Stanford University scientists have revealed a novel, non-invasive method for delivering light to desired locations within the human body, using ultrasound waves to stimulate light-emitting nanoparticles injected into the bloodstream.
The research team behind the sci-fi-sounding process said their approach could offer a safe, non-invasive light-generating method for delicate surgery in difficult-to-illuminate areas and generate localized light for genetic engineering research. The ability to generate precise points of light within the human body could also enable less-invasive light-based treatments.
“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,” explained Guosong Hong, an assistant professor of materials science and engineering in the School of Engineering and senior author on the paper detailing the work.
Ultrasound Penetrates Much Deeper Into the Body Than Light
A critical component of life, light is also a necessary tool in a wide range of medical treatments and procedures. Recent breakthroughs have also shown light’s ability to stimulate cell growth, treat cancer, and even manipulate neural signals.
Still, visible light does not easily pass through human tissue, making internal lighting challenging for surgeons and medical professionals who use it in advanced treatments. In many cases, the only option is to remove healthy tissue or insert an optical fiber.
According to Hong, unlike light, ultrasound waves penetrate “much deeper into the body than light.” The professor also noted that ultrasound, which is already approved for several medical uses, is “very convenient to use.”
To take advantage of these benefits, Hong and colleagues collected large ceramic particles with a unique ability: when subjected to mechanical force, they emit light. Critically, the type of mechanical stress needed to generate enough usable light within the human body can be created using medically safe levels of ultrasound.
Tuning Waves to Produce Behavioral Outcomes
After processing the raw material into tiny nanoparticles small enough to travel safely throughout the human bloodstream, they coated them with a biocompatible coating that allowed them to be suspended in a solution rather than sinking to the bottom. Next, they injected the solution into lab mice. According to Hong, the injected nanoparticles will be carried to wherever blood vessels deliver nutrients and blood cells to live tissue, noting that they can use the circulatory system to “also generate light.”
Next, the team created a small ultrasound-producing hat and placed it on the heads of the injected mice. As hoped, when they targeted ultrasound waves at different parts of the animal’s brain, they literally ‘lit up.’ They also noted that the animal would change direction, either left or right, depending on which part of the brain was being stimulated by ultrasound.
“We can noninvasively tune this emission in different brain regions to produce a variety of behavioral outcomes,” Professor Hong explained.
However, the professor added, the approach, which manipulates cellular activity within the brain, also has “other potential uses as well.”
“This is a general method that can enable any application that requires light in deep tissue,” Hong explained.
For example, the nanoparticles used in the experiments produced blue light at 490 nanometers. In addition to demonstrating the ability to excite neurons, the team noted that this wavelength is already used in photodynamic cancer therapy. Unlike conventional light sources, light generated by ultrasound-stimulated nanoparticles can be targeted directly at the cancerous cells.
Paving the Way for Clinical Applications
Next, the research team is exploring ultrasound-based treatments using nanoparticles that emit ultraviolet (UV) light. UV light is used in several medical applications, including killing viruses and bacteria without the use of chemicals or medications.
Following the successful experiments, Hong has also teamed up with Michael Lin, a professor of neurobiology and bioengineering in the schools of Engineering and Medicine, to explore pairing his light-producing approach with an existing gene-editing system. The researchers note that this could be highly beneficial, as gene editing can create “off-target effects” that could potentially be turned on and off with a targeted light source.
When discussing potential human applications, the team noted that they need to test the nanoparticles’ safety first. This includes searching for nanoparticles that emit light and break down more readily in the body than the nanoparticles used in the mouse experiments, even though the mice showed no ill effects from the larger nanoparticles.
“What we’re demonstrating here is a proof of concept showing that you can produce light emission in a programmable manner deep within the body,” Hong said. “If we can replace the material with one that is safer to be used in humans, that will start to pave the way for clinical applications.”
The study “An ultrasound-scanning in vivo light source” was published in Nature Materials.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.