Lactate biosensors for spectrally and spatially multiplexed fluorescence imaging

l-Lactate is increasingly appreciated as a key metabolite and signaling molecule in mammals. However, investigations of the inter- and intra-cellular dynamics of l-lactate are currently hampered by the limited selection and performance of l-lactate-specific genetically encoded biosensors. Here we now report a spectrally and functionally orthogonal pair of high-performance genetically encoded biosensors: a green fluorescent extracellular l-lactate biosensor, designated eLACCO2.1, and a red fluorescent intracellular l-lactate biosensor, designated R-iLACCO1. eLACCO2.1 exhibits excellent membrane localization and robust fluorescence response. To the best of our knowledge, R-iLACCO1 and its affinity variants exhibit larger fluorescence responses than any previously reported intracellular l-lactate biosensor. We demonstrate spectrally and spatially multiplexed imaging of l-lactate dynamics by coexpression of eLACCO2.1 and R-iLACCO1 in cultured cells, and in vivo imaging of extracellular and intracellular l-lactate dynamics in mice.