Choline Oxidase-Incorporated ATRP-Based Cerium Nanogels as Nanozymes for Colorimetric Detection of Hydrogen Peroxide and Choline

Choline is an important molecule in monitoring food safety and infant nutrition. Here, we report Ce nanogels synthesized by atom transfer radical polymerization (ATRP) employing Ce-coordinated acryloyl-lysine polymer brushes (Ce@SiO₂ NGs) as highly efficient cascade nanozymes for colorimetric detection of choline. The synthesized Ce@SiO₂ NGs demonstrated remarkable peroxidase-like activity with a porous exterior, which are essential to entrap choline oxidase (COx) to yield COx@Ce@SiO₂ NGs and construct a cascade reaction system to detect choline. Immobilized COx catalyzed the oxidation of choline in food samples to produce H₂O₂, which subsequently induced the oxidation of chromogenic substrate 3,3',5,5'-tetramethylbenzidine (TMB) to produce blue color signals. This method enabled the selective and sensitive detection of target choline with a satisfactory linear range of 4-400 μM, which is sufficient to analyze foodborne choline. The practical utility of the COx@Ce@SiO₂ NG-based assay was successfully validated to determine choline spiked in commercially available milk and infant formula with high accuracy and precision values. This approach provides a simple and affordable method of choline detection and has the potential to lead to more developments in ATRP-based nanozymes for diverse biosensing applications.