A label-free colorimetric aptasensor for sensitive detection of aflatoxin B1 in peanuts based on dual catalytic hairpin assembly

Aflatoxin B1 (AFB1) is considered one of the most toxic and carcinogenic substances. Developing sensitive and accurate methods for detecting AFB1 in foodstuffs remains a major challenge. Herein, a label-free colorimetric aptasensor was constructed for the detection of AFB1 in peanuts, utilizing dual catalytic hairpin assembly (CHA) for signal amplification. Where, the recognition of AFB1 by its aptamer (Apta) induces the formation of an AptaAFB1 complex, causing the trigger chain (T) to release from the Apta-T complex. The released T triggers the first CHA reaction in the presence of hairpins H1, H2, and H3, producing H1-H2-H3 complexes. Each sticky end of these complexes serves as the initiating strand for the second CHA cycle, exposing a G-rich sequence from H5 that induces the formation of a G-quadruplex/hemin DNAzyme. This DNAzyme catalyzes the H2O2-mediated oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB), resulting in a color change. Under optimal conditions, the colorimetric signal is linearly related to the logarithm of AFB1 concentration in the range of 50 pM to 1.1 nM, with a detection limit of 13.49 pM. The spiked recoveries for AFB1 in peanuts range from 95.28 % to 104.50 %. This aptasensor provides a sensitive and accurate method for detecting trace amounts of AFB1, which is crucial for ensuring food safety.