Site-specific immobilization of tyrosinase on magnetic polystyrene nanospheres as dual-functional biosensor for enhanced colorimetric analysis of atrazine in vegetables.

The enzyme-based colorimetric sensor allows rapid and visual detection of food contaminants but is limited by low sensitivity and impurity interference. In the present work, a colorimetric biosensor for atrazine detection was fabricated through oriented immobilization of tyrosinase onto magnetic polystyrene nanospheres (MPSNPs). MPSNPs carriers were prepared by surface amination of monodisperse polystyrene nanospheres, followed by concanavalin A modification to introduce specific affinity sites for glycosyl groups on tyrosinase. Then, tyrosinase was bound to these specific sites via affinity self-assembly. The obtained MPSNPs immobilized tyrosinase (MPSNP-ConA/Tyr) were characterized and displayed uniform and stable structure, excellent enzyme activity, and good adsorption properties for the target atrazine. The MPSNP-ConA/Tyr, combined with 4-aminoantipyrine/catechol colorimetric indicator and smartphone, was used to analyze atrazine in three vegetable samples. The method enabled atrazine enrichment, enzyme activity inhibition reaction, and quantitative analysis in a single platform. This MPSNP-ConA/Tyr based method exhibited good linearity in the range of 0.1-2.0 mg L-1 (γ > 0.9953) with a limit of detection (LOD) of 0.054 mg L-1. The accuracy evaluated by recoveries ranged from 73.1% to 100.5% with relative standard deviations (RSDs) of 1.2-12.5%. A comparison with the GC-MS/MS method was performed using real vegetable samples (cucumber, carrot, and lettuce), and comparable atrazine concentrations were obtained, validating the practical applicability of the proposed method.