4-Mercaptobenzenesulfonic Acid-Functionalized SiO2@Au Nanoshells for Specific Enrichment and SALDI-MS Detection of Quaternary Ammonium Compounds

MBSA-SiO2@Au nanoshells enabled selective enrichment and SALDI-MS of QACs. • The bifunctional platform served as both adsorbent and ionization matrix. • The method achieved 0.5–1.5 ng/mL LODs with 20–40-fold sensitivity enhancement. • Recoveries of 87.0–108.8% were achieved in white radish, carrot, and potato matrices. The widespread use and persistence of quaternary ammonium compounds (QACs) in food environments raise concerns about their detection at trace levels in complex matrices. In this study, we developed a negatively charged 4-mercaptobenzenesulfonic acid functionalized SiO 2 @Au core-shell nanocomposite (MBSA-SiO 2 @Au) that serves as both a selective adsorbent and an efficient surface-assisted laser desorption/ionization (SALDI) matrix. The sulfonate modified gold shell provides a stable negative surface potential to promote electrostatic interactions with cationic QACs, and their plasmonic properties synergistically enhance laser energy absorption and ionization efficiency. Critical enrichment parameters, including adsorbent amount, solution pH, adsorption time, and redispersion volume, were optimized. The optimized method achieved limits of detection of 0.5 ng/mL for paraquat (PQ), dodecyltrimethylammonium chloride (DTAC), and didodecyldimethylammonium chloride (DDAC), and 1.5 ng/mL for dodecyldimethylbenzylammonium chloride (DBAC), with excellent linearity (R 2 ≥ 0.9843), achieving an enrichment factor of approximately 33.3, and a 20- to 40-fold sensitivity enhancement after enrichment. Application to real food samples, including white radish, carrot, and potato, revealed no detectable QAC residues and satisfactory recoveries ranging from 87.0 to 108.8%. The bifunctional MBSA-SiO 2 @Au-based SALDI platform minimizes organic solvent consumption and offers a rapid, green, and sensitive approach for monitoring QACs in food safety applications.