Selective fluorescent detection of Zn²⁺ by a rhodanine-based chemosensor

A rhodanine-based fluorescent chemosensor DHM, 3-[(E)-{[4-(diethylamino)-2- hydroxyphenyl]methylidene}amino]-2-sulfanylidene-1,3-thiazolidin-4-one, has been designed and synthesized. Sensor DHM showed unique optical properties with large fluorescence change on detecting Zn²⁺. Most cations did not disturb the binding of DHM with Zn²⁺, while Co²⁺ and Cu²⁺ displayed fluorescence quenching and Fe²⁺, Fe³⁺, and Ni²⁺ did some interference. With outcomes of Job plot and electrospray ionization (ESI)-mass data, the binding ratio of DHM to Zn²⁺ was determined as a 1:1. Moreover, DHM could detect Zn²⁺ with a low detection limit (1.33 μM). DHM could efficiently analyze Zn²⁺ in a real environment with positive recovery and relative standard deviation (RSD) and be recyclable reliably with ethylenediaminetetraacetic acid (EDTA). DHM-doped test kits can be readily used for recognizing Zn²⁺. The binding feature of DHM to Zn²⁺ was illustrated by ESI-mass, nuclear magnetic resonance (NMR) titration, and calculations.