A team of researchers led by Columbia Engineering has developed new nanoscale sensors of force that can change intensity and/or color when pushed or pulled. These “all-optical” nanosensors are probed with light only, offering fully remote read-outs without the need for wires or connections. The researchers have achieved both the most sensitive force response and largest dynamic range ever realized in similar nanoprobes, with 100 times better force sensitivity than existing nanoparticles and an operational range spanning more than four orders of magnitude in force. This breakthrough technology is expected to revolutionize optical force sensors and disrupt technologies in various fields, from robotics to cellular biophysics and medicine to space travel.
The new nanosensors can operate with benign, biocompatible, and deeply penetrating infrared light, allowing for remote monitoring of technological and physiological systems. By enabling early detection of malfunction or failure, these sensors will have a profound impact on fields such as human health, energy, and sustainability. The team was able to build these nanosensors by exploiting the photon-avalanching effect within nanocrystals, where the absorption of a single photon sets off a chain reaction leading to the emission of many photons. The optically active components within the nanocrystals are atomic ions from the lanthanide row of elements, such as thulium, that are doped into the nanocrystal.
The researchers discovered that the photon avalanching process is highly sensitive to factors such as the spacing between lanthanide ions, and tapping the nanoparticles with an atomic force microscopy tip revealed their extreme force sensitivity. This unexpected observation led the team to design new nanoparticles that change luminescence color depending on the applied force or demonstrate photon avalanching only when force is applied. Collaborating with researchers at the Molecular Foundry at Lawrence Berkeley National Lab, the team synthesized and characterized dozens of samples to optimize the particles’ optical properties. Next steps include applying these force sensors to important systems like developing embryos and adding self-calibrating functionality to enable each nanocrystal to function as a standalone sensor.
The development of new force sensors addresses the difficulty in probing environmentally sensitive processes within multiscale systems, as emphasized by 2021 Nobel Laureate Ardem Patapoutian. These sensors will enable sensitive and dynamic mapping of critical changes in forces and pressures in real-world environments currently unreachable with existing technologies. By achieving high-resolution, multiscale function with a single nanosensor, this technology can be employed for studying forces at various levels, from subcellular to whole-system levels, in engineered and biological systems. The ability to monitor and detect malfunctions or failures remotely will have broad applications in fields such as robotics, cellular biophysics, medicine, and space travel.
