Substituent-dependent fluorescent sensors for zinc ions based on carboxamidoquinoline

A series of carboxamidoquinoline-based fluorescent sensors (the AQZ family) were synthesized and characterized. The AQZ family members were highly soluble in water and showed good selectivity for Zn²⁺via enhanced fluorescence in aqueous buffer solution. Fluorescence signals could be tuned from dual-wavelength ratiometric changes to changes in the intensity of a single wavelength upon binding Zn²⁺ through the introduction of different substituents onto the quinoline ring. Concentrations of free Zn²⁺ of 10^-5-10^-6 M could be detected using the sensors. Changes of substituents and their positions on the quinoline ring influenced the sensitivity for Zn²⁺, but had little effect on Zn²⁺ affinities.