A ratiometric fluorescent biosensor based on catalytic hairpin assembly reaction for ultrasensitive detection of aflatoxin-producing genes

Aflatoxins as the world's most toxic contamination is metabolized by Aspergillus flavus and its production is closely related to aflatoxin-producing genes. It is significant to monitor the aflatoxin-producing genes as early as possible to prevent the contamination and spread of aflatoxins. Therefore, a label-free and free separation fluorescent biosensor using the selective cation exchange reaction in conjunction with the signal amplification of catalytic hairpin assembly (CHA) was developed for the detection of aflatoxin-producing gene utilizing CdTe quantum dots (CdTe QDs) and Nitrogen-doped carbon quantum dots (NCQDs) as the beacon molecule. There were two types of hairpin structures in this sensing system, hairpin probe 1 (HP1) was generated by Ag+ and the recognition probe with the complex C-Ag+-C structure and hairpin probe 2 (HP2) was the DNA fragments showing a hairpin arrangement. Target nor-1 gene may activate the CHA, which created a significant quantity of HP1-HP2 double-stranded DNAand recycled the target nor-1 gene. The released amounts of Ag + suppressed the fluorescence signal of CdTe QDs, while it wasn't observed the discernible effect on NCQDs. This fluorescent biosensor displayed the excellent sensitivity for aflatoxin-producing nor-1 gene in a dynamic range of 5 pM-50 nM with a detection limit of 1.66 pM. This fabricated sensor also showed the visible distinguish for different concentrations of nor-1 gene. It exhibited the potential to offer vital enhancements for food quality control through a simple, fast and sensitive monitoring test system.