Recent MOFs have drawn attention for applications ranging from biosensing, bioimaging, and biomolecule separation due to their tunable composition, rigid structure, controllable pore size, and large surface area. MOF would be an ideal material for colorimetric assay as well owing to the abundance of catalytic active sites in the framework. However, it is hard to find out MOFs that can provide superior peroxidase-like activity and with good stability in the aqueous solution. Since Fe offers more stability while Co more activity, we are interested in preparing heterometallic MOFs and utilizing such cooperative crystallization to tune colorimetric performance. Our results showed the improved colorimetric performance of Fe-Co MIL 88 compared with Fe MIL 88 and good stability in water. We applied the streptavidin-modified Fe-Co MIL 88 to capture the biotinylated glucose oxidases (GOx). The glucose oxidases that are captured by MOF can in situ generate abundant H2O2 once the glucose is added, which can be converted to hydroxyl radical by the metal ion in the framework. Hydroxyl radical can turn the TMB dye from colorless to blue. Our detection limit for biotinylated glucose oxidases is 0.15 picomole. The good sensitivity for biotinylated GOx detection was enabled by the highly efficient cascade reaction between the HRP-mimic MOF and the Glucose oxidase. Next, we apply the Fe-Co MIL88 based platform for the detection of a cancer biomarker in biofluids like serum. The MOF structure not only acts as the platform for target enrichment and isolation from the complex matrix but also acts as one part of the enzyme cascade reaction to produce the detection signal, providing superior performance to existing methods. Overall, our work demonstrates the powerful potential of MOF materials in the field of biosensing.

Co–Fe MOF coupled glucose oxidase as cascade nanozyme for extracellular vesicle detection

ACS Fall 2021

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