The combination of ternary electrochemiluminescence system of g-C3N4 nanosheet/TEA/Cu@Cu2O and G-quadruplex-driven regeneration strategy for ultrasensitive bioanalysis.

Graphitic carbon nitride nanosheet (g-C3N4 NS) with superior photoelectronic properties was served as ECL emitter to in-situ generate Cu@Cu2O nanoparticles as coreaction accelerator for constructing neoteric ternary ECL system (g-C3N4 NS/TEA/Cu@Cu2O system). Impressively, compared to individual g-C3N4 NS, the designed Cu@Cu2O/g-C3N4 NS not only displayed an enhanced current intensity with advance onset potential, but also observed a strong ECL response, which reduced the ECL potential down to 1.3 V for beneficial construction of biosensor, owe to the significant role of Cu@Cu2O in accelerating the reaction between g-C3N4 NS and trimethylamine (TEA). Notably, the enzyme-free target induced recycle amplification was performed to produce two different kinds of single stranded DNAs labeled with ferrocene (Fc, quencher) for the formation of G-quadruplex. Herein, based on the strong ECL signal deriving from the ternary ECL system as a "switch on" mode, and a weak ECL signal due to the co-quenching pattern of ferrocene and hemin as a "switch off" mode, an original "on-off" ECL biosensing platform was developed to ultrasensitively detect microRNA-21. Furthermore, the reversible formation and dissociation of G-quadruplex could achieve the regeneration of ECL biosensor in a rapid step with the aid of potassium ion (K+) and 18-crown-6-ether. In addition, the developed strategy exhibited a great sensitivity with a detection limit of 48 aM to pave a path for real applications of biomolecules detection in clinical diagnosis.