"On-off" switchable colorimetric nanozyme based on a MOF-on-MOF architecture for the ultrasensitive detection of...

Glutathione (GSH) and hydrogen peroxide (H₂O₂) are both critical biomarkers for human health. GSH serves as a key non-protein thiol that maintains cellular redox homeostasis, and its abnormal levels are closely associated with neurodegenerative diseases. H₂O₂, as a potent oxidant, finds extensive applications in medicine, environmental science, and energy fields. In this study, a novel switchable colorimetric nanozyme (FeCo-MOF-on-ZIF-67) was developed via a MOF-on-MOF strategy, enabling ultrasensitive detection of GSH and H₂O₂. The detection process involves an initial step for GSH, followed by the complete oxidation of GSH by H₂O₂, which subsequently allows for H₂O₂ detection. During colorimetric detection, increasing concentrations of GSH lead to a decrease in absorbance, exhibiting a negative linear correlation. In contrast, increasing concentrations of H₂O₂ result in an increase in absorbance, showing a positive linear correlation. This switching mechanism is achieved through the specific reduction-induced quenching of the peroxidase-like activity of FeCo-MOF by GSH, followed by the competitive restoration of catalytic activity upon the introduction of H₂O₂. Experimental results demonstrate that the detection ranges for GSH and H₂O₂ are 1-200 nM and 2-200 nM, with detection limits as low as 0.74 nM and 1.72 nM, respectively-substantially outperforming conventional colorimetric methods. Real-sample analysis confirmed excellent biocompatibility and practical application potential of the sensing platform, with favorable recoveries and low RSD values for GSH in pond water, bovine serum and H₂O₂ in tap water.