The chemists used a type of artificial membrane called a phospholipid bilayer that is organic and closely resembles the membranes of living cells. By using different types of phospholipids, they can vary the physical and chemical characteristics of the membranes in a way that mimics the variations found in nature, Zare says.
The researchers found two ways to use the vesicles to produce minuscule chemical reactions.
The first approach involves immersing the vesicles in a liquid containing a second chemical that will react with the chemical that they contain. A laser-based tool called optical tweezers allows them to manipulate these delicate, microscopic objects easily. Using the optical tweezers, the researchers position a vesicle between two electrodes. Zapping the membrane sac with a mild electrical pulse causes pores to open in the membrane wall, allowing the chemical inside the vesicle to mix and react with the chemical outside.
The second approach allows the reaction of controlled amounts of chemical reagents. The researchers create two sets of vesicles each filled with a different chemical. They then use the optical tweezers to position a pair of vesicles, each containing one of the two chemicals that they want to react, between the electrodes. By zapping the two vesicles with a slightly stronger electrical pulse, the researchers can cause the two membrane sacs to break down and then recombine into a single, larger vesicle. The recombination happens so fast that very little of the chemicals trapped inside the original vesicles escapes.
In their initial experiments, the researchers used different fluorescent dyes to
study the chemical reactions that resulted. But, according to Zare, they can use
a variety of other instruments to measure these micro-chemical reactions.
Many of the reactions that take place within a cell do not work in the same way
at larger volumes.
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Contact: David F. Salisbury
salisbury@stanford.edu
650-725-1944
Stanford University
19-Mar-1999