Synergistically fluorinated triazine COFs as adsorption-ionization integrated matrix for analysis and in situ MALDI imaging of PFOS

Per- and polyfluoroalkyl substances (PFASs), like perfluorooctane sulfonic acid (PFOS), will accumulate continuously in organisms and pose toxic risks. Matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) is an effective method for analyzing their biological accumulation characteristics and microscopic spatial distribution. Currently, traditional organic matrices lack specific enrichment capabilities for PFOS, while inorganic adsorption matrices are prone to damaging the ion source. Therefore, the development of organic matrices with dual functions of adsorption and ionization is necessary to overcome these limitations and achieve high-sensitivity in situ MSI of trace PFOS in biological tissues.

A novel MALDI matrix for ultrasensitive detection and in situ tissue imaging of trace PFOS was developed, using fluorine-engineered triazine covalent organic framework TAPT-DFTA fabricated by Schiff-base condensation as an integrated adsorption-ionization matrix. Featuring a sea urchin-like nanostructure and a high specific surface area of 1057.50 m²/g, TAPT-DFTA delivers excellent detection reproducibility with signal RSD values lower than 6.3%. DFT simulations confirm its spontaneous PFOS capture driven by synergistic F-F interactions and hydrophobic forces. Under optimized conditions, it achieves a monolayer adsorption capacity of 63.33 mg/g and an ultralow PFOS LOD of 100 pg/mL, alongside robust salt tolerance and strong anti-interference performance toward biological macromolecules. The matrix further supports high-spatial-resolution MALDI imaging to clearly map PFOS accumulation and spatial distribution in mouse kidney and brain tissues.

This work innovatively constructs fluorinated triazine COFs TAPT-DFTA via fluorine engineering to integrate PFOS adsorption and MALDI ionization, breaking single-function drawbacks of traditional matrices. This fluorination tuning strategy balances framework laser stability and energy transfer efficiency, resolving the core trade-off problem that restricts COFs-based MALDI matrix performance. It achieves ppt-level PFOS detection and tissue in-situ imaging, offering a new paradigm for trace persistent organic pollutant spatial analysis.