An azine based sensor for selective detection of Cu2+ ions and its copper complex for sensing of phosphate ions in physiological conditions and in living cells

Abstract

A simple and cost effective unsymmetrical azine based Schiff base, 5-diethylamino-2-[(2-hydroxy-benzylidene)hydrazonomethyl]-phenol (1) was synthesized which selectively detect Cu²⁺ ions in the presence of other competitive ions through "naked eye" in physiological conditions (EtOH-buffer (1:1, v/v, HEPES 10mM, pH=7.4)). The presence of Cu²⁺ induce color change from light yellow green to yellow with the appearance of a new band at 450nm in UV-Vis spectra of Schiff base 1. The fluorescence of Schiff base 1 (10μM) was quenched completely in the presence of 2.7 equiv. of Cu²⁺ ions. Sub-micromolar limit of detection (LOD=3.4×10^-7M), efficient Stern-Volmer quenching constant (K_SV=1.8×10⁵Lmol^-1) and strong binding constant (log K_b=5.92) has been determined with the help of fluorescence titration profile. Further, 1-Cu²⁺ complex was employed for the detection of phosphate ions (PO₄^3-, HPO₄^2- and H₂PO₄^-) at micromolar concentrations in EtOH-buffer of pH7.4 based on fluorescence recovery due to the binding of Cu²⁺ with phosphate ions. Solubility at low concentration in aqueous medium, longer excitation (406nm) and emission wavelength (537nm), and biocompatibility of Schiff base 1 formulates its use in live cell imaging.

Keywords: Copper; Fluorescence; Live cell imaging; Phosphorus; Schiff base; UV–Vis.