Homogeneous Multicycle Cascaded DNA Circuit for Sensitive "Signal On-Off-Super On" PEC Biosensing.

The minor changes of miRNA levels due to various diseases and cancers bring great challenges for early diagnosis. Here we propose a "signal on-off-super on" PEC biosensor based on a homogeneous multicycle cascaded DNA circuit and a SnSe/CdS photoanode for sensitive detection of biomarker miRNA-222. Specifically, a Z-type SnSe/CdS heterojunction with greatly enhanced photoanodic performance was developed to provide the initial "on" signal. The target miRNA-222 was converted to a dendritic DNA structure through a cascade DNA circuit. The PEC signal can be switched off by the dendritic DNA structure and further switched super on by the loading of photosensitizer manganese porphyrin (MnPP). It is worth noting that the homogeneous multicycle cascaded DNA circuit not only improved the reaction kinetics but also avoided the leakage of signal. Compared with the traditional "signal-on" or "signal-off" readout, this "signal on-off-super on" strategy avoids the false response and background, thereby enhancing the sensitivity and accuracy of the PEC biosensor. The detection limit of the constructed PEC sensor is 0.3 fM in the linear range from 1 fM to 10 nM. The PEC biosensor with outstanding reproducibility, stability, and sensitivity provides a promising platform for biomarker detection and early disease diagnosis.