MOF-mediated cascade reaction system for ultrasensitive detection of alkaline phosphatase activity and organophosphorus pesticides

A metal–organic-framework (MOF) fluorescent sensor is reported based on NH₂-MIL-101(Fe) propelled pesticide and alkaline phosphatase (ALP) catalytic reaction. Different from previous reports, a cascade reaction system combined with MOF structural changes to generate fluorescence was employed. The rationale is that ALP can hydrolyze L-ascorbic acid 2-phosphate (AAP) into L-ascorbic acid (AA), which can reduce Fe³⁺ to decompose structurally NH₂-MIL-101(Fe), resulting in 2-aminoterephthalic acid (NH₂-BDC) with intense fluorescence. The  fluorescence can be decreased to different degrees due to inhibition of organophosphate pesticides (OPPs) on the activity of ALP. By taking chlorpyrifos (CPY) as the model compound of an OPP pesticide and adding ALP and CPY into the NH₂-MIL-101(Fe) framework, the resulting cascade reaction fluorescence sensors exhibit a good sensitivity for CPY and ALP sensing. The working ranges are  0.02–2 μg/L and 0.2–20 mU/mL with detection limits (LOD) of 5.31 ng/L and 0.05 mU/mL, respectively. The proposed sensor has been actually applied to satisfactory detection of CPY and ALP in food and serum samples. This fluorescence-based assay may extend the application of MOF-based biosensors.