Engineers create chip-based tractor beam for biological particles

MIT researchers have developed a miniature chip-based “tractor beam,” like the one that captures the Millennium Falcon in the movie “Star Wars,” that could one day help biologists and clinicians study DNA, classify cells and to investigate disease mechanisms. .

The search appears in Natural communications.

Small enough to fit in the palm of your hand, the device uses a beam of light emitted from a silicon photonic chip to manipulate particles just millimeters from the chip’s surface. Light can penetrate the glass coverslips that protect samples used in biological experiments, allowing cells to remain in a sterile environment.

Traditional optical tweezers, which trap and manipulate particles using light, typically require bulky microscope setups, but chip-based optical tweezers could offer a more compact, mass-manufacturable, widely accessible, high-throughput solution. for optical manipulation in biological experiments.

However, other similar integrated optical tweezers can only capture and manipulate cells very close to or directly on the chip surface. This contaminates the chip and can stress the cells, limiting compatibility with standard biological experiments.

Using a system called an integrated optical array, MIT researchers have developed a new integrated optical tweezer modality that allows cells to be trapped and tweezed more than a hundred times farther from the chip surface.

“This work opens new possibilities for on-chip optical tweezers by enabling cell trapping and hair removal at much greater distances than previously demonstrated. It is exciting to think about the different applications that could be made possible by this technology “, says Jelena Notaros, research director. Robert J. Shillman Professor of Electrical and Computer Engineering Career Development (EECS) and member of the Electronics Research Laboratory.

Lead author and EECS graduate student Tal Sneh joins Notaros on the article; Sabrina Corsetti, EECS graduate student; Milica Notaros Ph.D.; Kruthika Kikkeri Ph.D.; and Joel Voldman, EECS William R. Brody Professor.

A new trapping method

Optical traps and tweezers use a focused beam of light to capture and manipulate tiny particles. The forces exerted by the beam will attract the microparticles toward the intensely focused light in the center, capturing them. By directing the beam of light, researchers can drag the microparticles with it, allowing them to manipulate tiny objects using contactless forces.

However, optical tweezers traditionally require a large microscope in a laboratory, as well as multiple devices to shape and control the light, limiting where and how they can be used.

“With silicon photonics, we can take this large system, typically lab scale, and integrate it onto a chip. This represents a great solution for biologists because it provides them with optical trapping and pinching without the overhead of a complicated bulk optical system setup,” says Notaros.

But until now, chip-based optical tweezers were only able to emit light very close to the surface of the chip, so these earlier devices could only capture particles a few microns away. the surface of the chip. Biological samples are typically stored in sterile environments using glass coverslips approximately 150 microns thick. The only way to handle them with such a chip is therefore to remove the cells and place them on its surface.

However, this leads to flea contamination. Each time a new experiment is performed, the chip must be discarded and the cells must be placed on a new chip.

To overcome these challenges, MIT researchers developed a silicon photonic chip that emits a beam of light that focuses about 5 millimeters above its surface. This way, they can capture and manipulate biological particles that remain inside a sterile coverslip, protecting the chip and particles from contamination.

Manipulate the light

The researchers achieve this by using a system called an integrated optical network. This technology involves a series of microscopic antennas fabricated on a chip using semiconductor manufacturing processes. By electronically controlling the optical signal emitted by each antenna, researchers can shape and direct the beam of light emitted by the chip.

Motivated by long-range applications like lidar, most previous integrated optical networks were not designed to generate the tightly focused beams needed for optical pinching. The MIT team found that by creating specific phase patterns for each antenna, they could form an intensely focused beam of light, which can be used for optical trapping and to pinch out millimeters of the chip’s surface.

“No one has previously created silicon-photonics-based optical tweezers that can trap microparticles over a millimeter distance. This is an improvement of several orders of magnitude over previous demonstrations,” says Notaros.

By varying the wavelength of the optical signal that powers the chip, the researchers were able to direct the focused beam over a range greater than a millimeter and with micrometer precision.

To test their device, the researchers began by attempting to capture and manipulate tiny polystyrene spheres. Once they were successful, they moved on to trapping and removing cancer cells provided by the Voldman Group.

“Many unique challenges have arisen in the process of applying silicon photonics to biophysics,” adds Sneh.

Researchers had to figure out how to track the movement of sample particles semi-automatically, determine the appropriate trap force to hold the particles in place, and efficiently post-process the data, for example.

Eventually, they were able to show the first cellular experiments with single-beam optical tweezers.

Building on these results, the team hopes to refine the system to allow an adjustable focal height for the light beam. They also want to apply the device to different biological systems and use multiple trap sites at the same time to manipulate biological particles in more complex ways.

“This is a very creative and important paper in many ways,” says Ben Miller, dean professor of dermatology and professor of biochemistry and biophysics at the University of Rochester, who was not involved in this work. .

“On the one hand, because silicon photonic chips can be manufactured at low cost, this potentially democratizes optical pinch experiments.

“This may seem like something that would only be of interest to a few scientists, but in reality, having these systems widely available will allow us to study fundamental problems in single-cell biophysics in a way previously reserved for a few laboratories, being given the high cost and complexity of the instrumentation.

“I can also imagine many applications in which one of these devices (or possibly a set of them) could be used to improve the sensitivity of disease diagnosis.”

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news in MIT research, innovation and education.