Fig. 1.

Schematic of the DNA sensing system, in which a thrombin-inhibiting aptamer is fused with a stem-and-loop structure. The thrombin-inhibiting aptamer into which a stem-and-loop structure is inserted forms a G-quartet structure, since the stem site is formed by the annealing of both of its sides. When the target DNA hybridizes with the loop site of the stem-and-loop structure, the stem site is dehybridized, which leads to the disruption of the G-quartet structure of the thrombin-inhibiting aptamer site, thus reducing its thrombin-inhibiting activity.