Selective and Sensitive Electrochemical Sensor for l-Methionine at Physiological pH Using Functionalized Triazole Polymer Film Modified Electrode S. Brillians Revin, S. Abraham John* Department of Chemistry, Gandhigram Rural Institute, Gandhigram – 624 302, Dindigul, Tamilnadu, India tel: + 91 451 245 2371; fax : + 91 451 245 3031 *e-mail: abrajohn@yahoo.co.in Received: February 23, 2012; & Accepted: April 13, 2012 Abstract This communication describes the determination of an essential amino acid, l-methionine (l-Met) in the presence of important interferents, ascorbic acid (AA) and uric acid (UA) at physiological pH using a glassy carbon electrode modified with an electropolymerized film of 3-amino-5-mercapto-1,2,4-triazole (p-AMTa). The bare glassy carbon electrode fails to show a voltammetric signal for l-Met in the presence of AA and UA at pH 7.2. However, the p- AMTa electrode separates the voltammetric signals of AA, UA and l-Met with pronounced oxidation currents. The amperometric current of l-Met was increased linearly from 1.0  10 7 to 110 4 M and the detection limit was found to be 4.12  10 10 M(S/N = 3). Keywords: l-Methionine, Ascorbic acid, Uric acid, Amperometry DOI: 10.1002/elan.201200106 Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/elan.201200106 l-Methionine (l-Met) is an essential amino acid which is involved in protein synthesis and methylation reactions. It exists in human fluids such as blood plasma [1–3] and serum and urine [4]. The abnormal concentration of l- Met mainly leads to coronary artery disease in the human body [5, 6] and hypermethioninemia and hyperhomocys- teinemia in infants [7]. Further, alteration of l-Met con- centration in human fluids linked to several critical dis- eases [8–10] and hence the determination of l-Met from human fluids is necessary for the identification of critical diseases. For a healthy human being, l-Met was measured in the level of ~ 30.4  5.63 mM in human plasma [1], ~ 25.5 mM in human serum [4] and ~ 5.9 mM in human urine [4]. Most importantly, ascorbic acid (AA) and uric acid (UA) always coexist with l-Met in human fluids [1, 11, 12] and therefore it is very important to determine l-Met in the presence of these two important interferents. Several methods have been developed for the determina- tion of l-Met which include gas chromatography-mass spectrometry [1,4], HPLC detection [13], spectrophotom- etry [14] and conductometry [15]. However, chromato- graphic techniques are very tedious, more time consum- ing process and high cost. In the case of spectrophotomet- ric and conductometric methods, only poor detection limits were reported [3,14]. When compared to the above methods, electrochemical method has several advantages such as less expensive, more convenient and highly selec- tive and sensitive. Considerable reports were reported in the literature for the determination of l-Met individually using different modified electrodes [16–26]. But, these re- ports showed only poor detection limits for l-Met [16– 26]. Very recently, we have reported that a triazole based polymer film, poly(3-amino-5-mercapto-1,2,4-triazole) (p- AMTa) [27] showed greater electrocatalytic activity to- wards UA than the previously reported thiadiazole poly- mer films which include poly(5-amino-2-mercapto-1,3,4- thiadiazole) (p-AMT) [28] and poly(2-amino-1,3,4-thia- diazole) (p-ATD) [29] due to the presence of hydrogen bonding interactions between NH group of the p- AMTa film and biomolecules [27]. In this short communi- cation, we wish to communicate the selective determina- tion of l-Met in the presence of AA and UA at physio- logical pH (7.2) using p-AMTa film modified glassy carbon (p-AMTa) electrode. Bare glassy carbon (GC) electrode fails to show the voltammetric signal for l-Met in the presence of AA and UA at pH 7.2. However, p- AMTa electrode separates the voltammetric signals of AA, UA and l-Met with pronounced oxidation currents. Further, the modified electrode also selectively determine l-Met in the presence of high concentration of cysteine (Cys). The amperometric current of l-Met was increased linearly from 1.0  10 7 –1  10 4 M and a detection limit was found to be 4.12  10 10 M(S/N = 3). The obtained de- tection limit in the present study was two orders higher than the reported papers [16–26]. For the clinical point of Electroanalysis 2012, 24, No. &,1–7  2012 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim &1& These are not the final page numbers! ÞÞ Short Communication