G-triplex/hemin DNAzyme: An ideal signal generator for isothermal exponential amplification reaction-based biosensing platform.

A short G-rich sequence with three G-tracts can form a G-triplex (G3), a recently identified noncanonical DNA structure. Until now, very limited functional study and application of G3 is reported. Herein, we integrated G3 with isothermal exponential amplification reaction (EXPAR) for achieving simple and sensitive biosensing strategy. In this strategy, the cascade EXPAR cycles produces larger numbers of short G-rich sequences, which self-assemble into G3 structure and then bind hemin to form G3/hemin DNAzyme. This G3/hemin DNAzyme-based EXPAR strategy could detect as low as 4.7 fM target DNA with colorimetric detection, and the sensitivity of G3/hemin DNAzyme-based EXPAR strategy was much higher than that of the conventional G-quadruplex/hemin DNAzyme-based EXPAR strategy. We explored the reason for higher sensitivity of G3/hemin DNAzyme-based EXPAR strategy. The experimental results demonstrated that G3/hemin DNAzyme is an ideal signal generator for EXPAR-based biosensing platform. This work opens a new avenue to develop effective signal amplification strategy for ultrasensitive biosensing. This work is also helpful for a deeper understanding of G3 structure and the future application of G3.