Fabrication of Cysteic acid/ gold nanoparticle Composite Film- Modified Glassy Carbon electrode for the Simultaneous Voltammetric Detection of Acetaminophen and Tramadol

In this study a voltammetric sensor by electrochemical deposition of gold nanoparticles (AuNPs) and L-Cysteine on glassy carbon electrode is fabricated. Simply, after formation of a compact and uniform cysteic acid layer film by electrochemical oxidation of L-cysteine, AuNPs is immobilized on its polymeric structure. As well as, the fabricated sensor show great sensitivity and selectivity for simultaneous determination of Acetaminophen (ACOP) and Tramadol (TRA) with square wave voltammetry (SWV) method in a wide linear range, with detection limits of 0.03 and 0.17 µM respectively. As an electrode modifiers, amino acids play an important roles in fabricating the electrode surface for immobilizing nanoparticles and increasing sensitivity. For instance l-cysteine due to the presence of sulfhydryl, can be electrochemically converted to cysteic acid (CA), an electroactive, stable, biocompatible, conductive polymer, that strongly adsorbed at surface of electrode [1,2]. In addition gold nanoparticles (AuNPs) in which have some advantages like conductivity, electro-catalytic activity, chemical stability, and large surface area have been extensively used [3-5]. In this work square wave voltammetry (SWV) and cyclic voltammetry (CV) were performed with µ-Autolab type ш, potentiostat/galvanostat instrument and driven by the NOVA 1.11 software. The modified GCE was utilized as the working electrode, a platinum wire as the counter electrode, and satAg/AgCl (3M KCl) as reference. All the chemicals were analytical grade and were used directly without purification. Moreover l-cysteine and hydrogen tetra-chloro-aurate (HAuCl4) were from Merck. The anodic peak current of ACOP is decreased from pH 2.0 to 5.0 then increased to pH 7.0 and re-decreased. In the case of TRA in the pH range of 2.0 to 4.0 no evident peak is observed. After that, in pH 5.0 the TRA peak appears and it reached to maximum at pH 7.0 then, it decreased. Thus, the electrochemical measurements were carried out in PBS (0.1 M, pH 7.0). In light of efficient and comparable results, the cysteic acid/AuNPs composite film was applied for the determination of ACOP and TRA in spiked serum samples using the standard addition method.