Engineers create chip-based tractor beam for biological particles

Researchers at MIT have developed a small chip-based “tractor beam” similar to the one seen on the Millennium Falcon in the “Star Wars” movies. This could one day help biologists and clinicians study DNA, classify cells, and investigate disease mechanisms. .

The study is published in the journal Nature Communications.

The device is small enough to fit in the palm of your hand and uses light beams emitted by a silicon photonics chip to manipulate particles a few millimeters away from the chip’s surface. Light can pass through cover glasses that protect samples used in biological experiments, keeping cells in a sterile environment.

Traditional optical tweezers, which use light to capture and manipulate particles, typically require bulky microscopy setups, whereas chip-based optical tweezers are more compact and high-volume applications for optical manipulation in biological experiments. It has the potential to provide production-ready, widely accessible, high-throughput solutions.

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

MIT researchers have developed a new method of integrated optical tweezing that enables the capture and tweezing of cells more than 100 times further away from the chip surface using a system called an integrated optical phased array.

“This study opens new possibilities for chip-based optical tweezers by enabling cell capture and tweezing at much longer distances than previously demonstrated. It’s exciting to think about different applications,” says Elena Notaros. Robert J. Shillman Career Development Professor of Electrical Engineering and Computer Science (EECS) and member of the Electronics Institute.

Notaros is joined on the paper by first author and EECS graduate student Tal Sneh. Sabrina Corsetti, EECS graduate student; Dr. Milica Notaros. Dr. Krutika Kikkeli. Joel Voldman, William R. Brody Professor of EECS;

new capture style

Optical traps and tweezers use focused beams of light to capture and manipulate small particles. The force exerted by the beam pulls the particles towards the central, strongly focused light and traps them. By manipulating light beams, researchers can pull microparticles with them, allowing them to manipulate small objects using non-contact forces.

However, optical tweezers have traditionally required large laboratory microscope setups and multiple devices to shape and control the light, limiting where and how they can be used. .

“Silicon photonics allows us to integrate this large-scale, typically laboratory-scale system on a chip, which provides optical trapping and tweezing capabilities without the overhead of complex bulk optics. “It’s a great solution for biologists to set up,” says Notaros.

But so far, chip-based optical tweezers have only been able to emit light very close to the chip surface, meaning these traditional devices can only capture particles a few microns away from the chip surface. Biological specimens are typically held in a sterile environment using coverslips that are approximately 150 microns thick, so the only way to manipulate biological specimens with such a chip is to extract cells and place them on its surface. .

However, it leads to chip contamination. Each time you perform a new experiment, you must discard the chip and attach the cells to a new chip.

To overcome these challenges, MIT researchers have developed a silicon photonics chip that emits a beam of light focused about 5 millimeters above the surface. In this way, biological particles remaining within the sterile coverslip can be captured and manipulated, protecting both the chip and the particles from contamination.

manipulate light

The researchers achieved this using a system called an integrated optical phased array. The technology involves a series of microscale antennas fabricated on a chip using semiconductor manufacturing processes. By electronically controlling the optical signals emitted by each antenna, researchers can shape and control the beam of light emitted by the chip.

Most conventional integrated optical phased arrays motivated by long-range applications such as LIDAR were not designed to produce the tightly focused beams required for optical tweezers. The MIT team discovered that by creating a specific phase pattern in each antenna, a strongly focused beam of light could be formed. This can be used to capture or tweeze light a few millimeters from the surface of the chip.

“Until now, no one had created silicon photonics-based optical tweezers that could capture microparticles over millimeter-scale distances. This is an order of magnitude improvement compared to previous demonstrations,” Notaros said. I say.

By changing the wavelength of the optical signal powering the chip, the researchers were able to control the focused beam over a range larger than a millimeter with microscale precision.

To test the device, the researchers began by capturing and manipulating small polystyrene spheres. Once successful, they moved on to cancer cell capture and tweezers provided by the Voldmann group.

“The process of applying silicon photonics to biophysics has presented many unique challenges,” Sneh added.

Researchers must, for example, semi-automatically track the movement of sample particles, determine the appropriate trap strength to hold particles in place, and determine how to effectively post-process the data. did.

Ultimately, they were able to demonstrate the first cell experiments using single-beam optical tweezers.

Based on these results, the team hopes to improve the system to be able to adjust the focal height of the light beam. They also hope to apply this device to a variety of biological systems and use multiple trapping sites simultaneously to manipulate biological particles in more complex ways.

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

“First, given that silicon photonic chips can be manufactured at low cost, they have the potential to democratize optical tweezers experiments.

“While it may sound like something that only a few scientists are interested in, the fact is that the widespread availability of these systems means that previously they were costly and only available to a few laboratories. It will allow us to study fundamental questions in single-cell biophysics in ways that were previously not possible due to the complexity of the instrumentation.

“We can also imagine many applications where one of these devices (or possibly an array of them) could be used to improve the sensitivity of disease diagnosis.”

This article is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site covering news about MIT research, innovation, and education.