Enzyme-triggered in situ formation of Ag nanoparticles with oxidase-mimicking activity for amplified detection of alkaline phosphatase activity

Given that alkaline phosphatase (ALP) is an important biomarker for many diseases, monitoring of its activity turns to be of great significance for related disease diagnosis and treatment. Herein, we report a new colorimetric assay based on the enzyme-triggered in situ formation of Ag nanoparticles (NPs) with high oxidase-mimicking activity for ALP activity detection. ALP first hydrolyzes the ascorbic acid phosphate (AAP) substrate to produce ascorbic acid (AA); the produced AA with strong reducing capacity then transforms Ag+ into Ag NPs; compared with the Ag+ precursor, the in situ formed Ag NPs have much higher oxidase-like activity to catalyze the 3,3',5,5'-tetramethylbenzidine (TMB) color reaction mediated by dissolved O2 at neutral pH. On the basis of this principle, amplified colorimetric detection of ALP activity with a linear scope of 0.15-5 U L-1 and a limit of detection down to 0.037 U L-1 was realized. In addition, our assay exhibited specific response toward ALP against other biological enzymes and species. Accurate and reliable determination of ALP activity in human plasma was also demonstrated by our assay, suggesting its great potential as a facile and efficient tool for monitoring of ALP activity in clinical practice.