Developers have made significant progress over the years with miniaturization, including microfluidic devices. But measuring the fluid flow within those devices -- with passages of 1 to 100 µm -- has not been easy. Researchers at the University of Illinois at Urbana-Champaign, with the University of California at Santa Barbara, have developed a particle-image velocimetry system that can measure fluid velocities at the single-cell level. The system uses an epifluorescence microscope and an intensified CCD camera to study and record 100- to 300-nm-diameter fluorescent seed particles. The scientists plan to implement their technique in miniature pumps, fluid mixers and rocket nozzles.