The high intrinsic peroxidase activity and excellent targeting ability of Trop-2-specific aptamer-linked TDN-PCN-222 (Fe) allow for the specific detection of Trop-2-positive tumor cells with a limit of detection (LOD) of 10 cells per mL, as well as the visual tracking of tumor cell Trop-2 status. Here, TACSTD2 is linked to neoplasm.