Novel hybrid nanomagnets functionalized with a rhodamine derivative were prepared, and their spectroscopic behavior in the selective detection and removal of Hg²⁺ was investigated. Selective sensing of mercury ions was followed by a structural transformation of the rhodamine motif to a highly conjugated xanthene moiety, causing a ca. 5.3-fold fluorescence enhancement. Moreover, the selective detection and removal of Hg²⁺ by the hybrid nanomagnets in the presence of other metal ions were confirmed by fluorescence spectroscopy. These findings provide a promising new method for the detection and removal of Hg²⁺ from environmental pollutants.