An easy way to prepare reusable rhodamine-based chemosensor for selective detection of Cu²⁺ and Hg²⁺ ions

Herein, a simple route was demonstrated for preparation of reusable spherical solid supported rhodamine-based chemosensor and its sensing ability toward metal ions were investigated. First, as solid-support material, aldehyde functional spherical crosslinked Poly (vinyl benzaldehyde-co-divinylbenzene) (P(VBA-co-DVB)) microbeads with a particle size of 2–5 μm were synthesis via precipitation polymerization. Rhodamine hydrazide was then attached to the reachable aldehyde groups (3.05 mmol/g) via imine linkages onto the microbeads. Resulting densely crosslinked almost uniform microspheres with a small particle size can be easily dispersed in any solvent and handled easily during the whole recycling process due to the crosslinked nature of the microbeads. All these features make the rhodamine tethered microspheres an ideal fluorescence chemosensor candidate for the detection of analytes in any solvent. The sensing studies against metal ions revealed that the microspheres show high selectivity and sensitivity fluorescence turn-on and colorimetric response towards Hg²⁺ and Cu²⁺ ions compare to the other competitor ions in CH₃CN: H₂O (v/v: 80/20, pH: 7.2) medium. The association constant (K_a) was determined from Benesi-Hildebrand graphics for the microsphere with Hg²⁺ and Cu²⁺. Furthermore, the detection limit of the chemosensor was calculated 3.90 × 10⁻⁷ and 5.06 × 10⁻⁷ M for Hg²⁺ and Cu²⁺, respectively. The fluorescence lifetime of the rhodamine tethered microbeads was also measured as 22.9 ns.