Midas Touch: Engineering Activity of Metal-Organic Frameworks via Coordination for Biosensing

The ever-increasing attention on the highly sensitive biosensors pushes people to explore functional nanomaterials for signal amplification. To endow inert metal-organic frameworks (MOFs) with enzyme mimicking activity, a simple strategy of introducing Cu²⁺ via coordination with 2,2'-bipyridine ligands of Zr-MOF, just like "Midas touch," is proposed. More details on the coordination environment of Cu active sites in Zr-MOF-Cu are disclosed via electron paramagnetic resonance and synchrotron-radiation-based X-ray absorption fine structure analyses. The as-prepared Zr-MOF-Cu exhibits unparalleled catalytic ability, which can catalyze ascorbic acid (AA) to dehydroascorbic acid and further stimulate the reaction with o-phenylenediamine to produce fluorescent signal probes with 8-fold signal amplification. On the basis of catalyzing the dephosphorylation process of l-ascorbic acid-2-phosphate to yield AA via alkaline phosphatase (ALP) and AA-dependent signal responses, a universal fluorescent system has been successfully constructed for quantitative measurement of the activity of ALP and the ALP-related enzyme-linked immunosorbent assay with carcinoembryonic antigen as a model. Moreover, the stable loading of Cu active sites endows the sensing platform with anti-inference capacity and enables its reuse without loss of catalytic activity after 6 months.