Researchers at Stanford have demonstrated a method to deliver precise points of light anywhere in the body without a single incision.
This noninvasive method could replace invasive procedures such as surgical implants or optical fiber insertions.
Published in Nature Materials on April 13, the study outlines a “light on demand” system that uses ultrasound to trigger light emission from within the bloodstream.
Ultrasound activation
Light is becoming a powerful tool for healing and brain research, but it has one major flaw.
Light doesn’t travel well through skin. Try holding a flashlight to your palm, and you’ll see a dull red glow, but nothing more; the dense forest of cells, fat, and bone acts like a brick wall for photons.
The inability of light to penetrate deep tissue has remained a fundamental barrier in medical science.
To treat a deep-seated tumor with light or to stimulate specific neurons in the brain, doctors have typically had to reach for the scalpel, cutting through healthy tissue to insert stiff optical fibers.
But Stanford researchers have just found a new, non-invasive way.
The new technique works by sending tiny particles through the blood that turn sound waves into tiny sparks of light. The current particles glow blue, specifically at 490 nanometers.
“With these materials, we can produce light emission in the brain, in the gut, in the spinal cord, in the muscle – virtually anywhere – without needing a physical implant,” said Guosong Hong, an assistant professor of materials science and engineering in the School of Engineering.
Researchers adapted large ceramic particles into tiny, body-friendly nanoparticles. These particles are tiny enough to be injected into the bloodstream, where they circulate like a fleet of microscopic lightbulbs waiting for a signal.
Notably, these specialized materials are “mechanoluminescent,” which only switch on when “squeezed” by the mechanical pressure of ultrasound waves.
Ultrasound travels through the body with ease — it’s how we see babies in the womb without harming them.
“Ultrasound is very convenient to use, and it penetrates much deeper into the body than light,” Hong noted.
Mind control of mice
To prove the system worked, the researchers turned to the most complex organ of all: the brain.
For the testing, mouse models were outfitted with an ultrasound-emitting “hat” to trigger light in specific brain regions. Targeting one brain region with light forced a left turn, while focusing on another directed the mouse to the right.
No holes were drilled in the skull, and no wires were attached to the brain tissue. It was wireless, noninvasive mind-control, powered by sound and light.
“We can noninvasively tune this emission in different brain regions to produce a variety of behavioral outcomes,” Hong said.
This successful brain demonstration proves that sound-triggered light can control cell behavior deep within the body.
Beyond neuroscience, this technique opens the door for any medical treatment that relies on light, such as precision cancer therapies or localized gene editing.
Moreover, ultraviolet wavelengths could be used to kill pathogens or for light-activated gene editing for pinpoint precision.
However, the current nanoparticles are made of ceramic materials that don’t easily break down.
The team is already looking into replacing these ceramics with biodegradable materials that the liver can safely process after the treatment.