Homogeneous assay of target molecules based on chemiluminescence resonance energy transfer (CRET) using DNAzyme-linked aptamers

We have designed a single-stranded DNAzyme–aptamer sensor for homogeneous target molecular detection based on chemiluminescence resonance energy transfer (CRET). The structure of the engineered single-stranded DNA (ssDNA) includes the horseradish peroxidase (HRP)-like DNAzyme, optimum-length linker (10-mer-length DNA), and target-specific aptamer sequences. A quencher dye was modified at the 3′ end of the aptamer sequence. The incorporation of hemin into the G-quadruplex structure of DNAzyme yields an active HRP-like activity that catalyzes luminol to generate a chemiluminescence (CL) signal. In the presence of target molecules, such as ochratoxin A (OTA), adenosine triphosphate (ATP), or thrombin, the aptamer sequence was folded due to the formation of the aptamer/analyte complex, which induced the quencher dye close to the DNAzyme structure. Consequently, the CRET occurred between a DNAzyme-catalyzed chemiluminescence reaction and the quencher dye. Our results showed that CRET-based DNAzyme–aptamer biosensing enabled specific OTA analysis with a limit of detection of 0.27 ng/mL. The CRET platform needs no external light source and avoids autofluorescence and photobleaching, and target molecules can be detected specifically and sensitively in a homogeneous manner.