The Eu(III) F -Transport Assay Vesicles were prepared using the same methods as those used during the HPTS assay; however, the concentrations of both NaCl (225 mM) and HEPES (0.5 mM) were changed. Also, the internal solution contained probe the previously reported Eu(III) probe (50 μM). Both the internal and external solutions were buffered to pH 7.0. The spectrophotometer was set up such that the luminescence intensity at λem = 615 nm was recorded when the Eu(III) probe was excited at an excitation wavelength of λex = 332 nm. Also, a 0.1 ms time-gate was added, producing a total acquisition time of 2 ms. The assay system was prepared by adding vesicles (0.4 mM) to quartz cuvettes containing the external solution (2.5 mL). An aqueous solution containing NaF (0.18 M), NaCl (225 mM), and HEPES (0.5 mM) was then added at t = 0 s as an ion pulse, resulting in a final NaF concentration of 3 mM. Like the HPTS assay, the vesicles were checked for leakage for 30 s before transport was initiated. At t = 30 s, the DMSO solutions of transporters at varied concentrations (5 μL) were added to the assay system to elicit transport, which was monitored over 600 s. At t = 630 s, the vesicles were lysed using Triton X-100 detergent to obtain the 100% efflux calibration value. Each transport experiment was stopped at t = 750 s, and each transport experiment performed for each tested transporter concentration was repeated twice to obtain standard errors. The data was then normalised and graphed as a function of time.