Carbon–nitrogen conjugate-composited Cu1.8S with enhanced peroxidase-like activity for the colorimetric detection of hydrogen peroxide and glutathione

Abstract

In this work, cystine–glucose Maillard conjugates were composited with Cu_1.8S microspheres (Cu_1.8S–cgmc) to achieve higher sensitivity for the colorimetric analysis. Enhanced peroxidase-like activity was obtained in Cu_1.8S–cgmc with a carbon elemental ratio of 1.83% compared to bare Cu_1.8S. The catalytic activity of Cu_1.8S–cgmc followed Michaelis–Menten kinetic behavior. The Michaelis–Menten constants of Cu_1.8S–cgmc on the substrate was over 2-fold lower than that of the bare Cu_1.8S, indicating the higher affinity of Cu_1.8S–cgmc. The adsorption equilibrium constant of Cu_1.8S–cgmc on the substrate was 9.89-fold higher than that of bare Cu_1.8S based on thermodynamic investigations. The conjugated structure and carboxyl, hydroxyl and amino groups on Cu_1.8S–cgmc improved its hydrophilicity and adsorption on the substrate. The affinity-improved Cu_1.8S–cgmc was applied as a peroxidase mimic in colorimetric detection with promoted sensitivity. Compared to bare Cu_1.8S, Cu_1.8S–cgmc had a 25.5-fold and 19.8-fold lower LOD for H₂O₂ and glutathione, respectively. The Cu_1.8S–cgmc-based colorimetric method showed excellent sensitivity and accuracy in practical colorimetric detection.