Shining a light *inside* the body with ultrasound-activated nanoparticles

In this latest science-fiction-becomes-reality breakthrough, scientists have invented a novel nanotechnology that uses non-invasive ultrasound to create light inside the body.

Researchers from Stanford University (CA, USA) have created a unique way to deliver light anywhere in the body, helping to unleash its therapeutic potential without the need for a single incision.

With a growing number of applications in biology and medicine, including surgery and targeted treatments, light is an increasingly promising therapeutic tool. However, it does not travel through tissue easily, which means that therapies attempting to harness its potential tend to be invasive, requiring tissue removal or optical fiber insertion. As a result, there is a need for easier and less intrusive light-based treatments.

Using ultrasound, which penetrates much deeper into the body than light, the authors of the new study may have found a way to achieve that. Their technology works by dispersing nanomaterials that can turn ultrasound waves into precise points of light throughout the bloodstream, creating an in vivo deep-tissue light source.

They started by adapting large ceramic particles into mechanoluminescent nanoparticles that can emit blue light with a wavelength of 490 nanometers. Then, the team added a biocompatible coating to allow the particles to be suspended in a solution, which was later injected into mice. The nanomaterials can reach every part of the body, carried by blood vessels, and, in response to mechanical stress like ultrasound waves, they produce light.

In tissue-mimicking phantoms (specialized tissues engineer to replicate the properties of human tissue) and animal models, the researchers demonstrated that they could create light in multiple locations at once, achieving tunable spatial resolution and dynamic light patterning.

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They also highlighted the functionality of their design by using electrophysiological recordings and immunostaining in neurons expressing the light-sensitive receptor opsin in both the brain and spinal cord.

Finally, to prove that the system was working inside the body, they used an ultrasound-producing hat on free-moving mice to generate light in different parts of the brain. The light targeted different neurons, which translated to temporally resolved behavioural control in the mice. In other words, stimulating one brain region resulted in a left turn, while focusing on another led the mouse to the right.

“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,” summarized senior author Guosong Hong. As a result, the potential uses are extensive.

“This is a general method that can enable any application that requires light in deep tissue,” Hong added. Alongside colleagues, Hong is currently experimenting with a material that emits ultraviolet light, which could be used to kill pathogens, as well as working on a system for light-activated gene editing.

Before any of this can be moved into humans, the ceramic nanoparticles must be replaced with a safer, biological material – but once that hurdle has been passed, it “will start to pave the way for clinical applications.”