FITC images of hydrodynamic focusing (HDF) for ratios of focusing droplet volume to sample droplet volume. Drops of deionized water were applied to the focusing inlet, and a solution of fluorescein in deionized water was loaded into the sample inlet. The focusing drop fed the outer two side channels simultaneously, while the sample drop fed the central channel. Due to channel design, the fluidic resistance is approximately equal between the focusing inlet and the pore and between the sample inlet and the pore. When the focusing drop has a larger radius than the sample drop, the focusing streams are wider due to a higher pressure. When the ratio is reversed, the sample stream is wider than the focusing streams.