A highly selective 2-hydroxybenzhydrazone based dual sensor for Cu2+and Fe2+ions: Spectroscopic, computational, cell imaging studies and logic gate construction

2-Hydroxybenzhydrazone based probe HNN demonstrated highly selective sensing ability towards Cu2+ and Fe2+ ion through colorimetric and fluorimetric methods respectively. The probe can be used as a "naked-eye" sensor based on its color change from almost colorless to bright yellow (for Cu2+) and pale yellow (for Fe2+). The colorimetric detection of Cu2+ involved enhancement in internal charge transfer (ICT). In the detection of Fe2+ through fluorescence, combined effect of restricted photo-induced electron transfer (PET) and paramagnetic nature of Fe2+ played major role. Job's plots based on absorption (Cu2+) and fluorescence (Fe2+) data along with mass spectral studies indicated 1:1 stoichiometry of metal to HNN in the complex. The binding of the probe HNN with both the metal ions was found chemically reversible by adding EDTA. Experimental observations on binding of the probe with metal ions were corroborated with density functional theory (DFT). The effect of pH and response time in sensing was also determined. The probe was found useful for in vivo detection and imaging of Fe2+ in MDA-MB-231 cells. Paper strips of the probe were made and used for naked-eye detection of Cu2+. The probe was also used in the construction of logic gate for detection of Cu2+and Fe2+.