New Nanochemistry Technique Encases Single Molecules in Microdroplets
Inventing a new tool to create chemical reactions between individual molecules, scientists at the National Institute of Standards and Technology have used microfluidics – the manipulation of fluids on a microscopic scale – to make microdroplets containing individual molecules of interest. By combining this new microfluidic “drop-on-demand” method with “optical tweezers” that could combine several drops and the cause of its molecular content of reacting, the research may lead to an installation compact, integrated to obtain a single molecule of information on the structure and role of organic materials such as proteins, enzymes and DNA.
With the help of NIST Nanotechnology Center for Science and Technology, physicists Carlos López-Mariscal and Kristian Helmerson created a microfluidic device with a small channel through which water can flow. Squeezed into a small stream of a mixture of oils with different viscosity or flow resistance, it puts pressure on the water then enters a narrowing. The sharp drop in water pressure, together with a pinch of detergent breaks the surface tension, divide it into small droplets. (The same effect occurs when a thread of water falling from a faucet breaks into small droplets.)
The droplet sizes are very uniform and can be adjusted by adjusting the width of the constriction. With this technique, the researchers made the drops of a micrometer in diameter, or half attoliter (half a billionth of a billionth of a liter) on the volume.
In the microfluidic channel, the water is mixed with the molecules of the desired concentration just right so that the droplets resulting from each selection, on average, only one molecule of interest. Within each drop, the individual molecules of interest dabble freely in the relatively wide, with water molecules that make up the bulk of every drop.
Using lasers, researchers can move two or more single molecule that contains drops that bind to and observe the reactions by optical methods. In their initial reactions, researchers are mixing fluorescent molecules that emit different colors, but in the future, imagine the most interesting chemical reactions, such as those between an infectious agent and an antibody, or a chromosome and a drug. Researchers can shape a laser beam in any desired pattern and therefore the trap, not only falls alone, but the parent of them, opening up new possibilities for single molecule spectroscopy.
More information: C. López-Mariscal and K. Helmerson. Optical hydrosomes capture. Proc. SPIE, vol. 7400, 740,026 (2009).