Myeloperoxidase (MPO) is an inflammation-associated heme enzyme implicated in cardiovascular oxidative stress, but sensitive activity-based detection in complex clinical samples remains challenging. Herein, we report a CRISPR/Cas12a-based triple-cascade amplification platform for rapid and sensitive MPO activity detection. The core sensing element consists of DNA nanowires containing multiple Cas12a activator strands, tethered to magnetic beads via biotin-labeled and phosphorothioate-modified linkers. In the chloride-containing assay system, MPO-catalyzed generation of HOCl oxidatively cleaves these linkers, releasing the nanowires and activating Cas12a, which, in turn, cleaves fluorescent reporters. This design integrates three amplification stages (MPO catalysis, multiactivator release, and Cas12a trans-cleavage), achieving ultrasensitive detection without additional nucleic acid amplification. Under the optimized chloride-containing conditions, the assay achieved a detection limit of 10.20 pg/mL for MPO. A preliminary pilot analysis using human serum samples from acute coronary syndrome patients and healthy individuals showed different signal distributions, supporting the feasibility of applying the platform to complex serum matrices, although contributions from eosinophil peroxidase/HOBr-mediated probe activation cannot be excluded. The platform is readily adaptable to lateral flow assays and portable fluorescence readouts, offering versatile formats for point-of-care-compatible analysis. This work provides a sensitive CRISPR/Cas12a-based strategy for MPO activity-related hypohalous oxidant assessment under defined assay conditions and demonstrates its preliminary applicability in complex serum matrices.
