Disclosed is a conjugated polymer-based nanoprobe, including a fluorescent conjugated polymer, a surface ligand, a target molecule, a near-infrared fluorescent dye and optionally a gadolinium-containing magnetic resonance contrast agent. This application also discloses a method for preparing the conjugated polymer-based nanoprobe, including: adding raw materials to an organic solvent followed by ultrasonication to obtain a mixture； and adding the mixture to ultrapure water and continuously ultrasonicating the reaction mixture. The conjugated polymer-based nanoprobe can be applied in a combined molecular imaging technique of near infrared fluorescence imaging, photoacoustic imaging and magnetic resonance imaging to effectively recognize metastatic lymph nodes and normal lymph nodes, and it can be retained in the metastatic lymph nodes for a long time, meeting the requirements for long-term observation. Moreover, the near-infrared fluorescent conjugated polymer-based nanoprobe can generate reactive oxygen under irradiation, which is suitable for the photodynamic treatment of tumors.
