Paper-based electrochemical platform modified with graphene nanoribbons: A new and affordable approach for analysis of 5-hydroxy-l-tryptophan

Abstract

Here, a new and inexpensive electrochemical paper-based analytical device (ePAD) containing a pencil-drawn three-electrode setup, in which the working electrode was modified with graphene nanoribbons (GNRs), is presented for the first time. Under optimal conditions, the GNRs-ePAD provided higher peak currents (ca. 91 %), lower electron transfer resistance (ca. 32-fold) and greater electroactive area (more than twice) when compared to the unmodified ePAD. This significant improvement can be attributed to the increase in the number of active sites available on the electrode surface due to the high conductivity of GNRs. In addition, the ePAD showed good reproducibility and acceptable repeatability, with relative standard deviations (RSDs) ≤ 8.4 % for peak currents and peak potentials. As proof of concept, the GNRs-ePAD was employed for analysis of 5-HTP in pharmaceuticals. As far as we know, this is the first report of the use of ePADs for determination of 5-HTP. The electroanalytical quantification was carried out using square-wave voltammetry (SWV). A linear range from 25 to 1000 μmol L−1 and a limit of detection of 7.6 μmol L−1 were obtained. The sensitivity achieved with the GNRs-ePAD was almost 5-fold greater than that obtained with the bare electrode. The results achieved during the analysis of pharmaceutical products showed good precision (RSD < 3 %) and great concordance with the values found by UV–vis spectrophotometry, utilized for comparison (relative error was < 2 %). None interference or matrix effects were observed during measurements. These results demonstrate promising potential for the GNRs-ePAD proposed here. This device shows itself as an interesting, efficient and low-cost analytical platform for analysis of electroactive species, being specially interesting for places with limited resources.