DNA abasic site-based aptamer for selective fluorescence light-up detection of fisetin by excited-state intramolecular proton transfer

Many efforts have been made for the developments of aptamers due to their wide applications for various targets. In this work, we tried to use an abasic site (AP site) that was embeded in a double-stranded DNA as a binding pocket for fisetin. With the AP site being wholly opposed and flanked by thymines (named T-T aptamer), the aptamer exhibits high binding selectivity and sensitivity for fisetin over the other flavonoids such as morin, rutin, apigenin, kaempferol, myricetin, quercetin, luteolin, baicalin, naringenin, genistein, chrysin, and galangin. Upon binding to the AP site, fisetin experiences a significant enhancement in fluorescence emisson by favoring the occurrence of its excited-state intramolecular proton transfer (ESIPT) reaction. The detection limit is about 50 nM at a signal-to-noise ratio of 3. Therefore, the realization for fisetin's selective analysis is beneficial from the novel aptamer design without any fluorophore modification. Thus, the almost negligible fluorescence background from the aptamer is achieved in our method.