Plasmonic sensing of alkaline phosphatase and its inhibitors through Ag(I)-mediated assembly of gold nanoparticles

Abstract

Alkaline phosphatase (ALP) is of extraordinary importance in living organisms and widely serves as a labeling enzyme in biochemical assays. Conventional methods based on the colorimetric readout of chemicals have issues in the photosensitivity and the difficulty in visibly distinguishing the color intensity. Herein, we developed a plasmonic assay for detecting ALP activity and its inhibitors based on gold nanoparticles (AuNPs) with good stability and naked-eye readout. Ag(I) specifically oxidizes TMB to produce positively charged oxTMB, which electrostatically aggregates negatively charged AuNPs. ALP as an enzyme specifically hydrolyzes a substrate to generate ascorbic acid, which reduces Ag(I) and modulates the aggregation of AuNPs. This plasmonic ALP assay has a linear detection range of 5–50 mU/mL with a limit of detection of 0.39 mU/mL. In combination with a smartphone, it enables monitoring ALP inhibitors including dimethoate and arsenic that are environmental contaminants. This plasmonic sensing strategy with good stability, visible readout, high specificity, low cost, and ease of operation provides a promising platform for enzyme detection and environmental monitoring.