A Piperazine Linked Rhodamine‐BODIPY FRET‐based Fluorescent Sensor for Highly Selective Pd2+ and Biothiol Detection

A class of rhodamine‐based fluorescent sensors for the selective and sensitive detection of Pd2+ metal ions in aqueous media has been developed. A rhodamine‐based sensor PMS and a rhodamine‐BODIPY Förster resonance energy transfer (FRET)‐pair sensor PRS have been incorporated with a piperazine linker and an O−N−S−N podand ligand for specific recognition of Pd2+ ion. Both probes displayed colorimetric and fluorescent ratiometric changes when exposed to Pd2+, due to their spirolactam rings opening and restoring rhodamine conjugation. PRS is highly selective to Pd2+ over 22 other metal ions, showing a 0.6‐fold ratiometric difference at I600nm/I515nm. Additionally, the lactam ring in Pd2+ coordinated PRS‐Pd could be switched back to the closed form in the presence of various thiols, providing a “red‐green traffic light” detection mechanism between red and green emission. Furthermore, PRS showed excellent cell viability and was successfully employed to image Pd2+ and the PRS‐Pd complex ensemble could interchangeably detect biothiols including glutathione (GSH) in A549 human lung cancer cells. A piperazine linked FRET pair employing rhodamine‐BODIPY was synthesized and modified to form chemosensor PRS. PRS was capable to detect Pd2+ and GSH interchangebly with colorimetric and fluorescent ratiometric changes, rendering a “traffic light” switching between red and green emission. The cell imaging experiments in A549 cells demonstrated the feasibility for the practical cellular sensing of Pd2+ and GSH in cancerous environment.