Label-free and sensitive assay for ICP-MS determination of alkaline phosphatase activity via manganese target

As an essential and universal enzyme, alkaline phosphatase (ALP) has been identified as an important biomarker of various diseases, thus highly sensitive assay of ALP activity is of great significance. Herein, a label-free and sensitive ICP-MS based assay was developed for ALP activity detection using MnO 2 nanosheets (MnO 2 NS) as the element target source. ALP triggered the hydrolysis of ascorbic acid-2-phosphate (AAP) to produce reductive ascorbic acid (AA), followed with the decomposition of MnO 2 NS to Mn 2+ ions, which were quantified directly by ICP-MS after selective separation of MnO 2 NS and Mn 2+ ions simply by filtration, and no further elemental labelling was needed. Under the selected conditions, the limit of detection (LOD) was 0.007 U L -1 for ALP. Additionally, this assay was also extended to investigate the inhibition effect of ALP inhibitor (Na 3 VO 4 ) with reasonable results. To our knowledge, this is the first endeavor for ALP activity detection using ICP-MS, which holds great promise for the early clinical diagnosis and biomedical research on ALP.