A fluorescent assay for alkaline phosphatase activity based on phosphorylation protection and DNAzyme-assisted amplification

The development of biosensors for alkaline phosphatase activity detection based on a phosphorylated DNA probe

Alkaline phosphatase (ALP) is a zinc-containing metalloprotein that shows very great significance in clinical diagnosis, which can catalyze the hydrolysis of phosphorylated species. ALP has the potential to serve as a valuable biomarker for detecting liver dysfunction and bone diseases. On the other hand, ALP is an efficient biocatalyst to amplify detection signals in the enzyme-linked assay. It has always been a major research focus to develop novel biosensors that can detect ALP activity with high selectivity and sensitivity. There have been numerous reports on the development of biosensors to determine ALP activity using a phosphorylated DNA probe. Among them, various beneficial strategies, such as λ exonuclease-mediated cleavage reaction, terminal deoxynucleotidyl transferase-triggered DNA polymerization, and Klenow fragment polymerase-catalyzed elongation, are employed to generate amplified and more intuitive signal. This review discusses and summarizes the development and advances of biosensors for ALP activity detection that use a well-designed phosphorylated DNA probe, aiming to provide some guidelines for the design of more sophisticated sensing strategies that exhibit improved sensitivity, selectivity, and adaptability in detecting ALP activity.

Fluorescent assay for alkaline phosphatase by integrating strand displacement amplification with DNAzyme-catalytic recycling cleavage of molecular beacons

A fluorescence sensing method for the quantification of alkaline phosphatase (ALP) was developed by integrating the strand displacement amplification with DNAzyme-catalytic recycling cleavage of molecular beacons. ALP can hydrolyze a 3'-phosphoralated primer into a 3'-hydroxy primer which can initiate the strand displacement amplification to produce the Mg2+-dependent DNAzyme. The DNAzyme can then catalyze the cleavage of the DNA molecular beacon labeled with FAM fluorophore at its 5'-end and BHQ1 quencher at its 3'-end, turning on the fluorescence of FAM fluorophore. The content of ALP in a sample can be deduced from the measured fluorescence intensity. Due to the cascading nature of its amplification strategy, the proposed method achieved sensitive and specific ALP detection in human serum samples. Its results were in good consistent with the corresponding values obtained by a commercial ALP detection kit. The limit of detection of the proposed method for ALP is about 0.015 U/L, lower than some methods recently reported in literature, demonstrating its potential for ALP detection in biomedical research and clinical diagnosis.