Colorimetric determination of the activity of alkaline phosphatase by exploiting the oxidase-like activity of palladium cube@CeO.sub.2 core-shell nanoparticles

Core-shell palladium cube@CeO.sub.2 (Pd cube@CeO.sub.2) nanoparticles are shown to display oxidase-like activity. This is exploited in a method for determination of the activity of alkaline phosphatase (ALP). The Pd cube@CeO.sub.2 nanoparticles were thermally synthesized from Ce(NO.sub.3).sub.3, L-arginine and preformed Pd cube seeds in water. The Pd cube@CeO.sub.2 nanoparticles catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by oxygen. This results in the formation of oxidized TMB (oxTMB) with an absorption peak at 652 nm. Ascorbic acid (AA) is generated from the hydrolysis of L-ascorbic acid 2-phosphate (AAP) catalyzed by ALP. It can reduce oxTMB to TMB, and this results in a decrease of the absorbance. The method allows for quantitative determination of the activity of ALP in the range from 0.1 to 4.0 U·L.sup.-1 and with a detection limit down to 0.07 U·L.sup.-1. Endowed with high sensitivity and selectivity, the assay can quantify ALP activity in biological system with satisfactory results.