Colorimetric liquid crystal-based assay for the ultrasensitive detection of AFB1 assisted with rolling circle amplification

The detection of AFB1 that is a group I carcinogen is significantly important for food safety. Herein, we report a colorimetric liquid crystal (LC)-based assay that allows the ultrasensitive detection of AFB1. When an aqueous solution of a cationic surfactant is transferred onto the LCs dispersed with the aqueous microdroplets containing the anionic surfactants and horseperoxidase (HRP), it triggers the release of HRP due to the interfacial charge interaction. Because HRP can catalyze the colorless 3,3'-5,5'-tetramethylbenzidine (TMB) into yellow products, the response of the LCs dispersed with the aqueous microdroplets to the cationic surfactant is visually determined. In the presence of AFB1, the rolling circle amplification on magnetic beads (MBs) is triggered due to the specific recognition of AFB1 by its aptamer, which results in the generation of long chain single-stranded DNA on MBs. As the cationic surfactants are captured by the negatively charged ssDNA, it prevents the release of HRP into the aqueous solution. In contrast, in the absence of AFB1, HRP is released into the aqueous solution. The developed AFB1 sensing assay shows very good linear relationship with the detection limit of AFB1 determined to be as low as 0.014 pg/mL. In addition, the detection of AFB1 in rice and peanut oil is also examined to demonstrate its capability for the analysis of the real samples. Overall, this method takes advantages of the unique aptamer/target recognition, specific enzymatic reaction, and simple colorimetric assay, which makes it very promising for the ultrasensitive detection of AFB1 in practical applications.