Electron Transfer-Enhanced Bimetallic MOF Nanozymes Enabling a Self-Validating Dual-Mode Aptasensor for Aflatoxin B₁

Aflatoxin B₁ (AFB₁) is a widespread mycotoxin that poses a substantial risk to food and health safety due to its potent toxicity and carcinogenic properties. Herein, a novel colorimetric-electrochemical dual-mode aptamer sensor utilizing the MIL-88@Pd/Pt nanozymes has been successfully constructed for the sensitive and reliable detection of AFB₁. These high-performance MIL-88@Pd/Pt nanozymes were synthesized through the in situ growth of bimetallic Pd/Pt nanoparticles on a MIL-88 surface, exhibiting exceptional peroxidase-like activity. Experiments and density functional theory (DFT) calculations revealed that the catalytic enhancement arises from facilitated electron transfer from the Pd/Pt domains to Fe centers of MIL-88, which lowers the activation barrier for H₂O₂ cleavage and promotes hydroxyl radical (·OH) generation. The sensor operates on a competitive assay principle, wherein an AFB₁ aptamer immobilized on magnetic beads releases the MIL-88@Pd/Pt nanozyme conjugate upon target binding. This target-induced release enables a dual-mode readout: the nanozymes in the supernatant provide a electrochemical signal, while the residual nanozymes on the beads generate an inverse colorimetric signal via the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB). Within optimal conditions, the AFB₁ detection range spans from 5 ng/mL to 100 ng/mL, with detection limits of 0.97 ng/mL (colorimetric) and 1.02 ng/mL (electrochemical). The dual-mode sensor was effectively applied to the determination of AFB₁ in real food and herb samples, demonstrating its potential as a robust, reliable, and self-validating platform for food safety monitoring and quality control.