Simultaneous Single and Two-photon Excitation of Fluorescent Proteins For Multicolor Imaging of Cellular Structures

Fluorescent proteins (FPs) have been widely used to observe the distribution, structures and activities of cellular organelles in living cells. Since FPs can be selectively expressed in different organelles, we can simultaneously map different organelles in a single cell by using a combination of different FPs. However, because different FPs have different absorption spectra at visible light region, we have to use different excitation lights for each FPs, which means that different FPs have to be imaged at different times and the co-localization study of labeled organelles become less convincing. To know the complex structures of different organelles in living cells, multiple cell organelles should be observed at the same time.