Selective fluorescence detection of Cu2+ in aqueous solution and living cells

A rhodamine B semicarbazide 3 was synthesized by the reaction of rhodamine B acid chloride 2 with hydrazine carboxamide hydrochloride under reflux with triethyl amine in acetonitrile. It was used as selective fluorescent and colorimetric sensor for visual detection of Cu2+ over competitive ions (Fe3+,Fe2+, Cr3+, Cd2+, Pb2+, Zn2+, Hg2+, Co2+, Ni2+, Ca2+, Mg2+, Ag2+, Mn2+, Sr2+, Cs2+, Na+, K+, Li+) in aqueous methanol (1:1, v/v), exhibiting a fast response time, less than few second and a detection limit of 1.6×10−7 mol/L at neutral pH. The proposed sensing system can be successfully applicable for determination of Cu2+ in waste water samples showing turn on fluorescence response and for further monitoring of intracellular Cu2+ levels in living cells with high sensitivity and selectivity at micro molar level concentrations using confocal fluorescence spectroscopy. The synthesis of probe 3 was confirmed by 1H NMR, 13C NMR and mass spectrometric analysis. -- Highlights: • New chemosensor rhodamine B semicarbazide 3 was synthesized. • Addition of Cu+2 ion into aqueous solution of probe 3 gave visual color changes as well as fluorescent off/on observations. • The proposed spirolactam ring opening mechanism of the synthesized probe triggered by copper ion was revealed by using mass spectrum. • High selectivity and sensitivity of probe 3 towards Cu+2 are excellent enough to detect micromolar level of Cu+2 ion even in aqueous media and living cells