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Physics Seminar: “Improving Optical Traps for Single-Molecule and Motor Protein Research”

Posted on 11/30/2011 7:25:51 PM

Daniel Cole, from Materials Science and Engineering, University of Pittsburgh, will present “Improving Optical Traps for Single-Molecule and Motor Protein Research” on Friday, December 2, 2011, in Weyandt Hall, room 331, at 2:30 p.m.


Optical traps use the momentum of light to exert forces on microscopic objects. As light is refracted and reflected through dielectric objects, the change in momentum of the light results in piconewton scale optical forces exerted on the diffracting object. Construction and use of optical traps has become relatively mature, but the performance of such instruments is limited with conventional approaches. Using feedback control, a versatile optical trap can be constructed that can be used to control either the position of trapped objects or apply specified forces. More importantly, feedback control offers techniques not only for controlling experimental conditions and protocols, but, with proper design can yield improved estimates of variables of interest.

This presentation discusses optical traps and various types of feedback control for the purpose of improving instrument performance for single molecule experiments. For various feedback approaches, the improvement of measurement SNR is discussed and is compared to the open-loop case. A technique is shown for effectively “cooling” the beads held in the optical trap, thereby limiting the effect that Brownian disturbances have on the beads’ motion. Finally, state-observation techniques are given for estimating molecular forces directly from measurements. Ultimately, feedback provides other advantages, including the ability to control other variables and to make a more robust instrument that can be easily adapted to changes in experimental conditions or the environment.

Department of Physics