Three polarity-sensitive organic molecules (DIAA, DIUA, and DISA) were designed and synthesized for functionalizing high-quality superparamagnetic Fe3O4 nanoparticles (NPs) via the ligand exchange strategy to prepare polarity-sensitive Fe3O4 NPs. The functional group is chosen to be the carboxyl group (one for DIAA and DIUA, two for DISA) that is a universal coordinating site for iron oxide NPs. The method for binding these functional molecules onto the surface of the NPs is simple and straightforward. Among the three molecules, the DISA molecules passivate the NPs' surface most efficiently owing to their particular structure with two carboxyl groups and a general good solubility. The DISA-functionalized Fe3O4 NPs (DISA Fe3O4 NPs) display distinctly different fluorescence emissions in various solvents of different polarities with the magnetism well preserving. The prepared polarity-sensitive Fe3O4 NPs that are dual functional can be used as a visualized polarity sensor and perform NPs' superparamagnetic properties simultaneously. It also provides a conceptual design for preparing the polarity-sensitive nanomaterials with multifunction.