the materials mentioned above, there has been
significant interest in the development of one such novel carbon
material, i.e., ordered mesoporous carbon (OMC). The OMC,
which was first synthesized in 1999, is particularly promising
(7) Gong, K.; Zhu, X.; Zhao, R.; Xiong, S.; Mao, L.; Chen, C. Anal. Chem. 2005,
77, 8158-8165.
(8) Teixeiraa, M.; Dockalb, E.; Cavalheiroc, E. Sens. Actuators, B 2005, 106,
619-625.
(9) Ralph, T. R.; Hitchman, M. L.; Millington, J. P.; Walsh, F. C. J. Electroanal.
Chem. 1994, 375, 1-15.
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(11) Terashima, C.; Rao, T. N.; Sarada, B. V.; Kubota, Y.; Fujishima, A. Anal.
Chem. 2003, 75, 1564-1572.
(12) Fei, S.; Chen; J.; Yao, S.; Deng, G.; He, D.; Kuang, Y. Anal. Biochem. 2006,
339, 29-35.
L
-Cysteine (CySH) is an important amino acid owing to its
crucial roles in biological systems. For example, it could be used
(13) Halbert, M. K.; Baldwin, R. P. Anal. Chem. 1985, 57, 591-595.
(14) Wang, Z.; Pang, D. J. Electroanal. Chem. 1990, 283, 349-358.
(15) Tan, W. T.; Bond, A. M.; Ngooi, S. W.; Lim, E. B.; Goh, J. K. Anal. Chim.
Acta 2003, 491, 181-191.
as a prospective radiation protector and cancer indicator.1-4
Moreover, the couple L-cystine/L-cysteine is generally used as a
model for the role of the disulfide bond and thiol group in proteins
in a variety of biological media.1 Therefore, it is very important to
investigate the electrochemical behavior and sensitive detection
of CySH.5-12 Unfortunately, at ordinary electrodes (Pt, Au,
graphite), the electrochemical behaviors of CySH are poor; no
(16) Fujiwara, S.; Pessoa, C.; Gushikem, Y. Electrochim. Acta 2003, 48, 3625-
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215-222.
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1996, 414, 253-256.
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195-211.
* Corresponding author. Tel.: +86-431-85099762. Fax: +86-413-85099762.
E-mail: guolp078@nenu.edu.cn.
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5328 Analytical Chemistry, Vol. 79, No. 14, July 15, 2007
10.1021/ac0703707 CCC: $37.00 © 2007 American Chemical Society
Published on Web 06/08/2007