A silicon-photonics chip has enabled the creation of a ‘tractor beam’ that can capture and maneuver biological particles with a precisely focused light beam. This innovative device may significantly aid biologists and clinicians in analyzing DNA, sorting cells, and exploring disease mechanics.
Researchers at MIT have crafted a small-scale, chip-based “tractor beam,” reminiscent of the one that ensnares the Millennium Falcon in “Star Wars.” This device holds promise for assisting biologists and medical professionals in studying DNA, sorting cells, and probing disease mechanisms.
Compact enough to fit in your hand, the device utilizes light emitted from a silicon-photonics chip to manipulate particles situated millimeters above its surface. The light can reach through the glass covers that guard biological samples, allowing cells to be maintained in a sterile environment.
Conventional optical tweezers, which capture and move particles using light, typically require large microscope arrangements. In contrast, chip-based optical tweezers could provide a more manageable, mass-producible, widely available solution for optical manipulation in biological research.
However, existing integrated optical tweezers are limited to capturing cells very close to or directly on the chip’s surface, which can lead to contamination and stress the cells, hindering compatibility with standard biological studies.
The MIT team has introduced a new method called an integrated optical phased array, allowing for the trapping and manipulation of cells located over a hundred times further away from the chip’s surface.
“This research opens up exciting new opportunities for chip-based optical tweezers by facilitating the trapping and manipulation of cells at significantly greater distances than previously achievable. It’s thrilling to consider the diverse applications this technology could enable,” remarks Jelena Notaros, a professor in Electrical Engineering and Computer Science (EECS) at MIT, and a member of the Research Laboratory of Electronics.
Contributing to this study is lead author and EECS graduate student Tal Sneh, along with graduate student Sabrina Corsetti; Milica Notaros, PhD ’23; Kruthika Kikkeri, PhD ’24; and Joel Voldman, the William R. Brody Professor of EECS. Their findings are published today in Nature Communications.
A New Trapping Technique
Optical traps and tweezers employ a focused light beam to seize and maneuver small particles. The beam’s forces draw microparticles towards the highly focused center of the light, effectively capturing them. By moving the light beam, researchers can guide the microparticles, allowing manipulation using non-contact forces.
Traditionally, optical tweezers need extensive microscope setups in laboratories and various devices to control light, which restricts their usability in diverse settings.
“Thanks to silicon photonics, we’ve managed to condense this typically bulky lab setup into a single chip. This presents a significant advantage for biologists, allowing them to utilize optical trapping and manipulation without the need for cumbersome equipment,” Notaros explains.
However, past chip-based optical tweezers could only emit light very close to the chip surface, limiting their ability to capture particles just a few microns above it. Biological samples are often maintained in sterile conditions using glass covers that can be about 150 microns thick, necessitating the removal of cells for manipulation, which risks contaminating the chip each time.
To address these issues, MIT researchers created a silicon photonics chip that focuses light approximately 5 millimeters above its surface, allowing for the manipulation of biological particles while keeping them inside a sterile cover slip, thereby protecting both the chip and the particles from contamination.
Controlling Light
The researchers achieved this using an integrated optical phased array system. This involves a series of microscale antennas designed on a chip through semiconductor manufacturing techniques. By electronically regulating the optical signals from each antenna, the researchers can shape and direct the emitted light beam from the chip.
Although previous integrated optical phased arrays were primarily developed for applications like lidar, they were not intended to produce the tightly focused beams necessary for optical tweezing. The MIT team found that by employing specific phase patterns for each antenna, they could generate a highly focused beam of light suitable for trapping and manipulating particles millimeters away from the chip.
“Prior to this work, no one had produced silicon-photonics-based optical tweezers capable of trapping microparticles over distances greater than a millimeter. This represents a monumental advancement compared to earlier efforts,” Notaros states.
By adjusting the wavelength of the optical signal powering the chip, the researchers managed to steer the focused beam over distances exceeding a millimeter with precision at the microscale.
Initially, the team tested their device on small polystyrene spheres. After successful manipulation, they proceeded to trap and attempt manipulation of cancer cells provided by the Voldman group.
“Integrating silicon photonics with biophysics presented its own set of unique challenges,” Sneh notes.
The researchers navigated issues such as tracking the movement of sample particles semiautomatically, determining the optimal trap strength to hold the particles steady, and efficiently processing data after capture.
Ultimately, they successfully conducted the first cell experiments using single-beam optical tweezers.
Building on these findings, the team aims to refine the system to allow for an adjustable height of the light beam’s focal point. They also aspire to apply the device to various biological contexts and utilize multiple trapping sites concurrently to manipulate biological particles in more intricate ways.
This research is backed by the National Science Foundation (NSF), an MIT Frederick and Barbara Cronin Fellowship, and the MIT Rolf G. Locher Endowed Fellowship.
