Superparamagnetic Nanostructures Coupled with an Entropy-Driven DNA Circuit for Elegant and Robust Photoelectrochemical Biosensing.

MicroRNA (miRNA) has become a key indicator of cancer diagnosis based on its abnormal expression levels. However, high-performance monitoring of miRNA is still a difficult task because of its low concentration, small size, and similarity of sequences. Herein, an elegant and robust photoelectrochemical (PEC) biosensor for miRNA-122 has been flexibly designed based on the split mode between entropy-driven DNA signal amplification and photocurrent expression. The entropy-driven DNA circuit uses a multichain composite structure instead of a DNA hairpin structure, leading to decrease the reversibility of each step of the signal amplification system. Also, the unique increasing entropy mechanism, rather than the free energy release from the new base pairs forming, improves the reaction efficiency and enhances more thermal stability and strong specific identification ability. Particularly, the biologically functionalized superparamagnetic Fe3O4@SiO2 complex endows this split mode PEC biosensor with excellent specificity and enhanced efficiency of electrode fabrication. Additionally, this strategy of only the CdTe-signal DNA modified on the ITO electrode for photocurrent readout overcomes the shortcomings of tediously long layer-by-layer assembly process and multiple rinsing steps, leading to efficient improvement of the stability and reproducibility for the as-designed PEC biosensor. This elegant strategy opens a new path for miRNA measurements with superior performance.