Scientists have developed engineered fluorescent nanobodies, tiny proteins that glow, capable of labeling multiple cellular proteins simultaneously in living cells. The breakthrough allows researchers to observe real-time protein interactions and dynamics inside intact cells, a significant advance over previous methods that required cells to be killed and fixed. These nanobodies can assign different colors to different proteins, creating a sort of molecular traffic map. The technology could accelerate drug discovery and deepen our understanding of how diseases develop at the cellular level.