Two near-infrared fluorescent probes based on dicyanoisfluorone for rapid monitoring of Zn2+ and Pb2+

Zinc (Zn2+) and lead (Pb2+) ions in the environment have important effects on human health and environmental safety. Therefore, it is necessary to effectively detect them by a convenient and reliable analysis method. In this study, two near-infrared fluorescent probes for the fast determination of Zn2+ and Pb2+ were synthesized by a simple Schiff base reaction between the dicyanoisophorone skeleton and carbohydrazide derivatives. Among them, the probe with the thiophene-2-carbohydrazide group showed a selective fluorescence response to Zn2+ and Pb2+ with a maximum emission wavelength of 670 nm. And the detection limits of the probe for Zn2+ and Pb2+ were 1.59 nM and 1.65 nM, respectively. In contrast the probe modified by the furan-2-carbohydrazide group achieved quantitative detection of Zn2+, with a detection limit of 2.7 nM. These results were attributed to the fact that the probes bind to Zn2+ and Pb2+ in stoichiometric ratios of 1:1, blocking the intramolecular PET effect. Furthermore, these two probes can be recycled through the action of EDTA and have been successfully used to detect Zn2+ and Pb2+ in real water samples.