T7 exonuclease-assisted and target-triggered cascade dual recycling signal amplification strategy for the sensitive and specific detection of adenosine

Adenosine is closely related to the development of cancer, and it can be regarded as a biomarker for cancer diagnosis and therapy. Here, a T7 exonuclease (T7 Exo)-assisted and target-triggered cascade dual recycling signal amplification strategy was developed for the sensitive and specific detection of adenosine. In this strategy, a capture strand (Cap)-inhibit strand (Inh) duplex and a DNA hairpin with intact G-quadruplex sequence are designed. In the presence of adenosine, Cap binds with adenosine specifically to form Cap-adenosine complex with recessed 5'-hydroxyl termini, causing the release of Inh. Under the action of T7 Exo, the adenosine is released from Cap-adenosine complex. Then the released adenosine interacts with the next Cap-Inh duplex to promote the release of a new Inh and the recycle I is completed. After that, the released Inh hybridizes with hairpin to form Inh-hairpin duplex with blunt 5'-hydroxyl termini. Under the same action of T7 Exo, the Inh gets released and a G-quadruplex sequence is obtained. Subsequently, the released Inh continues opening hairpin and the recycle II is accomplished. Finally, plenty of G-quadruplex sequences are generated and then interact with Nmethyl-mesoporphyrin IX (NMM) to obtain enhanced fluorescence signal. The limit of detection (LOD) of the proposed strategy is estimated to be 9.8 x 10(-7) mol L-1, and the linear range of the strategy is from 5.0 x 10(-6) mol L-1 to 7.0 x 10(-4) mol L-1. Besides, the proposed strategy is capable of distinguishing adenosine from its analogues. This strategy holds promise in adenosine related biomedical research, clinical diagnosis and disease treatment.