Covalent organic framework-based aptananozyme (COF@NH2 apt-AFM1): A novel platform for colorimetric and fluorescent aptasensing of AFM1 in milk

Nanozymes are valued for their cost-effectiveness and robustness but are often limited their lack of specificity. This study introduces a Covalent Organic Framework-based aptananozyme (COF@NH₂ apt- AFM₁) for label-free, dual-mode detection of Aflatoxin M₁ (AFM₁) in milk. The aptananozyme enables colorimetric detection by catalyzing the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂) and provides fluorescent signals for sensitive AFM₁ identification. The dual-mode aptasensor achieves remarkable limits of detection (LOD) 7 pg/mL (colorimetric) and 5 pg/mL (fluorescent). Validation with High Performance Liquid Chromatography (HPLC) on milk samples showed recovery 97–99 % (colorimetric) and 96–101 % (fluorescent), confirming its stability and repeatability. Characterization of the COF and aptananozyme involved Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), UV–visible absorption spectroscopy, Fluorescence emission spectroscopy, Field emission scanning electron microscopy (FE-SEM), optical microscope images and Dynamic light scattering (DLS). This sensor demonstrates high sensitivity, accuracy and broader application potential.