Highly Sensitive Colorimetric Detection of Glutathione in Human Serum Based on Iron–Copper Metal–Organic Frameworks

Emerging metal–organic framework (MOF)-based mimic enzymes have been exploited to design a colorimetric sensor for the detection of biomolecules. However, it is challenging to figure out the glutathione (GSH) detection method and the corresponding sensing mechanism using an MOF-based colorimetric sensor. In this work, a novel iron–copper MOF with high activity is synthesized by a wet-chemical method. A GSH colorimetric sensor based on the peroxidase-like properties of the iron–copper MOF is developed. Hydrogen peroxide is converted to hydroxyl radicals by the peroxidase-like properties of the iron–copper MOF mimic enzyme, which can catalyze the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidized TMB (ox-TMB). The kinetic constant of the MOF mimic enzyme (0.02 mM for H2O2) is superior to horseradish peroxidase (HRP). The GSH content can be quantified by proposing a sensor based on the colorimetric method and color turn-off mechanism. The turn-off mechanism of GSH analysis includes two aspects. On the one hand, the blue ox-TMB can be deoxidized to colorless TMB by GSH. On the other hand, hydroxyl radicals (•OH) can be consumed by GSH. The linear range and limit of detection are 2–20 and 0.439 μM, respectively. At the same time, GSH detection also shows good specificity and anti-interference characteristics. Therefore, MOF-based colorimetric sensors have been used to qualitatively and quantitatively measure GSH contents in human serum. The mechanism and application of the iron–copper MOF pave a way for the development of mimic enzymes with polymetallic active sites in the field of colorimetric sensing.