A xanthene-based colorimetric sensor, 2-((5-chloro-2-oxoindolin-3-ylidene)amino)-
3',6'-bis(diethylamino)spiro[isoindoline-1,9'-xanthen]-3-one, was designed and its metal sensing
properties was evaluated in aqueous solutions. The sensor showed colorimetric response toward
Hg2+ from colorless solution to pink among various metal ions such as Na+
, Mg2+, Ca2+, Mn2+
Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Al3+, Cd2+ and Pb2+. The addition of Hg2+ exhibits an absorption
enhancement of the sensor based on a spirocycle ring-opening process and a subsequent
hydrolysis reaction. The detection limit of the sensor for Hg2+ was found to be 7.88×10−8 M.