A turn-on fluorescent sensor for Zn(II) based on fluorescein-coumarin conjugate

• A novel fluorescein-coumarin conjugate Schiff-base has been synthesized.
• The compound exhibits high sensitivity and selectivity for Zn2+.
• The Schiff-base ligand can be synthesized easily.

A novel fluorescent sensor, 7-hydroxy-4-methylcoumarin-8-carbaldehyde-(fluorescein) hydrazone was designed and synthesized for selective recognition of Zn2+ in HEPES buffer medium of PH 7.4. This reagent could be used as a probe for Zn2+ by monitoring changes in the absorption and the fluorescence spectral patterns. More importantly, this sensor displays an extreme selectivity, sensitivity and color change for Zn2+ over other earth- and transition metal ions, which was mainly due to the spirolactam ring-opening power of Zn2+. Upon the addition of Zn2+, an overall emission change of 33-fold was observed and the detection limit was low as 6.54 ppb. Photoinduced electron transfer process, coupled with the intramolecular charge transfer process, are proposed to explain the observed spectral response.