A Convenient and Label-Free Colorimetric Detection for L-Histidine Based on Inhibition of Oxidation of 3,3′,5,5′-Tetramethylbenzidine-H2O2 System Triggered by Copper Ions

Abstract

L-Histidine (L-His) is an essential amino acid, which is used to synthesize proteins and enzymes. The concentration of L-His in the body is controlled to regulate tissue growth and repair of tissues. In this study, a rapid and sensitive method was developed for colorimetric L-his detection using Cu2+ ions to inhibit the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB)–H2O2 system. H2O2 can oxidize TMB to oxTMB in the presence of copper, and the change in color from colorless (TMB) to blue (oxTMB) is similar to that observed in the presence of peroxidase. However, because the imidazole ring and carboxyl group of L-His can coordinate with Cu2+ ions to form stable L-His–Cu2+ complexes, the color of the TMB–H2O2 solution remains unchanged after the addition of L-His. Therefore, because L-His effectively hinders the colorimetric reaction of TMB with H2O2, this assay can be used to quantitatively determine the concentration of L-His in samples. Under optimized conditions, our colorimetric sensor exhibited two linear ranges of 60 nM to 1 μM and 1 μM to 1 mM for L-His detection and a detection limit of 50 nM (S/N = 3); furthermore, the assay can be performed within 20 min. Moreover, the proposed assay was used to determine the concentration of L-His in urine samples, suggesting that this convenient and label-free colorimetric method presents promising applications in bioanalytical chemistry and clinical diagnosis.

A Copper-Based Biosensor for Dual-Mode Glucose Detection

“…To demonstrate the prepared Cu 2 O NPs possess the peroxidase-like catalytic activity as peroxidase mimics, the oxidation discoloration of TMB in the presence of H 2 O 2 (TMB-H 2 O 2 system) was selected ( Liang et al, 2022 ). In the presence of the Cu 2 O NPs and H 2 O 2 , the peroxidase substrate TMB could be catalyzed to the oxidation state of TMB (ox TMB) by OH radicals produced from H 2 O 2 and the solution will turn to blue ( Zhang Z. et al, 2021 ). An electron paramagnetic resonance (EPR) analysis result shown in Supplementary Figure S4 (ESI†) further illustrated the existence of hydroxyl radicals in the system.…”