Engineered DNAzyme Enables Homogeneous Detection of Cereulide via Polychromic Fluorescence Modality

Cereulide, the exotoxin of emetic Bacillus cereus, has garnered considerable attention due to its capacity to produce foodborne poisonings and great chemical stability. Herein, a G-quadruplex-hemin DNAzyme-based biosensor was developed to detect cereulide in the homogeneous solution. Due to the special ring structure and high affinity to K⁺, cereulide can be attracted and intercalated into the G-quadruplex; thus, the properties of the G4 DNAzyme can be altered. The melting temperature (T_m) of the G4 DNAzyme in the presence or absence of cereulide was 58.75 and 50.10 °C, respectively, proving the intercalation of cereulide into the G4 DNAzyme. By using the polychromic fluorescence modality of CdTe quantum dots and o-phenylenediamine to assess the variation in the catalytic activity of the DNAzyme, the intercalation of cereulide had bidirectional effects in G4 DNAzyme-mediated reactions, showing that the fluorescence intensity of CdTe quantum dots displayed a linear relationship with the concentration of cereulide from 0.16 to 40 μg/mL with the limit of detection (LOD) of 0.10 μg/mL, while the fluorescence intensity of DAP exhibited a linear relationship with the concentration of cereulide from 0.02 to 40 μg/mL with the LOD of 0.01 μg/mL. It will be a perspective step of controlling cereulide as a hazardous material in food or the environment.