Efficient Fluorescence Resonance Energy Transfer-Based Ratiometric Fluorescent Cellular Imaging Probe for Zn2+ Using a Rhodamine Spirolactam as a Trigger

This letter described the design and synthesis of a novel fluorescein-appended rhodamine spirolactam derivative and its preliminary application as a ratiometric fluorescent cellular imaging probe for Zn2+. The ratiometric fluorescent signal change of the probe is based on an intramolecular fluorescence resonance energy transfer (FRET) mechanism modulated by a specific metal ion induced ring-opening process of the rhodamine spirolactam (acting as a trigger). In the new developed sensing system, the emission peaks of the two fluorophores are well-resolved, which can avoid the emission spectra overlap problem generally met by spectra-shift type probes and benefits for observation of fluorescence signal change at two different emission wavelengths with high resolution. It also benefits for a large range of emission ratios, thereby a high sensitivity for Zn2+detection. Under optimized experimental conditions, the probe exhibits a stable response for Zn2+ over a concentration range from 2.0 × 10−7 to 2.0 × 10−5...