pH-Lemon – GPI can be found within the vesicles of the secretory pathway and on the cell surface. The construct can be used to image pH variations within vesicles and on the outer side of the plasma membrane.The pKa of the probes is appr. 6.7. CFP should be excited at 430 nm and emission can be collected at 480 nm and 535 nm (FRET channel). Alternatively, the pH sensitive YFP can be excited directly using 480 nm illumination light.