Ultra-Stable and broadband absorption Fe3O4-Gold/Polydopamine nanohybrid enabling ultrasensitive fluorescence Quenching-Mediated immunochromatography assay

Efficient fluorescence quenching agents guarantee the construction of rapid, robust and sensitive fluorescence quenching-based “turn-on” analytical sensors. Herein, we synthesized a Fe₃O₄-gold/polydopamine nanohybrid (Fe₃O₄@Au/PDA) via coating a gold/polydopamine hybrid layer onto the surface of Fe₃O₄. The resultant Fe₃O₄@Au/PDA exhibited exceptional broadband absorption, efficient fluorescence quenching ability, remarkable colloidal stability and rapid magnetic response, rendering it ideal candidates as fluorescence quenching agents. Thus, quantum dot nanobeads were chosen as the fluorophore, while Fe₃O₄@Au/PDA served as the quencher, enabling the successful establishment of a fluorescence quenching-based “turn-on” immunochromatographic assay (FQ-ICA) for the sensitive detection of aflatoxin B₁ (AFB₁) in soybean sauce. Quantitative assessment revealed that the Fe₃O₄@Au/PDA-modulated FQ-ICA achieved a limit of detection of 0.001 ng/mL, with linearity ranging from 0.001 to 0.5 ng/mL in soybean sauce sample. Furthermore, owing to its uniform broadband absorption spanning the entire UV–vis range, we demonstrate the feasibility of using Fe₃O₄@Au/PDA as a universal fluorescence quencher to construct multicolor FQ-ICA for the simultaneous detection of three mycotoxins. In summary, the synthesized Fe₃O₄@Au/PDA nanocomposite can be served as a versatile fluorescence quenching agent for fabricating diverse fluorescence quenching-based “turn-on” assay biosensors.