Enrichment and characterization of foodborne fungal spores by ferric ion-based surface-assisted laser desorption/ionization mass spectrometry

We developed a novel surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) method to detect fungal spores, which is a critical concern in food safety. A combination of Fe³⁺ and trifluoroacetic acid (TFA) was initially confirmed as an effective light absorber, facilitating the desorption and ionization of small organics in SALDI-MS. This approach was then successfully applied to the analysis of small organics derived from Aspergillus niger, aflatoxigenic Aspergillus flavus, and non-aflatoxigenic A. flavus, enabling the differentiation of closely related species and strains. Additionally, Fe³⁺ and Gd³⁺ were used as magnetic probes to trap and concentrate spores from sample solutions, and TFA-mediated lysis and SALDI-MS analysis were performed. We demonstrated that the proposed method can be used to trap trace amounts of fungal spores in a peanut extract and complement Fe³⁺-SALDI MS analysis. The limit of detection of the method against fungal spores was as low as ∼10⁴ spores mL⁻¹.