A rapid selective colorimetric and On-Off fluorimetric sensor for detecting Cu²⁺ ions in aqueous media based on a simple bis-schiff-base derivative

A simple colorimetric and fluorimetric On-Off sensor L (3,3'-dimethyl -[1,1'-biphenyl]-4,4'-diyl)bis(azanylylidene)bis(methanylylidene)bis(naphthalen-2-ol) for Cu²⁺ ions bearing o-tolidine substituents has been designed and synthesised, and exhibits significant fluorimetric and colorimetric response for Cu²⁺ in DMSO/H₂O (8:2, v/v) HEPES buffer (pH 7.2) solution. The detection limit of the sensor towards Cu²⁺ is 7.25 × 10^{- 8} M and the association constant K_a of 9.86 × 10⁴ M^{- 1} was determined. Furthermore, other anions, including Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺ and Mg²⁺ have almost no influence on the probe's behaviour. Test strips based on the sensor L were fabricated, which could act as convenient and efficient Cu²⁺ test kits.