Ming Wu, a UC Berkeley Professor of electrical engineering and computer sciences invented the new optoelectronic tweezers.
Wu transformed the optical energy from low powered light emitting diodes (LED) into electrical energy via a photoconductive surface. The idea is to allow the LED to switch on and off the photoconductive material via its fine projection. As the optical pattern can be easily transformable through optical projection, this method allows a high flexibility of switching different optical landscapes.
The manipulation/tweezing process is done by the variations between the electric field actuated by the light pattern. The particles will be either attracted or repelled from the actuated point due to its induced electrical dipole. Particles suspended in a liquid will be susceptible to the electrical field gradient, this is known as dielectrophoresis.
One clear advantage is that the electrical conductivity is different between different kinds of cells. Living cells have a lower conductive medium while the dead ones have minimum or no conductive medium. The system may be able to manipulate roughly 10,000 cells or particles at the same time.
See comments by Professor Kishan Dholakia on this new technique, K. Dholakia, Nature Materials 4, 579–580 (01 Aug 2005) News and Views.
"The system was able to move live E. coli bacteria and 20-micrometre-wide particles, using an optical power output of less than 10 microwatts. This is one-hundred-thousandth of the power needed for [direct] optical tweezers".
Another notably new type of optical tweezers is optothermal tweezers invented by Yuebing Zheng at The University of Texas at Austin. The strategy is to use light to create a temperature gradient and exploit the thermophoretic migration of matter for optical trapping. The team further integrated thermophoresis with laser cooling to develop opto-refrigerative tweezers to avoid thermal damages for noninvasive optical trapping and manipulation.