Mn²⁺-Assisted DNA Oligonucleotide Adsorption on Ti₂C MXene Nanosheets

As a new type of 2D nanomaterial, MXene (transition metal carbide/nitride) nanosheets are already widely used in catalysis, sensing, and energy research. DNA is a popular sensing molecule. Compared to other 2D materials such as graphene oxide, MoS₂, and WS₂, few fundamental studies were carried out on DNA adsorption by MXene. Due to its exfoliation and delamination process, the surface of MXene is abundant in -F, -OH, and -O- groups, rendering the surface negatively charged and repelling DNA. In previous studies, surface modification of MXene was performed to promote DNA adsorption. Herein, Mn²⁺ was discovered to promote DNA adsorption on unmodified Ti₂C MXene. Different from Ca²⁺ and Mg²⁺, Mn²⁺ can inverse the ζ-potential of the Ti₂C MXene to positive. DNA mainly uses its phosphate backbone for adsorption, while its bases contribute significantly less. In addition, delayed DNA desorption was observed through the addition of inorganic phosphate due to the formation of manganese phosphate to gradually extract Mn²⁺ from the DNA/MXene complex. Finally, DNA-induced DNA desorption from the Ti₂C MXene can hardly distinguish the complementary DNA from a random DNA, which is very different from that for graphene oxide. This difference is likely due to the distinct surface chemistry between the MXene and graphene oxide.