A surface-enhanced Raman scattering and fluorescence dual-mode aptasensor based on magnetic plasmonic core-shell nanostructures and N-doped carbon dots for aflatoxin B1 detection

Aflatoxin B1 (AFB1) contamination in foods threatens human health worldwide, and accurate and rapid detection of AFB1 is essential. Herein, a surface-enhanced Raman scattering (SERS) and fluorescence dual-mode aptasensor is constructed for sensitive detection of AFB1 based on ZnFe₂O₄ magnetic nanoparticle@gold nanoparticles-silver shell nanostructures (MNP@AuNPs-Ag) and fluorescent N-doped carbon dots (N-CDs). Specifically, Raman beacon molecule cyanine 3-modified aptamer (Apt-Cy3) is coupled on the MNP@AuNPs-Ag surface, and complementary DNA (cDNA) is modified on the N-CDs surface (N-CDs-cDNA). In the absence of AFB1, thanks to the DNA hybridization, low fluorescence for the supernatant and low SERS for the precipitate appear after magnetic separation. However, in the presence of AFB1, most of N-CDs-cDNA are free as the aptamer preferentially binds to AFB1, resulting in a strong fluorescent signal in the supernatant, while the change in the secondary structure of the aptamer shortens the spatial distance between Cy3 and MNP@AuNPs-Ag, producing a strong SERS signal. Based on the principle, the dual-mode aptasensor is developed and quantifies AFB1 using SERS and fluorescence signals with the low detection limits of 0.88 and 9.74 pg/mL, respectively. What's more, the dual-mode aptasensor is applied to the detection of AFB1 in real food samples successfully. This work exploits magnetic plasmonic core-shell nanostructures and fluorescent N-CDs to obtain fluorescence and SERS signals from the supernatant and the precipitate respectively after magnetic separation. The strategy not only provides a robust method for detection of AFB1 but also offers new insights for the design of dual-mode aptasensor.