on the hypsochromic shift of the absorption and emission
spectra of OBO; as such, it can function as a sensitive and
selective Ca2+ probe. The major attribute is that OBO and the
OBO−Ca2+ complex possess two different strong emission
bands in the visible region under one single visible light
excitation. This means that ratiometric emission measurement
of Ca2+ is possible with negligible background fluorescence
interference. The developed Ca2+ probe has been successfully
applied to monitor the transient changes of [Ca2+]i in living
cells by a confocal laser scanning microscope (CLSM). The
most important merits of this probe are its good watersolubility,
nontoxicity, strong emissions, and visible light
excitation