Dual anion colorimetric and fluorometric sensing of arsenite and cyanide ions

Abstract

A naphthalene appended probe, 2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine carbothioamide, was synthesized and found to recognize AsO₂⁻ and CN⁻ ions with turn-on emission fluorescence over different anions in a DMF : H₂O (HEPES buffer, pH = 7.2) (9 : 1, v/v solution) medium. The probe was characterized using different techniques including NMR, IR, CHNS, UV-visible and ESI mass spectroscopy. This probe shows colorimetric change and an enhancement in the fluorescence emission with arsenite and cyanide ions among the other anions. The 1 : 1 and 1 : 2 stoichiometries of the probe with arsenite and cyanide ions, respectively, were calculated from the Job's plots based on the UV-visible spectra. The binding constant was established using the B–H (Benesi–Hildebrand) plots for both anions arsenite and cyanide as 3.1 × 10⁵ and 1.9 × 10⁶, respectively. The limit of detection (LOD) of arsenite and cyanide ions was 66 nM and 77 nM, respectively, using the emission spectra. The binding affinity of probe L with both anions was determined using NMR, DFT optimization, ESI-mass spectroscopy, electrochemical behavior and optical studies. The probe is the first chemical sensor that detects both major toxic anions with significantly high detection limits.