Aminopyridine‐Vanillin Schiff Base as a Turn On Fluorescent Sensor for Highly Selective Zn (II) Metal Detection

In this study, we report the development of a Schiff base ligand, aminopyridine with vanillin (APySB-V) for detection of Zn (II) metal ions. The probe, initially non-fluorescent, exhibits a significant fluorescence "off-on" response at 560 nm upon binding to Zn (II) ions. This fluorescence enhancement is induced by a combination of excited-state intramolecular proton transfer (ESIPT) inhibition and chelation-enhanced fluorescence (CHEF) effects. The APySB-V probe exhibits exceptional selectivity for Zn (II) ions compared to other competing metal ions and achieves a detection limit as low as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:mrow><mml:mn>1.21</mml:mn> <mml:mo>×</mml:mo> <mml:msup><mml:mn>10</mml:mn> <mml:mrow><mml:mo>-</mml:mo> <mml:mn>7</mml:mn></mml:mrow> </mml:msup> <mml:mspace></mml:mspace> <mml:mi>M</mml:mi> <mml:mo>.</mml:mo></mml:mrow> <mml:annotation>$$ 1.21\times {10}^{-7}\ \mathrm{M}. $$</mml:annotation></mml:semantics> </mml:math> Furthermore, density functional theory (DFT) calculations were employed to illuminate the electronic structure of APySB-V and understand the underlying sensing mechanism. The practical applicability of the probe was enhanced through the development of test paper strips allowing rapid, on-site detection of metal ions in environmental samples. In addition, the high sensitivity and selectivity of APySB-V towards Zn (II) suggests its potential utility in bioimaging applications for tracking zinc ions in living cells. The fast response time and strong fluorescence enhancement of the probe establish its suitability for real-time monitoring of Zn (II) contamination in industrial and environmental monitoring.