A flow cytometry assay for the glucose transporter SLC2A3/GLUT3 was developed with a genetically-encoded biosensor for measuring free glucose, FLII12Pglu-700uDelta6 (Addgene #17866). This biosensor consists of the E. Coli glucose/galactose-binding protein MglB sandwiched between ECFP and Citrine-YFP. An increase in glucose concentration (dynamic range 0.05 - 11 mM) results in an increased FRET efficiency that can be observed by an increase in Citrine acceptor emission and a decrease in ECFP donor emission.