Using the model, we investigated how step 2, i.e., the activation in the sender phase and its diffusion to the chloroform phase, is involved in transport efficiency. We found minimizing the length of the aqueous sender phase is crucial. As the sender length increases, the distance activated molecules must diffuse can exceed their lifetime, 𝑡, defined as the time needed for 1/e molecules to decay. In other words, only a small fraction of the volume close to the chloroform interface on the sender phase can contribute to the transport. This volume is on the order of √𝐷𝑡 ≈ 1 mm. In the region farther away than 1 mm, the concentration of activated sender molecules is homogeneous, which means that molecules are activated and deactivated but not transported to the receiver phase (see Supporting Notes and Fig. ). We reduced the sender length from 25.4 mm to 3.5 mm in our experiments. This reduction increased the efficiency by 10-fold to 2.5 ± 0.01%, in line with the model (Fig. , Fig. ). Thus, only 40 molecules of fuel are needed to transport one Cbz-D molecule to the receiver. Moreover, the model showed a further decrease in the sender phase length, increasing efficiency. While this was experimentally not feasible, it offers an optimistic prospect for future miniaturization, such as using microfluidics or phospholipid membranes.