A New Eosin Y and Hydroxybenzaldehyde Coupled Probe for Instantaneous Sensing of Cu²⁺ by Colorimetric and ‘Turn‐off’ Fluorescence Methods

Abstract Xanthene‐based organic chemosensors for detecting metal ions are a topic of research. While Rhodamine and Fluorescein‐based sensors are more common, fewer research articles exist on Eosin‐based sensors. Herein, a new chemosensor ( EY‐S ) is reported that was obtained efficiently in two high‐yielding reaction steps from commercially procured Eosin Y. EY‐S is a fluorescent molecule that can selectively detect cupric (Cu 2+ ) ions in the presence of other competing metal ions. The colorimetric sensing of Cu 2+ ions was studied using uv‐vis spectroscopy. The green fluorescence of EY‐S was effectively quenched by Cu 2+ and quantified by fluorescence titration. A high magnitude of the Stern‐Volmer ( K sv ) constant advocated efficient quenching. Job's plot confirmed a 1 : 1 complexation ratio between EY − S and Cu 2+ . The association constant ( K a ) for the host‐guest complexation was determined to be 1.59×10 5 M −1 . The limit of detection (LOD) associated with the detection of Cu 2+ was 3.29 nM, indicating the high sensitivity of the EY − S sensor. Cu 2+ detection was also tested using actual water samples collected from various sources, and EY−S′ performance remained uncompromised. The sensor could detect Cu 2+ in acidic, neutral, and essential media, with the sensing being most efficient at higher pH. The EY‐S sensor/probe could be easily recycled multiple times without significantly declining Cu 2+ detection performance. A mechanism of binding between EY‐S and Cu 2+ was also proposed.