Selective Recognition and Reversible “Turn-Off” Fluorescence Sensing of Acetate (CH₃COO⁻) Anion at Ppb Level Using a Simple Quinizarin Fluorescent Dye

A simple and cost-effective optical sensing system based on quinizarin fluorescent dye (QZ) for the selective and reversible sensing of CH3COO− anions is reported. The anion binding affinity of QZ towards different anions was monitored using electronic absorption and fluorescence emission titration studies in DMSO. The UV-visible absorption spectrum of QZ showed a decrease in the intensity of the characteristic absorption peaks at λ = 280, 323, and 475 nm, while a new peak appeared at λ = 586 nm after the addition of CH3COO− anions. Similarly, the initial strong emission intensity of QZ was attenuated following titration with CH3COO− anions. Notably, similar titration using other anions, such as F−, Cl−, I−, NO3−, NO2−, and H2PO4-, caused no observable changes in both absorption and emission spectra. The selective sensing of CH3COO− anions was also reflected by a sharp visual color change from bright green to faint green under room light. Further, the binding was found to be reversible, and this makes QZ a potential optical and colorimetric sensor for selective, reversible, and ppb-level detection of CH3COO− anions in a DMSO medium

‘Turn-on’ fluorescence sensing of Al(III) ions in water using a simple N-hydroxy-4-amino-1,8-naphthalimide chemosensor

A simple fluorophore, N-hydroxy-4-amino-1,8-naphthalimide (Nap-OH), has been designed and used as a fluorescent “turn-on” chemosensor for sensing metal cations in water. Nap-OH exhibited solvent-dependent photophysics in different solvents and displayed high selectivity and reversible sensing ability for Al(III) ions with femtomolar (10−15 M) sensitivity. The initial emission intensity of Nap-OH was drastically enhanced upon the addition of Al(III) ions and the calculated Stern-Volmer binding constant (KSV) is 4.70 × 104 M−1. The selective sensing of Al(III) was also reflected by sharp visual color changes and further demonstrated the use of Nap-OH for sensing Al(III) in real-water samples