Invention is one ‘HOT’ scientific commodity

David Grier’s holographic optical tweezers have caused some rather scientifically alarming things to appear on the television in his laboratory.

David Grier, Associate Professor in Physics, works in his lab with a microscope and a laser for his holographic optical tweezers technology. The HOT technology transforms multiple beams of light into precision tools capable of manipulating microscopic particles. He and Eric Dufresne (Ph.D., ’00) received a patent for the invention last April.

“You can watch a hundred years of progress going away before your very eyes,” said Grier, Associate Professor in Physics.

When combined with a laser and a microscope, the HOT technology transforms multiple beams of light into precision tools capable of manipulating microscopic particles. Grier and Eric Dufresne (Ph.D., ’00) received a patent for the invention last April.

“The idea is you can use a beam of light to trap a particle and move it in three dimensions, just like a Star Trek tractor beam,” Grier said. “We use beams of light to move particles into interesting arrangements and watch how they react to being placed in such ways. We actually watch them using consumer electronics.”

Once Grier has the particles stuck fast within his optical clutches, he can probe some time-honored but- never-tested theories of 19th-century physics.

“You find that while these theories work under the conditions for which they were originally intended to work, people have since applied them in places where they really oughtn’t to apply them, and they end up with qualitatively wrong answers,” Grier said.

The basic theory that scientists use to understand how proteins configure themselves to carry out basic biological processes was developed more than 50 years ago. It is the same theory that also applies to the dispersal of tiny solids in liquids, such as paint and ink. But the theory was originally formulated for other purposes, so it does not account for all of the interactions that occur during these processes.

“We’ve been able to show that that theory makes qualitatively wrong predictions,” Grier said. Under some circumstances, particles with like charges attract rather than repel one another. “That goes against common sense. It goes contrary to 50 years of theoretical understanding.”

The desire to clear up such theoretical misunderstandings motivated Grier to develop HOT technology. He had learned about optical tweezers as a postdoctoral fellow working at AT&T Bell Laboratories. The technique works because dielectric particles––those that do not conduct electric current––experience forces that draw them to where the light is brightest.

But the original optical tweezers could efficiently trap and manipulate only one particle at a time. Grier and Dufresne devised a computer-generated hologram to split one light beam into many beams to make an array of optical tweezers.

Their invention exemplifies how basic research begets practical applications while also enhancing undergraduate education. A research group led by physics professor Gabriel Spalding at Illinois Wesleyan University in Bloomington fabricated the first round of computer-generated holograms that Grier’s team designed. One of Spalding’s undergraduates will work with Grier’s group over the summer through the Materials Research and Science Engineering Center’s Research Experiences for Undergraduates program.

On the technology-transfer front, the University’s ARCH Development Corporation has licensed the HOT technology to a new company. Called Arryx, the company will make the invention commercially available to the computer, biotechnology and chemical sensor industries.

One potential application is in photonics, computer devices that transmit information via light instead of electricity. Such devices would greatly increase computer power, but they would require chips with structures far smaller than anything modern technology can produce. The only way to make these devices is through a process called self-assembly, which involves mixing together materials that will configure themselves into structures at the desired scale.

“The drawback of self-assembly is you get what you get, unless you’re able to tool up a system that spontaneously makes what you want,” Grier said.

One of the keys to doing that is to control the interaction between the microscopic constituents that are mixed together. And the way to control those interactions is with holographic optical tweezers. It could become known as the tool of choice, both for probing the nagging mysteries of 19th-century physics, and for pushing back the 21st century’s technological frontiers..