A Julolidine Coupled Azine-based Reversible Chromo-fluorogenic Probe for Specific Detection of Cu²⁺ Ions

Among the various essential trace elements for living organisms, the copper (Cu²⁺) ions are the most important. However, Cu²⁺ ions are vital for the human body and are associated with necessary physiological processes; insufficient or excessiveness has many hazardous effects on our bodies. In the present contribution, strategically, we have introduced a julolidine-coupled azine-based, 9,9'-((1E,1'E)-hydrazine-1,2-diylidene bis(methanylylidene)) bis(1,2,3,5,6,7-hexahydropyrido [3,2,1-ij] quinolin-8-ol) (HDBQ) reversible chromo-fluorogenic probe for specific detection of Cu²⁺ ions. Probe HDBQ exhibits observable orange colorimetric change from yellow, which is visible to the naked eye in daylight. The highly green fluorescence HDBQ becomes a non-fluorescent one with the incorporation of Cu²⁺ ions. Interestingly, the colorimetric change and non-fluorescent HDBQ-Cu²⁺ complex reverse to the original HDBQ in the presence of ethylenediamine tetraacetic acid (EDTA). The detection and quantification limit of HDBQ towards the detection of Cu²⁺ ions is found to be in the µM range, which is much lower than the limit (31.5 µM) recommended by WHO. We have also performed a colorimetric and fluorometric paper-based test strips-based experiment employing HDBQ for real-time on-site detection of Cu²⁺ ions. Using the reversibility characteristics of HDBQ for the consecutive addition of Cu²⁺ and EDTA, we have established the INHIBIT molecular logic gate. The present report brings a precise and sensitive probe for the detection of Cu²⁺ ions in real environmental and biological samples.