THz near-field imaging for identification of individual spores of grain storage fungi

Fungal contamination during grain storage poses a significant threat to food security and quality control. Rapid, non-destructive detection and early-stage identification of fungus spores are therefore crucial for ensuring the safety of stored grain. Terahertz scattering-type scanning near-field optical microscopy can overcome the diffraction limit, offering great potential for microbial imaging and detection. In this study, we acquired both atomic force microscopy topography images and terahertz near-field images, processed by harmonic demodulation, of Aspergillus niger , Aspergillus flavus Link, and Aspergillus terreus spores. Data analysis revealed significant differences in morphological and near-field characteristics among the three species. Specifically, Aspergillus niger exhibited the smallest average spore diameter (2.940 ± 0.385 µm), followed by Aspergillus flavus (3.287 ± 0.436 µm), while Aspergillus terreus showed the largest size (4.230 ± 0.731 µm). One-way analysis of variance confirmed that these differences were statistically significant ( P < 0.05). In addition, distinct variations in AFM-derived height and near-field signal amplitude were observed, further enabling clear differentiation of the three species. These findings demonstrate the feasibility of THz s-SNOM for microbiological detection and highlight its strong potential for non-destructive grain quality assessment and early-stage food safety monitoring in grain storage systems. • Proposed a THz scattering-type scanning near-field optical microscopy approach. • Aspergillus niger, Aspergillus flavus Link, and Aspergillus terreus were imaged and distinguished. • A non-labelled and non-invasive method for detecting fungal spores in stored grain has been proposed.