Multilayered Sandwich Structure Sensor: Confinement‐Mediated H 2 O 2 Enrichment Strategy for Ultrasensitive and Long‐term Stable Prostate Cancer Biomarker Detection

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Sarcosine (Sar), a critical potential biomarker for prostate cancer (PCa), is primarily detected via enzyme cascade reactions involving sarcosine oxidase (SOx) and peroxidase. Nevertheless, the intermediate product hydrogen peroxide (H 2 O 2 ) tends to diffuse to the bulk solution phase without entering subsequent reaction, leading to suboptimal detection sensitivity and compromised analytical performance. To tackle this challenge, a multilayered sandwich nanozyme cascade sensor (designated as Cu‐MOF/Rf@BDC) is proposed through a confinement‐mediated H 2 O 2 enrichment strategy. Its innovative architecture spatially restricts the H 2 O 2 diffusion while maintaining optimal reaction proximity, thereby enhancing the utilization efficiency of H 2 O 2 by local concentration effects. The confined microenvironment ultimately achieves the ultrasensitive Sar detection with a 3.31 nmol L −1 detection limit (1–2 orders lower than previously reported methods). In clinical urine samples tested for Sar detection, the sensor exhibits strong consistency with commercial enzyme‐linked immunosorbent assay (ELISA) kits, confirming the reliability of its analytical performance. Significantly, the sensor demonstrates a 3.6‐fold shorter preparation time and 6.0–12.0‐fold longer signal duration compared to ELISA kits. These dual advantages accelerate the detection process and improve efficiency for large‐scale clinical screening of PCa biomarkers. Furthermore, the developed sensor exhibits exceptional selectivity and repeatability, underscoring its potential practicality in complex analytical matrices.