Fluorescence lifetime imaging of sDarken as a tool for the evaluation of serotonin levels

Recent advances in the development of genetically encoded biosensors have resulted in a variety of different neurotransmitter sensors for the precise measurement of the dynamics of neurotransmitters, neuromodulators, peptides and hormones in real time. However, intensity-based measurements of fluorescent biosensors are limited by their dependence on the expression level of the sensor, the intensity of the excitation light, and photobleaching overtime. Here, we show that the FLIM of sDarken (a GPCR-based genetically encoded sensor for serotonin) decreases with increasing serotonin concentrations. Different members of the sDarken family, with different affinities for serotonin, show concentration-dependent changes in fluorescence lifetime according to their dynamic range. We believe that this feature of sDarken is a value-adding complement to intensity-based information and may lead to a better understanding of serotonin dynamics in health and disease.