Fig. 2. Examination of adenosine-triggered strand displacement. (a) Rational design of AA and TS sequences for the displacement reaction. The functional regions I and II in AA were designed to hybridize with the 5′-end of TS. The hybridization with 14 base pairs is shown here for clear legibility. (b) Structure of 2-aminopurine and schematic illustration of its fluorescence on/off status. (c) Fluorescence emission spectra of AA and AA–TS duplex in solution. Ex = 307 nm. (d) Effects of hybridization length on the fluorescence intensity and melting temperature of the AA–TS duplex (Em = 370 nm). (e) Relationship between fluorescence recovery and hybridization length of the AA–TS duplex in the presence of adenosine (5 mM). (f) Fluorescence emission spectra of the AA–TS solutions in the presence of adenosine. The number of base pairs was 14. (g) Fluorescence recovery of the AA–TS solution in the presence of nucleosides (1 mM). Error bars represent s. e. m (n = 3).