TRAPPING SINGLE MOLECULES

at room temperature, and studying their properties has been accomplished by Adam Cohen and his colleagues at Harvard. Pinning down one molecule at a time is difficult at low temperatures, much less at warm temperatures, where the molecules are more agitated. The feat was carried off by using an Anti-Brownian Electrokinetic (ABEL) trap. In this device the fluorescently labeled molecule is tracked in a fluorescence microscope and its instantaneous motion slowed by the application of carefully timed bits of electricity applied to electrodes that surround the sample. Actually, the electrodes are kept at some distance from the molecule, the better not to pollute the local aqueous environment with chemical effects. The electric kicks are imparted to the molecule along micro-channels in an underlying chip. The faster this feedback process can be applied the better the trapping. An ABEL trap can hold smaller samples at room temperature than any other trap scheme. To hold a molecule to the same tiny volume of solution with laser light alone, enormous power would be needed, and
this would “cook” the object rather than trap it. The ABEL trap is gentle, and requires mere microwatts of laser power. Cohen (cohen@chemistry.harvard.edu) talked about the application of this process to the dynamics of membrane proteins at this week’s AVS meeting. (http://www.avssymposium.org/overview.asp Cohen website https://www2.lsdiv.harvard.edu/labs/cohen/ Paper IPF-MoM1 )