Rhodamine-Appended Benzophenone Probe for Trace Quantity Detection of Pd2+ in Living Cells

Designing a fluorogenic probe for the determination of Pd2+ is a challenging analytical task. Pd2+ is a potentially toxic and harmful substance even at a very low level of contamination in the end product. Herein, a promising spirolactam-functionalized chemosensor, rhodamine-appended benzophenone (HBR), is designed and characterized by spectroscopic (1H NMR, 13C NMR, ESI-MS, and FT-IR) data along with the single-crystal X-ray diffraction technique. It acts as a highly sensitive and selective fluorogenic chemosensor for Pd2+ ions over other environmentally relevant cations in aqueous ethanol (1:1, v/v) at pH 7.4. The limit of detection (LOD) is 34 nM that is far below the WHO recommended Pd uptake (47 μM). The plausible mechanism involves the specific binding of HBR with Pd2+ and the formation of 1:1 stoichiometry of the complex, which has been supported by ESI-MS, FT-IR data, Job plot, and association constant data (Benesi–Hildebrand plot). The computation study has been attempted to explain the ring cleavage fluorescence enhancement scheme of HBR upon binding with Pd2+. Furthermore, this “turn-on” probe has successfully applied to image the Pd2+ ion in cultured MDA-MB-231 cells.