Rhodamine derivative-modified filter papers for colorimetric and fluorescent detection of Hg2+ in aqueous media

Mercury pollution is a widespread problem. In this work, a solid-state sensor based on rhodamine derivative-modified cellulose filter papers for detection of Hg2+ ions in aqueous media is demonstrated. A three-step approach, involving the introduction of atom transfer radical polymerization (ATRP) initiating sites, surface-initiated ATRP (SI-ATRP) of pentafluorophenyl methacrylate, and post-functionalization of the reactive surface with amino-containing spirolactam rhodamine derivatives in ester–amine reaction, was developed for the covalent immobilization of mercury-responsive probes on the cellulose filter paper. This solid-state sensor exhibits highly selective recognition of Hg2+ ions in a Tris–HNO3 buffer solution (pH = 7.24) over various environmentally relevant metal ions with remarkably enhanced fluorescent emission intensity and distinct color change from colorless to pink. The response of a rhodamine derivative-modified cellulose filter paper to Hg2+ ions is fast (<2 min). The positive fluorescence response and color change of this functionalized filter paper thus provide a disposable solid-state sensor for fluorescent and "naked-eye" detection of Hg2+ ions.