Graphene quantum dots with Zn2+ and Ni2+ conjugates can cleave supercoiled DNA

Graphene quantum dots (GQDs), inheriting the superb property of graphene oxide, possess smaller lateral size and high biocompatibility, thus having potential in biomedical applications. We previously discovered that GQDs, combining with Cu²⁺ ions, could cleave DNA primarily through an oxidative pathway; yet, oxidative DNA cleavage is not practically preferred in biology. In this work, we explore the DNA cleavage ability of GQDs with Zn²⁺ and Ni²⁺. Zn²⁺ and Ni²⁺ alone are incapable of cleaving supercoiled DNA, but when combining with the GQDs, Zn²⁺ and Ni²⁺ exhibit DNA cleavage activity. However, the activity of these two systems is much lower than that of GQDs/Cu²⁺, and GQDs/Ni²⁺ is less active than GQDs/Zn²⁺. The functional mechanism of GQDs/Ni²⁺ and GQDs/Zn²⁺ is different from that of GQDs/Cu²⁺. The GQDs play a key role in the two systems; the redox inactive Zn²⁺ and Ni²⁺ ions assist to generate the oxidative species that eventually lead to the DNA cleavage. The current results together with our previous result indicate that GQDs together with metal ions can cleave supercoiled DNA, and their cleavage activities depend on the properties of metal ions: for redox active metal ions, metal ions play key roles, for redox inactive metal ions, GQDs are dominant.