Ultrasensitive Assay of Alkaline Phosphatase Based on the Fluorescent Response Difference of the Metal–Organic Framework Sensor

The assay of alkaline phosphatase (ALP) is important in clinical diagnosis because the abnormal expression of this enzyme is related to many serious diseases. In this work, using a luminescent metal–organic framework (MOF) as the sensor, a fluorescent method was developed for the activity assay of ALP. With nanoscale particle size, the prepared MOF sensor exhibited good dispersability and stable photoluminescence in aqueous suspension. The emission of this MOF is inert to p-nitrophenylphosphate (NPP) but could be efficiently quenched by its dephosphorylated product, p-nitrophenol. Taking advantage of this feature, this MOF was added to the system of ALP-catalyzed NPP dephosphorylation to transduce the proceeding of the reaction real-timely to the fluorescent signal. The enzyme activity could be calculated based on the recorded kinetic trace. This method presented a low detection limit (2 × 10–3 U L–1) and a wide quantification range (0.6–90 U L–1) in our experiments, showing its quantification capability challenges the best of current ALP analytical methods. As a practical application, our method was successfully applied to the ALP analysis in human serum samples.