Phosphorus-Doped Yolk-Shell Carbon Nanocages Derived from Metal-organic Frameworks for Enhanced Magnetic Solid-phase Extraction of Brevetoxins in Seawater

Brevetoxins (BTXs), lipophilic cyclic polyether neurotoxins released by Karenia brevis during harmful algal blooms, pose significant ecological and public health threats through seawater contamination and trophic accumulation. Despite their importance, direct detection of BTXs in seawater remains largely unexplored due to trace-level concentrations and severe matrix interferences. BTX-1, a representative toxin with well-defined structure and high stability, serves as a model compound. Here, we report the novel analytical strategy for BTX-1 determination in seawater, enabled by yolk–shell phosphorus-doped carbon nanocages (Y-Co/P-NCNCs) as high-performance magnetic solid-phase extraction (MSPE) sorbents. The unique yolk–shell architecture provides dual external–internal diffusion pathways that shorten transport distances and accelerate adsorption kinetics, while phosphorus doping introduces polar defects and structural heterogeneity that enhance specific interactions with BTX-1 molecules. Coupled with HPLC–MS/MS, the developed MSPE protocol achieved high enrichment efficiency, excellent selectivity, and rapid recovery, with recoveries of 83.5% to 105.4%, limits of detection down to 5.0 pg mL⁻¹, and relative standard deviations below 11.8%. This work not only establishes a robust platform for trace BTX-1 monitoring in seawater but also demonstrates a generalizable materials design strategy for yolk–shell heteroatom-doped carbons in the enrichment of bulky, hydrophobic marine toxins from complex environmental matrices.