Simple hydrazide-based fluorescent sensors for highly sensitive and selective optical signaling of Cu2+ and Hg2+ in aqueous solution

Two new water-soluble hydrazide-based fluorescent probes of poly 3-{[1-(2-hydrazino-2-oxoethyl)piperidin-4-ylidene]methyl}thiophene hydrochloride (PM1·HCl) and poly 3-{[1-(3-hydrazino-3-oxopropyl)piperidin-4-ylidene]methyl}thiophene hydrochloride (PM2·HCl) have been designed and synthesized. PM1·HCl selectively recognizes Cu2+ and Hg2+ in aqueous solution with different emission characteristics (blue-shifted for Cu2+ and red-shifted for Hg2+) and color changes, and the color response of the sensory materials can be tuned for detection with the naked eye. Detection limits of sensor PM1·HCl for Cu2+ and Hg2+ were estimated to be 2.0 × 10−10 M and 2.0 × 10−9 M, respectively. Fluorescence sensor PM2·HCl also showed high sensitivity toward Cu2+ in aqueous media, and the detection limit was measured to be as low as 2.0 × 10−10 M. Upon addition of Hg2+ to the PM2·HCl aqueous solution, no significant changes of the fluorescence spectra were observed.