Visual detection of aflatoxin B1 and zearalenone via activating a new catalytic reaction of “naked” DNAzyme

Here, we have found for the first time that the catalytic activity of "naked" DNAzyme, a single-stranded G-quadruplex DNAzyme (S.DNAzyme), can be modulated by aflatoxin B1 (AFB1) and zearalenone (ZEN). In fact, S.DNAzyme can mimic the activity of horseradish peroxidase to perform oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) to colored ABTS˙+ (dark green). This catalytic activity can be inhibited upon addition of AFB1, leading to color fade of the solution. But with ZEN, the solution color will change to a yellowish-brown or yellow color. Thus, we have exploited this finding to achieve label-free, naked-eye detection of AFB1 or ZEN, and have explored the possible detection mechanisms. This approach is able to detect AFB1 and ZEN concentrations as low as 0.18 μM and 0.29 μM, respectively. Even in real samples, the limit of detection values of these two analytes are lower than 3 μM. Notably, S.DNAzyme cross-reacted with three other tested aflatoxins, including aflatoxin B2, aflatoxin G1 and aflatoxin M1, revealing the potential for a broadly applicable method to identify the family of aflatoxins. The AFB1- or ZEN-triggered new catalytic reaction between "naked" DNAzyme and ABTS may offer new opportunities for on-site visual detection of mycotoxins.