Polydopamine-Mediated Flexible Spatial Barrier Facilitates Multilayer Assembly of Nanozymes to Co-Strength Point-of-Care Immunoassays

The development of effective diagnostic strategies is crucial for ensuring the public health security. Here, we present a composite probe with exceptional peroxidase-like activity suitable for ultrasensitive and rapid immune-quantitative analysis. The probe is prepared via the polydopamine (PDA)-mediated flexible spatial barrier strategy, which overcomes performance limitations associated with inadequate or excessive loading that causes aggregation. The NU-902@CeO₂@PDA@CeO₂ (NCPC) exhibits remarkable peroxidase-like activity, achieving 310-fold and 111-fold enhancements over horseradish peroxidase and CeO₂ in catalytic constant, respectively. Furthermore, NCPC maintains superior stability compared to natural enzymes, overcoming a key limitation of biological catalysts. When applied to chloramphenicol as an antibiotic model, the NCPC-mediated immunoassay reduces the detection time by 83.88% and achieves a limit of detection of 4.99 pg/mL, outperforming enzyme-linked immunosorbent assays by 194-fold. The NCPC-mediated strategy will greatly improve the quantitative analysis performance in the fields of in vitro diagnostics, food safety, and environmental monitoring, thereby ensuring public health safety.