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

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.