A dual-probe system for autofluorescence-free determination of trace-level polystyrene nanoplastics

Nanoplastics (NPs) are new types of pollutants that have emerged in food which has attracted widespread attention. However, due to the small size and low concentration, and the complexity of food matrices, the selective and sensitive determination of NPs in food is challenging. Herein, we report a dual-probe system for determination of trace-level polystyrene (PS) NPs with high sensitivity and selectivity. The proposed dual-probe system was composed of magnetic Fe₃O₄ nanoparticles functionalized with PS-specific peptides (Fe₃O₄@Au-PSBP) and a high-quality Li⁺-doped ZnGa₂O₄:Cr³⁺ persistent luminescence nanoparticles (PLNPs) modified with ethylene glycol chitosan. By integrating peptide-based specific recognition, persistent luminescence signaling, and magnetic separation with pH-switchable charge reversal, the proposed system enables effective capture and sensitive detection of PS NPs in complex matrices. Under the optimized conditions, the method showed a linear range of 50-800 pg mL^-1 and a detection limit of 8.11 pg mL^-1. The precision for the determination of 50 pg mL^-1 PS NPs was 5.24% (RSD, n = 11). The method was successfully applied to the analysis of PS NPs in different matrices, including bottled purified water, saltwater (3.5% salinity), artificial lake water, and tea beverage, with recoveries ranging from 91.25% to 110.53%. More importantly, the proposed system can be readily adapted for the analysis of other targets by replacing the recognition unit, providing a versatile and selective sensing strategy for trace-level hazardous analytes.