Molecular recognition between nucleobases plays a crucial role in all kinds of biological processes. However, real-space investigation of the recognition capability of nucleobases in the presence of interfering compounds remains unexplored. Herein, based on the combination of scanning tunneling microscopy imaging and density functional theory modeling, we report the impact of the presence of melamine (M) on the formation and chirality of guanine (G)-tetrads on Au(111). Although M can interact with G by double hydrogen bonding, the Hoogsteen base pairing of G is not compromised, forming identical individual G-tetrads as would have happened without the presence of M. G-tetrads coexist with M on the surface not only in separate domains, but also within the mixture network of G-tetrads and M-dimers. Although the adsorption orientation of G-tetrads in the mixture network diversifies into two distinct angles, all G-tetrads in the network keep the same chirality, emphasizing the high preference of homochirality in such biochemical systems.

Theranostic nanoagents that integrate the diagnoses and therapies within a single nanomaterial are compelling in their use for highly precise and efficient antitumor treatments. Herein, polyethylene glycol (PEG)-modified cobalt sulfide nanosheets (CoS-PEG NSs) are synthesized and unitized as a powerful theranostic nanoagent for efficient photothermal conversion and multimodal imaging for the first time. We demonstrate that the obtained CoS-PEG NSs show excellent compatibility and stability in water and various physiological solutions, and can be effectively internalized by cells, but exhibit a low cytotoxicity. The CoS-PEG NSs exhibit an efficient photothermal conversion capacity, benefited from the strong near-infrared (NIR) absorption, high photothermal conversion efficiency (~33.0%), and excellent photothermal stability. Importantly, the highly effective photothermal killing effect on cancer cells after exposure to CoS-PEG NSs plus laser irradiation has been confirmed by both the standard Cell Counting Kit-8 and live-dead cell staining assays, revealing a concentration-dependent photothermal therapeutic effect. Moreover, utilizing the strong NIR absorbance together with the T2-MR contrast ability of the CoS-PEG NSs, a high-contrast triple-modal imaging, i.e., photoacoustic (PA), infrared thermal (IRT), and magnetic resonance (MR) imaging, can be achieved, suggesting a great potential for multimodal imaging to provide comprehensive cancer diagnosis. Our work introduces the first bioapplication of the CoS-PEG nanomaterial as a potential theranostic nanoplatform and may promote further rational design of CoS-based nanostructures for precise/efficient cancer diagnosis and therapy.