Electrochemiluminescent carbon dot-based determination of microRNA-21 by using a hemin/G-wire supramolecular nanostructure as co-reaction accelerator.

An efficient coreaction accelerator scheme is introduced in an electrochemiluminescence (ECL) based method for sensitive determination of microRNA-21. It is making use of a domino type hemin/G-wire supramolecular DNA nanostructure (where "G-wire" represents a guanine-rich DNA structure) without a base pairing dependence. A glassy carbon electrode was modified with carbon dots (prepared from fullerene) and TiO2 nanoneedles. In the first step, a first hairpin 1 (H1) binds to microRNA-21 to form the hybridized complex in solution. This is followed by a T7 exonuclease (T7 Exo)-assisted target recycling to obtain a simulated target which can unfold hairpin 2 (H2) to form a double-stranded structure. After cleavage by T7 Exo, the G-rich sequences in H2 re-fold into G-quadruplexes on the electrode to form hemin/G-wire supramolecular nanostructure with the strand 1 (S1, a custom-made G-rich sequence) and hemin. As a result, the hemin/G-wire catalyzes the reaction of peroxothiosulfate that generates ECL. Thus, the signal is strongly enhanced. The method allows for the determination of microRNA-21 with a detection limit as low as 0.1 fM. It is conceived to represent a valuable tool in cancer research. Graphical abstract The hemin/G-wire supramolecular nanostructures assembled on a carbon dot (CD)-based glassy carbon electrode (GCE), thereby achieving electrochemiluminescence (ECL) signal amplification of the CD/S2O82- system and sensitive detection of microRNA-21.