Imagine being able to control molecular events inside living organisms without genetic modification or invasive manipulations.

Researchers at the Beckman Institute for Advanced Science and Technology are tapping into plant biotechnology by leveraging ultrasound waves to activate stress-sensitive molecules, called mechanophores, inside living plant tissue.

This technique opens new possibilities for biosensing, controlling and regulating specific metabolic chemicals, synthetic molecular control in plant systems and lays the groundwork to further guide plant stability and crop resilience.

Ying Diao, professor of chemical and biomolecular engineering and materials science and engineering, led the project along with Jeffrey Moore, the Stanley O. Ikenberry Endowed Chair Emeritus of chemistry, Andrew Leakey, the Michael Aiken Chair of plant biology, and Yun-Sheng Chen, professor of electrical and computer engineering and bioengineering.

Combining expertise in nanotechnology, molecular engineering and plant biology, the team used tomato leaves as a model to demonstrate remote molecular control in plants. Their work appears in the journal PNAS.

 Mechanochemistry takes advantage of mechanical energy, or force, to drive chemical reactions. Stress-sensitive molecules called mechanophores can be designed to change color, emit light or release specific chemicals and have practical applications in self-healing materials, damage detection and targeted drug release.

Although mechanophores function well within polymers and other synthetic materials, the complexity of biological systems has made it challenging to apply mechanochemistry techniques to living plants.

Jennifer Moller, co-first author and program manager and research scientist in the Leakey Lab, explained that every component of the project had its own limitations.

“From how nanoparticles behave, to how ultrasound travels through tissue, to how plants respond to stress. Integrating all of that into a single experiment was a challenge,” Moller said.

As obstacles rose at each stage of the project, collaboration was crucial.

Moore and co-first author Fangbai Xie developed fluorogenic mechanophore particles, a type of mechanophore molecule that emits fluorescent light when activated. This was important to visualize and confirm mechanophore activation within the plant.

Diao, Chen and co-first author Junxi Yi then worked to create fluorogenic-embedded nanoparticles, or FMNPs, that would be injected into the plant tissue.

Mechanophores from the Moore Group were incorporated onto silica nanoparticles which enabled force-trigged blue fluorescence, minimizing interference from the plant’s chlorophyll, the primary source of autofluorescence in leaves.

Next, the FMNPs needed to be activated inside living tomato plant leaves while preserving the plant’s integrity and biological function.

Ultrasound waves, often used for medical imaging and therapy, can be used to noninvasively activate mechanophores. However, the force required to activate these mechanophores often exceeds biocompatible, tissue-safe levels and would damage the plant.

The researchers found that low-frequency ultrasound activated the mechanophores but caused significant tissue damage while high-frequency ultrasound preserved the tissue but was unable to activate the mechanophores.

Addressing this significant challenge, the team created and incorporated gas-filled microstructures, or gas vesicles, which amplified the mechanical effects of high frequency ultrasound waves by enhancing acoustic cavitation.

“Gas vesicles are air-filled protein nanostructures that can amplify local cavitation generated by ultrasound. By incorporating them into the system, we were able to enhance the mechanical activation of the synthesized mechanophore particles,” Yi said.

Moller ensured the biocompatibility of gas vesicle-amplified focused ultrasound, GV-FUS, by monitoring plant health and physiological indicators like visible tissue damage, chlorophyll autofluorescence and photosynthetic performance.

Ultimately, the team established GV-FUS as a feasible, noninvasive strategy capable of activating FMNPs in living plant tissue.

“The ability to activate molecules inside specific tissues could change how we study—and eventually engineer plants,” Moller said.

Their work enabled remote-controlled, ultrasound-triggered functionalities for plant applications and importantly, expanded the design space for bio-integrated nanostructures in fields ranging from plant biotechnology to synthetic biology.

Editor’s note:

The publication titled “Ultrasound-Drive Mechanophore Activation in Living Plants” can be accessed online at https://doi.org/10.1073/pnas.2533066123

This research was financially supported by the Beckman Institute for Advanced Science and Technology Seed Funding Program with support from the Arnold and Mabel Foundation.