Hydrodynamic focusing on a silicon chip: Mixing nanoliters in microseconds

We describe the formation and control of nanoscale, submerged fluid jets. The focusing process necessary to achieve these small length scales is characterized experimentally and theoretically. Fast mixing is one important application of nanoscale fluid control: We demonstrate this with a continuous-flow mixer capable of mix times of less than 10 mu s and sample consumption rates of nanoliters per second. This new technique facilitates the study of fast reaction kinetics on time scales unattainable with conventional mixing technology.