Revolutionary All-Optical Nanoscale Force Sensors Unveiled
These sensors, described in a study published in Nature, are designed as luminescent nanocrystals that respond to mechanical pressure by changing their intensity or color. What sets them apart is their ability to operate using light alone, allowing fully remote read-outs with no need for physical connections or wires. This "all-optical" capability means the sensors can function in environments that were previously inaccessible to conventional force sensors.
Unparalleled Sensitivity and Dynamic Range
The sensors demonstrate remarkable sensitivity and a dynamic range far exceeding existing technologies. They provide a 100-fold improvement in force sensitivity over current nanoparticles that rely on rare-earth ions for optical response. Furthermore, their dynamic range spans over four orders of magnitude in force, making them uniquely equipped to measure forces from piconewtons to micronewtons.
Jim Schuck, associate professor of mechanical engineering at Columbia, remarked, "We expect our discovery will revolutionize the sensitivities and dynamic range achievable with optical force sensors, and will immediately disrupt technologies in areas from robotics to cellular biophysics and medicine to space travel."
Versatility Across Scales and Systems
These new nanosensors can function across scales, enabling their use from subcellular systems to macroscopic engineered environments. For example, they could be deployed in developing embryos, migrating cells, nanoelectromechanical systems (NEMS), or advanced batteries. This versatility eliminates the need for multiple sensor types, as a single nanosensor can continuously monitor forces across these varied scales.
"What makes these force sensors unique—apart from their unparalleled multiscale sensing capabilities—is that they operate with benign, biocompatible, and deeply penetrating infrared light," explained Natalie Fardian-Melamed, a postdoctoral scholar and co-lead author of the study. "This allows one to peer deep into various technological and physiological systems and monitor their health from afar."
Leveraging the Photon-Avalanching Effect
The researchers built these nanosensors by exploiting the photon-avalanching effect. In this phenomenon, the absorption of a single photon triggers a cascade of emitted photons, amplifying the sensor's response to external stimuli. The core technology relies on nanocrystals doped with rare-earth ions, such as thulium. By adjusting the spacing between these ions, the team achieved unprecedented sensitivity to mechanical forces.
This discovery was initially unexpected. While tapping on the nanoparticles with an atomic force microscopy (AFM) tip, the researchers observed a dramatic response in the photon avalanching behavior. "We discovered this almost by accident," Schuck noted. "We suspected these nanoparticles were sensitive to force, but their response far exceeded our expectations."
Customized Sensor Designs for Specific Applications
Following their initial findings, the team developed specialized nanosensors tailored to respond to forces in different ways. Some sensors change the color of their luminescence under applied force, while others begin photon avalanching only when force is applied. These advancements provide unprecedented flexibility for sensing applications.
Real-World Impact and Future Directions
The researchers are now focusing on applying these sensors to practical systems. For instance, they aim to study force dynamics in developing embryos, an area with significant implications for developmental biology and medicine. Additionally, they plan to integrate self-calibrating capabilities into the sensors, allowing them to function autonomously.
Schuck highlighted the broader significance of the discovery, citing the work of Nobel Laureate Ardem Patapoutian, who emphasized the challenges of probing environmentally sensitive processes. "These sensors allow one to sensitively and dynamically map critical changes in forces and pressures in real-world environments that are currently unreachable with today's technologies," he said.
With their combination of high sensitivity, wide dynamic range, and adaptability, these nanosensors represent a transformative advancement in force-sensing technology, with the potential to redefine the limits of engineering, biology, and physics.
Journal Reference:
Natalie Fardian-Melamed, et al. Infrared nanosensors of piconewton to micronewton forces. Nature, 2025; DOI: 10.1038/s41586-024-08221-2
For more information, visit Columbia University’s official release
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