An ultrasensitive dual-mode approach for AFB1 detection: Colorimetric/label-free SERS aptasensor based on a self-assembled core-shell structured Ag@Au IP6 bifunctional nanozyme

A sensitive and accurate assay of aflatoxin B1 (AFB1) is critically important to ensure food safety. This work designed a dual-mode aptasensor for the convenient and sensitive detection of AFB1 in foodstuff. The aptasensor based on a bifunctional nanozymes was prepared by combining the hybridization chain reaction (HCR) amplification and alkaline phosphatase (ALP)-induced self-assembly reaction. The Ag@Au IP6 nanozyme demonstrated better peroxidase-like activity, effectively initiating the TMB−H2O2 color reaction and facilitating the generation of the blue oxidation product oxTMB. Furthermore, Ag@Au IP6 as a surface-enhanced Raman scattering (SERS) substrate featuring a core-shell structure can notably enhance the Raman signal of oxTMB. When AFB1 existed, the trigger probe exposed and initiated HCR, leading to the introduction of ALP, consequently mediating the generation of Ag@Au IP6 nanozymes, enhancing both SERS signal and colorimetric signal in the TMB-H2O2 system. Consequently, the dual-mode aptasensor is capable of achieving SERS/colorimetric detection with no need for the modification of signal molecules and the replacement of material or reagent. In on-site detection, the visual sensing assay could achieve with collecting and transforming the colorimetric signal to RGB value by a color-assist App in smartphones. Within optimal conditions, the detection limit of dual-mode aptasensor as low as 0.58 pg/L, and with a linear range from 2 pg/L to 200 pg/L, which can meet the needs for AFB1 precise quantification and on-site detection.