Fluorescent, calcium-binding probe compounds having visible-light excitation and emission wavelengths, and a method of usage for these probe compounds in making wavelength-ratiometric or intensity-ratiometric measurements of calcium ion concentration in samples. The probe compounds generally relate to...http://www.google.com/patents/US5409835?utm_source=gb-gplus-sharePatent US5409835 - Long-wavelength fluorescent probe compounds for calcium ions and their use in ratiometrically measuring calcium ion concentrations
