In this work, a colon-targeting near-infrared (NIR) probe (DGO) was developed to monitor peroxynitrite (ONOO-) in ulcerative colitis (UC) with fast (60 s) and low detection limits (0.04 μM). DGO could effectively distinguish human colon cancer cells (HCT116) from hepatocellular cells (HepG2) and aggregate in HCT116 cells under the mediation of glucose groups, demonstrating significant colon-targeting potential. The mice experiment further confirmed that DGO enabled real-time monitoring of ONOO- dynamics and effectively distinguished between health, pathology, and recovery status after drug (curcumin) treatment, achieving early diagnosis of UC.