Experimental Setup. A programmable syringe pump (Kd
Scientific, Ismatec, Switzerland) was connected to both inlets via
Teflon tubing and silica capillary to limit the pressure drop. To
image the mixing under pressure-driven flow, one inlet was initially
filled with a 10 mM phosphate buffer (pH ) 7), and the second
inlet was filled with the buffer solution containing 220 íM
fluorescein. Fluorescein (Fluka, Switzerland) was diluted in 10
mM phosphate buffer (pH ) 7).