Photonic crystals in biology - NanoTR-VI

Poster Session, Thursday, June 17Theme F686 - N1123Multi wall carbon nanotubes as a sensor and p-aminophenol as a mediator for rapid and sensitivedetermination of cysteamine in presence of tryptophanHassan Karimi-Maleh * Ali A. Ensafi,1 Department of Chemistry, Isfahan university of technology, Isfahan, IranAbstract— In this work, we describe the determination of two important biological compounds, cysteamine (CA) andtryptophan (TP) by electrochemical methods using multi wall carbon nanotubes as a sensor and p-aminophenol as a mediatorfor the first time. The proposed method was successfully applied to the determination of CA in both capsule andurine samples.Cysteamine (CA) or 2-mercaptoethylamine is the chemicalcompound with the formula HSCH2CH2NH2 [1]. It is thesimplest stable aminothiol and a degradation product of theamino acid cysteine. Under the trade name Cystagon,cysteamine is used in the treatment of disorders of cystineexcretion. Cysteamine cleaves the disulfide bond with cystineto produce molecules that can escape the metabolic defect incystinosis and cystinuria. It is also used for treatment ofradiation sickness [2]. Cysteamine crosses the plasma andlysosomes, and it reacts with crystallized cystine within thelysosomes to form cysteine and cysteine–cysteamine mixeddisulfides, which leave through the lysine porter [3]. Thecysteamine and its disulfide, cystamine, have been shown tobe neuroprotective in a number of cell culture and animalmodels [4]. Tryptophan (TP) is one of the 20 standard aminoacids, as well as an essential amino acid in the human diet. Itis encoded in the standard genetic code as the codon UGG.Several methods have been proposed for the determination ofcysteamine and trptophan in biological samples includingchromatography [5,6], electrophoresis [7], gaschromatography with flame photometric detection [8] ionexchange chromatography [9] and electrochemical methods[10, 11] using modified electrodes. Therefore, incontinuation of our studies concerning the preparation ofchemically modified electrodes [12-15], we have usedvoltammetric and electrochemical impedance spectroscopictechniques at pH 5.0 to demonstrate the electrochemicalbehavior of CA and TP on the multi-wall carbon nanotubespaste electrode modified with p-aminophenol as a mediator forthe first time. The results show that the proposed method ishighly selective and sensitive in the determination of CA andTP out performing any method reported in the literature onelectrochemistry for simultaneous determination of these twosubstances. The detection limit, linear dynamic range, andsensitivity to CA with carbon nanotubes paste electrodemodified with p-aminophenol (p-APMCNTPE) arecomparable to, and even better than, those recently developedwhich use voltammetric methods.Using differential pulse voltammetry, CA and TA in mixturecan each be measured independently from the other with apotential difference of 600 mV. Using the modified electrode,the kinetics of CA electrooxidation was considerablyenhanced by lowering the anodic overpotential through acatalytic fashion. The mechanism of CA electrochemicalbehavior at the modified electrode surface was analyzed byCyclic voltammetric (CV), chronoamperometric, andelectrochemical impedance spectroscopy (EIS) methods in anaqueous solution at pH=5.0. The electrocatalytic currentsincrease linearly with the CA and TP concentrations over theranges 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 and5.5 mol L -1 , respectively. The proposed method wassuccessfully applied to the determination of CA in bothcapsule 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