October 30, 2007

Infrared light used as better optical tweezers on silicon

What's new in the optical tweezer from MIT's Matt Lang and David Appleyard is that they used infrared light to move particles on silicon, the basis of microchips. (Unlike visible light, the infrared does not bounce off the silicon.) That means that MIT's optical tweezer can be used not just for study but to build structures on the surface of chips.

16 live E. coli cells to spell out "MIT" on a chip

Lang and Appleyard proved their technique by getting 16 live E. coli cells to spell out "MIT" on a chip. The long-term potential is more practical: Lang envisions using the system to cram high-resolution sensors in very small spaces — for disease detectors, for example — and to connect silicon-based electronics to living tissues and other "biological interfaces."

Arthur Ashkin, a retired Bell Laboratories scientist who is considered the father of optical tweezers, cautioned that the MIT work could not be considered a breakthrough, since no devices using the technology have yet been built.

Functional integration of optical trapping techniques with silicon surfaces and environments can be realized with minimal modification of conventional optical trapping instruments offering a method to manipulate, track and position cells or non-biological particles over silicon substrates.
This technique supports control and measurement advances including the optical control of silicon-based microfluidic devices and precision single molecule measurement of biological interactions at the semiconductor interface. Using a trapping laser in the near infra-red and a reflective imaging arrangement enables object control and measurement capabilities comparable to trapping through a classical glass substrate. The transmission efficiency of the silicon substrate affords the only reduction in trap stiffness. We implement conventional trap calibration, positioning, and object tracking over silicon surfaces. We demonstrate control of multiple objects including cells and complex non-spherical objects on silicon wafers and fabricated surfaces.