A Novel Fluorescent Probe Based on Schiff Base for Dual Sensing of Zn2+ and CN-

A novel Schiff base probe 4'-hydroxy. 3'-((2-pyridin-2-ylmethylimino)methyl)-4-biphenyl carbonitrile (HPBC) for dual sensing of Zn2+ and CN- was synthesized and characterized by various techniques such as UV-Vis, fluorescence, HRMS and NMR spectroscopy. HPBC was highly selective toward these two ions with different fluorescence signals in two different media. In EtOH. H2O (2:3, V/V; HEPES, pH 7.4), HPBC selectively bound Zn2+ to form a 1.1 ligand/metal complex. Addition of Zn2+ to the solution of HPBC resulted in a blue shift (Delta lambda = 15 nm) with a pronounced fluorescence enhancement at 468 nm, while there was no enhancement in the presence of other metal ions, especially Cd2+. HPBC displayed an "ON-OFF-ON-mode fluorescence change with alternative addition of Zn2+ and EDTA. Hence, HPBC is a reversible and reusable sensor for Zn2+. The dynamic range of the assay is linear up to 4.0 mu mol/L Zn2+ ion and the limit of detection was 36.5 nmol/L, which was thousand fold lower than the WHO guideline (about 76 mu mol/L) for drinking water. The fluorescence response of HPBC toward Zn2+ was pH-dependent, and the maximal signal was observed at near neutral pH values, which makes it suitable for application in physiological conditions. Cell imaging studies demonstrate that this sensor is capable of sensing Zn2+ in living cells. In DMSO-H2O (3.7, V/V) medium, addition of cyanide ion to HPBC led to deprotonation of the phenol hydrogen, resulting in a color change from colorless to pale yellow and a significant fluorescence enhancement at 510 nm. The probe exhibited high selectivity and sensitivity for CN- ion and the detection limit was 5.75. 10(-7) mol/L. Finally, the use of a test strip of probe HPBC to detect cyanide was reported.