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 (Cu²⁺) ions in the presence of other competing metal ions. The colorimetric sensing of Cu²⁺ ions was studied using uv-vis spectroscopy. The green fluorescence of EY-S was effectively quenched by Cu²⁺ 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 Cu²⁺. The association constant (K_a) for the host-guest complexation was determined to be 1.59×10⁵ M⁻¹. The limit of detection (LOD) associated with the detection of Cu²⁺ was 3.29 nM, indicating the high sensitivity of the EY−S sensor. Cu²⁺ detection was also tested using actual water samples collected from various sources, and EY−S′ performance remained uncompromised. The sensor could detect Cu²⁺ 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 Cu²⁺ detection performance. A mechanism of binding between EY-S and Cu²⁺ was also proposed.