BCECF is an ideal dual-excitation ratiometric pH indicator for measuring changes ± 1 pH unit around pH 7 with a pKa of ~6.98. pH measurements with BCECF are made by determining the pH-dependent ratio of emission intensity (detected at 535 nm) when the dye is excited at ~490 nm versus the emission intensity when excited at its isobestic point of ~440 nm.