Microfluidic devices have made chemical and biological analysis faster, more selective and less taxing on the supply of material under study. However, commonly used lithographic manufacturing methods cannot produce pumps and valves approximately 100 µm across. Now researchers at the Colorado School of Mines in Golden have constructed valves that are only several microns across by using optical trapping to assemble groups of 1.5- to 3-µm silica spheres.As reported in the Aug. 26 issue of Applied Physics Letters, they fused the spheres into linear arrays using a photopolymerizing solution and the optical trapping laser. The researchers expect that these types of valve structures may someday be combined with micropumps to construct complex lab-on-chip devices.