Near‐Infrared Excitation/Emission Metal‐Free Probe with Frequency Up‐Conversion for Dual‐Modality Imaging

Abstract A multimodal fluorescent probe with near‐infrared excitation/emission, exceptional photostability, and superior biocompatibility is essential for exploring complex life science challenges and significant diseases. Carbon dots (CDs), due to their rich optical properties and favorable biocompatibility, have garnered growing interest in the field of bioimaging. Here, it is demonstrated for the first time that nitrogen‐doped CDs (N‐CDs) exhibit frequency up‐conversion luminescence (FUCL) with excitation (λ = 740–820 nm) and emission (λ = 723 nm) in the near‐infrared S(NIR) region. These N‐CDs also possess outstanding photostability, biocompatibility, and the ability to target biomolecules, such as nucleic acids. Utilizing a self‐developed optical imaging microscope, N‐CDs as probes enable multifunctional imaging, including visualization of the mitosis process and corresponding changes in chromosome diameter in onion root tip cells; dual‐modality (fluorescence intensity and lifetime) multicolor imaging of mouse kidney tissue structure; and monitoring of cortical vascular distribution and blood flow dynamics in mice.