Mechanical force is an essential feature for many physical and biological processes. Remote measurement of mechanical signals with high sensitivity and spatial resolution is needed for a wide range of applications, from robotics to cellular biophysics and medicine and even to space travel.
Nanoscale luminescent force sensors excel at measuring piconewton forces, while larger sensors have proven powerful in probing micronewton forces. However, large gaps remain in the force magnitudes that can be probed remotely from subsurface or interfacial sites, and no individual, non-invasive sensor has yet been able to make measurements over the large dynamic range needed to understand many systems.
In a paper published today by Nature, a team led by Columbia Engineering researchers and collaborators report that they have invented new nanoscale sensors of force. They are luminescent nanocrystals that can change intensity and/or colour when you push or pull on them. These "all-optical" nano-sensors are probed with light only and therefore allow for fully remote read-outs -- no wires or connections are needed.
The researchers, led by Jim Schuck, associate professor of mechanical engineering, and Natalie Fardian-Melamed, a postdoctoral scholar in his group, along with the Cohen and Chan groups at Lawrence Berkeley National Lab (Berkeley Lab), developed nano-sensors that have attained both the most sensitive force response and largest dynamic range ever realied in similar nanoprobes.
They have 100 times better force sensitivity than the existing nanoparticles that utilise rare-earth ions for their optical response, and an operational range that spans more than four orders of magnitude in force, a much larger range -- 10-100 times larger -- than any previous optical nano-sensor.
“We expect our discovery will revolutionise 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,” Schuck says
The new nano-sensors achieve high-resolution, multiscale function with the same nano-sensor for the first time. This is important as it means that just this nano-sensor, rather than a suite of different classes of sensors, can be employed for the continuous study of forces, from the subcellular to the whole-system level in engineered and biological systems, such as developing embryos, migrating cells, batteries, or integrated NEMS, very sensitive nanoelectromechanical systems in which the physical motion of a nanometre-scale structure is controlled by an electronic circuit, or vice versa.
“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," Fardian-Melamed says. “This allows one to peer deep into various technological and physiological systems, and monitor their health from afar. Enabling the early detection of malfunction or failure in these systems, these sensors will have a profound impact on fields ranging from human health to energy and sustainability.”
