Single-chromophore-based photoswitchable nanoparticles enable dual-alternating-color fluorescence for unambiguous live cell imaging

A class of spiropyran dyes is developed and their fluorescence colors are reversibly photoswitched from red to green, blue, or nearly dark, thus alternating between two colors. These optically switchable dual-color nanoparticles have undergone endocytosis and have identified themselves from fluorescence interference including autofluorescence, thus enabling a new tool for live cell imaging.