A cyanine‐based dual‐modal probe for fluorimetric detection of mercury ion and colorimetric sensing of pH

Abstract A fluorescent probe derived from cyanine‐rhodanine conjugate was developed for dual detection of mercury (Hg 2+ ) ion and pH. Addition of Hg 2+ ion to the weakly fluorescent probe solution in dimethyl sulphoxide/water (DMSO/H 2 O, 7:3, v/v ) induced discernible colour change and fluorescence enhancement while other metal cations including Li + , Na + , K + , Ag + , Cu 2+ , Fe 2+ , Zn 2+ , Co 2+ , Ni 2+ , Mn 2+ , Sr 2+ , Ca 2+ , Mg 2+ , Al 3+ , Cr 3+ and Fe 3+ did not cause obvious change in colour and fluorescence emission. The detection limit of the probe toward Hg 2+ ion is 1.61 × 10 −7 M. The probe also exhibited remarkable pH‐responsive effect. It acts as a dual chromogenic and spectroscopic probe for determining different pH scales over a wide range of pH 1.0–14.0: bright yellow with maximum wavelength ( λ max ) 416 nm for pH 1.0–2.0, orange with λ max 470 nm for pH 3.0–9.0, and pale yellow with λ max below 400 nm for pH 10.0–14.0. Plausible sensing mechanisms of the probe toward Hg 2+ ion and pH have been proposed.