National Institute of Standards and Technology, www.nist.gov

Engineers at the National Institute of Standards and Technology have developed a microfluidic “droplet-on-demand” device that spits out droplets about 1 micrometer in diameter (or about half a billionth of a billionth of a liter) that contain a single molecule of a compound of interest. Their goal is to give material scientists and chemical engineers a way to observe chemical reactions between single molecules

The device has a channel through which water flows. The water, which has been laced with molecules of interest to a specific concentration, is squeezed into a narrow stream by a mixture of oils whose viscosity or resistance to flow exerts pressure on it. The water then enters a narrow constriction in the channel and its pressure drops abruptly. Adding detergent at this point breaks up the water’s surface tension, splitting it into small droplets of uniform size. And their size can be adjusted by changing the width of the constriction. The resulting droplets pick up on average just one of the molecules of interest.

Currently, researchers use lasers to move and merge two or more single-molecule-carrying droplets into one larger droplet. They can then watch any chemical reactions using various optical methods.