A Julolidine Coupled Azine-based Reversible Chromo-fluorogenic Probe for Specific Detection of Cu 2+  Ions

Among the various essential trace elements for living organisms, the copper (Cu ) ions are the most important. However, Cu 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 Cu 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 Cu ions. Interestingly, the colorimetric change and non-fluorescent HDBQ-Cu 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 Cu 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 Cu ions. Using the reversibility characteristics of HDBQ for the consecutive addition of Cu and EDTA, we have established the INHIBIT molecular logic gate. The present report brings a precise and sensitive probe for the detection of Cu ions in real environmental and biological samples.