Highly selective and sensitive fluorometric probe for Cd2+ ions based on 4-(quinolin-2-ylmethylene)aminoanisole Schiff base

Herein, we report a reversible and easy assembled fluorometric probe (4-(quinolin-2-ylmethylene)aminoanisole, QMAA) for the highly selective and sensitive detection of cadmium ion (Cd2+) in DMF solution with PBS buffer (0.01 M, pH = 7.30). The strong fluorescence response of QMAA to Cd2+ along with a bright blue fluorescence was mainly ascribed to the formation of the complex QMAA-CdCl2. The results show that the complexation can inhibit the C=N isomerisation and photo-induced electron transfer (PET), and further lead to the occurrence of chelation fluorescence enhancement. The 1:1 stoichiometry of the complex between QMAA and cadmium ion was studied by fluorescence titration, Job's plot analysis, H-1 NMR, FT-IR, and ESI-MS data, and was further confirmed by the single crystal structure of the complex QMAA-CdCl2. Density functional theory (DFT) calculations have verified the mechanism of fluorescence enhancement. In addition, the limit of detection of QMAA for Cd2+ was as low as 0.1547 mu M (at 10(-7) M level), which was lower than the acceptable limit of Cd2+ level in drinking water defined by World Health Organization. The analog experiments about nature contamination of Cd2+ in real samples were finished.

Automated summary

A reversible and easily assembled fluorometric probe QMAA was developed for the selective and sensitive detection of cadmium ion in DMF solution with PBS buffer. The strong fluorescence response of QMAA to Cd2+ was attributed to the formation of the QMAA-CdCl2 complex, inhibiting C=N isomerisation and PET. The detection limit of QMAA for Cd2+ was lower than the WHO-defined acceptable limit in drinking water.