Cellular uptake was quantified in three cell lines by live-cell flow cytometry. The fold-increase in fluorescence at 42 °C, as compared to 37 °C, was measured for HeLa cervical cancer cells, MCF7 breast cancer cells, and primary HUVECs. All cell lines demonstrated the effect of Arg density modulation by temperature-triggered micelle assembly in controlling cellular uptake, as the fold-increase in cellular fluorescence of Arg5-ELPBC was significantly greater than ELPBC or Arg5-ELP controls within each cell line. Data represents the average of 3 experiments ± SEM.