An ultra-sound scanning in vivo light source

 

Advances concerning the interaction of technological devices with biological tissues still face significant limitations. In many cases, researchers must choose between achieving high spatiotemporal imaging resolution and using flexible systems capable of investigating multiple regions of the body. While implantable devices provide cellular-level precision, they are invasive and restricted to highly localized sites, making them ill-suited for investigation of dynamic or spatially distributed biological processes.

In this work, researchers at Stanford University developed a material capable of emitting light within tissues using focused ultrasound. To achieve this, they synthesized biocompatible mechanoluminescent nanotransducers (MLNTs), composed of Sr₄Al₁₄O₂₅:Eu,Dy, derived from bulk material. The surface of the nanoparticles was functionalized with polyethylene glycol (PEG), forming a stable colloidal dispersion in an aqueous medium. These particles exhibited sizes ranging from 30 to 110 nm and stability of up to one week, retaining the same diffraction patterns and emission spectra as the bulk material.

Experimental validation was carried out in mice injected with MLNTs and stimulated with focused ultrasound. As a demonstration, the researchers were able to observe the three-dimensional distribution of different regions in the brains of living animals. Ultrasound, which can penetrate tissues and can be precisely focused, is thus confirmed as a powerful non-invasive tool for studying biological processes.

The authors propose that light emission originates when ultrasound induces mechanical deformations that activate energy traps in the material. This process involves electric fields generated by the movement of dislocations associated with intergranular sliding. The hypothesis is consistent with the observed proportional relationship between the intensity of emitted light and ultrasonic pressure. They additionally observed that by increasing the ultrasound frequency, the luminous spot decreased in size, allowing the light emission to be tuned in a manner analogous to optical focusing with lenses.

The ability to generate light within biological tissues in a controlled spatiotemporal manner opens applications in gene editing, photodynamic therapy, deep-tissue imaging, and drug delivery, laying the groundwork for new reconfigurable light-based biotechnologies.

For further information, consult: Nature Materials