Communication of bifunctional G-quadruplex chaperone with aptamer for highly selective adenosine signaling by an ESIPT fluorogen.

Adenosine (Ade) is an important bioactive molecule in energy metabolism, signaling, immune regulation, and cardiovascular protection, etc. Ade in serums during ischemic episode can abnormally reach to a few to tens of μM from the normal nM level. The currently developed aptamer methods for Ade and adenylate are widely used as the straightforward and cascade biosensing models. However, an ideal label-free method with high Ade-over-adenylate selectivity, turn-on fluorescence even at a few of μM level, and reference correction from sample matrix fluctuation has not yet been elucidated. Herein, we found that duplex can communicate with a G-quadruplex (G4) chaperone to light up the green tautomer fluorescence of 3-hydroxyflavone based on the excited state intramolecular proton transfer (ESIPT) process, while the normal blue reference emission at shorter wavelength is not affected. Accordingly, engineering the duplex with a newly screened aptamer also succeeded in favoring the ESIPT emission via responding to Ade, while the densely packed negative charge density in the G4 chaperone inhibited adenylate association with the aptamer. Therefore, the G4 chaperone is bifunctional. The aptamer-G4 ensemble was effectively applied to the serum analysis without any interference from the serum matrix. The specificity of aptamer-G4 ensemble towards Ade was also confirmed by adenosine deaminase (ADA), which was able to monitor the Ade dynamics and the ADA activity. It is expected that our method could be applied to other aptamers by chaperoning an appropriate G4 structure.