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.