Rhodamine-Ferrocene Conjugate Chemosensor for Selectively Sensing Copper(II) with Multisignals: Chromaticity, Fluorescence, and Electrochemistry and Its Application in Living Cell Imaging

A ferrocene unit is introduced into the salicylaldehyde Rhodamine 6G hydrazone with an alkynyl group to constitute a new chemosensor, R6G-FC, for specifically sensing Cu²⁺ over other metal ions with multisignals. Upon interaction with Cu²⁺ in aqueous solution, R6G-FC expresses a detectable fluorescence enhancement along with changes in UV-vis absorption spectra and electrochemical parameters due to the binding-induced spirolactam ring-opening process in Rhodamine 6G. The complexation process between R6G-FC and Cu²⁺ can be carried out within a wide pH range in a short response time and with a good reversibility. R6G-FC also exhibits an excellent performance in sensing Cu²⁺ in the "dip-stick" method with an evident color gradation, and confocal fluorescence microscopy imaging results reveal that R6G-FC can be used to visualize Cu²⁺ in living HeLa cells with low cytotoxicity.