Third Day Poster Session, 17 June 2010 - NanoTR-VI

Poster Session, Thursday, June 17
Theme F686 - N1123
Multi wall carbon nanotubes as a sensor and p-aminophenol as a mediator for rapid and sensitive
determination of cysteamine in presence of tryptophan
Hassan Karimi-Maleh * Ali A. Ensafi,
1 Department of Chemistry, Isfahan university of technology, Isfahan, Iran
Abstract— In this work, we describe the determination of two important biological compounds, cysteamine (CA) and
tryptophan (TP) by electrochemical methods using multi wall carbon nanotubes as a sensor and p-aminophenol as a mediator
for the first time. The proposed method was successfully applied to the determination of CA in both capsule and
urine samples.
Cysteamine (CA) or 2-mercaptoethylamine is the chemical
compound with the formula HSCH2CH2NH2 [1]. It is the
simplest stable aminothiol and a degradation product of the
amino acid cysteine. Under the trade name Cystagon,
cysteamine is used in the treatment of disorders of cystine
excretion. Cysteamine cleaves the disulfide bond with cystine
to produce molecules that can escape the metabolic defect in
cystinosis and cystinuria. It is also used for treatment of
radiation sickness [2]. Cysteamine crosses the plasma and
lysosomes, and it reacts with crystallized cystine within the
lysosomes to form cysteine and cysteine–cysteamine mixed
disulfides, which leave through the lysine porter [3]. The
cysteamine and its disulfide, cystamine, have been shown to
be neuroprotective in a number of cell culture and animal
models [4]. Tryptophan (TP) is one of the 20 standard amino
acids, as well as an essential amino acid in the human diet. It
is encoded in the standard genetic code as the codon UGG.
Several methods have been proposed for the determination of
cysteamine and trptophan in biological samples including
chromatography [5,6], electrophoresis [7], gas
chromatography with flame photometric detection [8] ion
exchange chromatography [9] and electrochemical methods
[10, 11] using modified electrodes. Therefore, in
continuation of our studies concerning the preparation of
chemically modified electrodes [12-15], we have used
voltammetric and electrochemical impedance spectroscopic
techniques at pH 5.0 to demonstrate the electrochemical
behavior of CA and TP on the multi-wall carbon nanotubes
paste electrode modified with p-aminophenol as a mediator for
the first time. The results show that the proposed method is
highly selective and sensitive in the determination of CA and
TP out performing any method reported in the literature on
electrochemistry for simultaneous determination of these two
substances. The detection limit, linear dynamic range, and
sensitivity to CA with carbon nanotubes paste electrode
modified with p-aminophenol (p-APMCNTPE) are
comparable to, and even better than, those recently developed
which use voltammetric methods.
Using differential pulse voltammetry, CA and TA in mixture
can each be measured independently from the other with a
potential difference of 600 mV. Using the modified electrode,
the kinetics of CA electrooxidation was considerably
enhanced by lowering the anodic overpotential through a
catalytic fashion. The mechanism of CA electrochemical
behavior at the modified electrode surface was analyzed by
Cyclic voltammetric (CV), chronoamperometric, and
electrochemical impedance spectroscopy (EIS) methods in an
aqueous solution at pH=5.0. The electrocatalytic currents
increase linearly with the CA and TP concentrations over the
ranges 0.5–300 mol L -1 and 10.0–650 mol L -1 , respectively.
The detection limits for CA and TP will be equal to 0.15 and
5.5 mol L -1 , respectively. The proposed method was
successfully applied to the determination of CA in both
capsule and urine samples.
*Corresponding author: h.karimi@ch.iut.ac.ir
[1] wikipedia. February 06, 2010.
[2] B.P. Lukashin and A.N. Grebeniuk, Radiatsionnaia biologiia,
radioecologiia / Rossiskaia akademiia nauk, 41, 310, 2001.
[3] L. Wood et al. Brain Research. 158, 158, 2007.
[4] P. Lochman et al. Electrophoresis, 24, 1200, 2003.
[5] M. Stachowicz et al. J. Pharm. Biomed. Anal. 17, 767, 1998.
[6] H. Kataoka, et. Al. J. Pharm. Biomed. Anal. 11, 963, 1993.
[7] A.J. Jonas and J.A. Schneider, Anal.Biochem. 114, 429 1981.
[8] H. Kataoka, et. al. J. Chromatogr. B 657, 9, 1994.
[9] M. Hsiung et. al. Biochem, Med. 19, 305, 1978.
[10] J.B. Raoof et. al. J. Mater. Sci. 44, 2688, 2009.
[11] J.B. Raoof. et. al.Electroanalysis, 20, 1259,2008.
[12] A.A. Ensafi and H. Karimi-Maleh, J. Elecroanal. Chem. 640, 75, 2010.
[13] A.A. Ensafi, et. al. J. Solid State Electrochem. In press.
[14] H. Karimi-Maleh, et. al. J. Solid State Electrochem. 14, 9, 2010.
[15] H. Karimi-Maleh et. al. J. Braz. Chem. Soc.20, 880, 2009.
Figure 1. SEM image of a) p-APMCNTPE, and b) CNPE.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 682