Determination of the biomarker L-tryptophan level in diabetic and normal human serum based on an electrochemical sensing method using reduced graphene oxide/gold nanoparticles/18-crown-6

A novel nanocomposite-modified electrode based on reduced graphene oxide (rGO) decorated with 18-crown-6 (Cr.6) and gold nanoparticles (GNPs) on the surface of a glassy carbon electrode (GCE) was successfully fabricated to investigate the electrochemical sensing of the biomarker L-tryptophan (L-Trp) in the presence of dopamine (DA), ascorbic acid (AA), urea, and glucose. The rGO-GNPs-Cr.6/GCE displayed high electrochemical catalytic activity for L-Trp determination using square-wave voltammetry (SWV). The electrochemical behavior of L-Trp at the rGO-GNPs-Cr.6/GCE displayed higher oxidation current and potential (oxidation peak current of 40 μA at 0.85 V) than rGO-GNPs/GCE, Cr.6/GCE, GNPs/GCE, rGO/GCE, and bare GCE. The SWV demonstrated a linear range of L-Trp concentration from 0.1 to 2.5 μM. A low limit of detection (LOD) was found for L-Trp, with LOD of about 0.48 μM and 0.61 μM in diabetic and normal serum, respectively. The fabricated sensor demonstrated high selectivity and sensitivity, and good stability and reproducibility for L-Trp sensing. Finally, the nanocomposite (rGO-GNPs-Cr.6)-modified GCE was applied for the determination of L-Trp in normal and diabetic human serum samples, and displayed excellent LOD and recoveries higher than 91.8%. Graphical Abstract.