A “turn-on” fluorescent copper biosensor based on DNA cleavage-dependent graphene-quenched DNAzyme

A novel and promising “turn-on” fluorescent Cu2+ biosensor is designed based on graphene–DNAzyme catalytic beacon. Due to the essential surface and quenching properties of two-dimensional graphene, it can function as both “scaffold” and “quencher” of the Cu2+-dependent DNAzyme, facilitating the formation of self-assembled graphene-quenched DNAzyme complex. However, Cu2+-induced catalytic reaction disturbs the graphene–DNAzyme conformation, which will produce internal DNA cleavage-dependent effect. In this case, the quenched fluorescence in graphene–DNAzyme is quickly recovered to a large extent in 15 min. Compared with common DNAzyme-based sensors, the presented graphene-based catalytic beacon greatly improves the signal-to-background ratio, hence increasing the sensitivity (LOD = 0.365 nM). Furthermore, the controllable DNA cleavage reaction provides an original and alternative internal method to regulate the interaction between graphene and DNA relative to the previous external sequence-specific hybridization-dependent regulation, which will open new opportunities for nucleic studies and sensing applications in the future.