Accumulation of intracellular maltose detected with FLIPmal sensors. (A) Cytosolic maltose accumulation measured in 30-second intervals after injection of buffer or 50 mM maltose to microtiter plate wells containing Escherichia coli BL21-Gold(DE3) cells expressing FLIPmal-40μΔ1-enhanced yellow fluorescent protein. The arrow indicates the time point of maltose addition using the injector of the Tecan Infinite M200 fluorimeter (note, in contrast to Figure 3A, this procedure allows the determination of rates). (B) Dose-response curve for maltose detected by FLIPmal-40μΔ-enhanced yellow fluorescent protein in E. coli BL21-Gold(DE3) cells. Intracellular maltose levels are around 700-fold lower compared with the external concentration (K0.5 = 7.4 mM). Error bars represent the standard deviation (n = 3).