Measurement of intracellular pH in Schizosaccharomyces pombe using
a pH sensing ratiometric GFP, phlourin. Phluorin was expressed in the
cell and aliquots permeabilized in buffers at various pHs. The emission at
512 nm was then captured following two separate excitations, 420 nm
and 460 nm. The ratio of emission intensities was plotted against pH to form
a standard curve. On the right the two emissions are shown as false colour
images, separately blue and green, and then combined to create the images.

Karagiannis and Young, 2001. J. Cell Sci. 114, 2929.