Single Particle Colorimetric Acid Phosphatase Activity Assay with CeO₂-modified Gold Nanoparticles

Acid phosphatase (ACP) is a ubiquitous phosphatase in living organisms. The abnormal variation of ACP is related to various diseases. Herein, we propose a colorimetric method based on CeO₂-modified gold core shell nanoparticles (Au@CeO₂ NPs) to analyze ACP activity with high sensitivity and specificity. In this design, 2-phospho-L-ascorbic acid trisodium salt (AAP) is dephosphorylated by ACP and produces reductive ascorbic acid (AA), which makes the CeO₂ shell decomposition. A remarkable blue shift of localized surface plasmon resonance peak (LSPR, from yellow to green) along with the scattering intensity ratio changes from individual Au@CeO₂ NPs are observed. ACP activity can be quantified by calculating the ratio changes of individual Au@CeO₂ NPs. This assay reveals limit of detection (LOD) of 0.044 mU/mL and the linear range of 0.05–5.0 mU/mL, which are much lower than most of spectroscopic measurements in bulk solution. Furthermore, the recovery measurements in real samples are satisfactory and the capacity for practical application is demonstrated. As a consequence, Au@CeO₂ NPs used in this assay will find new applications for the ultrasensitive detection of enzyme activity.