Ultrasensitive Aptasensing of Fumonisin B1 Enabled by Pt/Pd@Covalent Organic Framework (COF)@Molybdenum (IV) Sulfide and Enzyme-Free DNA Walker- Hybridization Chain Reaction (HCR) Cascade Amplification

Fumonisin B1 (FB1) is a toxic mycotoxin in cereals, demanding sensitive detection. We constructed an electrochemical aptasensor based on hybridization chain reaction (HCR)‑synergized DNA walker dual‑cycle cascade amplification. The electrode substrate, Pt/Pd@COF@MoS2 composite, provides high conductivity, large surface area, and abundant active sites for capture DNA loading. Signal amplification follows a recognition‑walking‑amplification process: target binding releases the DNA walker, which cleaves hairpin HP1 on magnetic beads with Mg2+ (Cycle I). The cleavage products are magnetically separated and trigger HCR on the electrode, forming DNA concatemers that electrostatically enrich methylene blue for amplified signals (Cycle II). Under the optimized conditions, the square‑wave voltammetric response is linear from 1 × 10−1 to 1 × 105 pg/mL, with a detection limit of 16 fg/mL. The aptasensor shows excellent selectivity, reproducibility, and stability, with recoveries of 89.4%–106.2% in spiked milk and corn flour. This cascade strategy converts single recognition events into exponential signal enrichment, providing a powerful platform for trace mycotoxin detection.