We designed Calcium Rubies, a family of functionalizable BAPTA-based red-fluorescent
calcium (Ca2+) indicators as new tools for biological Ca2+ imaging. The specificity of this
Ca2+-indicator family is its side arm, attached on the ethylene glycol bridge that allows
coupling the indicator to various groups while leaving open the possibility of aromatic
substitutions on the BAPTA core for tuning the Ca2+-binding affinity. Using this possibility we
now synthesize and characterize three different CaRubies with affinities between 3 and 22 …