pH-Lemon targeted to the cytosol. The construct can be used to image cytosolic acidifications in a dynamic manner. 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.