A facile dual-mode SERS/fluorescence aptasensor for AFB detection based on gold nanoparticles and magnetic nanoparticles.

Aflatoxin B (AFB) is a virulent metabolite secreted by Aspergillus fungi, impacting crop quality and posing health risks to human. Herein, a dual-mode Raman/fluorescence aptasensor was constructed to detect AFB. The aptasensor was assembled by gold nanoparticles (AuNPs) and magnetic nanoparticles (MNPs), while the surface-enhanced Raman scattering (SERS) and fluorescence resonance energy transfer (FRET) effects were both realized. AuNPs were modified with the Raman signal molecule 4-MBA and the complementary chain of AFB aptamer (cDNA). MNPs were modified with the fluorescence signal molecule Cy5 and the AFB aptamer (AFB apt). Through base pairing, AuNPs aggregated on the surface of MNPs, forming a satellite-like nanocomposite, boosting SERS signal via increased "hot spots" but reducing fluorescence signal due to the proximity of AuNPs to Cy5. Upon exposure to AFB, AFB apt specifically bound to AFB, causing AuNPs detachment from MNPs, weakening the SERS signal while restoring the fluorescence signal. AFB concentration displayed a good linear relationship with SERS/fluorescence signal in the range of 0.01 ng/mL-100 ng/mL, with a detection limit as low as 5.81 pg/mL. The use of aptamer assured the high selectivity toward AFB. Furthermore, the spiked recovery in peanut samples ranged from 91.4 % to 95.6 %, indicating the applicability of real sample detection. Compared to single-signal sensor, this dual-signal sensor exhibited enhanced accuracy, robust anti-interference capability, and increased flexibility, promising for toxin detection in food safety applications.