Fluorescent Biosensors for Neuronal Metabolism and the Challenges of Quantitation

• Genetically encoded biosensors give quantitative readouts of key brain metabolites.• Biosensors allow investigation of the relationship between activity and metabolism.• Environmental changes (pH, temperature) can masquerade as changes in analyte. Over the past decade, genetically encoded fluorescent biosensors that report metabolic changes have become valuable tools for understanding brain metabolism. These sensors have been targeted to specific brain regions and cell types in different organisms to track multiple metabolic processes at single cell (and subcellular) resolution. Here, we review genetically encoded biosensors used to study metabolism in the brain. We particularly focus on the principles needed to use these sensors quantitatively while avoiding false inferences from variations in sensor fluorescence that arise from differences in expression level or environmental influences such as pH or temperature.