Laser Tweezer : More details

Last update: 03/02/2007 07:40 PM

Optical Tweezers, also known as, laser tweezers, has been under study since Arthur Ashkin, a scientist in Bell Labs, discovered in 1970 that microscopic dielectric spherical particles (beads) get trapped under the influence of strongly focused laser beam. The trap is stable in 3 dimensions and allows for noninvasive study at microscopic scales. With a proper bead position detection system, dynamics of a variety of biological systems can also be studied at nanometers scale. This is made possible by attaching molecules like DNA to the bead and studying bead motion under the combined influence of laser trap and forces exerted by the molecule under study.

At Electrical Engineering Department, Iowa State University, we have setup optical tweezers and its instrumentation is under progress. It is being studied by Hullas Sehgal and Tanuj Aggarwal, both pursuing PhD. The work here began in 2003 and since then it has advanced to a sophisticated and state of the art instrumentation with the capability to detect position (using photodetectors) and actuate trap position (using AODs) at high bandwidth. Currently we are calibrating the instruments and working on operating the tweezers in closed loop, i.e., trap position actuation will be controlled based on the position feedback obtained from photodetector signal.

The optical tweezers lab is very well equipped with modern instruments of high quality and performance, comparable to the best research labs across the world. This includes expensive equipments like Nikon Microscope with high NA (1.4, oil immersion) objective, diode laser (1064nm, 500mw), Spatial light Modulators (SLM, holoeye, 1280 x 768, liquid crystal), Acousto Optic Deflectors (AOD, Intraction), quadrant and position sensitive photodetectors (Pacific Silicon Sensors). Most of these equipments are computer controlled and hence capable of remote and automated control. Not all of these instruments are installed in the optical tweezers setup yet as the work is under progress.

Research Direction

The controls group at ECpE, ISU is well reputed in the field of AFM for their invaluable contributions in its advancement. Similar achievement is expected out of the relatively newer project of studying optical tweezers. While most of the researchers of optical tweezers belong to biology or physics background, we are interested in the dynamics and controls aspect of this instrument. The vision is to develop control strategies to enhance the performance of optical tweezers for better and faster position detection, study collective behavior of particles in random motion, study the dynamic aspect of biomolecules. The main challenges in this field are, setting up instrument because it requires very precise alignment of a variety of optics, inability to 'see' at nanometer scale, significant data corruption due to instrument and environmental noise, and lack of accurate knowledge about the physics working behind the optical tweezers. We hope to bridge the gaps and extend the knowledge base that might prove to be very useful in future.

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