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

In this work, cystine-glucose Maillard conjugates were composited with Cu1.8S microspheres (Cu1.8S-cgmc) to achieve higher sensitivity for the colorimetric analysis. Enhanced peroxidase-like activity was obtained in Cu1.8S-cgmc with a carbon elemental ratio of 1.83% compared to bare Cu1.8S. The catalytic activity of Cu1.8S-cgmc followed Michaelis-Menten kinetic behavior. The Michaelis-Menten constants of Cu1.8S-cgmc on the substrate was over 2-fold lower than that of the bare Cu1.8S, indicating the higher affinity of Cu1.8S-cgmc. The adsorption equilibrium constant of Cu1.8S-cgmc on the substrate was 9.89-fold higher than that of bare Cu1.8S based on thermodynamic investigations. The conjugated structure and carboxyl, hydroxyl and amino groups on Cu1.8S-cgmc improved its hydrophilicity and adsorption on the substrate. The affinity-improved Cu1.8S-cgmc was applied as a peroxidase mimic in colorimetric detection with promoted sensitivity. Compared to bare Cu1.8S, Cu1.8S-cgmc had a 25.5-fold and 19.8-fold lower LOD for H2O2 and glutathione, respectively. The Cu1.8S-cgmc-based colorimetric method showed excellent sensitivity and accuracy in practical colorimetric detection.