By the end of the project, we expect to have a collection of FASTs covering the entire visible spectrum in terms of emission wavelength, using fluorogens with different cell-uptake ability for selective intracellular or extracellular labeling. The second part of the project focuses on the design of: (i) biosensors for imaging various analytes, including neurotransmitters, ions, second messengers and endogenous proteins, (ii) biosensors for detecting key metabolites in biological samples for diagnostic applications, and (iii) the creation of probes for the live-cell observation of specific RNA molecules and genomic DNA loci in living cells. In a last part of the project not yet started, we will focus on the design of signal integrators for cell circuit mapping. The identification of circuits of active cells is essential in understanding complex behaviors. To do so, we propose to design genetically encoded molecular tools acting as integrators to permanently label transiently activated cells for post hoc analysis of the entire system. Our signal integrators will be composed of a genetically encoded sensing unit that can convert genetically encoded non-fluorescent precursors into a fluorescent species in presence of a given signal, but is otherwise inactive in its absence. Repetitive activation of a given subset of cells will thus lead to specific accumulation of fluorophores in activated cells. This fluorophore accumulation will lead to signal amplification and thus high contrast, facilitating post hoc detection of active cell circuits.