A feasible and efficient voltammetric sensor based on electropolymerized L-arginine for the detection of L-tryptophan in dietary supplements

Abstract

In this study, we present an effective voltammetric sensor as a cost-effective and feasible tool to detect tryptophan (TRYP) – an essential amino acid that plays several key roles in different physiological processes – in commercial dietary supplements. The sensor consisted of a glassy carbon electrode modified with poly(L-arginine) (GCE/p-ARG), which was electrochemically synthesized from L-arginine monomers by using cyclic voltammetry. The presence of p-ARG contributed to significantly decrease the charge transfer resistance and favor the occurrence of electron transfer processes at the electrode/electrolyte interface. Such improved electrochemical properties were able to improve the electrode’s sensitivity toward TRYP, whose detection was greatly enhanced as a consequence of multiple intermolecular interactions established between the amino acid and p-ARG moieties. By using chemometrics, we thoroughly evaluated the influence of each variable involved in the electropolymerization process – monomer concentration, number of voltammetric scans and scan rate – on the sensitivity of the modified electrodes toward TRYP. Under optimized conditions, TRYP was detected in the range from 1.0 to 7.0 μmol L-1 by using square wave voltammetry (SWV). Limits of detection and quantification were found to be equal to 0.30 and 0.91 μmol L-1, respectively, which enabled the effective application of the proposed sensor to detect TRYP in commercial dietary supplements with good precision and accuracy. This study consistently shows that the GCE/p-ARG is a promising candidate to provide inexpensive, fast, and reliable determinations of TRYP in commercial products.